CN114614106B

CN114614106B - Electrochemical device and electronic device

Info

Publication number: CN114614106B
Application number: CN202210351952.2A
Authority: CN
Inventors: 刘文元
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2020-12-17
Filing date: 2020-12-17
Publication date: 2024-03-12
Anticipated expiration: 2040-12-17
Also published as: CN112635710B; CN112635710A; CN114614106A

Abstract

Embodiments of the present application provide an electrochemical device and an electronic device, wherein the electrochemical device includes: a positive electrode, a negative electrode, and a separator; the positive electrode includes: a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is positioned on one surface or two surfaces of the positive electrode current collector; a separator located between the positive electrode and the negative electrode; the average value of the particle numbers of the particle diameters not smaller than d1 in the thickness direction of the positive electrode active material layer on either side of the positive electrode current collector is N1, the average value of the particle numbers of the particle diameters not smaller than 0.5d1 is N2, and N1 and N2 satisfy: n1 is more than or equal to 0 and less than or equal to 4, N2 is more than or equal to 0 and less than or equal to 8, wherein d1 is the thickness of the positive electrode current collector, and the energy density of the electrochemical device can be improved and the processing performance of the positive electrode can be improved by controlling N1 and N2 in the embodiment of the application.

Description

Electrochemical device and electronic device

The present application is a divisional application of patent application number 202011501664.8, entitled "electrochemical device and electronic device", filed on 12/17 th 2020.

Technical Field

The present application relates to the field of electrochemical energy storage, and in particular to electrochemical devices and electronic devices.

Background

With the development of society, there is an increasing demand for electrochemical devices (e.g., lithium ion batteries), particularly for energy storage performance and processability of electrochemical devices, and it is desirable that electrochemical devices store as much electricity as possible and can be conveniently processed.

Disclosure of Invention

According to the embodiment of the application, the energy density of the electrochemical device is optimized by controlling the relation between the particle size in the positive electrode material and the thickness of the positive electrode current collector, and meanwhile, the processing performance is improved by limiting the number of large particles in the positive electrode active material layer.

Embodiments of the present application provide an electrochemical device including: a positive electrode, a negative electrode, and a separator; the positive electrode includes: the positive electrode current collector and the positive electrode active material layer are arranged on one surface or two surfaces of the positive electrode current collector; a separator disposed between the positive electrode and the negative electrode; in the thickness direction of the positive electrode active material layer, the average value of the particle numbers of the positive electrode active material layer on any surface of the positive electrode current collector, the particle diameter of which is not less than d1, is N1, the average value of the particle numbers of which is not less than 0.5d1, is N2, and the N1 and N2 satisfy the following conditions: n1 is more than or equal to 0 and less than or equal to 4, N2 is more than or equal to 0 and less than or equal to 8, wherein d1 is the thickness of the positive current collector, and the unit is mu m.

In some embodiments, the thickness d1 of the positive electrode current collector satisfies: d1 is more than or equal to 5 mu m and less than or equal to 15 mu m.

In some embodiments, the positive electrode active material layer has a positive electrode material therein;

the Dv50 of the positive electrode material satisfies: dv50 is more than or equal to 0.5d1 and less than or equal to 1.2d1;

and/or, dv99 of the positive electrode material satisfies: dv99 is more than or equal to 0.5d1 and less than or equal to 2d1.

the Dv50 of the positive electrode material satisfies: dv50 is less than or equal to 5 mu m and less than or equal to 15 mu m;

and/or, dv99 of the positive electrode material satisfies: dv99 is less than or equal to 5 μm and less than or equal to 40 μm.

the Dv50 of the positive electrode material and the Dv99 of the positive electrode material satisfy:

1.3≤Dv99/Dv50≤8.0。

in some embodiments, the thickness d2 of the positive electrode active material layer on either side of the positive electrode current collector satisfies:

10μm≤d2≤40μm。

1≤d2/d1≤4。

the thickness d2 of the positive electrode active material layer on either side of the positive electrode current collector and Dv99 of the positive electrode material satisfy: dv99 is more than or equal to 0.5d2 and less than or equal to 1.7d2.

In some embodiments, the positive electrode has a compacted density of 3.1g/cm or greater ³ And less than or equal to 6.0g/cm ³ 。

In some embodiments, the electrolyte further comprises at least one of a polynitrile compound or a thioredoxin double bond compound; the polynitrile compound comprises at least one of 1,3, 6-hexane trimethyl nitrile, 1,2, 3-tris (2-cyanoethoxy) propane, 1, 2-bis (2-cyanoethoxy) ethane, adiponitrile and succinonitrile; the sulfur-oxygen double bond compound comprises at least one of methylene methane disulfonate, 1, 3-propane sultone, 2, 4-butane sultone or vinyl sulfate.

In some embodiments, the polynitrile compound content is A and the sulfur-oxygen double bond compound content is B, based on the total weight of the electrolyte, satisfying 0.1.ltoreq.A/B.ltoreq.5.

An electronic device comprising an electrochemical device according to any of the above is also presented in an embodiment of the present application.

The embodiment of the application proposes an electrochemical device and an electronic device, in the electrochemical device, in the layer thickness direction of a positive electrode active material on any side of a positive electrode current collector, the average value of the particle numbers of the particle diameter not less than d1 is N1, the average value of the particle numbers of the particle diameter not less than 0.5d1 is N2, and N1 and N2 satisfy: n1 is more than or equal to 0 and less than or equal to 4, N2 is more than or equal to 0 and less than or equal to 8. By controlling N1, N2 in the embodiments of the present application, the energy density of the electrochemical device can be optimized while improving the processability.

Drawings

Fig. 1 shows a schematic view of an electrochemical device according to an embodiment of the present application;

FIG. 2 shows a schematic of a positive electrode of an embodiment of the present application;

fig. 3 shows a top view of a positive electrode active material layer in an embodiment of the present application;

FIG. 4 shows a cross-sectional electron microscope view of one positive electrode in an embodiment of the present application;

fig. 5 shows a schematic view of a positive electrode in an embodiment of the present application.

Detailed Description

The following examples will allow those skilled in the art to more fully understand the present application, but are not intended to limit the present application in any way.

In some technologies, in order to increase the compaction density of the positive electrode of an electrochemical device, particles with different particle diameters are used in the positive electrode material for mixing, and the positive electrode material has a wide particle diameter distribution range, so that the positive electrode current collector is easily expanded and increased, and further, the positive electrode current collector is easily broken, and in order to prevent the positive electrode current collector from breaking, a thicker positive electrode current collector is required, and the increase in the thickness of the positive electrode current collector leads to the increase in the overall weight of the electrochemical device, so that the energy density of the electrochemical device is reduced. On the other hand, in order to reduce the elevated temperature of the electrochemical device during use, it is necessary to reduce the thickness of the positive electrode active material layer coated on the positive electrode current collector, which is liable to cause particle scratches on the surface of the positive electrode, affecting the processability.

To at least partially solve the above-described problems, an electrochemical device is proposed in an embodiment of the present disclosure, as shown in fig. 1 and 2, including: a positive electrode 10, a negative electrode 20, and a separator 30. Wherein the positive electrode 10 includes: the positive electrode collector 11 and the positive electrode active material layer 12, the positive electrode active material layer 12 is disposed on one or both sides of the positive electrode collector 11, the positive electrode collector 11 may be an aluminum foil, and the positive electrode active material layer 12 may include a positive electrode material therein. A separator 30 is provided between the positive electrode 10 and the negative electrode 20.

In the thickness direction of the positive electrode active material layer 12, the average value of the number of particles having a particle diameter of not less than d1 is N1, the average value of the number of particles having a particle diameter of not less than 0.5d1 is N2, and N1 and N2 satisfy: n1 is more than or equal to 0 and less than or equal to 4, N2 is more than or equal to 0 and less than or equal to 8, wherein d1 is the thickness of the positive current collector, and the unit is mu m.

Referring to fig. 3, fig. 3 schematically shows a top view of the positive electrode active material layer, a straight line of 80 μm in length is defined on the positive electrode active material layer shown in fig. 3, that is, a horizontal line in the drawing, and then lines are drawn every 20 μm along the thickness direction of the positive electrode active material layer 12 at the horizontal line, the lines are parallel to each other, the particles intersecting with the lines are the particles on the lines, and N1 and N2 are determined by performing statistical averaging of the particle sizes of the particles on the lines, wherein the particle size is the longest diameter of the particles.

In some embodiments, if the average particle number N1 of the positive electrode active material layer 12 having a particle diameter not smaller than d1 is too large, defects such as scratches, pits, etc. easily occur on the positive electrode at the time of coating; when the average value of the particle numbers of the particle diameters of not less than 0.5d1 is N2, the expansion of the positive electrode current collector is increased, and the positive electrode current collector 11 is easily broken; and the larger the particles in the positive electrode active material layer 12, the larger the volume of the gaps inside the positive electrode active material layer 12, resulting in a decrease in the energy density of the electrochemical device. Therefore, in the embodiments of the present application, 0.ltoreq.n1.ltoreq.4 and 0.ltoreq.n2.ltoreq.8 are defined, and by limiting N1 and N2, it is possible to prevent the occurrence of scratches, pits, and the like on the positive electrode, and to reduce the expansion of the positive electrode current collector, improve the processability, and optimize the energy density of the electrochemical device.

In some embodiments, the thickness d1 of the positive electrode current collector 11 satisfies: d1 is more than or equal to 5 mu m and less than or equal to 15 mu m. In some embodiments, the thickness d1 of the positive electrode current collector 11 is less than 5 μm, which results in a decrease in strength of the positive electrode current collector and is easily broken, and when the thickness d1 of the positive electrode current collector 11 is greater than 15 μm, which results in an increase in weight and volume of the electrochemical device, which reduces energy density of the electrochemical device. The thickness d1 of the positive electrode current collector 11 is limited to a range of 5 μm to 15 μm, and the positive electrode current collector has sufficient strength to prevent breakage while securing the energy density of the electrochemical device.

In some embodiments, the positive electrode active material layer 12 has a positive electrode material therein, and the Dv50 of the positive electrode material satisfies: dv50 is more than or equal to 0.5d1 and less than or equal to 1.2d1. In some embodiments, dv50 represents a particle size of up to 50% by volume from the small particle size side in a volume-based particle size distribution. When the thickness d1 of the positive electrode current collector is large, the positive electrode current collector is not easy to scratch by particles of the positive electrode material, when the thickness of the positive electrode current collector is small, the positive electrode current collector is easy to scratch by particles of the positive electrode material, the particle size of the positive electrode material needs to be matched with the thickness d1 of the positive electrode current collector and cannot be too large, meanwhile, the particle size of the particles of the positive electrode material is not too small relative to the thickness of the positive electrode current collector, otherwise, the consumption of electrolyte is increased, and therefore, in some embodiments, the Dv50 is limited to be more than or equal to 0.5d1 and less than or equal to 1.2d1.

In some embodiments, dv99 of the positive electrode material satisfies: dv99 is more than or equal to 0.5d1 and less than or equal to 2d1.Dv99 represents a particle size of 99% by volume in the volume-based particle size distribution from the small particle size side. Some embodiments of the present application define the relationship between Dv99 and d1 of the cathode material, by defining Dv99 not to be too large relative to d1, it is possible to limit particles not having too large volume in the cathode material, and by defining Dv99 not to be too small relative to d1, it is possible to ensure that the particle size of the particles of the cathode material is distributed within a certain range, thereby improving the energy density of the electrochemical device.

In some embodiments, the positive electrode active material layer 12 has a positive electrode material therein, and the Dv50 of the positive electrode material satisfies: dv50 is less than or equal to 5 mu m and less than or equal to 15 mu m; in some embodiments, when Dv50 is less than 5 μm, the particle size of the positive electrode material is too small, the electrolyte is consumed more, and side reactions may be increased, thereby affecting the cycle performance of the electrochemical device, and when Dv50 is greater than 15 μm, the rate performance of the positive electrode material may be affected.

In some embodiments, dv99 of the positive electrode material satisfies: dv99 is less than or equal to 5 μm and less than or equal to 40 μm. In some embodiments, when Dv99 is less than 5 μm, the particle size distribution of the positive electrode material is narrow, which is disadvantageous for improving the energy density of the electrochemical device, and when Dv99 is greater than 40 μm, the particle size distribution of the positive electrode material is wide, which easily increases the expansion of the positive electrode current collector.

In some embodiments, the positive electrode active material layer 12 has a positive electrode material therein; the Dv50 of the positive electrode material and the Dv99 of the positive electrode material satisfy: dv99/Dv50 is less than or equal to 1.3 and less than or equal to 8.0. In some embodiments, the ratio of Dv99 to Dv50 characterizes the ratio of large-sized particles to normal-sized particles in the positive electrode material, and by defining the ratio of Dv99 to Dv50, the distribution of particles of the positive electrode material can be defined, and when Dv99/Dv50 is 1.3 or less and 8.0 or less, the distribution of the positive electrode material is ensured to be reasonable, so that the gaps between the positive electrode materials can be reduced, and the energy density of the electrochemical device can be improved.

In some embodiments, the thickness d2 of the positive electrode active material layer 12 on either side of the positive electrode current collector 11 satisfies: d2 is more than or equal to 10 mu m and less than or equal to 40 mu m. In some implementations of the present application, the positive electrode active material layer 12 is disposed on one or both sides of the positive electrode current collector 11, and when the thickness d2 of the positive electrode active material layer 12 is less than 10 μm, the energy stored in the unit area of the positive electrode active material layer 12 is smaller, which is not beneficial to improving the overall energy density of the electrochemical device, and when the thickness d2 of the positive electrode active material layer 12 is greater than 40 μm, the positive electrode material loaded in the unit area of the positive electrode current collector 11 is too much, which easily results in the positive electrode material falling off.

In some embodiments, the thickness d2 of the positive electrode active material layer 12 on either side of the positive electrode current collector 11 satisfies 1.ltoreq.d2/d1.ltoreq.4. In some embodiments, the thickness d1 of the positive electrode current collector 11 affects the strength of the positive electrode current collector 11, and the strength of the positive electrode current collector 11 affects the amount of positive electrode material that can be loaded per unit area thereof, i.e., affects the thickness of the positive electrode active material layer, and thus, the thickness d2 of the positive electrode active material layer 12 is related to the thickness d1 of the positive electrode current collector 11, and when d2/d1 is greater than 4, the thickness of the positive electrode active material layer 12 is excessively large, which may cause tearing of the positive electrode current collector 11 due to an excessive amount of positive electrode material loaded per unit area on the positive electrode current collector 11, and when d2/d1 is less than 1, the amount of positive electrode material loaded on the positive electrode current collector 11 is excessively small, resulting in a lower energy density of the electrochemical device.

In some embodiments, the positive electrode active material layer 12 has a positive electrode material therein; the thickness d2 of the positive electrode active material layer 12 on either side of the positive electrode current collector 11 satisfies with Dv99 of the positive electrode material: dv99 is more than or equal to 0.50d2 and less than or equal to 1.7d2. In some embodiments, when Dv99 is less than 0.5d2, arranging a plurality of positive electrode material particles in the thickness direction of the positive electrode active material layer 12 may cause an increase in direct current resistance of the electrochemical device, and when Dv99 is greater than 1.7d2, the particle size of the positive electrode material particles is excessively large with respect to the thickness d2 of the positive electrode active material layer 12, which is disadvantageous for improving the compacted density of the positive electrode.

In some embodiments, the positive electrode has a compacted density of 3.1g/cm or greater ³ And less than or equal to 6.0g/cm ³ . The compacted density of the positive electrode material affects the energy density of the electrochemical device when the compacted density is less than 3.1g/cm ³ The electrochemical device has insufficient energy density when the compacted density is greater than 6.0g/cm ³ And the expansion of the positive electrode current collector is increased, so that the processing is not facilitated.

In some embodiments, the electrolyte further comprises at least one of a polynitrile compound or a thioredoxin double bond compound; the polynitrile compound includes at least one of 1,3, 6-hexane trimethyl nitrile, 1,2, 3-tris (2-cyanoethoxy) propane, 1, 2-bis (2-cyanoethoxy) ethane, adiponitrile (ADN), succinonitrile (SN); the thioxy double bond compound comprises at least one of methylene methane disulfonate, 1, 3-Propane Sultone (PS), 2, 4-butane sultone or vinyl sulfate (DTD). Specifically, in some embodiments, the polynitrile compound can form a stable fixed electrolyte interfacial film on the positive electrode, and the sulfur-oxygen double bond compound can form a complete high ion conductivity solid electrolyte interfacial film on the surface of the negative electrode, so that the ion conductivity is further improved, and the quick charge performance and the safety performance of the electrochemical device are improved.

In some embodiments, the polynitrile compound content is A and the sulfur-oxygen double bond compound content is B, based on the weight of the electrolyte, satisfying 0.1.ltoreq.A/B.ltoreq.5. Within the above range, it is possible to ensure that both the positive electrode and the negative electrode are formed with a good solid electrolyte interfacial film.

In some embodiments, a% ranges from 0.1% to 10%.

In some embodiments, B% ranges from 0.1% to 5%.

In some embodiments, the electrochemical device may be any device that undergoes an electrochemical reaction, such as a primary battery, a secondary battery. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

In some embodiments of the present application, the electrolyte contains a lithium salt, which may be at least one of an organic lithium salt or an inorganic lithium salt, and in some embodiments of the present application, the lithium salt contains at least one of a fluorine element, a boron element, or a phosphorus element.

In some alternative embodiments, the lithium salt comprises LiPF ₆ 、LiBF ₄ 、LiClO ₄ 、LiB(C ₆ H ₅ ) ₄ 、LiCH ₃ SO ₃ 、LiCF ₃ SO ₃ 、LiN(SO ₂ CF ₃ ) ₂ 、LiC(SO ₂ CF ₃ ) ₃ 、LiSiF ₆ One or more of LiBOB or lithium difluoroborate. For example, the lithium salt is LiPF ₆ Since it can give high ionic conductivity and improve cycle characteristics.

In some embodiments of the present application, the mass of lithium salt is less than or equal to 25% of the total mass of the electrolyte; the excessive concentration of lithium salt and the excessive viscosity of the electrolyte affect the rate capability of the electrochemical device using the electrolyte.

In some embodiments of the present application, the electrolyte comprises a nonaqueous organic solvent, wherein the nonaqueous organic solvent comprises one or a combination of two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, gamma-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, or propyl butyrate in any proportion.

The electrolyte may include a nonaqueous solvent therein, which may include a carbonate compound, a carboxylate compound, an ether compound, or a combination thereof. The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof. Examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), propylene Carbonate (PC), butylene Carbonate (BC), vinyl Ethylene Carbonate (VEC), or a combination thereof. Examples of the fluorocarbonate compound are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethyl ethylene carbonate, or a combination thereof.

Examples of carboxylate compounds are methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, gamma-butyrolactone, decalactone, valerolactone, mevalonic acid lactone, caprolactone, methyl formate, or combinations thereof.

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

In some embodiments of the present application, a negative electrode of the above-described electrochemical device includes a negative electrode current collector and a negative electrode active material layer disposed on one or both sides of the negative electrode current collector. The positive electrode current collector may be an aluminum foil or a nickel foil, and the negative electrode current collector may be a copper foil or a nickel foil. The specific kind of the anode material is not particularly limited, and may be selected according to the need. The anode material is capable of absorbing/releasing lithium, and may include carbon materials, metal compounds, oxides, sulfides, nitrides of lithium such as LiN ₃ Lithium metal, metals that form alloys with lithium, and polymeric materials. The carbon material may include low graphitized carbon, graphitizable carbon, artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, pyrolytic carbon, coke, glassy carbon, organic polymer compound sintered body, carbon fiber, and activated carbon. Among them, the coke may include pitch coke, needle coke, and petroleum coke. The organic polymer compound sintered body refers to a material obtained by calcining a polymer material such as phenol plastic or furan resin at an appropriate temperature to carbonize it. The polymeric material may include polyacetylene and polypyrrole.

In the negative electrode material, a material having a charge and discharge voltage close to those of lithium metal is selected. This is because the lower the charge and discharge voltage of the anode material, the easier the lithium ion battery has a higher energy density. Among them, the negative electrode material can be selected from carbon materials because their crystal structure is changed only slightly at the time of charge and discharge, and thus, good cycle characteristics and large charge and discharge capacities can be obtained. For example, graphite is chosen because it gives a large electrochemical equivalent and a high energy density.

The anode material may include elemental lithium metal, metal elements and semimetal elements capable of forming an alloy with lithium, alloys and compounds including such elements, and the like. For example, they are used together with a carbon material, in which case good cycle characteristics as well as high energy density can be obtained. In addition to alloys comprising two or more metallic elements, alloys used herein also include alloys comprising one or more metallic elements and one or more semi-metallic elements. The alloy may be in solid solutions, eutectic crystals, intermetallic compounds and mixtures thereof. The metal element and the half metal element may include tin (Sn), lead (Pb), aluminum (Al), indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y), or hafnium (Hf). In addition, an inorganic compound excluding lithium, such as MnO, may be used in the anode material ₂ 、V ₂ O ₅ 、V ₆ O ₁₃ Either NiS or MoS.

In some embodiments of the present application, a conductive agent or a binder may be added to the positive electrode active material layer of the above-described electrochemical device, and in some embodiments of the present application, a carbon material may be further included in the positive electrode active material layer, and the carbon material may include at least one of conductive carbon black, graphite, graphene, carbon nanotubes, carbon fibers, or carbon black. The binder may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

In some embodiments, the barrier film comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. In particular polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through a shutdown effect. In some optional embodiments, an inorganic or organic coating is applied to the surface of the separator to enhance the hardness of the cell or to promote adhesion of the separator to the anode and cathode interfaces.

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

The present application also proposes an electronic device comprising an electrochemical device according to any of the above. The electronic device of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copier, a portable printer, a headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-compact disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable audio recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a power assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large-sized battery, a lithium ion capacitor, and the like. For example, electronic devices include cell phones that include lithium ion batteries.

In order to better illustrate the beneficial effects of the electrolyte solution proposed in the embodiments of the present application, the following description will be made with reference to the embodiments, and the lithium ion batteries prepared in the following embodiments differ only in the electrolyte solutions used, and in the following embodiments, performance tests will be performed on the lithium ion batteries using different electrolyte solutions to illustrate the effect of the electrolyte solution on the performance of the lithium ion batteries.

Taking an electrochemical device as an example of a lithium ion battery, a specific preparation method and testing the prepared lithium ion battery are used to illustrate the preparation and performance of the lithium ion battery of the present application, and those skilled in the art will understand that the preparation method described in the present application is merely an example, and any other suitable preparation method is within the scope of the present application.

The test method of the lithium ion battery is described first below

1. Calculation method of positive electrode current collector thickness d1, positive electrode active material layer thickness d2, particle number (N1 and N2):

step 1) the positive electrode was cut using IB-09010 CP/ion polisher and then placed in a ZEISS SEM (Sigma-02-33) for testing. Obtaining 5 cross section microscopic morphology images of the positive electrode with 500-1000 times of magnification, wherein the upper and lower surfaces of the positive electrode and the edges of positive electrode material particles can be clearly seen;

Step 2) selecting a cross-section micro-topography diagram (as shown in fig. 4) of the positive electrode meeting the requirement, firstly, making a straight line parallel to the upper surface or the lower surface of the positive electrode as a horizontal line, and making 5 equally-spaced vertical lines perpendicular to the horizontal line (also called as a thickness direction), wherein the distance between every two adjacent vertical lines is required to be 20 μm. The intersection points of the vertical lines 1, 2, 3, 4 and 5 with the upper surface of the positive electrode are respectively denoted as A1', A2', A3', A4' and A5'; the intersections with the lower surface of the positive electrode are denoted B1', B2', B3', B4', and B5', respectively; the intersection points with the upper surface of the positive electrode current collector are respectively denoted as A1, A2, A3, A4 and A5; the intersection points with the lower surface of the positive electrode current collector are respectively marked as B1, B2, B3, B4 and B5; the average value of the lengths of the line segments A1B1, A2B2, A3B3, A4B4 and A5B5 is the thickness d1 of the positive electrode current collector; the average value of the lengths of the line segments A1', A2', A3', A4', and A5 'is the active layer thickness d2A on the upper side of the positive electrode current collector, the average value of the lengths of the line segments B1', B2', B3', B4', and B5' is the thickness d2B of the positive active material layer on the lower side of the positive current collector, the thickness d2= (d2a+d2b)/2 of the positive active material layer;

Step 3) indicates all particles having a particle size of greater than or equal to d1 (e.g., the particles indicated by the white double-arrow lines in fig. 4) and all particles having a particle size of greater than or equal to 0.5d1 and less than d1 (e.g., the particles indicated by the black double-arrow lines in fig. 4), the particle size of the particles referring to the longest diameter on one particle;

step 4) counting the number of particles greater than or equal to 0.5d1 on A1A1', A2A2', A3A3', A4A4', A5A5', B1B1', B2B2', B3B3', B4B4 'and B5B5' and averaging;

step 5) selecting another 4 positive electrode section microscopic morphology graphs meeting the requirements, repeating the steps 1) -4), and calculating the particle number average value N1 with the particle size not less than d1 and the particle number average value N2 with the particle size not less than 0.5d 1.

Dv50 and Dv99 test methods

Dv50 and Dv99 are particle sizes of samples analyzed using a Mastersizer 3000 laser particle size distribution tester. Dv50 represents the particle size at which 50% of the volume is accumulated from the small particle size side in the volume-based particle size distribution. Dv99 represents a particle size which reaches 99% by volume from the small particle size side in the volume-based particle size distribution. During testing, the sample injection system is Hydro 2000SM wet dispersion, the measuring range is 0.01 mu m-3500 mu m, the light source is Red light Helium neon laser/blue light Solid state light source, and the detection angle is 0-144 degrees. The sample test time was 6s, the background test time was 6s, the number of sample tests snap was 6000, the average was taken 3 times in the test cycle, the rotation speed of the stirring pump was 3000rpm, and the analysis mode was set to General purpose.

3. Method for testing compaction density

Selecting a positive electrode, punching into 10 pieces with an area of 15.4025cm ² Weigh the weight Mi of each small disc (i represents 1,2, … …, 10), and measure the thickness Di of each disc (i represents 1,2, … …, 10)

Alternatively selecting a positive electrode, scraping the positive electrode active material layer on the positive electrode by a scraper, and punching into 10 pieces with an area of 15.4025cm ² Weighing the small discs, calculating the average value of m, weighing the thickness of each small disc, and calculating the average value of d;

the compacted density of each of the pellets with the positive electrode active material layer was PDi calculated using the following formula:

PDi＝(Mi-m)/15.4025/(Di-d))

the average of the compaction of 10 small disks was taken as the compacted density of the positive electrode.

4. Positive electrode elongation

On a positive electrode which is not cold-pressed, two line segments A and B (as shown in figure 5) perpendicular to the length direction of the positive electrode are marked, the distance AB is 2m, after cold pressing, the distance L between the two line segments is measured by a tape measure, and the extensibility of the positive electrode is (L-2)/2 multiplied by 100 percent

5. Number of particle scratches

The number of particle scratches in this application is the number of particle scratches occurring within 1m×0.1m of the counted positive electrode. Counting 20 positive electrodes, and calculating the total scratch number.

6. Rate capability

Placing the lithium ion battery in an incubator at 25+/-2 ℃ for standing for 2 hours, charging to 4.25V at a constant current of 0.2 ℃, then charging to 0.02C at a constant voltage of 4.25V, and standing for 15 minutes; then discharging to 2.8V with 8C constant current, which is a charge-discharge cycle process,

8C rate retention = 8C discharge capacity/0.2C discharge capacity x 100%.

The following describes the preparation method of the lithium ion battery in each example.

The lithium ion batteries of examples 1 to 4 and comparative examples 1 to 2 were prepared as follows:

example 1

Preparation of a positive electrode material: preparation of a Dv50 of 10.3 μm, a Dv99 of 18 μm and a specific surface area of 9.88m ² Positive electrode material precursor Ni/g _0.8 Co _0.1 Mn _0.1 (OH) ₂ Mixing it with LiOH, al ₂ O ₃ Mixing according to stoichiometric ratio, calcining at 800 deg.C for 16 hr to obtain primary substance, mixing the primary substance with H ₃ BO ₃ Uniformly mixing, sintering at 400 ℃ for 4 hours to coat boron, wherein the molar percentage of boron is 0.3%. Through screening parameter adjustment, the coated LiNi _0.8 Co _0.1 Mn _0.095 Al _0.005 O ₂ The Dv50 of the positive electrode material was controlled to 10. Mu.m, and the Dv99 was controlled to 17. Mu.m.

Preparation of electrochemical device:

preparation of the Positive electrode

The positive electrode material obtained in the above is fully stirred and uniformly mixed in an N-methyl pyrrolidone solvent system according to the mass ratio of the positive electrode material to the conductive agent acetylene black to the binder polyvinylidene fluoride (PVDF) of 96:2:2, and then the mixture is coated on an Al foil of a positive electrode current collector with the thickness of 8 mu m on two sides, and the mixture is dried, cold-pressed and striped to obtain a single-layer positive electrode active material layer with the thickness d2 of 25 mu m and the compaction density of 3.4g/cm ³ Is provided.

In the preparation process, the prepared positive electrode material is screened according to the thickness of the current collector to obtain the positive electrode material with specified Dv50 and Dv 99; and determining the range of d2 from the value with Dv 99; the thickness of the positive electrode active material layer is controlled by adjusting the parameters of the coating process and the pressure during cold pressing.

Preparation of negative electrode

The preparation method comprises the steps of adopting copper foil as a negative electrode current collector, uniformly coating graphite slurry on the surface of the copper foil, mixing artificial graphite, sodium carboxymethylcellulose and styrene-butadiene rubber in the graphite slurry according to a mass ratio of 97.7:1.3:1, drying at 85 ℃, then carrying out cold pressing, cutting and slitting, and drying for 4 hours under a vacuum condition at 85 ℃ to prepare the negative electrode.

Electrolyte preparation

Ethylene Carbonate (EC): diethyl carbonate (DEC): propylene Carbonate (PC):propyl Propionate (PP): mixing Vinylene Carbonate (VC) according to a mass ratio of 20:30:20:28:2, and then adding 1mol/L LiPF ₆ And mixing uniformly to obtain the electrolyte of the lithium ion battery.

The positive electrode and the negative electrode were wound with a polyethylene separator (thickness 9 μm) therebetween, thereby preparing a wound electrode assembly. The electrode assembly is subjected to top side sealing, code spraying, vacuum drying, electrolyte injection, high-temperature standing and formation and capacity, and a finished lithium ion battery can be obtained.

Example 2

Example 2 and example 1 differ only in that the positive electrode current collector Al foil used has a thickness of 10 μm.

Example 3

Example 3 differs from example 1 only in that the positive electrode current collector Al foil used has a thickness of 12 μm.

Example 4

Example 4 and example 1 differ only in that the positive electrode current collector Al foil used has a thickness of 14 μm.

Comparative example 1

Comparative example 1 differs from example 2 only in that the thickness of the positive electrode active material layer in comparative example 1 was 60 μm.

Comparative example 2

Comparative example 2 differs from example 2 only in the preparation of the positive electrode material: preparation of a Dv50 of 10.3 μm, a Dv99 of 45 μm and a specific surface area of 7.33m ² Positive electrode material precursor Ni/g _0.8 Co _0.1 Mn _0.1 (OH) ₂ Mixing it with LiOH, al ₂ O ₃ Mixing according to stoichiometric ratio, calcining at 800 deg.C for 16 hr to obtain primary substance, mixing the primary substance with H ₃ BO ₃ Uniformly mixing, sintering at 400 ℃ for 4 hours to coat boron, wherein the molar percentage of boron is 0.3%. Through screening parameter adjustment, the coated LiNi _0.8 Co _0.1 Mn _0.095 Al _0.005 O ₂ The Dv50 of the positive electrode material was controlled to 10 μm and the Dv99 was controlled to 42 μm.

TABLE 1

The test results of examples 1 to 4 are shown in Table 1, and the values of N1 and N2 are adjusted by improving the thickness d1 of the Al foil in examples 1 to 4.

Examples 1 to 4 each satisfy 0.ltoreq.N1.ltoreq.4 and 0.ltoreq.N2.ltoreq.8, the positive electrode elongation rates of examples 1 to 4 are each low, N1 of comparative example 1 and N2 of comparative example 2 are greater than 4 and N2 is greater than 8, and the elongation rates of comparative example 1 and comparative example 2 are each not less than 1%, so that it can be seen that the positive electrode elongation rate can be improved when 0.ltoreq.N1.ltoreq.4 and 0.ltoreq.N2.ltoreq.8 is satisfied, thereby improving the case of the electrode segment banding.

No particle scratches were found on the positive electrodes of examples 1 to 4, and on the positive electrodes of comparative examples 1 and 2, it was found that, in addition, when 0.ltoreq.n1.ltoreq.4 and 0.ltoreq.n2.ltoreq.8 were satisfied, the positive electrodes were prevented from suffering from particle scratch defects.

The Al foil thickness d1 in examples 1-4 satisfies 5 μm.ltoreq.d1.ltoreq.15μm because the energy density of the electrochemical device decreases when d1 is excessively large. When d1 is less than 5 μm, the strength may be reduced, resulting in breakage of the positive electrode, and the thickness of the positive electrode current collector may be controlled, thereby improving the processability of the positive electrode.

N1 affects the particle scratch on the positive electrode, N2 affects the elongation of the positive electrode, N1 is greater than 4 and N2 is greater than 8 in comparative examples 1 and 2, so that the positive electrode elongation is not less than 1% in both comparative examples 1 and 2, and the positive electrode has the particle scratch thereon. In comparative example 1, the N2 value is large, resulting in high positive electrode elongation and easy positive electrode breakage, but the N1 value is small, so that the particle scratch is only 1 place. In comparative example 2, the N1 value is large and thus the scratch is severe, and the N2 value in comparative example 2 is small compared to comparative example 1 and thus the positive electrode expansion rate in comparative example 2 is smaller than that in comparative example 1.

The preparation method of the lithium ion batteries in examples 5 to 8 is as follows:

examples 5 to 8 differ from example 2 only in the preparation of the positive electrode material, examples 5 to 8 being two kinds of LiNi having Dv50 of 10 μm and 3.5, respectively _0.8 Co _0.1 Mn _0.095 Al _0.005 O ₂ Mixing.

Example 5

Preparation of positive electrode material A: preparation of a Dv50 of 10.3 μm, a Dv99 of 18 μm and a specific surface area of 9.88m ² Positive electrode material precursor Ni/g _0.8 Co _0.1 Mn _0.1 (OH) ₂ Mixing it with LiOH, al ₂ O ₃ Mixing according to stoichiometric ratio, calcining at 800 deg.C for 16 hr to obtain primary substance, mixing the primary substance with H ₃ BO ₃ Uniformly mixing, sintering at 400 ℃ for 4 hours to coat boron, wherein the molar percentage of boron is 0.3%. Through screening parameter adjustment, the coated LiNi _0.8 Co _0.1 Mn _0.095 Al _0.005 O ₂ The Dv50 of the positive electrode material a was controlled to 10 μm and the Dv99 was controlled to 17 μm.

Preparation of positive electrode material B: preparation of a Dv50 of 3.8 μm, a Dv99 of 12 μm and a specific surface area of 15.2m ² Positive electrode material precursor Ni/g _0.8 Co _0.1 Mn _0.1 (OH) ₂ Mixing it with LiOH, al ₂ O ₃ Mixing according to stoichiometric ratio, calcining at 800 deg.C for 16 hr to obtain primary substance, mixing the primary substance with H ₃ BO ₃ Uniformly mixing, sintering at 400 ℃ for 4 hours to coat boron, wherein the molar percentage of boron is 0.3%. Through screening parameter adjustment, the coated LiNi _0.8 Co _0.1 Mn _0.095 Al _0.005 O ₂ The Dv50 of the positive electrode material B was controlled to 3.5 μm and Dv99 was controlled to 11 μm.

Positive electrode material a and positive electrode material B were mixed according to 8:2, and mixing the materials in a weight ratio.

Example 6

Example 6 and example 5 differ only in that the mixing ratio of the positive electrode materials a and B is 6:4.

Example 7

Example 7 and example 5 differ only in that the mixing ratio of the positive electrode materials a and B is 4:6.

example 8

Example 8 and example 5 differ only in that the mixing ratio of the positive electrode materials a and B is 2:8.

TABLE 2

The test results of examples 5 to 8 are shown in Table 2, and the positive electrode expansion rates of examples 5 to 8 are all less than 1%, and no particle scratches are found on the positive electrode, so that it is known that the values of N1 and N2 can be adjusted by adjusting the mixing ratio of the positive electrode material A and the positive electrode material B, and that as long as N1 and N2 satisfy N1 not less than 0 and not more than 4, N2 not less than 0 and not more than 8, the small positive electrode expansion rate can be ensured and the occurrence of particle scratches can be prevented, thereby improving the processability.

The preparation method of the lithium ion batteries in examples 9 to 11 is as follows:

example 9

Example 9 and example 2 differ only in that the thickness of the positive electrode active material layer on either side of the positive electrode was 10 μm.

Example 10

Example 10 and example 2 differ only in that the thickness of the positive electrode active material layer on either side of the positive electrode was 30 μm.

Example 11

Example 11 and example 2 differ only in that the thickness of the positive electrode active material layer on either side of the positive electrode was 40 μm.

TABLE 3 Table 3

The test results of examples 9 to 11 are shown in Table 3, and the positive electrode extensibility of examples 9 to 11 is less than 1% and there is no particle scratch on the positive electrode, and it is found that the values of N1 and N2 can be adjusted by changing the thickness d2 of the positive electrode active material layer on the positive electrode, thereby improving the processability. D2, however, cannot be too small, otherwise the risk of particle scratching increases.

The preparation method of the lithium ion batteries in examples 12 to 14 is as follows:

examples 12-14 differ from example 2 in the preparation of the positive electrode material by controlling the precursor Dv99 and the specific surface area, as well as the size of the positive electrode material Dv99 by controlling the sieving process parameters.

Example 12:

preparation of a positive electrode material: preparation of a Dv50 of 10.3 μm, a Dv99 of 13.8 μm and a specific surface area of 10.98m ² Positive electrode material precursor Ni/g _0.8 Co _0.1 Mn _0.1 (OH) ₂ Mixing it with LiOH, al ₂ O ₃ Mixing according to stoichiometric ratio, calcining at 800 deg.C for 16 hr to obtain primary substance, mixing the primary substance with H ₃ BO ₃ Uniformly mixing, sintering at 400 ℃ for 4 hours to coat boron, wherein the molar percentage of boron is 0.3%. Through screening parameter adjustment, the coated LiNi _0.8 Co _0.1 Mn _0.095 Al _0.005 O ₂ The Dv50 of the positive electrode material was controlled to 10. Mu.m, and the Dv99 was controlled to 13. Mu.m.

Example 13

Preparation of a positive electrode material: preparation of a Dv50 of 10.3 μm, a Dv99 of 23.4 μm and a specific surface area of 9.29m ² Positive electrode material precursor Ni/g _0.8 Co _0.1 Mn _0.1 (OH) ₂ Mixing with LiOH and Al2O3 according to stoichiometric ratio, calcining at 800 deg.C for 16 hr to obtain primary substance, mixing the primary substance with H ₃ BO ₃ Uniformly mixing, sintering at 400 ℃ for 4 hours to coat boron, wherein the molar percentage of boron is 0.3%. Through screening parameter adjustment, the coated LiNi _0.8 Co _0.1 Mn _0.095 Al _0.005 O ₂ The Dv50 of the positive electrode material was controlled to 10. Mu.m, and the Dv99 was controlled to 22. Mu.m.

Example 14

Preparation of a positive electrode material: preparation of a Dv50 of 10.3 μm, a Dv99 of 30.4 μm and a specific surface area of 8.66m ² Positive electrode material precursor Ni/g _0.8 Co _0.1 Mn _0.1 (OH) ₂ Mixing it with LiOH, al ₂ O ₃ Mixing according to stoichiometric ratio, calcining at 800 deg.C for 16 hr to obtain primary substance, mixing the primary substance with H ₃ BO ₃ Uniformly mixing, sintering at 400 ℃ for 4 hours to coat boron, wherein the molar percentage of boron is 0.3%. Through screening parameter adjustment, the coated LiNi _0.8 Co _0.1 Mn _0.095 Al _0.005 O ₂ The Dv50 of the positive electrode material was controlled to 10 μm and the Dv99 was controlled to 28 μm.

TABLE 4 Table 4

The test results of examples 12 to 14 are shown in Table 4, and the positive electrode ductility of examples 12 to 14 is less than 1% and there is no particle scratch on the positive electrode, and it is found that N1 and N2 can be adjusted by changing Dv99 of the positive electrode material, thereby improving the processability. However, the smaller the Dv99 of the positive electrode material, the more difficult the process is to control and the higher the production cost, so in some embodiments of the present application 5 μm or less Dv99 or less 40 μm is defined.

The preparation method of the lithium ion batteries in examples 15 to 16 is as follows:

example 15

The difference between example 15 and example 2 is that the positive electrode has a compacted density of 3.1g/cm ³ 。

Example 16

The difference between example 16 and example 2 is that the positive electrode has a compacted density of 3.7g/cm ³ 。

TABLE 5

The test results of examples 15 to 16 are shown in Table 5, and the positive electrode in examples 15 and 16 each have an elongation of less than 1% and no particle scratch on the positive electrode, and it is found that the impact on N1 and N2 is small by changing the compacted density of the positive electrode, but if the compacted density is too large, the elongation of the pole piece may be increased, which is detrimental to the processability, and if the compacted density is too small, the energy density may be low.

The preparation method of the lithium ion batteries in examples 17 to 19 is as follows:

the main difference between examples 17-19 and example 2 is the preparation of the cathode material

Example 17

Preparation of a positive electrode material: preparation of a Dv50 of 10.3 μm, a Dv99 of 18 μm and a specific surface area of 9.88m ² Positive electrode material precursor Ni/g _0.5 Co _0.2 Mn _0.3 (OH) ₂ And Li is added with ₂ CO ₃ 、Al ₂ O ₃ Mixing according to stoichiometric ratio, calcining at 880 deg.C for 24 hr to obtain primary substance, mixing the primary substance with H ₃ BO ₃ Uniformly mixing, sintering at 400 ℃ for 4 hours to coat boron, wherein the molar percentage of boron is 0.3%. Through screening parameter adjustment, the coated LiNi _0.5 Co _0.2 Mn _0.295 Al _0.005 O ₂ The Dv50 of the positive electrode material was controlled to 10. Mu.m, and the Dv99 was controlled to 17. Mu.m.

Example 18

Preparation of a positive electrode material: preparation of a Dv50 of 10.3 μm, a Dv99 of 18 μm and a specific surface area of 9.88m ² Positive electrode material precursor Ni/g _0.6 Co _0.2 Mn _0.2 (OH) ₂ And Li is added with ₂ CO ₃ 、Al ₂ O ₃ Mixing according to stoichiometric ratio, calcining at 850 deg.C for 22 hr to obtain primary substance, mixing the primary substance with H ₃ BO ₃ Uniformly mixing, sintering at 400 ℃ for 4 hours to coat boron, wherein the molar percentage of boron is 0.3%. Through screening parameter adjustment, the coated LiNi _0.6 Co _0.2 Mn _0.195 Al _0.005 O ₂ The Dv50 of the positive electrode material was controlled to 10. Mu.m, and the Dv99 was controlled to 17. Mu.m.

Example 19

Preparation of a positive electrode material: preparation of a Dv50 of 10.3 μm, a Dv99 of 18 μm and a specific surface area of 9.88m ² Positive electrode material precursor Ni/g _0.70 Co _0.05 Mn _0.25 (OH) ₂ And Li is added with ₂ CO ₃ 、Al ₂ O ₃ Mixing according to stoichiometric ratio, calcining at 830 deg.C for 19 hr to obtain primary substance,and then combining the primary material with H ₃ BO ₃ Uniformly mixing, sintering at 400 ℃ for 4 hours to coat boron, wherein the molar percentage of boron is 0.3%. Through screening parameter adjustment, the coated LiNi _0.70 Co _0.05 Mn _0.245 Al _0.005 O ₂ The Dv50 of the positive electrode material was controlled to 10. Mu.m, and the Dv99 was controlled to 17. Mu.m.

TABLE 6

The test results of examples 17 to 19 are shown in Table 6, and the kinds of the positive electrode materials are changed, so that the effect on the test results is not great. The control of the relation of N1, N2 and d1 is beneficial to improving the processing performance of all positive electrode materials, especially nickel cobalt manganese ternary positive electrode materials.

Examples 20 to 31

Examples 20 to 31 differ from example 2 in the composition of the electrolyte, specifically in that substances shown in table 7 were further added to the electrolyte, and the content of the added substances in table 7 was calculated based on the mass of the electrolyte.

TABLE 7

As can be seen from comparative examples 2 and examples 20 to 31, the 8C rate retention of examples 20 to 31 is significantly higher than that of example 2, and it can be seen that the addition of at least one of the polynitrile compound or the thiooxy double bond compound shown in table 7 to the electrolyte can improve the rate performance of the lithium ion battery.

The foregoing description is only of the preferred embodiments of the present application and is presented as a description of the principles of the technology being utilized. It should be understood by those skilled in the art that the scope of the disclosure in this application is not limited to the specific combination of the above technical features, but also covers other technical features formed by any combination of the above technical features or their equivalents. Such as the technical proposal formed by the mutual replacement of the above-mentioned characteristics and the technical characteristics with similar functions disclosed in the application.

Claims

1. An electrochemical device, comprising: a positive electrode, a negative electrode, and a separator;

The positive electrode includes: the positive electrode current collector comprises a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is positioned on one surface or two surfaces of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode material;

a separator located between the positive electrode and the negative electrode;

in the layer thickness direction of the positive electrode active material layer, the average value of the particle numbers of the particle diameters not smaller than d1 of the positive electrode active material layer on either side of the positive electrode current collector is N1, the average value of the particle numbers of the particle diameters not smaller than 0.5d1 is N2, and N1 and N2 satisfy: n1 is more than or equal to 0 and less than or equal to 4, N2 is more than or equal to 0 and less than or equal to 8, wherein d1 is the thickness of the positive current collector, and the unit is mu m;

the Dv50 of the positive electrode material satisfies: 0.5d1.ltoreq.Dv50.ltoreq.1.2d1, and/or that the cathode material has a Dv99 of: dv99 is more than or equal to 0.5d1 and less than or equal to 2d1;

wherein the electrochemical device further comprises an electrolyte comprising at least one of a polynitrile compound or a sulfur-oxygen double bond compound;

n1 and N2 were tested as follows: determining a straight line with the length of 80 mu m on the positive electrode active material layer, wherein the straight line is perpendicular to the thickness direction of the positive electrode active material layer, drawing a line on the straight line every 20 mu m along the thickness direction of the positive electrode active material layer, wherein each line is parallel to each other, determining the particle number of particles which are intersected with the line and have the particle size of not less than d1 on each line, averaging to obtain N1, determining the particle number of particles which are intersected with the line and have the particle size of not less than 0.5d1 on each line, and averaging to obtain N2, wherein the particle size of the particles is the longest particle diameter of the particles.

2. The electrochemical device according to claim 1, wherein,

the thickness d1 of the positive electrode current collector satisfies: d1 is more than or equal to 5 mu m and less than or equal to 15 mu m.

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

4. The electrochemical device according to claim 1, wherein,

1.3≤Dv99/Dv50≤8.0。

5. the electrochemical device according to claim 1, wherein,

the thickness d2 of the positive electrode active material layer on either side of the positive electrode current collector satisfies:

10μm≤d2≤40μm。

6. the electrochemical device according to claim 1, wherein,

1≤d2/d1≤4。

7. the electrochemical device according to claim 1, wherein,

8. The electrochemical device according to claim 1, wherein,

the compaction density of the positive electrode is more than or equal to 3.1g/cm ³ And less than or equal to 6.0g/cm ³ 。

9. The electrochemical device according to claim 1, wherein the polynitrile compound comprises at least one of 1,3, 6-hexanetrinitrile, 1,2, 3-tris (2-cyanoethoxy) propane, 1, 2-bis (2-cyanoethoxy) ethane, adiponitrile, succinonitrile; the sulfur-oxygen double bond compound comprises at least one of methane disulfonic acid methylene ester, 1, 3-propane sultone, 2, 4-butane sultone or vinyl sulfate.

10. The electrochemical device according to claim 1, wherein the polynitrile compound content is a% and the sulfur-oxygen double bond compound content is B% based on the weight of the electrolyte, satisfying 0.1.ltoreq.a/b.ltoreq.5.

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