WO2023123025A1 - Electrochemical device and electronic device - Google Patents

Abstract

The present application relates to an electrochemical device and an electronic device. Specifically, the present application provides an electrochemical device, comprising a negative electrode and an electrolyte. The negative electrode comprises: a negative current collector; an undercoat layer comprising a volume expansion resin and formed on at least one surface of the negative current collector; and a negative active material layer, the negative active material layer comprising a negative active material and formed on the undercoat layer. The electrolyte solution comprising propyl propionate. According to the design, the safety performance of the electrochemical device under thermal runaway can be fully improved, and the voltage drop of the electrochemical device under low-temperature storage can be effectively reduced.

Description

Electrochemical devices and electronic devices technical field

The present application relates to the field of energy storage, in particular to an electrochemical device and an electronic device, especially a lithium ion battery.

Background technique

With the popularization and application of smart products, people's demand for electronic products such as mobile phones, laptops, and cameras is increasing year by year, and electrochemical devices, as power sources for electronic products, play an increasingly important role in our daily life. Among them, lithium-ion batteries are widely used in the field of consumer electronics due to their advantages such as large specific energy, high working voltage, low self-discharge rate, small size, and light weight.

However, in recent years, due to the frequent occurrence of explosions of electronic products caused by lithium-ion batteries, the safety of lithium-ion batteries has attracted people's attention. Ensuring the safety of lithium-ion batteries is the primary problem to be solved in expanding their applications. In addition, with the application of lithium-ion batteries under extreme conditions, how to improve the discharge performance of electrochemical devices at low temperatures is also a hot spot of concern.

In view of this, it is necessary to provide an electrochemical device and an electronic device with high safety under high temperature and high pressure and low voltage drop under low temperature storage.

Contents of the invention

The embodiments of the present application solve the problems existing in the prior art to some extent by adjusting the composition of the negative electrode applied in the electrochemical device and the components in the electrolyte.

In one aspect of the present application, the present application provides an electrochemical device, which includes a negative electrode and an electrolyte solution, the negative electrode includes: a negative electrode current collector; an undercoat layer, the undercoat layer includes a volume expansion resin and is formed on the on at least one surface of a negative electrode current collector; and a negative electrode active material layer including a negative electrode active material and formed on the undercoat layer; and the electrolyte solution includes propyl propionate.

According to an embodiment of the present application, based on the total weight of the electrolyte, the content of the propyl propionate is x%; based on the weight of the primer layer, the content of the volume expansion resin is a%; and wherein 5≤x≤50 and x/a≥1.

According to an embodiment of the present application, 0.1≤a≤10.

According to an embodiment of the present application, when the internal temperature of the electrochemical device is 20°C to 40°C, the volume of the volume expansion resin is V ₀ , wherein the internal temperature of the electrochemical device reaches 140°C to 160°C Within the range, the volume of the volume expansion resin is V ₁ , wherein V ₁ /V ₀ ≥2.

According to an embodiment of the present application, the volume expansion resin includes at least one of polyethylene, polypropylene, polyethylene vinyl acetate or polypropylene.

According to an embodiment of the present application, the volume expansion resin includes thermally expandable microspheres.

According to an embodiment of the present application, the undercoat layer further includes a conductive agent, and the conductive agent includes at least one of carbon nanotubes, graphene or carbon black.

According to an embodiment of the present application, the primer layer further includes a binder, and the binder includes polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, styrene-butylene At least one of diene rubber or fluorine-containing rubber.

According to an embodiment of the present application, the electrolyte solution also includes a compound having a cyano group, and the compound having a cyano group includes succinonitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, 1,3,5 -pentanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane or 1,2,4-tris at least one of (2-cyanoethoxy)butane.

According to an embodiment of the present application, the electrolyte also includes fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, vinylene carbonate, 1-propyl phosphoric acid cyclic anhydride or lithium difluorophosphate at least one of the

According to an embodiment of the present application, the negative electrode satisfies H ₁ /H≤0.1, wherein along the direction perpendicular to the negative electrode current collector, the thickness of the undercoat layer is H ₁ μm, and the thickness of the negative electrode active material layer is is Hμm.

According to an embodiment of the present application, the thickness of the undercoat layer is H ₁ μm and 0.5≦H ₁ ≦5.

According to an embodiment of the present application, the negative electrode satisfies W ₁ /W≤0.5, wherein the weight of the undercoat layer is W ₁ mg/1540.25mm2, and the weight of the negative electrode active material layer is W mg/1540.25mm2.

According to an embodiment of the present application, the weight of the primer layer is W ₁ mg/1540.25mm2, and 20≤W _1≤100 .

In another aspect of the present application, the present application provides an electronic device comprising the electrochemical device described in the present application.

The application ensures the high safety performance of the electrochemical device under high pressure and high temperature by using a combination of a specific negative electrode structure and electrolyte, and can effectively reduce the voltage drop of the electrochemical device under low temperature storage.

Additional aspects and advantages of the embodiments of the present application will be partially described, shown, or explained through the implementation of the embodiments of the present application in the subsequent description.

Detailed ways

Embodiments of the present application will be described in detail below. The examples of the present application should not be construed as limiting the present application.

Unless otherwise expressly indicated, the following terms used herein have the meanings indicated below.

The terms "comprising", "comprising" and "comprising" are used in their open, non-limiting sense.

Additionally, amounts, ratios, and other values are sometimes presented herein in a range format. It should be understood that such range formats are used for convenience and brevity, and are to be read flexibly to encompass not only the values expressly designated as range limitations, but also all individual values or subranges encompassed within the stated range, as if expressly Specify each value and subrange generically.

In the detailed description and claims, a list of items linked by the terms "one or more of", "one or more of", "one or more of" or other similar terms Can mean any combination of the listed items. For example, if the items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if the items A, B, and C are listed, 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 present application found that the safety problem of electrochemical devices (eg, lithium-ion batteries) is essentially related to thermal runaway. For example, during the use of electronic products, abuse of the electronic products will inevitably be involved, such as overcharging the electrochemical device due to charging the electronic products overnight. Abuse will cause the electrochemical device to heat up or even become hot, which will easily induce and intensify the side reactions inside the electrochemical device. These side reactions mainly include the decomposition of the positive and negative active materials and the reaction between the positive and negative active materials and the electrolyte, and most of these reactions are exothermic reactions, which will cause the internal temperature of the electrochemical device to further increase (such as , whose internal temperature is as high as 120 °C and above), eventually leading to thermal runaway of the electrochemical device.

To solve this problem, the commonly used technology at present is to coat the surface of the separator of the electrochemical device with a low melting point polymer. When the internal temperature of the electrochemical device rises, the polymer will melt and be sucked into the micropores of the separator matrix by capillary action to promote the closure of the separator, thereby cutting off the transmission channel of lithium ions, terminating the occurrence of charge and discharge reactions, ensuring Safety of electrochemical devices under abuse. However, the disadvantage of this method is that when thermal runaway occurs, the temperature tends to rise rapidly, and at this time, the polymer has no time to melt and close the pores of the diaphragm in a large area by means of capillary action, so that it is too late to terminate the occurrence of the charge and discharge reaction; However, as the temperature continues to rise and the side reactions intensify, the structure of the positive and negative electrodes will be irreversibly damaged, resulting in a greatly reduced thermal stability, thereby causing safety issues.

In order to solve the above problems, the present application uses a volume expansion resin in the primer layer of the negative electrode, so that the volume expansion resin can quickly absorb heat and cause volume expansion when the internal temperature of the electrochemical device rises rapidly or even thermal runaway occurs. , block the electron transport between the negative electrode active material layer and the negative electrode current collector, stop the electrochemical reaction, and improve the safety performance of the electrochemical device. The present application also adds propyl propionate to the electrolyte, which can not only enhance the swelling effect on the volume expansion resin, improve the porosity of the pole piece, but also form a more uniform solid electrolyte interface film (SEI) on the surface of the negative electrode active material particles. film), thereby reducing the voltage drop of the electrochemical device under low-temperature storage. As follows, the present application will describe each component of the electrochemical device proposed in the present application in detail.

I. Negative electrode

The negative electrode includes a negative electrode current collector, an undercoat layer formed on at least one surface of the negative electrode current collector, and a negative electrode active material layer formed on the undercoat layer, wherein the negative electrode active material layer contains the negative electrode active material. The negative electrode active material layer may be one or more layers, and each layer of the multilayer negative electrode active material may contain the same or different negative electrode active materials. The negative electrode active material is any material capable of reversibly intercalating and deintercalating metal ions such as lithium ions. In some embodiments, the charge capacity of the negative active material is greater than the discharge capacity of the positive active material, so as to prevent unintentional deposition of lithium metal on the negative electrode during charging.

A main feature of the negative electrode of the present application is that the negative electrode primer layer includes a volume expansion resin. When the internal temperature of the electrochemical device rises rapidly or even thermal runaway occurs, the volume expansion resin can quickly absorb heat, cause volume expansion, block the electron transmission between the negative electrode active material layer and the negative electrode current collector, and terminate the electrochemical reaction. occur, thereby improving the safety performance of electrochemical devices.

In some embodiments, based on the weight of the primer layer, the content of the volume expansion resin is a%, wherein 0.1≤a≤10. In some embodiments, 0.5≤a≤8. In some embodiments, 1≦a≦5. In some embodiments, 2≤a≤3. In some embodiments, a is 0.1, 0.5, 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 the range consisting of any two values above. When the content of the volume expansion resin in the primer layer is within the above range, it is helpful to further improve the safety performance of the electrochemical device.

In some embodiments, the volume expansion resin satisfies the following relationship: V ₁ /V ₀ ≥ 2, wherein when the internal temperature of the electrochemical device is in the range of 20°C to 40°C, the volume of the volume expansion resin is V ₀ , when the internal temperature of the electrochemical device reaches the range of 140°C to 160°C, the volume of the volume expansion resin is V ₁ . In some embodiments, V ₁ /V ₀ ≧5. In some embodiments, V ₁ /V ₀ ≧7. In some embodiments, V ₁ /V ₀ ≧10. In some embodiments, V ₁ /V ₀ is 2, 3, 5, 7, 10, 12, 15, 20 or within a range consisting of any two of the above values. When the volume change of the volume expansion resin satisfies the above relationship, it is helpful to further improve the safety performance of the electrochemical device.

In some embodiments, the volume expansion resin includes at least one of polyethylene, polypropylene, polyethylene vinyl acetate, or polypropylene.

In some embodiments, the volume expansion resin includes thermally expandable microspheres.

In some embodiments, the volume expansion rate of the thermally expandable microspheres when the internal temperature of the electrochemical device rises above 130°C is compared to the volume of the thermally expandable microspheres when the internal temperature of the electrochemical device is 20°C to 40°C 5 times or more without cracking. In some embodiments, the volume expansion rate of the thermally expandable microspheres when the internal temperature of the electrochemical device rises above 130°C is compared to the volume of the thermally expandable microspheres when the internal temperature of the electrochemical device is 20°C to 40°C 7 times or more without cracking. In some embodiments, the volume expansion rate of the thermally expandable microspheres when the internal temperature of the electrochemical device rises above 130°C is compared to the volume of the thermally expandable microspheres when the internal temperature of the electrochemical device is 20°C to 40°C 10 times or more without cracking.

The heat-expandable microspheres can be obtained by enclosing a material that is easily expandable when heated in an elastic shell. Such heat-expandable microspheres can be prepared by any appropriate method, such as coacervation method, interfacial polymerization method and the like.

Heat-expandable substances may include, but are not limited to, propane, propylene, butene, n-butane, isobutane, isopentane, neopentane, n-pentane, n-hexane, isohexane, heptane, octane , Petroleum ether, halides of methane, tetraalkylsilane and other low-boiling liquids; or azodicarbonamide gasified by pyrolysis, etc.

Substances constituting the shell include, but are not limited to, polymers composed of at least one of the following monomers: acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fuma Nitrile monomers such as nitrile; carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, etc.; vinylidene chloride; vinyl acetate; methyl (meth)acrylate, Ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, isobornyl (meth)acrylate, cyclo(meth)acrylate (Meth)acrylate monomers such as hexyl ester, benzyl (meth)acrylate, and β-carboxyethyl acrylate; styrene monomers such as styrene, α-methylstyrene, and chlorostyrene; acrylamide, Amide monomers such as substituted acrylamide, methacrylamide, and substituted methacrylamide. Polymers composed of these monomers may be homopolymers or copolymers. As the copolymer, for example, it includes, but is not limited to, vinylidene chloride-methyl methacrylate-acrylonitrile copolymer, methyl methacrylate-acrylonitrile-methacrylonitrile copolymer, methyl methacrylate - Acrylonitrile copolymer, acrylonitrile-methacrylonitrile-itaconic acid copolymer, etc.

In the process of preparing the above-mentioned heat-expandable microspheres, an inorganic foaming agent or an organic foaming agent can be used. Inorganic foaming agents include, but are not limited to, ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium borohydride, various azides, and the like. Organic foaming agents include, but are not limited to, chlorofluoroalkane compounds such as trichloromonofluoromethane and dichloromonofluoromethane; azobisisobutyronitrile, azodicarbonamide, barium azodicarboxylate, etc. Nitrogen compounds; hydrazine compounds such as p-toluenesulfonyl hydrazide, diphenylsulfone-3,3'-disulfonyl hydrazide, 4,4'-oxobisbenzenesulfonyl hydrazide, allyl disulfonyl hydrazide, etc.; Semicarbazide compounds such as p-toluenesulfonylsemicarbazide and 4,4'-oxobis(benzenesulfonylsemicarbazide); triazoles such as 5-morpholino-1,2,3,4-thiotriazole Compounds; N-nitroso compounds such as N,N'-dinitrosopentamethylenetetramine, N,N'-dimethyl-N,N'-dinitrosoterephthalamide, etc. .

Commercially available products can also be used for the above-mentioned heat-expandable microspheres. For example, commercially available heat-expandable microspheres may include, but are not limited to, the trade name "Matsumoto Microsphere" manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. (grades: F-30, F-30D, F-36D, F-36LV, F -50, F-50D, F-65, F-65D, FN-100SS, FN-100SSD, FN-180SS, FN-180SSD, F-190D, F-260D, F-2800D), Japan Fillite Co.,Ltd .Manufactured under the trade name "Expancel" (grades: 053-40, 031-40, 920-40, 909-80, 930-120), "DAIFOAM" manufactured by Kureha Chemical Industry Co., Ltd. (grades: H750, H850, H1100, S2320D, S2640D, M330, M430, M520), Sekisui Chemical Co., Ltd. "ADVANCELL" (grade: EML101, EMH204, EHM301, EHM302, EHM303, EM304, EHM401, EM403, EM501), etc.

In some embodiments, at room temperature, the particle size of the heat-expandable microspheres is 0.5 μm-80 μm. In some embodiments, at room temperature, the particle size of the heat-expandable microspheres is 5 μm-45 μm. In some embodiments, at room temperature, the particle size of the heat-expandable microspheres is 10 μm-20 μm. In some embodiments, at room temperature, the particle size of the heat-expandable microspheres is 10 μm-15 μm. In some embodiments, at room temperature, the average particle size of the heat-expandable microspheres is 6 μm-45 μm. In some embodiments, the thermally expandable microspheres have an average particle diameter of 15 μm-35 μm at room temperature. The particle size and average particle size of the heat-expandable microspheres can be obtained by the particle size distribution measurement method in the laser light scattering method.

In some embodiments, the negative electrode primer layer further includes a conductive agent, and the conductive agent includes at least one of carbon nanotubes, graphene or carbon black. The main function of the conductive agent is to improve the conductivity of the undercoat layer, optimize the transmission of electrons, reduce the internal resistance, and improve the impedance characteristics of the electrochemical device. In addition, when both thermally expandable microspheres and graphene are used in the negative undercoat layer, the electrochemical device can exhibit particularly excellent high-temperature safety performance and low-temperature impedance characteristics.

In some embodiments, the negative electrode primer layer also includes a binder, which includes polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, styrene-butadiene At least one of rubber or fluorine-containing rubber. The main function of the binder is to enhance the bonding between the particles in the undercoat layer and the bonding between the negative electrode current collector and the negative electrode active material layer, so as to avoid the negative electrode of the electrochemical device from appearing during the charge-discharge cycle. Separation between the negative electrode current collector, the negative electrode undercoat layer and the negative electrode active material layer.

In some embodiments, the negative electrode satisfies H ₁ /H≤0.1, wherein along the direction perpendicular to the negative electrode current collector, the thickness of the undercoat layer is H ₁ μm, and the thickness of the negative electrode active material layer is Hμm. In some embodiments, 0.02≦H ₁ /H≦0.1. In some embodiments, 0.05≦H ₁ /H≦0.1. In some embodiments, H ₁ /H is 0.001, 0.002, 0.005, 0.008, 0.01, 0.02, 0.05, 0.08, 0.1 or is within a range consisting of any two values above. When H ₁ /H is within the above range, in the case of thermal runaway, the primer layer can not only fully exert its function, but also be easily infiltrated by the electrolyte, so that the propyl propionate in the electrolyte can play a role to further improve High-temperature safety performance and low-temperature discharge performance of electrochemical devices.

In some embodiments, the undercoat layer has a thickness of H ₁ μm, where 0.5≦H ₁ ≦5. In some embodiments, 1≦H ₁ ≦3. In some embodiments, _H1 is 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or is in a range consisting of any two of the above values.

In some embodiments, the negative electrode satisfies W ₁ /W≤0.5, wherein the weight of the undercoat layer is W ₁ mg/1540.25mm2, and the weight of the negative electrode active material layer is W mg/1540.25mm2. In some embodiments, 0.01≦W ₁ /W≦0.5. In some embodiments, 0.05≤W ₁ /W≤0.1. In some embodiments, W ₁ /W is 0.01, 0.02, 0.05, 0.08, 0.1, 0.2, 0.5 or is within a range consisting of any two values above. When W ₁ /W is within the above range, the primer layer can not only fully exert its function to control the thermal runaway of the electrochemical device, but also be easily wetted by the electrolyte so as to improve the low-temperature discharge performance of the electrochemical device.

In some embodiments, 20≦W ₁ ≦100. In some embodiments, 30≦W ₁ ≦80. In some embodiments, 40≦W ₁ ≦50. In some embodiments, W ₁ is 20, 30, 40, 50, 60, 70, 80, 90, 100 or within a range consisting of any two of the above values.

The present application has no special limitation on the negative electrode current collector, which may be any known current collector. For example, examples of the negative electrode current collector include, but are not limited to, metal materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative current collector is copper.

When the negative electrode current collector is a metal material, the form of the negative electrode current collector may include, but not limited to, metal foil, metal cylinder, metal strip, metal plate, metal film, expanded metal, stamped metal, foamed metal, etc. In some embodiments, the negative electrode current collector is a metal film. In some embodiments, the negative electrode current collector is copper foil. In some embodiments, the negative electrode current collector is a rolled copper foil based on a rolling method or an electrolytic copper foil based on an electrolytic method.

In some embodiments, the thickness of the negative electrode current collector is greater than 1 μm or greater than 5 μm. In some embodiments, the thickness of the negative electrode current collector is less than 100 μm or less than 50 μm. In some embodiments, the thickness of the negative electrode current collector is within the range formed by any two values above.

In the present application, there is no particular limitation on the negative electrode active material, as long as it can reversibly intercalate and deintercalate metal ions such as lithium ions. Examples of negative electrode active materials may include, but are not limited to, carbon materials such as natural graphite and artificial graphite; metals such as silicon (Si) and tin (Sn); or oxides of metal elements such as Si and Sn. The negative electrode active materials can be used alone or in combination.

The negative active material layer may further include a negative binder. The negative electrode binder can improve the combination of the negative electrode active material particles and the combination of the negative electrode active material and the current collector. The type of negative electrode binder is not particularly limited, as long as it is a material stable to the electrolyte solution or the solvent used in electrode production. In some embodiments, the negative binder includes a resin binder. Examples of resin binders include, but are not limited to, fluororesins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and the like. When using a water-based solvent to prepare the negative electrode mixture slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salt, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or Its salt, polyvinyl alcohol, etc.

The negative electrode can be prepared by the following method: first coat the undercoat slurry containing volume expansion resin, conductive material and binder on the negative electrode current collector; then coat the negative active material of negative active material, resin binder, etc. The layered slurry is dried and then rolled to obtain a negative electrode.

II. Electrolyte

The electrochemical device of the present application further includes an electrolytic solution including an electrolyte, a solvent for dissolving the electrolyte, and an additive.

A main feature of the electrolyte of the present application is that the electrolyte includes propyl propionate. Propyl propionate can not only enhance the swelling effect on the volume expansion resin, increase the porosity of the pole piece, but also form a more uniform solid electrolyte interfacial film (SEI film) on the surface of the negative electrode active material particles, thereby reducing the storage temperature of the electrochemical device at low temperature. The lower voltage drop optimizes the low-temperature discharge performance of the electrochemical device.

In some embodiments, based on the total weight of the electrolyte, the content of the propyl propionate is x%, wherein 5≤x≤50. In some embodiments, 10≤x≤30. In some embodiments, x is 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or within a range consisting of any two of the above values. When the content of propyl propionate in the electrolyte is within the above range, it is helpful to further improve the voltage drop of the electrochemical device under low temperature storage.

In some embodiments, x/a > 2. In some embodiments, x/a > 3. In some embodiments, x/a≧5. In some embodiments, x/a is 2, 3, 5, 8, 10, 20, 30, 40, 50 or is within a range consisting of any two values above. Propyl propionate can reduce the swelling of the volume expansion resin in the electrolyte, especially under low temperature conditions, and inhibit the increase of the internal resistance of the battery. Therefore, by adjusting the relationship between the content of propyl propionate in the electrolyte and the content of the volume expansion resin in the primer layer so that x/a is within the above range, the safety performance and low-temperature storage voltage drop of the electrochemical device can be further improved.

In some embodiments, the electrolyte solution may further include a compound having a cyano group (—CN).

In some embodiments, the compound having a cyano group includes, but is not limited to, one or more of the following: succinonitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane , 1,6-dicyanohexane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile Nitrile, 1,4-dicyanopentane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, ethylene glycol bis(propionitrile) ether, 3 ,5-dioxa-pimelonitrile, 1,4-bis(cyanoethoxy)butane, diethylene glycol bis(2-cyanoethyl)ether, triethylene glycol bis(2-cyano ethyl) ether, tetraethylene glycol bis(2-cyanoethyl) ether, 1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy ) butane, 1,5-bis(2-cyanoethoxy)pentane, ethylene glycol bis(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-methanol Base-3-hexene, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 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(cyanoethoxymethylene)pentane, 1,2,7 - Tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane or 1,2,5-tris(cyanoethoxy)pentane.

The above-mentioned compounds having a cyano group may be used alone or in any combination. If the electrolyte contains two or more compounds with cyano groups, the content of the compounds with cyano groups refers to the total content of the two or more compounds with cyano groups.

In some embodiments, based on the total weight of the electrolytic solution, the content of the compound having a cyano group is Y%, wherein 0.1≤Y≤15. In some embodiments, 0.5≤Y≤10. In some embodiments, 1.0≤Y≤8.0. In some embodiments, 3.0≤Y≤5.0. In some embodiments, Y is 0.1, 0.2, 0.5, 0.8, 1, 2, 5, 8, 10, 12, 15 or is in a range consisting of any two values above.

When a compound having a cyano group is added to the electrolyte, the safety performance of the electrochemical device under high temperature and high pressure can be further improved and its voltage drop under low temperature storage can be further suppressed. This is because the compound with cyano group can form a protective film with excellent performance on the surface of the negative electrode, which can stabilize the active metal in the positive electrode active material, inhibit the dissolution of the active metal, and improve the stability and safety of the electrochemical device under high temperature and high pressure. performance. In addition, compounds with cyano groups can accelerate the swelling of propyl propionate to the volume expansion resin, thereby realizing the rapid transport of ions and electrons and reducing the impedance and voltage drop of electrochemical devices. In addition, a further optimized effect can be achieved by combining multiple compounds having cyano groups.

In some embodiments, the electrolyte also includes fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, vinylene carbonate, 1-propyl phosphoric acid cyclic anhydride or lithium difluorophosphate at least one of . These additives can not only promote the swelling effect of propyl propionate on the volume expansion resin, but also help to form a more uniform SEI film on the surface of the negative active material particles, thereby further improving the electrochemical performance of the electrochemical device, especially the high temperature safety performance.

In some embodiments, the electrolyte solution further comprises any non-aqueous solvent known in the prior art as a solvent for the electrolyte solution.

In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonate, chain carbonate, cyclic carboxylate, chain carboxylate, cyclic Ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorinated solvents.

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 butylene carbonate. In some embodiments, the cyclic carbonate has 3-6 carbon atoms.

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 carbonate Chain carbonates such as ethyl n-propyl carbonate, ethyl n-propyl carbonate, di-n-propyl carbonate, etc. Examples of chain carbonates substituted with fluorine may include, but are not limited to, one or more of the following: bis(fluoromethyl)carbonate, bis(difluoromethyl)carbonate, bis(trifluoromethyl)carbonate base) carbonate, bis(2-fluoroethyl)carbonate, bis(2,2-difluoroethyl)carbonate, bis(2,2,2-trifluoroethyl)carbonate, 2-fluoroethyl methyl carbonate, 2,2-difluoroethyl methyl carbonate and 2,2,2-trifluoroethyl methyl carbonate, etc.

In some embodiments, examples of the cyclic carboxylate may include, but are not limited to, one or more of the following: one or more of γ-butyrolactone and γ-valerolactone. In some embodiments, some of the hydrogen atoms of the cyclic carboxylate may be replaced by fluorine.

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

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.

In some embodiments, examples of the chain ethers 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-ethoxy Methoxyethane and 1,2-ethoxymethoxyethane, etc.

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 phosphate Diethyl ester, ethylene methyl phosphate, ethylene ethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tris(2,2,2- phosphate Trifluoroethyl) ester and tris(2,2,3,3,3-pentafluoropropyl) phosphate, etc.

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, dimethylsulfone, disulfone Ethyl sulfone, ethyl methyl sulfone, methyl propyl 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 replaced by fluorine.

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.

In some embodiments, the solvent used in the electrolyte of the present application includes cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application comprises an organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propionic acid Propyl ester, n-propyl acetate, ethyl acetate and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application comprises: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone and combinations thereof .

In some embodiments, the electrolyte is not particularly limited, and any known substance as an electrolyte can be used arbitrarily. In the case of lithium secondary batteries, lithium salts are generally used. Examples of electrolytes may include, but are not limited to, inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAlF ₄ , LiSbF ₆ , LiWF ₇ ; lithium tungstates such as LiWOF ₅ ; HCO ₂ Li, CH ₃ CO ₂ Li, CH ₂ FCO ₂ Li, CHF ₂ CO ₂ Li, CF ₃ CO ₂ Li, CF ₃ CH ₂ CO ₂ Li, CF 3 CF ₂ CO ₂ Li, CF ₃ CF ₂ CF ₂ CO ₂ Li, CF ₃ CF _{2 CF 2} Lithium carboxylate salts such as CF ₂ CO ₂ Li; FSO ₃ Li, CH ₃ SO ₃ Li, CH ₂ FSO ₃ Li, CHF ₂ SO ₃ Li, CF ₃ SO ₃ Li, CF ₃ CF ₂ SO ₃ Li, CF ₃ CF ₂ CF ₂ SO ₃ Li, CF ₃ CF ₂ CF ₂ CF ₂ SO ₃ Li and other sulfonate lithium salts; LiN(FCO) ₂ , LiN(FCO)(FSO ₂ ), LiN(FSO ₂ ) ₂ , LiN( FSO ₂ )(CF ₃ SO ₂ ), LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , cyclic lithium 1,2-perfluoroethanebissulfonylimide, cyclic 1 , 3-perfluoropropane bissulfonylimide lithium, LiN(CF ₃ SO ₂ )(C ₄ F ₉ SO ₂ ) and other imide lithium salts; LiC(FSO ₂ ) ₃ , LiC(CF ₃ SO ₂ ) _3. LiC(C ₂ F ₅ SO ₂ ) ₃ and other methylated lithium salts; bis(malonato)borate lithium salt, difluoro(malonate) borate lithium salt, etc. (malonato)boric acid Lithium salts; lithium tris(malonato)phosphate, lithium difluorobis(malonato)phosphate, lithium tetrafluoro(malonato)phosphate and other (malonato)phosphate lithium salts; and LiPF ₄ (CF ₃ ) ₂ , LiPF ₄ (C ₂ F ₅ ) ₂ , LiPF ₄ (CF ₃ SO ₂ ) ₂ , LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ , LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiBF ₃ C ₃ F ₇ , LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , LiBF ₂ (CF ₃ SO ₂ ) ₂ , LiBF ₂ (C ₂ F ₅ SO ₂ ) ₂ and other fluorine-containing Organolithium salts; lithium difluorooxalate borate, lithium bis(oxalate)borate and other lithium oxalate borate salts; lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, tri(oxalato)phosphoric acid Lithium oxalatophosphate lithium salts, etc.

In some embodiments, the electrolyte is selected from LiPF ₆ , LiSbF ₆ , FSO ₃ Li, CF ₃ SO ₃ Li, LiN(FSO ₂ ) ₂ , LiN(FSO ₂ )(CF ₃ SO ₂ ), LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , cyclic lithium 1,2-perfluoroethanebissulfonimide, cyclic lithium 1,3-perfluoropropanebissulfonimide, LiC(FSO ₂ ) ₃ , LiC(CF ₃ SO ₂ ) ₃ , LiC(C ₂ F ₅ SO ₂ ) ₃ , LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (C ₂ F ₅ ) _3. Lithium difluorooxalate borate, lithium bis(oxalate)borate or lithium difluorobis(oxalato)phosphate, which help to improve the output power characteristics, high-rate charge and discharge characteristics, and high-temperature storage characteristics of electrochemical devices and cycle characteristics, etc.

The content of the electrolyte is not particularly limited as long as the effect of the present application is not impaired. 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 formed by any two values above. When the electrolyte concentration is within the above range, the lithium as charged particles will not be too small, and the viscosity can be kept in an appropriate range, so it is easy to ensure good electrical conductivity.

When two or more electrolytes are used, the electrolyte includes at least one salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte includes a salt selected from the group consisting of monofluorophosphate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte includes a lithium salt. In some embodiments, the salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is present at greater than 0.01% or greater than 0.1% by weight of the electrolyte. In some embodiments, the salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate comprises less than 20% or less than 10% by weight of the electrolyte. In some embodiments, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate is within the range formed by any two of the above values.

In some embodiments, the electrolyte includes one or more substances selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate and one or more salts other than these. Other salts include the lithium salts exemplified above, and in some examples, LiPF ₆ , LiN(FSO ₂ )(CF ₃ SO ₂ ), LiN(CF ₃ SO ₂ ) ₂ , LiN( C ₂ F ₅ SO ₂ ) ₂ , cyclic lithium 1,2-perfluoroethanebissulfonimide, cyclic lithium 1,3-perfluoropropanebissulfonimide, LiC(FSO ₂ ) ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiC(C ₂ F ₅ SO ₂ ) ₃ , LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (C ₂ F ₅ ) ₃ . In some embodiments, the additional salt is LiPF ₆ .

In some embodiments, the additional salts are present at greater than 0.01% or greater than 0.1% by weight of the electrolyte. In some embodiments, the additional salts are present at less than 20%, less than 15%, or less than 10% by weight of the electrolyte. In some embodiments, the content of other salts is within the range formed by any two values above. Salts other than these having the above content contribute to the balance of the electrical conductivity and viscosity of the electrolytic solution.

III. Positive electrode

The positive electrode includes a positive electrode collector and a positive electrode active material layer disposed on at least one surface of the positive electrode collector.

The positive electrode active material layer contains a positive electrode active material, and the positive electrode active material layer may be one or more layers. Each layer of the multilayer positive active material may contain the same or different positive active material. The positive active material is any material capable of reversibly intercalating and deintercalating metal ions such as lithium ions.

In the present application, there is no particular limitation on the type of positive electrode active material, as long as it can store and release metal ions (eg, lithium ions) electrochemically. In some embodiments, the positive active material is a material containing lithium and at least one transition metal. Examples of positive active materials may include, but are not limited to, lithium transition metal composite oxides and lithium transition metal phosphate compounds.

In some embodiments, the transition metals in the lithium transition metal composite oxide include V, Ti, Cr, Mn, Fe, Co, Ni, Cu, and the like. In some embodiments, lithium transition metal composite oxides include lithium cobalt composite oxides such as LiCoO ₂ , lithium nickel composite oxides such as LiNiO ₂ , lithium manganese composite oxides such as LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ MnO ₄ , lithium nickel manganese cobalt composite oxides such as LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _0.5 Mn _0.3 Co _0.2 O _{2 ,} etc., in which a part of the transition metal atom which is the main body of these lithium transition metal composite oxides is Na, K, B, F, Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, W and other elements substituted . Examples of lithium transition metal composite oxides may include, but are not limited to, LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , LiNi _0.45 Co _0.10 Al _0.45 O ₂ , LiMn _1.8 Al _0.2 O ₄ and LiMn _1.5 Ni _0.5 O ₄ etc. Examples of combinations of lithium transition metal composite oxides include, but are not limited to, combinations of LiCoO ₂ and LiMn ₂ O ₄ , wherein a part of Mn in LiMn ₂ O ₄ may be replaced by transition metals (for example, LiNi _0.33 Co _0.33 Mn _0.33 O ₂ ), part of Co in LiCoO ₂ can be replaced by transition metals.

In some embodiments, the transition metals in the lithium-containing transition metal phosphate compound include V, Ti, Cr, Mn, Fe, Co, Ni, Cu, and the like. In some embodiments, lithium-containing transition metal phosphate compounds include iron phosphates such as LiFePO ₄ , Li ₃ Fe ₂ (PO ₄ ) ₃ , LiFeP ₂ O ₇ , and cobalt phosphates such as LiCoPO ₄ , wherein as these lithium transition metal phosphate compounds Some of the transition metal atoms of the main body are replaced by other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc.

A substance having a different composition may adhere to the surface of the positive electrode active material. Examples of surface attachment substances may include, but are not limited to: oxides such as alumina, silica, titania, zirconia, magnesia, calcium oxide, boron oxide, antimony oxide, bismuth oxide; lithium sulfate, sodium sulfate, potassium sulfate , magnesium sulfate, calcium sulfate, aluminum sulfate and other sulfates; lithium carbonate, calcium carbonate, magnesium carbonate and other carbonates; carbon, etc. By attaching the substance on the surface of the positive electrode active material, the oxidation reaction of the electrolyte solution on the surface of the positive electrode active material can be suppressed, and the life of the electrochemical device can be improved. When the amount of the surface-attached substance is too small, the effect cannot be fully expressed; when the amount of the surface-attached substance is too large, it will hinder the entry and exit of lithium ions, so the resistance may increase. In the present application, a positive electrode active material having a substance different from its composition adhered to the surface of the positive electrode active material is also referred to as a "positive electrode active material".

In some embodiments, the shape of the positive electrode active material particles includes, but is not limited to, block shape, polyhedron shape, spherical shape, ellipsoidal shape, plate shape, needle shape and columnar shape. In some embodiments, the positive active material particles include primary particles, secondary particles, or a combination thereof. In some embodiments, primary particles may agglomerate to form secondary particles.

The positive electrode may also include a conductive material. The present application does not limit the type of conductive material, and any known conductive material can be used. Examples of the conductive material may 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; The above conductive materials may be used alone or in any combination.

The positive electrode may also include a binder. The present application has no particular limitation on the type of adhesive. For example, in the case of coating, any material may be used as long as it can be dissolved or dispersed in a liquid medium used in electrode production. Examples of adhesives may include, but are not limited to, one or more of the following: polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic Polyamide, cellulose, nitrocellulose and other resin-based polymers; styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber and other rubber-like Polymer; styrene-butadiene-styrene block copolymer or its hydrogenated product, ethylene-propylene-diene terpolymer (EPDM), styrene-ethylene-butadiene-ethylene copolymer, styrene - Thermoplastic elastomeric polymers such as isoprene-styrene block copolymer or its hydrogenated products; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene - Soft resinous polymers such as α-olefin copolymers; fluorine-based polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; A polymer composition and the like having ion conductivity of alkali metal ions (especially lithium ions). The above positive electrode binders may be used alone or in any combination.

The present application does not limit the type of solvent used to form the positive electrode slurry, as long as it is a solvent capable of dissolving or dispersing the positive electrode active material, conductive material, binder, and thickener used as needed. Examples of the solvent used to form the positive electrode slurry may include any one of aqueous solvents and organic solvents. Examples of the aqueous medium may include, but are not limited to, water, a mixed medium of alcohol and water, and the like. Examples of organic media may 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; acetone, methyl ethyl ketones such as ketone and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; diethyl ether, propylene oxide, tetrahydrofuran (THF ) and other ethers; amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide, etc.

Thickeners are generally used to adjust the viscosity of the slurry. In the case of using an aqueous medium, thickeners and styrene-butadiene rubber (SBR) emulsions can be used for slurrying. The present application has no particular limitation on the type of thickener, and its examples may include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, Phosphorylated starch, casein and their salts, etc. The above-mentioned thickeners can be used alone or in any combination.

In the present application, there is no special limitation on the type of the positive electrode collector, which may be any known material suitable for being used as the positive electrode collector. Examples of the positive current collector may include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive current collector is a metal material. In some embodiments, the positive current collector is aluminum.

In order to reduce the electronic contact resistance of the positive electrode current collector and the positive electrode active material layer, the surface of the positive electrode current collector may include a conductive aid. Examples of conductive aids may include, but are not limited to, carbon and noble metals such as gold, platinum, and silver.

The positive electrode can be produced by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector. The manufacture of the positive electrode using the positive electrode active material can be carried out by a conventional method, that is, the positive electrode active material and the binder, as well as the conductive material and thickener as required, etc. are dry mixed, made into a sheet, and the obtained The sheet is pressed onto the positive current collector; or these materials are dissolved or dispersed in a liquid medium to make a slurry, and the slurry is coated on the positive current collector and dried to form a positive electrode current collector. A positive electrode active material layer, whereby a positive electrode can be obtained.

IV. Isolation film

In order to prevent a short circuit, a separator is usually provided between the positive electrode and the negative electrode. In this case, the electrolytic solution of the present application is usually used by permeating the separator.

The material and shape of the separator are not particularly limited as long as the effect of the present application is not significantly impaired. The separator can be resin, glass fiber, inorganic material, etc. formed of materials stable to the electrolyte solution of the present application. In some embodiments, the separator includes a porous sheet or a non-woven fabric-like substance with excellent liquid retention properties. Examples of the material of the resin or fiberglass separator may include, but are not limited to, polyolefin, aramid, polytetrafluoroethylene, polyethersulfone, and the like. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials for the above separators may be used alone or in any combination.

The separator can also be a laminate of the above materials, examples of which include, but are not limited to, a three-layer separator laminated in the order of polypropylene, polyethylene, and polypropylene, and the like.

Examples of materials of inorganic substances may include, but are not limited to, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, sulfates (eg, barium sulfate, calcium sulfate, etc.). Inorganic forms may include, but are not limited to, granular or fibrous.

The form of the separator may be in the form of a film, examples of which include, but are not limited to, non-woven fabrics, woven fabrics, microporous films, and the like. In thin film form, the pore diameter of the isolation membrane is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent film-shaped separator, the following separator can also be used: a separator formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and/or negative electrode using a resin-based binder, For example, a separator is formed by using a fluororesin as a binder to form porous layers on both sides of the positive electrode with 90% of the alumina particles having a particle size of less than 1 μm.

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

When a porous material such as a porous sheet or nonwoven fabric is used as the separator, the porosity of the separator is arbitrary. In some embodiments, the isolation membrane has a porosity greater than 10%, greater than 15%, or greater than 20%. In some embodiments, the separator has a porosity of less than 60%, less than 50%, or less than 45%. In some embodiments, the porosity of the isolation membrane is within the range formed by any two values above. When the porosity of the separator is within the above range, insulation and mechanical strength can be ensured, and membrane resistance can be suppressed, so that the electrochemical device has good safety characteristics.

The average pore diameter of the separator is also arbitrary. In some embodiments, the average pore size of the isolation membrane is less than 0.5 μm or less than 0.2 μm. In some embodiments, the average pore size of the isolation membrane is greater than 0.05 μm. In some embodiments, the average pore diameter of the isolation membrane is within the range formed by any two values above. When the average pore diameter of the separator exceeds the above-mentioned range, short circuits are likely to occur. When the average pore diameter of the isolation membrane is within the above range, the electrochemical device has good safety characteristics.

IV. Electrochemical device components

The electrochemical device assembly includes an electrode group, a current collecting structure, an outer casing and a protection element.

The electrode group may have either a laminated structure in which the positive electrode and the negative electrode are laminated with the separator interposed therebetween, or a structure in which the positive electrode and the negative electrode are wound in a spiral shape with the separator interposed therebetween. In some embodiments, the ratio of the mass of the electrode group to the internal volume of the battery (electrode group occupancy) is greater than 40% or greater than 50%. In some embodiments, the electrode set occupancy is less than 90% or less than 80%. In some embodiments, the occupancy of the electrode group is within the range formed by any two values above. When the electrode group occupancy ratio is within the above range, the capacity of the electrochemical device can be ensured, and at the same time, the decrease in characteristics such as repeated charge-discharge performance and high-temperature storage due to an increase in internal pressure can be suppressed.

The current collecting structure is not particularly limited. In some embodiments, the current collecting structure is a structure that reduces the resistance of the wiring portion and the bonding portion. When the electrode group has the above-mentioned laminated structure, it is suitable to use a structure in which the metal core portions of the electrode layers are bundled and welded to the terminal. When the area of one electrode increases, the internal resistance increases, so it is also suitable to provide two or more terminals in the electrode to reduce the resistance. When the electrode group has the above-mentioned winding structure, the internal resistance can be reduced by providing two or more lead wire structures on the positive electrode and the negative electrode respectively, and bundling them on the terminals.

The material of the outer case is not particularly limited, as long as it is stable to the electrolyte solution used. As the exterior case, metals such as nickel-plated steel sheets, stainless steel, aluminum or aluminum alloys, and magnesium alloys, or laminated films of resin and aluminum foil can be used, but not limited to. In some embodiments, the outer casing is aluminum or aluminum alloy metal or a laminated film.

Metal exterior cases include, but are not limited to, encapsulation and sealing structures formed by welding metals together by laser welding, resistance welding, or ultrasonic welding; or riveted structures using the above-mentioned metals through resin spacers. The exterior case using the above-mentioned laminated film includes, but is not limited to, a package sealing structure formed by thermally bonding resin layers to each other, and the like. In order to improve the sealability, a resin different from the resin used in the laminated film may be interposed between the above-mentioned resin layers. When thermally bonding the resin layer through the collector terminal to form a closed structure, a resin having a polar group or a modified resin into which a polar group is introduced can be used as the sandwiched resin due to the bonding between the metal and the resin. In addition, the shape of the exterior body is also arbitrary, and for example, any of cylindrical, square, laminated, button-shaped, large, and the like may be used.

Protection elements can use positive temperature coefficient (PTC) whose resistance increases when abnormal heat generation or excessive current flows, temperature fuses, thermistors, cut off by causing the internal pressure of the battery or the internal temperature to rise sharply at the time of abnormal heat generation A valve (current cut-off valve) for the current flowing in the circuit, etc. The above-mentioned protection elements can be selected under the condition that they do not work in the normal use of high current, and can also be designed in such a way that abnormal heat dissipation or thermal runaway will not occur even if there is no protection element.

Electrochemical devices of the present application include any device capable of undergoing an electrochemical reaction. For example, specific examples thereof include lithium metal secondary batteries or lithium ion secondary batteries.

The present application further provides an electronic device, which includes the electrochemical device according to the present application.

The application of the electrochemical device of the present 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 the present application can be used in, but not limited to, notebook computers, pen-based computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-worn Stereo headphones, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, power assist Bicycles, bicycles, lighting equipment, toys, game consoles, clocks, electric tools, flashlights, cameras, large household storage batteries and lithium-ion capacitors, etc.

The lithium ion battery is taken as an example below and the preparation of the lithium ion battery is described in conjunction with specific examples. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation methods are described in this application. within range.

1. Preparation of lithium ion battery

1. Preparation of negative electrode

(1) Application of volume expansion resin in the undercoat of the negative electrode

The volume expansion resin, conductive agent (carbon nanotube, graphene or a mixture of carbon nanotube and graphene) and styrene-butadiene rubber are mixed with deionized water according to a certain mass ratio to obtain the primer coating slurry. The mass ratio of conductive agent to styrene-butadiene rubber is 2:3, and the rest is volume expansion resin.

Mix artificial graphite, styrene-butadiene rubber and sodium carboxymethyl cellulose with deionized water in a mass ratio of 96%:2%:2%, and stir evenly to obtain active material layer slurry. Then, the above slurry for the undercoat layer and the above slurry for the active material layer were successively coated on the 8 μm copper foil. Drying, cold pressing, cutting into pieces and welding tabs to obtain the negative electrode.

(2) Application of volume expansion resin on the current collector of the negative electrode

Mixing carbon nanotubes and styrene-butadiene rubber with deionized water according to the mass ratio of 40%:60% to obtain negative electrode bottom coating slurry. A composite current collector is used as the negative electrode current collector, and the composite current collector includes two metal foils and a resistance layer located between the two metal foils, wherein the application uses two 8 μm copper foils as the above two metal foils 50wt% volume expansion resin Matsumoto Microsphere F-30D, 20wt% carbon nanotubes and 30wt% styrene-butadiene rubber were uniformly mixed as a resistance layer, and the thickness of the resistance layer was 5 μm. Drying, cold pressing, cutting into pieces and welding tabs to obtain the negative electrode.

(3) No volume expansion resin is used in the negative electrode

Mix artificial graphite, styrene-butadiene rubber and sodium carboxymethyl cellulose with deionized water in a mass ratio of 96%:2%:2%, and stir evenly to obtain active material layer slurry. Then the active material layer slurry was successively coated on the 8 μm copper foil. Drying, cold pressing, cutting into pieces and welding tabs to obtain the negative electrode.

2. Preparation of positive electrode

Lithium cobaltate, Super-P and binder were mixed with N-methylpyrrolidone (NMP) according to the mass ratio of 97:2:1, and stirred evenly to obtain positive electrode slurry. The positive electrode slurry was coated on a 12 μm aluminum foil, dried, cold pressed, cut into pieces, and tabs were welded to obtain a positive electrode.

3. Preparation of electrolyte

In a dry argon environment, mix EC, PC and DEC (weight ratio 1:1:1), add LiPF ₆ and mix well to form a basic electrolyte, in which the concentration of LiPF ₆ is 12.5%. According to requirements, different contents of additives were added to the basic electrolyte to obtain electrolytes of different examples and comparative examples.

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

material name	abbreviation	material name	abbreviation
Vinyl carbonate	EC	Propyl propionate	PP
diethyl carbonate	DEC	Fluoroethylene carbonate	FEC
Succinonitrile	SN	Adiponitrile	ADN
Ethylene glycol bis(2-cyanoethyl) ether	EDN	1,3,6-Hexanetrinitrile	HTCN
1,2,3-tris(2-cyanoethoxy)propane	TCEP	1,3-Propane sultone	P.S.
lithium difluorophosphate	LiDFP	vinyl sulfate	DTD
vinylene carbonate	VC	1-Propylphosphoric acid cyclic anhydride	T3P
Methyl propionate	MP	ethyl propionate	EP
Propylene carbonate	PC	the	the

4. Preparation of isolation membrane

Polyethylene (PE) porous polymer film is used as the isolation membrane.

5. Preparation of Li-ion battery

Wind the obtained positive electrode, separator and negative electrode in sequence, place them in the outer packaging foil, and leave a liquid injection port. The electrolyte solution is poured from the liquid injection port, packaged, and then the lithium-ion battery is produced through processes such as formation and capacity.

2. Test method

1. High-temperature short-circuit deformation rate test of lithium-ion batteries

At 25°C, let the lithium-ion battery stand still for 30 minutes, then charge it to 4.7V with a constant current at a rate of 0.5C, then charge it at a constant voltage at 4.7V to 0.05C, let it stand for 60 minutes, and measure the thickness T of the lithium-ion battery ₁ . The battery was then short-circuited at 100 mΩ for 10 seconds, and the thickness T ₂ of the Li-ion battery was measured. The high-temperature short-circuit deformation rate of the lithium-ion battery is calculated by the following formula:

Short-circuit deformation rate=[(T ₂ -T ₁ )/T ₁ ]×100%.

2. Lithium-ion battery overcharge deformation rate test

At 25°C, let the lithium-ion battery stand still for 30 minutes, then charge it to 4.7V with a constant current at a rate of 0.5C, then charge it at a constant voltage at 4.7V to 0.05C, let it stand for 60 minutes, and measure the thickness T of the lithium-ion battery ₃ . Then charge at a constant current of 0.1C for 60 minutes, let stand for 30 minutes, repeat this step 5 times to make the lithium-ion battery reach 150% state of charge (SOC), and measure the thickness T ₄ of the lithium-ion battery. Calculate the overcharge deformation rate of the lithium-ion battery by the following formula:

Overcharge deformation rate=[(T ₄ -T ₃ )/T ₃ ]×100%.

3. Voltage drop test of lithium ion battery under low temperature storage

At 25°C, charge the lithium-ion battery with a constant current of 1C to 4.7V, then charge it with a constant voltage to a current of 0.05C, then discharge it with a constant current of 1C to 3.2V, let it stand for 5 minutes, and then test the voltage. After storage at -20°C for 24 hours, the voltage was retested. The voltage drop of a lithium-ion battery is calculated according to the following formula:

Voltage drop = voltage before storage - voltage after storage.

3. Test results

Table 1 shows the effect of the use of volume expansion resin in the primer layer and the addition of propyl propionate in the electrolyte on the safety performance of lithium-ion batteries at high temperature and high pressure and the voltage drop under low temperature storage, where the volume expansion resin is selected from Matsumoto Microsphere F-30D.

Table 1

Referring to Table 1, comparing Examples 1-1 to 1-15 with Comparative Examples 1-1 to 1-3, it can be seen that the electrochemical devices described in Examples 1-1 to 1-15 have a high temperature and high pressure The overcharge deformation rate and short circuit deformation rate, as well as its voltage drop under low temperature storage, all decreased significantly. This demonstrates that when the undercoat layer includes a volume-expanding resin and the electrolyte includes propyl propionate, not only the safety performance of the electrochemical device at high pressure and high temperature can be substantially improved, but also its voltage drop under low-temperature storage can be effectively reduced.

Comparing Examples 1-1 to 1-8 with Examples 1-9, it can be concluded that when x/a≥1, the electrochemical performance of the electrochemical device can be further improved, especially the safety of the electrochemical device at high temperature performance.

Comparing Examples 1-1 to 1-8, 1-10 and 1-12 with Examples 1-9, 1-11, 1-13 and 1-14, it can be seen that when the electrochemical device simultaneously satisfies 0.1≤a When ≤10, 5≤x≤50 and x/a≥1, the electrochemical performance of the electrochemical device can be further improved.

Comparative Examples 1-4 and 1-5 involved the application of the volume expansion resin in the negative electrode current collector, but not in the negative electrode undercoat layer. Comparing Comparative Examples 1-5 with Comparative Examples 1-3, it can be seen that the application of volume expansion resin in the current collector does not significantly improve the high-temperature safety performance and low-temperature voltage drop of the electrochemical device. The reason is speculated as follows: when the internal temperature of the electrochemical device rises rapidly or even thermal runaway occurs, the volume expansion resin in the primer layer can respond faster than the volume expansion resin in the composite current collector, thus It absorbs heat in time, expands in volume, blocks the electron transmission between the active layer and the current collector, and improves safety performance.

In addition, referring to Comparative Examples 1-6 and 1-7 and Examples 1-15, adding methyl propionate or ethyl propionate to the electrolyte does not improve the high-temperature safety performance and low-temperature performance of the electrochemical device as much as propionate Propyl acetate is so obvious. This is because the swelling effect of propyl propionate on the volume expansion resin is just right, which is more conducive to the rapid expansion of the resin at high temperature and the rapid migration of lithium ions at low temperature.

Table 2 shows the impact of volume expansion resins and conductive agents of different components in the negative electrode primer layer on the safety performance of lithium-ion batteries under high temperature and high pressure and the voltage drop at low temperatures, wherein the volume expansion resins, conductive agents and binders The weight ratio is 5:85:10.

Table 2

The results in Table 2 show that an electrochemical device with excellent safety performance at high temperature and high pressure and low voltage drop at low temperature can be obtained even if the composition of volume expansion resin and conductive agent in the undercoat layer is changed. Referring to Examples 2-3 and 2-5, when thermally expandable microspheres and graphene are used at the same time, the improvement effect on the electrochemical performance of the electrochemical device is more significant.

Table 3 shows the effect of electrolyte additives on the safety performance of lithium-ion batteries at high temperature and high pressure and the voltage drop at low temperature. The only difference between Examples 3-1 to 3-29 and Example 1-1 lies in the parameters listed in Table 3.

table 3

Referring to Table 3, comparing Examples 3-1 to 3-14 with Example 1-1, it can be seen that adding a compound with a cyano group to the electrolyte can further improve the safety of the electrochemical device under high temperature and high pressure performance and suppress its voltage drop under low temperature storage. In particular, the above effects can be further optimized by using a plurality of compounds having a cyano group in combination. With further reference to the results of Examples 3-20 and 3-29, it can be seen that when the content of the compound with cyano group in the electrolyte is not more than 15%, its effect on improving the electrochemical performance of the electrochemical device is more obvious.

In addition, referring to the results of Examples 3-15 to 3-19 and Examples 3-21 to 3-28, it can be seen that when further adding fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate When at least one of ester, vinylene carbonate, and phosphoric acid cyclic anhydride, the safety performance of the corresponding electrochemical device under high temperature and high pressure can be further improved, and its voltage drop under low temperature storage can be further reduced.

Table 4 shows the influence of the ratio of the thickness _H1 of the undercoat layer to the thickness H of the negative electrode active material layer on the safety performance of the lithium-ion battery under high temperature and high pressure and the voltage drop under low temperature storage. The difference between Examples 4-1 to 4-5 and Example 1-1 lies in the parameters listed in Table 4.

Table 4

The results show that an electrochemical device with excellent safety performance at high temperature and high pressure and low voltage drop at low temperature can be obtained even if the ratio relationship of H ₁ /H is adjusted. However, when H ₁ /H satisfies H ₁ /H≦0.1, an electrochemical device with better effect can be obtained.

Table 5 shows the influence of the ratio of the weight _W1 of the undercoat layer to the weight W of the negative electrode active material layer on the safety performance at high temperature and high pressure and the voltage drop at low temperature of the lithium-ion battery. The difference between Examples 5-1 to 5-5 and Example 1-1 lies in the parameters listed in Table 5.

table 5

the	W 1	W	W 1 /W	Overcharge deformation rate (%)	Short circuit deformation rate (%)	Voltage drop (V)
Example 1-1	100	250	0.4	14.6	16.7	0.57
Example 5-1	100	200	0.5	13.2	14.1	0.51
Example 5-2	80	200	0.4	12.6	13.2	0.48
Example 5-3	50	200	0.25	11.8	12.1	0.37
Example 5-4	50	300	0.17	11.5	12.4	0.32
Example 5-5	200	300	0.67	18.9	19.3	0.63

The results show that an electrochemical device with excellent safety performance at high temperature and high pressure and low voltage drop at low temperature can be obtained even if the ratio relationship of W ₁ /W is adjusted. However, when W ₁ /W satisfies W ₁ /W≦0.5, an electrochemical device with better effect can be obtained.

References to "embodiment", "partial embodiment", "an embodiment", "another example", "example", "specific example" or "partial example" in the entire specification mean that At least one embodiment or example in the present application includes a specific feature, structure, material or characteristic described in the embodiment or example. Thus, descriptions that appear throughout the specification such as: "in some embodiments", "in an embodiment", "in one embodiment", "in another example", "in an example In", "in a particular example" or "example", they are not necessarily referring to the same embodiment or example in this application. Furthermore, the particular features, structures, materials, or characteristics herein may be combined in any suitable manner in one or more embodiments or examples.

Although illustrative embodiments have been shown and described, those skilled in the art should understand that the foregoing embodiments are not to be construed as limitations on the present application, and that changes may be made in the embodiments without departing from the spirit, principle and scope of the application. , substitution and modification.

Claims (15)

1. An electrochemical device comprising a negative electrode and an electrolyte,

   The negative pole includes:

   Negative current collector;

   an undercoat layer comprising a volume expansion resin and formed on at least one surface of the negative electrode current collector; and

   a negative active material layer comprising a negative active material and formed on the undercoat layer; and

   The electrolyte solution includes propyl propionate.
2. The electrochemical device according to claim 1, wherein based on the total weight of the electrolyte, the content of the propyl propionate is x%; based on the weight of the primer layer, the content of the volume expansion resin is a%; and wherein 5≤x≤50 and x/a≥1.
3. The electrochemical device according to claim 2, wherein 0.1≤a≤10.
4. The electrochemical device according to claim 1, wherein when the internal temperature of the electrochemical device is 20°C to 40°C, the volume of the volume expansion resin is V ₀ , wherein the internal temperature of the electrochemical device reaches 140 In the range of °C to 160 °C, the volume of the volume expansion resin is V ₁ , wherein V ₁ /V ₀ ≥2.
5. The electrochemical device according to claim 4, wherein the volume expansion resin comprises at least one of polyethylene, polypropylene, polyethylene vinyl acetate, or polypropylene.
6. The electrochemical device according to claim 1, wherein the volume expansion resin comprises thermally expandable microspheres.
7. The electrochemical device according to claim 1, wherein the undercoat layer further comprises a conductive agent comprising at least one of carbon nanotubes, graphene, or carbon black.
8. The electrochemical device according to claim 1, wherein the primer layer further comprises a binder, and the binder comprises polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose , styrene-butadiene rubber or at least one of fluorine-containing rubber.
9. The electrochemical device according to claim 1, wherein the electrolytic solution also includes a compound with a cyano group, and the compound with a cyano group includes succinonitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, 1,3,5-pentanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane or 1, At least one of 2,4-tris(2-cyanoethoxy)butane.
10. The electrochemical device according to claim 1, wherein the electrolyte also includes fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, vinylene carbonate, 1-propyl phosphoric acid cyclic anhydride or at least one of lithium difluorophosphate.
11. The electrochemical device according to claim 1, wherein the negative electrode satisfies H ₁ /H≤0.1, wherein along the direction perpendicular to the negative electrode current collector, the thickness of the undercoating layer is H ₁ μm, and the negative electrode The thickness of the active material layer was H μm.
12. The electrochemical device according to claim 1, wherein the thickness of the undercoat layer is H ₁ μm and 0.5≤H ₁ ≤5.
13. The electrochemical device according to claim 1, wherein the negative electrode satisfies W ₁ /W≤0.5, wherein the weight of the undercoat layer is W ₁ mg/1540.25mm ² , and the weight of the negative electrode active material layer is Wmg /1540.25mm ² .
14. The electrochemical device according to claim 1, wherein the weight of the undercoat layer is W ₁ mg/1540.25mm ² , and 20≤W ₁ ≤100.
15. An electronic device comprising the electrochemical device according to any one of claims 1-14.