Electrochemical devices and electronic devices

Abstract

This application relates to an electrochemical device and an electronic device. Specifically, this application provides an electrochemical device comprising a negative electrode and an electrolyte. The negative electrode comprises: a negative electrode current collector; a base coating comprising a volume-expanding resin and formed on at least one surface of the negative electrode current collector; and a negative electrode active material layer comprising a negative electrode active material and formed on the base coating; and the electrolyte comprising propyl propionate. This design not only significantly improves the safety performance of the electrochemical device under thermal runaway but also effectively reduces its voltage drop during low-temperature storage.

Description

Technical Field

[0001] This application relates to the field of energy storage, specifically to an electrochemical device and an electronic device, particularly a lithium-ion battery. Background Technology

[0002] 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 the power source for electronic products, are playing an increasingly important role in our daily lives. Among them, lithium-ion batteries are widely used in the consumer electronics field due to their advantages such as high specific energy, high operating voltage, low self-discharge rate, small size, and light weight.

[0003] However, in recent years, frequent incidents of electronic product explosions caused by lithium-ion batteries have brought the safety of lithium-ion batteries to the forefront of public attention. Ensuring the safety of lithium-ion batteries is the primary issue to be addressed in expanding their applications. Furthermore, with the increasing use of lithium-ion batteries under extreme conditions, improving the discharge performance of electrochemical devices at low temperatures is also a hot topic of interest.

[0004] In view of this, it is indeed necessary to provide an electrochemical device and an electronic device that have high safety under high temperature and high pressure and low voltage drop under low temperature storage. Summary of the Invention

[0005] The embodiments of this application address, to some extent, the problems existing in the prior art by adjusting the composition of the negative electrode and the components of the electrolyte used in the electrochemical device.

[0006] In one aspect of this application, an electrochemical device is provided, comprising a negative electrode and an electrolyte, wherein the negative electrode comprises: a negative electrode current collector; a base coating comprising a volume-expanding resin and formed on at least one surface of the negative electrode current collector; and a negative electrode active material layer comprising a negative electrode active material and formed on the base coating; and the electrolyte comprises propyl propionate.

[0007] According to an embodiment of this application, the content of propyl propionate is x% based on the total weight of the electrolyte; the content of the volume-expanding resin is a% based on the weight of the primer layer; and wherein 5 ≤ x ≤ 50 and x / a ≥ 1.

[0008] According to an embodiment of this application, 0.1 ≤ a ≤ 10.

[0009] According to an embodiment of this application, when the internal temperature of the electrochemical device is between 20°C and 40°C, the volume of the volume-expanding resin is V0; when the internal temperature of the electrochemical device reaches the range of 140°C to 160°C, the volume of the volume-expanding resin is V1, wherein V1 / V0 ≥ 2.

[0010] According to embodiments of this application, the volume-expanding resin includes at least one of polyethylene, polypropylene, vinyl acetate, or polypropylene.

[0011] According to an embodiment of this application, the volume-expanding resin comprises thermally expandable microspheres.

[0012] According to embodiments of this application, the base coating further includes a conductive agent, which includes at least one of carbon nanotubes, graphene, or carbon black.

[0013] According to embodiments of this application, the base coating further includes an adhesive, the adhesive comprising at least one of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, styrene-butadiene rubber, or fluorinated rubber.

[0014] According to embodiments of this application, the electrolyte further includes a cyano compound, which includes at least one selected from succinic anion, 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(2-cyanoethoxy)butane.

[0015] According to embodiments of this application, the electrolyte further includes at least one of fluoroethylene carbonate, 1,3-propanesulfonic acid lactone, ethylene sulfate, vinylene carbonate, 1-propyl phosphate cycloanhydride, or lithium difluorophosphate.

[0016] According to an embodiment of this application, the negative electrode satisfies H1 / H≤0.1, wherein the thickness of the undercoating layer is H1μm along the direction perpendicular to the negative electrode current collector, and the thickness of the negative electrode active material layer is Hμm.

[0017] According to an embodiment of this application, the thickness of the base coating is H1 μm and 0.5 ≤ H1 ≤ 5.

[0018] According to an embodiment of this application, the negative electrode satisfies W1 / W≤0.5, wherein the weight of the undercoating layer is W1mg / 1540.25mm. 2 The weight of the negative electrode active material layer is W mg / 1540.25 mm. 2 .

[0019] According to an embodiment of this application, the weight of the base coating is W1mg / 1540.25mm. 2 And 20≤W1≤100.

[0020] In another aspect of this application, an electronic device is provided that includes the electrochemical device described in this application.

[0021] This application ensures high safety performance of the electrochemical device under high pressure and high temperature by using a specific combination of negative electrode structure and electrolyte, and can effectively reduce the voltage drop of the electrochemical device under low temperature storage.

[0022] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Detailed Implementation

[0023] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0024] Unless otherwise expressly stated, the terms used herein have the meanings indicated below.

[0025] The terms “including,” “containing,” and “comprise” are used in their open, non-restrictive sense.

[0026] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0027] In the detailed description and claims, a list of items connected by the terms "one or more of," "one or more of," "one or more of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0028] This study found that safety issues of electrochemical devices (e.g., lithium-ion batteries) are inherently related to thermal runaway. For example, the misuse of electronic products is unavoidable, such as charging them overnight, leading to overcharging of the electrochemical device. This misuse causes the device to heat up, even become extremely hot, which can easily induce and exacerbate side reactions within the device. These side reactions mainly include the decomposition of the positive and negative electrode active materials and the reaction between these materials and the electrolyte. Most of these reactions are exothermic, which further increases the internal temperature of the electrochemical device (e.g., reaching 120°C or higher), ultimately leading to thermal runaway.

[0029] To address this issue, a common technique involves coating the separator surface of an electrochemical device with a low-melting-point polymer. When the internal temperature of the electrochemical device rises, the polymer melts and is drawn into the micropores of the separator substrate via capillary action, causing the separator to close its pores. This cuts off the lithium-ion transport channels, terminates the charge-discharge reaction, and ensures the safety of the electrochemical device during abuse. However, this method has drawbacks: when thermal runaway occurs, the temperature often rises rapidly, and the polymer does not have enough time to melt and close the separator over a large area via capillary action, thus failing to terminate the charge-discharge reaction in time. Furthermore, as the temperature continues to rise, side reactions intensify, and the structure of the positive and negative electrodes suffers irreversible damage, leading to a significant decrease in their thermal stability and potentially causing safety problems.

[0030] To address the aforementioned issues, this application utilizes a volume-expanding resin in the bottom coating of the negative electrode. This allows the resin to rapidly absorb heat and expand in the event of rapid temperature increases or even thermal runaway within the electrochemical device. This expansion blocks electron transport between the negative electrode active material layer and the negative electrode current collector, terminating the electrochemical reaction and improving the safety performance of the electrochemical device. Furthermore, this application adds propyl propionate to the electrolyte. This not only enhances the swelling effect of the volume-expanding resin and increases the porosity of the electrode, but also forms a more uniform solid electrolyte interphase (SEI) film on the surface of the negative electrode active material particles, thereby reducing the voltage drop of the electrochemical device during low-temperature storage. The various components of the proposed electrochemical device will be described in detail below.

[0031] I. Negative electrode

[0032] The negative electrode includes a negative electrode current collector, a base coating formed on at least one surface of the negative electrode current collector, and a negative electrode active material layer formed on the base coating, wherein the negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer can be one or more layers, and each layer of multiple negative electrode active materials can contain the same or different negative electrode active materials. The negative electrode active material is any substance capable of reversibly inserting and de-intercalating metal ions such as lithium ions. In some embodiments, the charging capacity of the negative electrode active material is greater than the discharging capacity of the positive electrode active material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0033] A key feature of the negative electrode in this application is that the negative electrode undercoating includes a volume-expanding resin. In the event of rapid temperature rise or even thermal runaway within the electrochemical device, the volume-expanding resin can quickly absorb heat and expand in volume, blocking electron transport between the negative electrode active material layer and the negative electrode current collector, thus terminating the electrochemical reaction and improving the safety performance of the electrochemical device.

[0034] In some embodiments, the content of the volume-expanding resin is a% based on the weight of the primer coating, where 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 a range consisting of any two of the above values. When the content of the volume-expanding resin in the primer coating is within the above range, it helps to further improve the safety performance of the electrochemical device.

[0035] In some embodiments, the volume-expanding resin satisfies the following relationship: V1 / V0 ≥ 2, wherein the volume of the volume-expanding resin is V0 when the internal temperature of the electrochemical device is in the range of 20°C to 40°C, and the volume of the volume-expanding resin is V1 when the internal temperature of the electrochemical device reaches the range of 140°C to 160°C. In some embodiments, V1 / V0 ≥ 5. In some embodiments, V1 / V0 ≥ 7. In some embodiments, V1 / V0 ≥ 10. In some embodiments, V1 / V0 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-expanding resin satisfies the above relationship, it helps to further improve the safety performance of the electrochemical device.

[0036] In some embodiments, the volume-expanding resin includes at least one of polyethylene, polypropylene, vinyl acetate, or polypropylene.

[0037] In some embodiments, the volume-expanding resin comprises thermally expandable microspheres.

[0038] In some embodiments, compared to the volume of the thermally expandable microspheres at an internal temperature of 20°C to 40°C, the volume expansion rate of the thermally expandable microspheres when the internal temperature of the electrochemical device is raised to above 130°C is more than 5 times without rupture. In some embodiments, compared to the volume of the thermally expandable microspheres at an internal temperature of 20°C to 40°C, the volume expansion rate of the thermally expandable microspheres when the internal temperature of the electrochemical device is raised to above 130°C is more than 7 times without rupture. In some embodiments, compared to the volume of the thermally expandable microspheres at an internal temperature of 20°C to 40°C, the volume expansion rate of the thermally expandable microspheres when the internal temperature of the electrochemical device is raised to above 130°C is more than 10 times without rupture.

[0039] The thermally expandable microspheres can be obtained by encapsulating a material that expands easily when heated within an elastic shell. These thermally expandable microspheres can be prepared using any suitable method, such as coagulation, interfacial polymerization, etc.

[0040] Substances that expand easily when heated 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-point liquids; or azodicarbonamide that vaporizes through pyrolysis.

[0041] The substances constituting the aforementioned shell include, but are not limited to, polymers composed of at least one of the following monomers: nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, and fumaric acid; carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid; vinylidene chloride; vinyl acetate; (meth)acrylate monomers such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isobornyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, and β-carboxyethyl acrylate; styrene monomers such as styrene, α-methylstyrene, and chlorostyrene; and amide monomers such as acrylamide, substituted acrylamide, methacrylamide, and substituted methacrylamide. The polymers composed of these monomers can be homopolymers or copolymers. Examples of such copolymers include, but are not limited to, vinylidene chloride-methyl methacrylate-acrylonitrile copolymer, methyl methacrylate-acrylonitrile-methacrylonitrile copolymer, methyl methacrylate-acrylonitrile copolymer, acrylonitrile-methacrylonitrile-itaconic acid copolymer, etc.

[0042] In the preparation of the above-mentioned thermally expandable microspheres, inorganic or organic foaming agents can be used. Inorganic foaming agents include, but are not limited to, ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium borohydride, and various azides. Organic foaming agents include, but are not limited to, chlorofluoroalkane compounds such as trichloromonofluoromethane and dichloromonofluoromethane; azo compounds such as azobisisobutyronitrile, azodicarbonamide, and barium azodicarbonate; hydrazine compounds such as p-toluenesulfonyl hydrazine, diphenyl sulfone-3,3'-disulfonyl hydrazine, 4,4'-oxobisbenzenesulfonyl hydrazine, and allylbissulfonyl hydrazine; aminourea compounds such as p-toluenesulfonylaminourea and 4,4'-oxobis(benzenesulfonylaminourea); triazole compounds such as 5-morpholino-1,2,3,4-thiotriazole; and N-nitroso compounds such as N,N'-dinitrospentamethylenetetramine and N,N'-dimethyl-N,N'-dinitrosterephthalamide.

[0043] The aforementioned thermally expandable microspheres can also be commercially available products. For example, commercially available thermally expandable microspheres may include, but are not limited to, those manufactured by Matsumoto Oils & Fats Co., Ltd. under the trade name "Matsumoto Microsphere" (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), and Japan Fillite. Products manufactured by Co., Ltd. under the brand name "Expancel" (grades: 053-40, 031-40, 920-40, 909-80, 930-120), products manufactured by Kureha Chemical Industry Co., Ltd. under the brand name "DAIFOAM" (grades: H750, H850, H1100, S2320D, S2640D, M330, M430, M520), products manufactured by Kureha Chemical Industry Co., Ltd. under the brand name "ADVANCELL" (grades: EML101, EMH204, EHM301, EHM302, EHM303, EM304, EHM401, EM403, EM501), products manufactured by Sekisui Chemical Industry Co., Ltd., etc.

[0044] In some embodiments, the particle size of the thermally expandable microspheres is 0.5 μm-80 μm at room temperature. In some embodiments, the particle size of the thermally expandable microspheres is 5 μm-45 μm at room temperature. In some embodiments, the particle size of the thermally expandable microspheres is 10 μm-20 μm at room temperature. In some embodiments, the particle size of the thermally expandable microspheres is 10 μm-15 μm at room temperature. In some embodiments, the average particle size of the thermally expandable microspheres is 6 μm-45 μm at room temperature. In some embodiments, the average particle size of the thermally expandable microspheres is 15 μm-35 μm at room temperature. The particle size and average particle size of the thermally expandable microspheres can be obtained using particle size distribution determination methods in laser scattering.

[0045] In some embodiments, the negative electrode undercoat further includes a conductive agent, which 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, optimize electron transport, reduce internal resistance, and improve the impedance characteristics of the electrochemical device. Furthermore, when thermally expandable microspheres and graphene are used simultaneously in the negative electrode undercoat, the electrochemical device can exhibit particularly excellent high-temperature safety performance and low-temperature impedance characteristics.

[0046] In some embodiments, the negative electrode undercoat further includes a binder, which includes at least one of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, styrene-butadiene rubber, or fluorinated rubber. The main function of the binder is to enhance the adhesion between particles in the undercoat and between the undercoat and the negative electrode current collector and the negative electrode active material layer, thereby preventing separation between the negative electrode current collector, the negative electrode undercoat, and the negative electrode active material layer at the negative electrode of the electrochemical device during charge-discharge cycles.

[0047] In some embodiments, the negative electrode satisfies H1 / H ≤ 0.1, wherein the thickness of the undercoating layer is H1 μm along the direction perpendicular to the negative electrode current collector, and the thickness of the negative electrode active material layer is H μm. In some embodiments, 0.02 ≤ H1 / H ≤ 0.1. In some embodiments, 0.05 ≤ H1 / H ≤ 0.1. In some embodiments, H1 / H is 0.001, 0.002, 0.005, 0.008, 0.01, 0.02, 0.05, 0.08, 0.1, or within a range consisting of any two of the above values. When H1 / H is within the above range, in the event of thermal runaway, the undercoating layer can not only fully perform its function but is also easily wetted by the electrolyte, allowing propyl propionate in the electrolyte to play its role, thereby further improving the high-temperature safety performance and low-temperature discharge performance of the electrochemical device.

[0048] In some embodiments, the thickness of the base coating is H1 μm, where 0.5 ≤ H1 ≤ 5. In some embodiments, 1 ≤ H1 ≤ 3. In some embodiments, H1 is 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or falls within a range consisting of any two of the above values.

[0049] In some embodiments, the negative electrode satisfies W1 / W≤0.5, wherein the weight of the undercoating layer is W1mg / 1540.25mm. 2 The weight of the negative electrode active material layer is W mg / 1540.25 mm. 2 In some embodiments, 0.01 ≤ W1 / W ≤ 0.5. In some embodiments, 0.05 ≤ W1 / W ≤ 0.1. In some embodiments, W1 / W is 0.01, 0.02, 0.05, 0.08, 0.1, 0.2, 0.5, or within a range consisting of any two of the above values. When W1 / W is within the above range, the undercoating layer can not only fully perform its function to control the thermal runaway of the electrochemical device, but also be easily wetted by the electrolyte to improve the low-temperature discharge performance of the electrochemical device.

[0050] In some embodiments, 20 ≤ W1 ≤ 100. In some embodiments, 30 ≤ W1 ≤ 80. In some embodiments, 40 ≤ W1 ≤ 50. In some embodiments, W1 is 20, 30, 40, 50, 60, 70, 80, 90, 100 or falls within a range consisting of any two of the above values.

[0051] This application does not impose any particular limitation on the negative electrode current collector, which can be any known current collector. For example, examples of negative electrode current collectors include, but are not limited to, metallic materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper.

[0052] When the negative electrode current collector is a metallic material, its form may include, but is not limited to, metal foil, metal cylinder, metal strip roll, metal plate, metal film, metal mesh, 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 rolled copper foil based on rolling or electrolytic copper foil based on electrolysis.

[0053] 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 of any two of the above values.

[0054] This application does not impose any particular restrictions on the negative electrode active material, as long as it can reversibly insert and extract 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 material can be used alone or in combination.

[0055] The negative electrode active material layer may also include a negative electrode binder. The negative electrode binder improves the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. When a negative electrode slurry is prepared using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, etc.

[0056] The negative electrode can be prepared by the following method: first, a base coating slurry containing volume-expanding resin, conductive material and binder is coated on the negative electrode current collector; then, a negative electrode active material layer slurry containing negative electrode active material, resin binder and the like is coated, dried and calendered to obtain the negative electrode.

[0057] II. Electrolyte

[0058] The electrochemical device of this application further includes an electrolyte, which comprises an electrolyte, a solvent for dissolving the electrolyte, and additives.

[0059] A key feature of the electrolyte in this application is that it comprises propyl propionate. Propyl propionate not only enhances the swelling effect on the volume-expanding resin and increases the porosity of the electrode, but also forms a more uniform solid electrolyte interphase (SEI) film on the surface of the negative electrode active material particles, thereby reducing the voltage drop of the electrochemical device under low-temperature storage and optimizing the low-temperature discharge performance of the electrochemical device.

[0060] In some embodiments, the propyl propionate content is x% based on the total weight of the electrolyte, where 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 of any two of the above values. When the propyl propionate content in the electrolyte is within the above range, it helps to further improve the voltage drop of the electrochemical device under low-temperature storage.

[0061] 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 within a range consisting of any two of the above values. Propyl propionate can reduce the swelling of volume-expanding resin in the electrolyte, especially at low temperatures, thus suppressing the increase in battery internal resistance. Therefore, by adjusting the relationship between the content of propyl propionate in the electrolyte and the content of volume-expanding resin in the undercoat layer to keep x / a within the above range, the safety performance of the electrochemical device and the low-temperature storage voltage drop can be further improved.

[0062] In some embodiments, the electrolyte may also include compounds having a cyano group (-CN).

[0063] In some embodiments, the cyano-containing compound includes, but is not limited to, one or more of the following: succinic acid, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, tetramethylsuccinic acid, 2-methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, ethylene glycol bis(propylene glycol) Nitrile ethers, 3,5-dioxa-heptanenitrile, 1,4-di(cyanoethoxy)butane, diethylene glycol di(2-cyanoethyl) ether, triethylene glycol di(2-cyanoethyl) ether, tetraethylene glycol di(2-cyanoethyl) ether, 1,3-di(2-cyanoethoxy)propane, 1,4-di(2-cyanoethoxy)butane, 1,5-di(2-cyanoethoxy)pentane, ethylene glycol di(4-cyanobutyl) ether, 1,4-dicyano-2-butene 1,4-Dicyano-2-methyl-2-butene, 1,4-Dicyano-2-ethyl-2-butene, 1,4-Dicyano-2,3-dimethyl-2-butene, 1,4-Dicyano-2,3-diethyl-2-butene, 1,6-Dicyano-3-hexene, 1,6-Dicyano-2-methyl-3-hexene, 1,3,5-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(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane, or 1,2,5-tris(cyanoethoxy)pentane.

[0064] The aforementioned cyano compounds can be used alone or in any combination. If the electrolyte contains two or more cyano compounds, the content of the cyano compounds refers to the total content of the two or more cyano compounds.

[0065] In some embodiments, the content of the cyano compound is Y%, based on the total weight of the electrolyte, where 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 within a range of any two of the above values.

[0066] Adding cyano compounds to the electrolyte can further improve the safety performance of electrochemical devices under high temperature and high pressure and further suppress voltage drop during low-temperature storage. This is because cyano compounds can form a high-performance protective film on the negative electrode surface, effectively stabilizing the active metal in the positive electrode active material, inhibiting the dissolution of the active metal, and improving the stability and safety performance of the electrochemical device under high temperature and high pressure. Furthermore, cyano compounds can accelerate the swelling of the volume-expanding resin by propyl propionate, thereby achieving rapid ion and electron transport and reducing the impedance and voltage drop of the electrochemical device. In addition, combining multiple cyano compounds can achieve further optimization effects.

[0067] In some embodiments, the electrolyte further includes at least one of fluoroethylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, vinylene carbonate, 1-propyl phosphate cycloanhydride, or lithium difluorophosphate. These additives not only promote the swelling effect of propyl propionate on the volume-expanding resin, but also help form a more uniform SEI film on the surface of the negative electrode active material particles, thereby further improving the electrochemical performance of the electrochemical device, especially its high-temperature safety performance.

[0068] In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the art that can be used as a solvent for an electrolyte.

[0069] In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonates, chain carbonates, cyclic carboxylic esters, chain carboxylic esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0070] In some embodiments, examples of the cyclic carbonate may include, but are not limited to, one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate. In some embodiments, the cyclic carbonate has 3-6 carbon atoms.

[0071] In some embodiments, examples of the chain carbonate may include, but are not limited to, one or more of the following: dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate (DEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, di n-propyl carbonate, and other chain carbonates. Examples of fluorine-substituted chain carbonates may include, but are not limited to, one or more of the following: bis(fluoromethyl) carbonate, bis(difluoromethyl) carbonate, bis(trifluoromethyl) carbonate, bis(2-fluoroethyl) carbonate, bis(2,2-difluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, 2-fluoroethylmethyl carbonate, 2,2-difluoroethylmethyl carbonate, and 2,2,2-trifluoroethylmethyl carbonate, etc.

[0072] In some embodiments, examples of the cyclic carboxylic acid ester may include, but are not limited to, one or more of the following: γ-butyrolactone and γ-valerolactone. In some embodiments, some hydrogen atoms of the cyclic carboxylic acid ester may be substituted with fluorine.

[0073] In some embodiments, examples of the chain carboxylic acid ester may include, but are not limited to, one or more of the following: methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, and ethyl pivalate. In some embodiments, some hydrogen atoms of the chain carboxylic acid ester may be substituted with fluorine. In some embodiments, examples of fluorinated chain carboxylic acid esters may include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, and 2,2,2-trifluoroethyl trifluoroacetate.

[0074] 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.

[0075] In some embodiments, examples of the chain ether may include, but are not limited to, one or more of the following: dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane, and 1,2-ethoxymethoxyethane, etc.

[0076] In some embodiments, examples of the phosphorus-containing organic solvent may include, but are not limited to, one or more of the following: trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene phosphate, ethylene phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tri(2,2,2-trifluoroethyl) phosphate, and tri(2,2,3,3,3-pentafluoropropyl) phosphate, etc.

[0077] In some embodiments, examples of the sulfur-containing organic solvent may include, but are not limited to, one or more of the following: sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methylpropyl sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate, and dibutyl sulfate. In some embodiments, some hydrogen atoms of the sulfur-containing organic solvent may be substituted with fluorine.

[0078] 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.

[0079] In some embodiments, the solvent used in the electrolyte of this application includes cyclic carbonates, linear carbonates, cyclic carboxylic acid esters, linear carboxylic acid esters, and combinations thereof. In some embodiments, the solvent used in the electrolyte of this application comprises an organic solvent selected from the group consisting of: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate, ethyl acetate, and combinations thereof. In some embodiments, the solvent used in the electrolyte of this application comprises: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone, and combinations thereof.

[0080] In some embodiments, the electrolyte is not particularly limited, and any substance known as an electrolyte can be used. In the case of lithium secondary batteries, lithium salts are typically used. Examples of electrolytes may include, but are not limited to, inorganic lithium salts such as LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, and LiWF7; lithium tungstates such as LiWOF5; lithium carboxylate salts such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, and CF3CF2CF2CF2CO2Li; and lithium carboxylate salts such as FSO3Li and CH3SO3Li. Lithium sulfonate salts such as CH2FSO3Li, CHF2SO3Li, CF3SO3Li, CF3CF2SO3Li, CF3CF2CF2SO3Li, and CF3CF2CF2CF2SO3Li; lithium sulfonate salts such as LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane disulfonylimide lithium, and cyclic 1,3-perfluoropropane disulfonylimide. Lithium, imide lithium salts such as LiN(CF3SO2)(C4F9SO2); methylated lithium salts such as LiC(FSO2)3, LiC(CF3SO2)3, and LiC(C2F5SO2)3; lithium malonate lithium salts such as bis(malonate)borate and difluoro(malonate)borate; lithium tri(malonate)phosphate, lithium difluorobis(malonate)phosphate, and lithium tetrafluoro(malonate)phosphate; and lithium malonate phosphates such as LiPF4(CF3)2 and LiPF4(C2F5)2. Fluorine-containing organic lithium salts such as LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2; lithium oxalate borate salts such as lithium difluorooxalate borate and lithium bis(oxalate) borate; and lithium oxalate phosphate salts such as lithium tetrafluorooxalate phosphate, lithium difluorobis(oxalate) phosphate, and lithium tri(oxalate) phosphate.

[0081] In some embodiments, the electrolyte is selected from LiPF6, LiSbF6, FSO3Li, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane disulfonylimide lithium, cyclic 1,3-perfluoropropane disulfonylimide lithium, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, lithium difluorooxalateborate, lithium bis(oxalate)borate, or lithium difluorobis(oxalate)phosphate, which helps to improve the output power characteristics, high-rate charge-discharge characteristics, high-temperature storage characteristics, and cycle characteristics of the electrochemical device.

[0082] There are no particular limitations on the content of the electrolyte, as long as it does not impair the effectiveness of this application. In some embodiments, the total molar concentration of lithium in the electrolyte is greater than 0.3 mol / L, greater than 0.4 mol / L, or greater than 0.5 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is less than 3 mol / L, less than 2.5 mol / L, or less than 2.0 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is within the range of any two of the above values. When the electrolyte concentration is within the above range, the amount of lithium as charged particles will not be too low, and the viscosity can be kept within an appropriate range, thus easily ensuring good conductivity.

[0083] When using two or more electrolytes, the electrolyte comprises at least one salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte comprises a salt selected from the group consisting of monofluorophosphate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte comprises a lithium salt. In some embodiments, the content of a salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is greater than 0.01% or greater than 0.1% based on the weight of the electrolyte. In some embodiments, the content of a salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is less than 20% or less than 10% based on the weight of the electrolyte. In some embodiments, the content of a salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is within the range of any two of the above values.

[0084] In some embodiments, the electrolyte comprises one or more substances selected from the group consisting of monofluorophosphates, borates, oxalates, and fluorosulfonates, and one or more other salts. Examples of other salts include lithium salts exemplified above, and in some embodiments, LiPF6, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane disulfonylimide lithium, cyclic 1,3-perfluoropropane disulfonylimide lithium, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, and LiPF3(C2F5)3. In some embodiments, the other salt is LiPF6.

[0085] In some embodiments, the content of other salts, based on the weight of the electrolyte, is greater than 0.01% or greater than 0.1%. In some embodiments, the content of other salts, based on the weight of the electrolyte, is less than 20%, less than 15%, or less than 10%. In some embodiments, the content of other salts is within the range of any two of the above values. The presence of other salts at the above-mentioned levels helps to balance the conductivity and viscosity of the electrolyte.

[0086] III. Positive electrode

[0087] The positive electrode includes a positive current collector and a layer of positive active material disposed on at least one surface of the positive current collector.

[0088] The positive electrode active material layer contains positive electrode active material, and the positive electrode active material layer can be one or more layers. Each layer in a multilayer positive electrode active material layer can contain the same or different positive electrode active materials. The positive electrode active material is any substance capable of reversibly inserting and de-intercalating metal ions such as lithium ions.

[0089] This application does not impose any particular limitation on the type of positive electrode active material, as long as it is capable of electrochemically adsorbing and releasing metal ions (e.g., lithium ions). In some embodiments, the positive electrode active material is a substance containing lithium and at least one transition metal. Examples of positive electrode active materials may include, but are not limited to, lithium transition metal composite oxides and lithium transition metal phosphate compounds.

[0090] In some embodiments, the transition metal in the lithium transition metal composite oxide includes V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium transition metal composite oxide includes lithium cobalt composite oxides such as LiCoO2, lithium nickel composite oxides such as LiNiO2, lithium manganese composite oxides such as LiMnO2, LiMn2O4, and Li2MnO4, and LiNi... 1 / 3 Mn1 / 3 Co 1 / 3 O2, LiNi 0.5 Mn 0.3 Co 0.2 Lithium-nickel-manganese-cobalt composite oxides, such as O2, in which a portion of the transition metal atoms that form the bulk of these lithium transition metal composite oxides are replaced by other elements such as Na, K, B, F, Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, and W. Examples of lithium transition metal composite oxides include, but are not limited to, LiNi. 0.5 Mn 0.5 O2, LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.45 Co 0.10 Al 0.45 O2, LiMn 1.8 Al 0.2 O4 and LiMn 1.5 Ni 0.5 O4, etc. Examples of combinations of lithium transition metal composite oxides include, but are not limited to, combinations of LiCoO2 and LiMn2O4, wherein a portion of the Mn in LiMn2O4 can be replaced by a transition metal (e.g., LiNi). 0.33 Co 0.33 Mn 0.33 In LiCoO2, some of the Co can be replaced by transition metals.

[0091] In some embodiments, the transition metal in the lithium transition metal phosphate compound includes V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium transition metal phosphate compound includes iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, and cobalt phosphates such as LiCoPO4, wherein a portion of the transition metal atoms that constitute the main body of these lithium transition metal phosphate compounds are replaced by other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc.

[0092] A substance with a different composition may be attached to the surface of the aforementioned positive electrode active material. Examples of such surface-attached substances include, but are not limited to: oxides such as aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon. By attaching a substance to the surface of the positive electrode active material, the oxidation reaction of the electrolyte on the surface of the positive electrode active material can be suppressed, thereby improving the lifespan of the electrochemical device. When the amount of surface-attached substance is too small, its effect cannot be fully realized; when the amount of surface-attached substance is too large, it will hinder the entry and exit of lithium ions, and thus the resistance may sometimes increase. In this application, the positive electrode active material on which a substance with a different composition is attached to the surface of the positive electrode active material is also referred to as "positive electrode active material".

[0093] In some embodiments, the shape of the positive electrode active material particles includes, but is not limited to, blocky, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar shapes. In some embodiments, the positive electrode active material particles include primary particles, secondary particles, or combinations thereof. In some embodiments, primary particles may aggregate to form secondary particles.

[0094] The positive electrode may also include a conductive material. This application does not limit the type of conductive material; any known conductive material may be used. Examples of conductive materials 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; graphene, etc. The above-mentioned conductive materials may be used alone or in any combination.

[0095] The positive electrode may also include a binder. This application does not particularly limit the type of binder. For example, in the case of coating, any material that can be dissolved or dispersed in the liquid medium used during electrode manufacturing is acceptable. Examples of adhesives may include, but are not limited to, one or more of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; thermoplastic elastomer-like polymers such as styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers, and styrene-isoprene-styrene block copolymers or their hydrides; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with ion conductivity of alkali metal ions (especially lithium ions). The above-mentioned positive electrode adhesive can be used alone or in any combination.

[0096] This 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 solvents used to form the positive electrode slurry may include any of aqueous solvents and organic solvents. Examples of aqueous media may include, but are not limited to, water and mixtures of alcohol and water. 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; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

[0097] Thickeners are typically used to adjust the viscosity of slurries. In the case of using an aqueous medium, thickeners and styrene-butadiene rubber (SBR) latex can be used for slurry preparation. This application does not particularly limit the type of thickener, examples of which 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. The above-mentioned thickeners can be used alone or in any combination.

[0098] This application does not impose any particular limitation on the type of positive electrode current collector, which can be any known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.

[0099] To reduce the electronic contact resistance between the positive current collector and the positive active material layer, the surface of the positive current collector may include a conductive additive. Examples of conductive additives may include, but are not limited to, carbon and precious metals such as gold, platinum, and silver.

[0100] The positive electrode can be manufactured by forming a layer of positive electrode active material containing positive electrode active material and binder on a current collector. The manufacture of a positive electrode using positive electrode active material can be carried out by conventional methods, namely, dry mixing the positive electrode active material, binder, and conductive material and thickener as needed, forming a sheet, and pressing the resulting sheet onto the positive electrode current collector; or dissolving or dispersing these materials in a liquid medium to form a slurry, coating the slurry onto the positive electrode current collector and drying it, thereby forming a layer of positive electrode active material on the current collector, thus obtaining the positive electrode.

[0101] IV. Separating membrane

[0102] To prevent short circuits, a separator is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0103] There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator may be a resin, glass fiber, inorganic material, or other material formed from a material stable to the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of materials for resin or glass fiber separators may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0104] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0105] Examples of inorganic materials may include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). Inorganic materials may be in, but are not limited to, particulate or fibrous forms.

[0106] The separator can be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous membranes, etc. In the form of a thin film, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separator, the following separator can also be used: a separator formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode, for example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0107] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the separator is within the range of any two of the above values. When the thickness of the separator is within the above range, insulation and mechanical strength can be ensured, and the rate capability and energy density of the electrochemical device can be ensured.

[0108] When using porous materials such as porous sheets or nonwoven fabrics as the separator, the porosity of the separator is arbitrary. In some embodiments, the porosity of the separator is greater than 10%, greater than 15%, or greater than 20%. In some embodiments, the porosity of the separator is less than 60%, less than 50%, or less than 45%. In some embodiments, the porosity of the separator is within the range of any two of the above values. When the porosity of the separator is within the above range, insulation and mechanical strength can be ensured, and membrane resistance can be suppressed, giving the electrochemical device good safety characteristics.

[0109] The average pore size of the separator is also arbitrary. In some embodiments, the average pore size of the separator is less than 0.5 μm or less than 0.2 μm. In some embodiments, the average pore size of the separator is greater than 0.05 μm. In some embodiments, the average pore size of the separator is within the range of any two of the above values. If the average pore size of the separator exceeds the above range, a short circuit is likely to occur. When the average pore size of the separator is within the above range, the electrochemical device has good safety characteristics.

[0110] IV. Electrochemical Device Components

[0111] Electrochemical device components include electrode arrays, current collectors, housings, and protective elements.

[0112] The electrode assembly can be either a laminated structure formed by stacking the positive and negative electrodes with the separator membrane in between, or a structure formed by spirally winding the positive and negative electrodes with the separator membrane in between. In some embodiments, the proportion of the electrode assembly's mass in the battery's internal volume (electrode assembly occupancy) is greater than 40% or greater than 50%. In some embodiments, the electrode assembly occupancy is less than 90% or less than 80%. In some embodiments, the electrode assembly occupancy falls within the range of any two of the above values. When the electrode assembly occupancy is within the above range, the capacity of the electrochemical device can be ensured, while suppressing the degradation of characteristics such as repeated charge-discharge performance and high-temperature storage associated with increased internal pressure.

[0113] There are no particular limitations on the current collector structure. In some embodiments, the current collector structure is one that reduces the resistance of the wiring portion and the joint portion. When the electrode group has the above-described laminated structure, it is suitable to use a structure formed by bundling the metal core portions of each electrode layer together and soldering them to the terminals. As the area of ​​an electrode increases, the internal resistance increases; therefore, it is also suitable to provide two or more terminals within the electrode to reduce the resistance. When the electrode group has the above-described wound structure, the internal resistance can be reduced by providing two or more lead structures on the positive and negative electrodes respectively and bundling them together on the terminals.

[0114] There are no particular restrictions on the material of the outer casing, as long as it is a substance stable to the electrolyte used. The outer casing can be, but is not limited to, nickel-plated steel, stainless steel, aluminum or aluminum alloy, magnesium alloy, or a laminated film of resin and aluminum foil. In some embodiments, the outer casing is an aluminum or aluminum alloy metal or a laminated film.

[0115] Metal casings include, but are not limited to, encapsulated and hermetically sealed structures formed by fusing metals together using laser welding, resistance welding, or ultrasonic welding; or riveted structures formed using the aforementioned metals with a resin gasket in between. Casings using the aforementioned laminated films include, but are not limited to, encapsulated and hermetically sealed structures formed by thermally bonding resin layers together. To improve sealing, a resin different from the resin used in the laminated film can be sandwiched between the resin layers. When forming a hermetically sealed structure by thermally bonding resin layers using current collectors, a resin with polar groups or a modified resin with introduced polar groups can be used as the sandwiched resin due to the bonding between the metal and the resin. Furthermore, the shape of the casing is arbitrary, and can be, for example, any of the following: cylindrical, square, laminated, button-shaped, or large.

[0116] Protective components can include positive temperature coefficient (PTC) devices that increase resistance when abnormal heat generation or excessive current flows, temperature fuses, thermistors, and valves (current cut-off valves) that cut off current flowing through the circuit by causing a rapid increase in internal battery pressure or temperature during abnormal heat generation. These protective components can be selected to avoid operation under normal high-current conditions, or they can be designed to prevent abnormal heat generation or thermal runaway even without the protective components.

[0117] The electrochemical device of this application includes any device capable of undergoing an electrochemical reaction. Specific examples include lithium metal secondary batteries or lithium-ion secondary batteries.

[0118] This application also provides an electronic device that includes the electrochemical device described in this application.

[0119] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0120] The following uses a lithium-ion battery as an example and combines specific embodiments to illustrate the preparation of a lithium-ion battery. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0121] I. Preparation of Lithium-ion Batteries

[0122] 1. Preparation of the negative electrode

[0123] (1) Apply volume-expanding resin to the undercoat of the negative electrode.

[0124] A base coating slurry is prepared by mixing volume-expanding resin, a conductive agent (carbon nanotubes, graphene, or a mixture of carbon nanotubes and graphene), and styrene-butadiene rubber with deionized water in a specific mass ratio. The mass ratio of the conductive agent to styrene-butadiene rubber is 2:3, with the remainder being volume-expanding resin.

[0125] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed with deionized water in a mass ratio of 96%:2%:2% and stirred until homogeneous to obtain an active material layer slurry. Then, the aforementioned base coating slurry and active material layer slurry were successively coated onto 8μm copper foil. After drying and cold pressing, the foil was cut and tabs were welded to obtain the negative electrode.

[0126] (2) Apply volume-expanding resin to the current collector of the negative electrode.

[0127] Carbon nanotubes and styrene-butadiene rubber (SBR) were mixed with deionized water at a mass ratio of 40%:60% to obtain a negative electrode undercoating slurry. A composite current collector was used as the negative electrode current collector, comprising two metal foils and a resistive layer located between the two metal foils. In this application, two 8μm copper foils were used as the two metal foils, and 50wt% volume-expanding resin Matsumoto Microsphere F-30D, 20wt% carbon nanotubes, and 30wt% SBR were uniformly mixed as the resistive layer, wherein the thickness of the resistive layer was 5μm. After drying, cold pressing, and then cutting and welding of tabs, the negative electrode was obtained.

[0128] (3) Volume-expanding resins should not be used in the negative electrode.

[0129] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed with deionized water in a mass ratio of 96%:2%:2% and stirred until homogeneous to obtain an active material layer slurry. This slurry was then sequentially coated onto 8μm thick copper foil. After drying, cold pressing, and subsequent cutting and tab welding, the negative electrode was obtained.

[0130] 2. Preparation of the positive electrode

[0131] Lithium cobalt oxide, Super-P, and binder were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 97:2:1 and stirred until homogeneous to obtain a positive electrode slurry. This positive electrode slurry was coated onto a 12μm aluminum foil, dried, cold-pressed, and then cut and welded to obtain the positive electrode.

[0132] 3. Preparation of electrolyte

[0133] In a dry argon atmosphere, EC, PC, and DEC (weight ratio 1:1:1) were mixed, and LiPF6 was added and mixed thoroughly to form a basic electrolyte with a LiPF6 concentration of 12.5%. Depending on the requirements, different amounts of additives were added to the basic electrolyte to obtain electrolytes for different embodiments and comparative examples.

[0134] The abbreviations and names of the components in the electrolyte are shown in the table below:

[0135] Material Name abbreviation Material Name abbreviation Ethylene carbonate EC Propyl propionate PP diethyl carbonate DEC Fluoroethylene carbonate FEC Succinic acid SN adiponitrile ADN Ethylene glycol di(2-cyanoethyl) ether EDN 1,3,6-Hexanetrionitrile HTCN 1,2,3-Tris(2-cyanoethoxy)propane TCEP 1,3-Propanesulfonate lactone PS Lithium difluorophosphate LiDFP vinyl sulfate DTD Vinyl carbonate VC 1-Propylphosphate cyclic anhydride T3P Methyl propionate MP Ethyl propionate EP propylene carbonate PC

[0136] 4. Preparation of the separating membrane

[0137] Polyethylene (PE) porous polymer film is used as the separator.

[0138] 5. Preparation of lithium-ion batteries

[0139] The obtained positive electrode, separator, and negative electrode are wound in sequence and placed in an outer packaging foil, leaving an injection port. Electrolyte is poured in through the injection port, the battery is sealed, and then processed through formation, capacity testing, and other procedures to produce a lithium-ion battery.

[0140] II. Testing Methods

[0141] 1. High-Temperature Short-Circuit Deformation Rate Test of Lithium-ion Batteries

[0142] At 25°C, the lithium-ion battery was left to stand for 30 minutes, then charged at a constant current rate of 0.5C to 4.7V, and then charged at a constant voltage rate of 4.7V to 0.05C. After standing for 60 minutes, the thickness T1 of the lithium-ion battery was measured. Then, the battery was short-circuited with 100mΩ for 10 seconds, and the thickness T2 of the lithium-ion battery was measured again. The high-temperature short-circuit deformation rate of the lithium-ion battery was calculated using the following formula:

[0143] Short-circuit deformation rate = [(T2-T1) / T1]×100%.

[0144] 2. Overcharge deformation rate test of lithium-ion batteries

[0145] At 25°C, the lithium-ion battery was left to stand for 30 minutes, then charged at a constant current rate of 0.5C to 4.7V, followed by constant voltage charging at 4.7V to 0.05C, and left to stand for 60 minutes. The thickness T3 of the lithium-ion battery was measured. Then, it was charged at a constant current rate of 0.1C for 60 minutes, left to stand for 30 minutes, and this process was repeated 5 times to bring the lithium-ion battery to 150% state of charge (SOC). The thickness T4 of the lithium-ion battery was measured again. The overcharge deformation rate of the lithium-ion battery was calculated using the following formula:

[0146] Overcharge deformation rate = [(T4-T3) / T3]×100%.

[0147] 3. Voltage drop test of lithium-ion batteries under low temperature storage

[0148] At 25°C, the lithium-ion battery was charged at a constant current of 1C to 4.7V, then charged at a constant voltage to a current of 0.05C, and then discharged at a constant current of 1C to 3.2V. After resting for 5 minutes, the voltage was tested. After storing at -20°C for 24 hours, the voltage was measured again. The voltage drop of the lithium-ion battery is calculated using the following formula:

[0149] Voltage drop = Voltage before storage - Voltage after storage.

[0150] III. Test Results

[0151] Table 1 shows the effects of using a volume-expanding resin in the undercoat and adding propyl propionate to the electrolyte on the safety performance of lithium-ion batteries under high temperature and high pressure and voltage drop under low temperature storage. The volume-expanding resin selected is Matsumoto Microsphere F-30D.

[0152] Table 1

[0153]

[0154]

[0155] 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 overcharge deformation rate and short-circuit deformation rate of the electrochemical devices described in Examples 1-1 to 1-15 under high temperature and high pressure, as well as their voltage drop under low temperature storage, are significantly reduced. This indicates that when the base coating includes a volume-expanding resin and the electrolyte includes propyl propionate, not only can the safety performance of the electrochemical device under high pressure and high temperature be significantly improved, but its voltage drop under low temperature storage can also be effectively reduced.

[0156] 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 performance of the electrochemical device at high temperatures.

[0157] 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≤10, 5≤x≤50 and x / a≥1, the electrochemical performance of the electrochemical device can be further improved.

[0158] Comparative Examples 1-4 and 1-5 involve applying volume-expanding resin to the negative electrode current collector, rather than to the negative electrode undercoat. Comparing Comparative Example 1-5 with Comparative Example 1-3, it can be seen that applying volume-expanding resin to the current collector does not significantly improve the high-temperature safety performance and low-temperature voltage drop of the electrochemical device. The speculated reason is as follows: In the event of rapid temperature rise or even thermal runaway in the electrochemical device, the volume-expanding resin in the undercoat can respond faster than the volume-expanding resin in the composite current collector, thereby absorbing heat in a timely manner, undergoing volume expansion, blocking electron transfer between the active layer and the current collector, and improving safety performance.

[0159] Furthermore, referring to Comparative Examples 1-6 and 1-7 and Examples 1-15, the addition of methyl propionate or ethyl propionate to the electrolyte did not significantly improve the high-temperature safety and low-temperature performance of the electrochemical device as much as propyl propionate. This is because propyl propionate has a more suitable swelling effect on the volume-expanding resin, which is more conducive to the rapid expansion of the resin at high temperatures and the rapid migration of lithium ions at low temperatures.

[0160] Table 2 shows the effects of different components of the volume-expanding resin and conductive agent in the negative electrode undercoat on the safety performance of lithium-ion batteries under high temperature and high pressure and voltage drop at low temperature. The weight ratio of volume-expanding resin, conductive agent and binder is 5:85:10.

[0161] Table 2

[0162]

[0163] Table 2 shows that even by changing the composition of the volume-expanding resin and conductive agent in the undercoat, an electrochemical device with excellent safety performance under high temperature and high pressure and low voltage drop at low temperature can still be obtained. Referring to Examples 2-3 and 2-5, the improvement in the electrochemical performance of the device is even more significant when thermally expandable microspheres and graphene are used simultaneously.

[0164] Table 3 shows the effects of electrolyte additives on the safety performance of lithium-ion batteries under high temperature and high pressure and on voltage drop at low temperature. Examples 3-1 to 3-29 differ from Example 1-1 only in the parameters listed in Table 3.

[0165] Table 3

[0166]

[0167]

[0168] Referring to Table 3, comparing Examples 3-1 to 3-14 with Example 1-1, it can be seen that adding a cyano compound to the electrolyte can further improve the safety performance of the electrochemical device under high temperature and high pressure and suppress its voltage drop during low-temperature storage. In particular, the combined use of multiple cyano compounds can further optimize the above effects. Further referring to the results of Examples 3-20 and 3-29, it can be seen that when the content of the cyano compound in the electrolyte is no more than 15%, its effect on improving the electrochemical performance of the electrochemical device is more significant.

[0169] Furthermore, as can be seen from the results of Examples 3-15 to 3-19 and Examples 3-21 to 3-28, when at least one of fluoroethylene carbonate, 1,3-propanesulfonic acid lactone, ethylene sulfate, vinylene carbonate, and cyclic phosphate anhydride is further added to the electrolyte, 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.

[0170] Table 4 shows the effect 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 lithium-ion batteries under high temperature and high pressure and the voltage drop under low temperature storage. The only difference between Examples 4-1 to 4-5 and Example 1-1 is the parameters listed in Table 4.

[0171] Table 4

[0172]

[0173]

[0174] The results show that even by adjusting the H1 / H ratio, an electrochemical device with excellent safety performance under high temperature and high pressure and low voltage drop at low temperature can be obtained. However, when the H1 / H ratio satisfies H1 / H≤0.1, an electrochemical device with even better performance can be obtained.

[0175] Table 5 shows the effect of the ratio of the weight W1 of the base coating to the weight W 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 at low temperature. Examples 5-1 to 5-5 differ from Example 1-1 only in the parameters listed in Table 5.

[0176] Table 5

[0177] <![CDATA[W1]]> W <![CDATA[W1 / 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

[0178] The results show that even by adjusting the W1 / W ratio, an electrochemical device with excellent safety performance under high temperature and high pressure and low voltage drop at low temperature can be obtained. However, when W1 / W satisfies W1 / W≤0.5, an electrochemical device with even better performance can be obtained.

[0179] Throughout this specification, references to "embodiment," "partial embodiment," "one embodiment," "another example," "example," "specific example," or "partial example" mean that at least one embodiment or example in this application includes a specific feature, structure, material, or characteristic described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in an example," "in a specific example," or "example," do not necessarily refer to the same embodiments or examples in this application. Furthermore, specific features, structures, materials, or characteristics described herein can be combined in any suitable manner in one or more embodiments or examples.

[0180] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrochemical device comprising a negative electrode and an electrolyte, The negative electrode includes: Negative electrode current collector; A base coating comprising a volume-expanding resin and formed on at least one surface of the negative electrode current collector; and A negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material and formed on the base coating layer; and The electrolyte comprises propyl propionate and a compound having a cyano group, wherein the content of propyl propionate is x% based on the total weight of the electrolyte; the content of the volume-expanding resin is a% based on the weight of the primer layer; and wherein 5 ≤ x ≤ 50 and x / a ≥ 1.

2. The electrochemical device according to claim 1, wherein 0.1 ≤ a ≤ 10.

3. The electrochemical device according to claim 1, wherein when the internal temperature of the electrochemical device is between 20°C and 40°C, the volume of the volume-expanding resin is V0, and when the internal temperature of the electrochemical device reaches the range of 140°C to 160°C, the volume of the volume-expanding resin is V1, wherein V1 / V0 ≥ 2.

4. The electrochemical device according to claim 3, wherein the volume-expanding resin comprises at least one of polyethylene, polypropylene, polyvinyl acetate, or polypropylene.

5. The electrochemical device according to claim 1, wherein the volume-expanding resin comprises thermally expandable microspheres.

6. The electrochemical device according to claim 1, wherein the undercoat further comprises a conductive agent, the conductive agent comprising at least one of carbon nanotubes, graphene or carbon black.

7. The electrochemical device according to claim 1, wherein the base coating further comprises an adhesive, the adhesive comprising at least one of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, styrene-butadiene rubber or fluorinated rubber.

8. The electrochemical device according to claim 1, wherein the cyano compound comprises at least one selected from succinic anion, 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(2-cyanoethoxy)butane.

9. The electrochemical device according to claim 1, wherein the electrolyte further comprises at least one of fluoroethylene carbonate, 1,3-propanesulfonic acid lactone, ethylene sulfate, vinylene carbonate, 1-propyl phosphate cycloanhydride, or lithium difluorophosphate.

10. The electrochemical device according to claim 1, wherein the negative electrode satisfies H1 / H≤0.1, wherein the thickness of the undercoating layer is H1µm along the direction perpendicular to the negative electrode current collector, and the thickness of the negative electrode active material layer is Hµm.

11. The electrochemical device according to claim 1, wherein the thickness of the undercoat is H1µm and 0.5≤H1≤5.

12. The electrochemical device according to claim 1, wherein the negative electrode satisfies W1 / W≤0.5, and wherein the weight per unit area of ​​the undercoating layer is W1mg / 1540.25mm². 2 The weight per unit area of ​​the negative electrode active material layer is Wmg / 1540.25mm². 2 .

13. The electrochemical device according to claim 1, wherein the weight per unit area of ​​the undercoating layer is W1 mg / 1540.25 mm². 2 And 20≤W1≤100.

14. An electronic device comprising an electrochemical device according to any one of claims 1-13.

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