Electrochemical apparatus and electronic device

Abstract

The present application provides an electrochemical apparatus and an electronic device. The electrochemical apparatus of the present application comprises a positive electrode sheet and an electrolyte, the positive electrode sheet containing carbon nanotube clusters, and the electrolyte comprising a compound represented by formula (I), and further comprising a second component, the second component comprising any one or both of a compound represented by formula (II) and a compound represented by formula (III). On the basis of the mass of the electrolyte, the content of the compound represented by formula I in the electrolyte in percentage by mass is A%, and the content of the second component in percentage by mass is C%, where A and C satisfy the conditions: 10≤(A+C)≤52 and 2≤A≤25. In the present application, the components and content of the components of the electrolyte in the electrochemical apparatus are controlled, so that the electrochemical apparatus can have good low-temperature discharge performance and low low-temperature impedance.

Description

An electrochemical device and electronic device Technical Field

[0001] This application relates to the field of new energy, and more specifically, to an electrochemical device and an electronic device. Background Technology

[0002] Electrochemical devices such as lithium-ion batteries have advantages such as high energy density, good cycle performance, safety, environmental friendliness, and no memory effect, and are widely used in portable electronic products, electric vehicles, aerospace, energy storage, and other fields. However, current lithium-ion batteries are greatly affected by temperature, especially at low temperatures, where the discharge performance of lithium-ion batteries is poor and the impedance is also high.

[0003] Therefore, there is a need for an electrochemical device that can improve the low-temperature discharge performance and low-temperature impedance of electrochemical devices.

[0004] Summary of the Invention

[0005] This application provides an electrochemical device and an electronic device. The electrochemical device in this application still has good working performance at low temperatures, has good low-temperature discharge performance, and also has low impedance at low temperatures.

[0006] In a first aspect, this application provides an electrochemical device comprising an electrolyte and a positive electrode, the positive electrode containing carbon nanotube clusters. The electrolyte comprises a compound of formula I and a second component, wherein the compound of formula I is: R is selected from any one of fluorinated or unsubstituted C2-C6 alkyl groups, C6-C12 nitrogen-containing heterocyclic groups, and fluorinated or unsubstituted C6-C12 aryl groups. The second component includes at least one of the compounds of formula II and formula III, wherein the compound of formula II is: Where R 13 and R 14 Each is independently a halogen-substituted or unsubstituted C1-C10 alkyl group, and R 13 and R 14 At least one of them contains a halogen. Compound III is: Where R 23 and R 24 Each is independently a halogen-substituted or unsubstituted C1-C10 alkyl group, and R 23 and R 24 At least one of them contains halogen. Based on the mass of the electrolyte, the mass percentage of compound I in the electrolyte is A%, and the mass percentage of the second component is C%, where A and C satisfy: 10≤(A+C)≤52 and 2≤A≤25.

[0007] In the above technical solution, the inventors discovered that both the Formula I compound and the second component have low freezing points and low binding energies with lithium ions, resulting in low interfacial energy barriers during delithiation, especially the Formula I compound, which has an even lower freezing point and binding energy with lithium ions. Therefore, when the total mass percentage of the Formula I compound and the second component in the electrolyte is not less than 10%, and the content of the Formula I compound is not less than 2%, the electrolyte at low temperatures can not only maintain a liquid phase but also have good ionic conductivity without affecting the electronic conductivity of the electrolyte. Furthermore, the inventors also discovered that the Formula I compound and the second component in the electrolyte need to be used together, and the total mass percentage of the Formula I compound and the second component needs to be controlled to be no more than 52%, and the content of the Formula I compound must be below 25%. Otherwise, the interface of the electrochemical device is not easily kept stable (an unstable interface in the electrochemical device will lead to rapid capacity depletion, resulting in poor low-temperature discharge performance of the electrochemical device). Furthermore, the inventors discovered that the carbon nanotube clusters in the positive electrode active material layer of the positive electrode sheet can provide a long-range conductive network, enabling the positive electrode sheet to have good electronic conductivity. Therefore, the synergistic effect of the electrolyte and the positive electrode sheet in this application enables the electrochemical device to still have good low-temperature discharge performance and low impedance in low-temperature environments, which is beneficial to improving the working performance of the electrochemical device at low temperatures.

[0008] In one possible implementation, 8 ≤ C ≤ 45.

[0009] In the above technical solution, the content of the second component is in the range of 8% to 45%, which is more conducive to improving the low-temperature discharge performance of the electrochemical device.

[0010] In one possible implementation, the compound of formula I includes at least one of the following:

[0011] In the above technical solution, the compound of Formula I has a lower freezing point and a lower binding energy with lithium ions, which is more conducive to reducing the impedance of the electrochemical device at low temperatures.

[0012] In one possible implementation, the compound of formula II includes at least one of the compounds shown below:

[0013] And / or, the compounds of formula III include at least one of the following compounds:

[0014] In the above technical solution, the compounds of formula II and formula III can better cooperate with the compound of formula I, reduce the impedance of the electrochemical device at low temperature, and improve the discharge performance of the electrochemical device at low temperature.

[0015] In one possible implementation, the carbon nanotube cluster is composed of bundled carbon nanotube units with a diameter greater than or equal to 0.2 μm; and in each carbon nanotube cluster, the average diameter of the carbon nanotube units is d, the average length is L0, 3 nm ≤ d ≤ 40 nm, and L0 ≥ 5 μm.

[0016] In the above technical solutions, carbon nanotube clusters that meet the above conditions can better improve the discharge performance of electrochemical devices at low temperatures.

[0017] In one possible implementation, the electrolyte further includes a third component, which includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate or propyl propionate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the mass percentage of the third component in the electrolyte is 16% to 35% based on the total mass of the electrolyte.

[0018] In the above technical solution, the third component can further reduce the viscosity of the electrolyte at low temperatures, increase the fluidity of the electrolyte, reduce the low-temperature impedance of the electrochemical device, and improve the low-temperature discharge performance of the electrochemical device.

[0019] In one possible implementation, the electrolyte further includes a fourth component, which comprises at least one of the following compounds:

[0020] Based on the total mass of the electrolyte, the mass percentage of the fourth component is 0.2% to 3%.

[0021] In the above technical solution, the fourth component can form a low-impedance S-based interface layer on the electrode surface of the electrochemical device, which reduces the lithium-ion insertion / extraction barrier at low temperatures, lowers the low-temperature impedance, and improves low-temperature discharge.

[0022] In one possible implementation, the electrolyte further includes a fifth component, which comprises at least one of vinyl sulfate, methyl vinyl sulfate, 1,4-butanesulfonyl lactone, 2,4-butanesulfonyl lactone, 1,3-propanesulfonyl lactone, vinylene carbonate, succinate, glutaronitrile, methylglutaronitrile, adiponitrile, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, ethylene glycol bis(propionitrile) ether, trans-butenedionitrile, fluoroethylene carbonate, and lithium difluorophosphate; the mass percentage of the fifth component is 0.02% to 8% based on the total mass of the electrolyte.

[0023] In the above technical solution, the fifth component can form a stable interface layer on the surface of the battery electrode, reduce the continuous reaction of the solvent, and improve low-temperature discharge.

[0024] Secondly, this application provides an electronic device comprising the aforementioned electrochemical device. Therefore, the electronic device provided by this application has excellent performance.

[0025] The beneficial effects of this application are:

[0026] This application provides an electrochemical device and an electronic device. The electrochemical device includes a positive electrode, a negative electrode, and an electrolyte. The electrolyte includes a compound of formula I and a second component. The second component includes at least one of a compound of formula II and a compound of formula III. The positive electrode contains carbon nanotube clusters. Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is A%, and the mass percentage of the second component is C%, with 10 ≤ (A+C) ≤ 52 and 2 ≤ A ≤ 25. By controlling the inclusion of the compound of formula I and the second component in the electrolyte, and ensuring that the types and mass percentages of the compound of formula I and the second component are within the scope of this application, the synergistic effect of the compound of formula I in the electrolyte, the second component, and the carbon nanotube clusters in the positive electrode can improve the temperature discharge performance and impedance at low temperatures of the electrochemical device, thereby enhancing its performance at low temperatures. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0028] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.

[0029] In a first aspect, this application provides an electrochemical device, including an electrolyte, a positive electrode, and a negative electrode. In the electrochemical device of this application, the synergistic effect of the Formula I compound in the electrolyte, the second component, and the carbon nanotube clusters in the positive electrode can improve the impedance and discharge performance of the electrochemical device at low temperatures, which is beneficial to improving the working performance of the electrochemical device at low temperatures.

[0030] The specific structure of the electrochemical device in this application is as follows:

[0031] electrolyte

[0032] The electrolyte plays a role in transporting lithium ions and electrons, ensuring the formation of pathways within the electrochemical device.

[0033] The electrolyte of this application includes a compound of formula I and a second component, wherein the compound of formula I is: R is selected from any one of fluorinated or unsubstituted C2-C6 alkyl groups, C6-C12 nitrogen-containing heterocyclic groups, and fluorinated or unsubstituted C6-C12 aryl groups. The second component includes at least one of the compounds of formula II and formula III, wherein the compound of formula II is: Where R 13 and R 14 Each is independently a halogen-substituted or unsubstituted C1-C10 alkyl group, and R 13 and R 14 At least one of them contains a halogen. Compound III is: Where R 23 and R 24 Each is independently a halogen-substituted or unsubstituted C1-C10 alkyl group, and R 23 and R 24 At least one of them contains halogen. Based on the total mass of the electrolyte of this application, the mass percentage of compound I in the electrolyte is A%, and the mass percentage of the second component is C%, wherein A and C satisfy: 10≤(A+C)≤52 and 2≤A≤25.

[0034] In the technical solution of this application, the inventors discovered that compounds of formula I, and compounds of formula II and III in the second component, all have low freezing points and low binding energies with lithium ions, resulting in low interfacial energy barriers during delithiation (especially compound I, which has an even lower freezing point and binding energy with lithium ions). Furthermore, the inventors found that compound I and the second component in the electrolyte need to be used together, and the amount of compound I should not be excessive; otherwise, the interface of the electrochemical device will not be easily stabilized, leading to rapid depletion of the electrochemical device's capacity and a deterioration in its low-temperature discharge performance. Therefore, when the total mass of the Formula I compound and the second component in the electrolyte of this application accounts for 10% to 52% based on the total mass of the electrolyte, and the content of the Formula I compound is 2% to 25%, the electrolyte can remain liquid at low temperatures, which not only has good ionic conductivity, but also keeps the interface of the electrochemical device stable. The Formula I compound and the second component in the electrolyte work together with the carbon nanotube clusters in the positive electrode of this application, so that the electrochemical device still has good discharge performance and low impedance in the low temperature environment, which is beneficial to improving the working performance of the electrochemical device at low temperatures.

[0035] Specifically, in the embodiments of this application, the total mass percentage of the compound of Formula I and the second component can be 10%, 15%, 17%, 23.7%, 31.9%, 37%, 44.9%, 49.3%, 52%, or within any range of any two of the above values, wherein the mass percentage of the compound of Formula I can be 2%, 7.2%, 9%, 12.5%, 18.7%, 22%, 24%, 25%, or within any range of any two of the above values.

[0036] As an example, the compound of formula I in the electrolyte of this application may specifically include at least one of the following compounds:

[0037] These Formula I compounds have lower freezing points and lower binding energies with lithium ions, which are more conducive to reducing the impedance of electrochemical devices at low temperatures.

[0038] In some embodiments of this application, the mass percentage of the second component can generally be controlled within the range of 8% to 45%, which is beneficial for improving the low-temperature discharge performance of the electrochemical device. For example, in addition to the second component, the compound of formula II in the second component of this application may specifically include at least one of the following:

[0039] The compound of formula III in the second component may specifically include at least one of the following:

[0040] The compounds in the second component mentioned above are more conducive to maintaining the interfacial stability of the electrochemical device, thereby better improving the discharge performance of the electrochemical device at low temperatures.

[0041] In addition, in some other embodiments, the electrolyte further includes a third component, which includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, or propyl propionate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Based on the mass of the electrolyte, the mass percentage of the third component in the electrolyte is 16% to 35%, specifically, the mass percentage of the third component can be 16%, 19%, 24%, 27%, 31%, 35%, etc., or within a range consisting of any two of the above values. The third component can reduce the viscosity of the electrolyte at low temperatures, increase the fluidity of the electrolyte at low temperatures, reduce the low-temperature impedance of the electrochemical device, and improve the discharge performance of the electrochemical device at low temperatures.

[0042] In some embodiments of this application, the electrolyte further includes a fourth component, which can form a low-resistivity S-based interface layer on the electrode surface of the electrochemical device, resulting in a reduction of the lithium-ion insertion / extraction barrier at low temperatures and improving the discharge performance of the electrochemical device at low temperatures. Specifically, the fourth component includes at least one of the following compounds:

[0043] Based on the total mass of the electrolyte, the mass percentage of the fourth component is 0.2% to 3%. For example, the mass percentage of the fourth component can be 0.2%, 0.4%, 1.3%, 1.8%, 2.4%, 3%, or within a range of any two of the above values.

[0044] In some embodiments of this application, the electrolyte further includes a fifth component, which includes at least one of the following: vinyl sulfate, methyl vinyl sulfate, 1,4-butanesulfonyl lactone, 2,4-butanesulfonyl lactone, 1,3-propanesulfonyl lactone, vinylene carbonate, succinate, glutaronitrile, methylglutaronitrile, adiponitrile, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, ethylene glycol bis(propionitrile) ether, trans-butenedionitrile, fluoroethylene carbonate, and lithium difluorophosphate. This fifth component can form a stable interface layer on the electrode surface of the battery, reducing the continuous reaction of the solvent and improving the low-temperature discharge performance of the electrochemical device. Based on the total mass of the electrolyte, the mass percentage of the fifth component is 0.02% to 8%.

[0045] Positive electrode sheet

[0046] The inventors discovered that when the positive electrode of this application contains carbon nanotube clusters, the carbon nanotube clusters can provide a long-range conductive network. In this way, under low-temperature conditions, the electronic conductivity of the positive electrode can match the ionic conductivity of the electrolyte, thereby enabling the electrochemical device to still have good low-temperature discharge performance and low impedance in a low-temperature environment.

[0047] Specifically, the carbon nanotube clusters of this application are formed by multiple carbon nanotube units arranged in a bundle. In each carbon nanotube cluster, the average diameter d of the carbon nanotube units satisfies 3nm≤d≤40nm, and the average length L0≥5μm. The diameter D of the entire carbon nanotube cluster is not less than 0.2μm.

[0048] It should be noted that "the diameter of a carbon nanotube unit" refers to the outer diameter of the cross-sectional circle perpendicular to its axial direction within the carbon nanotube unit (using the cross-sectional circle with the largest diameter); similarly, "the diameter of a carbon nanotube cluster" refers to the outer diameter of the cross-sectional circle perpendicular to its axial direction within the carbon nanotube cluster (using the cross-sectional circle with the largest diameter). Furthermore, "bundled arrangement" in this application refers to the arrangement of carbon nanotube units that are contacted and stacked together through their sidewalls. Moreover, in this application, the carbon nanotube unit can be either a multi-walled carbon nanotube unit or a single-walled carbon nanotube unit; this application does not impose any limitation on this.

[0049] In this application, the structure of the positive electrode generally includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the carbon nanotube cluster is generally located within the positive active material layer. Furthermore, it should be noted that "a positive active material layer disposed on at least one surface of the positive current collector" means that the positive active material layer can be disposed on one surface or on two surfaces along the thickness direction of the positive current collector. Moreover, in this application, the "surface of the positive current collector" can be the entire region of the positive current collector or only a portion thereof; there are no particular limitations, as long as the purpose of this application is achieved.

[0050] In some embodiments of this application, the positive electrode active material layer further contains a positive electrode active substance, which can be any substance capable of reversibly intercalating and deintercalating Li. + Na + Substances containing alkali metal ions are used to ensure the normal charging and discharging of the electrochemical device. For example, positive electrode active materials include, but are not limited to, at least one of lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium nickel oxide, and ternary materials. Ternary materials include, but are not limited to, LiNi x Co y Mn z O2, LiNi x Co y Al z At least one of O2, etc., and the contents of Ni, Co, Mn, Al, etc., can be adjusted to ensure that x+y+z=1. For example, the ternary material can be LiNi. 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.88 Co 0.08 Mn 0.04 O2, LiNi 0.8 Co 0.15 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1O2, LiNi 0.88 Co 0.1 Mn 0.02 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.88 Co 0.1 Al 0.02 O2, etc.

[0051] In some embodiments of this application, the positive electrode active material layer generally also contains a positive electrode binder. There are no particular restrictions on the type of positive electrode binder used in the manufacture of the positive electrode active material layer. In the case of the coating method, any material that can be dissolved or dispersed in the liquid medium used in the electrode manufacturing process is acceptable. Positive electrode binders include, but are not limited to, any one or at least two 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 elastomers 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).

[0052] In the positive electrode, there are no particular restrictions on the type of positive current collector; it can be any known material suitable for use as a positive current collector. Materials for the positive current collector include, but are not limited to, metals such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and materials such as carbon cloth and carbon paper.

[0053] In preparing the positive electrode sheet, the components of the aforementioned positive electrode active material layer can be dissolved or dispersed in a liquid solvent to form a positive electrode slurry. This slurry is then coated onto a positive electrode current collector and dried, thereby forming the positive electrode active material layer on the current collector, thus obtaining the positive electrode sheet. When preparing the positive electrode sheet using this method, there are no particular limitations on the solvent in the positive electrode slurry, as long as it can dissolve or disperse the aforementioned components. Specifically, the solvent in the positive electrode slurry includes, but is not limited to, N-methylpyrrolidone (NMP) and ethylene carbonate (EC). Alternatively, in preparing the positive electrode sheet, the various components of the positive electrode active material layer can be dry-mixed to form a sheet, which is then pressed onto the positive electrode current collector.

[0054] Negative electrode sheet

[0055] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The composition of the negative electrode active material layer includes the negative electrode sheet active material. That is, in this application, the negative electrode active material layer can be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. Moreover, in this application, the "surface of the negative electrode current collector" can be the entire area of ​​the negative electrode current collector or a part of the negative electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0056] The negative electrode active material layer generally contains a negative electrode active material, and this application does not impose any particular limitation on the negative electrode active material. Specifically, the negative electrode active material may include at least one of carbon materials or silicon-based materials. More specifically, carbon materials include, but are not limited to, at least one of natural graphite, artificial graphite, mesophase microcarbon spheres, hard carbon, or soft carbon; silicon-based materials include, but are not limited to, at least one of silicon, silicon-oxygen composite materials, or silicon-carbon composite materials.

[0057] In some embodiments, the negative electrode active material layer typically also contains a negative electrode conductive agent. This application does not particularly limit the type of negative electrode conductive agent, as long as it achieves the purpose of this application. For example, negative electrode conductive agents include, but are not limited to, at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots, or graphene.

[0058] In some embodiments, the negative electrode active material layer may also contain a negative electrode binder and a thickener. This application does not impose any particular limitation on the types of negative electrode binders and thickeners, as long as they can achieve the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener in the negative electrode slurry may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0059] In the negative electrode sheet, the material of the negative electrode current collector includes, but is not limited to, copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal, etc., and this application does not have any particular limitations. Among them, the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the material of the polymer substrate includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene propylene copolymer, polyethylene terephthalate, polyethylene terephthalate, or poly(p-phenylene terephthalamide).

[0060] Furthermore, this application does not impose any particular limitations on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode active material layer is 30 μm to 160 μm.

[0061] Furthermore, similar to the preparation of the positive electrode sheet, the preparation of the negative electrode sheet can be achieved either by preparing a negative electrode slurry, coating the slurry onto a negative electrode current collector, and drying it to form a negative electrode active material layer on the current collector, thus obtaining the negative electrode sheet; or by dry mixing the components of the negative electrode active material layer to form a sheet, which is then pressed onto the negative electrode current collector to form the negative electrode active material layer, thereby obtaining the negative electrode sheet. The solvent in the negative electrode slurry includes any one of aqueous solvents and organic solvents. Aqueous solvents include, but are not limited to, mixtures of alcohol and water or water itself. Organic solvents 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. In some other embodiments, when using aqueous solvents, the negative electrode slurry composition may also include a thickener and styrene-butadiene rubber (SBR) emulsion to slurry the negative electrode slurry, thereby adjusting its viscosity. The types of thickeners in the positive electrode slurry include, but are not limited to, at least one of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts.

[0062] Separating membrane

[0063] 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.

[0064] 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 material can be resin, glass fiber, inorganic materials, etc., formed from materials 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 resin or glass fiber separator materials 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.

[0065] 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.

[0066] Inorganic materials 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.). The forms of inorganic materials include, but are not limited to, particulate or fibrous forms.

[0067] The separator can be in the form of a thin film, including but not limited to non-woven fabric, woven fabric, and microporous membranes. In the thin film form, 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 separators, the following separators can also be used: separators 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.

[0068] 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. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, and the rate capability and energy density of the electrochemical device can be ensured.

[0069] Secondly, this application also provides an electronic device that includes an electrochemical device according to this application.

[0070] 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.

[0071] Example

[0072] The following uses a lithium-ion secondary battery as an example to illustrate the implementation of the electrochemical device of this application in more detail through embodiments and comparative examples. Those skilled in the art will understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0073] Test methods and equipment:

[0074] Low-temperature discharge (-20℃, 3.0V) performance test:

[0075] The electrochemical device was placed in a 25°C constant temperature chamber and charged to 4.52V with a constant current of 0.5C. It was then charged to 0.05C with a constant voltage at 4.52V, and finally discharged to 3.0V with a constant current of 0.2C. This discharge capacity was recorded as the initial discharge capacity D1. The device was then charged again to 4.52V with a constant current of 0.5C, and then charged to 0.05C with a constant voltage at 4.52V. The electrochemical device was then removed and placed in a -20°C constant temperature chamber for 1 hour, and then discharged to 3.0V with a constant current of 0.2C. This discharge capacity was recorded as the low-temperature discharge capacity D2. The low-temperature discharge capacity retention rate of the electrochemical device at -20°C and 3.0V was calculated using the following formula:

[0076] Low-temperature discharge capacity retention rate = Low-temperature discharge capacity D2 / Initial discharge capacity D1.

[0077] The higher the low-temperature discharge capacity retention rate, the better the low-temperature discharge performance.

[0078] Low temperature (-20℃) impedance test

[0079] The electrochemical device was placed in a 25°C constant temperature chamber and charged to 4.52V with a constant current of 0.5C. It was then charged to 0.05C at 4.52V with a constant voltage, and finally discharged to 3.0V with a constant current of 0.2C. The device was then removed and placed in a -20°C constant temperature chamber for 1 hour, followed by 5 hours of discharge with a constant current of 0.1C. The open-circuit voltage at this point was recorded as OCV1. Discharge was then continued at 1C for 1 second (data was collected every 5ms), and the open-circuit voltage at this point was recorded as OCV2. The discharge current at this point was I0. The low-temperature impedance of the electrochemical device at -20°C was calculated using the following formula: -20°C impedance = (OCV1 - OCV2) / I0.

[0080] The unit of OCV is volt (V), the unit of I0 is milliampere (mA), and the unit of impedance is milliohm (mΩ).

[0081] Example 1-1

[0082] <Preparation of Electrolyte>

[0083] In an argon-atmospheric glove box with a water content <10 ppm, ethylene carbonate (EC) and propylene carbonate (PC) were mixed in a 1:1 mass ratio to prepare the base solvent. Then, lithium hexafluorophosphate (LiPF6), compound I, compound II, and / or compound III were added and mixed thoroughly to obtain the electrolyte. Based on the total mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, and the mass percentages of compounds I, II, and / or III are shown in Table 1, with the remainder being the base solvent. Furthermore, the compounds referred to by the symbols in the table can be found in the above-mentioned content of this document.

[0084] <Preparation of the positive electrode>

[0085] Lithium cobalt oxide, carbon nanotube clusters, and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 97:1.5:1.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred uniformly under vacuum to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto the upper and lower surfaces of a 9 μm thick aluminum foil current collector. After drying and pressure treatment, the foil was cut to the specified size to obtain the positive electrode sheet. The diameter D of the carbon nanotube clusters in the preparation process was 0.15 μm, the average diameter d of the carbon nanotube units within the clusters was 10 nm, and the average length L0 was 5 μm.

[0086] <Preparation of Negative Electrode Sheets>

[0087] Artificial graphite, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNTs): carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95.8:2.4:0.5:0.5:0.8. Deionized water was then added as a solvent and the mixture was stirred until homogeneous, resulting in a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was uniformly coated onto the upper and lower surfaces of a 6 μm thick copper foil used as a negative electrode current collector. After drying and pressure treatment, the foil was cut into specified sizes to obtain the negative electrode sheet.

[0088] <Isolation membrane>

[0089] A porous polyethylene film with a thickness of 15μm was used as the separator.

[0090] <Preparation of Electrochemical Devices>

[0091] The positive and negative electrode sheets prepared as described above are connected to the tabs. They are then laminated using a separator to obtain a laminate. The laminate, along with the electrolyte, is then housed in an aluminum laminated housing. The opening of the housing is heat-sealed, and the electrochemical device is fabricated through processes such as formation and degassing.

[0092] Examples 1-2 to Examples 1-11

[0093] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-1. The mass percentage of LiPF6 remains unchanged when the content of compound II or compound III changes.

[0094] Examples 1-12 to Examples 1-11

[0095] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-1. The mass percentage of LiPF6 remains unchanged when the content of compound I changes.

[0096] Examples 1-12 to Examples 1-15

[0097] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-1. The mass percentage of LiPF6 remains unchanged when the content of compound I changes.

[0098] Examples 1-16 to Examples 1-25

[0099] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-13.

[0100] Table 1

[0101] Examples 2-1 to 2-7

[0102] Except for adjusting the relevant preparation parameters of carbon nanotube clusters in <Preparation of Positive Electrode Sheet> according to Table 2, the rest are the same as in Examples 1-14.

[0103] Table 2

[0104] Examples 3-1 to 3-10

[0105] Except for the addition of a third component and the adjustment of the relevant preparation parameters according to Table 3 in the <Preparation of Electrolyte>, the rest is the same as in Examples 1-13.

[0106] Table 3

[0107] Comparative Examples 1 to 2

[0108] Except for the use of other conductive agents of the same mass percentage instead of carbon nanotube clusters in the <Preparation of Positive Electrode>, the rest is the same as in Examples 1-3.

[0109] Comparative Examples 3 to 6

[0110] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-1. The content of LiPF6 remains unchanged when the contents of compound I and the second component change.

[0111] As shown in Table 1, in this application, the synergistic effect of the Formula I compound in the electrolyte and the second component with the carbon nanotube clusters in the positive electrode enables the electrochemical device to maintain good low-temperature discharge performance and low impedance even at low temperatures, which is beneficial to improving the working performance of the electrochemical device at low temperatures. Furthermore, limiting the content of the second component to the range of 8% to 45% is beneficial to further improving the low-temperature discharge performance of the electrochemical device.

[0112] As shown in Table 2, when the carbon nanotube clusters of the positive electrode in this application meet the conditions of D≥0.2μm, 3nm≤d≤40nm, and L0≥5μm, the low-temperature discharge performance of the electrochemical device can be further improved.

[0113] As shown in Table 3, adding 16% to 35% of the third component to the electrolyte can reduce the low-temperature impedance of the electrochemical device and improve its discharge performance at low temperatures.

[0114] The above are merely embodiments of this application and are not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An electrochemical device, characterized in that, The electrolyte comprises an electrolyte and a positive electrode, wherein the positive electrode contains carbon nanotube clusters; the electrolyte comprises a compound of formula I and a second component, wherein the compound of formula I is: R is selected from any one of fluorinated or unsubstituted C2-C6 alkyl, C6-C12 nitrogen-containing heterocyclic group, and fluorinated or unsubstituted C6-C12 aryl group; The second component comprises at least one of a compound of formula II and a compound of formula III, wherein the compound of formula II is: Where R 13 and R 14 Each is independently a halogen-substituted or unsubstituted C1-C10 alkyl group, and R 13 and R 14 At least one of them contains halogen; The compound of formula III is: Where R 23 and R 24 Each is independently a halogen-substituted or unsubstituted C1-C10 alkyl group, and R 23 and R 24 At least one of them contains halogen; Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is A%, and the mass percentage of the second component is C%, wherein A and C satisfy: 10≤(A+C)≤52 and 2≤A≤25.

2. The electrochemical device according to claim 1, characterized in that, 8≤C≤45。 3. The electrochemical device according to claim 1, characterized in that, The compound of formula I includes at least one of the following compounds:

4. The electrochemical device according to claim 1, characterized in that, The compound of formula II includes at least one of the following compounds: And / or, the compound of formula III comprises at least one of the following compounds:

5. The electrochemical device according to claim 1, characterized in that, The carbon nanotube cluster is composed of bundled carbon nanotube units, the diameter of the carbon nanotube cluster is ≥0.2μm; and in each carbon nanotube cluster, the average diameter of the carbon nanotube unit is d, the average length is L0, 3nm≤d≤40nm, and L0≥5μm.

6. The electrochemical device according to claim 1, characterized in that, The electrolyte further includes a third component, which includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate or propyl propionate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Based on the total mass of the electrolyte, the mass percentage of the third component is 16% to 35%.

7. The electrochemical device according to claim 1, characterized in that, The electrolyte further includes a fourth component, which comprises at least one of the following compounds: Based on the total mass of the electrolyte, the mass percentage of the fourth component is 0.2% to 3%.

8. The electrochemical device according to claim 1, characterized in that, The electrolyte further includes a fifth component, which comprises at least one of the following: vinyl sulfate, methyl vinyl sulfate, 1,4-butane sulphol, 2,4-butane sulphol, 1,3-propane sulphol, vinylene carbonate, succinate, glutaronitrile, methylglutaronitrile, adiponitrile, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, ethylene glycol bis(propionitrile) ether, trans-butenedionitrile, fluoroethylene carbonate, and lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage of the fifth component is 0.02% to 8%.

9. An electronic device, characterized in that, It contains the electrochemical device as described in any one of claims 1 to 8.

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