Electrochemical apparatus and electronic apparatus

Abstract

The present application provides an electrochemical apparatus and an electronic apparatus. The electrochemical apparatus of the present application comprises a positive electrode sheet and an electrolyte. The electrolyte comprises a compound represented by formula (I), and the positive electrode sheet contains a lithium transition metal composite oxide, which has a P6(3)mc crystal structure. In the present application, by means of a synergistic effect of the compound represented by formula I in the electrolyte and the lithium transition metal composite oxide having a P63mc crystal structure in the positive electrode sheet, cycle capacity attenuation of the electrochemical apparatus under a high voltage can be significantly mitigated, and growth in the thickness of the electrochemical apparatus during cycling can be significantly inhibited.

Description

An electrochemical device and an electronic device Technical Field

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

[0002] Electrochemical devices such as lithium-ion batteries (lithium-ion batteries) are widely used in portable electronic products, electric vehicles, aerospace, and energy storage due to their advantages such as high energy density, good cycle performance, safety, environmental friendliness, and lack of memory effect. With the widespread application of lithium-ion batteries, users are also placing higher demands on their energy density.

[0003] Currently, the energy density of lithium-ion batteries can be increased by raising their operating voltage. However, as the positive electrode potential of lithium-ion batteries increases, the electrolyte becomes more unstable at the positive electrode interface. This makes lithium-ion batteries more prone to cycle capacity decay. At the same time, under high voltage, the electrolyte is very likely to react at the electrode interface, resulting in a rapid increase in the thickness of the lithium-ion battery during cycling.

[0004] Summary of the Invention

[0005] This application provides an electrochemical device and an electronic device. The electrochemical device of this application can effectively improve the cycle capacity decay under high voltage, and at the same time, it can effectively suppress the thickness growth of the electrochemical device during the cycle.

[0006] In a first aspect, embodiments of this application provide an electrochemical device comprising a positive electrode and an electrolyte, wherein the electrolyte comprises a compound of formula I: 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 positive electrode contains a lithium transition metal complex oxide with a P63mc crystal structure.

[0007] In the aforementioned technical solution, the inventors discovered that the lithium transition metal composite oxide with a P63mc crystal structure (hereinafter referred to as "P63mc structure composite oxide") has a stable crystal structure and exhibits no significant phase transition under high voltage. However, it exhibits numerous interfacial side reactions with the electrolyte, which causes the transition metal in the lithium transition metal composite oxide to dissolve and deposit on the negative electrode, thus degrading the interfacial layer of the negative electrode. The inventors further discovered that the sulfonyl fluoride group in the compound of formula I can form a stable and low-impedance interfacial layer on the negative electrode, thereby reducing the degradation of the interfacial layer of the negative electrode by the transition metal. Therefore, in the electrochemical device, the synergistic effect of the P63mc structure composite oxide in the positive electrode and the compound of formula I in the electrolyte can improve the capacity decay phenomenon of the electrochemical device under high voltage, while also effectively suppressing thickness growth during cycling.

[0008] In one possible implementation, the compound of formula I includes at least one of the compounds shown below:

[0009] In the above technical solution, the compound of formula I that meets the above conditions can better synergize with the composite oxide of P63mc structure in the positive electrode, thereby further improving the cycle capacity decay phenomenon of the electrochemical device under high voltage and suppressing the thickness growth during the cycle process.

[0010] In one possible implementation, the mass percentage of compound I is 1% to 30% based on the total mass of the electrolyte.

[0011] In the above technical solution, controlling the content of compound I in the electrolyte can not only work synergistically with the positive electrode to improve the cycle capacity decay phenomenon of the electrochemical device under high voltage and suppress the thickness growth during the cycle, but also avoids negatively affecting the positive electrode, thereby improving the high voltage cycle performance of the electrochemical device.

[0012] In one possible implementation, the XRD pattern of lithium transition metal composite oxide at full discharge of 3.0V exhibits characteristic peaks in the range of 17.5° to 19.5°.

[0013] In one possible implementation, the electrolyte also includes a compound of formula II: Wherein R1 is any one of C1 to C10 alkyl groups, and R2 is any one of C1 to C10 alkyl groups substituted with halogen; based on the total mass of the electrolyte, the mass percentage of compound II is 8% to 60%.

[0014] In the above technical solution, the compound of formula II can form a stable interface layer on the positive electrode, which can reduce the probability of dissolution of transition metals in lithium transition metal composite oxides, thereby reducing the adverse effects of transition metal dissolution on the positive electrode structure and improving the cycle capacity decay phenomenon of electrochemical devices under high voltage.

[0015] In one possible implementation, the compound of formula II includes at least one of the compounds shown below:

[0016] In the above technical solution, the compound of formula II can better reduce the degradation of the cathode structure caused by the dissolution of transition metals, thereby further improving the cycle capacity decay phenomenon of electrochemical devices under high voltage.

[0017] In one possible implementation, the sum of the mass percentages of compounds of formula I and formula II is 10% to 80% based on the total mass of the electrolyte.

[0018] In the above technical solutions, electrolytes that meet the above conditions can better improve the capacity decay phenomenon of electrochemical devices under high voltage and can also better suppress the thickness growth of electrochemical devices under cycling.

[0019] In one possible implementation, based on the total mass of the electrolyte, the sum of the mass percentages of compounds of formula I and formula II in the electrolyte components is 24% to 64%; the mass percentage of compound I is 3% to 22%, and the mass percentage of compound II is 21% to 45%.

[0020] In the above technical solution, the electrolyte that meets the above conditions can further improve the capacity decay phenomenon of the electrochemical device under high voltage and further suppress the thickness growth of the electrochemical device under cycling.

[0021] In one possible implementation, the electrolyte also includes a compound of formula III: Where R 21 R 22 R 23 and R 24 Each is independently a hydrogen atom, a fluorine atom, or a halogenated or unsubstituted C1-C3 alkyl group, and R 21 R 22 R 23 and R 24 At least one of them contains fluorine; the mass percentage of compound III is 3% to 13% based on the total mass of the electrolyte.

[0022] In the above technical solution, the combination of compound III and compound I can form an inorganic + organic interface layer on the negative electrode sheet, thereby further reducing the thickness growth rate of the electrochemical device during the cycling process.

[0023] In one possible implementation, the compound of formula III includes at least one of the following compounds:

[0024] In the above technical solution, the compound of formula III can better cooperate with the compound of formula I, which is beneficial to further reduce the thickness growth rate of the electrochemical device during the cycling process.

[0025] In one possible implementation, the ratio of the mass percentage of compound I to the mass percentage of compound III is 0.2 to 4.2 based on the total mass of the electrolyte; and / or, the ratio of the mass percentage of compound II to the mass percentage of compound III is 0.07 to 1.35 based on the total mass of the electrolyte.

[0026] In the above technical solution, when the mass ratio of compound I to compound III meets the above conditions, the thickness increase of the electrochemical device during the cycling process can be further suppressed.

[0027] In one possible implementation, the mass percentage of fluoride ions in the electrolyte is 0.1% to 2%, based on the total mass of the electrolyte.

[0028] In the above technical solution, the mass percentage of fluoride ions is controlled within the above range, which is beneficial to improving the cycle life of the electrochemical device.

[0029] In one possible implementation, the electrolyte further includes a second 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, and trans-butenedionitrile; the second component has a mass percentage content of 0.1% to 5% based on the total mass of the electrolyte.

[0030] In the above technical solution, adding a second component to the electrolyte helps to reduce the phenomenon of interfacial reaction of the electrolyte, further improves the interfacial stability of the electrochemical device, thereby improving the high-voltage cycling performance of the electrochemical device and reducing the thickness growth during cycling.

[0031] Secondly, embodiments of this application provide an electronic device that includes the electrochemical device described above.

[0032] The beneficial effects of this application are:

[0033] This application provides an electrochemical device and an electronic device. The electrochemical device includes an electrolyte and a positive electrode. The electrolyte includes a compound of formula I, where R in the compound of formula I is selected from any one of fluorine-substituted or unsubstituted C2-C6 alkyl groups, C6-C12 nitrogen-containing heterocyclic groups, and fluorine-substituted or unsubstituted C6-C12 aryl groups. The positive electrode contains a lithium transition metal composite oxide having a P63mc crystal structure. By using a lithium transition metal composite oxide positive electrode containing an electrolyte with a P63mc crystal structure and an electrolyte containing a compound of formula I in combination, the capacity decay phenomenon of the electrochemical device under high voltage can be improved, and the thickness growth during cycling can also be effectively suppressed. Detailed Implementation

[0034] 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. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0035] The electrochemical and electronic devices of the embodiments of this application will be described in detail below.

[0036] In a first aspect, this application provides an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte. In the electrochemical device of this application, the compound of formula I in the electrolyte components can synergistically interact with the composite oxide with the P63mc structure in the positive electrode, thereby improving the capacity decay of the electrochemical device under high voltage and suppressing the thickness increase of the electrochemical device during cycling.

[0037] The specific structure of the electrochemical device in this application is as follows:

[0038] Positive electrode sheet

[0039] The positive electrode of this application contains a composite oxide with a P63mc structure. The inventors discovered that this lithium transition metal composite oxide has a stable crystal structure and exhibits no significant phase transition under high voltage. However, the inventors also found that the P63mc composite oxide exhibits numerous interfacial side reactions with the electrolyte, leading to the dissolution of the transition metal and its deposition on the negative electrode, thus degrading the interfacial layer of the negative electrode. Therefore, the inventors added a compound of formula I to the electrolyte. The sulfonyl fluoride group in the compound of formula I can form a stable and low-impedance interface layer on the negative electrode, thereby reducing the degradation of the interface layer of the negative electrode by the over-dissolved plating metal. The synergistic effect of the two can improve the capacity decay phenomenon of electrochemical devices under high voltage, and at the same time, it can also effectively suppress the thickness growth during cycling.

[0040] In this application, the structure of the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer contains a positive active material; specifically in this application, the positive active material is a lithium transition metal composite oxide having a P63mc crystal structure.

[0041] Additionally, it should be noted that "a positive electrode active material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode active material layer can be disposed on one surface or on two surfaces in the thickness direction of the positive electrode current collector. Moreover, in this application, the "surface of the positive electrode current collector" can be the entire area of ​​the positive electrode current collector or a part of the positive electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0042] Specifically, lithium transition metal composite oxides with P63mc structure exhibit characteristic peaks in the XRD patterns ranging from 17.5° to 19.5° when the electrochemical device is at full discharge 3.0V. For example, lithium cobalt oxide with a P63mc crystal structure has a characteristic peak at 17.8° at full discharge 3.0V.

[0043] In some embodiments, the positive electrode active material layer further includes a positive electrode conductive agent; this application does not limit the type of positive electrode conductive agent, as long as it can achieve the purpose of this application. For example, the positive electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The aforementioned conductive carbon black may include, but is not limited to, Super P, acetylene black, or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0044] In some embodiments, the positive electrode active material layer also contains a positive electrode binder. The type of positive electrode binder used in the manufacture of the positive electrode active material layer is not particularly limited; in the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used during electrode manufacturing is acceptable. The positive electrode binder may include, but is not limited to, at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber, SBR), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose (CMC-Na), potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode active material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0045] In the positive electrode sheet, 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. Furthermore, to reduce the electronic contact resistance between the positive current collector and the positive active material layer, a conductive additive or conductive coating can be applied to the surface of the positive current collector. Conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. The conductive coating can be a mixture of inorganic oxides, conductive agents, and positive electrode binders. Additionally, this application does not impose any particular limitation on the thickness of the positive current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. This application also does not impose any particular limitation on the thickness of the positive active material layer, as long as it achieves the purpose of this application. For example, the thickness of a single-sided positive electrode material layer is 30 μm to 120 μm.

[0046] 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.

[0047] electrolyte

[0048] In this application, the electrolyte includes a compound of formula I, the general structural formula of which is shown below:

[0049] R is selected from any one of the following: fluorinated or unsubstituted C2-C6 alkyl, C6-C12 nitrogen-containing heterocyclic group, and fluorinated or unsubstituted C6-C12 aryl group.

[0050] As previously described, the sulfonyl fluoride group in Formula I can form a stable and low-impedance interface layer on the negative electrode, thereby reducing the degradation of the interface layer of the negative electrode by the transition metal. In synergy with the P63mc structure composite oxide in the positive electrode, it can improve the capacity decay phenomenon of the electrochemical device under high voltage, while also effectively suppressing thickness growth during cycling.

[0051] In other embodiments, in order to better cooperate with the positive electrode without negatively impacting it, the mass percentage of compound I can be in the range of 1% to 30% based on the total mass of the electrolyte. Specifically, it can be 1%, 3%, 5%, 13%, 17%, 25%, 30%, or within a range consisting of any two of the above values.

[0052] Specifically, the compound of formula I in the electrolyte components can be at least one of the following compounds:

[0053] These Formula I compounds can better combine with the P63mc structure in the positive electrode, thereby further improving the capacity decay phenomenon of the electrochemical device under high voltage and suppressing the thickness growth during cycling.

[0054] In some other embodiments, the electrolyte also includes a compound of formula II: Wherein R1 is any one of C1 to C10 alkyl groups, and R2 is any one of C1 to C10 alkyl groups substituted with halogen; based on the total mass of the electrolyte, the mass percentage of compound II is 8% to 60%. Compound II can form a stable interface layer on the positive electrode, which can reduce the dissolution probability of transition metals in lithium transition metal composite oxides, thereby reducing the adverse effects of transition metal dissolution on the interface layer of the positive electrode, and further improving the cycle capacity decay phenomenon of electrochemical devices under high voltage.

[0055] Specifically, the mass percentage of the compound of formula II can be 8%, 9%, 21%, 36%, 42%, 45%, 50%, 60%, or within any range of two of the above values. Furthermore, to better reduce the degradation of the interface layer between the transition metal and the positive electrode, thereby further improving the capacity decay of the electrochemical device under high voltage, the compound of formula II in the electrolyte composition can be at least one of the following:

[0056] Furthermore, when both Formula I and Formula II compounds are present in the electrolyte, the sum of their mass percentages, based on the total mass of the electrolyte, can be controlled within the range of 10% to 80%. This can further improve the capacity decay phenomenon of the electrochemical device under high voltage. Specifically, the sum of the mass percentages of Formula I and Formula II compounds can be 10%, 24%, 41%, 58%, 59%, 64%, 75%, 80%, or any range consisting of any two of the above values. In particular, the range of 24% to 64% is more conducive to improving the capacity decay of the electrochemical device under high voltage. In this case, the mass percentage of Formula I compound is in the range of 3% to 22%, and the mass percentage of Formula II compound is in the range of 21% to 45%.

[0057] In some other embodiments, the electrolyte also includes a compound of formula III: Where R 21 R 22 R 23 and R 24 Each is independently composed of a hydrogen atom, a fluorine atom, or a halogen-substituted or unsubstituted C1-C3 alkyl group, and R 21 R 22 R 23 and R 24 At least one of the components contains fluorine; the mass percentage of compound III is 3% to 13% based on the total mass of the electrolyte. Compound III can combine with compound I to form an inorganic + organic interface layer on the negative electrode, thereby further reducing the thickness growth rate of the electrochemical device during cycling. Specifically, compound III in the electrolyte composition can be at least one of the following compounds:

[0058] These Formula III compounds can better complement Formula I compounds, which is beneficial for further suppressing the thickness growth of electrochemical devices during cycling.

[0059] Furthermore, when the electrolyte contains compounds of formula I, formula II, and formula III simultaneously, the ratio of the mass percentage of compound I to the mass percentage of compound III, based on the total mass of the electrolyte, is 0.2 to 4.2; and / or, the ratio of the mass percentage of compound II to the mass percentage of compound III, based on the total mass of the electrolyte, is 0.07 to 1.35. This further suppresses the thickness increase of the electrochemical device during cycling.

[0060] In some embodiments of this application, the mass percentage of fluoride ions in the electrolyte is 0.1% to 2% based on the total mass of the electrolyte, which is beneficial to improving the cycle life of the electrochemical device.

[0061] In addition, in some embodiments of this application, in order to reduce the phenomenon of interfacial reaction of the electrolyte and further improve the interfacial stability of the electrochemical device, thereby improving the high-voltage cycling performance of the electrochemical device and reducing the thickness growth during cycling, the electrolyte composition also includes a second component. The second component includes at least one of vinyl sulfate, methyl vinyl sulfate, 1,4-butane sulfonyl lactone, 2,4-butane sulfonate lactone, 1,3-propane sulfonyl lactone, vinylene carbonate, succinate, glutaronitrile, methylglutaronitrile, adiponitrile, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, ethylene glycol bis(propionitrile) ether, and trans-butenedionitrile; based on the total mass of the electrolyte, the mass percentage of the second component is 0.1% to 5%.

[0062] Negative electrode sheet

[0063] 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.

[0064] The negative electrode active material layer 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 natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO2, etc. x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 At least one of Li-Al alloys or metallic lithium.

[0065] 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.

[0066] 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.

[0067] 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).

[0068] 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.

[0069] 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.

[0070] Separating membrane

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] Secondly, this application also provides an electronic device that includes an electrochemical device according to this application.

[0078] 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.

[0079] Example

[0080] 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.

[0081] Test methods and equipment:

[0082] High voltage (4.52V) cycle capacity decay performance test and cycle thickness growth test

[0083] The electrochemical device was placed in a 45°C constant temperature chamber and charged to 4.52V with a constant current of 0.5C. Then, it was charged to 0.05C at 4.52V with a constant voltage. The thickness of the cell at the center of the electrochemical device was measured at five points using a micrometer, and the average value was recorded as the initial cycle thickness M0. Next, it was discharged to 3.0V with a constant current of 0.5C, and the discharge capacity at this point was recorded as the initial discharge capacity D0. This constitutes one charge-discharge cycle. This process was repeated 500 times. The thickness M1 (the thickness at full charge on the last cycle, i.e., the thickness at 0.05C with a constant voltage at 4.52V) and the remaining discharge capacity D1 were recorded after each cycle. The capacity retention rate and thickness growth rate of the electrochemical device after high-voltage cycling are calculated using the following formulas: Capacity retention rate = Remaining discharge capacity D1 / Initial discharge capacity D0 × 100%; Thickness growth rate = (Cycled electrochemical device thickness M1 - Initial cycle thickness M0) / Initial cycle thickness M0 × 100%.

[0084] A higher capacity retention rate indicates a greater improvement in the high-voltage cycle capacity decay of the electrochemical device.

[0085] Full loading process

[0086] Place the electrochemical device in a 25°C constant temperature chamber and charge it to 4.52V with a constant current of 0.2C. Then charge it to 0.05C at 4.52V with a constant voltage, let it stand for 5 minutes, and then discharge it to 3.0V with a constant current of 0.2C. Repeat the above procedure 5 times. At this point, the electrochemical device is in a fully discharged state.

[0087] Example 1-1

[0088] <Preparation of Electrolyte>

[0089] In an argon-atmospheric glove box with a water content of <10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a mass ratio of 1:1:3 to prepare a base solvent. Then, lithium hexafluorophosphate (LiPF6) and compound of formula I were added. Based on the total mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, the mass percentage of compound I is shown in Table 1, and the remainder was the base solvent.

[0090] In addition, the compounds referred to by the codes in the table can be found in the above content of this article.

[0091] <Preparation of the positive electrode>

[0092] A composite oxide with a P63mc structure, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated on the upper and lower surfaces of a 9 μm thick aluminum foil for the positive electrode current collector. After drying and pressure treatment, the foil was cut into the specified size to obtain the positive electrode sheet.

[0093] <Preparation of Negative Electrode Sheets>

[0094] 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.

[0095] <Isolation membrane>

[0096] A porous polyethylene film with a thickness of 15μm was used as the separator.

[0097] <Preparation of Electrochemical Devices>

[0098] 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.

[0099] Examples 1-2 to Examples 1-16

[0100] 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 content of compound I changes.

[0101] Table 1

[0102] Examples 2-1 to 2-11

[0103] Except for the addition of compound II in the <Preparation of Electrolyte> section and the adjustment of the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-10. The content of LiPF6 remains unchanged when the content of compound I or compound II changes.

[0104] Table 2

[0105] Examples 3-1 to 3-12

[0106] Except for the addition of compound III in the <Preparation of Electrolyte> section and the adjustment of the relevant preparation parameters according to Table 3, the rest is the same as in Examples 2-4. The content of LiPF6 remains unchanged when the content of compound III changes.

[0107] Table 3

[0108] Examples 4-1 to 4-13

[0109] Except for the addition of a second component and adjustment of the relevant preparation parameters according to Table 4 in the <Preparation of Electrolyte> section, the rest is the same as in Examples 1-5. The content of LiPF6 remains unchanged when the content of compound III changes.

[0110] Table 4

[0111] Comparative Example 1

[0112] Except for omitting the compound of formula II and adjusting the relevant preparation parameters according to Table 1 in the <Preparation of Electrolyte> section, the rest is the same as in Examples 1-2. The mass percentage of LiPF6 remains unchanged.

[0113] Comparative Example 2

[0114] Except for the use of the same mass fraction of lithium cobalt oxide with R3m crystal structure instead of lithium cobalt oxide with P63mc crystal structure in the <Preparation of Positive Electrode>, the rest is the same as in Examples 1-2.

[0115] Comparative Example 3

[0116] Except for the omission of compound II in the <Preparation of Electrolyte> section and the adjustment of the relevant preparation parameters according to Table 1, the rest was the same as in Comparative Example 2. The mass percentage of LiPF6 remained unchanged.

[0117] As shown in Table 1, in the electrochemical device of this application, the synergistic effect of the compound of formula I in the electrolyte and the composite oxide of P63mc structure in the positive electrode sheet can effectively improve the cycle capacity decay phenomenon of the electrochemical device under high voltage, and at the same time, it can effectively suppress the thickness growth during the cycle.

[0118] As shown in Table 2, the presence of compound II in the electrolyte can further improve the capacity decay of the electrochemical device under high voltage. Furthermore, a fluoride ion mass percentage of no more than 2% in the electrolyte can further enhance the cycle life of the electrochemical device.

[0119] As shown in Table 3, the combination of compound III and compound I can further reduce the thickness growth rate of the electrochemical device during cycling. Moreover, when the mass percentage ratio of compound I to compound III is in the range of 0.2 to 4.2, and the mass percentage ratio of compound II to compound III is in the range of 0.07 to 1.35, the thickness growth of the electrochemical device during cycling can be further suppressed.

[0120] As shown in Table 4, the presence of a second component in the electrolyte can improve the high-voltage cycling performance of the electrochemical device and reduce thickness growth during cycling.

[0121] 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, It includes a positive electrode and an electrolyte, wherein the electrolyte comprises a compound of formula I: R is selected from any one of fluorinated or unsubstituted C2-C6 alkyl, C6-C12 nitrogen-containing heterocyclic group, or fluorinated or unsubstituted C6-C12 aryl group; the positive electrode contains a lithium transition metal composite oxide, which has a P63mc crystal structure.

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

3. The electrochemical device according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is 1% to 30%.

4. The electrochemical device according to claim 1, characterized in that, When the electrochemical device is fully discharged at 3.0V, the XRD pattern of the lithium transition metal composite oxide has characteristic peaks in the range of 17.5° to 19.5°.

5. The electrochemical device according to claim 1, characterized in that, The electrolyte also includes a compound of formula II: Wherein R1 is any one of C1 to C10 alkyl groups, and R2 is any one of C1 to C10 alkyl groups substituted with halogen; based on the total mass of the electrolyte, the mass percentage of the compound of formula II is 8% to 60%.

6. The electrochemical device according to claim 5, characterized in that, The compound of formula II includes at least one of the following compounds:

7. The electrochemical device according to claim 5 or 6, characterized in that, Based on the total mass of the electrolyte, the sum of the mass percentages of the compound of formula I and the compound of formula II is 10% to 80%.

8. The electrochemical device according to claim 7, characterized in that, Based on the total mass of the electrolyte, the sum of the mass percentages of the compound of formula I and the compound of formula II is 24% to 64%; the mass percentage of the compound of formula I is 3% to 22%, and the mass percentage of the compound of formula II is 21% to 45%.

9. The electrochemical device according to claim 5, characterized in that, The electrolyte also includes a compound of formula III: Where R 21 R 22 R 23 and R 24 Each is independently composed of a hydrogen atom, a fluorine atom, or a halogen-substituted or unsubstituted C1-C3 alkyl group, and R 21 R 22 R 23 and R 24 At least one of them contains fluorine; Based on the total mass of the electrolyte, the mass percentage of the compound of formula III is 3% to 13%.

10. The electrochemical device according to claim 9, characterized in that, The compound of formula III includes at least one of the following compounds:

11. The electrochemical device according to claim 9 or 10, characterized in that, Based on the total mass of the electrolyte, the mass percentage of compound I is 0.2 to 4.2 to the mass percentage of compound III; and / or, based on the total mass of the electrolyte, the mass percentage of compound II is 0.07 to 1.35 to the mass percentage of compound III.

12. The electrochemical device according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass percentage of fluoride ions in the electrolyte is 0.1% to 2%.

13. The electrochemical device according to claim 1, characterized in that, The electrolyte further includes a second component, which comprises at least one of the following: vinyl sulfate, methyl vinyl sulfate, 1,4-butane sulpholactone, 2,4-butane sulpholactone, 1,3-propane sulpholactone, vinylene carbonate, succinate, glutaronitrile, methylglutaronitrile, adiponitrile, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, ethylene glycol bis(propionitrile) ether, and trans-butenedionitrile; Based on the total mass of the electrolyte, the mass percentage of the second component is 0.1% to 5%.

14. An electronic device, characterized in that, It includes the electrochemical device as described in any one of claims 1 to 13.

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