Nonaqueous electrolyte solution, electrochemical device, and electronic device

Abstract

The invention provides a non-aqueous electrolyte, an electrochemical device and an electronic device. Based on the total mass of the non-aqueous electrolyte, the mass contents of ethylene carbonate, propylene carbonate, diethyl carbonate and propyl propionate are respectively A%, B%, C% and D%, 10 < = A < = 20, 9 < = B < = 15, 10 < = C < = 20, 10 < = D < = 25, and 1 < = (C + D) / (A + B) < = 1.3. The electrochemical device disclosed by the invention contains the non-aqueous electrolyte disclosed by the invention, and impedance increase of the electrochemical device in a circulating process can be well inhibited.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and more particularly, to a non-aqueous electrolyte, an electrochemical device, and an electronic device. Background Art

[0002] Electrochemical devices such as lithium-ion batteries are widely used in portable electronic products, electric vehicles, aerospace, energy storage, etc. due to their high energy density, good cycle performance, safety, environmental protection, and no memory effect. In existing electrochemical devices, as the number of cycles of the electrochemical device increases, the impedance during the cycling process will increase significantly, resulting in poor cycle stability. Summary of the Invention

[0003] The present application provides a non-aqueous electrolyte, an electrochemical device, and an electronic device. When the non-aqueous electrolyte in the present application is used in an electrochemical device, it can significantly improve the phenomenon of impedance growth during the cycling process of the electrochemical device.

[0004] In a first aspect, the present application provides a non-aqueous electrolyte, which includes ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate. Based on the total mass of the non-aqueous electrolyte, the mass contents of ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate are A%, B%, C%, and D% respectively, where 10 ≤ A ≤ 20, 9 ≤ B ≤ 15, 10 ≤ C ≤ 20, 10 ≤ D ≤ 25, and 1 ≤ (C + D) / (A + B) ≤ 1.3.

[0005] In the above non-aqueous electrolyte, the inventors found that when the above non-aqueous electrolyte is used in an electrochemical device, the components in the non-aqueous electrolyte synergistically act to significantly inhibit the impedance growth during the cycling process of the electrochemical device, which is beneficial to improving the cycle stability of the electrochemical device.

[0006] In a possible implementation, the non-aqueous electrolyte further includes succinonitrile. Based on the total mass of the non-aqueous electrolyte, the mass content of succinonitrile is G%; 3 ≤ D / G ≤ 8; and / or, 2 ≤ G ≤ 3.5.

[0007] In the above technical solution, the introduction of succinonitrile can significantly improve the floating charge performance of the battery cell.

[0008] In a possible implementation, the non-aqueous electrolyte further includes 1,3,6-hexanetricarbonitrile. Based on the total mass of the non-aqueous electrolyte, the mass content of 1,3,6-hexanetricarbonitrile is H%; 2 ≤ D / H ≤ 7; and / or, 2 ≤ H ≤ 4.5.

[0009] In the above technical solution, the introduction of 1,3,6-hexanetricarbonitrile can significantly improve the hot box performance of the battery cell.

[0010] In a possible implementation, the non-aqueous electrolyte further includes fluoroethylene carbonate and / or 1,3-propanesultone.

[0011] In the above technical solution, when the non-aqueous electrolyte is used in an electrochemical device, the fluoroethylene carbonate and 1,3-propanesultone in the non-aqueous electrolyte can play a role in protecting the positive and negative electrodes of the electrochemical device, thereby improving the high-temperature cycling performance of the electrochemical device.

[0012] In a possible implementation, based on the total mass of the non-aqueous electrolyte, the mass content of fluoroethylene carbonate is E%, 2 ≤ E ≤ 4; and / or, based on the total mass of the non-aqueous electrolyte, the mass content of 1,3-propanesultone is F%, 2 ≤ F ≤ 3.5.

[0013] In a possible implementation, the non-aqueous electrolyte further includes lithium tetrafluoroborate. Based on the total mass of the non-aqueous electrolyte, the mass content of lithium tetrafluoroborate is I%, 0.01 ≤ I ≤ 0.2.

[0014] In the above technical solution, adding lithium tetrafluoroborate to the non-aqueous electrolyte can improve the high-temperature storage performance and cycle life of the electrochemical device.

[0015] In a possible implementation, the non-aqueous electrolyte further includes trimethylacetonitrile and / or fluoroacetonitrile.

[0016] In the above technical solution, trimethylacetonitrile and fluoroacetonitrile in the non-aqueous electrolyte have low viscosities, which can improve the kinetic performance of the non-aqueous electrolyte; in addition, trimethylacetonitrile and fluoroacetonitrile can also improve the stability of the positive electrode in the electrochemical device, which is beneficial to improving the high-temperature cycling performance of the electrochemical device.

[0017] In a possible implementation, based on the total mass of the non-aqueous electrolyte, the mass content of trimethylacetonitrile is J%, 0.1 ≤ J ≤ 0.5; and / or, based on the total mass of the non-aqueous electrolyte, the mass content of fluoroacetonitrile is K%, 0.1 ≤ K ≤ 5.

[0018] In a second aspect, the present application provides an electrochemical device, which includes a positive electrode, a negative electrode, and the above non-aqueous electrolyte. Therefore, the impedance growth of the electrochemical device provided by the present application during the cycling process can be well inhibited.

[0019] In a possible implementation, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector; the positive electrode active material layer includes doping elements, and the doping elements include at least one of titanium element, magnesium element, and aluminum element. Based on the total mass of the positive electrode, the mass content of the doping elements is M ppm, 4000 ≤ M ≤ 8500.

[0020] In the above technical solution, when the positive electrode active material layer contains a specific content of doping elements, the specific content of doping elements can act together with the non-aqueous electrolyte, reduce the impedance growth during the cycling process of the electrochemical device, and improve the cycling stability of the electrochemical device. Moreover, when specific doping elements are contained, the stability of the positive electrode itself can also be improved, thereby improving the high-temperature cycling performance of the electrochemical device.

[0021] In a third aspect, the present application provides an electronic device, which includes the above-mentioned electrochemical device. Therefore, the electronic device provided by the present application has good use performance.

[0022] Advantages of the present application:

[0023] The present application provides a non-aqueous electrolyte, an electrochemical device and an electronic device. The non-aqueous electrolyte includes ethylene carbonate, propylene carbonate, diethyl carbonate and propyl propionate. Based on the total mass of the non-aqueous electrolyte, the mass contents of ethylene carbonate, propylene carbonate, diethyl carbonate and propyl propionate are A%, B%, C% and D% respectively, where 10 ≤ A ≤ 20, 9 ≤ B ≤ 15, 10 ≤ C ≤ 20, 10 ≤ D ≤ 25, and 1 ≤ (C + D) / (A + B) ≤ 1.3. By controlling the components in the non-aqueous electrolyte and the contents of each component, the phenomenon of impedance growth during the cycling process of the electrochemical device can be significantly improved. Specific embodiments

[0024] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. For those not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are followed. The reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0025] The non-aqueous electrolyte, the electrochemical device and the electronic device of the embodiments of the present application will be specifically described below.

[0026] In a first aspect, the present application provides a non-aqueous electrolyte, which includes ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate. Based on the total mass of the non-aqueous electrolyte, the mass contents of ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate are A%, B%, C%, and D% respectively, where 10 ≤ A ≤ 20, 9 ≤ B ≤ 15, 10 ≤ C ≤ 20, 10 ≤ D ≤ 25, and 1 ≤ (C + D) / (A + B) ≤ 1.3. For example, A can be 10, 12, 16, 18, 20, etc. or within the range composed of any two of the above values; B can be 9, 10, 12, 13, 15, etc. or within the range composed of any two of the above values; C can be 10, 12, 14, 16, 18, 20, etc. or within the range composed of any two of the above values; D can be 10, 13, 15, 18, 20, 22, 25, etc. or within the range composed of any two of the above values. (C + D) / (A + B) can be 1, 1.1, 1.2, 1.3, etc. or within the range composed of any two of the above values. The non-aqueous electrolyte of the present application can be used in an electrochemical device, which can play a role in transporting lithium ions and electrons and ensure the formation of a path inside the electrochemical device.

[0027] The inventors found that although ethylene carbonate and propylene carbonate have high conductivity, their viscosities are also relatively large, which is not conducive to improving the kinetic performance of the electrochemical device; while diethyl carbonate and propyl propionate have relatively low viscosities, but their antioxidant capabilities are poor, which is not conducive to maintaining the stability of the positive electrode in the electrochemical device. When ethylene carbonate and propylene carbonate, and diethyl carbonate and propyl propionate are used in combination and their mass contents are controlled within the above ranges, and at the same time the dosage relationship is limited within the above ranges, the non-aqueous electrolyte can significantly improve the impedance growth phenomenon during the cycling of the electrochemical device, which is beneficial to improving the cycling stability of the electrochemical device.

[0028] In some embodiments of the present application, in order to improve the floating charge performance of the electrochemical device, the non-aqueous electrolyte further includes succinonitrile, and based on the total mass of the non-aqueous electrolyte, the mass content of succinonitrile is G%; 3 ≤ D / G ≤ 8; and / or, 2 ≤ G ≤ 3.5. Specifically, D / G can be 3, 4, 5, 6, 7, 8, etc. or within the range composed of any two of the above values; G can be 2, 2.2, 2.5, 3, 3.5, etc. or within the range composed of any two of the above values.

[0029] In some embodiments of the present application, in order to improve the thermal box performance of the electrochemical device, the non-aqueous electrolyte further includes 1,3,6-hexanetricarbonitrile, and based on the total mass of the non-aqueous electrolyte, the mass content of 1,3,6-hexanetricarbonitrile is H%; 2 ≤ D / H ≤ 7; and / or, 2 ≤ H ≤ 4.5. Specifically, D / H can be 2, 3, 4, 5, 6, 7, etc. or within the range composed of any two of the above values; H can be 2, 2.5, 3, 3.5, 4, 4.5, etc. or within the range composed of any two of the above values.

[0030] In addition, in some embodiments of the present application, the non-aqueous electrolyte further includes fluoroethylene carbonate and / or 1,3-propane sultone. Fluoroethylene carbonate and 1,3-propane sultone can play a role in protecting the positive and negative electrodes of the electrochemical device, thereby improving the high-temperature cycling performance of the electrochemical device. Based on the total mass of the non-aqueous electrolyte, the mass content of fluoroethylene carbonate is E%, and the mass content of 1,3-propane sultone is F%, preferably 2 ≤ E ≤ 4, 2 ≤ F ≤ 3.5. Specifically, E can be 2, 2.5, 3, 3.5, 4, etc. or within the range composed of any two of the above values; F can be 2, 2.2, 2.8, 3, 3.2, 3.5, etc. or within the range composed of any two of the above values.

[0031] Furthermore, in some embodiments of the present application, in order to improve the high-temperature storage performance and cycle life of the electrochemical device, the non-aqueous electrolyte further includes lithium tetrafluoroborate, and based on the total mass of the non-aqueous electrolyte, the mass content of lithium tetrafluoroborate is I%, 0.01 ≤ I ≤ 0.2. Specifically, I can be 0.01, 0.05, 0.08, 0.1, 0.15, 0.2, etc. or within the range composed of any two of the above values.

[0032] In addition, in some embodiments of the present application, the non-aqueous electrolyte further includes trimethylacetonitrile and / or fluoroacetonitrile. Trimethylacetonitrile and fluoroacetonitrile have relatively low viscosities, which can improve the kinetic performance of the non-aqueous electrolyte and also improve the stability of the positive electrode in the electrochemical device, facilitating the improvement of the high-temperature cycling performance of the electrochemical device. Based on the total mass of the non-aqueous electrolyte, the mass contents of trimethylacetonitrile and fluoroacetonitrile are J% and K% respectively, preferably 0.1 ≤ J ≤ 0.5, 0.1 ≤ K ≤ 5. Specifically, J can be 0.1, 0.2, 0.3, 0.4, 0.5, etc. or within the range composed of any two of the above values, and K can be 0.1, 0.5, 1, 1.5, 2, 3, 4.5, 5, etc. or within the range composed of any two of the above values.

[0033] Second aspect, the present application also provides an electrochemical device, which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte according to the present application. Therefore, during the cycling process of the electrochemical device of the present application, the growth of its impedance can be well suppressed. It should be noted that in the subsequent specific embodiments of the present application, a lithium-ion secondary battery (i.e., a lithium-ion battery) is taken as an example of the electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to lithium-ion secondary batteries. For example, the electrochemical device of the present application may include, but is not limited to: lithium metal secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries (i.e., lithium-ion polymer batteries), etc.

[0034] Except for the non-aqueous electrolyte, the structure of each part of the electrochemical device of the present application is specifically as follows:

[0035] Positive electrode

[0036] The positive electrode (also referred to as the "positive electrode tab") includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. That is, in the present application, the positive electrode active material layer can be provided on one surface in the thickness direction of the positive electrode current collector, or can be provided on two surfaces in the thickness direction of the positive electrode current collector. Moreover, in the present application, the "surface of the positive electrode current collector" can be the entire area of the positive electrode current collector or a partial area of the positive electrode current collector, and there is no special limitation in the present application as long as the purpose of the present application can be achieved.

[0037] In some embodiments of the present application, the positive electrode active material layer includes a doping element, and the doping element can be at least one of titanium element, magnesium element, and aluminum element; based on the total mass of the positive electrode, the mass content of the doping element is M ppm, and 40000 ≤ M ≤ 8500.

[0038] The inventors found that when the positive electrode contains the above doping elements, although the cycling performance of the electrochemical device can be improved, the growth of the impedance of the electrochemical device during the cycling process is more obvious; therefore, controlling the content of the doping element within the above range and synergistically acting with the non-aqueous electrolyte in the present application can not only maintain the high cycling performance of the electrochemical device, but also reduce the growth of the impedance of the electrochemical device during the cycling process, and at the same time can also improve the high-temperature cycling performance of the electrochemical device.

[0039] The components of the positive electrode active material layer include a positive electrode active substance, and the positive electrode active substance can be any substance that can reversibly intercalate and deintercalate Li + 、Na + and other alkali metal ions to ensure that the electrochemical device can be normally charged and discharged, and the doping element is generally also provided by the positive electrode active substance. For example, the positive electrode active substance includes, but is not limited to, lithium iron phosphate (LiFePO 4 ), lithium cobalt oxide (LiCoO 2) at least one of lithium manganese oxide, lithium nickel oxide, ternary materials, etc., and the ternary materials include but are not limited to LiNi x Co y Mn z O 2 、LiNi x Co y Al z O 2 etc., and the contents of Ni, Co, Mn, Al, etc. can be adjusted, as long as x + y + z = 1 is ensured. For example, the ternary material can be LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.88 Co 0.08 Mn 0.04 O 2 、LiNi 0.8 Co 0.15 Mn 0.05 O 2 、LiNi 0.8 Co 0.1 Mn 0.1 O 2 、LiNi 0.88 Co 0.1 Mn 0.02 O 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 、LiNi 0.88 Co 0.1 Al 0.02 O 2 etc.

[0040] In some embodiments, the components of the positive electrode active material layer further include a positive electrode conductive agent; the present application places no restrictions on the type of the positive electrode conductive agent, and any known conductive material can be used. Specifically, the positive electrode conductive agent includes but is not limited to at least one of acetylene black, carbon black such as Super-P, amorphous carbon such as needle coke, carbon nanotubes, graphene, etc.

[0041] In some embodiments, the components of the positive electrode active material layer generally further contain a positive electrode binder. There is no particular limitation on the type of the 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 during electrode manufacture is acceptable. The positive electrode binder includes, but is 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, polybutene rubber, and ethylene-propylene rubber; thermoplastic elastomer-like polymers such as styrene-butadiene-styrene block copolymer or its hydride, ethylene-propylene-diene terpolymer (EPDM), styrene-ethylene-butadiene-ethylene copolymer, and styrene-isoprene-styrene block copolymer or its hydride; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, and propylene-α-olefin copolymer; fluorine-based polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer; and polymer compositions having ionic conductivity of alkali metal ions (especially lithium ions), etc.

[0042] In the positive electrode, there is no particular limitation on the type of the positive electrode current collector, and it can be made of any known material suitable for use as a positive electrode current collector. The materials of the positive electrode current collector include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum. In addition, in order to reduce the electron contact resistance between the positive electrode current collector and the positive electrode active material layer, a conductive aid or a conductive coating, etc. can be provided on the surface of the positive electrode current collector. The conductive aid includes, but is not limited to, carbon and precious metals such as gold, platinum, and silver. The conductive coating can be a mixture layer of inorganic oxides, conductive agents, and positive electrode binders.

[0043] When preparing the positive electrode, the components in the above positive electrode active material layer can be dissolved or dispersed in a liquid solvent to form a positive electrode slurry, and then the positive electrode slurry is coated on the positive electrode current collector and dried, so as to form a positive electrode active material layer on the positive electrode current collector, and thus a positive electrode can be obtained. When preparing the positive electrode in this way, there is no particular limitation on the solvent in the positive electrode slurry, as long as it can dissolve or disperse the above components. Specifically, the solvents in the positive electrode slurry include, but are not limited to, N-methylpyrrolidone (NMP), ethylene carbonate (EC), etc. In addition, when preparing the positive electrode, the respective components in the positive electrode active material layer can also be dry-mixed to form flakes, and then the obtained flakes are pressed onto the positive electrode current collector.

[0044] Negative electrode

[0045] The negative electrode (which may also be referred to as the "negative electrode tab") 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 components of the negative electrode active material layer include a negative electrode active substance. That is, in the present application, the negative electrode active material layer may be disposed on one surface in the thickness direction of the negative electrode current collector, or may be disposed on both surfaces in the thickness direction of the negative electrode current collector. Moreover, in the present application, the "surface of the negative electrode current collector" may be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector, and there is no particular limitation in the present application as long as the object of the present application can be achieved.

[0046] The negative electrode active material layer generally contains a negative electrode active material, and there is no particular limitation on the negative electrode active material in the present application. Specifically, the negative electrode active material may include at least one of a carbon material or a silicon-based material. More specifically, the carbon material includes but is not limited to at least one of natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon or soft carbon; the silicon-based material includes but is not limited to at least one of silicon, silicon-oxygen composite material or silicon-carbon composite material.

[0047] In some embodiments, the negative electrode active material layer usually further contains a negative electrode conductive agent. There is no particular limitation on the type of the negative electrode conductive agent in the present application as long as the object of the present application can be achieved. For example, the negative electrode conductive agent includes but is not limited to at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots or graphene.

[0048] In some embodiments, the negative electrode active material layer may also contain a negative electrode binder and a thickener. There is no particular limitation on the types of the negative electrode binder and the thickener in the present application as long as the object of the present application can be achieved. 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.

[0049] In the negative electrode, the material of the negative electrode current collector includes but is not limited to copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or a polymer substrate coated with a conductive metal, etc., and there is no particular limitation in the present application. 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, poly(ethylene naphthalate) or poly(p-phenylene terephthalamide).

[0050] In addition, in the present application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the object of the present 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.

[0051] In addition, similar to the preparation of the positive electrode, when preparing the negative electrode, it can be configured into a negative electrode slurry, and then the negative electrode slurry is coated on the negative electrode current collector and dried, so as to form a negative electrode active material layer on the negative electrode current collector, thereby obtaining a negative electrode; or the components in the negative electrode active material layer can be dry-mixed, made into sheets, and then the obtained sheets are pressed onto the negative electrode current collector to form a negative electrode active material layer, thereby obtaining a negative electrode. The solvent in the negative electrode slurry includes any one of aqueous solvents and organic solvents. Aqueous solvents include, but are not limited to, a mixed solvent of alcohol and water or water, etc. 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; aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide, etc. In addition, in some other embodiments, when using an aqueous solvent, the components of the negative electrode slurry will also include a thickener and a styrene-butadiene rubber (SBR) emulsion to slurrize the negative electrode slurry, thereby adjusting the viscosity of the negative electrode slurry. 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, etc.

[0052] Separator

[0053] In order to prevent short circuit, a separator is usually provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application usually penetrates into the separator for use.

[0054] There is no particular limitation on the material and shape of the separator, as long as the effects of the present application are not significantly impaired. The material of the separator can be a resin, glass fiber, inorganic substance, etc. formed by a material stable to the electrolyte of the present application. In some embodiments, the separator includes a porous sheet or a non-woven fabric-like substance with excellent liquid retention properties, etc. Examples of the materials of the resin or glass fiber separator include, but are not limited to, polyolefin, aromatic polyamide, polyimide (PI), polyamide (PA), polytetrafluoroethylene, polyethersulfone, spandex, or aramid, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned materials of the separator can be used alone or in any combination.

[0055] The separator membrane may also be a material formed by laminating the above materials. Examples thereof include, but are not limited to, a three-layer separator membrane laminated in the order of polypropylene, polyethylene, and polypropylene, etc.

[0056] The inorganic materials include, but are not limited to, oxides such as alumina and silica, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). The forms of the inorganic materials include, but are not limited to, granular or fibrous forms.

[0057] The separator membrane may be in the form of a thin film, including, but not limited to, non-woven fabric, woven fabric, microporous membrane, etc. In the thin film form, the pore size of the separator membrane is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separator membranes, the following separator membranes may also be used: a separator membrane formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode by using a resin-based binder. For example, a separator membrane formed by using a fluororesin as a binder to form a porous layer on both sides of the positive electrode with 90% of the alumina particles having a particle size less than 1 μm.

[0058] The thickness of the separator membrane is arbitrary. In some embodiments, the thickness of the separator membrane is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator membrane is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator membrane is within the above range, insulation and mechanical strength can be ensured, and the rate characteristics and cycle performance of the electrochemical device can be ensured.

[0059] In the present application, the separator membrane may include a substrate and a surface treatment layer. The substrate may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate, and the surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder. The present application places no particular limitation on the above-mentioned inorganic particles. For example, it may include at least one of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The present application places no particular limitation on the above-mentioned binder. For example, it may be at least one of the aforementioned binders. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0060] The electrochemical device of the present application further includes a packaging bag for accommodating the positive electrode, the separator membrane, the negative electrode, and the electrolyte, as well as other components known in the art in the electrochemical device. The present application places no limitation on the above-mentioned other components. The present application places no particular limitation on the packaging bag, and it may be a packaging bag well-known in the art as long as it can achieve the purpose of the present application.

[0061] In a third aspect, the present application further provides an electronic device, which includes the electrochemical device according to the present application.

[0062] The use of the electrochemical device of the present application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device of the present application can be used in, but is not limited to, laptop computers, pen input computers, mobile computers, e-book players, mobile phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal TVs, hand-held cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0063] Examples

[0064] Taking a lithium-ion secondary battery as an example, examples and comparative examples are given to more specifically illustrate the implementation manners of the electrochemical device of the present application. Those skilled in the art will understand that the preparation methods described in the present application are only examples, and any other suitable preparation methods are within the scope of the present application.

[0065] Test methods and equipment:

[0066] Impedance growth test during cycling

[0067] The impedance growth rate after 400 cycles at 45 °C is used to evaluate the impedance increase during the cycling of the lithium-ion battery. The smaller the impedance growth rate after 400 cycles at 45 °C, the better the performance of the lithium-ion battery in suppressing the growth during cycling.

[0068] Place the lithium-ion battery in an incubator at 45 °C and let it stand for 30 minutes to make the lithium-ion battery reach a constant temperature. Charge the lithium-ion battery at a constant current of 0.2C to 4.5V at 45 °C, then charge it at a constant voltage of 4.5V to 0.05C, let it stand for 5 minutes, then discharge it at a constant current of 0.2C for 4h, let it stand for 5 minutes, and measure the initial DC impedance R of the lithium-ion battery. 0 ; Then charge it at a constant current of 1.8C to 4.15V, charge it at a constant voltage of 4.15V until the current is 1C; then charge it at a constant current of 1C to 4.25V, then charge it at a constant voltage of 4.25V until the current is 0.8C; then charge it at a constant current of 0.8C to 4.5V, then charge it at a constant voltage of 4.5V until the current is 0.05C; place it for 5 minutes; then discharge it at a constant current of 1C to 3.0V, let it stand for 5 minutes. This is one charge-discharge cycle. Repeat the above charge / discharge cycle steps 400 times. Charge the lithium-ion battery at a constant current of 0.2C to 4.5V at 45 °C, charge it at a constant voltage of 4.5V to 0.05C, let it stand for 5 minutes, then discharge it at a constant current of 0.2C for 4h, and measure the DC impedance R of the lithium-ion battery after 400 cycles at 45 °C after standing for 5 minutes. 1 .

[0069] The impedance growth rate after 400 cycles at 45 °C = (R 1 / R 0 -1) × 100%. The smaller the impedance growth rate after 400 cycles at 45 °C, the better the performance of the lithium-ion battery in suppressing the impedance growth during cycling; the specific data of the impedance growth rates of the lithium-ion batteries during the high-temperature cycling process in each example and comparative example are shown in "Impedance growth rate at 45 °C, 400 cls / %" in Tables 1-7.

[0070] Test method for DC impedance: Charge the lithium-ion battery at a constant current of 0.2C to 4.5V, then charge it at a constant voltage of 4.5V until the current reaches 0.05C, and then discharge it at a constant current of 0.2C for 4h to make the state of charge (SOC) of the lithium-ion battery 20%. Discharge it at 0.1C for 10s to obtain voltage V 0 ; Discharge it at 1C for 1s to obtain voltage V 1 . The DC impedance R = (V 0 V 1 ) / 0.1C.

[0071] High-temperature (45°C) cycle capacity retention performance test

[0072] Evaluate the cycle performance of the lithium-ion battery through the capacity retention rate after 400 cycles at 45°C. The larger the capacity retention rate after 400 cycles at 45°C, the better the cycle performance of the lithium-ion battery.

[0073] Place the lithium-ion battery in an incubator at 45°C and let it stand for 30 minutes to make the lithium-ion battery reach a constant temperature. Charge the lithium-ion battery that has reached a constant temperature at a constant current of 0.2C to 4.5V at 45°C, charge it at a constant voltage of 4.5V to 0.05C, let it stand for 5 minutes, then discharge it at a constant current of 0.2C to 3.0V, let it stand for 5 minutes, and test the initial discharge capacity C of the lithium-ion battery 0 ; Then charge it at a constant current of 1.8C to 4.15V, charge it at a constant voltage of 4.15V until the current reaches 1C; then charge it at a constant current of 1C to 4.25V, and then charge it at a constant voltage of 4.25V until the current reaches 0.8C; then charge it at a constant current of 0.8C to 4.5V, and then charge it at a constant voltage of 4.5V until the current reaches 0.05C; place it for 5 minutes; then discharge it at a constant current of 1C to 3.0V and let it stand for 5 minutes. This is one charge-discharge cycle. Repeat the above charge / discharge cycle steps 400 times, and measure the discharge capacity C of the lithium-ion battery after 400 cycles 1 .

[0074] The capacity retention rate after 400 cycles at 45°C = C 1 / C 0 × 100%. The higher the capacity retention rate after 400 cycles at 45°C, the better the high-temperature cycle performance of the lithium-ion battery; the specific data of the high-temperature cycle performance of the lithium-ion battery in each example and comparative example are shown in "Capacity retention rate / % at 45°C and 400cls" in Tables 1-7.

[0075] Float charge performance test

[0076] At 45 °C, the lithium-ion battery is charged at a constant current of 0.7C to 4.5V, and then charged at a constant voltage for 90 days. The thickness of the battery is measured and recorded with a micrometer, and the thickness of the lithium-ion battery is measured and recorded every 3 days during this period. Calculate the floating charge thickness expansion rate of the battery according to the following formula, and use the time when the thickness expansion rate reaches 10% as an index to evaluate the pros and cons of the floating charge performance of the lithium-ion battery:

[0077] Thickness expansion rate = (thickness during floating charge - initial thickness) / initial thickness * 100%, and the specific data is shown in "45 °C, 40D floating charge / %" in the table.

[0078] Hot box test

[0079] At 25 °C, the lithium-ion battery is charged at a constant current of 0.7C to 4.5V and then charged at a constant voltage of 4.5V until the current is 0.05C. The battery is placed in a high-temperature box and heated to 135 degrees at a temperature rise rate of 5 ± 2 °C / min, and then maintained for 1h. Record the changes in the voltage, temperature of the battery, and the temperature of the hot box, and observe whether the lithium-ion battery catches fire. If it does not catch fire, it means that the hot box test is passed; the number of tests for each example and comparative example is 10, and record the passing situation.

[0080] Example 1-1

[0081] <Preparation of electrolyte>

[0082] In an argon atmosphere glove box with a water content of less than 10 ppm, ethyl methyl carbonate and ethyl acetate are mixed in a mass percentage of 1:1 to prepare a basic solvent, and then lithium salt lithium hexafluorophosphate (LiPF 6 )), ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate are added to form an electrolyte. Based on the total mass of the electrolyte, the mass percentage content of LiPF 6 is 12.5%, and the mass contents of ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate are shown in Table 1, and the balance is the basic solvent.

[0083] <Preparation of positive electrode>

[0084] Lithium cobaltate, conductive agent conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:2:3, and N-methylpyrrolidone (NMP) is added and stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry is evenly coated on the upper and lower surfaces of a positive electrode current collector aluminum foil with a thickness of 9 μm, dried, and pressure-treated, and then cut into a specified size to obtain a positive electrode.

[0085] <Preparation of negative electrode>

[0086] Mix artificial graphite, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNT), and carboxymethyl cellulose (CMC) in a mass ratio of 95.8:2.4:0.5:0.5:0.8, then add deionized water as a solvent and stir evenly to prepare a negative electrode slurry with a solid content of 45 wt%. Uniformly coat the negative electrode slurry on the upper and lower surfaces of a negative electrode current collector copper foil with a thickness of 6 μm, cut it into a specified size after drying and pressing treatment to obtain a negative electrode.

[0087] <Separator membrane>

[0088] Use a porous polyethylene film with a thickness of 15 μm as the separator membrane.

[0089] <Preparation of electrochemical device>

[0090] Stack the above-prepared positive electrode, separator membrane, negative electrode, and separator membrane in sequence, with the separator membrane in the middle of the positive electrode and the negative electrode to play a role in isolation, and then wind to obtain an electrode assembly. After welding the electrode tabs, put the electrode assembly into an aluminum-plastic film packaging bag, place it in a vacuum oven at 85 °C for 12 h to remove moisture, inject the above-prepared electrolyte, and obtain a lithium-ion battery through vacuum packaging, standing, formation, shaping, and capacity testing processes.

[0091] Examples 1-2 to Examples 1-24

[0092] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Example 1-1.

[0093] Comparative Examples 1 to Comparative Examples 10

[0094] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Example 1-1.

[0095] Table 1

[0096]

[0097]

[0098] Example 2-1

[0099] Except for further adding succinonitrile in <Preparation of electrolyte> and adjusting the relevant preparation parameters according to Table 2, the rest are the same as in Example 1-7. When the mass percentage content of succinonitrile changes, the content of LiPF 6 remains unchanged.

[0100] Examples 2-2 to Examples 2-9

[0101] Except for adjusting the relevant preparation parameters according to Table 2, the rest are the same as in Example 2-1.

[0102] Table 2

[0103]

[0104]

[0105] Example 3-1

[0106] Except for further adding 1,3,6-hexanetricarbonitrile in <Preparation of electrolyte> and adjusting relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-7. When the mass percentage content of succinonitrile changes, the content of LiPF 6 remains unchanged.

[0107] Examples 3-2 to 3-9

[0108] Except for adjusting relevant preparation parameters according to Table 3, the rest is the same as in Example 3-1.

[0109] Table 3

[0110]

[0111] Example 4-1

[0112] Except for further adding trimethylacetonitrile and / or fluoroacetonitrile in <Preparation of electrolyte> and adjusting relevant preparation parameters according to Table 4, the rest is the same as in Examples 1-7. When the mass percentage content of trimethylacetonitrile and fluoroacetonitrile changes, the content of LiPF 6 remains unchanged.

[0113] Examples 4-2 to 4-21

[0114] Except for adjusting relevant preparation parameters according to Table 4, the rest is the same as in Example 4-1.

[0115] Table 4

[0116]

[0117]

[0118] Example 5-1

[0119] Except for preparing the positive electrode in the following manner, the rest is the same as in Examples 1-7.

[0120] <Preparation of positive electrode>

[0121] Lithium cobaltate doped with titanium element, conductive agent conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:2:3, N-methylpyrrolidone (NMP) is added, and they are stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry is evenly coated on the upper and lower surfaces of a positive electrode current collector aluminum foil with a thickness of 9 μm, dried, pressure-treated, and then cut into a specified size to obtain a positive electrode. In the obtained positive electrode, based on the total mass of the positive electrode, the content of titanium element is 4000 ppm.

[0122] Examples 5-2 to 5-6

[0123] Except for adjusting the relevant preparation parameters of the positive electrode according to Table 5, the rest are the same as in Example 5-1.

[0124] Example 5-7

[0125] Except for preparing the positive electrode in the following manner, the rest are the same as in Example 1-7.

[0126] <Preparation of Positive Electrode>

[0127] Lithium cobaltate doped with magnesium element, conductive agent conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:2:3, N-methylpyrrolidone (NMP) is added, and they are stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry is evenly coated on the upper and lower surfaces of a positive electrode current collector aluminum foil with a thickness of 9 μm, dried, pressure-treated, and then cut into a specified size to obtain a positive electrode. In the obtained positive electrode, based on the total mass of the positive electrode, the content of magnesium element is 4000 ppm.

[0128] Examples 5-8 to 5-12

[0129] Except for adjusting the relevant preparation parameters of the positive electrode according to Table 5, the rest are the same as in Example 5-7.

[0130] Example 5-13

[0131] Except for preparing the positive electrode in the following manner, the rest are the same as in Example 1-7.

[0132] <Preparation of Positive Electrode>

[0133] Lithium cobalt oxide doped with aluminum element, conductive agent conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:2:3, and N-methylpyrrolidone (NMP) is added. After being stirred evenly under the action of a vacuum mixer, a positive electrode slurry with a solid content of 70 wt% is obtained. The positive electrode slurry is evenly coated on the upper and lower surfaces of a positive electrode current collector aluminum foil with a thickness of 9 μm, dried, pressure-treated, and then cut into a specified size to prepare a positive electrode. In the prepared positive electrode, based on the total mass of the positive electrode, the content of aluminum element is 4000 ppm.

[0134] Examples 5-14 to 5-18

[0135] Except for adjusting the relevant preparation parameters of the positive electrode according to Table 5, the rest are the same as in Example 5-13.

[0136] Table 5

[0137]

[0138]

[0139] Example 6-1

[0140] Except for further adding fluoroethylene carbonate and / or 1,3-propane sultone in <Preparation of electrolyte> and adjusting the relevant preparation parameters according to Table 6, the rest are the same as in Example 1-7. When the mass percentage content of fluoroethylene carbonate and 1,3-propane sultone changes, the content of LiPF 6 remains unchanged.

[0141] Examples 6-2 to 6-11

[0142] Except for adjusting the relevant preparation parameters according to Table 6, the rest are the same as in Example 6-1.

[0143] Table 6

[0144]

[0145]

[0146] Example 7-1

[0147] Except for further adding lithium tetrafluoroborate in <Preparation of electrolyte> and adjusting the relevant preparation parameters according to Table 7, the rest are the same as in Example 1-7. When the mass percentage content of lithium tetrafluoroborate changes, the content of LiPF 6 remains unchanged.

[0148] Examples 7-2 to 7-5

[0149] Except for adjusting the relevant preparation parameters according to Table 7, the rest is the same as in Example 7-1.

[0150] Table 7

[0151]

[0152] As can be seen from Table 1, when the non-aqueous electrolyte of the present application is used in an electrochemical device, it can well inhibit the impedance growth of the electrochemical device during the cycling process and improve the cycling performance of the electrochemical device.

[0153] As can be seen from Table 2, when 2% - 3.5% of succinonitrile is added to the non-aqueous electrolyte, or when D / G is in the range of 3 - 8, the floating charge performance of the electrochemical device can be significantly improved, and the impedance growth rate during the cycling of the electrochemical device can also be further inhibited.

[0154] As can be seen from Table 3, when 2% - 4.5% of 1,3,6 - hexanetricarbonitrile is added to the non-aqueous electrolyte, or when D / H is in the range of 2 - 7, the hot box performance of the electrochemical device can be significantly improved.

[0155] As can be seen from Table 4, when trimethylacetonitrile or fluoroacetonitrile is added to the non-aqueous electrolyte, the high-temperature cycling performance of the electrochemical device can be significantly improved; in particular, when the mass content of trimethylacetonitrile is 0.1% - 0.5%, or the mass content of fluoroacetonitrile is 0.1% - 5%, or when trimethylacetonitrile and fluoroacetonitrile are added simultaneously, the improvement of the high-temperature cycling performance of the electrochemical device is more obvious.

[0156] As can be seen from Table 5, when the positive electrode contains doping elements such as titanium element, magnesium element and aluminum element, and the total content of the doping elements is in the range of 4000 ppm - 8500 ppm, the electrochemical device not only has a low impedance growth during the cycling process, but also has good high-temperature cycling performance.

[0157] As can be seen from Table 6, when fluoroethylene carbonate and / or 1,3 - propane sultone is added to the non-aqueous electrolyte, the high-temperature cycling performance of the electrochemical device can be improved; in particular, when the mass content of fluoroethylene carbonate is 2% - 4%, or the mass content of 1,3 - propane sultone is 2% - 3.5%, or when fluoroethylene carbonate and 1,3 - propane sultone are added simultaneously, the improvement of the high-temperature cycling performance of the electrochemical device is more obvious.

[0158] As can be seen from Table 7, when 0.01% - 0.2 of lithium tetrafluoroborate is added to the non-aqueous electrolyte, the cycling performance of the electrochemical device can be further improved.

[0159] The above are only embodiments of the present application and are not intended to limit the protection scope of the present application. For those skilled in the art, various modifications and changes can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A non-aqueous electrolyte, characterized in that: It includes ethylene carbonate, propylene carbonate, diethyl carbonate and propyl propionate. Based on the total mass of the non-aqueous electrolyte, the mass contents of ethylene carbonate, propylene carbonate, diethyl carbonate and propyl propionate are A%, B%, C% and D%, respectively, 10≤A≤20, 9≤B≤15, 10≤C≤20, 10≤D≤25, and 1≤(C+D) / (A+B)≤1.

3.

2. The non-aqueous electrolyte according to claim 1, characterized in that It also includes succinonitrile, and the mass content of succinonitrile is G%, 3≤D / G≤8 based on the total mass of the non-aqueous electrolyte; and / or, 2≤G≤3.5。 3. The non-aqueous electrolyte according to claim 1, characterized in that It also includes 1,3,6-hexane trinitrile, and the mass content of the 1,3,6-hexane trinitrile is H%, based on the total mass of the non-aqueous electrolyte, 2≤D / H≤7; and / or, 2≤H≤4.5。 4. The non-aqueous electrolyte according to any one of claims 1 to 3, characterized in that: It also includes fluoroethylene carbonate and / or 1,3-propane sultone.

5. The non-aqueous electrolyte according to claim 4, characterized in that Based on the total mass of the non-aqueous electrolyte, the mass content of the fluoroethylene carbonate is E%, 2≤E≤4; and / or, Based on the total mass of the non-aqueous electrolyte, the mass content of the 1,3-propane sultone is F%, 2≤F≤3.

5.

6. The non-aqueous electrolyte according to any one of claims 1 to 3, characterized in that: It also includes lithium tetrafluoroborate, and the mass content of the lithium tetrafluoroborate is 1% based on the total mass of the non-aqueous electrolyte, and 0.01≤1≤0.

2.

7. The non-aqueous electrolyte according to any one of claims 1 to 3, characterized in that: It also includes trimethylacetonitrile and / or fluoroacetonitrile.

8. The non-aqueous electrolyte according to claim 7, characterized in that Based on the total mass of the non-aqueous electrolyte, the mass content of trimethylacetonitrile is J%, 0.1≤J≤0.5; and / or, Based on the total mass of the non-aqueous electrolyte, the mass content of the fluoroacetonitrile is K%, and 0.1≤K≤5.

9. An electrochemical device, characterized in that: The invention comprises a positive electrode, a negative electrode and the non-aqueous electrolyte according to any one of claims 1 to 8.

10. The electrochemical device according to claim 9, characterized in that The positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector; the positive electrode active material layer includes a doping element, the doping element includes at least one of titanium, magnesium and aluminum, and based on the total mass of the positive electrode, the mass content of the doping element is M ppm, 4000≤M≤8500.

11. An electronic device, characterized in that: It comprises the electrochemical device according to claim 9 or 10.

Images