Non-aqueous electrolyte, lithium-ion battery, and electronic device

Abstract

The present application discloses a non-aqueous electrolyte, a lithium-ion battery, and an electronic device. The non-aqueous electrolyte comprises a non-aqueous solvent and a lithium salt. The non-aqueous electrolyte contains a specific amount of lithium difluorophosphate, propyl propionate, 1,2,3-tris(2-cyanoethoxy)propane, and boron-containing lithium salt. The total content of the lithium difluorophosphate and 1,2,3-tris(2-cyanoethoxy)propane in the non-aqueous electrolyte is set to a specific range, and the total content of the propyl propionate and boron-containing lithium salt is set to a specific range. The use of the non-aqueous electrolyte can not only improve the initial efficiency of lithium-ion batteries, but also inhibit the increase in resistance, and significantly improve the low-temperature output performance and high-temperature storage performance of lithium-ion batteries.

Description

Non-aqueous electrolytes, lithium-ion batteries and electronic devices Technical Field

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

[0002] In recent years, information-related or communication equipment (small devices such as personal computers and mobile phones), as well as large-scale equipment such as energy storage systems for applications requiring high energy density, electric vehicles, hybrid vehicles, fuel cell vehicles auxiliary power supplies, and energy storage systems for energy-intensive applications have received considerable attention. As one of the potential candidates, non-aqueous electrolyte batteries such as lithium-ion batteries and sodium-ion batteries have been actively developed.

[0003] While various types of non-aqueous electrolyte batteries have been put into practical use, their characteristics are not yet fully satisfactory for all applications. This is especially true in automotive applications such as electric vehicles, where high input / output performance is required even in cold conditions. Therefore, improving low-temperature performance is crucial. Furthermore, the requirement for minimal increase in internal resistance during repeated charge-discharge cycles at high temperatures is also essential, and safety performance is a primary concern.

[0004] As a means to improve the low-temperature characteristics and battery performance under repeated charge-discharge cycles of non-aqueous electrolyte batteries, the optimization of various battery components, primarily the active materials of the positive and negative electrodes, has been studied. Non-aqueous electrolyte technologies are no exception, proposing the use of various additives to suppress the degradation caused by the decomposition of non-aqueous electrolytes on the surfaces of the active positive and negative electrodes. Summary of the Invention

[0005] In existing technical literature, non-aqueous electrolyte batteries that use non-aqueous electrolytes cannot fully satisfy both high-temperature durability and low-temperature output performance, leaving room for improvement.

[0006] In view of the above-mentioned problems, the inventors of this application have conducted in-depth research and disclosed a non-aqueous electrolyte for lithium-ion batteries. This non-aqueous electrolyte is a non-aqueous electrolyte in which lithium salts are dissolved in a non-aqueous solvent. The non-aqueous electrolyte contains specific amounts of lithium difluorophosphate, propyl propionate, 1,2,3-tris(2-cyanoethoxy)propane, and boron-containing lithium salts. The total content of lithium difluorophosphate and 1,2,3-tris(2-cyanoethoxy)propane in the non-aqueous electrolyte is set within a specific range, and the total content of propyl propionate and boron-containing lithium salts is set within a specific range. By using this non-aqueous electrolyte, not only can the initial efficiency of lithium-ion batteries be improved, but the increase in resistance can also be suppressed, significantly improving the output performance and high-temperature storage performance of lithium-ion batteries, thus completing this application.

[0007] That is, this application provides the following (1) to (3):

[0008] (1) A non-aqueous electrolyte for lithium-ion batteries, comprising a non-aqueous electrolyte in which lithium salts are dissolved in a non-aqueous solvent, wherein, based on the total mass of the non-aqueous electrolyte, the non-aqueous electrolyte contains:

[0009] (I) Lithium difluorophosphate with a content of 0.01% by mass or more and 4% by mass or less

[0010] (II) Propionate with a content of 8% or more by mass and less than 60% by mass

[0011] (III) 1,2,3-tris(2-cyanoethoxy)propane in a content of 0.7% by mass or more and 5% by mass.

[0012] (IV) Boron-containing lithium salts with a content of 0.01% by mass or more and 3% by mass or less.

[0013] The total content of (I) and (III) is 1.15% by mass or more and 6.5% by mass or less, and the total content of (II) and (IV) is 8.05% by mass or more and 60.05% by mass or less.

[0014] (2) A lithium-ion battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is the aforementioned non-aqueous electrolyte; the positive electrode comprises lithium cobalt oxide having at least three elements selected from aluminum, magnesium, titanium, zirconium, lanthanum, iridium, cerium and tungsten; and / or, the negative electrode comprises a negative electrode active material selected from at least one of lithium metal, lithium alloy, carbon material capable of inserting and de-intercalating lithium, elemental tin, tin compounds, elemental silicon, silicon oxide compounds, silicon carbide compounds and lithium titanate compounds.

[0015] (3) An electronic device comprising the lithium-ion battery described above.

[0016] The effects of the invention

[0017] By using this non-aqueous electrolyte, not only can the initial efficiency of lithium-ion batteries be improved, but the increase in resistance can also be suppressed, significantly improving the low-temperature output performance and high-temperature storage performance of lithium-ion batteries. Detailed Implementation

[0018] Embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application. Unless otherwise expressly stated, the terms used in this application have the meanings described below.

[0019] Non-aqueous electrolyte

[0020] The non-aqueous electrolyte for lithium-ion batteries disclosed in this application is a non-aqueous electrolyte in which lithium salts are dissolved in a non-aqueous solvent. Based on the total mass of the non-aqueous electrolyte, the non-aqueous electrolyte contains:

[0021] (I) Lithium difluorophosphate with a content of 0.01% by mass or more and 4% by mass or less

[0022] (II) Propionate with a content of 8% or more by mass and less than 60% by mass

[0023] (III) 1,2,3-tris(2-cyanoethoxy)propane in a content of 0.7% by mass or more and 5% by mass.

[0024] (IV) Boron-containing lithium salts with a content of 0.01% by mass or more and 3% by mass or less.

[0025] The total content of (I) and (III) is 1.15% by mass or more and 6.5% by mass or less, and the total content of (II) and (IV) is 8.05% by mass or more and 60.05% by mass or less.

[0026] The non-aqueous electrolyte contains (I) lithium difluorophosphate, (II) propyl propionate, (III) 1,2,3-tris(2-cyanoethoxy)propane, and (IV) boron-containing lithium salt. It is particularly important that the total content of lithium difluorophosphate and 1,2,3-tris(2-cyanoethoxy)propane is set within a specific range, and the total content of propyl propionate and boron-containing lithium salt is also set within a specific range. Although the reason for the improved initial efficiency characteristics and low-temperature output of the lithium-ion battery is unclear, it is believed that during the first charging cycle, components (I) to (IV) react with the active portion of the positive electrode surface, forming a stable coating on the positive electrode surface. It is speculated that this coating layer inhibits oxygen desorption from the positive electrode structure, reducing electrolyte damage to the positive electrode surface. As a result, it not only improves initial efficiency characteristics but also suppresses the increase in battery resistance, significantly improving the low-temperature output performance and high-temperature storage performance of the lithium-ion battery.

[0027] Specifically, the (IV) boron-containing lithium salt is selected from lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium tetracyanoborate, lithium tetra(trifluoromethyl)borate, lithium (trifluoromethyl)trifluoroborate, lithium bis(trifluoromethyl)difluoroborate, lithium pentafluoroethyltrifluoroborate, lithium dicyanoborate borate, lithium dicyanoborate, lithium bis(malonate)borate, lithium (2-fluoromalonate)difluoroborate, lithium malonate oxalate borate, lithium bis(salicylate)borate, lithium bis(catechol)borate, and lithium methoxytricyanoborate. At least one of the following lithium salts—lithium ethoxytricyanoborate, lithium tetramethoxyborate, lithium tetraethoxyborate, lithium tetra(trifluoromethoxy)borate, lithium tetra(2,2,2-trifluoroethoxy)borate, lithium polytetra(hydroquinoneoxy)borate, lithium di(trifluoroborate)sulfate, lithium difluoroborate, lithium methane disulfonate difluoroborate, lithium difluorophosphoryloxytrifluoroborate, lithium di(difluorophosphoryloxy)difluoroborate, and lithium tetra(difluorophosphoryloxy)borate—can further enhance battery performance due to the excellent stability of the resulting coating. The (IV) boron-containing lithium salt can be only one type or two or more types.

[0028] Specifically, from the viewpoint of improving the initial efficiency characteristics of lithium-ion batteries, based on the total mass of the non-aqueous electrolyte, the content of lithium difluorophosphate is 0.01% by mass or more, preferably 0.03% by mass or more, more preferably 0.07% by mass or more, and even more preferably 0.11% by mass or more.

[0029] Furthermore, from the viewpoint of improving the initial efficiency characteristics of lithium-ion batteries, the upper limit of the content of lithium difluorophosphate is 4% by mass or less, preferably 3.7% by mass or less, more preferably 2.6% by mass or less, even more preferably 1.3% by mass or less, and particularly preferably 0.82% by mass or less.

[0030] In some embodiments, the lithium difluorophosphate content is set as a1% by mass, where a1 is 0.01, 0.03, 0.05, 0.07, 0.11, 0.13, 0.16, 0.23, 0.3, 0.36, 0.45, 0.82, 1.1, 1.3, 1.6, 2, 2.6, 3.2, 3.7, 4, or within a range consisting of any two of the above values. For example, 0.01 to 0.07, 0.03 to 0.11, 0.11 to 0.23, 0.23 to 0.36, 0.36 to 0.82, 0.45 to 1.1, 1.1 to 2.6, 2 to 4, 0.3 to 0.82, 0.13 to 0.82. When within the above ranges, it helps to further improve the initial efficiency characteristics of the lithium-ion battery.

[0031] Specifically, from the viewpoint of improving the low-temperature discharge capacity of lithium-ion batteries, the content of 1,2,3-tris(2-cyanoethoxy)propane is 0.7% by mass or more, preferably 0.8% by mass or more, and more preferably 1.2% by mass or more, based on the total mass of the non-aqueous electrolyte.

[0032] Furthermore, as an upper limit for the content of 1,2,3-tris(2-cyanoethoxy)propane, from the viewpoint of improving the low-temperature discharge capacity of lithium-ion batteries, the content of 1,2,3-tris(2-cyanoethoxy)propane is 5% by mass or less, preferably 4.9% by mass or less, more preferably 4.1% by mass or less, even more preferably 3.6% by mass or less, and particularly preferably 2.7% by mass or less.

[0033] In some embodiments, the content of 1,2,3-tris(2-cyanoethoxy)propane is set as a3% by mass, where a3 is 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.6, 2, 2.1, 2.5, 2.7, 3, 3.5, 3.6, 4.1, 4.9, 5, or within a range consisting of any two of the above values. For example, values ​​of 0.7 to 1.2, 0.8 to 3.5, 0.9 to 1.6, 0.9 to 1.5, 1 to 1.6, 1.2 to 2.7, 1.5 to 2.7, 1.6 to 4.1, 2 to 3.5, 2 to 5, 1.2 to 3, 1.6 to 2.7, 3.5 to 4.9, 0.9 to 3, 0.8 to 2.1, 1.2 to 3.5, 0.7 to 2.7, 1.5 to 3, 1.2 to 1.6, and 2 to 4.1, when within the above ranges, help to further improve the low-temperature discharge capacity.

[0034] Furthermore, from the viewpoint of improving the low-temperature discharge capacity of lithium difluorophosphate and 1,2,3-tris(2-cyanoethoxy)propane, the total content of lithium difluorophosphate and 1,2,3-tris(2-cyanoethoxy)propane is based on a total non-aqueous electrolyte mass of 1.25% by mass or more, preferably 1.65% by mass or more.

[0035] Furthermore, from the viewpoint of improving electrochemical properties under low-temperature conditions, the upper limit of the total content of lithium difluorophosphate and 1,2,3-tris(2-cyanoethoxy)propane is 6.5% by mass or less, preferably 6.2% by mass or less.

[0036] In some embodiments, the total content of lithium difluorophosphate and 1,2,3-tris(2-cyanoethoxy)propane is set as a1+a3 mass%, where a1+a3 is 1.25, 1.35, 1.65, 2.55, 3.15, 3.8, 4.05, 4.55, 5.1, 5.35, 5.45, 6.2, 6.5, or within a range of any two of the above values. For example, 1.25 to 1.65, 1.35 to 2.55, 1.35 to 3.15, 1.65 to 3.8, 2.55 to 4.05, 3.15 to 5.1, 4.05 to 6.2, 1.25 to 4.05, 1.65 to 4.05, 1.25 to 1.65, 2.55 to 5.1. When within the above ranges, it helps to further improve the low-temperature discharge capacity of lithium-ion batteries.

[0037] Specifically, from the viewpoint of suppressing the increase in resistance, based on the total mass of the non-aqueous electrolyte, the content of propyl propionate is 8% by mass or more, preferably 9% by mass or more, and more preferably 10.7% by mass or more.

[0038] Furthermore, from the viewpoint of suppressing the increase in resistance, the content of propyl propionate is 60% by mass or less as the upper limit of the content of propyl propionate. It is more preferably 58.9% by mass or less, more preferably 41.6% by mass or less, even more preferably 39.5% by mass or less, and particularly preferably 32.7% by mass or less.

[0039] In some embodiments, the content of propyl propionate is set as a2% by mass, where a2 is 8, 8.5, 9, 9.2, 9.5, 10.7, 11, 11.5, 12, 12.5, 12.9, 13.6, 14, 14.5, 15.6, 16, 16.6, 17, 17.8, 18.5, 18.9, 19, 19.5, 29.3, 32.7, 35, 39.5, 41.6, 46, 49, 52, 55, 58.9, 60, or within a range consisting of any two of the above values. For example, 8.5 to 17.8, 9 to 18.9, 9.2 to 14.5, 9.5 to 19.5, 11.5 to 17.8, 11.5 to 16.6, 13.6 to 18.5, 13.6 to 17.8, 14 to 18.9, 15.7 to 19.5, 12 to 17.8, 15.6 to 29.3, 15.6 to 39.5, 15.6 to 58.9, 32.7 to 41.6, 32.7 to 58.9, and 15.6 to 41.6, when within the above ranges, help to further suppress the increase in resistance.

[0040] Specifically, from the viewpoint of improving the high-temperature storage characteristics of lithium-ion batteries, based on the total mass of the non-aqueous electrolyte, the content of boron-containing lithium salt is 0.01% by mass or more, preferably 0.03% by mass or more, more preferably 0.07% by mass or more, and even more preferably 0.12% by mass or more.

[0041] Furthermore, from the viewpoint of improving the high-temperature storage characteristics of lithium-ion batteries, the upper limit of the boron-containing lithium salt content is 3% by mass or less, preferably 2.5% by mass or less, more preferably 2.1% by mass or less, even more preferably 1.8% by mass or less, and particularly preferably 1.2% by mass or less.

[0042] In some embodiments, the content of boron-containing lithium salt is set as a4% by mass, where a4 is 0.01, 0.03, 0.05, 0.07, 0.08, 0.1, 0.12, 0.15, 0.19, 0.21, 0.27, 0.3, 0.35, 0.4, 0.45, 0.51, 0.6, 0.7, 0.79, 0.9, 1, 1.2, 1.5, 1.8, 2, 2.5, 3, or within a range consisting of any two of the above values. For example, 0.01 to 0.12, 0.02 to 0.21, 0.1 to 0.45, 0.51 to 2, 0.6 to 3, 1.2 to 2.5, 0.1 to 0.8, 0.79 to 1.8, 1.5 to 3, 0.12 to 0.45, and 0.35 to 0.79, when within the above ranges, help to further improve the high-temperature storage characteristics of lithium-ion batteries.

[0043] Furthermore, from the viewpoint of suppressing the increase in resistance, the total content of propyl propionate and boron-containing lithium salt is 8.05% by mass or more, preferably 8.55% by mass or more, based on the total mass of the non-aqueous electrolyte.

[0044] Furthermore, from the viewpoint of improving electrochemical properties under low-temperature conditions, the upper limit of the total content of propyl propionate and boron-containing lithium salt is 60.05% by mass or less, preferably 58.95% by mass or less.

[0045] In some embodiments, the total content of propyl propionate and boron-containing lithium salt is a2+a4% by mass, where a2+a4 is 8.05, 8.55, 9.05, 10.5, 10.75, 11, 11.5, 12, 12.95, 13, 13.65, 14, 14.5, 15, 15.65, 16, 16.5, 17, 17.85, 18, 18.5, 18.95, 19, 19.55, 20.05, 29.35, 32.75, 39.55, 41.65, 58.95, 60.05, or within a range consisting of any two of the above values. For example, 8.05 to 29.35, 10.75 to 32.75, 15.65 to 41.65, and 29.35 to 58.95, when within the above ranges, help to further suppress the increase in resistance.

[0046] In addition, the non-aqueous electrolyte may also include other nitrile compounds. The inventors also unexpectedly discovered that other nitrile compounds can reduce the impedance of the reaction between the aforementioned substances (I) to (IV) and the active part of the positive electrode surface to form a coating, improve lithium-ion charge transport, suppress the increase in resistance, and improve initial efficiency and low-temperature performance.

[0047] Other nitrile compounds include at least one of succinic anion, adiponitrile, ethylene glycol di(propionitrile) ether, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane, or 1,2,5-tris(cyanoethoxy)pentane.

[0048] The other nitrile compounds mentioned above may be only one type or two or more types. For example, they include succinate and adiponitrile; or succinate and ethylene glycol di(propionitrile) ether; or adiponitrile and ethylene glycol di(propionitrile) ether; or succinate and 1,3,6-hexanetrionitrile; or adiponitrile and 1,3,6-hexanetrionitrile; or ethylene glycol di(propionitrile) ether and 1,3,6-hexanetrionitrile.

[0049] Specifically, from the viewpoint of suppressing the increase in resistance, based on the total mass of the non-aqueous electrolyte, the content of other nitrile compounds is 0.3% by mass or more, preferably 0.6% by mass or more, more preferably 0.9% by mass or more, and more preferably 1.4% by mass or more.

[0050] Furthermore, as an upper limit for the content of other nitrile compounds, from the viewpoint of improving the low-temperature discharge capacity of lithium-ion batteries, the content of other nitrile compounds is 8% by mass or less, preferably 7.9% by mass or less, more preferably 7.1% by mass or less, further preferably 6.2% by mass or less, and particularly preferably 5.3% by mass or less.

[0051] In some embodiments, the total content of other nitrile compounds is b% by mass, where b is 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.4, 1.5, 2, 2.5, 3, 3.5, 3.9, 4, 4.6, 5.3, 6.2, 7.1, 7.9, 8, or within a range consisting of any two of the above values. For example, 0.3 to 5.3, 0.6 to 4.6, 0.9 to 3.9, 0.4 to 2, 0.45 to 4.6, 0.8 to 2.5, 1.4 to 3.9, 2.5 to 8, 0.9 to 6.2, 0.45 to 5.3, 0.6 to 1.4. When within the above ranges, it helps to further suppress the increase in resistance and improve the low-temperature discharge capacity of the lithium-ion battery.

[0052] In addition, the non-aqueous electrolyte may also include a first substance. The inventors also unexpectedly discovered that the first substance can inhibit the decomposition and regeneration of the coating formed by the reaction of the aforementioned substances (I) to (IV) with the active part of the positive electrode surface during the charging and discharging process, thereby further inhibiting the increase in resistance and improving the initial efficiency and low-temperature performance.

[0053] The first substance includes at least one of lithium monofluorophosphate, fluoroethylene carbonate, vinylene carbonate, lithium difluorophosphate, lithium fluorosulfonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, 1,3-propanediol cyclosulfonate, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate.

[0054] The first substance mentioned above may be only one or more. For example, it may include lithium difluorophosphate and lithium fluorosulfonate; or lithium difluorophosphate and fluoroethylene carbonate; or lithium difluorophosphate and 1,3-propanesulfonate lactone; or lithium fluorosulfonate and 1,3-propanesulfonate lactone; or vinyl sulfate and 1,3-propanesulfonate lactone; or tris(trimethylsilane) phosphate and lithium difluorophosphate; or tris(trimethylsilane) borate and lithium difluorophosphate.

[0055] Specifically, from the viewpoint of suppressing the increase in resistance, based on the total mass of the non-aqueous electrolyte, the content of the first substance is 0.3% by mass or more, preferably 0.9% by mass or more, more preferably 1.6% by mass or more, and more preferably 2.8% by mass or more.

[0056] Furthermore, from the viewpoint of suppressing the increase in resistance, the content of the first substance is 10% by mass or less as the upper limit of the content of the first substance, preferably 9.7% by mass or less, more preferably 8.2% by mass or less, even more preferably 7.1% by mass or less, and particularly preferably 6.7% by mass or less.

[0057] In some embodiments, the total content of the first substance is c by mass%, where c is 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 1.6, 2, 2.5, 2.8, 3, 3.5, 3.9, 4, 4.5, 5, 5.5, 6, 6.5, 7.1, 7.5, 8.2, 8.6, 9, 9.3, 9.7, 10, or within a range consisting of any two of the above values. For example, 0.3 to 8.2, 0.45 to 7.5, 0.6 to 9.7, 5.5 to 9.7, 6 to 8.6, 2.8 to 6.5, 1 to 6.5, 0.7 to 7.1, 1.5 to 9.3, 0.45 to 3.9, 0.7 to 4.5. When within the above ranges, it helps to further suppress the increase in resistance.

[0058] The lithium salt used in the non-aqueous electrolyte of this application includes lithium hexafluorophosphate. Based on the total mass of the non-aqueous electrolyte, the content of lithium hexafluorophosphate is 9-15% by mass, preferably 9-13% by mass, and more preferably 9-12% by mass. By setting the content within the above range, the improvement of initial efficiency characteristics and the enhancement of low-temperature discharge characteristics can be achieved in a more balanced manner.

[0059] The non-aqueous electrolyte of this application may further comprise any non-aqueous solvent known in the prior art that can be used as a solvent for a non-aqueous electrolyte. Examples include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, and sulfur-containing organic solvents. Chain carboxylic acid esters are preferred, such as ethyl acetate, ethyl fluoroacetate, ethyl propionate, and propyl propionate.

[0060] Lithium-ion batteries

[0061] The lithium-ion battery of this application includes a positive electrode, a negative electrode, and the aforementioned non-aqueous electrolyte in which lithium salts are dissolved in a non-aqueous solvent. Components such as the positive electrode and negative electrode, other than those containing an aqueous electrolyte, can be used without particular restrictions.

[0062] For example, as positive electrode active materials for lithium-ion batteries, composite metal oxides containing one or more lithium-containing metals selected from the group consisting of cobalt, manganese, and nickel, or olivine-type phosphates containing one or more lithium-containing metals selected from iron, cobalt, nickel, and manganese are used. These positive electrode active materials can be used alone or in combination of two or more.

[0063] As such lithium composite metal oxides, for example, those selected from LiCoO2, LiMn2O4, LiNiO2, LiCo + , ,

[0067] , , + ,

[0066] , + Ni x O2(0.01 < x < 1), LiNi x Mn y Co z O2(x + y + z = 1), solid solutions of Li2MnO3 and LiMO2 (M is a transition metal such as Co, Ni, Mn, Fe), LiNi 1 / 2 Mn 3 / 2 ​​​​​​​​​​​​​​​​​​​​The conductive agent for the positive electrode is not particularly limited as long as it is an electronically conductive material that does not cause chemical changes. Examples include natural graphite (flake graphite, etc.), artificial graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal cracking black. Alternatively, graphite and carbon black can be appropriately mixed. The amount of conductive agent added to the positive electrode mixture is preferably 1-10% by mass, particularly preferably 1.5-5% by mass. The type of binder for the positive electrode is not particularly limited, and may include at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, copolymers of styrene and butadiene, and carboxymethyl cellulose.

[0068] The positive electrode can be made as follows: the above-mentioned positive electrode active material is mixed with a conductive agent and a binder, and a high-boiling-point solvent such as 1-methyl-2-pyrrolidone is added and kneaded to make a positive electrode mixture slurry. This slurry is then coated onto an aluminum foil or similar material of a current collector, dried, and pressurized to form a positive electrode mixture layer, thereby producing the positive electrode.

[0069] The density of the positive electrode, excluding the current collector, is typically 3.5 g / cm³. 3 In order to further improve the battery capacity, a value of 3.8 g / cm³ is preferred. 3 The above, more preferably 4g / cm 3 The above is further optimized to 4.1 g / cm³. 3 That's all. Furthermore, as an upper limit, 4.6 g / cm³ is preferred. 3 the following.

[0070] As negative electrode active materials for lithium-ion batteries, the following negative electrode active materials can be used alone or in combination: lithium metal or lithium alloy, and carbon materials capable of intercalating and deintercalating lithium (easily graphitized carbon, difficult-to-graphitize carbon with an interfacial spacing of 0.37 nm or more on the (002) facets, graphite with an interfacial spacing of 0.34 nm or less on the (002) facets, etc.), tin (elemental), SnO x (1≤x<2) Tin compounds, silicon (elemental), SiO x (1≤x<2) and other silicon oxide compounds, silicon carbide compounds, or Li4Ti5O 12 Lithium titanate compounds, etc.

[0071] Among these, highly crystalline carbon materials such as artificial graphite or natural graphite are preferred in terms of lithium-ion insertion and extraction capabilities. Carbon materials with a graphitic crystal structure having a lattice plane (002) spacing (d002) of 0.340 nm or less, particularly 0.335–0.337 nm, are even more preferred. From the viewpoint of improving energy density, silicon oxide compounds, silicon carbide compounds, or mixtures thereof with graphite are preferred.

[0072] The negative electrode can be made as follows: using the same conductive agent, binder, and high-boiling-point solvent as the positive electrode to make a negative electrode slurry, then coating it onto the copper foil of the current collector, drying it, and pressing it to form a negative electrode slurry layer, thereby obtaining the negative electrode.

[0073] The density of the negative electrode, excluding the current collector, is typically 1.1 g / cm³. 3 In order to further improve the battery capacity, a value of 1.5 g / cm³ is preferred. 3 The above, more preferably 1.7 g / cm³ 3 That's all. Furthermore, as an upper limit, 2.2 g / cm³ is preferred. 3 the following.

[0074] There are no particular restrictions on the structure of lithium batteries; they can be coin-shaped, cylindrical, prismatic, or pouch batteries with single or multiple layers of separators.

[0075] There are no particular restrictions on the use of separators for batteries, but single-layer or multi-layered microporous membranes, woven fabrics, or non-woven fabrics made of polypropylene, polyethylene, or other polyolefins can be used.

[0076] The application of the lithium-ion battery 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 lithium-ion battery 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, 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.

[0077] The preparation of lithium-ion batteries is described below with reference to specific embodiments. 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.

[0078] Example

[0079] The following are examples of non-aqueous electrolytes of this application, but this application is not limited to these examples.

[0080] Manufacturing of lithium-ion batteries

[0081] The positive electrode active material (97% by mass) and acetylene black (1.5% by mass) from Table 1-1 were mixed and added to a solution obtained by dissolving 1.5% by mass of polyacrylonitrile in 1-methyl-2-pyrrolidone. This mixture was then used to prepare a positive electrode paste. The paste was coated onto aluminum foil, dried, pressurized, and then cut to the specified size to fabricate the positive electrode. The density of the positive electrode, excluding the current collector, was 4.15 g / cm³. 3 .

[0082] In addition, 96% by mass of the negative electrode active material and 2% by mass of styrene-butadiene rubber from Table 1-1 were mixed and added to a solution obtained by dissolving 2% by mass of lithium carboxymethyl cellulose in deionized water, and then mixed to prepare a negative electrode paste. This negative electrode paste was coated onto copper foil, dried, pressurized, and then cut into specified sizes to fabricate the negative electrode. The density of the negative electrode, excluding the current collector, was 1.6 g / cm³. 3 .

[0083] The positive and negative electrodes prepared as described above are each connected to a wire. They are then stacked using a 10 μm thick polypropylene porous membrane. Furthermore, LiPF6, serving as the supporting electrolyte, is dissolved in a solution containing (I) lithium difluorophosphate, (II) propyl propionate, (III) 1,2,3-tris(2-cyanoethoxy)propane, (IV) a boron-containing lithium salt, and ethylene carbonate and propylene carbonate. Based on 100 parts by mass of the total non-aqueous electrolyte, the contents and composition of (I) to (IV) are shown in Tables 1 and 2, with LiPF6 comprising 14%, and the remainder being ethylene carbonate and propylene carbonate (mass ratio 1.1:1.3).

[0084] The laminated body and 3.2g of electrolyte are then housed together in an aluminum laminated casing. The opening of the casing is heat-sealed, and a lithium-ion battery is manufactured through formation, capacity testing, and other steps. This lithium-ion battery is a pouch-shaped structure with a width of 35mm, a height of 48mm, and a thickness of 5mm.

[0085] Table 1

[0086] Table 1 shows the positive and negative electrode materials and electrolyte component codes of the prepared lithium-ion batteries. The detailed composition is shown in Tables 1-1, 1-2, and 1-3, respectively.

[0087] The values ​​in parentheses in the table above are all mass percentages.

[0088] Table 1-1 Positive Electrode

[0089] Table 1-2 Negative Electrode

[0090] Table 1-3 Electrolytes

[0091] Test methods

[0092] Initial efficiency

[0093] The secondary batteries obtained in the examples and comparative examples were repeatedly charged to 4.6V and discharged to 3.0V at 0.2C three times at 25°C. Then, the ratio of discharge amount to charge amount when charging to 4.6V at 1C and discharging to 3.0V at 1C was evaluated.

[0094] A: The charge / discharge efficiency is over 97%;

[0095] B: Charge / discharge efficiency is above 95% and less than 97%;

[0096] C: Charge / discharge efficiency is above 93% and less than 95%;

[0097] D: Charge / discharge efficiency is less than 93%.

[0098] Resistance increase suppression

[0099] The secondary batteries obtained in the examples and comparative examples were charged at a constant current of 0.2C at 25°C until the battery voltage reached 4.6V, and then charged at a constant voltage of 4.6V until the charging current reached 0.02C. Next, they were discharged at a constant current of 0.2C until the battery voltage reached 3.87V (SOC: 50%), and the voltage change was measured after 30 seconds of discharge at 0.2C, 0.5C, 1.0C, 2.0C, 2.5C, and 3.0C. The discharge current and the measured voltage change were plotted, and the slope was taken as the resistance value (Ω). The calculated resistance value was evaluated according to the following criteria: the smaller the resistance value, the better the battery characteristics of the secondary battery.

[0100] A: Resistance value is less than 0.3Ω;

[0101] B: Resistance value is 0.3Ω or higher and less than 0.5Ω;

[0102] C: Resistance value is 0.5Ω or higher and less than 0.8Ω;

[0103] D: Resistance value is 0.8Ω or higher.

[0104] Low temperature output characteristics

[0105] The secondary batteries obtained in the examples and comparative examples were charged to 4.6V using a constant current constant voltage (CCCV) method at 25°C to prepare battery cells. The prepared battery cells were then discharged to 3.0V using a constant current method at 0.2C and 1C at -20°C, and the capacity was calculated. The discharge capacity retention rate, expressed as the ratio of capacitance (=(capacity at 1C / capacity at 0.2C)×100(%)), was then calculated. These measurements were performed on five lithium-ion secondary battery cells, and the average of the calculated discharge capacity retention rates was used as the output characteristic, evaluated according to the following criteria. A higher value indicates better output characteristics.

[0106] A: The average discharge capacity retention rate is over 85%;

[0107] B: The average discharge capacity retention rate is above 80% and below 85%;

[0108] C: The average discharge capacity retention rate is above 75% and less than 80%;

[0109] D: The average discharge capacity retention rate is less than 75%.

[0110] High temperature preservation characteristics

[0111] The secondary batteries obtained in the examples and comparative examples were charged at 25°C with a constant current of 140mA (0.2CmA) until the battery voltage reached 4.6V. Then, they were charged at 4.6V with a constant voltage until the charging current reached 14mA. Next, they were discharged at a constant current of 140mA until the battery voltage reached 3.0V. The discharge capacity at this point is denoted as C. Ini Next, after charging at 25°C, the battery was stored at 60°C for 4 weeks while still charged. After storage, the temperature was returned to 25°C, and then discharged at a constant current of 140mA until the battery voltage reached 3.0V. The discharge capacity at this point is denoted as C. 4w Calculate the high-temperature storage capacity ratio (%) = C 4w / C Ini / ×100, evaluated according to the following criteria. A higher high-temperature storage capacity ratio indicates better high-temperature storage characteristics of the lithium-ion battery.

[0112] A: The high-temperature storage capacity ratio is over 85%;

[0113] B: The high-temperature storage capacity ratio is above 80% and less than 85%;

[0114] C: The high-temperature storage capacity ratio is above 75% and less than 80%;

[0115] D: The capacity for high-temperature storage is less than 75%.

[0116] Table 2

[0117] In Table 2, a1 represents the content of (I) lithium difluorophosphate, a2 represents the content of (II) propyl propionate, a3 represents the content of (III) 1,2,3-tris(2-cyanoethoxy)propane, a4 represents the total content of (IV) boron-containing lithium salts, b represents the total content of other nitrile compounds, and c represents the total content of the first substance.

[0118] When a non-aqueous electrolyte contains 0.01% to 4% by mass of lithium difluorophosphate, 8% to 60% by mass of propyl propionate, 0.7% to 5% by mass of 1,2,3-tris(2-cyanoethoxy)propane, 0.01% to 3% by mass of boron-containing lithium salt, a total content of lithium difluorophosphate and 1,2,3-tris(2-cyanoethoxy)propane of 1.15% to 6.5% by mass, and a total content of propyl propionate and boron-containing lithium salt of 8.05% to 60.05% by mass, it can not only improve the initial efficiency of lithium-ion batteries, but also suppress the increase in resistance, and significantly improve the low-temperature output performance and high-temperature storage performance of lithium-ion batteries.

[0119] In particular, when the non-aqueous electrolyte also contains other nitrile compounds, it can reduce the resistance of the coating formed by the reaction of the aforementioned substances (I) to (IV) with the active part of the positive electrode surface, improve lithium-ion charge transport, suppress the increase of resistance, and further improve the low-temperature output performance and high-temperature storage performance of lithium-ion batteries.

[0120] In particular, when the non-aqueous electrolyte also contains the first substance, the inventors unexpectedly discovered that the first substance can inhibit the decomposition and regeneration of the coating formed by the reaction of the aforementioned substances (I) to (IV) with the active part of the positive electrode surface during the charging and discharging process, thereby further inhibiting the increase in resistance.

[0121] Throughout this specification, references to "embodiment," "partial embodiment," "one embodiment," "another example," "example," "specific example," or "partial example" mean that at least one embodiment or example in this application includes a specific feature, structure, material, or characteristic described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in an example," "in a specific example," or "example," do not necessarily refer to the same embodiments or examples in this application. Furthermore, specific features, structures, materials, or characteristics in this application can be combined in any suitable manner in one or more embodiments or examples.

[0122] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A non-aqueous electrolyte, characterized in that, The non-aqueous electrolyte comprises a non-aqueous solvent and a lithium salt, and based on the total mass of the non-aqueous electrolyte, the non-aqueous electrolyte contains: (I) Lithium difluorophosphate with a content of 0.01% by mass or more and 4% by mass or less (II) Propionate with a content of 8% or more by mass and less than 60% by mass (III) 1,2,3-tris(2-cyanoethoxy)propane in a content of 0.7% by mass or more and 5% by mass. (IV) Boron-containing lithium salts with a content of 0.01% by mass or more and 3% by mass or less. The total content of (I) and (III) is 1.15% by mass or more and 6.5% by mass or less, and the total content of (II) and (IV) is 8.05% by mass or more and 60.05% by mass or less.

2. The non-aqueous electrolyte according to claim 1, characterized in that, The (IV) includes lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium tetracyanoborate, lithium tetra(trifluoromethyl)borate, lithium (trifluoromethyl)trifluoroborate, lithium bis(trifluoromethyl)difluoroborate, lithium pentafluoroethyltrifluoroborate, lithium dicyanoborate borate, lithium bis(malonate)borate, lithium (2-fluoromalonate)difluoroborate, lithium malonate oxalate borate, lithium bis(salicylate)borate, and lithium bis(catechol)borate. At least one of lithium methoxytricyanoborate, lithium ethoxytricyanoborate, lithium tetramethoxyborate, lithium tetraethoxyborate, lithium tetra(trifluoromethoxy)borate, lithium tetra(2,2,2-trifluoroethoxy)borate, lithium polytetra(hydroquinoneoxy)borate, lithium di(trifluoroborate)sulfate, lithium difluoroborate, lithium methane disulfonate difluoroborate, lithium difluorophosphoryloxytrifluoroborate, lithium di(difluorophosphoryloxy)difluoroborate, and lithium tetra(difluorophosphoryloxy)borate.

3. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, Based on the total mass of the non-aqueous electrolyte, the content of (I) is 0.05% by mass or more and 3.7% by mass or less; or the content of (III) is 0.8% by mass or more and 4.1% by mass or less; or the total content of (I) and (III) is 1.25% by mass or more and 6.5% by mass or less.

4. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, Based on the total mass of the non-aqueous electrolyte, the content of (I) is 0.07% by mass or more and 2.6% by mass or less; or the content of (III) is 1.2% by mass or more and 3.6% by mass or less; or the total content of (I) and (III) is 1.35% by mass or more and 6.2% by mass or less.

5. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, Based on the total mass of the non-aqueous electrolyte, the content of (I) is 0.11% by mass or more and 1.3% by mass or less; or the content of (III) is 1.2% by mass or more and 2.7% by mass or less; or the total content of (I) and (III) is 1.35% by mass or more and 6.5% by mass or less.

6. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, Based on the total mass of the non-aqueous electrolyte, the content of (II) is 8.5% by mass or more and 39.5% by mass or less; or the content of (IV) is 0.03% by mass or more and 2.5% by mass or less; or the total content of (II) and (IV) is 8.55% by mass or more and 39.55% by mass or less.

7. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, Based on the total mass of the non-aqueous electrolyte, the content of (II) is 9% by mass or more and 41.6% by mass or less; or the content of (IV) is 0.05% by mass or more and 1.8% by mass or less; or the total content of (II) and (IV) is 10.75% by mass or more and 41.65% by mass or less.

8. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, Based on the total mass of the non-aqueous electrolyte, the content of (II) is 15.6% by mass or more and 58.9% by mass or less; or the content of (IV) is 0.12% by mass or more and 1.8% by mass or less; or the total content of (II) and (IV) is 32.75% by mass or more and 58.95% by mass or less.

9. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, The non-aqueous electrolyte further comprises other nitrile compounds, including at least one selected from succinic anhydride, adiponitrile, ethylene glycol di(propionitrile) ether, 1,3,5-pentanetricarbonyl anhydride, 1,2,3-propanetricarbonyl anhydride, 1,3,6-hexanetricarbonyl anhydride, 1,2,6-hexanetricarbonyl anhydride, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane, or 1,2,5-tris(cyanoethoxy)pentane.

10. The non-aqueous electrolyte according to claim 9, characterized in that, The other nitrile compounds include succinic anionyl and adiponitrile; or the other nitrile compounds include succinic anionyl and ethylene glycol di(propionyl) ether; or the other nitrile compounds include adiponitrile and ethylene glycol di(propionyl) ether; or the other nitrile compounds include succinic anionyl and 1,3,6-hexanetricarbonyl; or the other nitrile compounds include adiponitrile and 1,3,6-hexanetricarbonyl; or the other nitrile compounds include ethylene glycol di(propionyl) ether and 1,3,6-hexanetricarbonyl.

11. The non-aqueous electrolyte according to claim 9, characterized in that, Based on the total mass of the non-aqueous electrolyte, the content of the other nitrile compounds is 0.3% by mass or more and 8% by mass or less.

12. The non-aqueous electrolyte according to claim 9, characterized in that, Based on the total mass of the non-aqueous electrolyte, the content of the other nitrile compounds is 0.6% by mass or more and 7.1% by mass or less.

13. The non-aqueous electrolyte according to claim 9, characterized in that, Based on the total mass of the non-aqueous electrolyte, the content of the other nitrile compounds is 1.4% by mass or more and 6.2% by mass or less.

14. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, The non-aqueous electrolyte further comprises a first substance, which includes at least one of lithium monofluorophosphate, fluoroethylene carbonate, vinylene carbonate, lithium fluorosulfonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, 1,3-propanediol cyclosulfonate, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate.

15. The non-aqueous electrolyte according to claim 14, characterized in that, The first substance comprises lithium difluorophosphate and lithium fluorosulfonate; or the first substance comprises lithium monofluorophosphate and fluoroethylene carbonate; or the first substance comprises lithium monofluorophosphate and 1,3-propanesulfonate lactone; or the first substance comprises lithium fluorosulfonate and 1,3-propanesulfonate lactone; or the first substance comprises vinyl sulfate and 1,3-propanesulfonate lactone; or the first substance comprises tris(trimethylsilane) phosphate and vinyl sulfate; or the first substance comprises tris(trimethylsilane) borate and vinyl sulfate.

16. The non-aqueous electrolyte according to claim 14, characterized in that, Based on the total mass of the non-aqueous electrolyte, the content of the first substance is 0.3% by mass or more and 10% by mass or less.

17. The non-aqueous electrolyte according to claim 14, characterized in that, Based on the total mass of the non-aqueous electrolyte, the content of the first substance is 0.9% by mass or more and 4.6% by mass or less.

18. The non-aqueous electrolyte according to claim 14, characterized in that, Based on the total mass of the non-aqueous electrolyte, the content of the first substance is 5.3% by mass or more and 8.2% by mass or less.

19. A lithium-ion battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, characterized in that, The non-aqueous electrolyte is the non-aqueous electrolyte according to any one of claims 1 to 18; the positive electrode comprises lithium cobalt oxide having at least three elements selected from aluminum, magnesium, titanium, zirconium, lanthanum, iridium, cerium, and tungsten; and / or, The negative electrode contains a negative electrode active material, which is selected from at least one of lithium metal, lithium alloy, carbon materials capable of inserting and de-intercalating lithium, elemental tin, tin compounds, elemental silicon, silicon oxide compounds, silicon carbide compounds, and lithium titanate compounds.

20. An electronic device comprising a lithium-ion battery as claimed in claim 19.

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