Electrolyte and lithium-ion batteries

Abstract

To provide an electrolyte capable of withstanding a high voltage, and when applied to a high-voltage lithium ion battery, the electrolyte capable of forming a stable protective film at an interface between battery sheet and the electrolyte, thereby securing stability of the interface between the sheet and the electrolyte, and thus, improving electrical performance of the high-voltage battery.SOLUTION: An embodiment of the present invention provides an electrolyte comprising: a solvent that is a fluorinated solvent; a lithium salt; and an additive comprising a triallyl isocyanurate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to the field of batteries, and more specifically to electrolytes and lithium-ion batteries. [Background technology]

[0002] In recent years, the new energy vehicle market has developed rapidly, and the market value of power batteries, primarily secondary alkali metal ion batteries, has grown explosively. However, the energy density of commercially available secondary alkali metal ion batteries is approaching its theoretical limit, and to fundamentally address the range concerns of electric vehicle buyers, increasing the energy density and voltage of current batteries is an intuitive and feasible approach.

[0003] Currently, fluorinated solvents such as fluoroethyl methyl carbonate (FEMC) are commonly used as solvents for electrolytes to improve their high-voltage resistance. Because the fluorine atoms in fluorinated solvents have a high electron-withdrawing force, they can further improve the oxidation stability of conventional carbonates. Therefore, fluorinated solvents are widely used as the main solvent in high-voltage system batteries, significantly improving the high-voltage resistance of lithium battery electrolytes. However, as battery voltage increases, the requirements for high-voltage resistance of the electrolyte also increase. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In response to the problems of the prior art, the object of the present invention is to provide an electrolyte that can withstand high voltage, and when the electrolyte is applied to a high-voltage lithium-ion battery, the electrolyte can form a stable protective film at the interface between the battery sheet and the electrolyte, thereby ensuring the stability of the interface between the sheet and the electrolyte, and thereby improving the electrical performance of the high-voltage battery. [Means for solving the problem]

[0005] To achieve the above objective, the present invention provides an electrolyte comprising a solvent which is a fluorinating solvent, a lithium salt, and an additive which includes triallyl isocyanurate.

[0006] In some embodiments, the additive further comprises 1-propene-1,3-sultone.

[0007] In some embodiments, the mass of 1-propene-1,3-sultone accounts for 0.01% to 1% of the total mass of the electrolyte, and the mass of triallyl isocyanurate accounts for 0.01% to 1% of the total mass of the electrolyte.

[0008] In some embodiments, the fluorinating solvent includes fluoroethylmethyl carbonate.

[0009] In some embodiments, the fluorinating solvent further comprises fluoroethylene carbonate.

[0010] In some embodiments, the mass ratio of fluoroethyl methyl carbonate to fluoroethylene carbonate is 7:3 to 10:0.

[0011] In some embodiments, the mass of the lithium salt is 12% to 20% of the total mass of the electrolyte.

[0012] In some embodiments, the lithium salt is one or more of the following: lithium hexafluoride phosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium methanesulfonate, lithium trifluoromethanesulfonate, lithium hexafluoride arsenate, lithium antimonate hexafluoride, lithium perchlorate, lithium difluorooxalate borate, lithium dioxalate borate, and lithium difluorophosphate.

[0013] The object of the present invention is to provide a lithium-ion battery containing an electrolyte that can withstand high voltage, wherein the electrolyte can form a stable protective film at the interface between the battery sheet and the electrolyte, thereby ensuring the stability of the interface between the sheet and the electrolyte, and thereby improving the electrical performance of the high-voltage battery. The present invention provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator between the positive electrode sheet and the negative electrode sheet, and an electrolyte according to any of the above embodiments.

[0014] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material located in the positive electrode current collector, wherein the positive electrode active material comprises lithium nickel manganese oxide, and the chemical formula of lithium nickel manganese oxide is Li a Ni x Mn y O 4‐z M z Here, 0.90 ≤ a ≤ 1.10, 0.4 ≤ x ≤ 0.6, 1.4 ≤ y ≤ 1.6, 0 ≤ z ≤ 0.1, and element M is one or more of Cl, Br, I, S, Se, Te, or F.

[0015] In some embodiments, the negative electrode current collector and the negative electrode active material located in the negative electrode current collector include artificial graphite. [Effects of the Invention]

[0016] The beneficial technical effects of this invention are as follows:

[0017] The electrolyte solvent is a fluorinated solvent, and by adding triallyl isocyanurate as an additive to the fluorinated solvent, the electrolyte can not only withstand high voltages, but when this electrolyte is applied to a battery, it forms a stable protective film at the interface between the sheet and the electrolyte, ensuring the stability of the interface and improving the electrical performance of the high-voltage battery.

[0018] Furthermore, by using a combination of 1-propene-1,3-sultone and triallyl isocyanurate as additives in a fluorinated solvent, when the electrolytic solution is applied to a battery, a stable protective film can be formed at the interface between the electrode sheet and the electrolytic solution even at high temperatures. This ensures the stability of the interface between the electrode sheet and the electrolytic solution even at high temperatures, and can significantly improve the high-temperature stability of high-voltage batteries.

[0019] Since the electrolytic solution uses a fluorinated solvent as the solvent and triallyl isocyanurate is added as an additive, the electrolytic solution of the present invention can form a stable protective film at the interface between the electrode sheet of a lithium-ion battery and the electrolytic solution, ensure the stability of the interface between the electrode sheet and the electrolytic solution, and improve the electrical performance and stability of high-voltage batteries. MODE FOR CARRYING OUT THE INVENTION

[0020] Exemplary embodiments are described in detail below. These exemplary embodiments can be implemented in different ways and should not be construed as limited to the embodiments set forth in the specification of the present invention. Rather, the purpose of providing these embodiments is to make the disclosure of the present invention thorough and complete, and to fully convey the scope of the present invention to those skilled in the art. Where specific techniques or conditions are not described in the embodiments, the techniques or conditions described in literature in the art shall be followed, or the instructions of the product shall be followed. Reagents and instruments without specified manufacturer names are all conventional products that can be purchased through normal channels.

[0021] Fluorinated solvents, such as fluorinated carbonate solvents, are important solvent components in high-voltage battery systems, offering excellent high-voltage stability and ensuring interfacial stability of the electrolyte on the positive electrode side. However, additives used in existing fluorinated solvents can form unstable interfacial films at the interface between the battery sheet and the electrolyte, potentially degrading the electrical performance of high-voltage batteries. Furthermore, since fluorine atoms in fluorinated solvents are easily cleaved at high temperatures, the cleaved fluorine atoms react with active hydrogen in the electrolyte to produce hydrofluoric acid (HF). This corrodes alkaline substances in the negative electrode solid-liquid interface film (SEI) and positive electrode solid-liquid interface film (CEI), leading to interfacial damage and a series of side reactions. Ultimately, this manifests as a series of problems affecting the battery's high-temperature performance, including the generation of high-temperature gases, reduced high-temperature capacity, cycle decay, and increased DC resistance (DCR).

[0022] The inventors of this invention have discovered that by using a perfluoro solvent (i.e., all solvents are fluorinated solvents) as the solvent for the electrolyte, and by using triallyl isocyanurate as an additive to the perfluoro solvent, a stable protective film can be formed at the interface between the sheet and the electrolyte when the electrolyte is applied to a high-voltage lithium-ion battery, thereby ensuring the stability of the interface between the sheet and the electrolyte and improving the electrical performance of the high-voltage battery. Furthermore, by using a combination of high-pressure resistant 1-propene 1,3-sultone (PST) and triallyl isocyanurate (TAIC) as additives to the perfluoro solvent, when this electrolyte is applied to a lithium-ion battery, 1-propene 1,3-sultone and triallyl isocyanurate effectively contribute to the formation of a protective film that remains stable even at high temperatures, significantly improving the stability of the electrolyte during high-temperature cycles. In addition, the DC resistance of the battery can be reduced, improving the high-temperature cycle stability and high-temperature storage capacity retention rate of the battery.

[0023] The present invention provides an electrolyte comprising a solvent, a lithium salt, and an additive, wherein the solvent is a fluorinated solvent and the additive contains triallyl isocyanurate. More specifically, the solvent is a fluorinated solvent, that is, the solvent in the electrolyte is a perfluoro solvent. The fluorinated solvent exhibits excellent high-voltage stability and can ensure the stability of the electrolyte interface on the positive electrode side. The structural formula of triallyl isocyanurate is as follows. [ka]

[0024] In the electrolyte of the embodiment of the present invention, by adding triallyl isocyanurate as an additive to the perfluoro solvent, when this electrolyte is applied to a high-voltage lithium-ion battery, the triallyl isocyanurate can form a protective film at the interface between the sheet (including the positive electrode sheet and the negative electrode sheet) and the electrolyte that is less susceptible to swelling by the perfluoro solvent. This protective film ensures the stability of the interface between the sheet and the electrolyte, thereby improving the electrical performance of the high-voltage battery.

[0025] In some embodiments, the additive further includes 1-propene-1,3-sultone. When 1-propene-1,3-sultone and triallyl isocyanurate are used in combination as additives in a perfluoro solvent, and the electrolyte is applied to the battery, 1-propene-1,3-sultone and triallyl isocyanurate can form a protective film that remains stable even at high temperatures at the interface between the sheets (including the positive and negative electrode sheets) and the electrolyte, significantly improving the stability of the electrolyte during high-temperature cycles. Furthermore, since 1-propene-1,3-sultone and triallyl isocyanurate can form a protective film on the negative electrode sheet, the electrolyte can have a certain degree of reduction resistance stability on the negative electrode side of the battery. Moreover, the protective film formed on the negative electrode side of the electrolyte is also called the negative electrode side solid-liquid interface film (SEI), and the negative electrode side solid-liquid interface film can effectively protect the contact interface between the negative electrode sheet and the electrolyte, thereby reducing side reactions of the electrolyte and ensuring stable battery cycles. Furthermore, the protective film formed on the positive electrode side of the electrolyte is also called the positive electrode solid-liquid interface film (CEI). The positive electrode solid-liquid interface film can effectively protect the contact interface between the positive electrode sheet and the electrolyte, thereby reducing side reactions of the electrolyte and ensuring a stable battery cycle.

[0026] In detail, TAIC itself contains unsaturated olefin functional groups, and PST is a sulfonate system containing unsaturated hydrocarbons. When PST is used alone as an additive to the perfluoro solvent without using TAIC as an additive, the concentration of sulfonic acid bases in the sulfur-containing protective film formed after the polymerization of PST increases. Since carbonates in the fluorinating solvent have a strong structural correlation with sulfonates, the polymer structure of PST easily swells due to the carbonates, causing the protective film to expand, exposing several new interfaces that react further with the electrolyte. This protective film is insufficient to protect the sheet and is unstable. Therefore, compared to using PST alone as an additive to the perfluoro solvent, adding triallyl isocyanurate as an additive to the perfluoro solvent allows TAIC to form an nitrogen-containing protective film at the interface between the sheet and the electrolyte that is less susceptible to swelling by carbonates in the fluorinating solvent. This sufficiently protects the sheet, ensuring the stability of the interface between the sheet and the electrolyte and improving the electrical performance of the high-voltage battery.

[0027] However, when TAIC is used alone as an additive in a perfluoro solvent, the thermal stability of the 6-membered amide of TAIC is low. Therefore, even if TAIC forms an N-containing protective film that is less prone to swelling by carbonates in the perfluoro solvent, this protective film is unstable with respect to heat. In the electrolyte of the embodiment of the present invention, the stability of the protective film at high temperatures can be improved by further including 1-propene 1,3-sultone as an additive. Specifically, since both 1-propene 1,3-sultone and triallyl isocyanurate are additives containing unsaturated functional groups, when the electrolyte of the present invention containing both 1-propene 1,3-sultone and triallyl isocyanurate is applied to a battery, both 1-propene 1,3-sultone and triallyl isocyanurate form films on both the positive electrode sheet side and the negative electrode sheet side. When both are used together, a long-chain copolymer protective film containing N and S can be formed. Compared to a short-chain polymer protective film formed using TAIC or PST alone, this long-chain copolymer protective film can achieve improved thermal stability and reduced swelling. Therefore, compared to electrolytes containing fluorinated solvents in conventional technology, when the electrolyte of the embodiment of the present invention is applied to a battery, a protective film that remains stable even at high temperatures is formed at the interface between the sheet and the electrolyte, thereby improving the high-temperature cycle stability and high-temperature storage capacity retention rate of the battery.

[0028] In some embodiments, the mass of 1-propene-1,3-sultone accounts for 0.01% to 1% of the total electrolyte mass, and the mass of triallyl isocyanurate accounts for 0.01% to 1% of the total electrolyte mass. In embodiments of the present invention, by adding appropriate masses of TAIC and PST, it is possible to ensure that the two additives form a copolymer protective film that remains stable even at high temperatures on the positive and negative electrode sides. The concentration ratio of short-chain polymers formed using TAIC or PST alone in the long-chain copolymer protective film is reduced, thereby improving thermal stability and reducing the swelling capacity of the protective film. However, if the amounts of both TAIC and PST added are too large, the thickness of the protective film will grow excessively, increasing the DC resistance of the battery and causing a decrease in high-temperature capacity and cycle life. In some embodiments, the mass of 1-propene-1,3-sultone accounts for 0.5% of the total electrolyte mass. In some embodiments, the mass of triallyl isocyanurate accounts for 0.5% of the total electrolyte mass.

[0029] In some embodiments, the fluorinating solvent includes fluoroethyl methyl carbonate (FEMC). The structural formula of fluoroethyl methyl carbonate is as follows: [ka]

[0030] In a further embodiment in which the fluorinating solvent contains fluoroethyl methyl carbonate, the fluorinating solvent further contains fluoroethylene carbonate (FEC). In an embodiment in which the fluorinating solvent is a fluorinated carbonate solvent, the fluorinated carbonate solvent has good high-voltage stability, thus ensuring interface stability of the electrolyte on the positive electrode side. In a further embodiment, the mass ratio of fluoroethyl methyl carbonate to fluoroethylene carbonate is 7:3 to 10:0. In a further embodiment, the mass ratio of fluoroethyl methyl carbonate to fluoroethylene carbonate is 7:3. If the proportion of fluoroethyl methyl carbonate in the solvent is high and the proportion of fluoroethylene carbonate is low, the fluoroethyl methyl carbonate is likely to decompose at the interface between the sheet and the electrolyte, which generates a large amount of by-products that are unstable at high temperatures, reducing the high-temperature performance of the battery. Therefore, maintaining the mass ratio of fluoroethyl methyl carbonate to fluoroethylene carbonate at 7:3 to 10:0 improves the high-temperature cycle stability and high-temperature storage capacity retention rate of the battery. Furthermore, when the mass ratio of fluoroethylmethyl carbonate to fluoroethylene carbonate is 7:3, the high-temperature cycle stability and high-temperature storage capacity retention rate of the battery are most favorable.

[0031] In some embodiments, the mass of the lithium salt is 12% to 20% of the total mass of the electrolyte. In some other embodiments, the lithium salt may be one or more of the following: lithium hexafluoride phosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetraborate (LiBF4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium hexafluoride arsenate (LiAsF6), lithium antimonate hexafluoride (LiSbF6), lithium perchlorate (LiClO4), Li[BF2(C2O4)], Li[PF2(C2O4)2], Li[N(CF3SO2)2], Li[C(CF3SO2)3], lithium boroate difluoride oxalate (LiODFB), lithium boroate dioxalate (LiBOB), and lithium phosphate difluoride (LiPO2F2). In some embodiments, the lithium salt may be LiPF6, with the mass of LiPF6 being 13% of the total mass of the electrolyte. In some embodiments, the lithium salt may include LiPF6 and bis(fluorosulfonyl)imide lithium (LiFSI), with the mass of the lithium salt being 12% to 20% of the total mass of the electrolyte and the mass of LiPF6 being 8% to 20% of the total mass of the electrolyte. In some embodiments, the additive further includes vinylene carbonate (VC), which contributes to the formation of the negative electrode film.

[0032] According to another aspect of the present invention, there is provided a lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator between the positive electrode sheet and the negative electrode sheet, and the above-mentioned electrolytic solution. Since the electrolytic solution is applied in this lithium ion battery, by using a fluorinated solvent as the solvent and triallyl isocyanurate as an additive, the electrolytic solution can form a stable protective film at the interface between the sheets of the lithium ion battery (including the positive electrode sheet and the negative electrode sheet) and the electrolytic solution, ensure the stability of the interface between the sheets and the electrolytic solution, and improve the electrical performance of high-voltage batteries. In some embodiments, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material disposed on the positive electrode current collector, the positive electrode active material comprises lithium nickel manganese oxide, and the chemical formula of the lithium nickel manganese oxide is Li a Ni x Mn y O 4‐z M z , wherein 0.90≤a≤1.10, 0.4≤x≤0.6, 1.4≤y≤1.6, 0≤z≤0.1, and the element M is one or more selected from the group consisting of Cl, Br, I, S, Se, Te and F. In some embodiments, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material disposed on the negative electrode current collector, and the negative electrode active material comprises artificial graphite.

[0033] Positive electrode sheet The positive electrode sheet of the lithium-ion battery provided in the present invention includes a positive electrode current collector and a positive electrode material layer provided on the positive electrode current collector. The positive electrode material layer includes a positive electrode active material capable of intercalating and releasing lithium (Li) (hereinafter also referred to as "positive electrode material capable of intercalating / releasing lithium Li"). Examples of positive electrode active materials capable of intercalating / releasing lithium (Li) include lithium nickel manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium iron phosphate, lithium titanate, and lithium-rich manganese-based materials. The positive electrode current collector can be, for example, aluminum foil or nickel foil, but other positive electrode current collectors commonly used in the art can also be used. In some embodiments, the positive electrode material layer may further include a positive electrode conductive agent and a positive electrode binder. In some embodiments, the positive electrode conductive agent is one of conductive carbon black (Super P), acetylene black, nanometal powder, carbon nanotubes, graphene, or a mixture thereof. In some embodiments, the positive electrode binder is one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, sodium carboxymethylcellulose, and styrene-butadiene rubber, or a mixture thereof.

[0034] electrolyte The electrolyte of the lithium-ion battery provided in the present invention comprises a lithium salt, an organic solvent, and additives. The organic solvent is a fluorinated solvent, and the additives include 1-propene-1,3-sultone and triallyl isocyanurate. Preferably, the mass of 1-propene-1,3-sultone accounts for 0.01% to 1% of the total mass of the electrolyte, and the mass of triallyl isocyanurate accounts for 0.01% to 1% of the total mass of the electrolyte. Preferably, the additive further comprises vinylene carbonate (VC).

[0035] The fluorinating solvent may be any common fluorinating solvent in this field, for example, fluoroethyl methyl carbonate (FEMC) is included as the fluorinating solvent. Preferably, the fluorinating solvent further includes fluoroethylene carbonate (FEC).

[0036] The lithium salt may be a general lithium salt in this field. For example, the lithium salt may include LiPF6 and lithium bisfluorosulfonylimide (LiFSI), with the lithium salt accounting for 12% to 20% of the total mass of the electrolyte and the LiPF6 accounting for 8% to 20% of the total mass of the electrolyte.

[0037] Negative electrode sheet The negative electrode sheet of the lithium-ion battery provided in the present invention includes a negative electrode current collector and a negative electrode active material provided on the negative electrode current collector. In some embodiments, the negative electrode current collector may be copper foil. In some embodiments, the negative electrode active material includes a negative electrode activator, a negative electrode conductive agent, a negative electrode binder, and a negative electrode thickener.

[0038] Negative electrode active materials include negative electrode materials capable of intercalating and releasing lithium (Li) (hereinafter also referred to as "negative electrode materials capable of intercalating / releasing lithium Li"). Examples of negative electrode materials capable of intercalating / releasing lithium (Li) include carbon materials, metal compounds, oxides, sulfides, lithium nitrides such as LiN3, lithium metal, metals that form alloys with lithium, and polymer materials.

[0039] Carbon materials include low-graphitizable carbon, easily graphitizable carbon, artificial graphite, natural graphite, mesocarbon microspheres, soft carbon, hard carbon, pyrolysis carbon, coke, glassy carbon, organic polymer compound sintered bodies, carbon fibers, and activated carbon. Among these, coke includes pitch coke, needle coke, and petroleum coke. Organic polymer compound sintered bodies are materials obtained by carbonizing polymer materials such as phenolic resins and furan resins by firing them at an appropriate temperature, and some of these materials can be classified as low-graphitizable carbon or easily graphitizable carbon. Examples of polymer materials include polyacetylene and polypyrrole.

[0040] Among these negative electrode materials capable of intercalating and releasing lithium (Li), materials with charge-discharge voltages close to those of lithium metal are selected. This is because a lower charge-discharge voltage for the negative electrode material makes it easier to increase the energy density of the electrochemical device (such as a secondary battery). Carbon materials can be selected as negative electrode materials because their crystal structure undergoes only small changes during charging and discharging, resulting in good cycle characteristics and a large charge-discharge capacity. Graphite, in particular, is selected because it can provide a large electrochemical equivalent and high energy density.

[0041] Furthermore, negative electrode materials capable of intercalating / releasing lithium (Li) include elemental lithium, metallic elements capable of forming alloys with lithium (Li), metalloid elements, alloys containing these elements, and compounds. In particular, these are often used in combination with carbon materials, as this results in good cycle characteristics and high energy density. The alloys used here include not only alloys containing two or more metallic elements, but also alloys containing one or more metallic elements and one or more metalloid elements. These alloys may be in the form of solid solutions, eutectic crystals (eutectic mixtures), intermetallic compounds, and mixtures thereof.

[0042] Examples of metallic and metalloid elements include tin (Sn), lead (Pb), aluminum (Al), indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y), and hafnium (Hf). Examples of the above alloys and compounds include those with the chemical formula: Ma s Mb t Li u A material having the chemical formula: Ma p Mc q Md r Examples of materials having the following characteristics are given. In these chemical formulas, Ma represents at least one metallic element and metalloid element capable of forming an alloy with lithium, Mb represents at least one metallic element and metalloid element other than lithium and Ma, Mc represents at least one nonmetallic element, Md represents at least one metallic element and metalloid element other than Ma, and s, t, u, p, q, and r satisfy s>0, t≧0, u≧0, p>0, q>0, and r≧0.

[0043] Furthermore, the negative electrode contains MnO2, V2O5, and V6O 13 Inorganic compounds that do not contain lithium (Li), such as NiS and MoS, can be used.

[0044] In some embodiments, the negative electrode conductive agent is one or a mixture of Super P, acetylene black, nanosilver powder, carbon nanotubes, and graphene. In some embodiments, the negative electrode binder is one or a mixture of vinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, and styrene-butadiene rubber (SBR). In some embodiments, the negative electrode thickener may be one or more of polyvinylpyrrolidone (PVP), sodium carboxymethylcellulose (CMC-Na), and polyvinyl alcohol (PVA).

[0045] Isolation film The isolation film of the lithium-ion battery provided in the present invention is located between the positive electrode sheet and the negative electrode sheet. For example, the isolation film includes an isolation film between a base layer and a surface treatment layer. The base layer is a nonwoven fabric, film, or composite film having a porous structure, and the material of the base layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene nonwoven fabric, polyethylene nonwoven fabric, polypropylene-polyethylene-polypropylene composite porous film, etc., can be selected. A surface treatment layer is provided on at least one surface of the base layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer layer and an inorganic layer.

[0046] Lithium-ion battery The above-mentioned positive electrode sheet, negative electrode sheet, electrolyte, and isolation film can be assembled into a lithium-ion battery using methods commonly used in this field. The positive electrode sheet, isolation film, negative electrode sheet, etc., are wrapped or stacked in sequence to form a bare cell, which is then sealed and packaged, for example, in an aluminum plastic film. After the electrolyte is injected, the battery is molded, packaged, and tested, and then electrochemical performance tests and cycle performance tests are performed on the assembled lithium-ion battery.

[0047] Those skilled in the art will understand that the above-described method for manufacturing lithium-ion batteries is merely one example. Other methods commonly used in the art can be employed without departing from the disclosure of this invention.

[0048] The method for manufacturing a lithium-ion battery is described below. The lithium-ion battery in this invention may be a primary lithium battery or a secondary lithium battery. In the following description, lithium nickel manganese oxide will be used as an example of the positive electrode active material. The positive electrode active material of this invention is not limited to this. The method for manufacturing a secondary lithium battery is as follows. (1) The manufacturing of the positive electrode sheet includes the following steps: Li 0.98 Ni 0.45 Mn 1.55 A positive electrode slurry is obtained by stirring a positive electrode active material such as O4, a positive electrode conductive agent such as Super P, a positive electrode binder such as PVDF, and the solvent N-methylpyrrolidone (NMP) in a constant mass ratio using a vacuum mixer until the mixture becomes uniform and transparent. The mass ratios of the positive electrode active material, positive electrode conductive agent, and positive electrode binder components are: positive electrode active material: 93%~98.5%, positive electrode conductive agent: 0.5%~3%, positive electrode binder: 0.5%~4%, and NMP is added so that the proportion of positive electrode material is 45%~70% of the total mass of the positive electrode slurry. Next, the positive electrode slurry is uniformly applied to a positive electrode current collector, and a positive electrode sheet is obtained through processes such as drying, rolling, and cutting. (2) Manufacturing of negative electrode sheets After mixing the components of the negative electrode material, deionized water is added and the mixture is thoroughly stirred and mixed in a vacuum mixer to prepare the negative electrode slurry. The mass ratio of each component of the negative electrode material is as follows: negative electrode active substance: 94%~98%, negative electrode conductive agent: 0.2%~1.5%, negative electrode thickener: 0.01~1.5%, and negative electrode binder: 1%~3%. Deionized water is added so that the proportion of the negative electrode material becomes 45%~70% of the total mass of the negative electrode slurry. Next, the negative electrode slurry is uniformly applied to the negative electrode current collector, and a negative electrode sheet is obtained through processes such as drying, rolling, and cutting. (3) Manufacturing of electrolyte In an argon-atmosphered glove box with a moisture content of <10 ppm, battery-grade fluoroethyl methyl carbonate and fluoroethylene carbonate are mixed to form an organic solvent. Then, a lithium salt and appropriate additives are added to the organic solvent and mixed uniformly to obtain an electrolyte. Lithium salt, 1-propene-1,3-sultone, and triallyl isocyanurate can be added as needed. (4) Manufacturing of isolation film Any of the above-mentioned isolation films may be used. (5) Manufacturing of lithium-ion batteries The positive electrode sheet, isolation film, and negative electrode sheet manufactured as described above are sequentially laminated or wound to obtain electrode components, and the isolation film is placed between the positive electrode sheet and the negative electrode sheet to provide isolation. The electrode components are wrapped in aluminum plastic film, dried, injected with electrolyte, packaged, molded, left to stand, and molded again to manufacture a lithium-ion battery.

[0049] Those skilled in the art will understand that the above-described method for manufacturing lithium-ion batteries is merely one example. Other methods commonly used in the art can be employed without departing from the disclosure of this invention.

[0050] The present invention will be further described below with reference to several specific embodiments and comparative examples. [Examples]

[0051] Example 1 (1) Manufacturing of positive electrode sheets Cathode active material: Li 0.98 Ni 0.45 Mn 1.55 A positive electrode slurry was obtained by stirring O4, a positive electrode binder (polyvinylidene fluoride (PVDF)), a positive electrode conductive agent (conductive carbon black (Super P)), and a solvent (N-methylpyrrolidone (NMP)) in a constant mass ratio using a vacuum mixer until the mixture was uniform and transparent. The mass ratio of the positive electrode active material, positive electrode binder, and positive electrode conductive agent was 98:1:1. NMP was added so that the proportion of positive electrode material was 50% of the total mass of the positive electrode slurry. Next, the positive electrode slurry was uniformly applied to a positive electrode current collector (aluminum foil), and a positive electrode sheet was obtained by processes such as drying, rolling, and cutting. (2) Manufacturing of negative electrode sheets After mixing the components of the negative electrode material, deionized water was added and the mixture was thoroughly stirred and mixed in a vacuum mixer to prepare the negative electrode slurry. The mass ratio of the components of the negative electrode material—negative electrode active substance: artificial graphite, conductive carbon black (super P), negative electrode thickener: sodium carboxymethylcellulose (CMC-Na), and negative electrode binder: styrene-butadiene rubber (SBR)—was 96:1:1:2, and deionized water was added so that the proportion of the negative electrode material was 50% of the total mass of the negative electrode slurry. Next, the negative electrode slurry was uniformly applied to a negative electrode current collector: copper foil, and a negative electrode sheet was obtained by drying, rolling, and cutting. (3) Manufacturing of electrolyte In an argon-atmosphered glove box with a moisture content of <10 ppm, battery-grade fluoroethyl methyl carbonate and fluoroethylene carbonate were mixed to form an organic solvent. The ratio of battery-grade fluoroethyl methyl carbonate to fluoroethylene carbonate was 7:3. Subsequently, a lithium salt and a suitable additive were added to the organic solvent and mixed uniformly to obtain an electrolyte. The lithium salt was LiPF6, and its mass was 13% of the total mass of the electrolyte. The additive was triallyl isocyanurate, and its mass was 0.01% of the total mass of the electrolyte. (4) Manufacturing of isolation film A 12 μm thick polypropylene (PP) film was used as the isolation film. (5) Manufacturing of lithium-ion batteries The positive electrode sheet, isolation film, and negative electrode sheet manufactured as described above were sequentially stacked to obtain an electrode component, and the isolation film was placed between the positive and negative electrode sheets to provide isolation. The electrode component was wrapped in aluminum plastic film, transferred to a vacuum oven and dried at 120°C, and after injecting the electrolyte solution manufactured as described above (3.0 g / Ah), a lithium-ion battery with a capacity of 1 Ah was manufactured through processes such as packaging, molding, and standing.

[0052] Example 2 The manufacturing method is the same as in Example 1, but differs in that the mass of triallyl isocyanurate in Example 2 is 0.5% of the total mass of the electrolyte.

[0053] Example 3 The manufacturing method in Example 3 is the same as that in Example 1, but differs in that the mass of triallyl isocyanurate in Example 3 is 1% of the total mass of the electrolyte.

[0054] Example 4 The manufacturing method is the same as in Example 1, but the difference is that the additives in Example 4 are triallyl isocyanurate and 1-propene 1,3-sultone, the mass of triallyl isocyanurate is 0.5% of the total mass of the electrolyte, and the mass of 1-propene 1,3-sultone is 0.01% of the total mass of the electrolyte.

[0055] Example 5 The manufacturing method is the same as in Example 4, but differs in that the mass of triallyl isocyanurate in Example 5 is 0.5% of the total mass of the electrolyte, and the mass of 1-propene 1,3-sultone is 0.5% of the total mass of the electrolyte.

[0056] Example 6 The manufacturing method is the same as in Example 4, but differs in that the mass of triallyl isocyanurate in Example 6 is 0.5% of the total mass of the electrolyte, and the mass of 1-propene 1,3-sultone is 1% of the total mass of the electrolyte.

[0057] Example 7 The manufacturing method is the same as in Example 5, but the difference is that the ratio of fluoroethyl methyl carbonate to fluoroethylene carbonate in Example 7 is 8:2.

[0058] Example 8 The manufacturing method is the same as in Example 5, but the difference is that the ratio of fluoroethyl methyl carbonate to fluoroethylene carbonate in Example 8 is 9:1.

[0059] Example 9 The manufacturing method in Example 9 is the same as that in Example 5, but differs in that the ratio of fluoroethyl methyl carbonate to fluoroethylene carbonate in Example 9 is 10:0. In other words, the electrolyte produced in Example 9 does not contain fluoroethylene carbonate.

[0060] Comparative Example 1 The manufacturing method is the same as in Example 1, but differs in that it does not contain triallyl isocyanurate, which is the electrolyte of Comparative Example 1.

[0061] Comparative Example 2 The manufacturing method is the same as in Example 1, but Comparative Example 2 differs in that the electrolyte does not contain triallyl isocyanurate, the additive is vinylene carbonate (VC), and the mass of vinylene carbonate is 0.5% of the total mass of the electrolyte.

[0062] Comparative Example 3 The manufacturing method is the same as in Example 1, but Comparative Example 3 differs in that the electrolyte does not contain triallyl isocyanurate, the additives are vinylene carbonate (VC) and ethylene sulfate (DTD), the mass of vinylene carbonate is 0.5% of the total mass of the electrolyte, and the mass of ethylene sulfate is 0.5% of the total mass of the electrolyte.

[0063] Comparative Example 4 The manufacturing method is the same as that of Example 1, but Comparative Example 4 differs in that the electrolyte does not contain triallyl isocyanurate, the additive is 1-propene 1,3-sultone, and the mass of 1-propene 1,3-sultone is 0.01% of the total mass of the electrolyte.

[0064] Comparative Example 5 The manufacturing method is the same as that of Comparative Example 4, but it differs in that the mass of 1-propene-1,3-sultone in the electrolyte of Comparative Example 5 is 0.5% of the total mass of the electrolyte.

[0065] Comparative Example 6 The manufacturing method is the same as that of Comparative Example 4, but the difference is that the mass of 1-propene-1,3-sultone in the electrolyte of Comparative Example 6 is 1% of the total mass of the electrolyte.

[0066] Subsequently, the lithium-ion batteries of the examples and comparative examples were subjected to the following tests. The specific test methods are as follows. (1) DC resistance (DCR) test of lithium-ion batteries at 25°C At the specified temperature, the battery is discharged to 50% SOC (state of charge, reflecting the remaining battery capacity) with a current of 1C. Then, the current is increased to 4C and maintained for 30 seconds. The difference between the updated stable voltage and the original platform voltage is detected, and the ratio of this value to the 4C current value is the battery's DC resistance. The DCR test result performed after the battery's first full charge is the battery's initial DCR. (2) Capacity retention rate of lithium-ion batteries during high-temperature storage (60°C) After fully charging lithium-ion batteries, they were placed in a 60°C constant temperature box for 15 days. After sufficient cooling, they were discharged at a rate of 1C to the cutoff voltage, and the ratio of capacity to initial discharge capacity was compared. (3) High-temperature 45°C cycle test The battery was periodically charged and discharged at 45°C, with a charge / discharge cutoff voltage range of 3.4V to 4.85V. The charge / discharge rate was 0.5C / 1C, and the discharge capacity for each cycle was recorded. The test ended when the battery capacity reached 80% SOC (State of Charge), and the actual number of cycles achieved was recorded.

[0067] To provide a clearer explanation, Table 1 shows the composition of the electrolytes for the examples and comparative examples.

[0068] [Table 1]

[0069] Table 2 shows the experimental results for Examples 1-9 and Comparative Examples 1-6.

[0070] [Table 2]

[0071] Based on the analysis of the above data, the following conclusions were reached. As can be seen from Comparative Examples 1-3 and Examples 1-3, compared to Comparative Examples 1-3, which used no additive in the perfluoro solvent or used other additives (e.g., VC in Comparative Example 2) alone, the high-temperature performance of the lithium-ion batteries in Examples 1-3, in which TAIC was added to the perfluoro solvent, showed a certain degree of improvement. For example, the number of high-temperature cycles increased significantly, and the DC resistance (DCR) decreased significantly.

[0072] As can be seen by comparing Comparative Examples 4-6 with Examples 1-3, while Comparative Examples 4-6 used a perfluoro solvent with 1-propene 1,3-sultone additive added alone, Examples 1-3 had TAIC added to the perfluoro solvent of the electrolyte. When this electrolyte was applied to a high-voltage lithium-ion battery, both the high-temperature capacity retention rate and the number of high-temperature cycles of the battery improved to a certain extent. This is because when 1-propene 1,3-sultone is used alone as an additive, the protective film formed by 1-propene 1,3-sultone swells and becomes unstable, whereas the protective film formed by TAIC in the examples of the present invention is stable, adequately protecting the sheet and ensuring the stability of the interface between the sheet and the electrolyte, thereby improving the electrical performance of the high-voltage battery.

[0073] As can be seen by comparing Comparative Examples 4-6 and Examples 1-3 with Examples 4-6, when 1-propene 1,3-sultone and triallyl isocyanurate are used as additives in combination with the perfluoro solvent, both the high-temperature storage capacity retention rate and the number of high-temperature cycles of the battery are significantly improved. For example, in Example 5, the DC resistance decreased to 60 mΩ, the high-temperature storage capacity retention rate increased to 96%, and the number of high-temperature cycles increased to 500. This is because when a perfluoro solvent is used as the electrolyte, 1-propene 1,3-sultone and triallyl isocyanurate, which have high voltage resistance, are used as additives in combination. Since both 1-propene-1,3-sultone and triallyl isocyanurate form a long-chain copolymer protective film on both the positive and negative electrode sheets, this long-chain copolymer protective film is more stable at high temperatures compared to short-chain polymer protective films formed using TAIC (Examples 1-3) or PST (Comparative Examples 4-6) alone, significantly improving the high-temperature cycle count and high-temperature storage capacity retention rate of the battery.

[0074] Referring to Examples 1-3, the mass of triallyl isocyanurate is limited to 0.01% to 1% of the total mass of the electrolyte. In this case, the high-temperature cycle count retention rate of the lithium-ion battery is good. For example, in Example 2, the high-temperature cycle count improved to 407. When the amount of TAIC added is increased from 0.01% to 0.5% (see Examples 1 and 2), the high-temperature storage capacity retention rate and high-temperature cycle count of the battery increase, and it can be seen that the protective film formed by the TAIC additive stabilizes under high-temperature conditions and the reaction at the solid-liquid interface decreases. However, when the amount of TAIC added reaches 1%, the high-temperature cycle performance of the battery decreases to a certain extent compared to the case where the amount of TAIC added is 0.5%. The battery performance is most preferable when the mass of triallyl isocyanurate is 0.5% of the total mass of the electrolyte.

[0075] Furthermore, referring to Examples 4 to 6, the mass of 1-propene-1,3-sultone is limited to 0.01% to 1% of the total mass of the electrolyte, and in this case, the DC resistance, high-temperature cycle count, and high-temperature storage capacity retention rate of the lithium-ion battery are all good. For example, in Example 5, the DC resistance decreased to 60 mΩ, the high-temperature storage capacity retention rate improved to 96%, and the high-temperature cycle count increased to 500. If too much 1-propene-1,3-sultone is added, the protective film grows excessively due to the large amount of 1-propene-1,3-sultone, forming an excessively thick protective film, which increases the DCR of the lithium-ion battery and leads to a decrease in high-temperature capacity and cycle life of the lithium-ion battery. The battery performance is most preferable when both the mass of 1-propene-1,3-sultone and the mass of triallyl isocyanurate are 0.5% of the total mass of the electrolyte.

[0076] As can be seen by comparing Examples 5 and 8-9, when the mass of triallyl isocyanurate and the mass of 1-propene 1,3-sultone are both 0.5% of the total mass of the electrolyte, significant changes in battery performance can be made by adjusting each solvent component in the perfluoro solvent. When the proportion of FEMC and the proportion of FEC in the perfluoro solvent were increased and the DCR of the battery increased significantly, the number of high-temperature cycles and the high-temperature storage capacity retention rate of the battery also decreased. This is because when the FEMC content increases, FEMC decomposes at the solid-liquid interface (i.e., the interface between the electrolyte and the sheet), thereby generating a large amount of by-products that are unstable at high temperatures, and these unstable by-products ultimately reduce the high-temperature performance of the battery. The highest high-temperature performance of the battery is most favorable when FEMC:FEC = 7:3.

[0077] As can be seen from Examples 4-5 and Comparative Examples 1-6, the high-temperature performance of the battery deteriorates significantly when the additive triallyl isocyanurate is not used or when other additives (e.g., VC in Comparative Example 2) are used alone, indicating that the combined use of TAIC and PST plays a very important role in the battery. Furthermore, as can be seen from Comparative Examples 1-6 and Examples 1-5, when using a perfluoro solvent, the high-temperature performance of the battery is optimized by using triallyl isocyanurate and 1-propene-1,3-sultone as additives in combination. In the case of conventional combined use of additives VC and DTD, a very large DCR exists in the lithium nickel manganese oxide high-voltage system, making room-temperature cycling impossible and resulting in a loss of capacity after high-temperature storage. This indicates that the combined use of TAIC and PST is essential to ensure the normal operation of the high-voltage system, especially in high-voltage systems where lithium nickel manganese oxide is used as the positive electrode active material and graphene as the negative electrode active material. [Industrial applicability]

[0078] In summary, in the electrolyte of the embodiment of the present invention, by using a perfluoro solvent as the solvent and adding triallyl isocyanurate as an additive to the perfluoro solvent, the electrolyte can not only withstand high voltages, but when this electrolyte is applied to a lithium-ion battery, a stable protective film can be formed at the interface between the sheet and the electrolyte, ensuring the stability of the interface and thereby improving the electrical performance of the high-voltage battery. Furthermore, the present invention allows the use of triallyl isocyanurate and 1-propene 1,3-sultone in combination with a perfluoro solvent-based electrolyte. By adding triallyl isocyanurate and 1-propene 1,3-sultone to the electrolyte in an optimal ratio, they can more effectively contribute to the formation of a stable protective film at the interface between the sheet and the electrolyte, thereby ensuring the stability of the interface between the sheet and the electrolyte at high temperatures, significantly improving the stability of the electrolyte during high-temperature cycles, and comprehensively improving the high-temperature performance of the battery. For example, it can reduce the battery's DCR and improve the battery's high-temperature cycle stability and high-temperature storage capacity retention rate.

[0079] Those skilled in the art should understand that the embodiments described above are merely illustrative and that various changes, substitutions, and modifications can be made without departing from the spirit and scope of the invention.

Claims

1. Solvent and, Lithium salts and Additives containing triallyl isocyanurate, Includes, An electrolyte characterized in that all of the aforementioned solvents are fluorinated solvents.

2. The electrolyte according to claim 1, characterized in that the additive further comprises 1-propene-1,3-sultone.

3. The electrolyte according to claim 2, characterized in that the mass of 1-propene 1,3-sultone accounts for 0.01% to 1% of the total mass of the electrolyte, and the mass of triallyl isocyanurate accounts for 0.01% to 1% of the total mass of the electrolyte.

4. The electrolyte according to claim 1, characterized in that the fluorinated solvent contains fluoroethyl methyl carbonate.

5. The electrolyte according to claim 4, characterized in that the fluorinating solvent further comprises fluoroethylene carbonate.

6. The electrolyte according to claim 5, characterized in that the mass ratio of the fluoroethyl methyl carbonate to the fluoroethylene carbonate is 7:3 to 10:

0.

7. The electrolyte according to claim 1, characterized in that the mass of the lithium salt is 12% to 20% of the total mass of the electrolyte.

8. The electrolyte according to claim 7, characterized in that the lithium salt is one or more of the following: lithium hexafluoride phosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium methanesulfonate, lithium trifluoromethanesulfonate, lithium hexafluoride arsenate, lithium antimonate hexafluoride, lithium perchlorate, lithium difluorooxalate borate, lithium dioxalate borate, and lithium difluorophosphate.

9. A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator between the positive electrode sheet and the negative electrode sheet, and an electrolyte according to any one of claims 1 to 8.

10. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material located in the positive electrode current collector, wherein the positive electrode active material comprises lithium nickel manganese oxide, and the chemical formula of the lithium nickel manganese oxide is Li ａ Ni ｘ Mn ｙ O ４‐ｚ M ｚ The lithium-ion battery according to claim 9, wherein 0.90 ≤ a ≤ 1.10, 0.4 ≤ x ≤ 0.6, 1.4 ≤ y ≤ 1.6, 0 ≤ z ≤ 0.1, and element M is one or more of Cl, Br, I, S, Se, Te, or F.

11. The lithium-ion battery according to claim 10, characterized in that the negative electrode sheet includes a negative electrode current collector and a negative electrode active material located in the negative electrode current collector, and the negative electrode active material includes artificial graphite.

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