Electrolyte and lithium-ion battery

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] The present invention relates to the field of batteries, and more particularly 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, mainly secondary alkali metal ion batteries, has grown explosively. However, the energy density of commercially available secondary alkali metal ion batteries is approaching its theoretical upper limit. In order to fundamentally resolve the range concerns of electric vehicle buyers, an intuitive and feasible solution is to increase the energy density of current batteries and increase the battery voltage.

[0003] Currently, fluorinated solvents such as fluoroethyl methyl carbonate (FEMC) are commonly used as electrolyte solvents to improve the high-voltage resistance of electrolytes. The fluorine atoms in fluorinated solvents have strong electron-withdrawing power, which can further improve the oxidation stability of traditional 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 voltages increase, the requirements for high-voltage resistance of electrolytes also increase. Summary of the Invention [Problem to be solved by the invention]

[0004] In response to the problems in the prior art, the object of the present invention is to provide an electrolyte that can withstand high voltages, 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 object, the present invention provides an electrolyte solution comprising a solvent that is a fluorinated solvent, a lithium salt, and an additive that 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 comprises 0.01% to 1% of the total mass of the electrolyte, and the mass of triallyl isocyanurate comprises 0.01% to 1% of the total mass of the electrolyte.

[0008] In some embodiments, the fluorinated solvent comprises fluoroethyl methyl carbonate.

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

[0010] In some embodiments, the mass ratio of fluoroethyl methyl carbonate to fluoroethylene carbonate is from 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 lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium methanesulfonate, lithium trifluoromethanesulfonate, lithium hexafluoroarsenate, lithium hexafluoroantimonate, lithium perchlorate, lithium difluorooxalate borate, lithium dioxalate borate, and lithium difluorophosphate.

[0013] The present invention provides a lithium-ion battery including an electrolyte capable of withstanding high voltages, the electrolyte forming 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 also provides a lithium-ion battery including a positive electrode sheet, a negative electrode sheet, a separator between the positive electrode sheet and the negative electrode sheet, and the electrolyte of any of the above embodiments.

[0014] In some embodiments, the positive electrode sheet includes a positive electrode current collector and an active positive electrode material on the positive electrode current collector, the active positive electrode material including lithium nickel manganese oxide, the chemical formula of which is Li a Ni x Mn y O 4‐z M z where 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] Some embodiments include a negative electrode current collector and a negative electrode active material on the negative electrode current collector, the negative electrode active material including artificial graphite. [Effects of the Invention]

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

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

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

[0019] Since the electrolyte solution of the present invention uses a fluorinated solvent as the solvent and contains triallyl isocyanurate as an additive, the electrolyte solution of the present invention can form a stable protective film at the interface between the sheet and the electrolyte solution of a lithium ion battery, ensuring the stability of the interface between the sheet and the electrolyte solution, and improving the stability and electrical performance of high-voltage batteries. DETAILED DESCRIPTION OF THE INVENTION

[0020] Although exemplary embodiments are described in detail below, these exemplary embodiments may be implemented in different ways and should not be construed as limiting the present invention to the embodiments described herein. Rather, the purpose of providing these embodiments is to ensure that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. If specific techniques or conditions are not described in the embodiments, they should be construed as referring to techniques or conditions described in the literature in this field or in the product instructions. Reagents, instruments, etc. for which manufacturer names are not specified are all conventional products that can be purchased through ordinary channels.

[0021] Fluorinated solvents, such as fluorinated carbonate solvents, are important solvent components in high-voltage battery systems, providing excellent high-voltage stability and ensuring the interfacial stability of the cathode electrolyte. 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, the fluorine atoms in fluorinated solvents are easily cleaved at high temperatures. These cleaved fluorine atoms react with active hydrogen in the electrolyte to generate hydrofluoric acid (HF), which corrodes the alkaline materials in the anode solid-liquid interfacial film (SEI) and cathode solid-liquid interfacial film (CEI). This leads to interfacial damage and a series of side reactions, ultimately resulting in a series of problems, such as high-temperature gas generation, reduced high-temperature capacity, cycle decay, and increased direct current resistance (DCR), affecting the battery's high-temperature performance.

[0022] The inventors of the present invention have discovered that by using a perfluorosolvent (i.e., all solvents are fluorinated) as the electrolyte solvent and adding triallyl isocyanurate to the perfluorosolvent as an additive, 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, ensuring the stability of the interface between the sheet and the electrolyte and improving the electrical performance of the high-voltage battery. Furthermore, the perfluorosolvent can also be combined with high-pressure-resistant additives 1-propene-1,3-sultone (PST) and triallyl isocyanurate (TAIC). 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 is stable even at high temperatures, significantly improving the stability of the electrolyte during high-temperature cycling. Furthermore, the DC resistance of the battery can be reduced, and the high-temperature cycle stability and high-temperature storage capacity retention of the battery can be improved.

[0023] The present invention provides an electrolyte solution, which includes a solvent, a lithium salt, and an additive, wherein the solvent is a fluorinated solvent, and the additive includes triallyl isocyanurate. Specifically, the solvent is a fluorinated solvent, i.e., the solvent in the electrolyte solution is a perfluorosolvent. The fluorinated solvent has 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 solution of the embodiment of the present invention, triallyl isocyanurate is added as an additive to a perfluorosolvent. When this electrolyte solution is applied to a high-voltage lithium-ion battery, the triallyl isocyanurate can form a protective film that is resistant to swelling by the perfluorosolvent at the interface between the sheet (including the positive electrode sheet and the negative electrode sheet) and the electrolyte solution. This protective film can ensure the stability of the interface between the sheet and the electrolyte solution, thereby improving the electrical performance of the high-voltage battery.

[0025] In some embodiments, the additive further comprises 1-propene-1,3-sultone. When the perfluorosolvent is combined with 1-propene-1,3-sultone and triallyl isocyanurate as additives, the 1-propene-1,3-sultone and triallyl isocyanurate can form a protective film that is stable even at high temperatures at the interface between the sheet (including the positive electrode sheet and the negative electrode sheet) and the electrolyte, significantly improving the stability of the electrolyte during high-temperature cycling. Furthermore, because 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. Furthermore, the protective film formed on the negative electrode side of the electrolyte is also called the negative electrode solid-liquid interfacial film (SEI). This negative electrode solid-liquid interfacial film can effectively protect the contact interface between the negative electrode sheet and the electrolyte, thereby reducing side reactions in the electrolyte and ensuring stable battery cycling. The protective film formed on the positive electrode side of the electrolyte is also called the positive electrode solid-liquid interfacial film (CEI). The positive electrode solid-liquid interfacial film can effectively protect the contact interface between the positive electrode sheet and the electrolyte, thereby reducing side reactions in the electrolyte and ensuring a stable battery cycle.

[0026] Specifically, TAIC itself contains unsaturated olefin functional groups, while PST is a sulfonate salt containing unsaturated hydrocarbons. When PST is used alone in a perfluorosolvent without TAIC as an additive, the sulfonate group concentration in the S-containing protective film formed after PST polymerization is high. Because carbonates in fluorinated solvents have a strong structural correlation with sulfonates, the PST polymer structure is easily swollen by carbonates, causing the protective film to expand and expose new interfaces for further reaction with the electrolyte. This protective film is insufficient to protect the sheet and is unstable. Therefore, compared to the use of PST alone in a perfluorosolvent, the addition of triallyl isocyanurate as an additive to a perfluorosolvent allows TAIC to form an N-containing protective film at the interface between the sheet and the electrolyte that is less susceptible to swelling by carbonates in the fluorinated solvent. This provides sufficient protection for the sheet, ensuring the stability of the interface between the sheet and the electrolyte and improving the electrical performance of high-voltage batteries.

[0027] However, when TAIC is used alone as an additive in a perfluorosolvent, the 6-membered cyclic amide of TAIC has low thermal stability. Even if TAIC forms an N-containing protective film that is resistant to swelling due to carbonate in the perfluorosolvent, the protective film is unstable to heat. In the electrolyte of an embodiment of the present invention, the additive further contains 1-propene-1,3-sultone, which can improve the stability of the protective film at high temperatures. 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 and negative electrode sheets. When the two are used together, a long-chain copolymer protective film containing N and S can be formed. Compared to short-chain polymer protective films formed using TAIC or PST alone, this long-chain copolymer protective film has improved thermal stability and reduced swelling. Therefore, compared to conventional electrolyte solutions containing fluorinated solvents, when the electrolyte solution of the embodiment of the present invention is applied to a battery, a protective film that is stable even at high temperatures is formed at the interface between the sheet and the electrolyte solution, thereby improving the high-temperature cycle stability and high-temperature storage capacity retention of the battery.

[0028] 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. In some embodiments of the present invention, adding appropriate masses of TAIC and PST ensures that the two additives form copolymer protective films on the positive and negative electrodes that are stable at high temperatures. 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 ability of the protective film. However, adding too much TAIC and PST together can result in excessive growth of the protective film thickness, increasing the battery's DC resistance, and reducing the battery's high-temperature capacity and cycle life. In some embodiments, the mass of 1-propene-1,3-sultone accounts for 0.5% of the total mass of the electrolyte. In some embodiments, the mass of triallyl isocyanurate accounts for 0.5% of the total mass of the electrolyte.

[0029] In some embodiments, the fluorinated solvent includes fluoroethyl methyl carbonate (FEMC), whose structural formula is: [ka]

[0030] In a further embodiment in which the fluorinated solvent includes fluoroethyl methyl carbonate, the fluorinated solvent further includes fluoroethylene carbonate (FEC). In an embodiment in which the fluorinated solvent is a fluorinated carbonate solvent, the fluorinated carbonate solvent has good high-voltage stability, thereby 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 will result in the production of large amounts of unstable by-products at high temperatures and reduce the high-temperature performance of the battery. Therefore, maintaining the mass ratio of fluoroethyl methyl carbonate to fluoroethylene carbonate between 7:3 and 10:0 can improve the high-temperature cycle stability and high-temperature storage capacity retention of the battery. Furthermore, when the mass ratio of fluoroethyl methyl 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 weight of the lithium salt is 12% to 20% of the total weight of the electrolyte. In some other embodiments, the lithium salt may be one or more of lithium hexafluorophosphate (LiPF), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF), lithium methanesulfonate (LiCHSO), lithium trifluoromethanesulfonate (LiCFSO), lithium hexafluoroarsenate (LiAsF), lithium hexafluoroantimonate (LiSbF), lithium perchlorate (LiClO), Li[BF(CO)], Li[PF(CO)], Li[N(CFSO)], Li[C(CFSO)], lithium difluorooxalate borate (LiODFB), lithium dioxalate borate (LiBOB), and lithium difluorophosphate (LiPOF). In some embodiments, the lithium salt may be LiPF6, where the mass of LiPF6 is 13% of the total mass of the electrolyte. In some embodiments, the lithium salt may include LiPF6 and lithium bis(fluorosulfonyl)imide (LiFSI), where the mass of the lithium salt is 12% to 20% of the total mass of the electrolyte and the mass of LiPF6 is 8% to 20% of the total mass of the electrolyte. In some embodiments, the additive further includes vinylene carbonate (VC), where the vinylene carbonate contributes to the formation of a negative electrode film.

[0032] According to another aspect of the present invention, a lithium-ion battery is provided, the lithium-ion battery including a positive electrode sheet, a negative electrode sheet, a separator between the positive and negative electrode sheets, and the above-described electrolyte. Since the above-described electrolyte is applied to the lithium-ion battery, the electrolyte uses a fluorinated solvent as a solvent and triallyl isocyanurate as an additive, thereby forming a stable protective film at the interface between the lithium-ion battery sheet (including the positive electrode sheet and the negative electrode sheet) and the electrolyte, ensuring the stability of the interface between the sheet and the electrolyte and improving the electrical performance of the high-voltage battery. In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material on the positive electrode current collector, the positive electrode active material including lithium nickel manganese oxide, the chemical formula of which is Li a Ni x Mn y O 4‐z M z where 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. In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material on the negative electrode current collector, the negative electrode active material including artificial graphite.

[0033] Positive electrode sheet The positive electrode sheet for the lithium-ion battery provided by the present invention includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. The positive electrode material layer includes a positive electrode active material capable of absorbing and desorbing lithium (Li) (hereinafter also referred to as a "positive electrode material capable of absorbing / desorbing lithium Li"). Examples of positive electrode active materials capable of absorbing / desorbing 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 this field can also be used. In some embodiments, the positive electrode material layer can further include a positive electrode conductive agent and a positive electrode binder. In some embodiments, the positive electrode conductive agent is one or a mixture of conductive carbon black (Super P), acetylene black, nanometal powder, carbon nanotubes, graphene, etc. In some embodiments, the positive electrode binder is one or a mixture of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, sodium carboxymethylcellulose, and styrene-butadiene rubber.

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

[0035] The fluorinated solvent may be a common fluorinated solvent in the art, for example, the fluorinated solvent includes fluoroethyl methyl carbonate (FEMC), and preferably, the fluorinated solvent further includes fluoroethylene carbonate (FEC).

[0036] The lithium salt may be a common lithium salt in the art, for example, the lithium salt may include LiPF6 and lithium bisfluorosulfonyl imide (LiFSI), the mass of the lithium salt is 12% to 20% of the total mass of the electrolyte, and the mass of LiPF6 is 8% to 20% of the total mass of the electrolyte.

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

[0038] The negative electrode active material includes a negative electrode material capable of absorbing and releasing lithium (Li) (hereinafter also referred to as "anode material capable of absorbing / releasing lithium Li"). Examples of anode materials capable of absorbing / 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, pyrolytic carbon, coke, glassy carbon, sintered organic polymers, carbon fiber, and activated carbon. Among these, coke includes pitch coke, needle coke, and petroleum coke. Sintered organic polymers are materials obtained by carbonizing polymeric materials such as phenolic resins and furan resins at appropriate temperatures. Some of these materials can be classified as low-graphitizable carbon or easily graphitizable carbon. Examples of polymeric materials include polyacetylene and polypyrrole.

[0040] Among these anode materials capable of absorbing and releasing lithium (Li), materials with charge / discharge voltages close to that of lithium metal are selected. This is because the lower the charge / discharge voltage of the anode material, the easier it is to increase the energy density of electrochemical devices (such as secondary batteries). Among these, carbon materials can be selected as anode materials because their crystalline 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 absorbing / desorbing lithium (Li) include lithium metal alone, metallic elements capable of forming alloys with lithium (Li), metalloid elements, alloys containing these elements, and compounds. In particular, these materials are used in combination with carbon materials, because this results in good cycle characteristics and high energy density. The alloys used here include alloys containing two or more metallic elements, as well as 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, or mixtures thereof.

[0042] Examples of metal elements 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 having the chemical formula: Ma s Mb t Li u and a material having the chemical formula: Ma p Mc q Md r In these chemical formulas, Ma represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, Mb represents at least one of a metal element and a metalloid element other than lithium and Ma, Mc represents at least one nonmetal element, Md represents at least one of a metal element and a 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] The negative electrode contains MnO2, V2O5, and V6O 13 Inorganic compounds that do not contain lithium (Li), such as NiS, MoS, etc., 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 carboxymethyl cellulose (CMC-Na), and polyvinyl alcohol (PVA).

[0045] Isolation Film The separator film of the lithium-ion battery provided by the present invention is positioned between the positive electrode sheet and the negative electrode sheet. For example, the separator film includes a substrate layer and a surface treatment layer. The substrate layer is a porous nonwoven fabric, film, or composite film, and the material of the substrate 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 substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or may be 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 isolating film can be assembled into a lithium ion battery by a method commonly used in the field. The positive electrode sheet, the isolating film, the negative electrode sheet, etc. are sequentially wound or stacked to form a bare cell, which is then sealed in, for example, an aluminum plastic film and packaged, the electrolyte is injected, and after molding, packaging and testing, the assembled lithium ion battery is subjected to an electrochemical performance test and a cycle performance test.

[0047] Those skilled in the art will appreciate that the above method for manufacturing a lithium ion battery is merely an example, and other methods commonly used in the art may be employed without departing from the teachings of the present invention.

[0048] A method for manufacturing a lithium ion battery will be described below. The lithium ion battery of the present invention may be a primary lithium battery or a secondary lithium battery. The following description will be given using lithium nickel manganese oxide as an example of the positive electrode active material. The positive electrode active material of the present invention is not limited to this. A method for manufacturing a secondary lithium battery is as follows. (1) The manufacturing process of the positive electrode sheet includes the following steps: 0.98 Ni 0.45 Mn 1.55 A cathode active material such as O4, a cathode conductive agent such as Super P, a cathode binder such as PVDF, and the solvent N-methylpyrrolidone (NMP) are mixed in a vacuum mixer at a specific mass ratio until uniform and transparent to obtain a cathode slurry. The mass ratio of the cathode active material, cathode conductive agent, and cathode binder components is 93% to 98.5%, 0.5% to 3%, and 0.5% to 4%. NMP is added so that the proportion of the cathode material in the total mass of the cathode slurry is 45% to 70%. The cathode slurry is then uniformly applied to a cathode current collector, followed by drying, rolling, cutting, and other processes to obtain a cathode sheet. (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 using a vacuum mixer to prepare a negative electrode slurry. The mass ratio of each component of the negative electrode material is 94% to 98% negative electrode active material, 0.2% to 1.5% negative electrode conductive agent, 0.01% to 1.5% negative electrode thickener, and 1% to 3% negative electrode binder. Deionized water is added so that the proportion of the negative electrode material is 45% to 70% of the total mass of the negative electrode slurry. Next, the negative electrode slurry is uniformly applied to a negative electrode current collector, and the negative electrode is subjected to steps such as drying, rolling, and cutting to obtain a negative electrode sheet. (3) Electrolyte production In an argon atmosphere glove box with a moisture content of <10 ppm, battery-grade fluoroethyl methyl carbonate and fluoroethylene carbonate are mixed to form an organic solvent. Lithium salt and appropriate additives are then added to the organic solvent and mixed uniformly to obtain the electrolyte. Lithium salt, 1-propene-1,3-sultone, and triallyl isocyanurate can be added as needed. (4) Production of isolation films It may be any of the isolating films described above. (5) Lithium-ion battery manufacturing The cathode sheet, separator film, and anode sheet prepared as above are stacked or wound in order to obtain an electrode assembly, and the separator film is placed between the cathode sheet and the anode sheet to provide isolation. The electrode assembly is then wrapped in aluminum plastic film, dried, infused with electrolyte, packaged, and molded, left to stand, and molded again to produce a lithium-ion battery.

[0049] Those skilled in the art will appreciate that the above method for manufacturing a lithium ion battery is merely an example, and other methods commonly used in the art may be employed without departing from the teachings of the present invention.

[0050] The present invention will be further explained below with reference to some specific embodiments and comparative examples. [Example]

[0051] Example 1 (1) Manufacturing of positive electrode sheets Cathode active material: Li 0.98 Ni 0.45 Mn 1.55 O4, cathode binder: polyvinylidene fluoride (PVDF), cathode conductor: conductive carbon black (Super P), and solvent: N-methylpyrrolidone (NMP) were mixed in a vacuum mixer at a specific mass ratio until the mixture was homogeneous and transparent, resulting in a cathode slurry. The mass ratio of cathode active material, cathode binder, and cathode conductor was 98:1:1, and NMP was added so that the cathode material accounted for 50% of the total mass of the cathode slurry. The cathode slurry was then uniformly applied to a cathode current collector: aluminum foil, followed by drying, rolling, and cutting to obtain a cathode sheet. (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 a negative electrode slurry. The mass ratio of the components of the negative electrode material (negative electrode active material: artificial graphite, conductive carbon black (Super P), negative electrode thickener: sodium carboxymethyl cellulose (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 then dried, rolled, and cut to obtain a negative electrode sheet. (3) Electrolyte production In an argon atmosphere glove box with a water 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. A lithium salt and appropriate additives were then added to the organic solvent and mixed uniformly to obtain the 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) Production of isolation films A 12 μm thick polypropylene (PP) film was used as the isolation film. (5) Lithium-ion battery manufacturing The cathode sheet, separator film, and anode sheet prepared above were stacked in this order to obtain an electrode assembly, with a separator film placed between the cathode and anode sheets to provide isolation. The electrode assembly was wrapped in aluminum plastic film and transferred to a vacuum oven to dry at 120°C. 3.0 g / Ah of the electrolyte prepared above was then injected, followed by packaging, molding, and storage to produce a lithium-ion battery with a capacity of 1 Ah.

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

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

[0054] Example 4 The manufacturing method is the same as that of Example 1, except that the additives of 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 solution, and the mass of 1-propene-1,3-sultone is 0.01% of the total mass of the electrolyte solution.

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

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

[0057] Example 7 The manufacturing method is the same as that of Example 5, except 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 that of Example 5, except that the ratio of fluoroethyl methyl carbonate to fluoroethylene carbonate in Example 8 is 9:1.

[0059] Example 9 The manufacturing method is the same as that of Example 5, except that the ratio of fluoroethyl methyl carbonate to fluoroethylene carbonate in Example 9 is 10:0, i.e., the electrolyte solution manufactured in Example 9 does not contain fluoroethylene carbonate.

[0060] Comparative Example 1 The manufacturing method was the same as that of Example 1, except that the triallyl isocyanurate in the electrolytic solution of Comparative Example 1 was not contained.

[0061] Comparative Example 2 The manufacturing method is the same as that of Example 1, except that the electrolyte solution of Comparative Example 2 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 solution.

[0062] Comparative Example 3 The manufacturing method is the same as that of Example 1, except that the electrolyte solution of Comparative Example 3 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 solution, and the mass of ethylene sulfate is 0.5% of the total mass of the electrolyte solution.

[0063] Comparative Example 4 The manufacturing method is the same as that of Example 1, except that the electrolyte solution of Comparative Example 4 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 solution.

[0064] Comparative Example 5 The manufacturing method is the same as that of Comparative Example 4, except 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, except 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] Thereafter, the lithium ion batteries of the examples and comparative examples were subjected to the following tests. Specific test methods are as follows. (1) 25°C DC resistance (DCR) test for lithium-ion batteries At the specified temperature, discharge the battery at 1C current to 50% SOC (state of charge, reflecting the remaining capacity of the battery), then increase the current to 4C and maintain for 30 seconds to detect the difference between the updated stable voltage and the original platform voltage. The ratio of this value to the current value at 4C is the battery's DC resistance. The DCR test result after the first full charge of the battery is the battery's initial DCR. (2) Capacity retention rate of lithium-ion batteries when stored at high temperatures (60°C) After fully charging the lithium-ion battery, it was placed in a thermostatic box at 60°C for 15 days, and after it had cooled sufficiently, it was discharged at a rate of 1C to the cutoff voltage, and the ratio of the capacity to the initial discharge capacity was compared. (3) High temperature 45℃ cycle test The battery was cyclically charged and discharged at 45°C with a charge / discharge cutoff voltage range of 3.4V to 4.85V and a charge / discharge rate of 0.5C / 1C, and the discharge capacity of each cycle was recorded. The test ended when the battery capacity reached 80% SOC (State of Charge), and the number of cycles actually achieved was recorded.

[0067] For a clearer explanation, Table 1 shows the compositions of the electrolyte solutions of the examples and comparative examples.

[0068] [Table 1]

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

[0070] [Table 2]

[0071] From the analysis of the above data, the following conclusions were reached. As can be seen from Comparative Examples 1 to 3 and Examples 1 to 3, compared to Comparative Examples 1 to 3 in which no additive was used in the perfluorosolvent or another additive (e.g., VC in Comparative Example 2) was used alone, the high-temperature performance of the lithium-ion batteries of Examples 1 to 3 in which TAIC was added to the perfluorosolvent was improved to a certain extent; for example, the number of high-temperature cycles was clearly increased and the direct current resistance (DCR) was clearly reduced.

[0072] Comparing Comparative Examples 4 to 6 with Examples 1 to 3 reveals that, in Comparative Examples 4 to 6, 1-propene-1,3-sultone additive was added alone to the perfluorosolvent, while in Examples 1 to 3, TAIC was added to the perfluorosolvent of the electrolyte, and when this electrolyte was applied to a high-voltage lithium-ion battery, both the high-temperature capacity retention 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 and sufficiently protects the sheet, 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 to 6 and Examples 1 to 3 with Examples 4 to 6, when a perfluorosolvent is used in combination with 1-propene-1,3-sultone and triallyl isocyanurate as additives, 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 perfluorosolvent is used as the electrolyte solvent, the high-voltage-resistant 1-propene-1,3-sultone and triallyl isocyanurate are used in combination as additives. Both 1-propene-1,3-sultone and triallyl isocyanurate form long-chain copolymer protective films on both the positive and negative electrode sheet sides. Compared with short-chain polymer protective films formed using only TAIC (Examples 1 to 3) or PST (Comparative Examples 4 to 6) alone, these long-chain copolymer protective films are stable even at high temperatures, and can significantly improve the number of high-temperature cycles and high-temperature storage capacity retention of the battery.

[0074] In Examples 1 to 3, the mass of triallyl isocyanurate is limited to 0.01% to 1% of the total mass of the electrolyte. At this time, the high-temperature cycle number retention of the lithium-ion battery is good. For example, in Example 2, the number of high-temperature cycles is improved to 407. Increasing the amount of TAIC added from 0.01% to 0.5% (see Examples 1 and 2) increases the high-temperature storage capacity retention and high-temperature cycle number of the battery. This indicates that the protective film formed by the TAIC additive stabilizes under high-temperature conditions and reduces reactions at the solid-liquid interface. However, when the amount of TAIC added reaches 1%, the high-temperature cycle performance of the battery decreases to a certain extent compared to when the amount of TAIC added is 0.5%. The battery performance is optimal when the mass of triallyl isocyanurate is 0.5% of the total mass of the electrolyte.

[0075] Furthermore, in Examples 4 to 6, the mass of 1-propene-1,3-sultone was limited to 0.01% to 1% of the total mass of the electrolyte. In this case, the DC resistance, high-temperature cycle count, and high-temperature storage capacity retention of the lithium-ion battery were all excellent. For example, in Example 5, the DC resistance decreased to 60 mΩ, the high-temperature storage capacity retention increased to 96%, and the high-temperature cycle count increased to 500. If too much 1-propene-1,3-sultone was added, the protective film would grow excessively due to the increased amount of 1-propene-1,3-sultone, resulting in an excessively thick protective film. This would increase the DCR of the lithium-ion battery, leading to a decrease in the high-temperature capacity and cycle life of the lithium-ion battery. The battery performance was optimal when the mass of 1-propene-1,3-sultone and the mass of triallyl isocyanurate were both 0.5% of the total mass of the electrolyte.

[0076] Comparing Example 5 with Examples 8 and 9, when the mass of triallyl isocyanurate and the mass of 1-propene-1,3-sultone were both 0.5% of the total mass of the electrolyte, significant changes in battery performance were observed even when adjusting the solvent components in the perfluorosolvent. Increasing the proportion of FEMC and decreasing the proportion of FEC in the perfluorosolvent significantly increased the battery's DCR, and the number of high-temperature cycles and high-temperature storage capacity retention of the battery also decreased. This is because, as the FEMC content increases, FEMC decomposes at the solid-liquid interface (i.e., the interface between the electrolyte and the sheet), thereby generating large amounts of unstable by-products at high temperatures. These unstable by-products ultimately reduce the high-temperature performance of the battery. The battery's high-temperature performance is most favorable when the FEMC:FEC ratio is 7:3.

[0077] As can be seen from Examples 4-5 and Comparative Examples 1-6, the high-temperature performance of the battery significantly deteriorated when the additive triallyl isocyanurate was not used or when other additives (e.g., VC in Comparative Example 2) were used alone. The combination of TAIC and PST also played a crucial role in the battery's performance. Furthermore, as can be seen from Comparative Examples 1-6 and Examples 1-5, when a perfluorosolvent was used as the solvent, the high-temperature performance of the battery was optimized by using triallyl isocyanurate and 1-propene-1,3-sultone as additives. When the conventional additives VC and DTD were used in combination, the lithium nickel manganese oxide high-voltage system exhibited a very large DCR, making room-temperature cycling impossible and failing to deliver its full capacity after high-temperature storage. This indicates that the combination of TAIC and PST is essential to ensure normal operation of the high-voltage system, especially when using lithium nickel manganese oxide as the positive electrode active material and graphene as the negative electrode active material. [Industrial Applicability]

[0078] In summary, the electrolyte of the present invention uses a perfluorosolvent as the solvent, and the addition of triallyl isocyanurate to the perfluorosolvent as an additive not only allows the electrolyte to withstand high voltages, but also, 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 between the sheet and the electrolyte, thereby improving the electrical performance of the high-voltage battery. Furthermore, the present invention also uses a perfluorosolvent-based electrolyte in combination with triallyl isocyanurate and 1-propene-1,3-sultone. Adding triallyl isocyanurate and 1-propene-1,3-sultone to the electrolyte in an optimal ratio can effectively form 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. This significantly improves the high-temperature cycle stability of the electrolyte, resulting in a comprehensive improvement in the high-temperature performance of the battery, such as reducing the DCR of the battery and improving the high-temperature cycle stability and high-temperature storage capacity retention of the battery.

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

Claims

1. a solvent that is a fluorinated solvent; A lithium salt, an additive comprising triallyl isocyanurate; An electrolyte solution comprising:

2. 2. The electrolyte solution according to claim 1, wherein the additive further comprises 1-propene-1,3-sultone.

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

4. 2. The electrolyte of claim 1, wherein the fluorinated solvent comprises fluoroethyl methyl carbonate.

5. 5. The electrolyte of claim 4, wherein the fluorinated solvent further comprises fluoroethylene carbonate.

6. 6. The electrolytic solution according to claim 5, wherein the mass ratio of the fluoroethyl methyl carbonate to the fluoroethylene carbonate is 7:3 to 10:

0.

7. 2. The electrolyte solution according to claim 1, wherein the mass of the lithium salt is 12% to 20% of the total mass of the electrolyte solution.

8. 8. The electrolyte of claim 7, wherein the lithium salt is one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium methanesulfonate, lithium trifluoromethanesulfonate, lithium hexafluoroarsenate, lithium hexafluoroantimonate, 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 the electrolyte solution according to any one of claims 1 to 8.

10. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material on the positive electrode current collector, the positive electrode active material including 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 10. The lithium ion battery of 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 of claim 10 , wherein the negative electrode sheet includes a negative electrode current collector and a negative electrode active material on the negative electrode current collector, the negative electrode active material including artificial graphite.

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