Lithium ion battery electrolyte and lithium ion battery containing the same

Abstract

The present invention provides a lithium-ion battery electrolyte and a lithium-ion battery containing the electrolyte, belonging to the technical field of lithium-ion batteries. The lithium-ion battery electrolyte comprises a lithium salt, a solvent, and an additive, wherein the additive must contain both fluorophenyl difluorophosphate and an unsaturated isocyanurate. The combined use of the two additives protects the positive terminal while minimizing a significant increase in battery impedance, ensuring high-temperature storage stability without degrading battery cycling performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium ion battery electrolyte and a lithium ion battery containing the electrolyte. Background Art

[0002] As demands for battery life and application environments continue to rise, lithium-ion battery cathode and anode materials are constantly breaking through theoretical limitations. Increases in voltage and nickel content, as well as the doping of different cathode materials and the addition of lithium-supplementing additives, have also placed higher demands on electrolyte solutions. Reducing the oxidative decomposition of electrolyte materials under cathode catalysis and in high-voltage (highly oxidizing) environments is currently an effective way to improve the cycling and high-temperature storage performance of lithium-ion batteries.

[0003] Unsaturated compounds are effective additives for protecting the positive electrode. For example, patent CN201710297453.9 discloses tri(allyl) phosphate and tri(propargyl) phosphate. Their double bonds can effectively increase the HOMO energy level of the additives, making them more susceptible to oxidative polymerization at the positive electrode, forming a protective layer; thereby inhibiting the decomposition of electrolyte components and the dissolution of the positive electrode material itself. Some other ingredients disclosed in the patent, such as ethoxypentafluorophosphazene and vinyl ethylene carbonate, also have similar properties.

[0004] The introduction of unsaturated bonds increases the HOMO energy level while also lowering its LUMO energy level, making it more susceptible to reduction at the negative electrode and depositing on the negative electrode surface, becoming a component of the SEI film. The formation of an excellent SEI film can inhibit further reduction and decomposition of electrolyte components, reduce the consumption of active Li, and inhibit the thickening of the SEI film and the increase in impedance, which is of great significance for improving battery capacity retention. However, traditional SEI films formed by the polymerization of carbon-carbon double bonds lack lone pairs of electrons or defects from heteroatoms, and often have higher internal resistance, which in turn reduces the battery's cycling performance.

[0005] The strong electronegativity of fluorine atoms in fluorinated compounds can lower the compound's LUMO energy level, making it easier for the fluorinated compound to be reduced at the negative electrode, forming inorganic components such as LiF, effectively reducing the negative electrode impedance. Therefore, developing electrolytes that can form excellent CEI and SEI films, while balancing positive and negative electrode protection and impedance control, is currently a research priority in lithium-ion battery technology. Summary of the Invention

[0006] The present invention addresses the problems existing in the prior art and provides a lithium-ion battery electrolyte and a lithium-ion battery containing the electrolyte, which can better coordinate the relationship between positive electrode protection and negative electrode impedance, thereby obtaining a lithium-ion battery with good high-temperature storage performance and good cycle performance.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] As a first aspect of the present invention, the present invention provides a lithium ion battery electrolyte comprising a lithium salt, a solvent, an additive A, and an additive B. The additive A is selected from at least one of the compounds represented by the following formula (I):

[0009]

[0010] Wherein, n represents an integer from 1 to 5;

[0011] The additive B is selected from at least one of the compounds represented by the following formula (II):

[0012]

[0013] Among them, R1, R2, and R3 independently represent a fluorine atom, a C1-C10 alkyl group, a C2-C10 alkenyl group, a C2-C10 alkynyl group, a C1-C10 alkoxy group, a C1-C10 fluoroalkyl group, a C1-C10 fluoroalkoxy group, a C2-C10 cyanoalkyl group, or a C2-C10 isocyanatealkyl group; and at least one of R1, R2, and R3 contains an unsaturated bond, such as a carbon-carbon double bond, a carbon-carbon triple bond, an isocyanate bond, etc.

[0014] As a second aspect of the present invention, the present invention provides the use of the above electrolyte in the preparation of lithium ion batteries.

[0015] As a third aspect of the present invention, the present invention provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned electrolyte.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The electrolyte disclosed in the present invention contains a negative electrode low-impedance film-forming additive of fluorophenyl difluorophosphate and an isocyanurate compound containing an unsaturated bond. By combining the two additives, it is possible to optimize the components of the negative electrode SEI film while protecting the positive electrode plate, keeping the internal resistance within a controllable range, thereby improving the high-temperature storage performance of the lithium-ion battery while ensuring the cycle stability of the lithium battery. DETAILED DESCRIPTION

[0018] The lithium ion battery electrolyte and the lithium ion battery of the present invention are described in detail below.

[0019] As a first aspect of the present invention, the present invention provides a lithium ion battery electrolyte comprising a lithium salt, a solvent, an additive A, and an additive B. The additive A is selected from at least one of the compounds represented by the following formula I:

[0020]

[0021] wherein n represents an integer from 1 to 5; specifically, n is 1, 2, 3, 4 or 5;

[0022] The additive B is selected from at least one of the compounds represented by the following formula II:

[0023]

[0024] Among them, R1, R2, and R3 independently represent a fluorine atom, a C1-C10 alkyl group, a C2-C10 alkenyl group, a C2-C10 alkynyl group, a C1-C10 alkoxy group, a C1-C10 fluoroalkyl group, a C1-C10 fluoroalkoxy group, a C2-C10 cyanoalkyl group, or a C2-C10 isocyanatealkyl group; and at least one of R1, R2, and R3 contains an unsaturated bond, such as a carbon-carbon double bond, a carbon-carbon triple bond, an isocyanate bond, etc.

[0025] As one embodiment of the present invention, R1, R2, and R3 independently represent a fluorine atom, a C1-C6 alkyl group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, a C1-C6 alkoxy group, a C1-C6 fluoroalkyl group, a C1-C6 fluoroalkoxy group, a C2-C6 cyanoalkyl group, or a C2-C6 isocyanatealkyl group; and at least one of R1, R2, and R3 groups contains an unsaturated bond, such as a carbon-carbon double bond, a carbon-carbon triple bond, an isocyanate bond, etc.

[0026] As one embodiment of the present invention, R1, R2, and R3 independently represent a fluorine atom, a C1-C3 alkyl group, a C2-C3 alkenyl group, a C2-C3 alkynyl group, a C1-C3 alkoxy group, a C1-C3 fluoroalkyl group, a C1-C3 fluoroalkoxy group, a C2-C3 cyanoalkyl group, or a C2-C3 isocyanatealkyl group; and at least one of R1, R2, and R3 groups contains an unsaturated bond, such as a carbon-carbon double bond, a carbon-carbon triple bond, an isocyanate bond, etc.

[0027] As an embodiment of the present invention, R1, R2, and R3 independently represent a fluorine atom, a methyl group, an ethyl group, a vinyl group, an allyl group, an alkynyl group, a propargyl group, a methoxy group, an ethoxy group, a cyanomethyl group, a cyanoethyl group, and a cyanopropyl group; and at least one of R1, R2, and R3 groups contains an unsaturated bond, such as a carbon-carbon double bond, a carbon-carbon triple bond, an isocyanate bond, etc.

[0028] As an embodiment of the present invention, the additive A is selected from at least one of the following formulas (1) to (6):

[0029]

[0030] As an embodiment of the present invention, the additive B is selected from at least one of the following formulas (7) to (9):

[0031]

[0032] The additive A of the present invention is a phenyl difluorophosphate compound, which has good wettability on the interface; and its difluorophosphate group may react to form a lithium fluorophosphate component under redox reaction, which has very low impedance in lithium batteries; the F-rich phenyl group can defluorinate to form an inorganic SEI film of lithium fluoride, further reducing impedance. However, the SEI film formed by this substance is mainly composed of inorganic components. Although it can reduce impedance to a certain extent, it does not fully protect the electrode surface. As the cycle proceeds, it will cause components such as solvents to continue to react with the electrodes, especially under high temperature conditions, causing battery cycle deterioration and storage gas production risks. Additive B is an isocyanurate compound containing unsaturated bonds. Its unsaturated bonds and heterocyclic structures have a lower LUMO energy level and a higher HOMO energy level. It is easy to redox polymerize to form a dense protective film, which has better protection for the electrodes under high temperature storage and high voltage, suppressing electrode side reactions and battery gas production. However, this dense protective film causes the battery internal resistance to increase, and the cycle and low-temperature discharge performance are greatly affected. The synergistic effect of additive A and additive B can form a SEI film composed of organic and inorganic components, which can effectively protect the electrode while suppressing the rapid increase of battery impedance and taking into account the high-temperature storage and cycling performance of the battery.

[0033] In the electrolyte of the present invention, the amount of additive A added is 0.1-10% by mass of the electrolyte, for example, 0.1-1%, 1-2%, 2-3%, 3-4%, 4-5%, 5-6%, 6-7%, 7-8%, 8-9%, 9-10%, and any numerical range within this interval; the amount of additive A added is preferably 0.3-3%; more preferably 1-3%. When the content of additive A is too high, the inorganic components on the electrode surface are excessive, making it difficult to effectively protect the electrode and isolate the side reactions of the electrolyte components; conversely, when the content of additive A is too low, the inhibitory effect on the impedance increase is not obvious, and the cycle performance is still poor.

[0034] In the electrolyte of the present invention, the amount of additive B added is 0.1-5% by mass of the electrolyte, for example, it can be 0.1-1%, 1-2%, 2-3%, 3-4%, 4-5% and any numerical range within this interval; the amount of additive B added is preferably 0.3-2%; when the content of additive B is too high, the SEI film on the electrode surface is too dense, the impedance increases significantly, and although gas production is effectively suppressed, the battery cycle performance and discharge performance deteriorate; conversely, when the content of additive B is too low, it is difficult to achieve effective protection of the electrode, and the battery capacity is likely to drop in the later stage of the cycle.

[0035] In the electrolyte of the present invention, the mass ratio of additive A to additive B is 0.5:1-20:1, preferably 2:1-10:1. The relative content of additive A and additive B will affect the film-forming quality and interface impedance of the SEI film on the surface of the positive and negative electrodes. When added in a suitable ratio, the two can further improve the cycle performance and high-temperature storage effect. If the relative content of additive A is too high, there will be too many inorganic components on the electrode surface, making it difficult to achieve effective protection of the electrode, ultimately resulting in poor cycle and high-temperature storage performance; conversely, if the relative content of additive A is too low, the battery impedance will be higher. Although it can inhibit battery gas production, the battery cycle performance will be seriously deteriorated.

[0036] As an embodiment of the present invention, the electrolyte of the present invention may optionally further include other additives, and the types of other additives are not limited, and conventional additives in the art can be used. For example, a combination of one or more of vinylene carbonate (VC), vinyl sulfate (DTD), vinyl ethylene carbonate, fluoroethylene carbonate, methyl propargyl carbonate, ethyl propargyl carbonate, dipropargyl carbonate, maleic anhydride, succinic anhydride, 1,3-propane sultone, 1,4-butane sultone, methylene methanedisulfonate, difluorobis(oxalato)lithium phosphate, bis(oxalato)borate, tris(oxalato)lithium phosphate, and difluorolithium phosphate.

[0037] In the electrolyte of the present invention, the addition amount of other additives accounts for 0-20% by mass of the electrolyte, preferably 1-15% by mass.

[0038] As an embodiment of the present invention, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethyl)sulfonylimide (LiTFSI), and lithium tetrafluoroborate (LiBF4); the total amount of the lithium salt accounts for 5-30% by mass of the electrolyte, preferably 7-20%.

[0039] As an embodiment of the present invention, the solvent is selected from a mixture of one or more of chain carbonates, cyclic carbonates, carboxylates, chain fluorinated carbonates, cyclic fluorinated carbonates, fluorinated carboxylates, and fluorinated ethers.

[0040] Furthermore, the chain carbonates mainly include one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; the cyclic carbonates mainly include one or more of ethylene carbonate, vinylene carbonate, and propylene carbonate; the carboxylates mainly include one or more of ethyl acetate, ethyl propionate, methyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate; the chain fluorocarbons mainly include one or more of methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, and bis(trifluoroethyl) carbonate; the cyclic fluorocarbons mainly include fluoroethylene carbonate, trifluoromethyl ethylene carbonate, bis(trifluoromethyl) carbonate, One or more of trifluoroethyl ethylene carbonate; the fluorocarboxylic acid esters mainly include one or more of methyl difluoroacetate, ethyl difluoroacetate, difluoroethyl acetate, ethyl trifluoroacetate, and trifluoroethyl acetate; the fluoroethers mainly include one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, tetrafluoromethyl butyl ether, 4-trifluoromethyl anisole, and 1,1,2,3,3,3-hexafluoropropyl 2,2,2-trifluoroethyl ether;

[0041] Furthermore, the total content of the solvent accounts for 50-95% by mass of the electrolyte, preferably 70-90% by mass.

[0042] As a second aspect of the present invention, the present invention provides the use of the aforementioned electrolyte in the preparation of a lithium-ion battery. A lithium-ion battery prepared using the electrolyte of the present invention can protect the positive terminal without significantly increasing the battery impedance, thereby ensuring the battery's high-temperature storage stability without degrading the battery's cycling performance.

[0043] As a third aspect of the present invention, the present invention provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and the above-mentioned electrolyte. The lithium-ion battery can be prepared using methods known to those skilled in the art.

[0044] As an embodiment of the present invention, the positive electrode sheet includes a positive electrode current collector, a positive electrode active material, a conductive agent and a binder;

[0045] The positive electrode current collector includes but is not limited to metal foil, such as aluminum foil; the positive electrode active material includes but is not limited to a combination of one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, etc.; the conductive agent includes but is not limited to conductive carbon black, conductive graphite, carbon fiber, single-arm carbon nanotube, multi-walled carbon nanotube, etc.; the binder includes but is not limited to styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyacrylate (PAA), polyimide (PI) and polytetrafluoroethylene (PTFE), etc.

[0046] As a preferred embodiment, the positive electrode active material is LiNi 1-x-y-z Co x Mn y Al z O2, where: 0≤x≤1, 0≤y≤1, 0≤z≤1 and 0≤x+y+z≤1;

[0047] As an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector, a negative electrode active material, a conductive agent and a binder;

[0048] The negative electrode current collector includes but is not limited to metal foil, such as copper foil; the negative electrode active material includes but is not limited to one or more combinations of artificial graphite, natural graphite, composite graphite, graphene, mesophase microspheres, nanosilicon, silicon-carbon composite materials, silicon dioxide / carbon composite materials, etc.; the conductive agent includes but is not limited to conductive carbon black, conductive graphite, carbon fiber, single-arm carbon nanotubes, multi-walled carbon nanotubes, etc.; the binder includes but is not limited to styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyacrylate (PAA) and polyimide (PI), etc.

[0049] As an embodiment of the present invention, the separator may be a conventional separator applicable to lithium-ion batteries in the art, including but not limited to polyethylene, polypropylene, polyvinylidene fluoride, and the like, and multilayer composite films thereof.

[0050] The technical scheme of the present invention will be clearly and completely described below by specific embodiments. Obviously, the described embodiments are only a part of embodiments of the present invention, rather than all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the scope of protection of the present invention. In addition, it is worth noting that the raw materials involved in the present invention are all common commercial products unless otherwise specified.

[0051] As used herein, the terms "comprises," "including," "having," "containing" or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a listed element is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0052] When amount, concentration or other value or parameter is represented with range, preferred range or the range that a series of upper preferred value and lower preferred value limit are expressed, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, no matter whether this range is disclosed separately.For example, when disclosing scope "1 to 5", described scope should be interpreted as including scope "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc.When numerical range is described in this article, unless otherwise stated, otherwise this scope is intended to include its end value and all integers and fractions within this range.

[0053] The singular includes plural references unless the context clearly dictates otherwise. "Optional" or "either" means that the subsequently described event or incident can or cannot occur, and that the description includes instances where the event occurs and instances where it does not.

[0054] The indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirement (i.e. the number of times the elements or components appear). Therefore, "a" and "an" should be interpreted as including one or at least one, and elements or components in the singular also include plural forms, unless the quantity clearly refers to only the singular form.

[0055] Moreover, the technical features involved in various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0056] Synthesis of compounds

[0057] Synthesis of Additive A:

[0058] Under a nitrogen atmosphere, add 76.6 g (0.5 mol) of phosphorus oxychloride to a three-necked flask and raise the temperature to 40°C. Add 46 g (0.25 mol) of pentafluorophenol dropwise to the reaction mixture while stirring for 30 minutes. After the addition is complete, raise the temperature to 150°C and reflux with stirring for 12 hours. After the reaction is complete, remove the unreacted phosphorus oxychloride by distillation to obtain crude pentafluorophenyl dichlorophosphate.

[0059] The crude product was dissolved in acetonitrile, and then 58 g of potassium fluoride reagent after dehydration was added. The temperature was raised to 150°C and the reaction was refluxed for 24 hours. After the reaction was completed, the reaction solution was subjected to vacuum distillation and the fraction at 110-140°C was collected. The liquid phase analysis showed a purity of more than 97%, which was the compound represented by formula (6). Synthesis of Additive B:

[0060] Under a nitrogen atmosphere, allyl alcohol (1.5 mol) was added to 100 ml of water, and then the temperature was raised to 60 ° C. Under stirring, isocyanuric acid (0.5 mol) was slowly added dropwise thereto, and the pH was adjusted to about 7. After the addition was completed, the temperature was raised to 80 ° C and refluxed for 12 hours. After the reaction was completed, the reaction product was cooled to 10 ° C, and ethanol and DMSO solvents were added to precipitate solid salts. After filtration, it was washed with acetone several times, and then distilled by reduced pressure distillation to obtain TAIC, which is the compound shown in formula (7).

[0061] Other compounds shown as additive B can be obtained by the same method by changing the type and ratio of alcohol.

[0062] Comparative Example 1

[0063] The electrolyte was prepared as follows: in a glove box, ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30 / 20 / 50, the temperature was lowered to below 10° C., and then lithium hexafluorophosphate was slowly added to prepare a 1.1 M lithium hexafluorophosphate solution; thereafter, 0.5% by mass of VC and 1% by mass of DTD were added to the electrolyte to obtain the electrolyte of Comparative Example 1.

[0064] The electrolyte of Comparative Example 1 was injected into a fully dried 4.3V NCM (nickel: cobalt: manganese = 6:2:2) / graphite soft-pack battery. After being placed at 45°C, formed in a high-temperature fixture, and sealed twice, the battery performance test was performed to obtain the battery used in Comparative Example 1.

[0065] Comparative Example 2

[0066] The preparation of the battery of Comparative Example 2 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (1) is added to the electrolyte of Comparative Example 2.

[0067] Comparative Example 3

[0068] The preparation of the battery of Comparative Example 3 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (5) is added to the electrolyte of Comparative Example 3.

[0069] Comparative Example 4

[0070] The preparation of the battery of Comparative Example 4 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 0.3% by mass of compound (7) is added to the electrolyte of Comparative Example 4.

[0071] Comparative Example 5

[0072] The preparation of the battery of Comparative Example 5 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 4% by mass of compound (5) and 1% by mass of compound (7) are added to the electrolyte of Comparative Example 5.

[0073] Comparative Example 6

[0074] The preparation of the battery of Comparative Example 6 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (5) and 2.5% by mass of compound (7) are added to the electrolyte of Comparative Example 5.

[0075] Example 1

[0076] The preparation of the battery of Example 1 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (1) and 0.3% by mass of compound (7) are added to the electrolyte of Example 1.

[0077] Example 2

[0078] The preparation of the battery of Example 2 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (2) and 0.3% by mass of compound (7) are added to the electrolyte of Example 2.

[0079] Example 3

[0080] The preparation of the battery of Example 3 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (3) and 0.3% by mass of compound (7) are added to the electrolyte of Example 3.

[0081] Example 4

[0082] The preparation of the battery of Example 4 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (4) and 0.3% by mass of compound (7) are added to the electrolyte of Example 4.

[0083] Example 5

[0084] The preparation of the battery of Example 5 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (5) and 0.3% by mass of compound (7) are added to the electrolyte of Example 5.

[0085] Example 6

[0086] The preparation of the battery of Example 6 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (6) and 0.3% by mass of compound (7) are added to the electrolyte of Example 6.

[0087] Example 7

[0088] The preparation of the battery of Example 7 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (1) and 0.3% by mass of compound (8) are added to the electrolyte of Example 7.

[0089] Example 8

[0090] The preparation of the battery of Example 8 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (1) and 0.3% by mass of compound (9) are added to the electrolyte of Example 8.

[0091] Example 9

[0092] The preparation of the battery of Example 9 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (1) and 0.5% by mass of compound (7) are added to the electrolyte of Example 9.

[0093] Example 10

[0094] The preparation of the battery of Example 10 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (5) and 0.5% by mass of compound (7) are added to the electrolyte of Example 10.

[0095] Example 11

[0096] The preparation of the battery of Example 11 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (5) and 1% by mass of compound (7) are added to the electrolyte of Example 11.

[0097] Example 12

[0098] The preparation of the battery of Example 12 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 1% by mass of compound (5) and 2% by mass of compound (7) are added to the electrolyte of Example 12.

[0099] Example 13

[0100] The preparation of the battery of Example 13 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 2% by mass of compound (5) and 1% by mass of compound (7) are added to the electrolyte of Example 13.

[0101] Example 14

[0102] The preparation of the battery of Example 14 is substantially the same as that of Comparative Example 1. The difference is that, in addition to VC and DTD, 3% by mass of compound (5) and 1% by mass of compound (7) are added to the electrolyte of Example 14.

[0103] Example 15

[0104] The preparation of the battery of Example 15 is substantially the same as that of Example 10. The difference is that in the electrolyte of Example 15, the lithium salt is changed from 1.1M LiPF6 to 0.9M LiPF6 plus 0.2M LiFSI.

[0105] Example 16

[0106] The preparation of the battery of Example 16 is substantially the same as that of Example 10. The difference is that in the electrolyte of Example 16, the lithium salt is changed from 1.1M LiPF6 to 0.7M LiPF6 plus 0.4M LiFSI.

[0107] The main components and proportions of each comparative example and embodiment are shown in Table 1.

[0108] Table 1 Components and contents of electrolytes in comparative examples and examples

[0109]

[0110]

[0111] Lithium-ion battery performance testing

[0112] Normal temperature cycle performance: The prepared lithium-ion battery is charged to 4.3V at 1C constant current and constant voltage at room temperature (25°C), and then discharged to 2.8V at 1C constant current, which is recorded as one cycle. The discharge capacity of the first cycle is recorded as DC1. After 1000 cycles of charge and discharge, the discharge capacity of the 1000th cycle is recorded as DC1000 , calculate the capacity retention rate after the 1000th cycle as follows:

[0113]

[0114] 45℃ high temperature cycle performance: The prepared lithium ion battery was charged to 4.3V at 1C constant current and constant voltage under high temperature (45℃) conditions, and then discharged to 2.8V at 1C constant current conditions, which was recorded as one cycle. The discharge capacity of the first cycle was recorded as DC1. After 800 cycles of charge and discharge, the discharge capacity of the 800th cycle was recorded as DC 800 , the capacity retention rate after the 800th cycle is calculated as follows:

[0115]

[0116] 60℃ storage performance: At room temperature (25℃), the lithium-ion battery is charged and discharged at 1C / 1C, and the average battery thickness is measured as d1. The battery is then charged to 4.3V under 1C constant current and constant voltage conditions and stored in a 60℃ high-temperature oven for 15 days. After 15 days, the battery is removed and its thickness is measured as d2. The thickness change rate after 15 days of storage at 60℃ is calculated as follows:

[0117]

[0118] The battery test results of Comparative Examples 1 to 6 and Examples 1 to 16 are shown in Table 2 below.

[0119] Table 2 Battery performance test results of comparative examples and embodiments

[0120]

[0121] The electrolyte disclosed by the invention contains two types of additives, fluorophenyl difluorophosphate and unsaturated isocyanurate, and can give lithium ion batteries better performance.

[0122] According to the test results, the conclusions can be summarized as follows:

[0123] The high-temperature storage thickness change rates of Comparative Examples 1, 4, and 6, as well as Examples 1, 10, 11, and 12, indicate that unsaturated isocyanurate can effectively improve battery gas production; however, possibly due to its high impedance, its addition alone or in excess can lead to rapid degradation of battery cycle performance.

[0124] The results of Comparative Example 5 and Examples 11, 13, and 14 demonstrate that the combination of an unsaturated isocyanurate compound and fluorophenyl difluorophosphate effectively improves battery cycling performance and reduces gas generation during high-temperature storage. This is likely due to the fluorine-containing additive's ability to effectively mitigate the impedance increase caused by the unsaturated isocyanurate, significantly contributing to the regulation of the negative electrode SEI film. However, it should be noted that cycling performance decreases when the content exceeds 3%, indicating that excessive content can prevent an imbalance between the organic and inorganic components of the negative electrode SEI film.

[0125] The results of Examples 1-6 and 7-9 show that compounds of similar structures have different performances when used as additives; among them, compounds (1), (5), (6) and compound (7) have better effects. However, from the comparison between Examples 1 and 9 and Examples 5 and 10, the influence of the amount of additive added on the performance trend is also different. The combination and amount of different additives need to be further adjusted;

[0126] The results of Example 10, Example 15, and Example 16 show that the addition of LiFSI can further improve the cycle performance and high-temperature storage effect on the original basis, making the application of this additive combination more promising.

[0127] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A lithium ion battery electrolyte, comprising a lithium salt, a solvent, an additive A and an additive B, wherein: The additive A is selected from at least one of the following formulas (1) to (6): ； The additive B is selected from at least one of the following formulas (7) to (9): ； The amount of additive A added to the electrolyte is 0.3-3% by mass; The amount of additive B added is 0.1~1% by mass of the electrolyte; The mass ratio of additive A to additive B is 0.5:1-20:

1.

2. The electrolyte according to claim 1, wherein: The amount of additive A added is 1-3% by mass of the electrolyte.

3. The electrolyte according to claim 1, wherein: The mass ratio of additive A to additive B is 2:1~10:

1.

4. The electrolyte according to claim 1, wherein: The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(trifluoromethyl)sulfonyl imide, lithium bis(trifluoromethyl)sulfonyl imide, and lithium tetrafluoroborate.

5. The electrolyte according to claim 1, wherein: The solvent is selected from a mixture of one or more of chain carbonates, cyclic carbonates, carboxylates, chain fluorinated carbonates, cyclic fluorinated carbonates, fluorinated carboxylates, and fluorinated ethers.

6. Use of the electrolyte according to any one of claims 1 to 5 in the preparation of lithium-ion batteries.

7. A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 5.

8. The lithium-ion battery according to claim 7, wherein: The positive electrode sheet includes a positive electrode current collector, a positive electrode active material, a conductive agent and a binder; the negative electrode sheet includes a negative electrode current collector, a negative electrode active material, a conductive agent and a binder.

9. The lithium-ion battery according to claim 8, wherein: The positive electrode active material is LiNi 1-x-y- z Co x Mn y Al z O2, wherein: 0≤x≤1, 0≤y≤1, 0≤z≤1 and 0≤x+y+z≤1; the negative electrode active material is one or more combinations of artificial graphite, natural graphite, composite graphite, graphene, mesophase microspheres, nanosilicon, silicon-carbon composite materials, and silicon monoxide / carbon composite materials.

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