Organic electrolyte and lithium-ion secondary battery

Abstract

The present application discloses an organic electrolyte and a lithium-ion secondary battery, relating to the field of battery technology. The organic electrolyte comprises: lithium tetrafluorooxalate phosphate and an isocyanate compound; the isocyanate compound is selected from a mixture of one or more of a monoisocyanate compound, a diisocyanate compound, and a polyisocyanate compound; wherein the mass ratio of the lithium tetrafluorooxalate phosphate to the isocyanate compound is 2-5:1. The present application, by applying lithium tetrafluorooxalate phosphate and an isocyanate compound to an organic electrolyte, can form a more stable organic-inorganic composite modified SEI film at the negative electrode interface through binding, thereby effectively reducing direct contact between the organic solvent and the negative electrode interface, improving the reversibility of lithium ion insertion / deinsertion, thereby helping to improve the battery's cycle life characteristics, high temperature storage stability, and low temperature discharge capability.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an organic electrolyte and a lithium-ion secondary battery. Background Art

[0002] With the rapid promotion and popularization of new energy vehicles and portable power tools, the development trend of these products towards lightweight, high energy density, and universal adaptability in various environments is becoming increasingly obvious. As the most direct source of energy for electronic devices, lithium-ion batteries are facing increasing performance requirements, requiring them to have higher energy density in various extreme environments. This means they should be able to stably provide more energy while occupying less space and operating in extreme environments. Therefore, the current biggest challenge for lithium-ion batteries is to improve their volumetric energy density and high and low temperature discharge performance, while ensuring that the batteries can meet long-term charge and discharge requirements.

[0003] CN113130997B discloses that LiTFOP can form a dense and strong composite film on the surface of the positive electrode, thereby reducing the oxidation activity of the positive electrode active material and blocking the contact between the positive electrode active material and the electrolyte, thereby inhibiting the oxidative decomposition of the electrolyte.

[0004] CN114128006A and CN107394267B disclose the use of LiTFOP in combination with other additives to improve the low-temperature characteristics of batteries.

[0005] CN114069045A / WO2022012601A1 discloses that fluorine-containing lithium salt additives can construct an interface film with stronger ionic conductivity and favorable charge migration, and the interface film can continuously modify the positive and negative electrode interface films, thereby suppressing the continuous growth of battery cell impedance during battery cycling and improving the long-term high-temperature cycling stability of the battery;

[0006] The above technologies disclose the use of lithium tetrafluorooxalophosphate (LiTFOP) as a conventional additive in electrolytes. However, the combination of lithium tetrafluorooxalophosphate and some other conventional additives has limited performance improvements on the cycle life, high-temperature storage stability, and low-temperature discharge capacity of lithium-ion batteries. Further research on organic electrolyte systems is needed to achieve lithium-ion batteries with higher electrical performance. Summary of the Invention

[0007] The purpose of this application is to explore the effect of organic electrolyte systems on the electrical properties of lithium-ion batteries, especially the use of LiTFOP as an additive in combination with isocyanate additives, to improve the electrical performance of the battery and simultaneously improve the battery's room temperature cycling, high temperature cycling, low temperature discharge performance and high temperature storage performance.

[0008] To achieve the above objectives, this application provides the following technical solutions:

[0009] In a first aspect, the present application provides an organic electrolyte, comprising:

[0010] lithium tetrafluorooxalophosphate, and

[0011] Isocyanate compounds;

[0012] The isocyanate compound is selected from a mixture of one or more of a monoisocyanate compound, a diisocyanate compound, and a polyisocyanate compound;

[0013] Wherein, the mass ratio of the lithium tetrafluorooxalophosphate to the isocyanate compound is 2-5:1.

[0014] In the present application, the inventors discovered through in-depth research that the application of lithium tetrafluorooxalophosphate and isocyanate compounds in organic electrolytes can form a more stable organic-inorganic composite modified SEI film through binding at the negative electrode interface, thereby effectively reducing the direct contact between the organic solvent and the negative electrode interface and improving the reversibility of lithium ion insertion / deinsertion; among them, the isocyanate compound can also react with water and hydrofluoric acid in the electrolyte, and form new substances by breaking the carbon-nitrogen double bond, which can significantly reduce the acidity and moisture of the electrolyte. Moreover, due to the special properties of the long carbon chain, when participating in the construction of the SEI film, the SEI film formed in the present application can be made more elastic, which plays a role in better protecting the negative electrode interface, thereby helping to improve the cycle life characteristics, high-temperature storage stability and low-temperature discharge capability of the battery.

[0015] Studies have shown that when the mass ratio of lithium tetrafluorooxalophosphate to isocyanate compound is 2-5:1, it can effectively improve the battery's cycle life characteristics, high-temperature storage stability, and low-temperature discharge capacity. When the mass ratio of lithium tetrafluorooxalophosphate to isocyanate compound is less than 2:1, the battery's normal temperature and high-temperature cycle life will be significantly shortened, the low-temperature capacity retention rate will decrease, and the battery's high-temperature gas production will increase slightly. When the mass ratio of lithium tetrafluorooxalophosphate to isocyanate compound is greater than 5:1, the battery's normal temperature cycle life, high-temperature cycle life, and low-temperature capacity retention rate will also be significantly shortened, and the battery's high-temperature gas production will increase slightly.

[0016] In some embodiments of the present application, the monoisocyanate compound is selected from compounds having a structure shown in Formula 1:

[0017] R1——NCO <Formula 1>,

[0018] In formula 1, R1 is selected from C 1～10 Alkyl, C 1～10 Alkenyl, C 1～10 Alkynyl, C1～10 Alkoxy, C 1～10 aryl groups;

[0019] In a preferred embodiment of the present application, the monoisocyanate compound is selected from any one or more of methyl isocyanate, n-butyl isocyanate, tert-butyl isocyanate, phenyl isocyanate, p-chlorophenyl isocyanate, 3-chlorophenyl isocyanate, 3,4-dichlorophenyl isocyanate, 3,5-dichlorophenyl isocyanate, p-methylphenyl isocyanate, 3-chloro-4-methylphenyl isocyanate, p-isopropylphenyl isocyanate, p-bromophenyl isocyanate, p-nitrophenyl isocyanate and 4-(p-chlorophenoxy)-phenyl isocyanate.

[0020] In some embodiments of the present application, the diisocyanate compound is selected from compounds having a structure shown in Formula 2:

[0021]

[0022] In formula 2, n is an integer from 2 to 10;

[0023] In a preferred embodiment of the present application, the diisocyanate compound is preferably one of isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI), or a mixture of the two.

[0024] In some embodiments of the present application, the polyisocyanate compound is selected from compounds having a structure shown in Formula 3:

[0025]

[0026] In formula 3, R2 is selected from C 1～10 R3, R4, R5 are independently selected from C 1～10 Alkylene, C 1～10 Alkenylene, C 1～10 alkyleneoxy;

[0027] In a preferred embodiment of the present application, the polyisocyanate compound is preferably any one of 4'4'4'-triisocyanatophenyl phosphate and 4'4'4'-triisocyanatophenyl thiophosphate, or a mixture of the two.

[0028] As a preferred technical solution of this application, the content of the lithium tetrafluorooxalophosphate is 0.1-6% based on the total weight of the organic electrolyte. The inventors have found through experiments that when the content of lithium tetrafluorooxalophosphate exceeds 6%, the battery's room temperature and high temperature cycle life are significantly shortened, the low-temperature capacity retention rate decreases, the high-temperature capacity retention rate and recovery rate decrease significantly, and the battery's high-temperature gassing phenomenon is aggravated.

[0029] The organic electrolyte of the present application further includes a non-aqueous solvent and a lithium salt. In the present application, there is no special restriction on the type and content of the non-aqueous solvent and the lithium salt.

[0030] In some embodiments of the present application, the lithium salt is selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium difluorophosphate (LiPO2F2), 4,5-dicyano-2-trifluoromethylimidazolium lithium (LiTDI), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tris(oxalato)phosphate (LiTOP), lithium difluorobis(oxalato)phosphate (LiODFP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0031] Preferably, the content of the lithium salt is 10-20%, more preferably 12-18%, and even more preferably 13-16%, based on the total mass of the organic electrolyte.

[0032] In some embodiments of the present application, the non-aqueous solvent is selected from ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate (EA), propyl acetate (PA), butyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate (PP), butyl propionate, methyl butyrate, ethyl butyrate Any one or more of esters, propyl butyrate, butyl butyrate, γ-butyrolactone (GBL), γ-valerolactone, δ-valerolactone, ethylene glycol dimethyl ether (DME), triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane (DOL), 1,4-dioxane (DOX), sulfolane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, difluoroethylene carbonate (DFEC), dimethyl fluorocarbonate, ethyl methyl fluorocarbonate, methyl difluoroacetate, and ethyl difluoroacetate are mixed;

[0033] Preferably, the content of the non-aqueous solvent is 66-88.85%, more preferably 70-88%, and even more preferably 75-87%, based on the total mass of the organic electrolyte.

[0034] The organic electrolyte of the present application also includes other conventional additives.

[0035] The additive is selected from vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,4-butane sultone (BS), 1,3-(1-propylene) sultone (PST), fluoromethyl vinyl carbonate, dimethyl sulfate (DMS), vinyl sulfate (DTD), methyl vinyl sulfate, propylene sulfate (TMS), vinyl sulfite, succinic anhydride, A mixture of one or more of biphenyl, diphenyl ether, toluene, xylene, cyclohexylbenzene, fluorobenzene, p-fluorotoluene, p-fluoroanisole, tert-butylbenzene, tert-amylbenzene, methylene disulfonate, ethylene glycol bis(propionitrile) ether, hexamethyldisilazane, heptamethyldisilazane, dimethyl methylphosphonate, diethyl ethylphosphonate, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, and dimethyl sulfoxide.

[0036] Preferably, the content of the additive is 1-5%, more preferably 2-5%, and even more preferably 2.5-4.5%, based on the total mass of the organic electrolyte.

[0037] The organic electrolyte provided herein can be prepared by any suitable method known in the art, for example:

[0038] The organic electrolyte is obtained by adding lithium salt, additives, isocyanate compounds and LiTFOP into a non-aqueous solvent in proportion and mixing them.

[0039] In a second aspect, the present application further provides a lithium-ion secondary battery, the lithium-ion secondary battery comprising:

[0040] positive electrode;

[0041] negative electrode;

[0042] diaphragm; and

[0043] The organic electrolyte described in the first aspect.

[0044] Based on the description of the first aspect, due to containing the above-mentioned organic electrolyte, the lithium ion secondary battery has excellent cycle life characteristics, high temperature storage stability and low temperature discharge capability.

[0045] In some embodiments of the present application, the positive electrode material can be selected from at least one of lithium manganese oxide, nickel cobalt lithium manganese oxide ternary material, lithium nickel manganese oxide or lithium-rich manganese-based material; preferably, it is a ternary high nickel (Ni≥90) material.

[0046] Preferably, the Ni or Mn content in the positive electrode material is greater than 65%

[0047] In some embodiments of the present application, the negative electrode material can be selected from at least one of artificial graphite, hard carbon, soft carbon, mesophase carbon microbeads, silicon-based negative electrode materials or lithium-containing metal composite oxide materials; preferably artificial graphite.

[0048] In some embodiments of the present application, the diaphragm can be selected from a polyethylene diaphragm or a PP-coated ceramic diaphragm; preferably, the PP-coated ceramic diaphragm.

[0049] The positive electrode and negative electrode used in the lithium-ion secondary battery provided in the present application can be prepared by conventional methods in the art or directly purchased, and the lithium-ion secondary battery provided in the present application can be assembled by conventional methods.

[0050] For example, the positive electrode and the negative electrode can be prepared by the following preparation methods:

[0051] The specific preparation steps of the positive electrode include: mixing ternary high-nickel (Ni≥90) material, conductive carbon black, single-walled carbon nanotubes and binder polyvinylidene fluoride in a mass ratio of 97.3:1:0.5:1.2, dispersing the mixture in N-methyl-2-pyrrolidone to obtain a positive electrode slurry, and evenly coating the positive electrode slurry on both sides of the aluminum foil; after drying, calendering and vacuum drying, welding aluminum lead wires with an ultrasonic welder to obtain a positive electrode sheet with a thickness of 100 to 200 μm.

[0052] The specific preparation steps of the negative electrode include: mixing graphite, conductive carbon black, binder styrene-butadiene rubber and carboxymethyl cellulose in a mass ratio of 95:1.5:1.5:3, dispersing in deionized water to obtain a negative electrode slurry, coating the negative electrode slurry on both sides of the copper foil, drying, rolling and vacuum drying, and welding nickel lead wires with an ultrasonic welder to obtain a negative electrode sheet with a thickness between 100 and 200 μm.

[0053] In a third aspect, the present application further provides a method for improving the cycle life characteristics, high temperature storage stability, and low temperature discharge capability of a lithium-ion secondary battery, the method comprising:

[0054] The organic electrolyte described in the first aspect is added into a lithium-ion secondary battery.

[0055] Compared with the prior art, this application has the following beneficial effects:

[0056] The present application applies lithium tetrafluorooxalophosphate and isocyanate compounds in an organic electrolyte, which can form a more stable organic-inorganic composite modified SEI film at the negative electrode interface through bonding, thereby effectively reducing direct contact between the organic solvent and the negative electrode interface and improving the reversibility of lithium ion insertion / deinsertion; wherein, the isocyanate compound can also react with water and hydrofluoric acid in the electrolyte, and form new substances by breaking the carbon-nitrogen double bond, which can significantly reduce the acidity and moisture of the electrolyte. Moreover, due to the special properties of the long carbon chain, when participating in the construction of the SEI film, the SEI film formed in the present application can be made more elastic, which can better protect the negative electrode interface, thereby helping to improve the cycle life characteristics, high-temperature storage stability and low-temperature discharge capability of the battery. DETAILED DESCRIPTION

[0057] The following will be combined with the embodiments of this application to clearly and completely describe the technical solutions of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0058] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0059] It should also be understood that the terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit the present application. As used in this specification and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0060] It should be further understood that the term "and / or" used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0061] Example 1

[0062] Example 1 provides a high-nickel lithium-ion soft-pack battery, and the preparation method of the lithium-ion battery is as follows:

[0063] The coating surface density is determined based on the battery capacity design and the capacity of the positive and negative electrode materials. The positive electrode active material is a ternary high-nickel (Ni≥90) material purchased from Xiamen Tungsten Industry; the negative electrode active material is artificial graphite purchased from Shenzhen BTR; and the separator is a 12μm thick PP-coated ceramic separator purchased from Xingyuan Materials.

[0064] The positive electrode preparation steps include: mixing a ternary high-nickel (Ni≥90) material, conductive carbon black, single-walled carbon nanotubes, and a binder, polyvinylidene fluoride, in a mass ratio of 97.3:1:0.5:1.2, dispersing the mixture in N-methyl-2-pyrrolidone to obtain a positive electrode slurry, and evenly coating the positive electrode slurry on both sides of an aluminum foil; drying, rolling, and vacuum drying the mixture, and then welding aluminum lead wires with an ultrasonic welder to obtain a positive electrode sheet with a thickness of 100 to 200 μm.

[0065] The negative electrode preparation steps include: mixing graphite, conductive carbon black, binder styrene-butadiene rubber and carboxymethyl cellulose in a mass ratio of 95:1.5:1.5:3, dispersing the mixture in deionized water to obtain a negative electrode slurry, coating the negative electrode slurry on both sides of a copper foil, drying, rolling and vacuum drying, and welding nickel lead wires with an ultrasonic welder to obtain a negative electrode sheet with a thickness of 100 to 200 μm;

[0066] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order and wound to obtain a bare battery cell;

[0067] Preparation of organic electrolyte: Ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), and propylene carbonate (PC) were mixed in a mass ratio of 55:20:20:5 to prepare a solvent. After mixing, lithium hexafluorophosphate, fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), vinylene carbonate (VC), an isocyanate compound additive represented by Formula 2 (n=6), and LiTFOP were added; wherein the ratio of LiTFOP to isocyanate compound was 2:1. The mass contents of each component are shown in Table 1.

[0068] The bare battery cell is placed in an aluminum-plastic film outer package, the prepared electrolyte is injected into the dried battery, and the battery is packaged, left to stand, formed, shaped, and capacity tested to complete the preparation of the lithium-ion battery.

[0069] Example 2

[0070] The difference from Example 1 is that the contents of the isocyanate compound represented by Formula 2 (n=6) and LiTFOP are different. The mass contents of each component are shown in Table 1.

[0071] Example 3

[0072] The difference from Example 2 is that the content of LiTFOP is different. The ratio of LiTFOP to the isocyanate compound represented by Formula 2 (n=6) is adjusted to 3:1. The mass content of each component is shown in Table 1.

[0073] Example 4

[0074] The difference from Example 2 is that the content of LiTFOP is different. The ratio of LiTFOP to the isocyanate compound represented by Formula 2 (n=6) is adjusted to 3.5:1. The mass content of each component is shown in Table 1.

[0075] Example 5

[0076] The difference from Example 2 is that the ratio of LiTFOP to the isocyanate compound represented by Formula 2 (n=6) is adjusted to 5:1, and the mass content of each component is shown in Table 1.

[0077] Example 6

[0078] The difference from Example 2 is that the isocyanate compound represented by Formula 2 (n=6) is changed to methyl isocyanate. The mass content of each component is shown in Table 1.

[0079] Example 7

[0080] The difference from Example 2 is that the isocyanate compound represented by Formula 2 (n=6) is adjusted to 4'4'4'-triisocyanatophenyl phosphate. The mass content of each component is shown in Table 1.

[0081] Comparative Example 1

[0082] The main difference from Example 2 is that no isocyanate compound is contained. The mass content of each component is shown in Table 1. The mass content of each component is shown in Table 1.

[0083] Comparative Example 2

[0084] The main difference from Example 2 is that the electrolyte does not contain LITFOP. The mass content of each component is shown in Table 1. The mass content of each component is shown in Table 1.

[0085] Comparative Example 3

[0086] The main difference from Example 2 is that the electrolyte does not contain LITFOP and isocyanate compound. The mass content of each component is shown in Table 1.

[0087] Comparative Example 4

[0088] The main difference from Example 2 is that the content of LITFOP in the electrolyte is different. The ratio of LiTFOP to the isocyanate compound shown in Formula 2 (n=6) is adjusted to 0.2:1. The mass content of each component is shown in Table 1.

[0089] Comparative Example 5

[0090] The main difference from Example 2 is that the content of LITFOP in the electrolyte is different. The ratio of LiTFOP to the isocyanate compound shown in Formula 2 (n=6) is adjusted to 0.6:1. The mass content of each component is shown in Table 1.

[0091] Comparative Example 6

[0092] The main difference from Example 2 is that the content of LITFOP in the electrolyte is different. The ratio of LiTFOP to the isocyanate compound shown in Formula 2 (n=6) is adjusted to 8:1. The mass content of each component is shown in Table 1.

[0093] Comparative Example 7

[0094] The main difference from Example 2 is that the content of LITFOP in the electrolyte is different. The ratio of LiTFOP to the isocyanate compound shown in Formula 2 (n=6) is adjusted to 10:1. The mass content of each component is shown in Table 1.

[0095] Comparative Example 8

[0096] The main difference from Example 2 is that the contents of the isocyanate compound represented by Formula 2 (n=6) and LiTFOP in the electrolyte are different. The ratio of LiTFOP to the isocyanate compound represented by Formula 2 (n=6) is adjusted to 2:1. The mass content of each component is shown in Table 1.

[0097] Comparative Example 9

[0098] The main difference from Example 2 is that the contents of the isocyanate compound represented by Formula 2 (n=6) and LiTFOP in the electrolyte are different. The ratio of LiTFOP to the isocyanate compound represented by Formula 2 (n=6) is adjusted to 5:1. The mass content of each component is shown in Table 1.

[0099] Table 1 Electrolyte formulations of Examples 1-7 and Comparative Examples 1-9

[0100]

[0101] Lithium-ion battery performance testing

[0102] Battery performance tests were performed on Examples 1 to 7 and Comparative Examples 1 to 9 using the following test methods:

[0103] 25℃ 1C / 1C normal temperature cycle test: Place the battery in a 25℃ environment, charge it at a constant current of 1C to 4.25V, charge it at a constant voltage of 4.25V to a cut-off current of 0.05C, leave it for 5 minutes, then discharge it at a constant current of 1C to 2.75V, the discharge capacity is recorded as C0, leave it for 5 minutes, this is one charge and discharge cycle, repeat the charge and discharge steps 1000 times, and obtain the discharge capacity C0 at the 1000th cycle. 1000 , capacity retention rate = C 1000 / C0*100%.

[0104] 45℃ 1C / 1C high temperature cycle test: Place the battery in a 45℃ explosion-proof oven, charge at 1C constant current to 4.25V, charge at 4.25V constant voltage to a cut-off current of 0.05C, leave for 5 minutes, then discharge at 1C constant current to 2.75V, the discharge capacity is recorded as C0, leave for 5 minutes, this is one charge and discharge cycle, repeat the charge and discharge steps 500 times, and obtain the discharge capacity C0 at the 500th cycle. 500 , capacity retention rate = C 500 / C0*100%.

[0105] Battery low-temperature discharge performance test: The battery capacity in a fully charged state is recorded as C0. It is placed in a -20°C constant temperature test freezer for 5 hours, and then discharged to 2.75V at a constant current of 0.5C. The discharge capacity is recorded as C1. The low-temperature capacity retention rate = C1 / C0*100%.

[0106] Battery 60 ℃ 30-day storage capacity retention rate, capacity recovery rate and thickness expansion rate test: charge to 4.25V at 1C constant current at 25 ℃, charge to a cut-off current of 0.05C at a constant voltage of 4.25V, and leave for 5 minutes. Then, the battery is discharged at 1C constant current, the discharge capacity is recorded as C0, and the battery thickness is recorded as D0. Then, the battery is placed in a 60 ℃ explosion-proof oven. After storage for 30 days, the battery thickness D1 is tested in the oven. Then, the battery is taken out and cooled to room temperature, and its discharge retention capacity C2 of 1C discharge to 2.75V is tested. Then, the charge and discharge steps are repeated for 3 weeks and the battery discharge capacity C3 in the third week is recorded. Thickness expansion rate = (D1-D0) / D0*100%, capacity retention rate = C2 / C0*100%, capacity recovery rate = C3 / C0*100%.

[0107] After the electrolytes in Examples 1-7 and Comparative Examples 1-9 were made into lithium-ion batteries, the room temperature cycle performance, high temperature cycle performance, and high temperature storage performance of the lithium-ion batteries were tested. The results are shown in Table 2:

[0108] Table 2 Battery performance test results of Examples 1-7 and Comparative Examples 1-9

[0109]

[0110]

[0111] Experimental results analysis:

[0112] The experimental results of Examples 1 to 7 show that a lithium tetrafluorooxalophosphate content of 0.1-6% and a mass ratio of lithium tetrafluorooxalophosphate to isocyanate compound of 2-5:1 can effectively improve the battery's cycle life characteristics, high-temperature storage stability, and low-temperature discharge capability. Furthermore, the combination of the isocyanate compound represented by Formula 2 (n=6) and LiTFOP significantly improves the battery's room-temperature cycling, high-temperature cycling, low-temperature discharge performance, and high-temperature storage performance, with a preferred ratio of 1:2.

[0113] By comparing the experimental results of Comparative Examples 1-3 and Example 2, it can be seen that the synergistic use of lithium tetrafluorooxalophosphate and isocyanate compounds significantly improves the cycle life characteristics, high temperature storage stability and low temperature discharge capacity of the battery.

[0114] Comparing the experimental results of Comparative Examples 4-7 and Example 2 shows that when the mass ratio of lithium tetrafluorooxalophosphate to isocyanate compound is less than 2:1, the battery's room-temperature and high-temperature cycle life are significantly shortened, the low-temperature capacity retention rate decreases, and the battery's high-temperature gas production increases slightly. When the mass ratio of lithium tetrafluorooxalophosphate to isocyanate compound is greater than 5:1, the battery's room-temperature cycle life, high-temperature cycle life, and low-temperature capacity retention rate are also significantly shortened, and the battery's high-temperature gas production increases slightly.

[0115] By comparing the experimental results of Comparative Examples 8 and 9 with those of Example 2, it can be seen that when the content of lithium tetrafluorooxalophosphate is greater than 6%, the normal temperature and high temperature cycle life of the battery will be greatly shortened, the low temperature capacity retention rate will decrease, the high temperature capacity retention rate and recovery rate will decrease significantly, and the high temperature gas production phenomenon of the battery will be aggravated.

[0116] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. An organic electrolyte, characterized in that The organic electrolyte comprises: lithium tetrafluorooxalophosphate, and Isocyanate compounds; The isocyanate compound is selected from a mixture of one or more of a monoisocyanate compound, a diisocyanate compound, and a polyisocyanate compound; Wherein, the mass ratio of the lithium tetrafluorooxalophosphate to the isocyanate compound is 2-5:1; The content of the lithium tetrafluorooxalophosphate is 0.1 to 6%, based on the total weight of the organic electrolyte; The monoisocyanate compound is selected from compounds having the structure shown in Formula 1: R1-NCO<Formula 1>, In formula 1, R1 is selected from 1～10 Alkyl, C 1～10 Alkenyl, C 1～10 Alkynyl, C 1～10 Alkoxy, C 1～10 aryl groups; The diisocyanate compound is selected from compounds having the structure shown in Formula 2: In formula 2, n is an integer from 2 to 10; The polyisocyanate compound is selected from compounds having the structure shown in Formula 3: In formula 3, R2 is selected from C 1～10 Alkylene; R3, R4, R5 are each independently selected from C 1～10 Alkylene, C 1～10 Alkenylene, C 1～10 of alkyleneoxy.

2. The organic electrolyte according to claim 1, characterized in that The monoisocyanate compound is selected from the group consisting of methyl isocyanate, n-butyl isocyanate, tert-butyl isocyanate, phenyl isocyanate, p-chlorophenyl isocyanate, 3-chlorophenyl isocyanate, 3,4-dichlorophenyl isocyanate, 3,5-dichlorophenyl isocyanate, p-methylphenyl isocyanate, 3-chloro-4-methylphenyl isocyanate, p-isopropylphenyl isocyanate, p-bromophenyl isocyanate, p-nitrophenyl isocyanate and 4-(p-chlorophenoxy)-phenyl isocyanate. Any one or more mixtures thereof.

3. The organic electrolyte according to claim 1, characterized in that The diisocyanate compound is selected from one of isophorone diisocyanate and hexamethylene diisocyanate, or a mixture of the two.

4. The organic electrolyte according to claim 1, characterized in that The polyisocyanate compound is selected from any one of 4'4'4'-triisocyanatophenyl phosphate and 4'4'4'-triisocyanatophenyl thiophosphate, or a mixture of the two.

5. The organic electrolyte according to claim 1, characterized in that The organic electrolyte further includes a lithium salt; The lithium salt is selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium 4,5-dicyano-2-trifluoromethylimidazolium, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tris(oxalato)phosphate, lithium difluorobisoxalatophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl imide). The content of the lithium salt is 10-20%, based on the total mass of the organic electrolyte.

6. The organic electrolyte according to claim 1, characterized in that The organic electrolyte further includes a non-aqueous solvent; The non-aqueous solvent is selected from any one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, γ-butyrolactone, γ-valerolactone, δ-valerolactone, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,4-dioxane, sulfolane, tetrahydrofuran, 2-methyltetrahydrofuran, difluoroethylene carbonate, dimethyl fluorocarbonate, ethyl methyl fluorocarbonate, methyl difluoroacetate, and ethyl difluoroacetate; The content of the non-aqueous solvent is 66-88.85% based on the total mass of the organic electrolyte.

7. The organic electrolyte according to claim 1, characterized in that The organic electrolyte further includes an additive; The additive is selected from one or more mixtures selected from vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,4-butane sultone, 1,3-(1-propylene) sultone, fluoromethyl vinyl carbonate, dimethyl sulfate, vinyl sulfate, methyl vinyl sulfate, propylene sulfate, vinyl sulfite, succinic anhydride, biphenyl, diphenyl ether, toluene, xylene, cyclohexylbenzene, fluorobenzene, p-fluorotoluene, p-fluoroanisole, tert-butylbenzene, tert-amylbenzene, methylene methanedisulfonate, ethylene glycol bis(propionitrile) ether, hexamethyldisilazane, heptamethyldisilazane, dimethyl methylphosphonate, diethyl ethylphosphonate, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, and dimethyl sulfoxide.

8. The organic electrolyte according to claim 7, characterized in that The content of the additive is 1-5%, based on the total mass of the organic electrolyte.

9. A lithium ion secondary battery, characterized in that: The lithium-ion secondary battery comprises: positive electrode; negative electrode; diaphragms; and The organic electrolyte according to any one of claims 1 to 8.

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