Electrolyte additive, electrolyte and lithium ion battery

Abstract

The application provides an electrolyte additive, an electrolyte and a lithium ion battery, which comprise a first additive m H n X p COOLi, wherein C m H n X p is at least one of a chain or cyclic alkyl group, a chain or cyclic alkenyl group, a chain or cyclic alkynyl group, and an aryl group, X is at least one halogen atom, 0<=n<2m+1, 0 The first additive provided by the application can form a supramolecular assembly through hydrogen bonding with a solvent or itself in the electrolyte, the supramolecular assembly has high surface energy, can preferentially adsorb active oxygen free radicals and oxygen generated after the positive material is damaged under high temperature and high pressure, and can effectively reduce the side reaction of the product on the negative electrode surface, thereby effectively improving the cycle performance and high-temperature storage performance of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium batteries, specifically to an electrolyte additive, an electrolyte, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, with their high energy density, long cycle life, high operating voltage, and low self-discharge rate, are widely used in smart wearables, computers, smartphones, and electric vehicles. The electrolyte, the "lifeblood" of the lithium-ion battery, is one of its essential components, responsible for energy transfer between the positive and negative electrodes and playing a crucial role in battery performance. Its solvents, lithium salts, and additives all significantly impact the battery's low-temperature performance, cycle life, storage performance, and safety. However, current electrolytes cannot effectively mitigate side reactions on the electrode surface under high voltage, posing a significant challenge to the cycle and storage performance of lithium-ion batteries and severely hindering their development at high voltage.

[0003] In view of this, it is indeed necessary to provide a technical solution to the above problems. Summary of the Invention

[0004] One of the objectives of this invention is to provide an electrolyte additive that addresses the shortcomings of existing technologies, thereby solving the problem that current electrolytes cannot improve the severe side reactions on the electrode surface under high voltage. By reducing the side reactions on the electrode surface under high voltage, the cycle life and high-temperature storage capacity of lithium-ion batteries are effectively improved.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An electrolyte additive includes a first additive, the structure of which is C m H n X p COOLi, where C m H n X p It is at least one of the following: chain or cyclic alkyl, chain or cyclic alkenyl, chain or cyclic alkynyl, aryl; X is at least one halogen atom; 0≤n<2m+1, 0<p≤2m+1, 4≤m≤18, p / (p+n)≥20%, m, n, p∈N.

[0007] Preferably, the first additive also satisfies the following condition: n < p.

[0008] Preferably, the first additive also satisfies the following conditions: 0≤n<m, 6≤m≤18.

[0009] Preferably, the first additive is at least one of the following structural formulas:

[0010]

[0011] 1. Preferably, the additive further includes a second additive, wherein the second additive is at least one of compounds with the structure of formulas I to IV.

[0012]

[0013]

[0014] Where M is an O atom and / or a N atom, X1~X 12 Each of the following is independently selected from at least one of hydrogen, alkyl groups having 1 to 15 carbon atoms and their substituents, alkenyl groups having 1 to 15 carbon atoms and their substituents, and alkynyl groups having 1 to 15 carbon atoms and their substituents, wherein the substituent is at least one of hydrogen, aryl, haloyl, amino, nitro, or sulfonyl.

[0015] Preferably, the second additive is at least one of the following structural formulas;

[0016]

[0017] Among them, R1~R 48 Each group is independently selected from at least one of hydrogen, alkyl with 1 to 10 carbon atoms, alkenyl with 1 to 10 carbon atoms, alkynyl with 1 to 10 carbon atoms, aryl, haloyl, amino, nitro, and sulfonyl.

[0018] Preferably, the additive further includes a third additive, which is at least one selected from vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, succinate, adiponitrile, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, propylene sulfonate lactone, methane disulfonate methylene ester, and ethylene glycol bis(propionitrile) ether.

[0019] A second objective of this invention is to provide an electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive is any of the electrolyte additives described above.

[0020] Preferably, the mass of the first additive is 0.1 to 10 wt% of the total mass of the electrolyte; the mass of the second additive is 0.1 to 10 wt% of the total mass of the electrolyte; and the mass of the third additive is 0.5 to 20 wt% of the total mass of the electrolyte.

[0021] A third objective of this invention is to provide a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator spaced between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is any of the electrolytes described above.

[0022] Compared to existing technologies, the advantages of this invention are as follows: The first additive provided by this invention can form supramolecular assemblies in the electrolyte through hydrogen bonding with the solvent or itself. These supramolecular assemblies have high surface energy and can preferentially adsorb reactive oxygen free radicals and oxygen generated after the destruction of the positive electrode material under high temperature and pressure, thereby effectively reducing side reactions occurring on the negative electrode surface and thus effectively improving the cycle performance and high-temperature storage performance of lithium-ion batteries. Specifically, the supramolecular assembly formed by the first additive of this invention includes an outer portion and an inner portion, and the COOLi structure dissociates to form COO. - They repel each other through electrostatic forces, forming the outer part of the assembly; C m H n X p The structure, as the inner part, contains more substituted halogen atoms, which can bond together through hydrogen bonds formed between halogen atoms and hydrogen atoms (not limited to C). m H n X p (Individual solvent molecules may also participate in the binding), ultimately forming supramolecular assemblies with structures such as spheres, rods, or bilayer membranes. Detailed Implementation

[0023] 1. Additives for electrolytes

[0024] A first aspect of the present invention aims to provide an additive for electrolytes, comprising a first additive, wherein the structure of the first additive is C m H n X p COOLi, where C m H n X p It is at least one of the following: chain or cyclic alkyl, chain or cyclic alkenyl, chain or cyclic alkynyl, aryl; X is at least one halogen atom; 0≤n<2m+1, 0<p≤2m+1, 4≤m≤18, p / (p+n)≥20%, m, n, p∈N.

[0025] Specifically, m can be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18; n can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, etc.; and p can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, etc. The amount of X substitution is selected according to the different carbon atoms in m. X can specifically be Cl or F. Preferably, X is F-substituted, and the substitution amount n < p. More preferably, n = 0, and p is a complete substitution. The inventors have discovered that for C in the first additive...m H n X p The more carbon and halogen atoms a structure has, the stronger the intermolecular hydrogen bonding, making it easier to form supramolecular assemblies. This also enhances its ability to adsorb reactive oxygen species (ROS) and oxygen under high temperature and pressure, more effectively reducing side reactions of ROS and oxygen on the negative electrode surface, thereby improving cycle performance under high voltage. Preferably, 6 ≤ m ≤ 18, C m H n X p It is a chain-like alkyl or aryl group.

[0026] Compared to other compounds containing halogen atoms or compounds with fewer halogen atoms and carbon atoms, the first additive of this invention can form supramolecular assemblies, thereby solving the problem of severe side reactions on the electrode surface under high temperature and high pressure.

[0027] In some embodiments, the first additive is at least one of the structural formulas in Table 1.

[0028] Table 1

[0029]

[0030] The first additive can be obtained by dissolving the corresponding precursor in a solvent, such as a 1:1 mixture of hexafluoroisopropanol and water, then adding the mixture to an aqueous lithium hydroxide solution at a 1:1 molar ratio, followed by rotary evaporation to remove the solvent and drying. For example, compound A4 is obtained by dissolving perfluorooctanoic acid in a 1:1 mixture of hexafluoroisopropanol and water, then adding the mixture to an aqueous lithium hydroxide solution at a 1:1 molar ratio, followed by rotary evaporation to remove the solvent and drying. Similarly, compound A5 is obtained by dissolving 2,4,6-trifluorobenzoic acid in a 1:1 mixture of hexafluoroisopropanol and water, then adding the mixture to an aqueous lithium hydroxide solution at a 1:1 molar ratio, followed by rotary evaporation to remove the solvent and drying.

[0031] Preferably, the additive further includes a second additive, which is at least one of compounds with the structure of formulas I to IV.

[0032]

[0033] Where M is an O atom and / or a N atom, X1~X 12 Each of the following is independently selected from at least one of hydrogen, alkyl groups having 1 to 15 carbon atoms and their substituents, alkenyl groups having 1 to 15 carbon atoms and their substituents, and alkynyl groups having 1 to 15 carbon atoms and their substituents, wherein the substituent is at least one of hydrogen, aryl, haloyl, amino, nitro, or sulfonyl.

[0034] The electrolyte of this invention employs a second additive, which can form a film on the surface of the electrode material (mainly the positive electrode). The P atoms contained therein can react with oxygen in the positive electrode to stabilize the structure of the positive electrode, thereby reducing the phase transition and side reactions of the positive electrode active material under high temperature and high pressure from the root. Combined with the ability of the supramolecular assembly of the first additive to capture reactive oxygen free radicals and oxygen, it not only further improves the cycle performance and high temperature storage performance of lithium-ion batteries, but also effectively improves the safety performance of lithium-ion batteries, enabling them to still have excellent safety performance at high temperatures of 132°C and 135°C.

[0035] More preferably, the second additive is a compound of formula I or III. This compound is not oxidized and, when applied to the electrolyte, can also consume some of the oxygen generated by the decomposition of the positive electrode material. It has a better synergistic effect with the first additive and further prevents the side reactions that occur on the negative electrode surface caused by the generated oxygen.

[0036] Preferably, the second additive is at least one of the following structural formulas;

[0037]

[0038] Among them, R1~R 48 Each group is independently selected from at least one of hydrogen, alkyl with 1 to 10 carbon atoms, alkenyl with 1 to 10 carbon atoms, alkynyl with 1 to 10 carbon atoms, aryl, haloyl, amino, nitro, and sulfonyl.

[0039] Specifically, the second additive includes, but is not limited to, at least one of the structural formulas in Table 2.

[0040] Table 2

[0041]

[0042]

[0043]

[0044] In some embodiments, the additive further includes a third additive, which is at least one selected from vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), vinyl sulfate (DTD), succinic anionyl nitrile (SN), adiponitrile (ADN), 1,3,6-hexanetrionitrile (HTCN), 1,2,3-tris(2-cyanoxy)propane, propenesulfonate lactone (PST), methanedisulfonate methylene ester (MMDS), and ethylene glycol bis(propionitrile) ether (EGBE). Preferably, the third additive is at least two of the above additives. Using two or more third additives together with the first and second additives not only enhances the efficacy of the third additive but also further promotes the effects of the first and second additives, thereby improving cycle performance, storage performance, and safety performance. Preferably, the third additive is a mixture of 1,3-propanesulfonate lactone (PS), fluoroethylene carbonate (FEC), and 1,2,3-tris(2-cyanoxy)propane.

[0045] 2. Electrolyte

[0046] A second aspect of the present invention aims to provide an electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive is any of the electrolyte additives described above.

[0047] In some embodiments, the mass of the first additive is 0.1 to 10 wt% of the total mass of the electrolyte. Specifically, it can be 0.1 to 0.5 wt%, 0.5 to 1 wt%, 1 to 2 wt%, 2 to 3 wt%, 3 to 4 wt%, 4 to 5 wt%, 5 to 6 wt%, 6 to 7 wt%, 7 to 8 wt%, 8 to 9 wt%, or 9 to 10 wt% of the total mass of the electrolyte. Preferably, the mass of the first additive is 0.5 to 5.0 wt% of the total mass of the electrolyte. In the electrolyte, an appropriate amount of the first additive can preferentially capture reactive oxygen free radicals and oxygen generated after the positive electrode material is damaged under high temperature and high pressure, thereby effectively reducing the side reactions of reactive oxygen free radicals and oxygen on the negative electrode surface.

[0048] In some embodiments, the mass of the second additive is 0.1 to 10 wt% of the total mass of the electrolyte. Specifically, it can be 0.1 to 0.5 wt%, 0.5 to 1 wt%, 1 to 2 wt%, 2 to 3 wt%, 3 to 4 wt%, 4 to 5 wt%, 5 to 6 wt%, 6 to 7 wt%, 7 to 8 wt%, 8 to 9 wt%, or 9 to 10 wt% of the total mass of the electrolyte. Preferably, the mass of the second additive is 0.5 to 3.0 wt% of the total mass of the electrolyte. When the first additive is added in an appropriate amount, the second additive is also added in an appropriate amount. The synergistic effect of the two can not only reduce the oxygen generated by side reactions under high temperature and high pressure at the source, but also effectively capture the oxygen that has already been generated. This effectively reduces the side reactions of the active material under high temperature and high pressure, improves the cycle performance and storage performance of the lithium-ion battery, and also ensures the safety performance of the lithium-ion battery.

[0049] In some embodiments, the mass of the third additive is 0.5–20 wt% of the total mass of the electrolyte. Preferably, the mass of the third additive is 5–13 wt% of the total mass of the electrolyte, specifically 5–6 wt%, 6–7 wt%, 7–8 wt%, 8–9 wt%, 9–10 wt%, 10–11 wt%, 11–12 wt%, or 12–13 wt%. More preferably, the mass of the third additive is 5–10 wt% of the total mass of the electrolyte.

[0050] In some embodiments, the lithium salt is at least one selected from lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2), lithium difluorobis(oxalate) phosphate (LiPF2(C2O4)2), lithium tetrafluorooxalate phosphate (LiPF4C2O4), lithium oxalate phosphate (LiPO2C2O4), lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI). The mass of the lithium salt is 8–20 wt% of the total mass of the electrolyte.

[0051] In some embodiments, the organic solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl butyrate (EB), and γ-butyrolactone (GBL); the mass of the organic solvent is 50-85 wt% of the total mass of the electrolyte.

[0052] 3. Lithium-ion batteries

[0053] A third aspect of this invention aims to provide a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator spaced between the positive and negative electrode, and an electrolyte, wherein the electrolyte is any of the electrolytes described above. Compared to other conventional electrolyte additives, the electrolyte of this invention, due to the addition of the first and second additives, is particularly suitable for applications at high voltage and high temperature of 4.4–4.5V.

[0054] The positive electrode sheet includes a positive current collector and a positive active material layer coated on the positive current collector. The positive active material layer includes a positive active material, a positive conductive agent, and a positive binder. The positive active material may be, but is not limited to, a chemical formula such as Li. a Ni x Co y M z O 2-b N b (where 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S) The positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 The positive electrode active material can be one or more combinations thereof, including O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, and TiS2. The positive electrode active material can also be modified. Methods for modifying the positive electrode active material are known to those skilled in the art. For example, coating, doping, and other methods can be used to modify the positive electrode active material. The materials used for modification can be one or more combinations thereof, including but not limited to Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W. The positive electrode current collector is typically a structure or component that collects current. The positive electrode current collector can be any material suitable for use as a positive electrode current collector in lithium-ion batteries. For example, the positive electrode current collector can be, but is not limited to, metal foil, and more specifically, aluminum foil.

[0055] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The negative electrode active material can be one or more of the following, including but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Specifically, the graphite can be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is typically a structure or component that collects current. The negative electrode current collector can be any material suitable for use as a negative electrode current collector in lithium-ion batteries, for example, the negative electrode current collector can be, but is not limited to, metal foil, and more specifically, copper foil.

[0056] The separator can be any material suitable for lithium-ion battery separators in the art, such as, but not limited to, one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0057] To make the technical solution and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto.

[0058] Example 1

[0059] A lithium-ion battery includes a positive electrode, a negative electrode, a separator spaced between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode uses LiCoO2 as the positive electrode active material, the negative electrode uses graphite as the negative electrode active material, and the separator is a polypropylene separator.

[0060] Preparation of electrolyte: In an argon-filled glove box with a moisture content <5 ppm and an oxygen content <5 ppm, ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (DEC), propyl propionate (PP), and ethyl propionate (EP) were mixed in a mass ratio of EC:PC:DEC:PP:EP = 1:1:1:1:1 to obtain an organic solvent. Then, lithium hexafluorophosphate (LiPF6) at 13.7 wt% of the total electrolyte weight was slowly added to the organic solvent to obtain a mixture of organic solvent and lithium salt. Finally, first additive A4 at 0.5 wt% of the total electrolyte weight, propane sulfonate lactone (PS), fluoroethylene carbonate (FEC), and 1,2,3-tris(2-cyanoxy)propane were added and stirred until homogeneous to obtain the electrolyte of Example 1.

[0061] The preparation method of the first additive A4 is as follows: perfluorooctanoic acid is dissolved in a solvent of hexafluoroisopropanol:water = 1:1, and then added to an aqueous lithium hydroxide solution at a molar ratio of 1:1. The solvent is removed by rotary evaporation and the mixture is dried.

[0062] Preparation of soft-pack batteries: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets, and wound to obtain a bare cell; the bare cell is placed in an aluminum-plastic film outer packaging and vacuum dried at 80°C. After the moisture content reaches the standard, the electrolyte prepared above is injected into the dried battery, and then it is packaged, left to stand, hot and cold pressed, formed, shaped, and capacity tested to complete the preparation of the lithium-ion battery.

[0063] Examples 2-25 and Comparative Examples 1-2 were prepared according to the above preparation method with only the first additive and the third additive added. The difference from Example 1 is the content of each substance in the electrolyte. The specific substances and their contents are shown in Table 3 below.

[0064] Table 3

[0065]

[0066]

[0067] Performance testing

[0068] The lithium-ion batteries and their electrolytes obtained in Examples 1-25 and Comparative Examples 1-2 were subjected to relevant performance tests.

[0069] (1) Lithium-ion battery cycle performance test

[0070] The lithium-ion batteries were placed in a 45°C constant temperature chamber and left to stand for 30 minutes to allow them to reach a constant temperature. The batteries were then charged at a constant current of 0.5C to a voltage of 4.4V, followed by charging at a constant voltage of 4.4V to a current of 0.05C, and finally discharging at a constant current of 0.5C to a voltage of 3.0V. This constitutes one charge-discharge cycle. This charging and discharging process was repeated, and the capacity retention rate of the lithium-ion batteries after 500 cycles was calculated.

[0071] (2) High-temperature storage volume expansion test

[0072] The lithium-ion battery was charged at a constant current of 0.5C to 4.4V, then charged at a constant voltage to a current of 0.05C until fully charged. The thickness THK1 of the lithium-ion battery under full charge was measured. The fully charged cell was then stored in a 60°C high-temperature furnace for 14 days, and the cell thickness THK2 was measured thermally. The expansion rate of the lithium-ion battery was calculated using the following formula:

[0073] Expansion rate = (THK2 - THK1) / THK1.

[0074] The test results are shown in Table 4 below.

[0075] Table 4

[0076]

[0077]

[0078] The test results from Examples 1-12 and Comparative Example 1, as well as Examples 20-21, 23-24 and Comparative Example 2, show that the addition of the first additive of the present invention can effectively improve the cycle performance and storage performance of lithium-ion batteries under high temperature and high pressure. In particular, the first additive with an A4 structure has a higher number of carbon atoms and halogen atoms, resulting in stronger intermolecular hydrogen bonding and easier formation of supramolecular assemblies. Furthermore, the resulting supramolecular assemblies have a large surface energy, which more effectively adsorbs reactive oxygen species and oxygen under high temperature and high pressure, reducing side reactions of reactive oxygen species and oxygen on the negative electrode surface, thereby improving cycle performance and storage performance under high temperature and high pressure.

[0079] Furthermore, the comparison of Examples 1-12 shows that as the content of the first additive increases, its effect in suppressing high-temperature expansion becomes more significant. However, excessive first additive can conversely affect cycle performance at high temperatures. Additionally, the comparison of Examples 1-19 shows that using two or more first additives improves the cycle and storage performance of lithium-ion batteries compared to using only one. In particular, the combination of A4 with other first additives can more effectively improve the cycle and storage performance of lithium-ion batteries under high temperature and high pressure.

[0080] Furthermore, the inventors have discovered that when the third additive is a mixture of 1 wt% propane sulfonate lactone (PS), 5 wt% fluoroethylene carbonate (FEC), and 3 wt% 1,2,3-tris(2-cyanoxy)propane, its synergistic effect with the first additive significantly improves the cycling performance under high temperature and high pressure. However, compared with the third additive in the 3:3:3 ratio, the expansion rate at high temperature is significantly increased, as can also be seen from the comparison of Examples 1-19 and Examples 20-25 above.

[0081] The inventors continued to experiment with and test the performance of lithium-ion batteries containing the first additive, the second additive, and the third additive. Specifically, refer to the preparation methods of Examples 26-53 and Comparative Examples 3-4 in Example 1 above. The difference from Example 1 is the content of each substance in the electrolyte; the specific substances and their contents are shown in Table 5 below.

[0082] Table 5

[0083]

[0084]

[0085]

[0086] Performance testing

[0087] The lithium-ion batteries and their electrolytes obtained in Examples 26-53 and Comparative Examples 3-4 were subjected to relevant performance tests.

[0088] (1) Lithium-ion battery cycle performance test

[0089] The lithium-ion batteries were placed in a 45°C constant temperature chamber and left to stand for 30 minutes to allow them to reach a constant temperature. The batteries were then charged at a constant current of 0.5C to a voltage of 4.4V, followed by charging at a constant voltage of 4.4V to a current of 0.05C, and finally discharging at a constant current of 0.5C to a voltage of 3.0V. This constitutes one charge-discharge cycle. This charging and discharging process was repeated, and the capacity retention rate of the lithium-ion batteries after 500 cycles was calculated.

[0090] (2) Overcharge test

[0091] Place 3 batteries in an explosion-proof box, charge the lithium-ion batteries at a constant current of 3.0C to 4.6V, and then charge them at a constant voltage for 7 hours. The test is considered successful if the batteries do not catch fire or explode.

[0092] (3) Short circuit test

[0093] The lithium-ion batteries were charged at a constant current of 0.5C to 4.4V, then charged at a constant voltage until the current reached 0.05C, until fully charged. Three batteries were placed in an explosion-proof chamber, and the positive and negative terminals were short-circuited with an 80mΩ resistance wire for 24 hours. The test was considered successful if no fire or explosion occurred. The test results are shown in Table 6 below.

[0094] Table 6

[0095]

[0096]

[0097]

[0098] As can be seen from Examples 1, 6, 26-53 and Comparative Examples 3-4 above, using the first additive and the second additive of this application together as electrolyte additives can not only further improve cycle performance, but also make the battery have good stability in overcharge and short circuit tests, and greatly improve safety performance.

[0099] As can be seen from the comparison of Examples 28-31 and 35-43, as the content of the second additive increases, the cycle performance of the lithium-ion battery also increases and can maintain good stability in short-circuit tests. However, when the content of the second additive is high, the cycle performance tends to be stable. Too much additive can lead to a decrease in cycle performance. This is mainly because the second additive can form a protective film on the surface of the electrode active material. Too much additive will result in a larger film thickness, which will affect the migration of lithium ions.

[0100] Furthermore, the comparison of Examples 36-39 shows that, similar to the B5 structure, the cycle performance of lithium-ion batteries can be further improved. This is mainly because the unoxidized B5 structure can be oxidized, thereby consuming more oxygen generated by the electrode material, thus improving cycle performance and safety performance. Additionally, the comparison of Examples 40-43 shows that when the H on the alkyl group is further replaced by halogen atoms, the cycle performance can be further improved.

[0101] Furthermore, the comparison of Examples 44-53 also shows that the synergistic effect of the two first additives and the second additive further improves the cycle performance and safety performance of lithium-ion batteries. In particular, as in Examples 51-53, the cycle performance under high temperature and high pressure can reach more than 80%, which greatly expands the application of lithium-ion batteries.

[0102] In summary, the first additive provided by this invention forms a supramolecular assembly structure that can effectively improve the cycle performance and high-temperature storage performance of lithium-ion batteries; and its synergistic effect with the second and third additives can further improve cycle performance, high-temperature storage performance and safety performance, effectively solving the problem that current electrolytes cannot improve the serious side reactions on the electrode surface under high voltage.

[0103] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. An electrolyte, characterized in that, The mixture includes lithium salts, organic solvents, and additives, wherein the additives include a first additive, the first additive being at least one of the following structural formulas: 、 、 、 、 ; It also includes a second additive, wherein the second additive is at least one of the following structural formulas; Among them, R1~R 48 Each group is independently selected from at least one of hydrogen, alkyl with 1 to 10 carbon atoms, alkenyl with 2 to 10 carbon atoms, alkynyl with 2 to 10 carbon atoms, aryl, haloyl, amino, nitro, and sulfonyl.

2. The electrolyte according to claim 1, characterized in that, It also includes a third additive, which is at least one of vinylene carbonate, fluorovinyl carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, succinate, adiponitrile, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, propylene sulfonate lactone, methane disulfonate, and ethylene glycol bis(propionitrile) ether.

3. The electrolyte according to claim 2, characterized in that, The mass of the first additive is 0.1 to 10 wt% of the total mass of the electrolyte; the mass of the second additive is 0.1 to 10 wt% of the total mass of the electrolyte; and the mass of the third additive is 0.5 to 20 wt% of the total mass of the electrolyte.

4. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator spaced between the positive electrode and the negative electrode, and an electrolyte, characterized in that, The electrolyte is the electrolyte according to any one of claims 1 to 3.

Images