Electrolyte and battery

Abstract

The invention relates to the technical field of batteries, in particular to an electrolyte and a battery. The electrolyte comprises a first additive, and the first additive is a fluorine-containing nitrile benzene additive. The fluorine-containing nitrile benzene additive has an efficient positive electrode film-forming effect, can form obvious and relatively good positive electrode protection, and remarkably improves the high-temperature and high-pressure performance of the battery, so that the problems of high-temperature storage, high-temperature cycle expansion and the like of the battery are solved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to electrolytes and batteries. Background Art

[0002] In the past 10 to 20 years, lithium-ion batteries have gradually become the mainstream energy storage device. With the gradual development of lithium-ion battery technology and other scientific and technological fields, there are more and more application fields and scenarios, and they are increasingly widely used in mobile electronic devices, large-scale energy storage equipment, electric vehicles, etc.

[0003] In order to further improve the performance of lithium-ion batteries, research and development of lithium-ion batteries with higher energy density has become the main direction of the industry. In order to increase the energy density of the battery, the battery voltage can be further increased. However, if the battery voltage is further increased, the high-temperature performance of lithium-ion batteries will face severe challenges. Under high temperature and high pressure, the positive electrode surface is more likely to catalyze the decomposition of the electrolyte, and more transition metals will dissolve and migrate to the negative electrode surface, further aggravating the decomposition of the negative electrode SEI, so that the negative electrode is more likely to have side reactions with the electrolyte. The intensification of the side reactions of the positive and negative electrode electrolytes and the accumulation of a large number of by-products will lead to a significant deterioration in the high-temperature and high-pressure storage performance of the battery, and significant high-temperature cycle expansion.

[0004] In order to improve the high temperature and high pressure performance of batteries, new electrolyte additives need to be developed urgently to achieve better commercialization of batteries. Summary of the invention

[0005] In view of this, the present invention provides an electrolyte and a battery. The electrolyte can form a good CEI protective film on the surface of the positive electrode, significantly improving the stability of the positive electrode, thereby improving the high temperature and high pressure performance of the battery.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides an electrolyte, which includes a first additive, wherein the first additive is selected from at least one of the compounds represented by formula (1):

[0008]

[0009] Wherein, R1 and R2 are independently selected from H (hydrogen), fluorine or trifluoromethyl, R1 and R2 are the same or different, and at most one of R1 and R2 is H; R3 is a nitrile group or an alkanenitrile group having 2-10 carbon atoms.

[0010] The first additive of the present invention is a fluorinated nitrile benzene additive. Fluorinated nitrile benzene additives have three functional groups (including phenyl, fluorine, nitrile), and the presence of phenyl makes the additive easier to form cathode electrolyte interface (Cathode electrolyte interphase, CEI) film at the positive electrode oxidation decomposition, fluorine can react on the positive electrode surface to form inorganic lithium fluoride (LiF), and nitrile tends to coordinate with the positive transition metal, reducing transition metal dissolution. The simultaneous presence of the three functional groups makes it easy for the additive to preferentially form a positive electrode film, and at the same time, LiF with high stability can be formed to participate in film formation, and at the same time, the presence of the nitrile functional group can also act on the transition metal site to reduce transition metal dissolution. Therefore, the fluorinated nitrile benzene additive of the present invention has an efficient positive electrode film-forming effect, can form a positive electrode protection with significantly better, significantly improve the high temperature and high pressure performance of the battery, thereby improving the problems such as battery high temperature storage and high temperature cycle expansion.

[0011] In an embodiment of the present invention, R1 and R2 are independently selected from fluorine or trifluoromethyl, and R1 and R2 are the same or different; R3 is a nitrile group or an alkanenitrile group having 2-5 carbon atoms.

[0012] Furthermore, R1 and R2 are both selected from F-containing substituents. More F substituents can make it easier for fluorine to react on the positive electrode surface to form inorganic lithium fluoride (LiF), forming LiF with higher stability to participate in film formation, and better improve the high-temperature storage and high-temperature cycle expansion of the battery.

[0013] In an embodiment of the present invention, R1 and R2 are independently selected from trifluoromethyl; and R3 is a nitrile group.

[0014] Furthermore, the nitrile group is directly connected to the benzene ring, which can better exert the synergistic cooperation of the phenyl group, the fluorine group, and the nitrile group to have a more efficient positive electrode film-forming effect and a better positive electrode protection effect.

[0015] In an embodiment of the present invention, the first additive is selected from at least one of the compounds represented by formula (2) to formula (7):

[0016]

[0017] Preferably, the first additive accounts for 0.1wt% to 10wt% of the total mass of the electrolyte. Exemplary is 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, or any range of any two of the above values ​​or any point value within the range. Within the above numerical range, the electrolyte of the present invention can form a good CEI protective film on the surface of the positive electrode, significantly improve the stability of the positive electrode, and thus improve the high temperature and high pressure performance of the battery.

[0018] Preferably, the first additive accounts for 1 wt% to 8 wt% of the total mass of the electrolyte.

[0019] More preferably, the first additive accounts for 2 wt% to 6 wt% of the total mass of the electrolyte.

[0020] In an embodiment of the present invention, the electrolyte further includes a second additive, and the second additive includes at least two of fluorinated compounds, nitrile compounds, and sulfonic acid additives.

[0021] In an embodiment of the present invention, the second additive includes a fluorinated compound and a sulfonic acid additive.

[0022] The fluorinated compound and / or sulfonic acid additive in the second additive can form a good protective film on the negative electrode, thereby stabilizing the negative electrode interface. The combination of the first additive and the second additive can play a synergistic role, stabilize the positive and negative electrode interfaces, and ensure the high temperature stability of the entire battery system.

[0023] In an embodiment of the present invention, the fluorinated compound includes but is not limited to at least one of fluorinated carbonates, fluorinated carboxylates, and fluorinated ethers.

[0024] In an embodiment of the present invention, the fluorinated compound includes but is not limited to fluoroethylene carbonate (FEC), methyl trifluoroethyl carbonate (FEMC), fluorodiethyl carbonate (FDEC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 2,2,2-trifluoroethyl acetate (FEA), 2,2-difluoroethyl acetate, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE).

[0025] The fluorinated compound mainly forms a film on the negative electrode, while the first additive represented by formula (1) mainly acts on the positive electrode. The combination of the first additive and the fluorinated compound can further improve the high temperature and high pressure performance of the battery.

[0026] In an embodiment of the present invention, the sulfonic acid additive includes but is not limited to at least one of 1,3-propane sultone (PS), 1-propylene-1,3-sultone (PST), 5-methylthiothiocyanate 2,2-dioxide, 1,3-propylene sultone, 2,4-butane sultone, and 1,4-butane sultone.

[0027] Sulfonic acid additives can form a film on the negative electrode, further reducing the problem of gas generation during battery cycle and storage. When used in combination with the additive of formula (1), both the positive and negative electrodes have excellent high-temperature performance, thereby improving the overall performance of the battery.

[0028] In an embodiment of the present invention, the second additive includes a fluorinated compound, a sulfonic acid additive and a nitrile compound.

[0029] In an embodiment of the present invention, the nitrile compound includes at least one of saturated polynitriles, unsaturated alkyl polynitriles, and oxygen-containing alkyl nitriles.

[0030] In an embodiment of the present invention, the saturated polynitrile includes but is not limited to at least one of 1,3,6-hexanetrinitrile, succinonitrile, adiponitrile, glutaronitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 1,8-dicyanooctane, 1,9-dicyanononane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 2,6-dicyanoheptane, 2,7-dicyanooctane, 3,5-dioxa-heptanedinitrile and 1,4-bis(cyanoethoxy)butane.

[0031] In an embodiment of the present invention, the oxygen-containing alkyl nitriles include, but are not limited to, at least one of ethylene glycol di(2-cyanoethyl) ether, diethylene glycol di(2-cyanoethyl) ether, triethylene glycol di(2-cyanoethyl) ether, tetraethylene glycol di(2-cyanoethyl) ether, ethylene glycol bis(propionitrile) ether, 3,6,9,12,15,18-hexaoxaeicosanoic acid dinitrile, 1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy)butane, 1,5-bis(2-cyanoethoxy)pentane, and ethylene glycol di(4-cyanobutyl) ether.

[0032] In an embodiment of the present invention, the unsaturated alkyl polynitrile includes but is not limited to at least one of 1,4-dicyano-2-butene, 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene, 1,6-dicyano-3-hexene, 1,6-dicyano-2-methyl-3-hexene, and 1,6-dicyano-2-methyl-5-methyl-3-hexene.

[0033] The nitrile compound additive mainly exerts the positive electrode protection effect through the positive electrode coordination adsorption effect. It can continue to exist and protect the positive electrode during the cycle and storage process. When used in combination with the first additive shown in formula (1) which is mainly film-forming, it can exert a synergistic effect and further significantly improve the high temperature and high pressure performance of the battery.

[0034] In an embodiment of the present invention, the second additive accounts for 0wt% to 30wt% of the total mass of the electrolyte; exemplary is 0wt%, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, or is a range value composed of any two of the above values ​​or any point value within the range value. Within the above numerical range, the second additive of the present invention can better play a synergistic role with the first additive, thereby being more helpful in improving the high temperature and high pressure performance of the battery.

[0035] Preferably, the second additive accounts for 8 wt% to 20 wt% of the total mass of the electrolyte.

[0036] In an embodiment of the present invention, the electrolyte further includes an organic solvent and an electrolyte salt.

[0037] In an embodiment of the present invention, the electrolyte salt includes but is not limited to at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethylsulfonyl imide, lithium difluorobisoxalatophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, tris(trifluoromethylsulfonyl)methyl lithium, and lithium bis(trifluoromethylsulfonyl)imide.

[0038] Preferably, the electrolyte salt accounts for 10 wt% to 20 wt% of the total mass of the electrolyte, and is exemplified by 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, or a range consisting of any two of the aforementioned values ​​or any point within the range.

[0039] In an embodiment of the present invention, the organic solvent is selected from carbonates and / or carboxylates.

[0040] Preferably, the carbonate is selected from one or more of the following fluorinated or unsubstituted solvents: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), and ethyl methyl carbonate.

[0041] Preferably, the carboxylate is selected from one or more of the following fluorinated or unsubstituted solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl butyrate, and ethyl butyrate.

[0042] When the organic solvent is a mixture of multiple solvents, the individual solvents may be mixed in any proportion.

[0043] In a specific embodiment of the present invention, the organic solvent includes ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP).

[0044] The present invention also provides a battery, which comprises the above electrolyte.

[0045] Preferably, the positive electrode charging cut-off voltage of the battery is ≥4.5V.

[0046] In an embodiment provided by the present invention, the battery is a lithium-ion battery.

[0047] In an embodiment of the present invention, the battery further includes a positive electrode sheet, a negative electrode sheet and a separator.

[0048] In the embodiment provided by the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one side or both sides of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder.

[0049] Preferably, the mass percentage of each component in the positive electrode active material layer is: 80wt% to 99.8wt% of positive electrode active material, 0.1wt% to 10wt% of conductive agent, and 0.1wt% to 10wt% of binder.

[0050] Preferably, the mass percentage of each component in the positive electrode active material layer is: 90wt% to 99.6wt% of positive electrode active material, 0.2wt% to 5wt% of conductive agent, and 0.2wt% to 5wt% of binder.

[0051] In the embodiment provided by the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one side or both sides of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material, a conductive agent and a binder.

[0052] Preferably, the mass percentage of each component in the negative electrode active material layer is: 80wt% to 99.8wt% of the negative electrode active material, 0.1wt% to 10wt% of the conductive agent, and 0.1wt% to 10wt% of the binder.

[0053] Preferably, the mass percentage contents of the components in the negative electrode active material layer are as follows: 90 wt% to 99.6 wt% of negative electrode active material, 0.2 wt% to 5 wt% of conductive agent, and 0.2 wt% to 5 wt% of binder.

[0054] Preferably, the conductive agent is selected from at least one of conductive carbon black (the conductive carbon black includes one or two of acetylene black and Ketjen black), conductive graphite, carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0055] Preferably, the binder is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0056] Preferably, the negative electrode active material includes a carbon-based negative electrode material.

[0057] Preferably, the carbon-based negative electrode material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0058] Preferably, the negative electrode active material may further include a silicon-based negative electrode material.

[0059] Preferably, the silicon-based negative electrode material is selected from at least one of nano-silicon, silicon oxide negative electrode material (SiO x , 0 < x < 2) or silicon-carbon negative electrode material.

[0060] Preferably, in the negative electrode active material, the mass ratio of the carbon-based negative electrode material to the silicon-based negative electrode material is 10:0 to 1:19.

[0061] Preferably, the positive electrode active material is selected from at least one of transition metal lithium oxides, lithium iron phosphate, and lithium-rich manganese-based materials; the chemical formula of the transition metal lithium oxide is Li 1+x Ni y Co z M (1-y-z) O2, where, -0.1 ≤ x ≤ 1; 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and 0 ≤ y + z ≤ 1; where, M is at least one of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0062] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0063] The electrolyte provided by the present invention contains a first additive, and the first additive is a fluoronitrile benzene-based additive. The fluoronitrile benzene-based additive has an efficient positive electrode film-forming effect, can form significantly better positive electrode protection, and significantly improves the high-temperature and high-pressure performance of the battery, thereby improving problems such as high-temperature storage and high-temperature cycle expansion of the battery. Description of the Drawings

[0064] Figure 1 The figure is the theoretical calculation result of the redox performance of the additive (BFBN) represented by formula (2) of the present invention. The figure shows that its HOMO is relatively high and it is easy to oxidize and form a film;

[0065] Among them, BFBN: 3,5-bis(trifluoromethylbenzonitrile)

[0066] SN: Succinonitrile

[0067] ADN: Adiponitrile

[0068] HTCN: 1,3,6-hexanetrinitrile

[0069] HOMO and LUMO refer to the highest occupied molecular orbital and the lowest unoccupied molecular orbital, respectively. According to the frontier orbital theory, the two are collectively referred to as frontier orbitals, and the electrons in the frontier orbitals are called frontier electrons. LUMO is an orbital that can accept electrons, and the lower the energy, the stronger the oxidation ability; HOMO is an orbital that can lose electrons, and the higher the energy, the stronger the reduction ability. DETAILED DESCRIPTION

[0070] The present invention discloses an electrolyte and a battery. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve the same. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are deemed to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0071] The Chinese and English names are as follows:

[0072] PC Propylene carbonate DEC Diethyl carbonate EC Ethylene carbonate PP Propyl Propionate

[0073] The reagents, instruments or materials used in the present invention can be obtained through commercial channels.

[0074] According to the electrolyte of the present invention, the new fluoronitrile benzene additive, the fluorinated compound additive, the nitrile compound additive, and the sulfonic acid additive can be purchased through commercial channels or prepared by methods known in the art.

[0075] The present invention will be further described below in conjunction with embodiments:

[0076] Examples 1 to 15 and Comparative Examples 1 to 3

[0077] 1) Preparation of positive electrode

[0078] The positive electrode active materials lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), SP (super P) and carbon nanotubes (CNT) are mixed in a mass ratio of 96:2:1.5:0.5, N-methylpyrrolidone (NMP) is added, and the mixture is stirred under the action of a vacuum mixer until the mixed system becomes a positive electrode active slurry with uniform fluidity; the positive electrode active slurry is evenly coated on both surfaces of an aluminum foil; the coated aluminum foil is dried, and then rolled and cut to obtain the desired positive electrode sheet.

[0079] 2) Negative electrode preparation

[0080] The negative electrode active materials artificial graphite, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP) and single-walled carbon nanotubes (SWCNTs) are mixed in a mass ratio of 96:1.5:1.5:0.95:0.05, deionized water is added, and the negative electrode active slurry is obtained under the action of a vacuum mixer; the negative electrode active slurry is evenly coated on both surfaces of the copper foil; the coated copper foil is dried at room temperature, and then transferred to an oven at 80°C for drying for 10 hours, and then cold pressed and cut to obtain the negative electrode sheet.

[0081] 3) Preparation of electrolyte

[0082] In a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm), EC / PC / DEC / PP were mixed evenly in a mass ratio of 10:20:40:30 (organic solvent), and then 14wt% of fully dried lithium hexafluorophosphate (LiPF6, electrolyte salt) based on the total mass of the electrolyte was quickly added thereto, and after dissolution, 12wt% of fluoroethylene carbonate, 2wt% of 1,3-propane sultone, 1.5wt% of adiponitrile, and 2% of 1,3,6-hexane trinitrile (fluoroethylene carbonate, 1,3-propane sultone, adiponitrile, and 1,3,6-hexane trinitrile were added based on the total mass of the electrolyte (fluoroethylene carbonate, 1,3-propane sultone, adiponitrile, and 1,3,6-hexane trinitrile were the second additives) were added. Finally, different types of fluorinated nitrile benzene additives were added at different contents, including substances of formula (2) to formula (7), and the specific addition contents were shown in Table 1. After stirring evenly, the desired electrolyte was obtained after passing the moisture and free acid tests.

[0083] 4) Battery assembly

[0084] The positive electrode sheet and the negative electrode sheet are wound with a separator in between to prepare a lithium-ion battery roll core, which is then packaged with an aluminum-plastic film, baked to remove moisture, and then injected with electrolyte. The lithium-ion battery is formed using a hot pressing process.

[0085] Table 1 Composition of new electrolyte additives in batteries of Examples and Comparative Examples (wt%)

[0086]

[0087] Note: “ / ” means “not added”.

[0088] Battery performance test 1

[0089] The lithium-ion batteries obtained in the above examples and comparative examples were subjected to 45°C cyclic expansion performance and 60°C storage tests respectively, with a voltage range of 3 to 4.5 V. The test results are shown in Table 2.

[0090] 1) 45℃ cyclic expansion performance test

[0091] Charge at 45°C at a rate of 1C within the charge and discharge cut-off voltage range, place the fully charged cell / battery in an open circuit at 25°C for 2 hours, and test the battery thickness before the cycle. Then, perform charge and discharge cycles at 45°C at a rate of 1C within the charge and discharge cut-off voltage range. After 500 cycles, fully charge the battery at 45°C, then place the fully charged cell / battery in an open circuit at 25°C for 2 hours, and test the battery thickness after the cycle. Calculate the thickness expansion rate of the battery after cycling:

[0092] Thickness expansion ratio = [(thickness after storage - thickness before storage) / thickness before storage] x 100%.

[0093] 2) 60℃ storage performance test

[0094] The prepared lithium-ion battery was charged at 25°C at a rate of 1C to a cut-off voltage, a cut-off current of 0.025C, and left to stand for 5 minutes. The thickness of the lithium-ion battery was tested (this was the thickness before storage). The fully charged cell / battery was placed in an open circuit at (60±2)°C for 35 days. After 35 days of storage, it was placed in an open circuit at room temperature for 2 hours. The thickness after storage was measured and the thickness expansion rate of the lithium-ion battery was calculated:

[0095] Thickness expansion ratio = [(thickness after storage - thickness before storage) / thickness before storage] x 100%.

[0096] Table 2 Performance test results of batteries of embodiments and comparative examples

[0097]

[0098]

[0099] It can be seen from the results in Table 2 that adding fluorinated nitrile benzene additives to the electrolyte of the present invention can form a significantly better positive electrode protection, significantly improve the high temperature and high pressure performance of the battery, and can improve the high temperature storage and high temperature cycle expansion of the battery.

[0100] Example 16

[0101] The difference from Example 5 is the preparation of the electrolyte: no second additive is added to the electrolyte. The preparation of the electrolyte is as follows:

[0102] In a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm), EC / PC / DEC / PP were mixed in a mass ratio of 10:20:40:30, and then 14wt% of fully dried lithium hexafluorophosphate (LiPF6) based on the total mass of the electrolyte was quickly added. Finally, the fluorinated nitrile benzene additive formula (2) was added, as shown in Table 3. After stirring evenly, the desired electrolyte was obtained after passing the moisture and free acid tests.

[0103] Example 17 Group

[0104] The difference from Example 5 is that only one or two second additives are added, and the preparation method of the electrolyte is the same:

[0105] Example 17a: The second additive is 12 wt % of fluoroethylene carbonate;

[0106] Example 17b: The second additive is 2 wt% of 1,3-propane sultone;

[0107] Example 17c: The second additive is 1.5 wt% of adiponitrile and 2% of 1,3,6-hexanetrinitrile;

[0108] Example 17d: The second additive is 12 wt% of fluoroethylene carbonate and 2 wt% of 1,3-propane sultone;

[0109] Example 17e: The second additive is 12 wt% of fluoroethylene carbonate, 1.5 wt% of adiponitrile and 2% of 1,3,6-hexanetrinitrile;

[0110] Example 17f: The second additive is 2 wt% 1,3-propane sultone, 1.5 wt% adiponitrile and 2% 1,3,6-hexanetrinitrile.

[0111] Example 18 Group

[0112] The difference from Example 5 is that the content of the second additive is different, and the preparation method of the electrolyte is the same:

[0113] Example 18a: The second additive is 14 wt% of fluoroethylene carbonate, 4 wt% of 1,3-propane sultone, 3.5 wt% of adiponitrile, and 4% of 1,3,6-hexanetrinitrile;

[0114] Example 18b: The second additive is 16 wt% of fluoroethylene carbonate, 6 wt% of 1,3-propane sultone, 5 wt% of adiponitrile, and 6% of 1,3,6-hexanetrinitrile.

[0115] Comparative Example 4

[0116] The difference from Example 16 is that the electrolyte is prepared without adding the fluorinated nitrile benzene additive formula (2). The electrolyte is prepared as follows:

[0117] In a glove box filled with argon (H2O < 0.1ppm, O2 < 0.1ppm), EC / PC / DEC / PP were mixed in a mass ratio of 10:20:40:30, and then 14wt% of fully dried lithium hexafluorophosphate (LiPF6) based on the total mass of the electrolyte was quickly added. After stirring evenly, the desired electrolyte was obtained after passing the moisture and free acid tests.

[0118] Comparative Example 5

[0119] The difference from Example 5 is the preparation of the electrolyte: no second additive is added to the electrolyte, and the amount of the fluorinated nitrile benzene additive formula (2) is different. The preparation of the electrolyte is as follows:

[0120] In a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm), EC / PC / DEC / PP were mixed in a mass ratio of 10:20:40:30, and then 14wt% of fully dried lithium hexafluorophosphate (LiPF6) based on the total mass of the electrolyte was quickly added. Finally, the fluorinated nitrile benzene additive formula (2) was added, as shown in Table 3. After stirring evenly, the desired electrolyte was obtained after passing the moisture and free acid tests.

[0121] Battery performance test 2

[0122] The lithium ion batteries obtained in Example 16 and Comparative Examples 4-5 were subjected to 45°C cyclic expansion performance and 60°C storage tests, respectively, with a voltage range of 3-4.5V, and the specific test methods were the same as those in Battery Performance Test 1. The test results are shown in Table 3.

[0123] Table 3 Performance test results of batteries of embodiments and comparative examples

[0124]

[0125]

[0126] It can be seen from the results in Table 3 that the type and content of the second additive in the electrolyte of the present invention have an impact on improving the high-temperature storage and high-temperature cyclic expansion of the battery. When the type and content of the second additive are within the protection scope of the present invention, the high-temperature storage and high-temperature cyclic expansion of the battery can be effectively improved.

[0127] Finally, it is particularly pointed out that all the technical features of the present invention can produce a synergistic effect. In order to better improve the battery performance, it is recommended that all the technical features be fully adopted during battery production to achieve a comprehensive improvement in battery performance.

[0128] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte includes a first additive, wherein the first additive is selected from at least one of the compounds represented by formula (1): Wherein, R1 and R2 are independently selected from H, fluorine or trifluoromethyl, R1 and R2 are the same or different, and at most one of R1 and R2 is H; R3 is a nitrile group or an alkanenitrile group having 2-10 carbon atoms.

2. The electrolyte according to claim 1, characterized in that R1 and R2 are independently selected from fluorine or trifluoromethyl, and R1 and R2 are the same or different; R3 is a nitrile group or an alkanenitrile group having 2 to 5 carbon atoms; Preferably, R1 and R2 are independently selected from trifluoromethyl; and R3 is a nitrile group.

3. The electrolyte according to claim 1, characterized in that The first additive is selected from at least one of the compounds represented by formula (2) to formula (7):

4. The electrolyte according to claim 1, characterized in that The first additive accounts for 0.1wt% to 10wt% of the total mass of the electrolyte; Preferably, the first additive accounts for 1 wt% to 8 wt% of the total mass of the electrolyte; More preferably, the first additive accounts for 2 wt% to 6 wt% of the total mass of the electrolyte.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The electrolyte further includes a second additive, and the second additive includes at least two of fluorinated compounds, nitrile compounds, and sulfonic acid additives.

6. The electrolyte according to claim 5, characterized in that The fluorinated compound includes at least one of fluorinated carbonate, fluorinated carboxylate, and fluorinated ether; And / or, the nitrile compound includes at least one of saturated polynitrile, unsaturated alkyl polynitrile and oxygen-containing alkyl nitrile; And / or, the sulfonic acid additive includes at least one of 1,3-propane sultone, 1-propylene-1,3-sultone, 5-methyloxathiolane 2,2-dioxide, 1,3-propylene sultone, 2,4-butane sultone and 1,4-butane sultone.

7. The electrolyte according to claim 5, characterized in that The second additive accounts for 0wt% to 30wt% of the total mass of the electrolyte; Preferably, the second additive accounts for 8 wt% to 20 wt% of the total mass of the electrolyte.

8. The electrolyte according to claim 1, characterized in that The electrolyte also includes an organic solvent and an electrolyte salt; Preferably, the organic solvent is selected from carbonates and / or carboxylates; Preferably, the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethylsulfonyl imide, lithium difluorobisoxalatophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, tris(trifluoromethylsulfonyl)methyllithium, and lithium bis(trifluoromethylsulfonyl)imide.

9. The electrolyte according to claim 8, characterized in that The electrolyte salt accounts for 10 wt% to 20 wt% of the total mass of the electrolyte.

10. A battery, characterized in that: The battery comprises the electrolyte according to any one of claims 1 to 9.

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