Compound, electrolyte film-forming additive, electrolyte and lithium ion battery

Abstract

The invention discloses a compound, an electrolyte film-forming additive, an electrolyte and a lithium ion battery, and belongs to the technical field of batteries. The structure of the provided compound is shown as a formula A; wherein R1 is selected from one or more of C1-C6 alkyl groups, fluorine substituted C1-C3 alkyl groups, and trimethylsilyl substituted C1-C3 alkyl groups; r2-R4 are independently selected from one or more of a hydrogen atom, a fluorine atom, a C1-C6 alkyl group, a fluorine-substituted C1-C3 alkyl group and an ester group, and at least one fluorine is contained in R2-R4. As a film-forming additive, the compound can give consideration to efficient film formation of a positive electrode and a negative electrode, and effectively avoids battery swelling caused by instability of a positive electrode interface film. The film-forming additive is combined with other auxiliary additives, so that the stability of a positive-negative electrode interface of the lithium ion battery with the high nickel-silicon negative electrode can be greatly improved, the cycle life of the battery can be greatly prolonged, and the high-temperature performance of the battery can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a compound, an electrolyte film-forming additive, an electrolyte, and a lithium-ion battery. Background Art

[0002] As a green and environmentally friendly high-energy battery, the lithium-ion battery is currently the most ideal and potential rechargeable battery. Compared with other batteries, it has a series of advantages such as no memory effect, fast charge and discharge, high energy density, long cycle life, and low environmental pollution. Therefore, it is widely used in small electronic devices such as laptops, cameras, mobile phones, electronic watches, etc. With the continuous development of electric vehicles, the demand for lithium-ion batteries with long endurance and high safety is also increasing. Among them, high-nickel lithium-ion batteries are the main development direction. At present, the energy density of high-nickel lithium-ion batteries obtained by using high-nickel cathode materials and silicon-containing anode materials can exceed 350 Wh / kg, and the pure electric endurance of electric vehicles can exceed 1000 km, greatly alleviating the "range anxiety" of passengers.

[0003] However, high-nickel lithium-ion batteries still have certain deficiencies in application, such as low safety and poor high-temperature performance. In an environment with a relatively high temperature, as the nickel content increases, the stability of the cathode material will decrease, which in turn makes the thermal stability and cycle performance of high-nickel lithium-ion batteries deteriorate. Moreover, due to the uneven surface reaction of the electrode material during the charge and discharge process, a large amount of highly oxidation-active Ni 4+ is generated, which is extremely likely to undergo side reactions with solvent molecules to produce gas, resulting in the loss of active lithium in the battery and rapid capacity decay. Therefore, it is of great significance to research and develop an electrolyte for high-nickel lithium-ion batteries suitable for use in high-temperature environments. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a compound, an electrolyte film-forming additive, an electrolyte, and a lithium-ion battery. The compound, as an electrolyte film-forming additive, can make the battery have more excellent capacity retention rate and lower high-temperature cycle volume expansion rate.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides a compound, the structure of which is shown in Formula A:

[0007]

[0008] Wherein, R1 is selected from one or more of C1-C6 alkyl, fluorine-substituted C1-C3 alkyl, and trimethylsilyl-substituted C1-C3 alkyl;

[0009] R2-R4 are independently selected from one or more of a hydrogen atom, a fluorine atom, a C1-C6 alkyl group, a fluorine-substituted C1-C3 alkyl group, and an ester group, and at least one of R2-R4 contains fluorine.

[0010] Preferably, the number of fluorine atoms in R2-R4 is 1 or 3.

[0011] The C1-C6 alkyl group includes, but is not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, sec-butyl, n-pentyl, neopentyl, hexyl, etc.

[0012] The fluorine-substituted C1-C3 alkyl group includes, but is not limited to, fluorine-substituted methyl, ethyl, n-propyl, and isopropyl. The number of fluorine atoms is an integer between 1 and 3, preferably 2 or 3.

[0013] The trimethylsilyl-substituted C1-C3 alkyl group includes, but is not limited to, trimethylsilyl-substituted methyl, ethyl, n-propyl, and isopropyl.

[0014] Preferably in the present invention, R1 is selected from methyl, difluoromethyl, trifluoromethyl, and methylene trimethylsilane;

[0015] Preferably, R2-R4 are independently selected from one or more of a hydrogen atom, a fluorine atom, a methyl group, a trifluoromethyl group, and a methyl formate group, and R2-R4 contains 1 fluorine atom or 1 trifluoromethyl group.

[0016] The present invention has no special limitation on the synthesis method of the above compounds, and any synthesis method well-known to those skilled in the art can be used.

[0017] In some embodiments of the present invention, the synthesis method of the compound is as follows: First, a sulfonic acid monomer is reacted with dichloroethylene to obtain an intermediate compound having a vinyl chloride sulfonate structure, and then it is subjected to a substitution reaction with an imidazole-based compound to obtain the target product. The specific chemical equation is as follows:

[0018]

[0019] Among them, the value ranges of R1-R4 are the same as above and will not be repeated here.

[0020] More preferably in the present invention, the structure of formula A is selected from any one of (I)-(VII);

[0021]

[0022] The present invention also provides an electrolyte film-forming additive, which includes the above compound.

[0023] As the main component of the film-forming additive, the compound can take into account the efficient film formation on both the positive and negative electrodes, form a special coating-type protective layer on the surface of the positive electrode by oxidation, and thus effectively isolate the direct contact between the highly active positive electrode particles and solvent molecules. Especially in high-temperature cases, it can effectively avoid the gas generation and battery swelling caused by the oxidation and decomposition of solvent molecules at the positive electrode interface. At the same time, the special fluorinated imidazole functional group structure of the compound can also participate in the film formation of the negative electrode, promote the generation of more inorganic components on the surface of the negative electrode, make the solid electrolyte film at the negative electrode interface have higher mechanical strength and ionic conductivity, and enhance the high-temperature thermal stability of the negative electrode interface film.

[0024] The present invention also provides an electrolyte, which includes a lithium salt, a water-insoluble organic solvent, and the above-mentioned electrolyte film-forming additive.

[0025] Preferably, the content of the electrolyte film-forming additive in the electrolyte of the present invention is 0.5 wt% - 2 wt%; in some specific embodiments of the present invention, it is preferably 0.5 wt% or 1 wt% or 2 wt%.

[0026] Preferably, the content of the lithium salt in the electrolyte is 11 wt% - 16 wt%; more preferably 13 wt% - 15 wt%; further preferably 13 wt%.

[0027] Preferably, the content of the water-insoluble organic solvent in the electrolyte is 76 wt% - 85.5 wt%; more preferably 76.5 wt% - 80 wt%.

[0028] Preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), and lithium difluoro(dioxalato)phosphate (LiDODFP).

[0029] The water-insoluble organic solvent includes, but is not limited to, ester or ether organic solvents;

[0030] The ester organic solvents include, but are not limited to, one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate, methyl trifluoroethyl carbonate, etc.;

[0031] The ether organic solvents include, but are not limited to, one or more of dimethyl ether, diethyl ether, methyl ethyl ether, ethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, etc.

[0032] Preferably, the electrolyte further comprises an auxiliary additive.

[0033] Combining the film-forming additive provided by the present invention with other auxiliary additives and introducing them into a high-nickel silicon anode lithium-ion battery can significantly improve the stability of the positive and negative electrode interfaces, effectively avoid the oxidation and decomposition of highly active Ni on the surface of the positive electrode 4+ catalyzing the oxidation and decomposition of solvent molecules, significantly improving the cycle life and high-temperature performance of the battery, and inhibiting the degradation of the interface structure under high-temperature conditions. At the same time, the special fluorinated imidazole structure can also induce the formation of a high-mechanical-strength solid electrolyte interface film rich in LiF on the surface of the negative electrode, thereby effectively alleviating the rapid attenuation of the electrochemical performance caused by the huge volume expansion of the silicon-containing negative electrode during charge and discharge. The above-mentioned auxiliary additive accounts for 3%-6% of the total weight of the electrolyte.

[0034] Preferably, the auxiliary additive is selected from one or more of vinylene carbonate, ethylene ethylene carbonate, fluorinated ethylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, ethylene sulfate, bis(ethylene sulfate), propylene sulfate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, 2,4-butane sultone, phenyl methanesulfonate, methylene methanedisulfonate, N-phenylbis(trifluoromethanesulfonyl)imide, triallyl phosphate, tris(trimethylsilyl) phosphate, trimethyl phosphite, triphenyl phosphite, tetramethyl methylenediphosphate, tripropargyl phosphate, (2-allylphenoxy)trimethylsilane, tris(trimethylsilyl) borate, 1,3,5-triallyl isocyanurate, isocyanatoethyl methacrylate, hexamethylene diisocyanate, p-phenylene diisocyanate, 2,4-toluene diisocyanate, adiponitrile, succinonitrile, glutaronitrile, 1,3,6-hexanetricarbonitrile, 1,2-bis(cyanoethoxy)ethane, lithium difluorophosphate. More preferably, it is fluorinated ethylene carbonate, lithium difluorophosphate and 1,3-propane sultone.

[0035] The present invention also provides a lithium-ion battery comprising the above-mentioned electrolyte.

[0036] The lithium-ion battery further comprises a positive electrode material, a negative electrode material and a separator.

[0037] The positive electrode material is preferably one or more of lithium cobaltate, lithium manganate, ternary nickel cobalt manganese lithium, lithium nickel manganate, lithium iron phosphate, lithium manganese iron phosphate; more preferably ternary nickel cobalt manganese lithium.

[0038] The negative electrode material is preferably artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon, silicon-carbon composite material, silicon monoxide or a mixed powder of silicon monoxide and artificial graphite; more preferably silicon-carbon.

[0039] The diaphragm is preferably a polypropylene, polyethylene diaphragm or a polyethylene diaphragm coated with aluminum oxide on one side; more preferably a polyethylene diaphragm coated with aluminum oxide on one side.

[0040] Preferably, the positive electrode material of the lithium-ion battery is selected from ternary nickel-cobalt-manganese lithium; the negative electrode material is selected from silicon-carbon; and the diaphragm is selected from a polyethylene diaphragm coated with alumina on one side.

[0041] In some specific embodiments of the present invention, the molar ratio of Ni:Co:Mn in the ternary nickel-cobalt-manganese-lithium is preferably 9:0.5:0.5.

[0042] The gram capacity of the silicon-carbon negative electrode is preferably 650 mAh g -1 The above-mentioned lithium-ion battery has excellent electrochemical performance, specifically, its performance at both room temperature and high temperature in the voltage range of 3.0-4.2V has been improved.

[0043] Compared with the prior art, the compound provided by the present invention has a structure as shown in Formula A; wherein, R1 is selected from one or more of C1-C6 alkyl, fluorine-substituted C1-C3 alkyl, and trimethylsilyl-substituted C1-C3 alkyl; R2-R4 are independently selected from one or more of hydrogen atoms, fluorine atoms, C1-C6 alkyl, fluorine-substituted C1-C3 alkyl, and ester groups, and R2-R4 contain at least one fluorine. The compound can be used as a film-forming additive to take into account efficient film formation of positive and negative electrodes, effectively avoid battery swelling caused by instability of the positive electrode interface film, and also make the negative electrode interface solid electrolyte film have higher mechanical strength and ionic conductivity. In addition, the film-forming additive is combined with other auxiliary additives and introduced into a high-nickel silicon negative electrode lithium ion battery, which can greatly improve the stability of the positive and negative electrode interface, improve the cycle life and high-temperature performance of the battery, inhibit the degradation of the interface structure under high temperature conditions, and effectively alleviate the rapid attenuation of the electrochemical performance of the silicon-containing negative electrode due to volume expansion during charging and discharging. DETAILED DESCRIPTION

[0044] To further illustrate the present invention, the compound, electrolyte film-forming additive, electrolyte and lithium-ion battery provided by the present invention are described in detail below with reference to the examples.

[0045] Example 1

[0046] (1) Preparation of compound (I), the specific steps are as follows:

[0047]

[0048] Under a nitrogen atmosphere, 150 mL of ultradry tetrahydrofuran was added to a clean and dry 250 mL brown three-necked flask equipped with a magnetic rotor. The flask was placed in an ice-water bath. After stirring was started, methanesulfonic acid (4.81 g, 0.05 mol) was added, and then dichloroethylene (4.85 g, 0.05 mmol) was added. After stirring and reacting for 2 h, triethylamine (1.01 g, 0.01 mol) was added to the reaction system. Then the ice-water bath was removed, and after continuing to stir and react for 2 h, about 50 mL of 1 mol / L hydrochloric acid aqueous solution was added to quench the reaction. Subsequently, the residual solution was washed three times with saturated sodium bicarbonate aqueous solution and deionized water in sequence. The organic phase was separated, dried with anhydrous sodium sulfate, and then the solvent was removed by distillation under reduced pressure. The residue was purified by silica gel column chromatography, and the eluent was dichloromethane. After removing the solvent by rotary evaporation, the intermediate product 2 was obtained with a yield of 77.2%. EIMS (m / z): calcd. for C3H5O3SCl, 155.96, found 156.13.

[0049]

[0050] Under a nitrogen atmosphere, to a clean and dry 500 mL three-necked flask equipped with a magnetic rotor, intermediate product 2 (4.68 g, 30.00 mmol), compound 3 (4.35 g, 32.00 mmol), cesium carbonate (13.03 g, 40.00 mmol) and ultradry N,N-dimethylformamide (300 mL) were added in sequence. Stirring was started, and the mixture was stirred and reacted at room temperature for 3 h. After the reaction was completed, 300 mL of distilled water pre-cooled to 0 °C was added, and then the mixed solution was extracted with chloroform (3 × 150 mL). The organic phases were separated, combined, and the solvent was removed by distillation under reduced pressure. Using ethyl acetate as the eluent, after purification by silica gel column chromatography, compound (I) was obtained with a yield of 81.4%. EIMS (m / z): calcd. for C7H7F3N2O3S, 256.01, found 256.08.

[0051] (II) Preparation of electrolyte 1 sample, the specific steps are as follows:

[0052] In an argon glove box with the water and oxygen contents both ≤ 0.1 ppm, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) are uniformly mixed in a volume ratio of 5:10:25:60 to obtain an organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) is slowly added to the organic solvent. After complete dissolution, fluoroethylene carbonate (FEC), lithium difluorophosphate (LiDFP), 1,3 - propane sultone (PS), and compound (I) are added as auxiliary additives. After stirring evenly, electrolyte 1 is obtained. Among them, the usage amounts of LiPF6, organic solvent, FEC, LiDFP, PS, and compound (I) are 13%, 77.5%, 6%, 0.5%, 2%, and 1% of the total mass of the electrolyte, respectively.

[0053] (III) Prepare the experimental battery 1 sample, and the specific steps are as follows:

[0054] Preparation of the positive electrode sheet: The positive electrode material lithium nickel cobalt manganese (Ni:Co:Mn molar ratio = 9:0.5:0.5), conductive agent carbon black (SuperP), carbon nanotubes (CNT, 5% mass fraction NMP solution), and binder polyvinylidene fluoride (PVDF, 5% mass fraction NMP solution) are weighed and mixed in a mass ratio of 97:0.7:0.8:1.5. After mixing, an appropriate amount of NMP is added to control the theoretical solid content to 65%. The positive electrode slurry is obtained by homogenization using a planetary homogenizer, and the positive electrode slurry is uniformly coated on an aluminum foil with a thickness of 13 μm. After drying, rolling, and cutting, a 50 mm × 70 mm positive electrode sheet is obtained.

[0055] Preparation of the separator: A polyethylene separator with single - sided alumina coating is used as the isolation membrane and is left standing in a drying room with a dew point of - 35°C for 72 h before use.

[0056] Preparation of the negative electrode sheet: The negative electrode material silicon - carbon (specific capacity 650 mAh·g -1 ), conductive agent SuperP, conductive agent single - walled carbon nanotubes (SWCNT, content 0.6%, deionized water solution with a solid content of 1%), thickening agent sodium carboxymethyl cellulose (CMC, deionized water solution with a solid content of 1.5%), and binder polyacrylic acid (PAA, deionized water solution with a solid content of 6%) are mixed in a mass ratio of 96.5:0.7:0.1:1.2:1.5 (excluding the solvent). After mixing, deionized water is added to control the theoretical solid content to 55%. The negative electrode slurry is obtained by homogenization using a planetary homogenizer, and the negative electrode slurry is uniformly coated on a copper foil with a thickness of 6 μm. After drying, rolling, and cutting, a 52 mm × 72 mm negative electrode sheet is obtained. The N / P ratio of the positive and negative electrodes is 1.1.

[0057] Preparation of the battery: The battery is fabricated in a drying room with an environmental dew point ≤ -35°C. The separator is folded in a Z shape, with the positive electrode sheet and the negative electrode sheet placed on each side. There are 12 layers of the positive electrode sheet and 13 layers of the negative electrode sheet. The positive electrode, separator, and negative electrode are aligned and stacked in sequence. The separator with the alumina-coated side faces the positive electrode to obtain an electrode assembly. Then, the electrode assembly is fixed with polyimide tape and the tabs are welded. Subsequently, it is placed in an aluminum-plastic film and vacuum baked at 90°C for 12 h. After cooling, the prepared electrolyte 1 is injected. Finally, after vacuum packaging, high-temperature infiltration, formation, aging, secondary packaging, and grading, the experimental battery 1 with a capacity of approximately 2.5 Ah is obtained.

[0058] Example 2

[0059] Compound (II) was prepared as follows:

[0060]

[0061] Under a nitrogen atmosphere, 150 mL of ultra-dry tetrahydrofuran was added to a clean and dry 250 mL brown three-necked flask equipped with a magnetic rotor. The flask was placed in an ice-water bath. After stirring was started, difluoromethanesulfonic acid (6.60 g, 0.05 mol) was added, followed by dichloroethylene (4.85 g, 0.05 mmol). After stirring and reacting for 2 h, triethylamine (1.01 g, 0.01 mol) was added to the reaction system. Then, the ice-water bath was removed, and after continuing to stir and react for 2 h, approximately 50 mL of 1 mol / L hydrochloric acid aqueous solution was added to quench the reaction. Subsequently, the residual solution was washed three times with saturated sodium bicarbonate aqueous solution and deionized water in sequence. The organic phase was separated, dried with anhydrous sodium sulfate, and then the solvent was removed by distillation under reduced pressure. The residue was purified by silica gel column chromatography with dichloromethane as the eluent. After removing the solvent by rotary evaporation, the intermediate product 5 was obtained with a yield of 72.3%. EIMS (m / z): calcd. for C3H3O3F3SCl, 191.95, found 192.17.

[0062]

[0063] Under a nitrogen atmosphere, into a clean and dry 500 mL three-necked flask equipped with a magnetic rotor, intermediate 5 (5.76 g, 30.00 mmol), compound 6 (2.75 g, 32.00 mmol), cesium carbonate (13.03 g, 40.00 mmol), and ultra-dry N,N-dimethylformamide (300 mL) were added successively. Stirring was started, and the mixture was stirred at room temperature for 3 h. After the reaction was completed, 300 mL of distilled water pre-cooled to 0 °C was added. Subsequently, the mixed solution was extracted with chloroform (3 × 150 mL). The organic phases were separated and combined, the solvent was removed by distillation under reduced pressure, and ethyl acetate was used as the eluent. After purification by silica gel column chromatography, compound (II) was obtained with a yield of 78.5%. EIMS (m / z): calcd. for C6H5F3N2O3S, 242.0, found 242.20.

[0064] The electrolyte solution 2 sample and the experimental cell 2 were prepared according to the method of Example 1, except that the film-forming additive compound in the electrolyte solution 2 sample was compound (II), and 1% of vinylene sulfate (DTD) was additionally added as an auxiliary additive. The lithium salt was 10% LiPF6 and 3% lithium bis(fluorosulfonyl)imide (LiFSI).

[0065] Example 3

[0066] Compound (III) was prepared as follows:

[0067]

[0068] Under a nitrogen atmosphere, into a clean and dry 500 mL three-necked flask equipped with a magnetic rotor, intermediate 5 (5.76 g, 30.00 mmol), compound 7 (3.20 g, 32.00 mmol), cesium carbonate (13.03 g, 40.00 mmol), and ultra-dry N,N-dimethylformamide (300 mL) were added successively. Stirring was started, and the mixture was stirred at room temperature for 3 h. After the reaction was completed, 300 mL of distilled water pre-cooled to 0 °C was added. Subsequently, the mixed solution was extracted with chloroform (3 × 150 mL). The organic phases were separated and combined, the solvent was removed by distillation under reduced pressure, and ethyl acetate was used as the eluent. After purification by silica gel column chromatography, compound (III) was obtained with a yield of 80.4%. EIMS (m / z): calcd. for C7H7F3N2O3S, 256.01, found 256.25.

[0069] The electrolyte 3 sample and the experimental cell 3 were prepared according to the method of Example 1, except that the film-forming additive compound in the electrolyte 3 sample was compound (III), and 1% of adiponitrile (ADN) was additionally added as an auxiliary additive. The lithium salt was 11% LiPF6 and 2% lithium difluoro(oxalato)borate (LiODFB).

[0070] Example 4

[0071] Compound (IV) was prepared as follows:

[0072]

[0073] Under a nitrogen atmosphere, 150 mL of ultra-dry tetrahydrofuran was added to a clean and dry 250 mL brown three-necked flask equipped with a magnetic rotor. The flask was placed in an ice-water bath. After stirring was started, trifluoromethanesulfonic acid (7.50 g, 0.05 mol) was added, and then dichloroethylene (4.85 g, 0.05 mmol) was added. After stirring and reacting for 2 h, triethylamine (1.01 g, 0.01 mol) was added to the reaction system. Then the ice-water bath was removed, and after continuing to stir and react for 2 h, about 50 mL of 1 mol / L hydrochloric acid aqueous solution was added to quench the reaction. Subsequently, the residual solution was washed three times with saturated sodium bicarbonate aqueous solution and deionized water in sequence. The organic phase was separated, dried with anhydrous sodium sulfate, and then the solvent was removed by distillation under reduced pressure. The residue was purified by a silica gel chromatography column with dichloromethane as the eluent. After removing the solvent by rotary evaporation, the intermediate product 9 was obtained with a yield of 68.2%. EIMS (m / z): calcd. for C3H2O3F3SCl, 209.94, found 210.09.

[0074]

[0075] Under a nitrogen atmosphere, intermediate product 9 (6.30 g, 30.00 mmol), compound 10 (2.75 g, 32.00 mmol), cesium carbonate (13.03 g, 40.00 mmol), and ultra-dry N,N-dimethylformamide (300 mL) were successively added to a clean and dry 500 mL three-necked flask equipped with a magnetic rotor. Stirring was started, and the mixture was stirred and reacted at room temperature for 3 h. After the reaction was completed, 300 mL of distilled water pre-cooled to 0 °C was added. Subsequently, the mixed solution was extracted with chloroform (3 × 150 mL). The organic phases were separated, combined, and the solvent was removed by distillation under reduced pressure. After purification by a silica gel chromatography column with ethyl acetate as the eluent, compound (IV) was obtained with a yield of 79.7%. EIMS (m / z): calcd. for C6H4F4N2O3S, 259.99, found 260.17.

[0076] Prepare electrolyte 4 sample and experimental cell 4 according to the method of Example 1, except that the solvents in the electrolyte 4 sample are EC, PC, EMC and methyltrifluoroethyl carbonate (FEMC), and the volume ratio is EC:PC:EMC:FEMC = 5:15:60:20. The film-forming additive compound is compound (IV), and 0.2% of hexamethylene diisocyanate (HDMI) is additionally added as an auxiliary additive.

[0077] Example 5

[0078] Prepare compound (V), and the specific steps are as follows:

[0079]

[0080] Under a nitrogen atmosphere, add 150 mL of ultradry tetrahydrofuran to a clean and dry 250 mL brown three-necked flask equipped with a magnetic rotor. Place the flask in an ice-water bath. After starting stirring, add trimethylsilyl methanesulfonic acid (8.40 g, 0.05 mol), and then add dichloroethylene (4.85 g, 0.05 mmol). After stirring and reacting for 2 h, add triethylamine (1.01 g, 0.01 mol) to the reaction system. Then remove the ice-water bath and continue stirring and reacting for 2 h. Add about 50 mL of 1 mol / L hydrochloric acid aqueous solution to quench the reaction. Subsequently, wash the residual solution three times with saturated sodium bicarbonate aqueous solution and deionized water in sequence. Separate the organic phase, dry it with anhydrous sodium sulfate, then distill off the solvent under reduced pressure. Purify the residue through a silica gel chromatographic column, and the eluent is dichloromethane. After rotary evaporation to remove the solvent, obtain intermediate 12 with a yield of 63.8%. EIMS (m / z): calcd. for C6H 13 O3SiSCl, 228.00, found 228.13.

[0081]

[0082] Under a nitrogen atmosphere, add intermediate 12 (6.84 g, 30.00 mmol), compound 13 (4.80 g, 32.00 mmol), cesium carbonate (13.03 g, 40.00 mmol) and ultradry N,N-dimethylformamide (300 mL) to a clean and dry 500 mL three-necked flask equipped with a magnetic rotor in sequence. Start stirring and stir the mixture at room temperature for 3 h. After the reaction is completed, add 300 mL of distilled water pre-cooled to 0 °C, and then extract the mixed solution with chloroform (3 × 150 mL). Separate and combine the organic phases, distill off the solvent under reduced pressure, and use ethyl acetate as the eluent. After purification through a silica gel chromatographic column, obtain compound (V) with a yield of 77.2%. EIMS (m / z): calcd. for C 11 H 17F3N2O3SSi, 342.07, found 342.23。

[0083] Prepare electrolyte 5 sample and experimental cell 5 according to the method of Example 1, except that the solvents in electrolyte 4 sample are PC, ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (F-EAE), with a volume ratio of 5:10:35:40:10, the film-forming additive compound is compound (V), and 0.1% of triallyl phosphate (TPP) is additionally added as the auxiliary additive.

[0084] Example 6

[0085] Prepare compound (VI), and the specific steps are as follows:

[0086]

[0087] Under a nitrogen atmosphere, add intermediate 12 (6.84 g, 30.00 mmol), compound 10 (2.75 g, 32.00 mmol), cesium carbonate (13.03 g, 40.00 mmol) and ultra-dry N,N-dimethylformamide (300 mL) to a clean and dry 500 mL three-necked flask equipped with a magnetic rotor in sequence. Start stirring and stir the mixture at room temperature for 3 h. After the reaction is completed, add 300 mL of distilled water pre-cooled to 0 °C, and then extract the mixed solution with chloroform (3 × 150 mL). Separate and combine the organic phases, distill off the solvent under reduced pressure, and use ethyl acetate as the eluent. After purification by silica gel chromatography column, compound (VI) is obtained with a yield of 79.4%. EIMS (m / z): calcd. for C9H 15 FN2O3SSi, 278.06, found 278.19。

[0088] Prepare electrolyte 6 sample and experimental cell 6 according to the method of Example 1, except that the film-forming additive compound in electrolyte 6 sample is compound (VI), and 0.1% of 1,3-propane sultone (PST) is additionally added as the auxiliary additive.

[0089] Example 7

[0090] Prepare compound (VII), and the specific steps are as follows:

[0091]

[0092] Under a nitrogen atmosphere, 9 (6.30 g, 30.00 mmol) of the intermediate product, 14 (4.61 g, 32.00 mmol) of the compound, cesium carbonate (13.03 g, 40.00 mmol), and ultra-dry N,N-dimethylformamide (300 mL) were successively added to a clean and dry 500 mL three-necked flask equipped with a magnetic rotor. Stirring was started, and the mixture was stirred at room temperature for 3 h. After the reaction was completed, 300 mL of distilled water pre-cooled to 0 °C was added, and then the mixed solution was extracted with chloroform (3 × 150 mL). The organic phases were separated and combined, the solvent was removed by distillation under reduced pressure, and the compound (VII) was obtained after purification by silica gel column chromatography with ethyl acetate as the eluent, with a yield of 69.5%. EIMS (m / z): calcd. for C8H6F4N2O5S, 317.99, found 318.13.

[0093] The electrolyte 7 sample and the experimental cell 7 were prepared according to the method of Example 1, except that the film-forming additive compound in the electrolyte 7 sample was the compound (VII), and 1% of methylene methanedisulfonate (MMDS) was additionally added as an auxiliary additive.

[0094] Example 8

[0095] The electrolyte 8 sample and the experimental cell 8 were prepared according to the method of Example 1, except that the film-forming additive compound in the electrolyte 8 sample was the compound (VI) with a content of 0.5%.

[0096] Example 9

[0097] The electrolyte 9 sample and the experimental cell 9 were prepared according to the method of Example 1, except that the film-forming additive compound in the electrolyte 8 sample was the compound (VI) with a content of 2%.

[0098] Comparative Example 1

[0099] The electrolyte 10 sample and the experimental cell 10 were prepared according to the method of Example 1, except that the film-forming additive compound proposed in the present invention was not added.

[0100] Comparative Example 2

[0101] The electrolyte 11 sample and the experimental cell 11 were prepared according to the method of Example 1, except that instead of adding the compound of the present invention, only tris(trimethylsilyl) phosphate (TMSP) was added.

[0102] The electrolyte compositions and contents of Examples 1 to 9 and Comparative Examples 1 to 2 are shown in Table 1.

[0103] The lithium-ion batteries prepared in Examples 1 to 9 and Comparative Examples 1 to 2 were respectively subjected to normal-temperature cycle performance tests and high-temperature cycle performance tests, and the test conditions were as follows:

[0104] (1) Battery room temperature cycle test

[0105] The prepared lithium-ion battery was placed in a constant temperature room at an ambient temperature of 25°C, with a current of 1C and a voltage of 4.2V, and constant current and constant voltage charging to a cutoff current of 0.05C. It was then discharged at a constant current of 1C to a voltage of 3V. This cycle was repeated 800 times, and the capacity retention rate was recorded. The capacity retention rate at the nth cycle (%) = (discharge capacity at the nth cycle / discharge capacity at the first cycle) * 100%.

[0106] (2) Battery high temperature cycle test

[0107] Before the test, the internal resistance of the battery is measured using an internal resistance tester, and the battery volume is measured using the drainage method, which is recorded as V0. The prepared lithium-ion battery is then placed in a high and low temperature environment at 45°C for 4 hours to stabilize the internal and external temperatures of the battery. With a current of 1C and a voltage of 4.2V, constant current and constant voltage charging is performed until the cutoff current is 0.05C, followed by a 1C constant current discharge to a voltage of 3V. The cycle is repeated for 800 cycles, and the capacity retention rate is recorded. The capacity retention rate of the nth cycle (%) = (discharge capacity of the nth cycle / discharge capacity of the first cycle) * 100%. After the test is completed, the battery volume V1 is measured, and the volume expansion rate (%) = (V1-V0) * 100% / V0.

[0108] Table 1 Electrolyte compositions and corresponding battery performances of various examples and comparative examples

[0109]

[0110]

[0111]

[0112] Lithium-ion batteries were prepared using the electrolytes prepared in Examples 1 to 9 and Comparative Examples 1 to 2. The battery performance test results are shown in Table 1. It can be seen that the compounds provided by the present invention exhibit better electrochemical properties as film-forming additives. Compared with the examples without additions, the expansion phenomenon of the silicon-carbon negative electrode battery after high-temperature cycling is also effectively alleviated. This is because such functional film-forming additive compounds can take into account the efficient film formation of both positive and negative electrodes. The coated protective layer formed by oxidation on the positive electrode surface can effectively isolate the direct contact between the highly active positive electrode particles and the solvent molecules, and can effectively alleviate the instability of the positive electrode interface under high temperature conditions. Its special fluorine-containing thiazole functional group structure can also participate in the negative electrode film formation, promote the generation of more inorganic LiF components on the negative electrode surface, and make the negative electrode interface solid electrolyte film also very stable and mechanically strong, thereby suppressing the volume growth and side reaction gas production of the silicon-carbon negative electrode during the cycle, so that the battery exhibits excellent electrochemical performance.

[0113] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A compound, characterized in that, The structure is as shown in formula A: Wherein, R1 is selected from one or more of C1-C6 alkyl, fluorine-substituted C1-C3 alkyl, and trimethylsilyl-substituted C1-C3 alkyl; R2-R4 are independently selected from one or more of a hydrogen atom, a fluorine atom, C1-C6 alkyl, fluorine-substituted C1-C3 alkyl, and an ester group, and at least one of R2-R4 contains fluorine.

2. The compound according to claim 1, wherein The R1 is selected from methyl, difluoromethyl, trifluoromethyl, and methylene trimethylsilane; The R2-R4 are independently selected from one or more of a hydrogen atom, a fluorine atom, methyl, trifluoromethyl, and methyl formate group, and R2-R4 contains 1 fluorine atom or 1 trifluoromethyl group.

3. The compound according to claim 1, wherein The structure of formula A is selected from any one of (I)-(VII):

4. An electrolyte film-forming additive, characterized in that, It includes the compound according to any one of claims 1-3.

5. An electrolyte, characterized in that, It includes a lithium salt, a water-insoluble organic solvent, and the electrolyte film-forming additive according to claim 4.

6. The electrolyte according to claim 5, wherein The content of the electrolyte film-forming additive in the electrolyte is 0.5 wt%-2 wt%; The content of the lithium salt in the electrolyte is 11 wt%-16 wt%; The content of the water-insoluble organic solvent in the electrolyte is 76 wt%-85.5 wt%.

7. The electrolyte according to claim 5, wherein The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and lithium difluoro(dioxalato)phosphate.

8. The electrolyte according to claim 5, characterized in that, The electrolyte further includes an auxiliary additive; The auxiliary additive is selected from one or more of vinylene carbonate, ethylene vinylene carbonate, fluoroethylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, ethylene sulfate, bis(ethylene sulfate), propylene sulfate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, 2,4-butane sultone, phenyl methanesulfonate, methylene methanedisulfonate, N-phenylbis(trifluoromethanesulfonyl)imide, triallyl phosphate, tris(trimethylsilyl) phosphate, trimethyl phosphite, triphenyl phosphite, tetramethyl methylenediphosphate, tripropargyl phosphate, (2-allylphenoxy)trimethylsilane, tris(trimethylsilyl) borate, 1,3,5-triallyl isocyanurate, isocyanatoethyl methacrylate, hexamethylene diisocyanate, p-phenylene diisocyanate, 2,4-toluene diisocyanate, adiponitrile, succinonitrile, glutaronitrile, 1,3,6-hexanetricarbonitrile, 1,2-bis(cyanoethoxy)ethane, and lithium difluorophosphate.

9. A lithium-ion battery, characterized in that, It includes the electrolyte according to any one of claims 5-8.

10. The lithium ion battery according to claim 9, characterized in that, The positive electrode material of the lithium ion battery is selected from ternary lithium nickel cobalt manganese; The negative electrode material is silicon carbon; The separator is selected from a polyethylene separator coated with alumina on one side.

Images