Functional additive, long-circulation electrolyte and lithium ion battery

Abstract

The invention provides a functional additive which has a structure as shown in a structural formula A, in the structural formula A, R1 to R4 are independently selected from hydrogen atoms, methyl, ethyl, cyclopropane, methoxyl or nitryl, and R5 to R5 are independently selected from hydrogen atoms, methyl, dimethyl, cyano, n-butenyl, 2-methyl-2-propenyl, trifluoromethyl, trimethylsilyl or fluorosulfonyl. Compared with the prior art, the functional additive provided by the invention can be adsorbed on the surface of a positive electrode material to form a protective belt, and when HF is generated by hydrolysis reaction of lithium salt in the electrolyte caused by trace water, favorable protonation reaction can be initiated, HF can be eliminated, erosion damage of HF to a positive electrode interface can be effectively avoided, and the service life of the electrolyte is prolonged. Meanwhile, the released F <-> is induced to form an SEI film rich in LiF on a negative electrode interface, relatively high lithium ion flux and Young modulus are shown, and high stability of the interface and high-speed transmission of interface charges during charging and discharging are facilitated. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the technical field of electrolyte additives, and more specifically, to a functional additive, a long-cycle electrolyte and a lithium-ion battery. Background Art

[0002] Compared with previous batteries, the commercialized lithium-ion secondary batteries have many advantages such as high specific energy, high voltage and long cycle life. They have been widely used in many small equipment fields (such as mobile phones, watches, etc.). With the vigorous development of lithium-ion batteries, they have begun to be used in the fields of electric vehicles and hybrid vehicles. However, with the rapid development of large mobile devices, more stringent requirements have been put forward for the service life, specific capacity and use conditions of lithium-ion batteries. Therefore, it is of great significance to further develop lithium-ion battery technology.

[0003] Ternary batteries, i.e., nickel-cobalt-manganese-lithium or nickel-cobalt-aluminum-lithium cathodes, are one of the main lithium-ion batteries used in electric vehicles today. In order to increase the range of electric vehicles, the battery energy density is currently increased by increasing the upper limit voltage of the cathode, increasing the nickel content, and doping the cathode with silicon. Increasing the upper limit voltage will directly lead to the instability of the cathode structure under high voltage conditions, which will directly affect the battery cycle life. Therefore, increasing the nickel content and matching the silicon anode are the main means of increasing energy density.

[0004] However, as the nickel content of the positive electrode increases (molar ratio greater than 0.85), some problems will arise. At present, the main problem can be solved by means of positive electrode coating, but the conventional electrolytes currently used are composed of lithium salts and organic solvents, which are highly sensitive to moisture. The water present in the battery will cause the hydrolysis of lithium salts to produce highly corrosive HF. Among them, HF will attack the interface of the battery, resulting in the dissolution of harmful transition metals (TMs) at the positive electrode and the damage of the solid electrolyte interface (SEI) at the negative electrode, which will eventually seriously endanger the electrochemical performance of the battery. These adverse effects are more obvious in high-nickel positive electrodes, especially under high pressure and high temperature conditions. At present, most reports are to reduce the hydrolysis of lithium salts by eliminating water in the electrolysis, thereby indirectly removing HF, rather than directly eliminating HF. More importantly, considering that the hydrolysis of lithium salts will not only produce HF, but also LiF, which is an excellent SEI component that inhibits dendrite growth. Therefore, directly neutralizing or eliminating HF generated by the presence of water, rather than directly eliminating water, will ensure that there is a high content of water-derived LiF in the SEI. However, there is currently no economical and sustainable strategy to decouple the interactions between water, HF, and LiF to achieve the goal of “retaining water while eliminating HF.” Summary of the invention

[0005] In view of this, the present invention provides a functional additive, a long-cycle electrolyte and a lithium-ion battery.

[0006] One of the purposes of the present invention is to provide a functional additive. The additive compound provided by the present invention can be adsorbed on the surface of the positive electrode material to form a protective zone. When the lithium salt in the electrolyte generates HF by hydrolysis reaction due to trace water, it can induce a favorable protonation reaction to eliminate HF, which can effectively avoid HF from corroding and damaging the positive electrode interface. At the same time, the F - A LiF-rich SEI film was induced at the negative electrode interface, which exhibited high lithium ion flux and Young's modulus, which was beneficial to the high stability of the interface and the high-speed transfer of interfacial charge during charge and discharge.

[0007] The second purpose of the present invention is to provide a long-cycle electrolyte containing the above-mentioned functional additives. The above-mentioned functional additives are used in combination with other conventional additives to achieve excellent results. When applied to a battery system with a high-nickel ternary positive electrode and a silicon negative electrode, the battery's cycle life and high-temperature performance can be significantly improved, and the degradation of the interface structure during long cycles and under high temperature conditions can be inhibited.

[0008] A third object of the present invention is to provide a lithium-ion battery containing the above-mentioned long-cycle electrolyte, which has excellent electrochemical properties.

[0009] The present invention provides a functional additive having a structure shown in structural formula A:

[0010]

[0011] Among them, R 1～4 R is independently selected from hydrogen, methyl, ethyl, cyclopropane, methoxy or nitro. 5～6 Independently selected from hydrogen, methyl, dimethyl, cyano, n-butenyl, 2-methyl-2-propenyl, trifluoromethyl, trimethylsilyl or fluorosulfonyl.

[0012] Preferably, the structural formula A is at least one of the following formulas (I) to (VII):

[0013]

[0014] Preferably, the preparation method of the functional additive comprises the following steps:

[0015] The o-phenylenediamine monomer and the o-dibromo monomer undergo a substitution reaction to obtain a functional additive.

[0016] The present invention also provides a long-cycle electrolyte, comprising a lithium salt, a non-aqueous organic solvent, a main additive and an auxiliary additive, wherein the main additive is the functional additive described in the above technical solution.

[0017] Preferably, the main additive accounts for 0.5% to 2% of the weight of the long-circulation electrolyte.

[0018] Preferably, 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(oxalatoborate), lithium difluorooxalatoborate, and lithium difluorobis(oxalatophosphate);

[0019] The lithium salt accounts for 11% to 16% of the weight of the electrolyte.

[0020] Preferably, the non-aqueous organic solvent is one or more of an organic ester solvent and an ether solvent; the organic ester solvent is one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate, and methyl trifluoroethyl carbonate; the ether solvent is 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, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether;

[0021] The non-aqueous organic solvent accounts for 76% to 85.5% of the electrolyte by weight.

[0022] Preferably, the auxiliary additive is selected from vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, di(2,2,2-trifluoroethyl) carbonate, vinyl sulfate, vinyl disulfate, propylene sulfate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, 2,4-butane sultone, phenyl methanesulfonate, methylene disulfonate, N-phenylbis(trifluoromethanesulfonyl)imide, triallyl phosphate, imide One or more of trimethyl phosphate, triphenyl phosphite, tetramethyl methylene diphosphate, propargyl phosphate, (2-allylphenoxy) trimethylsilane, 1,3,5-triallyl isocyanurate, isocyanoethyl methacrylate, hexamethylene diisocyanate, p-phenylene diisocyanate, 2,4-toluene diisocyanate, adiponitrile, succinonitrile, glutaronitrile, 1,3,6-hexanetrinitrile, 1,2-bis(cyanoethoxy)ethane, and lithium difluorophosphate;

[0023] The auxiliary electrolyte additive accounts for 3% to 6% of the electrolyte weight.

[0024] The present invention also provides a lithium-ion battery, comprising: a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the long-cycle electrolyte described in the above technical solution.

[0025] Preferably, the active material of the positive electrode is selected from lithium cobalt oxide, lithium manganese oxide, ternary nickel cobalt manganese lithium, lithium nickel manganese oxide, lithium iron phosphate or lithium manganese iron phosphate;

[0026] The active material of the negative electrode is selected from artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon, silicon-carbon composite material, silicon oxide or silicon oxide-graphite;

[0027] The diaphragm is selected from polypropylene, polyethylene diaphragm or polyethylene diaphragm coated with aluminum oxide on one side.

[0028] The present invention provides a functional additive having a structure shown in structural formula A:

[0029]

[0030] Among them, R 1～4 R is independently selected from hydrogen, methyl, ethyl, cyclopropane, methoxy or nitro. 5～6 Independently selected from hydrogen atoms, methyl, dimethyl, cyano, n-butenyl, 2-methyl-2-propylene, trifluoromethyl, trimethylsilyl or fluorosulfonyl. Compared with the prior art, the functional additive provided by the present invention can be adsorbed on the surface of the positive electrode material to form a protective band. When the lithium salt in the electrolyte generates HF by hydrolysis reaction due to trace water, it can induce a favorable protonation reaction to eliminate HF, which can effectively avoid HF from corroding and damaging the positive electrode interface. At the same time, the F released by it - A LiF-rich SEI film was induced at the negative electrode interface, which exhibited high lithium ion flux and Young's modulus, which was beneficial to the high stability of the interface and the high-speed transfer of interfacial charge during charge and discharge. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The invention provides a functional additive, a long-cycle electrolyte and a lithium-ion battery.

[0033] One of the purposes of the present invention is to provide a functional additive, wherein the functional additive has a structure shown in structural formula A:

[0034]

[0035] Among them, R 1～4 R is independently selected from hydrogen, methyl, ethyl, cyclopropane, methoxy or nitro. 5～6Independently selected from hydrogen, methyl, dimethyl, cyano, n-butenyl, 2-methyl-2-propenyl, trifluoromethyl, trimethylsilyl or fluorosulfonyl.

[0036] In the present invention, the structural formula A is preferably at least one of the following formulas (I) to (VII):

[0037]

[0038] Compared with the prior art, the additive compound provided by the present invention can be adsorbed on the surface of the positive electrode material to form a protective zone. When the lithium salt in the electrolyte generates HF by hydrolysis reaction due to trace water, it can induce a favorable protonation reaction to eliminate HF, which can effectively avoid HF from corroding and damaging the positive electrode interface. At the same time, the F - A LiF-rich SEI film was induced at the negative electrode interface, which exhibited high lithium ion flux and Young's modulus, which was beneficial to the high stability of the interface and the high-speed transfer of interfacial charge during charge and discharge.

[0039] In the present invention, the preparation method of the functional additive preferably comprises the following steps:

[0040] The o-phenylenediamine monomer and the o-dibromo monomer undergo a substitution reaction to obtain a functional additive.

[0041] The synthetic route is as follows, but is not limited to the preparation method provided by the present invention:

[0042]

[0043] The preparation method adopted by the present invention has simple process, clear route, mild conditions, easy control, and broad application prospects.

[0044] The second object of the present invention is to provide a long-circulation electrolyte containing the above-mentioned functional additives, wherein the long-circulation electrolyte comprises a lithium salt, a non-aqueous organic solvent, a main additive and an auxiliary additive, wherein the main additive is the functional additive described in the above-mentioned technical scheme.

[0045] In the present invention, the main additive preferably accounts for 0.5% to 2% of the weight of the long-circulation electrolyte.

[0046] In the present invention, the lithium salt is preferably selected from one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethylsulfonyl imide (LiTFSI), lithium bisfluorosulfonyl imide (LiFSI), lithium bisoxalate borate (LiBOB), lithium difluorooxalate borate (LiODFB), and lithium difluorodioxalate phosphate (LiDODFP). The present invention has no particular restrictions on the source of the lithium salt, and commercially available products known to those skilled in the art can be used.

[0047] In the present invention, the lithium salt preferably accounts for 11% to 16% of the weight of the electrolyte.

[0048] In the present invention, the non-aqueous organic solvent is preferably one or more of an organic ester solvent and an ether solvent; wherein the organic ester solvent is preferably one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate, and methyl trifluoroethyl carbonate; the ether solvent is preferably 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, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether. The present invention has no special restrictions on the source of the non-aqueous organic solvent, and commercially available products known to those skilled in the art can be used.

[0049] In the present invention, the non-aqueous organic solvent preferably accounts for 76% to 85.5% by weight of the electrolyte.

[0050] In the present invention, the auxiliary additive is preferably selected from vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, di(2,2,2-trifluoroethyl) carbonate, vinyl sulfate, vinyl disulfate, propylene sulfate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, 2,4-butane sultone, phenyl methanesulfonate, methylene disulfonate, N-phenylbis(trifluoromethanesulfonyl)imide, triallyl phosphate , trimethyl phosphite, triphenyl phosphite, tetramethyl methylene diphosphate, propargyl phosphate, (2-allylphenoxy) trimethylsilane, 1,3,5-triallyl isocyanurate, isocyanoethyl methacrylate, hexamethylene diisocyanate, p-phenylene diisocyanate, 2,4-toluene diisocyanate, adiponitrile, succinonitrile, glutaronitrile, 1,3,6-hexane trinitrile, 1,2-bis(cyanoethoxy)ethane, one or more of lithium difluorophosphate. The present invention has no particular restrictions on the source of the auxiliary additives, and commercially available products known to those skilled in the art can be used.

[0051] In the present invention, the auxiliary electrolyte additive preferably accounts for 3% to 6% of the weight of the electrolyte.

[0052] The functional additive compound prepared by the present invention can react with free HF in the electrolyte, and the mechanism is as follows:

[0053]

[0054] Specifically, the NH bond of the basic piperazine group is used as an active site to capture H from HF. + , triggering a favorable protonation reaction, thereby consuming HF; at the same time, releasing F to the negative electrode - And with Li + The LiF is combined to form a uniform LiF-rich SEI film on the negative electrode.

[0055] The present invention combines the above-mentioned functional additives with other conventional additives to achieve excellent results. When applied to a battery system with a high-nickel ternary positive electrode and a silicon negative electrode, the cycle life and high-temperature performance of the battery can be significantly improved, and the degradation of the interface structure during long cycles and under high temperature conditions can be inhibited.

[0056] A third object of the present invention is to provide a lithium-ion battery containing the above-mentioned long-cycle electrolyte, which has excellent electrochemical properties.

[0057] In the present invention, the lithium-ion battery comprises: a positive electrode, a negative electrode, a separator and an electrolyte, and the electrolyte is the long-cycle electrolyte described in the above technical solution.

[0058] In the present invention, the lithium-ion battery is a lithium-ion battery containing the long-cycle electrolyte described in the above technical solution.

[0059] In the present invention, the active material of the positive electrode is preferably selected from lithium cobalt oxide, lithium manganese oxide, ternary nickel cobalt manganese lithium, nickel manganese oxide, lithium iron phosphate or lithium manganese iron phosphate, and more preferably ternary nickel cobalt manganese lithium (Ni: Co: Mn = 9: 0.5: 0.5). The present invention has no special restrictions on the source of the active material of the positive electrode, and commercial sources or self-made sources known to those skilled in the art can be used.

[0060] In the present invention, the active material of the negative electrode is preferably selected from artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon carbon, silicon carbon composite material, silicon oxide or silicon oxide-graphite, more preferably silicon oxide-graphite, and the gram capacity is preferably 600-700 mAh·g -1 The present invention has no particular limitation on the source of the active material of the negative electrode, and any commercial source or self-made source known to those skilled in the art may be used.

[0061] In the present invention, the diaphragm is preferably selected from polypropylene, polyethylene diaphragm or polyethylene diaphragm coated with aluminum oxide on one side, more preferably polyethylene diaphragm coated with aluminum oxide on one side. The present invention has no particular limitation on the source of the diaphragm, and commercial products known to those skilled in the art can be used.

[0062] Compared with the prior art, the lithium ion battery made with the non-aqueous electrolyte provided by the present invention has better electrochemical performance, specifically, the cycle life of the high-nickel lithium ion battery in the voltage range of 3.0V to 4.2V at both room temperature and high temperature is improved.

[0063] The present invention provides a functional additive having a structure shown in structural formula A:

[0064]

[0065] Among them, R 1～4 R is independently selected from hydrogen, methyl, ethyl, cyclopropane, methoxy or nitro. 5～6 Independently selected from hydrogen atoms, methyl, dimethyl, cyano, n-butenyl, 2-methyl-2-propylene, trifluoromethyl, trimethylsilyl or fluorosulfonyl. Compared with the prior art, the functional additive provided by the present invention can be adsorbed on the surface of the positive electrode material to form a protective band. When the lithium salt in the electrolyte generates HF by hydrolysis reaction due to trace water, it can induce a favorable protonation reaction to eliminate HF, which can effectively avoid HF from corroding and damaging the positive electrode interface. At the same time, the F released by it - A LiF-rich SEI film was induced at the negative electrode interface, which exhibited high lithium ion flux and Young's modulus, which was beneficial to the high stability of the interface and the high-speed transfer of interfacial charge during charge and discharge.

[0066] In order to further illustrate the present invention, the following examples are provided for detailed description. In the following examples of the present invention, if no specific conditions are specified, the reaction is carried out according to conventional conditions or conditions recommended by the manufacturer, and if no manufacturer is specified for the reagents or instruments used, all of them are conventional products that can be purchased commercially.

[0067] Example 1

[0068] The specific steps for preparing compound (I) are as follows:

[0069]

[0070] Under nitrogen atmosphere, 150 mL of ultra-dry N,N-dimethylformamide was added to a clean and dry 250 mL three-necked flask equipped with a magnetic rotor and a reflux condenser, followed by sodium bicarbonate (33.60 g, 400 mmol), and monomer 1 (5.44 g, 40 mmol) was added after stirring, and the mixture was heated to 80°C. Then, monomer 2 (10.16 g, 42 mmol) was added to the reaction system. After the addition was completed, the reaction was continued to stir for 8 h. After the reaction was completed and cooled to room temperature, the liquid was filtered and the solid was washed with 50 mL of petroleum ether. The organic phases were combined, washed with saturated brine and dried over anhydrous sodium sulfate, and the solvent was removed by distillation under reduced pressure. The residue was purified by silica gel chromatography, and the eluent was a mixture of ethyl acetate and petroleum ether (volume ratio 4:1). After the solvent was removed by rotary evaporation, compound (I) was obtained with a yield of 67.2%. EIMS (m / z): calcd.for C 14 H 20 N2,216.16, found 216.25.

[0071] Prepare the electrolyte 1 sample, the specific steps are as follows:

[0072] In an argon glove box with a water and oxygen content of ≤0.1ppm, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DEC), propyl acetate (EP) and propyl propionate (PP) are uniformly mixed in a volume ratio of 5:10:25:20:40 to obtain an organic solvent, and then lithium hexafluorophosphate (LiPF6) is slowly added to the organic solvent. After complete dissolution, fluoroethylene carbonate (FEC), lithium difluorophosphate (LiDFP), tris(trimethylsilyl) phosphate (TMSP) and compound (I) are added, and the electrolyte 1 is obtained after stirring. The amount of LiPF6, organic solvent, FEC, LiDFP, TMSP and compound (I) used is 13%, 78%, 6%, 0.5%, 0.5% and 2% of the total mass of the electrolyte, respectively.

[0073] Prepare the experimental battery 1 sample, the specific steps are as follows:

[0074] Preparation of positive electrode sheet: The positive electrode material ternary nickel cobalt manganese lithium (Ni: Co: Mn = 9: 0.5: 0.5), conductive agent carbon black (SuperP) and carbon nanotubes (CNT, 5% by mass fraction of NMP solution) binder polyvinylidene fluoride (PVDF, 5% by mass fraction of 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%. A planetary homogenizer is used to homogenize to obtain a positive electrode slurry, and the positive electrode slurry is evenly 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.

[0075] Preparation of diaphragm: A polyethylene diaphragm coated with aluminum oxide on one side was used as the isolation membrane and was placed in a dry room with a dew point of -35°C for 72 hours before use.

[0076] Preparation of negative electrode sheet: The negative electrode material is silicon dioxide (gram capacity 650mAh g -1 ), conductive agent SuperP, thickener sodium carboxymethyl cellulose (CMC, deionized water solution with a solid content of 1.5%), binder polyacrylic acid (PAA, deionized water solution with a solid content of 6%), mixed at a mass ratio of 95:1:1.5:2.5 (excluding solvent), added deionized water after mixing, controlled theoretical solid content of 55%, homogenized by a planetary homogenizer to obtain negative electrode slurry, and evenly coated the negative electrode slurry on the composite modified copper foil prepared above, and obtained 52mm×72mm negative electrode sheet after drying, rolling and cutting. The N / P ratio of positive and negative electrodes is 1.1.

[0077] Preparation of battery: The battery was made in a dry room with an ambient dew point of ≤-35°C, the separator was folded in a Z shape, the positive electrode sheet and the negative electrode sheet were placed on each side, there were 12 layers of positive electrode sheets and 13 layers of negative electrode sheets, the positive electrode, separator and negative electrode were aligned and stacked in order, an alumina-surface separator was coated on the positive electrode to obtain an electrode group, and then the electrode group was fixed with polyimide tape and the ear was welded, and then placed in an aluminum-plastic film, and then vacuum-baked at 90 degrees °C for 12 hours, and after cooling, the above-prepared electrolyte 1 was injected, and finally after vacuum packaging, high-temperature infiltration, formation, aging, secondary sealing and capacity division, an experimental battery 1 with a capacity of about 2.5Ah was obtained.

[0078] Example 2

[0079] The specific steps for preparing compound (II) are as follows:

[0080]

[0081] Under nitrogen atmosphere, 150 mL of ultra-dry N,N-dimethylformamide was added to a clean and dry 250 mL three-necked flask equipped with a magnetic rotor and a reflux condenser, followed by sodium bicarbonate (33.60 g, 400 mmol), and monomer 1 (5.44 g, 40 mmol) was added after stirring, and the mixture was heated to 80°C. Then, monomer 3 (9.44 g, 42 mmol) was added to the reaction system. After the addition was completed, the reaction was continued to stir for 8 h. After the reaction was completed and cooled to room temperature, the liquid was filtered and the solid was washed with 50 mL of petroleum ether. The organic phases were combined, washed with saturated brine and dried over anhydrous sodium sulfate, and the solvent was removed by distillation under reduced pressure. The residue was purified by silica gel chromatography, and the eluent was a mixture of ethyl acetate and petroleum ether (volume ratio 4:1). After the solvent was removed by rotary evaporation, compound (II) was obtained with a yield of 63.1%. EIMS (m / z): calcd.for C 12 H 15 N3,201.13,found 201.35.

[0082] Electrolyte 2 sample was prepared according to the steps of Example 1, except that the auxiliary additives were FEC, di(2,2,2-trifluoroethyl) carbonate (TFDEC), and 1,3-propane sultone (PS), and the functional additive was compound (III), wherein the usage amounts of LiPF6, organic solvent, FEC, TFDEC, PS, and compound (II) were 13%, 76%, 6%, 1%, 2%, and 2% of the total mass of the electrolyte, respectively.

[0083] The experimental battery 2 sample was prepared according to the procedure of Example 1.

[0084] Example 3

[0085] The specific steps for preparing compound (III) are as follows:

[0086]

[0087] Under nitrogen atmosphere, 150 mL of ultra-dry N,N-dimethylformamide was added to a clean and dry 250 mL three-necked flask equipped with a magnetic rotor and a reflux condenser, followed by sodium bicarbonate (33.60 g, 400 mmol), and monomer 4 (4.32 g, 40 mmol) was added after stirring. The mixture was heated to 80°C, and then monomer 5 (11.25 g, 42 mmol) was added to the reaction system. After the addition was completed, the reaction was continued to stir for 8 h. After the reaction was completed and cooled to room temperature, the liquid was filtered and the solid was washed with 50 mL of petroleum ether. The organic phases were combined, washed with saturated brine and dried over anhydrous sodium sulfate, and the solvent was removed by distillation under reduced pressure. The residue was purified by silica gel chromatography, and the eluent was a mixture of ethyl acetate and petroleum ether (volume ratio 4:1). After the solvent was removed by rotary evaporation, compound (III) was obtained with a yield of 70.2%. EIMS (m / z): calcd.for C 14 H 20 N2,216.16, found 216.42.

[0088] Electrolyte 3 sample was prepared according to the steps of Example 1, except that the auxiliary additives were FEC, PS and 1,3,6-hexanetricarbonitrile (HTCN), and the functional additive was compound (III), wherein the usage amounts of LiPF6, organic solvent, FEC, PS, HTCN and compound (III) were 13%, 76%, 6%, 2%, 1% and 2% of the total mass of the electrolyte, respectively.

[0089] The experimental battery 3 sample was prepared according to the steps of Example 1.

[0090] Example 4

[0091] The specific steps for preparing compound (IV) are as follows:

[0092]

[0093] Under nitrogen atmosphere, 150 mL of ultra-dry N,N-dimethylformamide was added to a clean and dry 250 mL three-necked flask equipped with a magnetic rotor and a reflux condenser, followed by sodium bicarbonate (33.60 g, 400 mmol), and monomer 6 (5.44 g, 40 mmol) was added after stirring. The mixture was heated to 80°C, and then monomer 7 (11.25 g, 42 mmol) was added to the reaction system. After the addition was completed, the reaction was continued to stir for 8 h. After the reaction was completed and cooled to room temperature, the liquid was filtered and the solid was washed with 50 mL of petroleum ether. The organic phases were combined, washed with saturated brine and dried over anhydrous sodium sulfate, and the solvent was removed by distillation under reduced pressure. The residue was purified by silica gel chromatography, and the eluent was a mixture of ethyl acetate and petroleum ether (volume ratio 4:1). After the solvent was removed by rotary evaporation, compound (IV) was obtained with a yield of 68.3%. EIMS (m / z): calcd.for C 10 H 13 FSN2O2,244.07,found245.11.

[0094] Electrolyte 4 sample was prepared according to the steps of Example 1, except that the lithium salt was LiPF6 and lithium bis(fluorosulfonyl)imide (LiFSI), the organic solvent was propylene carbonate (PC), ethyl methyl carbonate (EMC), methyl trifluoroethyl carbonate (FEMC), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (FEAE) in a volume ratio of 20:50:10:20, the auxiliary additives were FEC, PS and 1,3-propene sultone (PST), and the functional additive was compound (IV), wherein the usage amounts of LiPF6, LiFSI, organic solvent, FEC, PS, PST and compound (IV) were 11%, 2%, 76.9%, 6%, 2%, 0.1% and 2% of the total mass of the electrolyte, respectively.

[0095] The experimental battery 4 sample was prepared according to the steps of Example 1.

[0096] Example 5

[0097] The specific steps for preparing compound (V) are as follows:

[0098]

[0099] Under nitrogen atmosphere, 150 mL of ultra-dry N,N-dimethylformamide was added to a clean and dry 250 mL three-necked flask equipped with a magnetic rotor and a reflux condenser, followed by sodium bicarbonate (33.60 g, 400 mmol), and monomer 8 (5.92 g, 40 mmol) was added after stirring, and the mixture was heated to 80°C, followed by monomer 9 (8.98 g, 42 mmol) was added to the reaction system, and the reaction was continued with stirring for 8 h after the addition was completed. After the reaction was completed and cooled to room temperature, the liquid was filtered and the solid was washed with 50 mL of petroleum ether, the organic phases were combined, washed with saturated brine and dried over anhydrous sodium sulfate, and the solvent was removed by distillation under reduced pressure. The residue was purified by silica gel chromatography, and the eluent was a mixture of ethyl acetate and petroleum ether (volume ratio 4:1). After the solvent was removed by rotary evaporation, compound (V) was obtained with a yield of 69.5%. EIMS (m / z): calcd.for C 13 H 18 N2,202.15,found 202.28.

[0100] Electrolyte 5 sample was prepared according to the steps of Example 1, except that the lithium salt was LiPF6 and lithium difluorooxalatoborate (LiODFB), the auxiliary additives were FEC, PS and hexamethylene diisocyanate (HDMI), and the functional additive was compound (V), wherein the usage amounts of LiPF6, LiFSI, organic solvent, FEC, PS, HDMI and compound (V) were 11%, 2%, 76.8%, 6%, 2%, 0.2% and 2% of the total mass of the electrolyte, respectively.

[0101] The experimental battery 5 sample was prepared according to the procedure of Example 1.

[0102] Example 6

[0103] The specific steps for preparing compound (VI) are as follows:

[0104]

[0105] Under nitrogen atmosphere, 150 mL of ultra-dry N,N-dimethylformamide was added to a clean and dry 250 mL three-necked flask equipped with a magnetic rotor and a reflux condenser, followed by sodium bicarbonate (33.60 g, 400 mmol), and monomer 10 (6.72 g, 40 mmol) was added after stirring, and the mixture was heated to 80°C. Then, monomer 11 (10.66 g, 42 mmol) was added to the reaction system. After the addition was completed, the reaction was continued to stir for 8 h. After the reaction was completed and cooled to room temperature, the liquid was filtered and the solid was washed with 50 mL of petroleum ether. The organic phases were combined, washed with saturated brine and dried over anhydrous sodium sulfate, and the solvent was removed by distillation under reduced pressure. The residue was purified by silica gel chromatography, and the eluent was a mixture of ethyl acetate and petroleum ether (volume ratio 4:1). After the solvent was removed by rotary evaporation, compound (VI) was obtained with a yield of 64.3%. EIMS (m / z): calcd.for C 11 H 13 F3N2O2,262.09,found262.28.

[0106] An electrolyte 6 sample was prepared according to the steps of Example 1, except that the lithium salts were LiPF6 and lithium tetrafluoroborate (LiBF4), the organic solvents were propylene carbonate (PC), ethyl methyl carbonate (EMC), methyl trifluoroethyl carbonate (FEMC), and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (FEAE) in a volume ratio of 20:50:10:20, the auxiliary additives were FEC, PS, and diethylene sulfate (DTD), and the functional additive was compound (VI), wherein the usage amounts of LiPF6, LiFSI, organic solvent, FEC, PS, HDMI, and compound (VI) were 11%, 2%, 74%, 8%, 2%, 1%, and 2% of the total mass of the electrolyte, respectively.

[0107] The experimental battery 6 sample was prepared according to the steps of Example 1.

[0108] Example 7

[0109] The specific steps for preparing compound (VII) are as follows:

[0110]

[0111] Under nitrogen atmosphere, 150 mL of ultra-dry N,N-dimethylformamide was added to a clean and dry 250 mL three-necked flask equipped with a magnetic rotor and a reflux condenser, followed by sodium bicarbonate (33.60 g, 400 mmol), and monomer 12 (6.68 g, 40 mmol) was added after stirring, and the mixture was heated to 80°C. Then, monomer 13 (10.16 g, 42 mmol) was added to the reaction system. After the addition was completed, the reaction was continued to stir for 8 h. After the reaction was completed and cooled to room temperature, the liquid was filtered and the solid was washed with 50 mL of petroleum ether. The organic phases were combined, washed with saturated brine and dried over anhydrous sodium sulfate, and the solvent was removed by distillation under reduced pressure. The residue was purified by silica gel chromatography, and the eluent was a mixture of ethyl acetate and petroleum ether (volume ratio 4:1). After the solvent was removed by rotary evaporation, compound (VII) was obtained with a yield of 66.2%. EIMS (m / z): calcd.for C 12 H 19 N3O2Si,265.12,found265.43.

[0112] An electrolyte sample 7 was prepared according to the steps of Example 1, except that the lithium salts were LiPF6, lithium perchlorate (LiClO4) and lithium bis(oxalatoborate) (LiBOB), the auxiliary additives were FEC, PS and propargyl phosphate (TPP), and the functional additive was compound (VII), wherein the amounts of LiPF6, LiClO4, LiBOB, organic solvent, FEC, PS, TPP and compound (VII) were 11%, 1%, 1%, 76.8%, 6%, 2%, 0.2% and 2% of the total mass of the electrolyte, respectively.

[0113] The experimental battery 7 sample was prepared according to the procedure of Example 1.

[0114] Example 8

[0115] Electrolyte 8 sample was prepared according to the steps of Example 1, except that the auxiliary additives were FEC, LiDFP and DTD, and the functional additive was compound (VII), wherein the usage amounts of LiPF6, organic solvent, FEC, LiDFP, DTD and compound (VII) were 13%, 79%, 6%, 0.5%, 1% and 0.5% of the total mass of the electrolyte, respectively.

[0116] The experimental battery 8 sample was prepared according to the procedure of Example 1.

[0117] Example 9

[0118] Electrolyte 9 sample was prepared according to the steps of Example 1, except that the auxiliary additives were FEC, LiDFP and DTD, and the functional additive was compound (VII), wherein the usage amounts of LiPF6, organic solvent, FEC, LiDFP, DTD and compound (VII) were 13%, 76.5%, 6%, 0.5%, 1% and 3% of the total mass of the electrolyte, respectively.

[0119] The experimental battery 9 sample was prepared according to the procedure of Example 1.

[0120] Comparative Example 1

[0121] The electrolyte 10 sample was prepared according to the steps of Example 1, except that the auxiliary additives were FEC, LiDFP and DTD, wherein the usage amounts of LiPF6, organic solvent, FEC, LiDFP and DTD were 13%, 79.5%, 6%, 0.5% and 1% of the total mass of the electrolyte respectively.

[0122] The experimental battery 10 samples were prepared according to the steps of Example 1.

[0123] Comparative Example 2

[0124] The electrolyte 11 sample was prepared according to the steps of Example 1, except that the auxiliary additives were FEC, LiDFP and DTD, and the functional additive was tris(trimethylsilyl) phosphate (TMSP), wherein the usage amounts of LiPF6, organic solvent, FEC, LiDFP, DTD and TMSP were 13%, 79%, 6%, 0.5%, 1% and 0.5% of the total mass of the electrolyte, respectively.

[0125] The experimental battery 11 sample was prepared according to the steps of Example 1.

[0126] The electrolyte compositions and contents of Examples 1 to 9 and Comparative Examples 1 to 2 are shown in Table 1.

[0127] The lithium ion batteries prepared in Examples 1 to 9 and Comparative Examples 1 to 2 were subjected to room temperature cycle performance tests and high temperature cycle performance tests, respectively, and the test conditions were as follows:

[0128] Battery cycle test at room temperature:

[0129] The prepared lithium-ion battery was placed in a constant temperature room with 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 cut-off current of 0.05C, and then discharged at a constant current of 1C to a voltage of 3V. The cycle was repeated 1000 times, and the capacity retention rate was recorded. The capacity retention rate of the nth cycle (%) = (discharge capacity of the nth cycle / discharge capacity of the first cycle) × 100%.

[0130] Battery high temperature cycle test:

[0131] Before the test, use an internal resistance tester to measure the internal resistance of the battery, and use the drainage method to measure the battery volume, which is recorded as V0. Then, place the prepared lithium-ion battery in a high and low temperature environment at 45°C for 4 hours to stabilize the temperature inside and outside the battery. With a current of 1C and a voltage of 4.2V, charge at constant current and constant voltage until the cut-off current is 0.05C, then discharge at a constant current of 1C to a voltage of 3V, cycle for 800 weeks, and record the capacity retention rate. The capacity retention rate of the nth cycle (%) = (the discharge capacity of the nth cycle / the discharge capacity of the first cycle) × 100%. After the test, measure the battery volume V1, and the volume expansion rate (%) = (V1-V0) × 100% / V0.

[0132] Table 1 Electrolyte composition and corresponding battery performance of each embodiment and comparative example battery

[0133]

[0134]

[0135] The battery performance test results of lithium ion batteries prepared using the electrolytes in Examples 1 to 10 and Comparative Examples 1 to 3 are shown in Table 1. It can be seen that the embodiment group using the functional additives of the present invention has significantly improved room temperature / high temperature cycle performance compared to the comparative example group without adding the functional compound or adding the conventional acid-removing additive, and the capacity loss caused by the loss of active lithium during the cycle is effectively and significantly alleviated. At the same time, the expansion of the battery cell after the cycle is effectively suppressed.

[0136] In summary, the present invention provides a functional additive, a long-cycle electrolyte and a lithium-ion battery, which have the following beneficial effects compared with the prior art:

[0137] (1) The functional additive compound provided by the present invention can form a special protection zone on the positive electrode surface, using the NH bond in its piperazine group as an active site to capture H from HF. + , triggering a favorable protonation reaction, thereby consuming HF and avoiding HF's corrosion and damage to the positive electrode interface, which can greatly enhance the interface stability of the high-nickel positive electrode under high voltage and high temperature conditions.

[0138] (2) Compared with the direct water removal additive, the functional additive provided by the present invention does not directly participate in water removal. On the one hand, it utilizes the beneficial LiF generated by the hydrolysis reaction, and on the other hand, it eliminates harmful HF and releases F to the negative electrode. -As a fluorine source, this will help form a LiF-enriched SEI film with enhanced lithium ion conductivity and Young's modulus; when combined with other auxiliary additives and introduced into high-nickel-silicon negative electrode lithium-ion batteries, the stability of the positive and negative electrode interfaces is greatly improved, and the erosion of HF on the positive electrode surface that causes the dissolution of transition metals can be effectively avoided. At the same time, a high mechanical strength solid electrolyte interface film rich in LiF is induced on the negative electrode surface, which can also effectively alleviate the rapid attenuation of electrochemical performance caused by the huge volume expansion of the silicon-containing negative electrode during the charge and discharge process.

[0139] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A functional additive, characterized in that: It has the structure shown in structural formula A: Among them, R 1～4 R is independently selected from hydrogen, methyl, ethyl, cyclopropane, methoxy or nitro. 5～6 Independently selected from hydrogen, methyl, dimethyl, cyano, n-butenyl, 2-methyl-2-propenyl, trifluoromethyl, trimethylsilyl or fluorosulfonyl.

2. The functional additive according to claim 1, characterized in that: The structural formula A is specifically at least one of the following formulas (I) to (VII):

3. The functional additive according to claim 1, characterized in that: The preparation method of the functional additive comprises the following steps: The o-phenylenediamine monomer and the o-dibromo monomer undergo a substitution reaction to obtain a functional additive.

4. A long-cycle electrolyte comprising a lithium salt, a non-aqueous organic solvent, a main additive and an auxiliary additive, characterized in that: The main additive is the functional additive according to any one of claims 1 to 3.

5. The long-circulation electrolyte according to claim 4, characterized in that: The main additive accounts for 0.5% to 2% of the weight of the long-circulation electrolyte.

6. The long-circulation electrolyte according to claim 4, characterized in that: 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(oxalatoborate), lithium difluorooxalatoborate, and lithium difluorobis(oxalatophosphate); The lithium salt accounts for 11% to 16% of the weight of the electrolyte.

7. The long-circulation electrolyte according to claim 4, characterized in that: The non-aqueous organic solvent is one or more of an organic ester solvent and an ether solvent; the organic ester solvent is one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate, and methyl trifluoroethyl carbonate; the ether solvent is 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, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether; The non-aqueous organic solvent accounts for 76% to 85.5% of the electrolyte by weight.

8. The long-circulation electrolyte according to claim 4, characterized in that: The auxiliary additive is selected from vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, di(2,2,2-trifluoroethyl) carbonate, vinyl sulfate, vinyl disulfate, propylene sulfate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, 2,4-butane sultone, phenyl methanesulfonate, methylene disulfonate, N-phenylbis(trifluoromethanesulfonyl)imide, triallyl phosphate, phosphorous acid One or more of trimethyl ester, triphenyl phosphite, tetramethyl methylene diphosphate, propargyl phosphate, (2-allylphenoxy) trimethylsilane, 1,3,5-triallyl isocyanurate, isocyanoethyl methacrylate, hexamethylene diisocyanate, p-phenylene diisocyanate, 2,4-toluene diisocyanate, adiponitrile, succinonitrile, glutaronitrile, 1,3,6-hexanetrinitrile, 1,2-bis(cyanoethoxy)ethane, and lithium difluorophosphate; The auxiliary electrolyte additive accounts for 3% to 6% of the electrolyte weight.

9. A lithium ion battery comprising: A positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the long-cycle electrolyte according to any one of claims 5 to 8.

10. The lithium ion battery according to claim 9, characterized in that: The active material of the positive electrode is selected from lithium cobalt oxide, lithium manganese oxide, ternary nickel cobalt manganese lithium, lithium nickel manganese oxide, lithium iron phosphate or lithium manganese iron phosphate; The active material of the negative electrode is selected from artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon, silicon-carbon composite material, silicon oxide or silicon oxide-graphite; The diaphragm is selected from polypropylene, polyethylene diaphragm or polyethylene diaphragm coated with aluminum oxide on one side.

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