Electrolyte additive and application thereof

Abstract

The application provides an electrolyte additive. The high-voltage electrolyte for high-nickel lithium ion batteries of the application improves the problem that the benzene boronic acid functional group is prone to hydrolysis to cause deterioration of the electrolyte by introducing a silicon-oxygen bond, expands the application of the electrolyte in battery cycles, the steric hindrance effect of the silicon-oxygen group insulates the reaction of water or hydrofluoric acid in the electrolyte and the boron element, retains the boron-oxygen bond, and forms a uniform and thin inorganic boron-containing low-impedance CEI layer on the surface of the positive electrode; meanwhile, the trifluoromethylsulfonyl group can improve the high-temperature storage performance of the battery, the additive is added into the non-aqueous organic solvent as a functional additive, the electrolyte has high high-voltage resistance, oxidation resistance and high-temperature resistance, and the lithium ion battery containing the electrolyte has good cycle performance under high voltage and high temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to an electrolyte additive and its application. Background Art

[0002] As a crucial component of the electrolyte, electrolyte additives primarily protect the positive and negative electrodes by forming a film at the interface. Currently, commercial electrolyte additives are categorized as film-forming additives, water and acid removal additives, and overcharge additives. These additives play a crucial role in a battery's specific capacity, operating temperature range, cycle efficiency, and safety performance.

[0003] Among high-voltage electrolyte additives, phenyl borate esters are rarely used. This is because the hydrolysis rate of phenyl borate esters is very fast, causing the electrolyte to turn yellow and deteriorate, resulting in ineffectiveness. In turn, phenyl borate ester additives cause rapid loss of battery capacity and poor cycle performance under high voltage and high temperature. They cannot meet the working requirements of lithium-ion battery electrolytes that are often subjected to high voltage and high temperature cycles.

[0004] Therefore, providing an electrolyte additive for lithium ion batteries that can be used in high voltage and high temperature batteries and have good cycle performance has become a problem to be solved. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide an electrolyte additive and its application. The electrolyte additive provided by the present invention is used in lithium-ion batteries, which can enable lithium-ion batteries to have good cycle performance under high voltage and high temperature conditions.

[0006] The present invention provides an electrolyte additive, which is one or more compounds selected from the group consisting of compounds having structures represented by Formula A-1, Formula A-2, and Formula A-3:

[0007]

[0008] In Formula A-1, Formula A-2 and Formula A-3, R1 and R2 are each independently selected from a trifluoromethanesulfonyl imide group and a boroxysilane group.

[0009] Preferably, the electrolyte additive is selected from one or more of compound (I), compound (II) and compound (III);

[0010]

[0011] The present invention also provides a lithium ion battery electrolyte, comprising a lithium salt, a non-aqueous organic solvent and an electrolyte additive, wherein the electrolyte additive is selected from the above electrolyte additives.

[0012] Preferably, the lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate or lithium difluorobis(oxalatophosphate).

[0013] Preferably, the non-aqueous organic solvent is any one or more of an organic ester solvent, an ether solvent, a sulfone solvent or a nitrile solvent.

[0014] Preferably, the electrolyte additive further comprises a second additive, and the second additive is selected from vinylene carbonate, ethylene carbonate, propylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, 2,4-butane sultone, N-phenylbis(trifluoromethanesulfonyl)imide, phenyl methanesulfonate, hydroquinone difluorosulfonate, methylene methanedisulfonate, 1,3,5-triallyl isocyanurate, hexadecene, 1,3,5-triallyl isocyanurate, 1,3-propane ...triallyl isocyanurate, 1,3-propane sultone, 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, Any one or more of methylene diisocyanate, p-phenylene diisocyanate, isocyanoethyl methacrylate, 2,4-toluene diisocyanate, vinyl sulfate, vinyl disulfate, propylene sulfite, triallyl phosphate, tripropargyl phosphate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, tris(vinyldimethylsilane)phosphate, propyldiprop-2-ynyl phosphate, ethyldiprop-2-ynyl phosphate or tetramethylmethylene diphosphate.

[0015] Preferably, the lithium-ion battery electrolyte comprises:

[0016] 10 to 16 parts by weight of a lithium salt;

[0017] 80-90 parts by weight of a non-aqueous organic solvent;

[0018] 0.1 to 10 parts by weight of electrolyte additives.

[0019] 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 selected from the above-mentioned lithium ion battery electrolyte.

[0020] Preferably, the active material of the positive electrode is selected from any one of lithium cobalt oxide, lithium manganese oxide, ultra-high nickel ternary nickel cobalt manganese lithium, lithium nickel manganese oxide, lithium iron phosphate or lithium manganese iron phosphate, preferably ultra-high nickel ternary nickel cobalt manganese lithium;

[0021] Preferably, the active material of the negative electrode is selected from any one of artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon composite material or silicon oxide; preferably artificial graphite;

[0022] Preferably, the diaphragm is selected from a polypropylene diaphragm or a polyethylene diaphragm; preferably a polyethylene diaphragm;

[0023] Preferably, the charge and discharge voltage of the lithium-ion battery is 3.0-4.2V.

[0024] Compared with the prior art, the present invention provides an electrolyte additive, selected from one or more compounds having the structures shown in Formula A-1, Formula A-2, and Formula A-3: In Formula A-1, Formula A-2, and Formula A-3, R1 and R2 are each independently selected from trifluoromethanesulfonyl imide and borosilane. The present invention is used in high-voltage electrolytes for high-nickel lithium-ion batteries. By introducing a silicon-oxygen bond, the problem of easy hydrolysis of the phenylboronic acid functional group leading to electrolyte deterioration is improved, thereby expanding its application in battery cycling. The large steric effect of the silicon-oxygen group isolates the reaction between water or hydrofluoric acid in the electrolyte and the boron element, retaining the borosulfonyl bond and forming a uniform and thin inorganic boron-containing low-impedance CEI layer on the positive electrode surface; at the same time, the trifluoromethanesulfonyl group can improve the high-temperature storage performance of the battery. The additive is added to a non-aqueous organic solvent as a functional additive, so that the electrolyte has high high-voltage resistance, oxidation resistance, and high-temperature resistance, so that the lithium-ion battery containing it has good cycle performance under high pressure and high temperature. DETAILED DESCRIPTION

[0025] The present invention provides an electrolyte additive, which is one or more compounds selected from the group consisting of compounds having structures represented by Formula A-1, Formula A-2, and Formula A-3:

[0026]

[0027] In Formula A-1, Formula A-2 and Formula A-3, R1 and R2 are each independently selected from a trifluoromethanesulfonyl imide group and a boroxysilane group.

[0028] In some preferred embodiments of the present invention, the electrolyte additive is selected from one or more of compound (I), compound (II) and compound (III);

[0029]

[0030] The present invention also provides a method for preparing an electrolyte additive having the structures of compound (I), compound (II) and compound (III), comprising the following steps:

[0031] A) mixing an aminophenylboronic acid compound with trifluoromethanesulfonyl chloride to react to obtain an intermediate product;

[0032] B) reacting the intermediate product with hexamethyldisilazane to obtain an electrolyte additive having the structures of compound (I), compound (II) and compound (III).

[0033] In step A), the aminophenylboronic acid compound is selected from (4-aminophenyl)boric acid, (3-aminophenyl)boric acid, and (2-aminophenyl)boric acid.

[0034] In step A), the reaction medium is a mixed solution of NaH and THF, and the reaction is carried out under nitrogen protection.

[0035] In step B), the catalyst of the reaction is selected from trimethylpentylammonium, the temperature of the reaction is 115℃, and the time is 10h.

[0036] The present application also provides a lithium ion battery electrolyte, comprising a lithium salt, a non-aqueous organic solvent and an electrolyte additive, wherein the electrolyte additive is selected from the electrolyte additives described above.

[0037] In the present application, the lithium ion battery electrolyte comprises:

[0038] 10-16 parts by weight of a lithium salt;

[0039] 80-90 parts by weight of a non-aqueous organic solvent;

[0040] 0.1-10 parts by weight of an electrolyte additive.

[0041] Specifically, the lithium ion battery electrolyte comprises 10-16 parts by weight of a lithium salt, which can be 10, 11, 12, 13, 14, 15, 16, or any value between 10 and 16 parts by weight, and the lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bisfluorosulfonylimide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, or lithium difluorodi(oxalato)phosphate, and preferably is lithium hexafluorophosphate.

[0042] The lithium ion battery electrolyte further comprises 80-90 parts by weight of a non-aqueous organic solvent, which can be 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, or any value between 80 and 90 parts by weight. The non-aqueous organic solvent is any one or more of an organic ester solvent, an ether solvent, a sulfone solvent, or a nitrile solvent.

[0043] The organic ester solvent is selected from one or more of vinyl carbonate, propylene carbonate, fluorovinyl carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, or ethyl butyrate.

[0044] The ether solvent is selected from one or more of dimethyl ether, diethyl ether, methyl ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, or 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0045] The sulfone solvent is selected from dimethyl sulfoxide and / or sulfolane.

[0046] The nitrile solvent is selected from any one or more of adiponitrile, succinonitrile or glutaronitrile.

[0047] The lithium-ion battery electrolyte further comprises 0.1 to 10 parts by weight of an electrolyte additive, which can be 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any value between 0.1 and 10 parts by weight, preferably any value between 0.1 and 5 parts by weight. The electrolyte additive is selected from the above-mentioned electrolyte additives. In some specific embodiments of the present invention, the electrolyte additive further comprises a second additive, which is selected from vinylene carbonate, ethylene carbonate, propylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, 2,4-butane sultone, N-phenylbis(trifluoromethanesulfonyl)imide, phenyl methanesulfonate, hydroquinone difluorosulfonate, methylene disulfonate, 1,3,5-triallyl isocyanurate, hexamethylenedisulfonate Any one or more of isocyanate, p-phenylene diisocyanate, isocyanoethyl methacrylate, 2,4-toluene diisocyanate, vinyl sulfate, vinyl bissulfate, propylene sulfite, triallyl phosphate, tripropargyl phosphate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, tris(vinyldimethylsilane)phosphate, propyl diprop-2-ynyl phosphate, ethyl diprop-2-ynyl phosphate or tetramethylmethylene diphosphate, preferably 1,3-propane sultone (PS).

[0048] 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 selected from the above-mentioned lithium ion battery electrolyte.

[0049] In the present invention, the active material of the positive electrode is selected from any one of lithium cobalt oxide, lithium manganese oxide, ultra-high nickel ternary nickel cobalt manganese lithium, lithium nickel manganese oxide, lithium iron phosphate or lithium manganese iron phosphate, preferably ultra-high nickel ternary nickel cobalt manganese lithium, and more preferably nickel cobalt manganese lithium NCM90.

[0050] The active material of the negative electrode is selected from any one of artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon composite material or silicon oxide; preferably artificial graphite;

[0051] The diaphragm is selected from a polypropylene diaphragm or a polyethylene diaphragm, preferably a polyethylene diaphragm.

[0052] In the present invention, the lithium ion battery is preferably a high nickel lithium ion battery.

[0053] In the present invention, the charge and discharge voltage of the lithium-ion battery is 3.0-4.2V.

[0054] The high-voltage electrolyte of the present invention is used for high-nickel lithium-ion batteries. By introducing silicon-oxygen bonds, the problem of easy hydrolysis of phenylboronic acid functional groups leading to electrolyte deterioration is improved, thereby expanding its application in battery cycles. The large steric effect of the silicon-oxygen group isolates the reaction between water or hydrofluoric acid in the electrolyte and the boron element, retaining the boron-oxygen bond, and forming a uniform and thin inorganic boron-containing low-impedance CEI layer on the positive electrode surface. At the same time, the trifluoromethanesulfonyl group can improve the high-temperature storage performance of the battery. The additive is added as a functional additive to the non-aqueous organic solvent, so that the electrolyte has high high-voltage resistance, oxidation resistance, and high-temperature resistance, and the lithium-ion battery containing the electrolyte has good cycle performance under high pressure and high temperature.

[0055] In order to further understand the present invention, the present invention is described below with reference to the embodiments, and the protection scope of the present invention is not limited by the following embodiments.

[0056] Example 1

[0057] Preparation of compound (I), the specific steps are as follows:

[0058]

[0059] First, NaH was added to THF and stirred for 10 minutes. Then, (4-aminophenyl)boric acid and trifluoromethanesulfonyl chloride were added dropwise at 0°C and added to a 250 mL three-necked flask connected to nitrogen. After reacting for 1 hour, the mixture was cooled to room temperature and then allowed to stand for 12 hours to react to obtain product (I). After the product (I) was dried, hexamethyldisilazane was added to the product (I). The hexamethyldisilazane and the product (I) were reacted at 115°C for 10 hours under the catalysis of a small amount of trimethylpentylammonium. After cooling, the solid product was filtered to remove the solvent and impurities. The solid product was washed with ether to remove impurities and distilled twice to obtain compound (I).

[0060] Prepare the electrolyte 1 sample as follows:

[0061] In an argon glove box with a water and oxygen content of ≤0.1ppm, propylene carbonate (PC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) are uniformly mixed in a mass ratio of PC:DEC:EMC = 10:25:50.5 to obtain an organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) is slowly added to the organic solvent. After complete dissolution, 1,3-propane sultone (PS) and compound (I) are added, and the mixture is stirred evenly to obtain electrolyte 1, wherein the amounts of LiPF6, organic solvent, PS, and compound (I) used are 13%, 85.5%, 1%, and 0.5% of the total mass of the electrolyte, respectively.

[0062] Prepare the experimental battery 1 sample, the specific steps are as follows:

[0063] The positive electrode material nickel cobalt manganese lithium (NCM90), the conductive agent carbon black (SuperP), and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96.5:1.5:2. After mixing, N-methylpyrrolidone (NMP) was added to control the theoretical solid content to 55%. The positive electrode slurry was obtained by homogenization using a vacuum defoamer, and the positive electrode slurry was evenly coated on a 17 μm thick aluminum foil. After drying, rolling, and cutting, a 50 mm × 70 mm positive electrode sheet was obtained.

[0064] The negative electrode material, artificial graphite, the conductive agent SuperP, the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 95:1:1.5:2.5. Deionized water was added to control the theoretical solid content to 52%. The mixture was homogenized using a vacuum defoamer to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on a 17μm thick copper foil. After drying, roller pressing, and cutting, a 52mm×72mm negative electrode sheet was obtained. The N / P ratio of the positive and negative electrodes was 1.1.

[0065] The polyethylene diaphragm coated with nano-alumina was cut into 55 mm × 75 mm sizes and vacuum-baked at 70°C for 48 h to remove water.

[0066] A soft-pack laminated battery was fabricated at an ambient dew point of ≤-45°C. The positive electrode, separator, and negative electrode were stacked in sequence, with the positive and negative tabs positioned on the same side. The separator was positioned between the positive and negative electrodes to provide isolation, resulting in a bare cell. The bare cell was placed in an aluminum-plastic film outer packaging, vacuum-baked at 90°C for 12 hours, cooled to below 40°C, and then injected with the prepared electrolyte. The battery was then packaged, subjected to high-temperature impregnation, formed, aged, packaged with secondary vacuum pumping, and then capacity divided to produce Experimental Cell 1.

[0067] Example 2

[0068] Preparation of compound (II), the specific steps are as follows:

[0069]

[0070] First, NaH was added to THF and stirred for 10 minutes. Then, (3-aminophenyl)boric acid and trifluoromethanesulfonyl chloride were added dropwise at 0°C and added to a 250 mL three-necked flask connected to nitrogen. After reacting for 1 hour, the mixture was cooled to room temperature and then allowed to stand for 12 hours to obtain product (II). After the product (II) was dried, hexamethyldisilazane was added to the product (II). The hexamethyldisilazane and the product (II) were reacted at 115°C for 10 hours in the presence of a small amount of trimethylpentylammonium as a catalyst. After cooling, the solid product was filtered to remove the solvent and impurities. The solid product was washed with ether to remove impurities and distilled twice to obtain compound (II).

[0071] Prepare the electrolyte 2 sample as follows:

[0072] In an argon glove box with a water and oxygen content of ≤0.1ppm, propylene carbonate (PC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were uniformly mixed in a mass ratio of PC:DEC:EMC = 10:25:50.5 to obtain an organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) was slowly added to the organic solvent. After complete dissolution, 1,3-propane sultone (PS) and compound (II) were added, and the mixture was stirred evenly to obtain electrolyte 2, wherein the amounts of LiPF6, organic solvent, PS, and compound (II) used were 13%, 85.5%, 1%, and 0.5% of the total mass of the electrolyte, respectively.

[0073] Prepare the experimental battery 2 sample, the specific steps are as follows:

[0074] The positive electrode material nickel cobalt manganese lithium (NCM90), the conductive agent carbon black (SuperP), and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96.5:1.5:2. After mixing, N-methylpyrrolidone (NMP) was added to control the theoretical solid content to 55%. The positive electrode slurry was obtained by homogenization using a vacuum defoamer, and the positive electrode slurry was evenly coated on a 17 μm thick aluminum foil. After drying, rolling, and cutting, a 50 mm × 70 mm positive electrode sheet was obtained.

[0075] The negative electrode material, artificial graphite, the conductive agent SuperP, the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 95:1:1.5:2.5. Deionized water was added to control the theoretical solid content to 52%. The mixture was homogenized using a vacuum defoamer to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on a 17μm thick copper foil. After drying, roller pressing, and cutting, a 52mm×72mm negative electrode sheet was obtained. The N / P ratio of the positive and negative electrodes was 1.1.

[0076] The polyethylene diaphragm coated with nano-alumina was cut into 55 mm × 75 mm sizes and vacuum-baked at 70°C for 48 h to remove water.

[0077] A soft-pack laminated battery was fabricated at an ambient dew point of ≤-45°C. The positive electrode, separator, and negative electrode were stacked in sequence, with the positive and negative tabs located on the same side. The separator was positioned between the positive and negative electrodes to provide isolation, resulting in a bare cell. The bare cell was placed in an aluminum-plastic film outer packaging, vacuum-baked at 90°C for 12 hours, cooled to below 40°C, and then injected with the prepared electrolyte. The battery was then packaged, subjected to high-temperature impregnation, formed, aged, packaged with secondary vacuum pumping, and then capacity divided to produce Experimental Cell 2.

[0078] Example 3

[0079] Preparation of compound (III), the specific steps are as follows:

[0080]

[0081] First, NaH was added to THF and stirred for 10 minutes. Then, (2-aminophenyl)boric acid and trifluoromethanesulfonyl chloride were added dropwise at 0°C and added to a 250 mL three-necked flask connected to nitrogen. After reacting for 1 hour, the mixture was cooled to room temperature and then allowed to stand for 12 hours to react to obtain product (III). After the product (III) was dried, hexamethyldisilazane was added to the product (III). The hexamethyldisilazane and the product (III) were reacted at 115°C for 10 hours in the presence of a small amount of trimethylpentylammonium as a catalyst. After cooling, the solid product was filtered to remove the solvent and impurities. The solid product was washed with ether to remove impurities and distilled twice to obtain compound (III).

[0082] Prepare the electrolyte 3 sample as follows:

[0083] In an argon glove box with a water and oxygen content of ≤0.1ppm, propylene carbonate (PC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were uniformly mixed in a mass ratio of PC:DEC:EMC = 10:25:50 to obtain an organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) was slowly added to the organic solvent. After complete dissolution, 1,3-propane sultone (PS) and compound (III) were added, and the mixture was stirred evenly to obtain electrolyte 3, wherein the amounts of LiPF6, organic solvent, PS, and compound (III) used were 13%, 85.5%, 1%, and 0.5% of the total mass of the electrolyte, respectively.

[0084] Prepare the experimental battery 3 sample, the specific steps are as follows:

[0085] The positive electrode material nickel cobalt manganese lithium (NCM90), the conductive agent carbon black (SuperP), and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96.5:1.5:2. After mixing, N-methylpyrrolidone (NMP) was added to control the theoretical solid content to 55%. The positive electrode slurry was obtained by homogenization using a vacuum defoamer, and the positive electrode slurry was evenly coated on a 17 μm thick aluminum foil. After drying, rolling, and cutting, a 50 mm × 70 mm positive electrode sheet was obtained.

[0086] The negative electrode material, artificial graphite, the conductive agent SuperP, the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 95:1:1.5:2.5. Deionized water was added to control the theoretical solid content to 52%. The mixture was homogenized using a vacuum defoamer to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on a 17μm thick copper foil. After drying, roller pressing, and cutting, a 52mm×72mm negative electrode sheet was obtained. The N / P ratio of the positive and negative electrodes was 1.1.

[0087] The polyethylene diaphragm coated with nano-alumina was cut into 55 mm × 75 mm sizes and vacuum-baked at 70°C for 48 h to remove water.

[0088] A soft-pack laminated battery was fabricated at an ambient dew point of ≤-45°C. The positive electrode, separator, and negative electrode were stacked in sequence, with the positive and negative tabs positioned on the same side. The separator was positioned between the positive and negative electrodes to provide isolation, resulting in a bare cell. The bare cell was placed in an aluminum-plastic film outer packaging, vacuum-baked at 90°C for 12 hours, cooled to below 40°C, and then injected with the prepared electrolyte. The battery was then packaged, subjected to high-temperature impregnation, formed, aged, packaged with secondary vacuum pumping, and then capacity divided to produce Experimental Cell 3.

[0089] Example 4

[0090] Compound (I), electrolyte 4 and experimental battery 4 were prepared according to the method of Example 1, except that the amount of additive compound (I) added to electrolyte 4 was 1%, wherein the amounts of LiPF6, organic solvent, PS and compound (I) used were 13%, 85%, 1% and 1% of the total mass of the electrolyte, respectively.

[0091] Example 5

[0092] Compound (II), electrolyte 5 and experimental battery 5 were prepared according to the method of Example 2, except that the amount of additive compound (II) added to electrolyte 5 was 1%, wherein the amounts of LiPF6, organic solvent, PS and compound (II) used were 13%, 85%, 1% and 1% of the total mass of the electrolyte, respectively.

[0093] Example 6

[0094] Compound (III), electrolyte 6 and experimental battery 6 were prepared according to the method of Example 3, except that the amount of additive compound (III) added to electrolyte 6 was 1%, wherein the amounts of LiPF6, organic solvent, PS and compound (III) used were 13%, 85%, 1% and 1% of the total mass of the electrolyte, respectively.

[0095] Comparative Example 1

[0096] Electrolyte 7 and experimental battery 7 were prepared according to the method of Example 1, except that trimethyl borate (TMB) was added as an additive to electrolyte 7, wherein the amounts of LiPF6, organic solvent, PS, and trimethyl borate were 13%, 85%, 1%, and 1% of the total mass of the electrolyte, respectively.

[0097] Comparative Example 2

[0098] Electrolyte 8 and experimental battery 8 were prepared according to the method of Example 1, except that the additive 3-cyano-5-fluorophenylboric acid (CFBA) was added to electrolyte 8, wherein the usage amounts of LiPF6, organic solvent, PS, and trimethyl borate were 13%, 85%, 1%, and 1% of the total mass of the electrolyte, respectively.

[0099] Comparative Example 3

[0100] Electrolyte 9 and experimental battery 9 were prepared according to the method of Example 1, except that tris(2-cyanoethyl)borate (TB) was added as an additive to electrolyte 9, wherein the amounts of LiPF6, organic solvent, PS, and trimethyl borate were 13%, 85%, 1%, and 1% of the total mass of the electrolyte, respectively.

[0101] The soft-pack batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were subjected to normal temperature and high temperature cycle performance tests and electrolyte acidity tests respectively:

[0102] Battery room temperature cycle test

[0103] The battery to be tested was placed in a constant temperature room at an ambient temperature of 25°C and allowed to stand for 4 hours. It was then charged at a current of 1C and a voltage of 4.2V under constant current and constant voltage until the cutoff current reached 0.05C. It was then discharged at a constant current of 1C to a voltage of 3V. This cycle was repeated 500 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%.

[0104] Battery high temperature cycle test:

[0105] In the test environment, the prepared soft-pack battery was placed in an explosion-proof test box at an ambient temperature of 45°C for 4 hours, and then charged with a constant current and constant voltage of 1C and a voltage of 4.2V to a cutoff current of 0.05C. Then, it was discharged with a constant current of 1C to a voltage of 3V. The cycle was repeated 500 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%.

[0106] Battery high temperature storage test

[0107] The battery to be tested is charged and discharged at room temperature for one week at a current of 1C, with a voltage range of 3 to 4.2V. The discharge capacity, internal resistance and volume of the first week are recorded. The internal resistance is tested using a battery internal resistance tester, and the volume is tested using the drainage method. Then charge to 4.2V at a constant current and constant voltage of 1C, with a cut-off current of 0.05C, and then place the battery in a constant temperature oven at 60°C for 7 days. After the time is up, take out the battery and cycle it at room temperature for 2 weeks at 1C / 1C, and record the discharge capacity in the first week after high temperature standing, the discharge capacity in the second week, the internal resistance and volume after storage. Calculate the capacity retention rate, capacity recovery rate, internal resistance growth rate and volume expansion rate of the battery after storage according to the following formula:

[0108] Capacity recovery rate = discharge capacity in the first week after high-temperature storage / discharge capacity in the first week × 100%;

[0109] Volume expansion rate = (volume after storage - volume in the first week) / volume in the first week × 100%

[0110] Table 1 Electrochemical performance of experimental batteries in each group

[0111]

[0112] From the comparison of the data of Examples 1 to 6 and Comparative Examples 1 to 3 in Table 1 above, it can be seen that the functional additives prepared by the present invention can simultaneously ensure a higher capacity retention rate, a lower volume expansion rate and a lower internal resistance growth rate in high-temperature storage, as well as a higher capacity retention rate in normal temperature cycling and high-temperature cycling, compared to borate ester and phenyl borate ester additives.

[0113] Electrolyte acidity test:

[0114] Take 20 g of the electrolyte prepared in Examples 1 to 6 and Comparative Examples 1 to 3 above, respectively, and weigh it in a conical flask, record the mass as m, and add 1 to 2 drops of neutral red methylene blue mixed indicator. Use triethylamine ultra-dry acetonitrile solution with a concentration of c to titrate, record the titration volume V of the standard solution, and calculate the acidity of the electrolyte according to the following formula:

[0115] Electrolyte acidity (ppm) = 20.006 × 1000 × V × c / m;

[0116] The remaining electrolyte was placed in a clean and dry aluminum-plastic bottle, sealed, and placed in a 60°C oven for three days. The electrolyte was then taken out and the acidity of the electrolyte was measured again according to the above method.

[0117] Table 2 Electrochemical performance of experimental batteries in each group

[0118]

[0119] As can be seen from the data of examples 1-6 and comparative examples 1-3 in Table 2, the functional additive prepared by the application can delay the hydrolysis of phenylboronic acid ester additives in the electrolyte, and can significantly inhibit the increase of acidity of the electrolyte during high-temperature storage, compared with the commonly used phenylboronic acid ester additives.

[0120] The above merely describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. An electrolyte additive for lithium ion batteries, characterized in that The additive is selected from one or more of compound (I), compound (II) and compound (III); Compound (I), Compound (II), Compound (III); The amount of the electrolyte additive added to the electrolyte is as follows: 10-16 parts by weight of a lithium salt; 80-90 parts by weight of a non-aqueous organic solvent; 0.1 to 10 parts by weight of electrolyte additives.

2. A lithium ion battery electrolyte, characterized in that: The electrolyte comprises a lithium salt, a non-aqueous organic solvent and an electrolyte additive, wherein the electrolyte additive is selected from the electrolyte additive according to claim 1.

3. The lithium-ion battery electrolyte according to claim 2, characterized in that The lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate or lithium difluorobis(oxalatophosphate).

4. The lithium-ion battery electrolyte according to claim 2, characterized in that The non-aqueous organic solvent is any one or more of an organic ester solvent, an ether solvent, a sulfone solvent or a nitrile solvent.

5. The lithium-ion battery electrolyte according to claim 2, characterized in that The electrolyte additive further includes a second additive selected from vinylene carbonate, ethylene carbonate, propylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, 2,4-butane sultone, N-phenylbis(trifluoromethanesulfonyl)imide, phenyl methanesulfonate, hydroquinone difluorosulfonate, methylene methanedisulfonate, 1,3,5-triallyl isocyanurate, hexamethylene Any one or more of 1,2-diisocyanate, 2,4-toluene diisocyanate, 1,2-diisocyanatoethyl methacrylate, 2,4-toluene diisocyanate, vinyl sulfate, vinyl bissulfate, propylene sulfite, triallyl phosphate, tripropargyl phosphate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, tris(vinyldimethylsilane)phosphate, propyldiprop-2-ynyl phosphate, ethyldiprop-2-ynyl phosphate or tetramethylmethylene diphosphate.

6. The lithium-ion battery electrolyte according to claim 2, characterized in that include: 10-16 parts by weight of a lithium salt; 80-90 parts by weight of a non-aqueous organic solvent; 0.1 to 10 parts by weight of electrolyte additives.

7. A lithium-ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is selected from the lithium ion battery electrolyte according to any one of claims 2 to 6.

8. The lithium-ion battery according to claim 7, characterized in that The active material of the positive electrode is selected from any one of lithium cobalt oxide, lithium manganese oxide, ultra-high nickel 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 any one of artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon composite material or silicon oxide; The diaphragm is selected from a polypropylene diaphragm or a polyethylene diaphragm.

9. The lithium-ion battery according to claim 7, characterized in that The active material of the positive electrode is selected from ultra-high nickel ternary nickel-cobalt-manganese lithium; The active material of the negative electrode is selected from artificial graphite; The diaphragm is selected from polyethylene diaphragms.

10. The lithium-ion battery according to claim 7, characterized in that The charge and discharge voltage of the lithium-ion battery is 3.0-4.2 V.

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