Electrolyte additive and preparation method thereof, electrolyte, and battery

Abstract

The present application discloses an electrolyte additive having a structure of Formula 1 or Formula 2. The present application also provides a method for preparing the electrolyte additive, an electrolyte, and a battery. The functional group of the electrolyte additive can react with HF to reduce the HF content in the electrolyte, and can also form a film on the surface of the positive electrode to prevent HF in the electrolyte from corroding the positive electrode. Compared with borate and phenyl borate additives, the electrolyte additive provided by the present application can have a higher capacity retention rate and a lower volume expansion rate under high temperature conditions, and the electrolyte additive can form intramolecular hydrogen bonds to improve its stability in high temperature environments.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytes, and in particular to an electrolyte additive and a preparation method thereof, an electrolyte, and a battery. Background Art

[0002] Currently, the market is placing increasing demands on electrolyte performance, with power batteries developing towards long cycle times, high voltages, and high temperatures. In actual applications, battery cells often operate at relatively high temperatures. Lithium hexafluorophosphate (LFP) readily reacts with trace amounts of water in the electrolyte at high temperatures, decomposing to produce acidic substances such as Lewis acids and hydrofluoric acid (HF). These acidic substances, in turn, promote further decomposition of LFP. Furthermore, these acidic substances also attack the cathode interface, leading to the dissolution of transition metal ions in the cathode and catalyzing the decomposition of the electrolyte, ultimately causing rapid degradation of battery cycle performance. The lithium salt and solvent ethylene fluorocarbonate (FEC) in the battery electrolyte are prone to gassing and decomposition at high temperatures, generating acidic substances such as Lewis acids and hydrofluoric acid (HF), which rapidly degrade battery cycle performance.

[0003] Therefore, how to effectively reduce the HF content in the electrolyte and improve the stability of the additive at high temperatures is a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0004] In view of this, the present application provides an electrolyte additive, the functional groups of which can react with HF to reduce the HF content in the electrolyte; the stability of the additive at high temperatures can be improved under the action of intramolecular hydrogen bonds; and at the same time, the problems of poor high-temperature cycle performance and easy gas production at high temperatures that exist in the battery during use can be effectively alleviated.

[0005] The present application provides an electrolyte additive having a structure of Formula 1 or Formula 2:

[0006]

[0007] The electrolyte additive can form a protective layer on the surface of the positive electrode, effectively inhibiting the corrosion of the positive electrode material by HF in the electrolyte and the dissolution of transition metals in the positive electrode material during cycling. The lone pair of electrons on the N element in the isoindole structure can complex with the high-valent transition metal ions on the surface of the positive electrode, inhibiting their dissolution under high pressure, and further improving the cycle life of the battery; the boron-oxygen bond has a strong polarity and a strong electrophilic property, and is easy to react with acid or water to remove water and acid in the electrolyte, thereby stabilizing the electrolyte; the electrolyte additive can also form intramolecular hydrogen bonds, making the molecule more stable at high temperatures. In the electrolyte additives of the structure of Formula 1 or Formula 2, the dotted line means that the hydrogen atoms of the methyl group form intramolecular hydrogen bonds with the oxygen atoms.

[0008] The present application also provides a method for preparing an electrolyte additive, comprising:

[0009] a) reacting isoindoline or 1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole with sodium hypochlorite to obtain intermediate a;

[0010] b) reacting the intermediate a, methylmagnesium bromide and trimethylborate to obtain the intermediate b;

[0011] c) reacting the intermediate b with 1-fluoro-2-(trifluoromethanesulfonyl)benzene to obtain the intermediate c;

[0012] d) mixing the intermediate c, hexamethyldisilazane and boric acid to react to obtain an electrolyte additive.

[0013] The present application uses isoindoline or 1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole as raw materials, wherein the structural formula of isoindoline is The structural formula of 1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole is Isoindoline or 1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole is first reacted with sodium hypochlorite to obtain intermediate a.

[0014] In some specific implementations, the reaction is carried out under alkaline conditions, and the reaction solution can be adjusted to 10-12 using sodium hydroxide solution, with a concentration of 0.5M to 1M. In some specific implementations, the reaction time in step a is 4 to 6 hours, and the reaction in step a is carried out at room temperature or under slight heating. After the reaction, the intermediate a is filtered and washed to obtain the intermediate. In some specific implementations, the molar ratio of the isoindoline or 1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole to sodium hypochlorite is 1:(1-6), preferably 1:(3-4).

[0015] In some specific implementations, isoindoline or 1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole is dissolved in water to form a solution, 0.5M to 1M sodium hydroxide solution is added to the solution, and the pH of the solution is adjusted to 10-12; sodium hypochlorite solution is added under stirring, and the reaction is carried out at room temperature or under slight heating for 4h to 6h. After the reaction is completed, the product is filtered and washed with water or an appropriate solvent to obtain intermediate a.

[0016] Then, the present invention dissolves the obtained intermediate a in an organic solvent, adds methyl magnesium bromide CH3BrMg at low temperature, and then adds trimethyl borate while maintaining the low temperature to react to obtain intermediate b.

[0017] In some specific implementations, the reaction temperature is -5°C to 5°C, the reaction time is 5 hours to 6 hours, the organic solvent includes diethyl ether and / or tetrahydrofuran, and the low temperature is -5°C to 5°C. In some specific implementations, the reaction is followed by acidification, separation, washing, and drying to obtain the intermediate b, and the organic layer is dried over anhydrous sodium sulfate, isolated, and purified. In some specific implementations, the molar ratio of the intermediate a, methylmagnesium bromide, and trimethylborate is 1:(1-4):(1-4), preferably 1:(2-3):(2-3).

[0018] In some specific implementations, in an anhydrous and oxygen-free atmosphere, intermediate a is dissolved in an organic solvent, the temperature is lowered to -5°C to 5°C, and pre-prepared methylmagnesium bromide is slowly added. The temperature is maintained at a low temperature, and trimethylborate is slowly added. The reaction is carried out for 5 to 6 hours until the reaction is completed. The mixture after the reaction is gradually added to dilute hydrochloric acid for acidification, the liquids are separated, washed, and dried over anhydrous sodium sulfate to obtain intermediate b.

[0019] Then, the present invention dissolves the obtained intermediate b and 1-fluoro-2-(trifluoromethanesulfonyl)benzene in acetophenone and reacts to obtain intermediate c.

[0020] In some specific implementations, the reaction is carried out under the conditions of a catalyst, and the catalyst includes ferric chloride. Using ferric chloride as a catalyst to catalyze the reaction can effectively improve the reaction rate, and iron powder can also be added at the same time to maintain the activity of ferric chloride, the amount of ferric chloride is 0.5% to 1% of the total mass of the raw material, and the amount of iron powder is 0.2% to 0.35% of the total mass of the raw material. In some specific implementations, the temperature of the reaction is 60°C to 80°C. In some specific implementations, the molar ratio of the intermediate b to 1-fluoro-2-(trifluoromethanesulfonyl)benzene is 1:(1-4), preferably 1:(1-2).

[0021] In some specific implementations, intermediate c and 1-fluoro-2-(trifluoromethanesulfonyl)benzene are dissolved in acetophenone, ferric chloride is added as a catalyst, iron powder is added to maintain the activity of the ferric chloride, and the reaction is carried out at 60° C. to 80° C. for 5 h to 6 h to obtain intermediate c.

[0022] Then, the present application mixes the obtained intermediate c, hexamethyldisilazane and boric acid, and reacts them to obtain an electrolyte additive.

[0023] In some specific implementations, the reaction is carried out under conditions of trimethylpentylammonium catalysis, with the amount of trimethylpentylammonium used being 0.5% to 1% of the total mass of the raw materials. In some specific implementations, the reaction time in step d is 10 to 12 hours, the reaction temperature is 115° C. to 120° C., and after the reaction, the electrolyte additive is obtained by cooling, filtering, washing, and distillation. In some specific implementations, the molar ratio of the intermediate c, hexamethyldisilazane, and boric acid is 1:(1-6):(2-6), preferably 1:(2-4):(3-4).

[0024] In some specific implementations, hexamethyldisilazane, intermediate c, hexamethyldisilazane and boric acid are reacted at 115°C to 120°C for 10 hours to 12 hours under the catalysis of a small amount of trimethylpentylammonium. After the reaction is completed, it is cooled and filtered to remove the solvent and impurities. The solid product is washed with ether to remove impurities and distilled to obtain an electrolyte additive.

[0025] The present application also provides an electrolyte comprising the above electrolyte additive.

[0026] The electrolyte has good compatibility with the positive electrode and the negative electrode, can improve the stability of the electrolyte at high temperatures, and enhance the stability of the battery.

[0027] The electrolyte comprises, by mass percentage, 5% to 20% of a lithium salt electrolyte, preferably 8% to 18%, more preferably 12% to 16%, 75% to 90% of an organic solvent, preferably 78% to 88%, more preferably 80% to 86%, 1% to 3% of a second additive, preferably 1% to 2%, more preferably 1% to 1.5%, and 0.5% to 3% of an electrolyte additive, preferably 0.5% to 2%, more preferably 0.5% to 1%.

[0028] In some specific implementations, the lithium salt electrolyte includes, but is not limited to, any one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonylimide), lithium bis(fluorosulfonylimide), lithium bis(oxalatoborate), lithium difluorooxalatoborate, or lithium difluorobis(oxalatophosphate), preferably lithium hexafluorophosphate. This application has no particular restrictions on the choice of lithium salt electrolyte. The organic solvent is any one or more of an organic ester solvent, an ether solvent, a sulfone solvent, or a nitrile solvent, preferably one or more of propylene carbonate, diethyl carbonate, or ethyl methyl carbonate. In some specific implementations, 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, hexamethylene disulfonate, 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, propyldiprop-2-ynyl phosphate, ethyldiprop-2-ynyl phosphate or tetramethylmethylene diphosphate.

[0029] In some specific implementations, the method for preparing the electrolyte includes: slowly adding lithium hexafluorophosphate to an organic solvent in an atmosphere with a water oxygen content of ≤0.1 ppm, adding an electrolyte additive and a second additive after complete dissolution, and stirring to obtain an electrolyte.

[0030] The present application also provides a battery comprising the above-mentioned electrolyte, a positive electrode sheet, a negative electrode sheet and a separator.

[0031] The preparation method of the positive electrode sheet comprises: mixing a positive electrode material, a conductive agent, a binder and an organic solvent, coating the mixture on an aluminum foil, drying, rolling and cutting the mixture to obtain a positive electrode sheet;

[0032] The preparation method of the negative electrode sheet comprises: mixing a negative electrode material, a conductive agent, a thickener, a binder and water, coating the mixture on a copper foil, drying, rolling and cutting the mixture to obtain the negative electrode sheet.

[0033] In some specific implementations, the positive electrode material is selected from any one of lithium cobalt oxide, lithium manganese oxide, ternary nickel cobalt manganese lithium, lithium nickel manganese oxide, lithium iron phosphate or lithium manganese iron phosphate, preferably ternary nickel cobalt manganese lithium. The electrolyte additive provided in the present application can form a film on the surface of the positive electrode to prevent HF in the electrolyte from corroding the positive electrode. The negative electrode material is selected from any one of artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon composite material or silicon oxide, preferably artificial graphite. The diaphragm is selected from a polypropylene diaphragm or a polyethylene diaphragm, preferably a polyethylene diaphragm; the charge and discharge voltage of the battery is 3.0V to 4.5V. The organic solvent includes N-methylpyrrolidone. The present application has no special restrictions on the selection of positive electrode materials, negative electrode materials, diaphragms, conductive agents, thickeners, binders, and organic solvents. The conductive agent includes, but is not limited to, one or more of carbon black, carbon nanotubes, polyaniline, or graphene, preferably carbon black; the positive electrode binder includes, but is not limited to, one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, or polyurethane, preferably polyvinylidene fluoride; the conductive agent includes, but is not limited to, one or more of SuperP, carbon nanotubes, or polyaniline, preferably SuperP; the thickener includes, but is not limited to, one or more of sodium carboxymethyl cellulose, polyvinyl alcohol, or polyacrylamide, preferably sodium carboxymethyl cellulose; the negative electrode binder includes, but is not limited to, one or more of styrene-butadiene rubber, polyacrylic acid, or polyvinyl alcohol, preferably styrene-butadiene rubber. The separator includes, but is not limited to, a polyethylene separator coated with a nano-alumina coating. The polyethylene separator coated with a nano-alumina coating can be purchased commercially or synthesized in-house, using one of the following synthesis methods: solution casting, melt drawing, solvent impregnation, electrospinning, or biaxial stretching.

[0034] In some specific implementations, the mass ratio of the positive electrode material, the conductive agent, and the binder is (94-97):(1-3):(1-3), preferably (96-97):(1-2):(1-2); the mass ratio of the negative electrode material, the conductive agent, the thickener, and the binder is (92-96):(1-3):(1-3):(2-4), preferably (94-96):(1-2):(1-2):(2-3).

[0035] The present invention first mixes the positive electrode material, conductive agent, and binder, adds N-methylpyrrolidone (NMP), and uses a vacuum defoamer to homogenize to obtain a positive electrode slurry. The positive electrode slurry is then evenly coated on aluminum foil, dried, rolled, and cut to obtain a positive electrode sheet. The negative electrode material, conductive agent, thickener, and binder are mixed, deionized water is added, and the mixture is homogenized using a vacuum defoamer to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on copper foil, dried, rolled, and cut to obtain a negative electrode sheet. In some specific implementations, the N / P ratio of the positive and negative electrodes is 1.1.

[0036] The present application then removes water from the diaphragm and produces a soft-pack laminated battery at an ambient dew point of ≤-45°C, stacks the positive electrode sheet, diaphragm, and negative electrode sheet in order, with the positive and negative electrode tabs on the same side, so that the diaphragm is located between the positive electrode sheet and the negative electrode sheet to act as an isolate, and obtains a bare battery cell. The bare battery cell is placed in an aluminum-plastic film outer packaging, vacuum-baked, cooled to 40°C, injected with the prepared electrolyte, and then subjected to packaging, high-temperature infiltration, formation, aging, secondary vacuum packaging, and capacity separation processes to obtain a battery. The electrolyte additive prepared in the present application can form a film on the positive electrode and improve the battery cycle performance. In some specific implementations, the vacuum baking time is 10h to 14h, and the vacuum baking temperature is 80°C to 120°C.

[0037] The electrolyte additive provided herein has the structures of Formula 1 and Formula 2. The functional groups of the electrolyte additive can react with HF, reducing the HF content in the electrolyte. It can also form a film on the surface of the positive electrode, preventing HF in the electrolyte from corroding the positive electrode. Compared to borate and phenyl borate additives, the electrolyte additive provided herein can have a higher capacity retention rate and a lower volume expansion rate under high temperature conditions. Furthermore, the electrolyte additive can form intramolecular hydrogen bonds, improving its stability in high-temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the H NMR spectrum of the electrolyte additive provided in Example 1 of the present application;

[0039] Figure 2 This is the nuclear magnetic hydrogen spectrum of the electrolyte additive provided in Example 2 of the present application. DETAILED DESCRIPTION

[0040] It should be understood that the expression "one or more of" includes individually each of the items recited after the expression and various combinations of two or more of the recited items, unless otherwise apparent from the context and usage. The expression "and / or" in conjunction with three or more recited items should be understood to have the same meaning, unless otherwise apparent from the context.

[0041] The terms "comprising", "having" or "containing", including their grammatical synonyms, should generally be understood as open and non-restrictive, e.g., not excluding other unrecited elements or steps, unless otherwise specifically stated or understood from the context.

[0042] It should be understood that the order of steps or the order in which certain actions are performed are not important as long as the present invention remains operable. Additionally, two or more steps or actions may be performed simultaneously.

[0043] The use of any and all examples or exemplary language, such as "such as" or "including," herein is intended merely to better illustrate the invention and does not limit the scope of the invention unless otherwise claimed. No language in this specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0044] In addition, the numerical ranges and parameters used to define the present invention are approximate values. The relevant numerical values ​​in the specific examples have been presented as accurately as possible. However, any numerical value inherently inevitably contains standard deviations due to individual testing methods. Therefore, unless otherwise expressly stated, all ranges, amounts, values, and percentages used in this disclosure should be understood to be modified by the word "about." As used herein, "about" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specified value or range.

[0045] The present invention will be further described below with reference to the following examples. The scope of protection of the present invention is not limited by the following examples.

[0046] Example 1

[0047] Preparation of electrolyte additives:

[0048]

[0049] 20 g (0.1 mol) of isoindoline is dissolved in water, 0.5 M to 1 M sodium hydroxide solution is added to adjust the pH to alkaline (pH 10-12), 350 mL of 1 M sodium hypochlorite solution is added under stirring, and the reaction is carried out at room temperature or under slightly heated conditions for 4 hours. The molar ratio of the isoindoline to sodium hypochlorite is 1:3.5. The product is filtered and washed with water or an appropriate solvent to obtain intermediate a. Under an anhydrous nitrogen atmosphere, an appropriate amount of anhydrous solvent (such as diethyl ether or tetrahydrofuran) and intermediate a are added to a dry reaction flask, the reaction flask is cooled to 0°C, and 200 mL of 1MCHMgBr (methyl bromide (CHBr) is slowly added to a reaction flask containing magnesium metal (Mg) and anhydrous ether (such as diethyl ether) solvent, and the reaction is generated under heating and stirring conditions). Stirring is continued at low temperature, 19.57 g (0.2 mol) of trimethylborate is slowly added to the reaction flask, and the reaction is carried out at low temperature for 5 hours. The molar ratio of intermediate a, methylmagnesium bromide and trimethylborate is 1:2:2. After the reaction is completed, dilute hydrochloric acid (HCl) is slowly added to acidify, and the mixture is separated into layers using a separatory funnel to separate the organic layer, and the organic layer is washed with water to remove acidic impurities. The organic layer was dried over anhydrous sodium sulfate, separated and purified to obtain intermediate b, 21.73 g (0.1 mol) of 1-fluoro-2-(trifluoromethanesulfonyl)benzene was dissolved in acetophenone, the molar ratio of intermediate b to 1-fluoro-2-(trifluoromethanesulfonyl)benzene was 1:1, 0.1 g of ferric chloride (FeCl) was added as a catalyst, 0.04 g of iron powder (Fe) was used to maintain the activity of FeCl, the mixture was heated to 60°C, and finally intermediate c was isolated.

[0050] After drying the intermediate c, hexamethyldisilazane was mixed with the intermediate c, and the hexamethyldisilazane and boric acid were reacted at 115°C for 10 hours under the catalysis of a small amount of trimethylpentylammonium. The molar ratio of intermediate c, hexamethyldisilazane and boric acid was 1:2:3. After cooling, the solid product was filtered to remove the solvent and unreacted products; the solid product was washed with ether to remove the remaining impurities, and after two distillations, the electrolyte additive was obtained, with the structure shown in Formula 1. The obtained electrolyte additive was subjected to nuclear magnetic resonance analysis, and the nuclear magnetic hydrogen spectrum was shown as follows Figure 1 shown.

[0051] Example 2

[0052] Preparation of electrolyte additives:

[0053]

[0054] 16.02 g (0.1 M) of 1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole was dissolved in water, and a 0.5 M to 1 M sodium hydroxide solution was added to the solution to adjust the pH to alkaline (pH 10-12). 400 mL of a 1 M sodium hypochlorite solution was added under stirring, and the reaction was maintained at room temperature or slightly heated for 4 hours. The molar ratio of 1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole to sodium hypochlorite was 1:4. The product was filtered and washed with water or an appropriate solvent to obtain intermediate a. Under an anhydrous nitrogen atmosphere, add an appropriate amount of anhydrous solvent (such as ether or tetrahydrofuran) and intermediate a to a dry reaction bottle, cool the reaction bottle to the desired low temperature of 0°C, slowly add 200 mL of 1M methylmagnesium bromide (CHMgBr), ensure that the reaction system remains at a low temperature, and under continuous stirring, slowly add 19.57 g (0.2 mol) of trimethylborate to the reaction bottle. Continue at low temperature for 5 hours. The molar ratio of intermediate a, methylmagnesium bromide and trimethylborate is 1:2:2. Dilute hydrochloric acid (HCl) is gradually added to the reaction mixture. ) is acidified, the mixture is separated using a separatory funnel, the organic layer is separated, the organic layer is washed with water to remove acidic impurities, the organic layer is dried over anhydrous sodium sulfate, and the intermediate b is isolated and purified. 43.5 grams (0.2 mol) of 1-fluoro-2-(trifluoromethanesulfonyl)benzene is dissolved in acetophenone, 0.1 g of ferric chloride (FeCl) is added as a catalyst, 0.04 g of iron powder (Fe) is used to maintain the activity of FeCl, and the mixture is heated to 60° C. The molar ratio of intermediate b to 1-fluoro-2-(trifluoromethanesulfonyl)benzene is 1:2. Finally, intermediate c is isolated. After drying the intermediate c, hexamethyldisilazane was mixed with the intermediate c, and hexamethyldisilazane and boric acid were reacted at 115°C for 10 hours under the catalysis of a small amount of trimethylpentylammonium. The molar ratio of intermediate c, hexamethyldisilazane and boric acid was 1:2:3. After cooling, the solid product was filtered to remove the solvent and some impurities. The solid product was washed with ether to remove the remaining impurities. After two distillations, the electrolyte additive was obtained, as shown in Formula 2. The obtained electrolyte additive was subjected to nuclear magnetic resonance analysis, and the nuclear magnetic hydrogen spectrum was as shown Figure 2 shown.

[0055] Example 3

[0056] Prepare the electrolyte:

[0057] 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 to obtain an organic solvent, and then lithium hexafluorophosphate (LiPF6) is slowly added to the organic solvent. After complete dissolution, 1,3-propane sultone (PS) and the electrolyte additive provided in Example 1 are added. The masses of LiPF6, organic solvent, PS, and the electrolyte additive provided in Example 1 are 13%, 85.5%, 1%, and 0.5% of the total mass of the electrolyte, respectively. After stirring evenly, the electrolyte is obtained.

[0058] Prepare the battery:

[0059] 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 an aluminum foil with a thickness of 17 μm. After drying, rolling, and cutting, a 50 mm × 70 mm positive electrode sheet was obtained.

[0060] The negative electrode material artificial graphite, conductive agent SuperP, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 95:1:1.5:2.5. After mixing, deionized water was added to control the theoretical solid content to 52%. The negative electrode slurry was obtained by homogenization using a vacuum defoamer, and the negative electrode slurry was evenly coated on a copper foil with a thickness of 17 μm. After drying, rolling, and cutting, a 52 mm × 72 mm negative electrode sheet was obtained, and the N / P ratio of the positive and negative electrodes was 1.1.

[0061] The polyethylene diaphragm coated with nano-alumina coating (purchased from Enjie New Materials Co., Ltd.) was cut into 55 mm × 75 mm pieces and vacuum-baked at 70 °C for 48 h to remove water.

[0062] A soft-pack laminated battery is produced at an ambient dew point of ≤-45°C. The positive electrode, separator, and negative electrode are stacked in sequence, with the positive and negative tabs on the same side and the separator positioned between the positive and negative electrodes to provide isolation. This results in a bare cell. The bare cell is placed in an aluminum-plastic film outer package, vacuum-baked at 90°C for 12 hours, cooled to below 40°C, and then injected with the prepared electrolyte. The battery is then packaged, impregnated at high temperature, formed, aged, packaged with secondary vacuum pumping, and then capacity divided to produce the battery.

[0063] Example 4

[0064] Prepare the electrolyte:

[0065] 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, and then lithium hexafluorophosphate (LiPF6) was slowly added to the organic solvent. After complete dissolution, 1,3-propane sultone (PS) and the electrolyte additive provided in Example 2 were added. The masses of LiPF6, organic solvent, PS, and the electrolyte additive provided in Example 1 were 13%, 85.5%, 1%, and 0.5% of the total mass of the electrolyte, respectively. After stirring evenly, electrolyte 2 was obtained.

[0066] Prepare the battery:

[0067] 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 an aluminum foil with a thickness of 17 μm. After drying, rolling, and cutting, a 50 mm × 70 mm positive electrode sheet was obtained.

[0068] The negative electrode material artificial graphite, conductive agent SuperP, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 95:1:1.5:2.5. After mixing, deionized water was added to control the theoretical solid content to 52%. The negative electrode slurry was obtained by homogenization using a vacuum defoamer, and the negative electrode slurry was evenly coated on a 17 μm thick copper foil. After drying, rolling, and cutting, a 52 mm × 72 mm negative electrode sheet was obtained, and the N / P ratio of the positive and negative electrodes was 1.1.

[0069] The polyethylene diaphragm coated with nano-alumina was cut into 55 mm × 75 mm pieces and vacuum-baked at 70°C for 48 h to remove water.

[0070] A soft-pack laminated battery is produced at an ambient dew point of ≤-45°C. The positive electrode, separator, and negative electrode are stacked in sequence, with the positive and negative tabs on the same side and the separator positioned between the positive and negative electrodes to provide isolation. This results in a bare cell. The bare cell is placed in an aluminum-plastic film outer package, vacuum-baked at 90°C for 12 hours, cooled to below 40°C, and then injected with the prepared electrolyte. The battery is then packaged, impregnated at high temperature, formed, aged, packaged with secondary vacuum pumping, and then capacity divided to produce the battery.

[0071] Example 5

[0072] The difference from Example 3 is that the masses of LiPF6, organic solvent, PS, and the electrolyte additive provided in Example 1 are 13%, 85%, 1%, and 1% of the total mass of the electrolyte, respectively.

[0073] Example 6

[0074] The difference from Example 4 is that the masses of LiPF6, organic solvent, PS, and electrolyte additive provided in Example 2 are 13%, 85%, 1%, and 1% of the total mass of the electrolyte, respectively.

[0075] Comparative Example 1

[0076] The difference from Example 3 is that the electrolyte additive provided in Example 1 is not added to the electrolyte, and trimethyl borate (TMB) is added instead, wherein the masses of LiPF6, organic solvent, PS, and trimethyl borate are 13%, 85%, 1%, and 1% of the total mass of the electrolyte, respectively.

[0077] Comparative Example 2

[0078] The difference from Example 3 is that the electrolyte additive provided in Example 1 is not added to the electrolyte, and the additive 3-cyano-5-fluorophenylboric acid (CFBA) is added instead, wherein the masses of LiPF6, organic solvent, PS, and 3-cyano-5-fluorophenylboric acid are 13%, 85%, 1%, and 1% of the total mass of the electrolyte, respectively.

[0079] Comparative Example 3

[0080] The difference from Example 3 is that the electrolyte additive provided in Example 1 is not added to the electrolyte, and instead the additive tris(2-cyanoethyl)borate (TB) is added, wherein the masses of LiPF6, organic solvent, PS, and tris(2-cyanoethyl)borate (TB) are 13%, 85%, 1%, and 1% of the total mass of the electrolyte, respectively.

[0081] Comparative Example 4

[0082] Prepare the electrolyte:

[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) are uniformly mixed in a mass ratio of PC:DEC:EMC = 10:25:50 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 isoindoline are added. The masses of LiPF6, organic solvent, PS, and isoindoline are 13%, 85.5%, 1%, and 0.5% of the total mass of the electrolyte, respectively. After stirring evenly, the electrolyte is obtained.

[0084] Prepare the battery:

[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 an aluminum foil with a thickness of 17 μm. After drying, rolling, and cutting, a 50 mm × 70 mm positive electrode sheet was obtained.

[0086] The negative electrode material artificial graphite, conductive agent SuperP, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 95:1:1.5:2.5. After mixing, deionized water was added to control the theoretical solid content to 52%. The negative electrode slurry was obtained by homogenization using a vacuum defoamer, and the negative electrode slurry was evenly coated on a copper foil with a thickness of 17 μm. After drying, rolling, and cutting, a 52 mm × 72 mm negative electrode sheet was obtained, and 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 is produced at an ambient dew point of ≤-45°C. The positive electrode, separator, and negative electrode are stacked in sequence, with the positive and negative tabs on the same side and the separator positioned between the positive and negative electrodes to provide isolation. This results in a bare cell. The bare cell is placed in an aluminum-plastic film outer package, vacuum-baked at 90°C for 12 hours, cooled to below 40°C, and then injected with the prepared electrolyte. The battery is then packaged, impregnated at high temperature, formed, aged, packaged with secondary vacuum pumping, and then capacity divided to produce the battery.

[0089] The performance tests of the batteries provided in Examples 3-6 and Comparative Examples 1-4 were performed using the following test methods:

[0090] Battery room temperature cycle test: After the battery to be tested is placed in a constant temperature room at an ambient temperature of 25°C and left to stand for 4 hours, it is charged at a current of 1C and a voltage of 4.2V to a cut-off current of 0.05C. Then, it is discharged at a constant current of 1C to a voltage of 3V. This cycle is repeated 500 times and the capacity retention rate is recorded. The capacity retention rate at the nth cycle (%) = (discharge capacity at the nth cycle / discharge capacity at the first cycle) × 100%;

[0091] Battery high-temperature cycle test: After the prepared soft-pack battery is placed in an explosion-proof test chamber at an ambient temperature of 45°C for 4 hours, it is charged at a current of 1C and a voltage of 4.2V to a cut-off current of 0.05C. Then, it is discharged at a constant current of 1C to a voltage of 3V. This cycle is repeated 500 times, 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%;

[0092] Battery high temperature storage test: 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 3-4.2V. 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:

[0093] Capacity recovery rate = discharge capacity in the first week after high-temperature storage / discharge capacity in the first week × 100%;

[0094] Volume expansion rate = (volume after storage - volume in the first week) / volume in the first week × 100%;

[0095] Internal resistance growth rate = (internal resistance after storage - internal resistance in the first week) / internal resistance in the first week × 100%.

[0096] The test results are shown in Table 1.

[0097] Table 1

[0098]

[0099] According to the data in Table 1, the electrolyte additive prepared by the present application can simultaneously ensure a higher capacity retention rate and a lower volume expansion rate in high-temperature storage, as well as a higher capacity retention rate in normal temperature cycling and high-temperature cycling, compared with borate and phenyl borate additives.

[0100] Test: Take 20g of the electrolyte prepared in Examples 3-6 and Comparative Examples 1-4 above, weigh it and record it as mass m, add 1-2 drops of neutral red methylene blue mixed indicator, and titrate with 0.1M triethylamine ultra-dry acetonitrile solution. Record the titration volume V of the standard solution, and calculate the acidity of the electrolyte according to the following formula:

[0101] Electrolyte acidity (ppm) = 20.006 × 1000 × V × c / m;

[0102] 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. The test results are shown in Table 2.

[0103] Table 2

[0104] Acidity before storage / ppm Acidity / ppm after storage at 60℃ for 3 days Example 3 8.7 40.7 Example 4 6.5 37.3 Example 5 8.5 38.5 Example 6 5.7 35.1 Comparative Example 1 9.7 75.5 Comparative Example 2 9.7 88.3 Comparative Example 3 9.7 54.7 Comparative Example 4 8.8 55.2

[0105] From the comparison of the data of Examples 3-6 and Comparative Examples 1-4 in Table 2, it can be seen that the electrolyte additive prepared by the present application can form intramolecular hydrogen bonds, improve its stability at high temperatures, and also has the effect of removing water and acid, inhibiting the increase of acidity in the electrolyte at high temperatures. At the same time, it can also form a film on the positive electrode, thereby improving the battery cycle performance.

[0106] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. An electrolyte additive, characterized in that Having the structure of Formula 1 or Formula 2: 。 2. An electrolyte, characterized in that The electrolyte additive according to claim 1 is included.

3. The electrolyte according to claim 2, characterized in that The composition is calculated by mass percentage and includes: 5% to 20% lithium salt electrolyte, 75% to 90% organic solvent, 0.5% to 3% electrolyte additive and 1% to 3% second additive.

4. The electrolyte according to claim 3, characterized in that The lithium salt electrolyte includes 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); The organic solvent includes one or more of propylene carbonate, diethyl carbonate or ethyl methyl carbonate; The second additive is selected from one or more of vinylene carbonate, vinyl 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 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.

5. A battery, characterized in that: The electrolyte comprises the electrolyte, the positive electrode sheet, the negative electrode sheet and the separator according to any one of claims 2 to 4.

6. The battery according to claim 5, characterized in that In the positive electrode sheet, the positive electrode active material is selected from one or more of lithium cobalt oxide, lithium manganese oxide, ternary nickel cobalt manganese lithium, lithium nickel manganese oxide, lithium iron phosphate or lithium manganese iron phosphate.

7. The battery according to claim 5, characterized in that In the negative electrode sheet, the negative electrode active material is selected from one or more 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.

8. A method for preparing the electrolyte additive according to claim 1, characterized in that: include: a) reacting isoindoline or 1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole with sodium hypochlorite to obtain intermediate a; b) reacting the intermediate a, methylmagnesium bromide and trimethylborate to obtain the intermediate b; c) reacting the intermediate b with 1-fluoro-2-(trifluoromethanesulfonyl)benzene to obtain the intermediate c; d) mixing the intermediate c, hexamethyldisilazane and boric acid to react to obtain an electrolyte additive.

9. The preparation method according to claim 8, characterized in that The molar ratio of the isoindoline or 1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole to sodium hypochlorite in step a is 1:(1-6); The molar ratio of the intermediate a, methylmagnesium bromide and trimethylborate in step b is 1:(1-4):(1-4); The molar ratio of the intermediate b to 1-fluoro-2-(trifluoromethanesulfonyl)benzene in step c is 1:(1-4); In step d, the molar ratio of the intermediate c, hexamethyldisilazane and boric acid is 1:(1-6):(2-6).

10. The preparation method according to claim 8, characterized in that The reaction in step a is carried out under alkaline conditions, and the reaction time in step a is 4h~6h; The reaction in step c is carried out in the presence of a catalyst, which includes ferric chloride; the reaction in step d is carried out in the presence of a catalyst, which includes trimethylpentyl ammonium.

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