Electrolyte, preparation method of electrolyte and lithium ion battery

Abstract

The application provides an electrolyte and a lithium ion battery containing the same. The electrolyte comprises a lithium salt, an organic solvent and an additive, and the additive comprises a morpholine compound as shown in formula 1, wherein R comprises any one of a carbon-based substituent group, a halogen substituent group, an ester-based compound, a carbonyl compound, a silicon-based compound or a sulfonic acid-based compound, the carbon-based substituent group having an unsaturation degree of 0-4 and a carbon atom number of 1-10. In the application, the electrolyte is directed to form a stable protective film on the positive electrode surface, increase the cycle performance of the battery cell and reduce the gas production of the high-voltage battery cell system.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to an electrolyte, a method for preparing the electrolyte, and a lithium-ion battery. Background Technology

[0002] With the expansion of applications for lithium-ion rechargeable batteries and the emergence of new application scenarios such as large-scale energy storage power stations and base station power supply, people's demand for high-energy lithium-ion rechargeable batteries has become more urgent.

[0003] To achieve high energy density in lithium-ion rechargeable batteries, methods typically involve increasing the battery's operating voltage or developing high-energy-density cathode materials. Currently, LiNi, a cathode material promising for high-voltage applications, is... 0.5 Mn 1.5 O4, with a charging voltage platform close to or higher than 5V, is difficult for non-aqueous organic electrolytes to match with high-voltage cathode materials, limiting the application of next-generation lithium-ion rechargeable batteries. Conventional commercial electrolytes undergo oxidative decomposition on the surface of the battery cathode at high potentials above 4.5V. This oxidative decomposition further deteriorates the performance of the cathode material, causing changes in morphology and structural collapse, ultimately leading to decreased cycle and storage performance and volume expansion in lithium-ion rechargeable batteries. Therefore, current commercial electrolytes are difficult to apply to high-voltage lithium-ion rechargeable battery systems. For example, 1M LiPF6 dissolved in carbonate solvents, at high voltages above 4.5V, accelerates the electrolyte reaction during charging due to the active cathode material, generating oxidation products such as CO2 and H2O. CO2 gas causes volume expansion of the battery cell, posing a potential threat to its safety performance; the presence of H2O causes hydrolysis of the LiPF6 electrolyte salt, and the product HF increases the acidity of the electrolyte system, further enhancing side reactions within the battery cell.

[0004] According to existing reports, the development of high-voltage electrolytes mainly focuses on the development of additives and the optimization of solvents. Currently, the commonly used method is to add trace additives to the electrolyte, such as maleic anhydride and its derivatives. However, the operating range of high-voltage electrolytes is 3V to 4.5V, and they cannot be used at higher potentials. In addition, while improving the high-voltage performance of the electrolyte, the cycle performance of the electrolyte has not been improved.

[0005] Therefore, how to prepare an electrolyte that can improve the cycling performance of battery cells under high voltage and reduce the gas generation capacity of high-voltage battery cell systems is an important research direction in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive includes a first additive comprising a morpholine compound as shown in Formula 1. Wherein, R includes any one of carbon-based substituents, halogen substituents, ester compounds, carbonyl compounds, silicon-based compounds, or sulfonic acid compounds, wherein the degree of unsaturation of the carbon-based substituent is 0 to 4 and the number of carbon atoms is 1 to 10.

[0007] The second objective of this invention is to provide a method for preparing an electrolyte, the method comprising: mixing iminodiacetic acid and acetic anhydride in a solvent, and then subjecting the mixture to high-temperature reflux, distillation, filtration and washing to obtain a precipitate; dissolving the precipitate in an acid solution; adding compound RI or R-OCH3; and filtering to obtain a morpholine compound.

[0008] A third objective of this invention is to provide a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte as described in one objective.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0010] The electrolyte in this invention, when applied to a battery, can form a stable protective film on the positive electrode surface, increasing the cycle performance of the battery cell and reducing gas production in the high-voltage battery cell system. Specifically, the battery's cycle performance can achieve a capacity retention rate of over 85.2% after 1000 cycles at 45°C, and the volume expansion rate after 30 days of storage at 60°C can be as low as 5.7%. Detailed Implementation

[0011] This invention provides an electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises a first additive, which includes a morpholine compound as shown in Formula 1. Wherein, R includes any one of carbon-based substituents, halogen substituents, ester compounds, carbonyl compounds, silicon-based compounds, or sulfonic acid compounds, wherein the degree of unsaturation of the carbon-based substituent is 0 to 4 and the number of carbon atoms is 1 to 10.

[0012] The electrolyte provided by this invention uses morpholine compounds as additives. These morpholine compounds preferentially undergo oxidation reactions on the high-voltage positive electrode surface to generate repeating units. The polymer CEI film stabilizes the high-voltage cathode surface, promoting the formation of a dense and stable protective film on the cathode material surface. This reduces the contact between the electrolyte and the active cathode material, inhibiting the oxidative decomposition of the electrolyte solvent on the active cathode surface. Furthermore, the diacid anhydrides and amino functional groups in morpholine compounds can absorb water and acidic protons from the electrolyte, suppressing side reactions and optimizing the cell's cycle performance. Compared to mono-anhydride compounds, diacid anhydride compounds exhibit higher reactivity, and the opening of the six-membered ring allows for the formation of an effective CEI film.

[0013] As a preferred technical solution of the present invention, the first additive includes any one or a combination of at least two of the compounds shown in Formulas 1 to 7, wherein typical but non-limiting examples of the combination include the combination of Formulas 2 and 3, the combination of Formulas 3 and 4, the combination of Formulas 4 and 5, the combination of Formulas 5 and 6, or the combination of Formulas 6 and 7, etc.

[0014]

[0015] Preferably, the first additive comprises a compound as shown in Formula 2 or Formula 6.

[0016] As a preferred technical solution of the present invention, based on the mass of the electrolyte as 100%, the first additive accounts for 0.01% to 20% of the mass fraction of the electrolyte. The mass fraction can be 0.01%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, or 20%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 0.5% to 5%.

[0017] In this invention, if the content of morpholine additives is too high, the CEI film formed at the positive electrode interface will be too thick. Usually, the CEI film has poor ion transport behavior and poor conductivity, which will deteriorate the cycle performance of the battery. If the content of morpholine additives is too low, a stable CEI film cannot be formed at the positive electrode interface, which will also deteriorate the battery performance.

[0018] As a preferred embodiment of the present invention, the additive further includes a second additive, which includes cyclic ester additives.

[0019] Preferably, the cyclic ester additives include any one or a combination of at least two of cyclic carbonate additives, cyclic sulfonyl lactone additives, or cyclic sulfate additives, wherein typical but non-limiting examples of the combinations include: a combination of cyclic carbonate additives and cyclic sulfonyl lactone additives, a combination of cyclic sulfonyl lactone additives and cyclic sulfate additives, or a combination of cyclic carbonate additives and cyclic sulfate additives, etc.

[0020] Preferably, the cyclic carbonate additive includes any one or a combination of at least two of vinylene carbonate, fluoroethylene carbonate, or ethylene ethylene carbonate, wherein typical but non-limiting examples of the combination include: a combination of vinylene carbonate and fluoroethylene carbonate, a combination of fluoroethylene carbonate and ethylene ethylene carbonate, or a combination of vinylene carbonate and ethylene ethylene carbonate, etc.

[0021] Preferably, the cyclic sulfonyl lactone additives include 1,3-propanesulfonyl lactone and / or 1,3-propenesulfonyl lactone.

[0022] Preferably, the cyclic sulfate additives include vinyl sulfate and / or propylene sulfate.

[0023] As a preferred embodiment of the present invention, based on the mass of the electrolyte (100%), the cyclic ester additive accounts for 0.05% to 20% of the mass fraction of the electrolyte. The mass fraction can be 0.05%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, or 20%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 0.1% to 5%.

[0024] In this invention, excessive or insufficient amounts of cyclic ester additives can affect the dissociation and solvation structure of lithium salts, thereby impacting the battery's interface structure and transport capabilities, and ultimately degrading battery performance.

[0025] Preferably, based on the mass of the electrolyte (100%), the cyclic carbonate additive accounts for 0.1% to 10% of the electrolyte by mass fraction. The mass fraction can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 1% to 2%.

[0026] Preferably, based on the mass of the electrolyte (100%), the cyclic sulfonyl lactone additive accounts for 0.1% to 5% of the electrolyte by mass. The mass fraction can be 0.1%, 1%, 2%, 3%, 4%, or 5%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 0.1% to 1%.

[0027] Preferably, based on the mass of the electrolyte (100%), the cyclic sulfate additive accounts for 0.5% to 5% of the electrolyte by mass. The mass fraction can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 0.5% to 2%.

[0028] As a preferred technical solution of the present invention, the lithium salt includes any one or a combination of at least two of LiPF6, LiBF4, LiFSI, LiTFSI, LiBOB, LiODFP, LiODFB, LiPO2F2 or CF3SO3Li. Typical but non-limiting examples of the combinations include: combinations of LiPF6 and LiBF4, combinations of LiFSI and LiTFSI, combinations of LiBOB and LiODFP, combinations of LiODFP and LiODFB, combinations of LiODFB and LiPO2F2, or combinations of LiPO2F2 and CF3SO3Li, etc.

[0029] Preferably, the concentration of the lithium salt in the electrolyte is from 0.1 mol / L to 2 mol / L, wherein the concentration may be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0030] As a preferred embodiment of the present invention, the organic solvent includes any one or a combination of at least two of ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, or diethyl carbonate. Typical but non-limiting examples of such combinations include combinations of ethylene carbonate and dimethyl carbonate, combinations of dimethyl carbonate and methyl ethyl carbonate, combinations of methyl ethyl carbonate and propylene carbonate, or combinations of propylene carbonate and diethyl carbonate.

[0031] Preferably, based on the mass of the electrolyte (100%), the organic solvent accounts for 55% to 99.5% of the mass fraction of the electrolyte. The mass fraction can be 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 99.5%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] The second objective of this invention is to provide a method for preparing an electrolyte, the method comprising: mixing iminodiacetic acid and acetic anhydride in a solvent, and then subjecting the mixture to high-temperature reflux, distillation, filtration and washing to obtain a precipitate; dissolving the precipitate in an acid solution; adding compound RI or R-OCH3; and filtering to obtain the morpholine compound described above.

[0033] In this invention, a mixture of iminodiacetic acid and acetic anhydride in a solvent is refluxed until the solution becomes clear. Excess acetic anhydride is then distilled off, filtered, and the precipitate is washed to obtain the precipitate. An iodinated compound is added, and the mixture is finally filtered to obtain morpholine compounds. The morpholine compounds prepared by this invention have mild reaction conditions, high reaction yields, and simple processing conditions.

[0034] As a preferred embodiment of the present invention, the solvent includes pyridine.

[0035] Preferably, the equivalent ratio of iminodiacetic acid and acetic anhydride is 1:4 to 1:6, wherein the equivalent ratio can be 1:4, 1:5 or 1:6, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0036] In this invention, the amount of solvent added is not limited; the amount of solvent added is sufficient to dissolve iminodiacetic acid and acetic anhydride.

[0037] Preferably, the high-temperature reflux temperature is between 130°C and 180°C, wherein the temperature can be 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, or 180°C, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0038] Preferably, the high-temperature reflux time is 1.5h to 2.5h, wherein the time can be 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2.0h, 2.1h, 2.2h, 2.3h, 2.4h or 2.5h, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Preferably, the distillation temperature is 60°C to 80°C, wherein the temperature may be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0040] Preferably, the washing solution includes acetic acid.

[0041] Preferably, the acid solution includes acetic acid.

[0042] A third objective of this invention is to provide a lithium-ion battery, which includes a positive electrode, a negative electrode, and the electrolyte described above.

[0043] As a preferred embodiment of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material coated on the positive electrode current collector.

[0044] Preferably, the positive electrode active material includes any one or a combination of at least two of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide. Typical but non-limiting examples of such combinations include: combinations of lithium cobalt oxide and lithium nickel oxide, combinations of lithium nickel oxide and lithium manganese oxide, combinations of lithium manganese oxide and lithium nickel manganese oxide, combinations of lithium nickel manganese oxide and lithium nickel cobalt manganese oxide, or combinations of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, etc.

[0045] As a preferred embodiment of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material coated on the negative electrode current collector.

[0046] Preferably, the negative electrode active material includes any one or a combination of at least two of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide, silicon carbide, or lithium titanate. Typical but non-limiting examples of such combinations include: a combination of soft carbon and hard carbon, a combination of artificial graphite and natural graphite, a combination of silicon and silicon oxide, or a combination of silicon carbide and lithium titanate.

[0047] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0048] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0049] Example 1

[0050] This embodiment provides a lithium-ion battery electrolyte:

[0051] The electrolyte consists of organic solvents, lithium salts, and additives.

[0052] The organic solvents include ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, wherein the mass ratio of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate is 3:5:2.

[0053] Lithium salts include lithium hexafluorophosphate, with a concentration of 1 mol / L.

[0054] The additives include morpholine compound additives and cyclic ester additives, wherein the morpholine compound additives are shown in Formula 2. The cyclic ester additives include vinylene carbonate, 1,3-propanesulfonate lactone, and vinyl sulfate. Based on 100% of the electrolyte mass, the mass fractions of the morpholine additives shown in Formula 2 are 1%, vinylene carbonate 2.5%, 1,3-propanesulfonate lactone 2.5%, and vinyl sulfate 5%.

[0055] The preparation method of the morpholine compounds shown in Formula 2 is as follows:

[0056] In a 250 mL round-bottom flask, iminodiacetic acid and acetic anhydride were dissolved in pyridine at an equivalent ratio of 1:5. The mixture was refluxed at 150 °C for 2 hours until the solution was clear. Excess acetic anhydride was removed by vacuum distillation in a rotary evaporator at 65 °C. The mixture was then filtered, and the precipitate was washed with acetic acid. The precipitate was dissolved in acetic acid, and compound CH3-I was added. The mixture was then filtered to obtain the target compound as shown in Formula 2.

[0057] Example 2

[0058] This embodiment provides a lithium-ion battery electrolyte:

[0059] The electrolyte consists of organic solvents, lithium salts, and additives.

[0060] The organic solvents include ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, wherein the mass ratio of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate is 3:5:2.

[0061] The lithium salts include lithium hexafluorophosphate, with a concentration of 0.5 mol / L.

[0062] The additives include morpholine compound additives and cyclic ester additives, wherein the morpholine compound additives are shown in Formula 6. Cyclic ester additives include vinylene carbonate and 1,3-propanesulfonate lactone. Based on 100% of the electrolyte mass, the mass fractions of the morpholine additive as shown in Formula 6 are 0.01%, vinylene carbonate is 0.025%, and 1,3-propanesulfonate lactone is 0.025%.

[0063] The preparation method of the morpholine compounds shown in Formula 6 is as follows:

[0064] In a 250 mL round-bottom flask, iminodiacetic acid and acetic anhydride were dissolved in pyridine at an equivalent ratio of 1:5. The mixture was refluxed at 150 °C for 2 hours until the solution was clear. Excess acetic anhydride was removed by vacuum distillation in a rotary evaporator at 65 °C. The mixture was then filtered, and the precipitate was washed with acetic acid. The precipitate was dissolved in acetic acid, and compound CH3COOCH3 was added. The mixture was then filtered to obtain the target compound as shown in Formula 6.

[0065] Example 3

[0066] This embodiment provides a lithium-ion battery electrolyte:

[0067] The electrolyte consists of organic solvents, lithium salts, and additives.

[0068] The organic solvents include ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, wherein the mass ratio of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate is 3:5:2.

[0069] Lithium salts include lithium hexafluorophosphate, with a concentration of 2 mol / L.

[0070] The additives include morpholine compound additives and cyclic ester additives, wherein the morpholine compound additives are shown in Formula 2. The cyclic ester additives include vinylene carbonate and 1,3-propanesulfonate lactone. Based on the mass of the electrolyte (100%), the morpholine additive as shown in Formula 2 comprises 20% by mass, vinylene carbonate comprises 5% by mass, 1,3-propanesulfonate lactone comprises 10% by mass, and vinyl sulfate comprises 5% by mass.

[0071] The preparation method of the morpholine compounds shown in Formula 2 is as follows:

[0072] In a 250 mL round-bottom flask, iminodiacetic acid and acetic anhydride were dissolved in pyridine at an equivalent ratio of 1:5. The mixture was refluxed at 150 °C for 2 hours until the solution was clear. Excess acetic anhydride was removed by vacuum distillation in a rotary evaporator at 65 °C. The mixture was then filtered, and the precipitate was washed with acetic acid. The precipitate was dissolved in acetic acid, and compound CH3-I was added. The mixture was then filtered to obtain the target compound as shown in Formula 2.

[0073] Example 4

[0074] This embodiment provides a lithium-ion battery electrolyte:

[0075] The electrolyte consists of organic solvents, lithium salts, and additives.

[0076] The organic solvents include ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, wherein the mass ratio of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate is 3:5:2.

[0077] Lithium salts include lithium hexafluorophosphate, with a concentration of 1 mol / L.

[0078] The additives include morpholine additives and cyclic ester additives, wherein the morpholine additives are shown in Formula 2. The cyclic ester additives include vinylene carbonate, 1,3-propanesulfonate lactone, and vinyl sulfate. Based on 100% of the electrolyte mass, the mass fractions of the morpholine additives as shown in Formula 2 are 0.5%, vinylene carbonate is 2.5%, 1,3-propanesulfonate lactone is 0.025%, and vinyl sulfate is 5%.

[0079] The preparation method of the morpholine compounds shown in Formula 2 is as follows:

[0080] In a 250 mL round-bottom flask, iminodiacetic acid and acetic anhydride were dissolved in pyridine at an equivalent ratio of 1:5. The mixture was refluxed at 150 °C for 2 hours until the solution was clear. Excess acetic anhydride was removed by vacuum distillation in a rotary evaporator at 65 °C. The mixture was then filtered, and the precipitate was washed with acetic acid. The precipitate was dissolved in acetic acid, and compound CH3-I was added. The mixture was then filtered to obtain the target compound as shown in Formula 2.

[0081] Example 5

[0082] This embodiment provides a lithium-ion battery electrolyte:

[0083] The electrolyte consists of organic solvents, lithium salts, and additives.

[0084] The organic solvents include ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, wherein the mass ratio of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate is 3:5:2.

[0085] Lithium salts include lithium hexafluorophosphate, with a concentration of 1 mol / L.

[0086] The additives include morpholine additives and cyclic ester additives, wherein the morpholine additives are shown in Formula 2. The cyclic ester additives include vinylene carbonate, 1,3-propanesulfonate lactone, and vinyl sulfate. Based on 100% of the electrolyte mass, the mass fractions of the morpholine additives as shown in Formula 2 are 5%, vinylene carbonate is 2.5%, 1,3-propanesulfonate lactone is 2.5%, and vinyl sulfate is 5%.

[0087] The preparation method of the morpholine compounds shown in Formula 2 is as follows:

[0088] In a 250 mL round-bottom flask, iminodiacetic acid and acetic anhydride were dissolved in pyridine at an equivalent ratio of 1:5. The mixture was refluxed at 150 °C for 2 hours until the solution was clear. Excess acetic anhydride was removed by vacuum distillation in a rotary evaporator at 65 °C. The mixture was then filtered, and the precipitate was washed with acetic acid. The precipitate was dissolved in acetic acid, and compound CH3-I was added. The mixture was then filtered to obtain the target compound as shown in Formula 2.

[0089] Example 6

[0090] This embodiment provides a lithium-ion battery electrolyte:

[0091] The electrolyte consists of organic solvents, lithium salts, and additives.

[0092] The organic solvents include ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, wherein the mass ratio of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate is 3:5:2.

[0093] Lithium salts include lithium hexafluorophosphate, with a concentration of 1 mol / L.

[0094] The additives include morpholine additives and cyclic ester additives, wherein the morpholine additives are shown in Formula 2. The cyclic ester additives include vinylene carbonate, 1,3-propanesulfonate lactone, and vinyl sulfate. Based on 100% of the electrolyte mass, the mass fractions of the morpholine additive as shown in Formula 2 are 15%, vinylene carbonate 2.5%, 1,3-propanesulfonate lactone 2.5%, and vinyl sulfate 5%.

[0095] The preparation method of the morpholine compounds shown in Formula 2 is as follows:

[0096] In a 250 mL round-bottom flask, iminodiacetic acid and acetic anhydride were dissolved in pyridine at an equivalent ratio of 1:5. The mixture was refluxed at 150 °C for 2 hours until the solution was clear. Excess acetic anhydride was removed by vacuum distillation in a rotary evaporator at 65 °C. The mixture was then filtered, and the precipitate was washed with acetic acid. The precipitate was dissolved in acetic acid, and compound CH3-I was added. The mixture was then filtered to obtain the target compound as shown in Formula 2.

[0097] Example 7

[0098] In this embodiment, except that the content of the morpholine compound shown in Formula 2 is replaced with 50% of the electrolyte by mass, and the amount of non-aqueous solvent is adjusted to make the total electrolyte content 100%, all other conditions are the same as in Example 1.

[0099] Comparative Example 1

[0100] This comparative example is identical to Example 1 except that no morpholine compounds as shown in Formula 2 are added and the amount of non-aqueous solvent is adjusted to make the total electrolyte amount 100%.

[0101] Comparative Example 2

[0102] In this comparative example, the morpholine compounds shown in Formula 2 are replaced with morpholine compounds with monoacyl anhydride functional groups as shown in Formula 8. All other conditions are the same as in Example 1.

[0103] Comparative Example 3

[0104] In this comparative example, the morpholine compound shown in Formula 2 is replaced with the morpholine (C4H9NO) shown in Formula 9. All other conditions are the same as in Example 1.

[0105] The preparation methods of the electrolytes in Examples 1 to 7 and Comparative Examples 1 to 3 are as follows:

[0106] The electrolyte was prepared in a glove box with a nitrogen content of 99.999%, an actual oxygen content of 0.1 ppm, and a moisture content of 0.1 ppm. Based on 100% of the total mass of the non-aqueous electrolyte, battery-grade organic solvents of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a mass ratio of 3:5:2 were mixed thoroughly. The fully dried lithium salt was then added to the aforementioned non-aqueous solvent, and additives were added to adjust the lithium salt concentration, thus preparing the non-aqueous lithium-ion battery electrolytes corresponding to Examples 1 to 7 and Comparative Examples 1 to 3.

[0107] The preparation method of lithium-ion batteries is as follows:

[0108] LiNi, the positive electrode active material 0.5 Mn 1.5 O4, conductive agent acetylene black, and binder polyvinylidene fluoride are mixed thoroughly in an N-methylpyrrolidone solvent system at a mass ratio of 95:3:2. The mixture is then coated onto aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet with a compacted density of 3.5 g / cm³. 3 .

[0109] The negative electrode active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly mixed in a deionized water solvent system at a mass ratio of 96:2:1:1. The mixture was then coated onto copper foil, dried, and cold-pressed to obtain the negative electrode sheet with a compacted density of 1.65 g / cm³. 3 .

[0110] A diaphragm was obtained by using 9 μm thick polyethylene as the base membrane and coating the base membrane with a 3 μm thick nano-alumina coating.

[0111] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as an insulator. The stacked electrodes then form a bare cell.

[0112] The bare battery cell is placed into an aluminum-plastic film, then baked at 80°C to remove water, and then injected with the corresponding electrolytes of Examples 1 to 7 and Comparative Examples 1 to 3 and sealed. After that, the finished soft-pack lithium-ion secondary batteries corresponding to Examples 1 to 7 and Comparative Examples 1 to 3 are obtained through processes such as standing, hot and cold pressing, formation, clamping, and capacity testing.

[0113] The test method for capacity retention rate during high-temperature cycling at 45℃ is as follows: At 45℃, the lithium-ion battery is charged at a constant current rate of 1C to 5V, then charged at a constant voltage of 5V until the current is less than 0.05C. After resting for 10 minutes, it is discharged at a constant current rate of 1C to 2.8V. The discharge capacity of the lithium-ion battery at this point is measured, which is the discharge capacity of the first cycle. The battery is cycled multiple times under the above conditions, and the capacity retention rate after 1000 cycles is calculated. The capacity retention rate after cycling is calculated using the following formula: Capacity retention rate (%) = (Discharge capacity corresponding to 1000 cycles / Discharge capacity of the first cycle) × 100%.

[0114] II. Volume Expansion Rate After 30 Days of Storage at 60℃: At 25℃, the lithium-ion battery was charged to 5V at a constant current of 1C, and then charged to 0.05C at a constant voltage. The volume of the lithium-ion battery was measured and recorded as V0. The fully charged battery was then placed in a 60℃ oven for 30 days, and the volume after storage was measured and recorded as V1. The volume expansion rate of the lithium-ion battery relative to its initial volume before storage was calculated using the following formula: Volume Expansion Rate (%) = (V1 - V0) / V0 × 100%.

[0115] The capacity retention rate and volume expansion rate of the lithium-ion secondary batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were tested at 45°C for high-temperature cycling and at 60°C for 30 days. The results are shown in the table below:

[0116] Table 1

[0117]

[0118]

[0119] As shown in Table 1, the optimal addition amount of morpholine compounds as additives in Examples 1 to 3 is within the range of 0.01% to 20%. This indicates that within this range, the additive can undergo an oxidation reaction at the positive electrode interface to generate a stable CEI film, which can effectively improve the high-temperature cycling and storage gas generation performance of the high-voltage battery cell system.

[0120] Table 2

[0121] Capacity retention rate after 1000 cycles at 45°C Volume expansion rate after 30 days of storage at 60℃ Example 1 85.2％ 5.7％ Example 4 80.2％ 14.9％ Example 5 78.7％ 16.5％ Example 6 73.4％ 27.9％

[0122] As shown in Table 2, when comparing Examples 1, 4 to 6, the high-temperature cycling performance of the battery cell first increases and then decreases as the proportion of morpholine compounds increases, while the high-temperature storage gas generation first decreases and then increases. This indicates that when the proportion of morpholine compounds is small, the generated CEI film cannot completely cover the interface between the cathode material and the electrolyte. When the proportion is large, the generated CEI film is thicker, and the improvement in the high-temperature cycling and storage gas generation performance of the battery is not significant enough.

[0123] Table 3

[0124] Capacity retention rate after 1000 cycles at 45°C Volume expansion rate after 30 days of storage at 60℃ Example 1 85.2％ 5.7％ Example 7 68.2％ 36.7％

[0125] As shown in Table 3, when the amount of morpholine compounds added is too high, it cannot play a protective role and leads to the deterioration of the battery cell performance.

[0126] Table 4

[0127] Capacity retention rate after 1000 cycles at 45°C Volume expansion rate after 30 days of storage at 60℃ Example 1 85.2％ 5.7％ Comparative Example 1 60.1％ 53.2％ Comparative Example 2 55.8％ Severe gas production Comparative Example 3 51.5％ Severe gas production

[0128] Severe gas production here refers to an extremely serious deterioration in gas production levels, to the point that it is difficult to obtain the true volume expansion rate through the water displacement method. The battery cell typically exhibits severe gas pocket bulging and leakage. Furthermore, in the current LiNi... 0.5 Mn 1.5 In lithium-ion battery systems composed of O4 positive electrode and graphite negative electrode, the current level is that the gas expansion rate after 30 days of storage is less than 40%. Therefore, as can be seen from the above examples, the addition of acid anhydride compounds can be superior to the current level in the industry.

[0129] Table 4 shows that, comparing Example 1 and Comparative Example 1, without the addition of morpholine compounds in the electrolyte of Comparative Example 1, the electrolyte undergoes complex side reactions due to the high reactivity of the cathode material interface, resulting in poor high-temperature cycle performance and storage performance of the battery cell. Comparing Comparative Examples 2 and 3 with Example 1, it is evident that replacing the diacid anhydride morpholine compounds with monoacyl anhydride morpholine compounds decreases the battery's capacity retention at 45°C and increases the volume expansion rate after 30 days of storage at 60°C. Replacing the diacid anhydride morpholine compounds with morpholine compounds without anhydride groups further degrades the battery's electrochemical performance. This is because the diacid anhydride and amino functional groups in the morpholine compounds can absorb water and acidic protons in the electrolyte, suppressing side reactions and thus optimizing the battery cell's cycle performance. Compared to monoacyl anhydride compounds, diacid anhydride compounds have higher reactivity, and the opening of the six-membered ring allows for the formation of an effective CEI film.

[0130] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises a lithium salt, an organic solvent, and additives, wherein the additives include a first additive, which comprises a morpholine compound as shown in Formula 1. Formula 1, Wherein, R includes any one of carbonyl substituents, halogen substituents, ester compounds, carbonyl compounds, silicon compounds or sulfonic acid compounds, wherein the degree of unsaturation of the carbonyl substituent is 0 to 4 and the number of carbon atoms is 1 to 10. Based on the mass of the electrolyte (100%), the first additive accounts for 0.5% to 20% of the mass fraction of the electrolyte. The additive further includes a second additive, which includes cyclic ester additives, and the cyclic ester additives include any one or a combination of at least two of cyclic carbonate additives, cyclic sulfonyl lactone additives, or cyclic sulfate additives.

2. The electrolyte according to claim 1, characterized in that, The first additive comprises any one or a combination of at least two of the compounds shown in Formulas 1 to 7; Formula 2 Formula 3 Formula 4 Formula 5 Formula 6 or Formula 7.

3. The electrolyte according to claim 1, characterized in that, Based on the mass of the electrolyte (100%), the cyclic ester additive accounts for 0.05% to 20% of the mass of the electrolyte.

4. The electrolyte according to claim 1, characterized in that, The lithium salt includes any one or a combination of at least two of LiPF6, LiBF4, LiFSI, LiTFSI, LiBOB, LiODFP, LiODFB, LiPO2F2 or CF3SO3Li.

5. The electrolyte according to claim 1, characterized in that, The method for preparing the morpholine compounds includes: mixing iminodiacetic acid and acetic anhydride in a solvent, and then subjecting the mixture to high-temperature reflux, distillation, filtration and washing to obtain a precipitate; dissolving the precipitate in an acid solution; adding compound RI or R-OCH3; and filtering to obtain the morpholine compounds. Wherein, R includes any one of carbon-based substituents, halogen substituents, ester compounds, carbonyl compounds, silicon-based compounds, or sulfonic acid compounds, wherein the degree of unsaturation of the carbon-based substituent is 0 to 4 and the number of carbon atoms is 1 to 10.

6. The electrolyte according to claim 5, characterized in that, The solvent includes pyridine; The equivalence ratio of the iminodiacetic acid, acetic anhydride, and solvent is 1:4 to 1:6; The high-temperature reflux temperature is 130°C to 180°C; the high-temperature reflux time is 1.5h to 2.5h. The distillation temperature is 60°C to 80°C; The washing solution includes acetic acid; The acid solution includes acetic acid.

7. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte as described in any one of claims 1 to 6.

8. The lithium-ion battery according to claim 7, characterized in that, The positive electrode includes a positive electrode current collector and a positive electrode active material coated on the positive electrode current collector. The positive electrode active material includes any one or a combination of at least two of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

9. The lithium-ion battery according to claim 7, characterized in that, The negative electrode includes a negative electrode current collector and a negative electrode active material coated on the negative electrode current collector. The negative electrode active material includes any one or a combination of at least two of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide, silicon carbide, or lithium titanate.

Images