Electrolyte and battery

Abstract

The invention relates to the field of batteries, in particular to an electrolyte and a battery. According to the electrolyte, a solvent formula with a specific proportion is mixed with an additive for use, the additive forms a solid electrolyte interface film on the surface of an electrode prior to the solvent in a battery activation stage, and the first additive can be in contact with trace water in the electrolyte preferentially, so that the content of HF in a circulation process is reduced; meanwhile, other additives can be matched to form a stable CEI film rich in inorganic components on the surface of an electrode, so that the side reaction on the surface of the electrode is reduced, the cycle life of the battery is prolonged, meanwhile, due to the addition of the low-viscosity solvent, the ionic conductivity in the electrolyte is improved, the ohmic resistance of the battery is reduced, and the service life of the battery is prolonged due to the uniformity of the CEI film. And due to low interface impedance, the electrolyte can meet the working condition under high magnification.

Description

Technical Field

[0001] This invention relates to the field of batteries, and more particularly to an electrolyte and a battery. Background Technology

[0002] With the increasing popularity of new energy electric vehicles, the demand for fast-charging power batteries is growing rapidly. Battery materials are developing rapidly, but some problems still exist. Among them, issues such as electrode interface instability and poor thermal stability caused by electrolyte affect the fast-charging performance and cycle life of batteries, thus posing a series of challenges to electrolyte modification.

[0003] Traditional electrolytes use ethylene carbonate (EC) as a solvent. EC helps form a solid electrolyte interfacial film (SEI film at the negative electrode and CEI film at the positive electrode). However, due to the uneven formation of the solid electrolyte interfacial film and poor oxidation stability, the battery is prone to polarization during cycling, which can induce Li... + Uneven deposition of ions produces lithium dendrites, causing battery failure or even short circuits and fires. At the same time, the instability of the solid electrolyte interface film can lead to continuous decomposition and gas generation of the electrolyte on the electrode surface, shortening the battery cycle life. Furthermore, the high viscosity of traditional carbonate-based electrolytes results in low electrolyte ionic conductivity, making it difficult to meet the requirements of long-term charge and discharge operation at high rates.

[0004] Therefore, how to reduce electrolyte viscosity to meet fast charging requirements is affected by solvent viscosity, and how to form a stable solid electrolyte interface film is affected by electrolyte solvent viscosity, as well as the content and type of additives. These factors in turn determine problems such as lithium deposition at the electrode interface, battery gas generation, and changes in internal resistance. Therefore, electrolyte formulation needs further improvement. Summary of the Invention

[0005] This invention provides an electrolyte and a battery. The electrolyte can form a stable solid electrolyte interface film rich in inorganic matter on the electrode surface, which can extend battery life and meet fast charging requirements.

[0006] This invention provides an electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises a first additive and a second additive, and the first additive comprises at least one of the compounds described in Formulas 1 to 8 below; Where M is N, P, C or S, A is P or S, n and m are each an independent integer from 0 to 1, R1 to R4 are each an independent hydrogen atom, halogen atom, alkyl group with 1 to 8 carbon atoms, alkoxy group, cycloalkyl group or amino group, and R5 is a hydrogen atom, alkyl group with 1 to 8 carbon atoms, alkoxy group, cycloalkyl group or amino group.

[0007] In some specific embodiments, the volume content of the first additive is 0.1% to 5% based on the total volume of the electrolyte.

[0008] In some specific embodiments, the volume content of the second additive is 1% to 5% based on the total volume of the electrolyte.

[0009] In some specific embodiments, the second additive includes at least one of fluoroethylene carbonate and vinylene carbonate.

[0010] In some specific embodiments, the additive also includes a third additive.

[0011] In some specific embodiments, the third additive includes a phosphorus-containing additive; the phosphorus-containing additive includes at least one of hexamethylphosphazene, hexamethylphosphoric acid triamine, trimethyl phosphite, triethyl phosphite, and lithium dihydrogen phosphate.

[0012] In some specific embodiments, the volume content of the third additive is 0.1% to 5% based on the total volume of the electrolyte.

[0013] In some specific embodiments, the volume content of the organic solvent is 85% to 98% based on the total volume of the electrolyte.

[0014] In some specific embodiments, the organic solvent includes at least two of a first organic solvent, a second organic solvent, and a third organic solvent.

[0015] In some specific embodiments, the first organic solvent includes dimethyl carbonate (DMC) and / or ethyl methyl carbonate (EMC).

[0016] In some specific embodiments, the second organic solvent includes ethylene carbonate (EC).

[0017] In some specific embodiments, the third organic solvent includes at least one selected from methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), ethyl butyrate (EB), methyl pentanoate (MEP), ethyl lactate (EL), methyl benzoate (MB), acetonitrile (AN), acrylonitrile (ACN), propionitrile (PN), isobutyronitrile (IBN), succinic anionyl (SN), glutaronitrile (GN), adiponitrile (ADN), 3-(trifluoromethyl)adiponitrile (ADN-CF3), and 1,3,6-hexanetrionitrile (HTN).

[0018] In some specific embodiments, the concentration of the lithium salt is 1~1.5 mol / L, based on the total volume of the electrolyte.

[0019] In some specific embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethanesulfonylimide.

[0020] A second aspect of the present invention also provides a battery comprising the electrolyte described above.

[0021] In some specific embodiments, the battery includes a lithium-ion battery.

[0022] Compared with the prior art, the present invention has the following beneficial effects: This invention exhibits multiple beneficial effects through a unique electrolyte formulation design. From the perspective of specific components, the specific proportions of lithium salt, organic solvent, and mixed additives, especially the use of the first additive, can be used in combination with other additives during the battery activation stage, working synergistically. During cycling, this electrolyte formulation significantly improves the electrochemical performance of the battery, especially at high rates, greatly reducing interfacial impedance and meeting the fast charging requirements of the battery. After 700 cycles at 2C rate, the capacity retention rate is 98%, and the average coulombic efficiency is 99.5%. Attached Figure Description

[0023] The above and other objects, features, and advantages of the invention will be apparent from the following description of preferred embodiments illustrating the gist of the invention and its use, and the accompanying drawings, in which: Figure 1 Electrochemical performance of button batteries assembled with the electrolytes used in Examples 1-7 and Comparative Example 1, where a is the first charge-discharge specific capacity curve of Example 1 and Comparative Example 1, and b is the rate performance curve of Examples 1-7 and Comparative Example 1. Detailed Implementation

[0024] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments described below are for illustrative purposes only and do not limit the scope of the invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the reagents and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the following embodiments, conditions and methods known in the art can be used for processing.

[0025] This invention provides an electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises a first additive and a second additive, and the first additive comprises at least one of the compounds described in Formulas 1 to 8 below; Where M is N, P, C or S, A is P or S, n and m are each an independent integer from 0 to 1, R1 to R4 are each an independent hydrogen atom, halogen atom, alkyl group with 1 to 8 carbon atoms, alkoxy group, cycloalkyl group or amino group, and R5 is a hydrogen atom, alkyl group with 1 to 8 carbon atoms, alkoxy group, cycloalkyl group or amino group.

[0026] The purpose of this invention is to improve battery fast-charging performance and extend battery cycle life. Firstly, it uses low-viscosity solvents such as methyl propionate (MP) or acrylonitrile (ACN) to increase the ionic conductivity of the solvent and improve performance. Simultaneously, it incorporates composite additives such as fluoroethylene carbonate (FEC), vinylene carbonate (VC), N-methylpyrrolidone (NMP), and other film-forming additives to form a stable solid electrolyte interface film rich in inorganic components during cycling, thereby achieving fast-charging performance and extending cycle life. In detail: The electrolyte of this invention, through the use of additives in a specific ratio of solvent formulation, achieves a slightly higher reduction potential during the battery activation stage due to the presence of cyclic carbonate groups and some cyclic carbonate groups combined with C=C double bonds. This allows the additives to preferentially form a solid electrolyte interface film on the electrode surface, hindering solvent decomposition and extending battery life. Specifically, the first additive preferentially contacts trace amounts of water in the electrolyte, reducing HF content during cycling. Simultaneously, it can be combined with other sulfur-containing additives to form a stable CEI film rich in inorganic components Li2SO4 and Li2S on the electrode surface, thereby reducing side reactions on the electrode surface and extending battery cycle life. Furthermore, the addition of a low-viscosity solvent increases the ionic conductivity of the electrolyte, thus reducing the ohmic resistance of the battery. Additionally, the uniformity and low interfacial impedance of the CEI film enable the electrolyte to meet high-rate operating conditions.

[0027] In this invention, alkyl groups having 1-8 carbon atoms include, but are not limited to, -CH3, -C2H5, =CH2, =CH-CH3, etc.

[0028] In some embodiments, the first additive comprises at least one of N-methylpyrrolidone, vinylene sulfate, vinyl sulfate, 1,3-dioxopentane (DOL), 2-vinyl-1,3-dioxopentane (VDOL), N-hydro-2-pyrrolidone, N-ethylpyrrolidone (NEP), N-propylpyrrolidone (NPP), 1-acetyl-2-pyrrolidone, 2-oxo-1-pyrrolidinecarboxaldehyde, 4-ethyl-1,3-dioxane-2-one, and 2-methylcyclopentanone.

[0029] In some embodiments, the volume content of the first additive is 0.1% to 5% based on the total volume of the electrolyte. As an example, the volume content of the first additive can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%, etc.

[0030] In this invention, by controlling the content of the first additive within the aforementioned range, it helps to extend the service life of the electrolyte. Simultaneously, the sulfur-containing additive forms Li₂SO₄ and Li₂S, which inhibit the formation of lithium dendrites. If the content of the first additive is too high, it will lead to an increase in electrolyte viscosity and a decrease in ionic conductivity, thus failing to meet the conductivity requirements for fast charging and reducing battery life. If the content of the first additive is too low, it will lead to excessively rapid additive consumption. While the battery's electrochemical performance may be good initially, its capacity will rapidly decline as the additive is consumed, resulting in a significant deterioration in electrochemical performance.

[0031] In some embodiments, the volume content of the second additive is 1% to 5% based on the total volume of the electrolyte. As an example, the volume content of the second additive can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%, etc.

[0032] In this invention, by controlling the content of the second additive within the above-mentioned range, it is helpful to decompose the main solvent EC before it decomposes on the electrode surface to form a solid electrolyte interface film with excellent performance.

[0033] In some embodiments, the second additive includes at least one of fluoroethylene carbonate and vinylene carbonate.

[0034] In some embodiments, the additive may further include a third additive.

[0035] In some embodiments, the third additive includes a phosphorus-containing additive; the phosphorus-containing additive includes at least one of hexamethylphosphononitrile, hexamethylphosphoric triamine, trimethyl phosphite, triethyl phosphite, and lithium dihydrogen phosphate.

[0036] In some embodiments, the volume content of the third additive is 0.1% to 5% based on the total volume of the electrolyte. As an example, the volume content of the third additive can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%, etc.

[0037] In some embodiments, the volume content of the organic solvent is 85% to 98% based on the total volume of the electrolyte. As an example, the volume content of the organic solvent can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, and 98%, etc.

[0038] In some embodiments, the organic solvent includes at least two of a first organic solvent, a second organic solvent, and a third organic solvent.

[0039] In some embodiments, the first organic solvent includes dimethyl carbonate and / or ethyl methyl carbonate.

[0040] In some embodiments, the second organic solvent comprises ethylene carbonate.

[0041] In some embodiments, the third organic solvent includes at least one selected from methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, ethyl butyrate, methyl neopentanoate, ethyl lactate, methyl benzoate, acetonitrile, acrylonitrile, propionitrile, isobutyronitrile, succinic anion, glutaronitrile, adiponitrile, 3-(trifluoromethyl)adiponitrile, and 1,3,6-hexanetricarbonitrile.

[0042] In some embodiments, the concentration of the lithium salt is 1 to 1.5 mol / L based on the total volume of the electrolyte. For example, the weight content of the lithium salt can be 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, and 1.5 mol / L, etc.

[0043] In some specific embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethanesulfonylimide.

[0044] A second aspect of the present invention also provides a battery comprising the electrolyte described above.

[0045] In some embodiments, the battery includes a lithium-ion battery.

[0046] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. The embodiments of this application are only examples, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] The percentages in the following examples and comparative examples refer to the volume percentage of the corresponding substance in the entire electrolyte.

[0048] Example 1 Electrolyte preparation steps: In an argon-filled glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl propionate (MP) are mixed in a volume ratio of EC: EMC:MP = 21:70:9. Then, 1% vinylene carbonate (VC), 1% ethylene sulfate (DTD), and 1% N-methylpyrrolidone (NMP) based on the total volume of the electrolyte are added to the mixed solution. Finally, lithium hexafluorophosphate is slowly added to make the concentration of lithium hexafluorophosphate (LiPF6) in the electrolyte 1 mol / L. After stirring evenly, the lithium-ion battery electrolyte is obtained.

[0049] Example 2 Electrolyte preparation steps: In an argon-filled glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl propionate (MP) are mixed in a volume ratio of EC: EMC:MP = 21:70:9. Then, 1% fluoroethylene carbonate (FEC), 1% vinylene carbonate (VC), 1% ethylene sulfate (DTD), and 1% N-methylpyrrolidone (NMP) are added to the mixed solution based on the total volume of the electrolyte. Finally, lithium hexafluorophosphate is slowly added to make the concentration of lithium hexafluorophosphate (LiPF6) in the electrolyte 1 mol / L. After stirring evenly, the lithium-ion battery electrolyte is obtained.

[0050] Example 3 Electrolyte preparation steps: In an argon-filled glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl propionate (MP) are mixed in a volume ratio of EC: EMC:MP = 21:70:9. Then, 0.5% fluoroethylene carbonate (FEC), 0.5% vinylene carbonate (VC), and 1% ethylene sulfate (DTD) based on the total volume of the electrolyte are added to the mixed solution. Finally, lithium hexafluorophosphate is slowly added to make the concentration of lithium hexafluorophosphate (LiPF6) in the electrolyte 1 mol / L. After stirring evenly, the lithium-ion battery electrolyte is obtained.

[0051] Example 4 Electrolyte preparation steps: In an argon-filled glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl propionate (MP) are mixed in a volume ratio of EC: EMC:MP = 21:70:9. Then, 1% fluoroethylene carbonate (FEC), 1% vinylene carbonate (VC), and 0.5% ethylene sulfate (DTD) are added to the mixed solution based on the total volume of the electrolyte. Finally, lithium hexafluorophosphate is slowly added to make the concentration of lithium hexafluorophosphate (LiPF6) in the electrolyte 1 mol / L. After stirring evenly, the lithium-ion battery electrolyte is obtained.

[0052] Example 5 Electrolyte preparation steps: In an argon-filled glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl propionate (MP) are mixed in a volume ratio of EC: EMC:MP = 21:70:9. Then, 1% vinylene carbonate (VC), 1% vinyl sulfate (DTD), 1% N-methylpyrrolidone (NMP), 1% trimethyl phosphite (TMP), and 1% lithium dihydrogen phosphate (LDP) are added to the mixed solution based on the total volume of the electrolyte. Finally, lithium hexafluorophosphate is slowly added to make the concentration of lithium hexafluorophosphate (LiPF6) in the electrolyte 1 mol / L. After stirring evenly, the lithium-ion battery electrolyte is obtained.

[0053] Example 6 Electrolyte preparation steps: In an argon-filled glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl propionate (MP) are mixed in a volume ratio of EC: EMC:MP = 21:70:9. Then, 1% vinylene carbonate (VC), 1% vinyl sulfate (DTD), 1% N-methylpyrrolidone (NMP), 1% triethyl phosphite (TEP), and 1% lithium dihydrogen phosphate (LDP) are added to the mixed solution based on the total volume of the electrolyte. Finally, lithium hexafluorophosphate is slowly added to make the concentration of lithium hexafluorophosphate (LiPF6) in the electrolyte 1 mol / L. After stirring evenly, the lithium-ion battery electrolyte is obtained.

[0054] Example 7 Electrolyte preparation steps: In an argon-filled glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl propionate (MP) are mixed in a volume ratio of EC: EMC:MP = 21:70:9. Then, 1% vinylene carbonate (VC), 1% vinyl sulfate (DTD), 1% N-methylpyrrolidone (NMP), 1% hexamethylphosphoric triamine (HMPA), and 1% lithium dihydrogen phosphate (LDP) are added to the mixed solution based on the total volume of the electrolyte. Finally, lithium hexafluorophosphate is slowly added to make the concentration of lithium hexafluorophosphate (LiPF6) in the electrolyte 1 mol / L. After stirring evenly, the lithium-ion battery electrolyte is obtained.

[0055] Comparative Example 1 Electrolyte preparation steps: In an argon-filled glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl propionate (MP) are mixed in a volume ratio of EC: EMC:MP = 21:70:9. Then, lithium hexafluorophosphate is slowly added to the mixed solution to make the concentration of lithium hexafluorophosphate (LiPF6) in the electrolyte 1 mol / L. After stirring evenly, the lithium-ion battery electrolyte is obtained.

[0056] The specific additives and amounts of electrolyte in the above embodiments and comparative examples are shown in Table 1. Table 1. Specific additives and amounts of electrolyte in the examples and comparative examples.

[0057] Application examples Button batteries were assembled in an inert gas atmosphere using the electrolytes from the above examples and comparative examples: The batteries were assembled in a glove box with a high-purity argon atmosphere containing less than 0.01 ppm of H2O and O2. The batteries were inverted and assembled in sequence with the 2032 negative electrode shell, gasket, LFP electrode, separator, 70 μL electrolyte, lithium sheet, gasket, spring sheet, and positive electrode shell. The batteries were then transferred to a battery packaging machine for packaging and placed in a battery settling chamber for 24 hours to complete the wetting process of the positive and negative electrode separators inside the battery, resulting in a complete battery.

[0058] Test case (1) Room temperature cycling performance test At room temperature, the prepared button batteries were subjected to 500 cycles of 2C using a Xinwei charge-discharge tester to analyze the effect of different lithium-ion battery electrolytes on the room temperature cycle performance of the batteries. The room temperature cycle performance test data of the batteries with different electrolytes are shown in Table 2.

[0059] Table 2. Long-cycle parameters of lithium-ion battery electrolytes in examples and comparative examples.

[0060] As shown in Table 2, compared with Comparative Example 1, the addition of different concentrations of additives in the electrolytes of Examples 1, 2, 3, and 4 significantly improved the capacity retention rate of the batteries after 300 cycles at 2C at room temperature. A comparison of Examples 1, 2, and 3 shows that increasing or decreasing the volume ratio affects the cycle capacity retention rate. Among these, Example 3 exhibits the best performance in fast charging and long-cycle operation, maintaining a capacity retention rate of 93.7% after 300 cycles at 2C at room temperature. This demonstrates that the lithium-ion batteries prepared with the electrolyte of this invention possess excellent room-temperature cycling performance. Furthermore, in Examples 5, 6, and 7, the capacity retention rate of the batteries after 700 cycles at 2C at room temperature is significantly improved. Therefore, the electrolyte formulation of this invention significantly enhances the battery performance at 2C rate, resulting in superior room-temperature cycling performance for lithium-ion batteries.

[0061] Figure 1 The figures show the electrochemical performance of button batteries assembled using the electrolytes in the examples and comparative examples. In example a, a is the first-cycle charge-discharge specific capacity curve for Example 1 and Comparative Example 1; and in example b, a is the rate performance curve. Figure 1As can be seen from the specific capacity-voltage curves of the comparative and embodiment examples, the use of mixed additives can promote the formation of a more stable interface film, thereby protecting the electrodes and extending the battery life.

[0062] Although preferred embodiments of the invention have been shown and described, it is conceivable that those skilled in the art can devise various modifications to the invention within the spirit and scope of the appended claims.

Claims

1. An electrolyte, characterized in that, It includes lithium salts, organic solvents, and additives, wherein the additives include a first additive and a second additive, and the first additive includes at least one of the compounds described in Formulas 1 to 8 below; Where M is N, P, C or S, A is P or S, n and m are each an independent integer from 0 to 1, R1 to R4 are each an independent hydrogen atom, halogen atom, alkyl group with 1 to 8 carbon atoms, alkoxy group, cycloalkyl group or amino group, and R5 is a hydrogen atom, alkyl group with 1 to 8 carbon atoms, alkoxy group, cycloalkyl group or amino group.

2. The electrolyte according to claim 1, characterized in that, Based on the total volume of the electrolyte, the volume content of the first additive is 0.1% to 5%; Based on the total volume of the electrolyte, the volume content of the second additive is 1% to 5%.

3. The electrolyte according to claim 1, characterized in that, The second additive includes at least one of fluoroethylene carbonate and vinylene carbonate.

4. The electrolyte according to claim 1, characterized in that, The additives also include a third additive; The third additive includes a phosphorus-containing additive; the phosphorus-containing additive includes at least one of hexamethylphosphononitrile, hexamethylphosphoric triamine, trimethyl phosphite, triethyl phosphite, and lithium dihydrogen phosphate.

5. The electrolyte according to claim 4, characterized in that, Based on the total volume of the electrolyte, the volume content of the third additive is 0.1% to 5%.

6. The electrolyte according to claim 1, characterized in that, Based on the total volume of the electrolyte, the volume content of the organic solvent is 85% to 98%.

7. The electrolyte according to claim 1, characterized in that, The organic solvent includes at least two of a first organic solvent, a second organic solvent, and a third organic solvent; The first organic solvent includes dimethyl carbonate and / or ethyl methyl carbonate; The second organic solvent includes ethylene carbonate; The third organic solvent includes at least one selected from methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, ethyl butyrate, methyl neopentanoate, ethyl lactate, methyl benzoate, acetonitrile, acrylonitrile, propionitrile, isobutyronitrile, succinic anion, glutaronitrile, adiponitrile, 3-(trifluoromethyl)adiponitrile, and 1,3,6-hexanetricarbonitrile.

8. The electrolyte according to claim 1, characterized in that, Based on the total volume of the electrolyte, the concentration of the lithium salt is 1~1.5 mol / L.

9. The electrolyte according to claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

10. A battery, characterized in that, Includes the electrolyte as described in any one of claims 1 to 9; The battery includes a lithium-ion battery.

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