Imidazole additive, electrolyte containing same and application thereof

Abstract

The invention relates to the technical field of batteries, and discloses an imidazole additive, an electrolyte containing the additive and application of the additive, when the imidazole compound serves as an electrolyte additive, a highly stable protective film can be formed on the surfaces of a positive electrode and a negative electrode, and decomposition of the electrolyte and expansion of a silicon negative electrode are effectively inhibited; wherein the imidazole compound contains a silicon-oxygen bond or a silicon-nitrogen bond, and can react with water and acid in the electrolyte, so that the acidity of the electrolyte is kept stable at high temperature, the gas production rate of the battery is further reduced, and the high-temperature cycle performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an imidazole additive, an electrolyte containing the additive, and their applications. Background Art

[0002] With the rapid development of fields such as electric vehicles and low-altitude drones, people's demand for high-performance lithium-ion batteries is increasing day by day; the theoretical capacity of the silicon anode of lithium-ion batteries is as high as 4200 mAh / g, far exceeding the theoretical capacity of the graphite anode of 372 mAh / g. However, during the charge and discharge process of lithium-ion batteries, there is serious volume expansion (up to more than 300%), resulting in the rupture of the electrode structure, the repeated growth of the solid electrolyte interface (SEI) film, and a sharp decline in cycle performance.

[0003] At present, there are various solutions for the expansion of silicon anodes, such as material modification, electrode structure design, electrolyte optimization, and binder development. Material modification usually improves the expansion of silicon from the perspectives of nanosized silicon particles, silicon-based composites, silicon-metal / oxide composites, etc.; the electrode structure usually designs the electrode porosity (30 - 50%), hollow structure, or three-dimensional porous current collector method to reserve expansion space; developing high-performance polymer binders to inhibit the expansion of silicon anodes. However, the most effective and convenient solution is electrolyte optimization, that is, adding an additive that inhibits the expansion of silicon anodes to the electrolyte to form a stable and flexible SEI film to inhibit silicon expansion.

[0004] The commonly used additive in the electrolyte is fluoroethylene carbonate (FEC), which can effectively inhibit the expansion of silicon anodes and improve the cycle performance of silicon-containing batteries. However, FEC is prone to gas generation during the cycle, resulting in a decline in the battery cycle performance. Therefore, it is necessary to develop an electrolyte additive to reduce the use of FEC, reduce the gas generation of the battery, and improve the battery cycle performance. Summary of the Invention

[0005] To solve the technical problems in the background art, the present invention proposes an imidazole additive, and the imidazole additive includes a compound shown in structural formula (I);

[0006] Wherein, R1 is a group containing a Si-N group or a Si-O group; R2 is an unsaturated group; n is an integer from 1 to 5.

[0007] The group containing a Si-N group is any one of structural formulas 1 - 3, and the group containing a Si-O group is any one of structural formulas 4 - 6; .

[0008] The R2 is one of an alkynyl group, a cyano group, or an alkenyl group.

[0009] The compound shown in Structural Formula I is .

[0010] In the present invention, the imidazole ring of the imidazole-based additive can effectively inhibit the decomposition of the electrolyte. The unsaturated groups undergo electrochemical active film formation and the functional group orientation effect promotes the formation of a highly stable electrolyte interface film on the surfaces of the positive and negative electrode materials. The groups containing Si-N or Si-O groups can undergo the cleavage of Si-N or Si-O and react with the acid and water in the electrolyte, thereby maintaining the acidity of the electrolyte at high temperatures and reducing gas swelling and the damage of the electrolyte to the SEI film.

[0011] The present invention also provides an electrolyte, which comprises the above-mentioned imidazole-based additive.

[0012] The proportion of the imidazole-based additive in the electrolyte is 0.1-5 wt%.

[0013] The electrolyte further comprises a lithium salt and an organic solvent; The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate or lithium difluoro(oxalato)borate; The organic solvent is at least one of organic esters, C1-C10 alkyl ethers, cyclic ethers, sulfones, dinitriles, ionic liquids; Preferably, the above-mentioned organic esters are at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, butyl propionate or ethyl butyrate; Preferably, the above-mentioned C1-10 alkyl ethers are at least one of dimethyl ether, diethyl ether or methyl ethyl ether; Preferably, the above-mentioned dinitriles are at least one of adiponitrile, succinonitrile or glutaronitrile; Preferably, the above-mentioned sulfones are at least one of dimethyl sulfoxide or sulfolane; Preferably, the above-mentioned ionic liquids are at least one of imidazole-based or pyrrole-based ionic liquids.

[0014] The proportion of the lithium salt in the electrolyte is 8-26 wt%; the proportion of the organic solvent in the electrolyte is 72-90 wt%; Preferably, the proportion of the lithium salt in the electrolyte is 10-16 wt%; the proportion of the organic solvent in the electrolyte is 80-90 wt%.

[0015] The electrolyte further comprises a non-imidazole film-forming additive, wherein the non-imidazole film-forming additive comprises fluoroethylene carbonate, and the proportion of the non-imidazole film-forming additive in the electrolyte is 0-20 wt %.

[0016] In the present invention, fluoroethylene carbonate is prone to gas production during the cycle, and the imidazole additive in the electrolyte reduces the usage of traditional electrolyte additives (non-imidazole film-forming additives), especially the usage of fluoroethylene carbonate. As a result, the gas production during battery cycling is further reduced, and the battery's cycling performance is improved.

[0017] The present invention also provides a lithium-ion battery, comprising the above-mentioned electrolyte; Preferably, the lithium-ion battery further comprises a positive electrode, a negative electrode, a separator, and an aluminum-plastic film; Further preferably, the positive electrode material is selected from one of lithium cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate or lithium manganese iron phosphate; More preferably, the positive electrode material is lithium nickel cobalt manganese oxide; Preferably, the active material of the negative electrode is selected from any one or a combination of graphite, silicon oxide, silicon carbon, lithium metal, and lithium titanate; More preferably, the active material of the negative electrode is selected from a combination of silicon carbon and graphite; Preferably, the diaphragm is selected from one of polypropylene (PP), polyethylene (PE) diaphragm or glass fiber diaphragm; More preferably, the above-mentioned diaphragm is selected from polypropylene (PP) diaphragm.

[0018] Beneficial effects of the present invention: (1) The present invention proposes an imidazole additive that can form a stable and tough protective film on the surface of the negative electrode, inhibiting the volume expansion of the silicon negative electrode during the charge and discharge process, thereby reducing the damage of the SEI film; (2) This imidazole additive contains Si-N or Si-O groups, which have the effect of removing water and acid, further preventing the electrolyte from generating gas and causing flatulence due to reaction with water and acid; (3) The electrolyte containing the above-mentioned imidazole additive proposed in the present invention has good compatibility with positive and negative electrode materials, can inhibit the expansion of the silicon negative electrode and the flatulence of the lithium-ion battery, and improve the battery cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the synthesis of compound (II); Figure 2 is the H NMR spectrum of compound (II); Figure 3 Schematic diagram of the synthesis of compounds (I-II); Figure 4 1H NMR spectrum of compound (I-II). Detailed implementation manners

[0020] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0022] Below, the technical solutions of the present invention will be described more clearly and completely in conjunction with specific examples and comparative examples.

[0023] Synthesis of compound (I-I) Under nitrogen protection, 135.17 g of 1-but-3-ynylimidazol-2-amine and 190 mL of trimethylchlorosilane were dissolved in 1 L of anhydrous toluene, heated to 85 °C, and refluxed and stirred for 6 hours for the silylation reaction. The silylation reaction was monitored by TLC (developing agent, ethyl acetate: n-hexane = 1:3). After the reaction of 1-but-3-ynylimidazol-2-amine was complete, the reaction solution was cooled to 25 °C, and toluene and excess trimethylchlorosilane were removed by distillation under reduced pressure. Then the residue was washed with 500 mL of n-hexane, the insoluble matter was filtered off, and the filtrate was concentrated to obtain compound (I-I).

[0024] Synthesis of compound (I-II) (1) 5 L of acetonitrile was cooled to 0 °C in an ice bath, 135.17 g of 1-but-3-ynylimidazol-2-amine was dissolved in the above acetonitrile, and while maintaining 0 °C, 0.25 L of HI aqueous solution with a concentration of 8 mol·L -1 was slowly added dropwise under stirring. After the addition of the HI aqueous solution was complete, a homogeneous mixed solution was obtained. 82.8 g of was added to the above mixed solution in three portions, and the mixture was stirred for 1 hour for the diazotization reaction. The diazotization reaction was monitored by TLC (developing agent, ethyl acetate: n-hexane = 1:3). Immediately after the reaction of 1-but-3-ynylimidazol-2-amine was complete, 3 L of saturated solution was added to quench the reaction, and then the mixture was extracted with 5 L of ethyl acetate, dried and concentrated to obtain the intermediate 1-(but-3-ynyl)-2-diazoiodoimidazole; (2)Under nitrogen protection, 246.05 g of 1-(but-3-ynyl)-2-diazoiodoimidazole, 330 mL of , 15 g of Ni catalyst and 130 g of Zn powder were added to anhydrous THF, heated to 60 °C, and stirred for 12 hours for nucleophilic substitution reaction. During the nucleophilic substitution reaction, TLC was used for monitoring (developing agent: n-hexane:ethyl acetate = 3:1). After the nucleophilic substitution reaction was completed, filtration, concentration, and column chromatography purification (initial solvent n-hexane, gradient solvent n-hexane:ethyl acetate = 4:1) were carried out to obtain compound (I-II).

[0025] Figure 1 is a schematic diagram for synthesizing compound (I-I), where ET3N is triethylamine and TOL is toluene.

[0026] Example 1

[0027] This example presents an electrolyte, and its preparation method is as follows: In an argon glove box with water and oxygen contents both ≤ 0.1 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were stirred evenly according to a mass ratio of 3:7 to obtain a mixed organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) was slowly added to the mixed organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and compound (I-I) were added, and after stirring evenly, an electrolyte was obtained. Among them, the usage amounts of lithium hexafluorophosphate, the mixed organic solvent, FEC, and compound (I-I) are 13 wt%, 84 wt%, 2 wt%, and 1 wt% of the total mass of the electrolyte, respectively.

[0028] Example 2

[0029] This example presents an electrolyte, and its preparation method is as follows: In an argon glove box with water and oxygen contents both ≤ 0.1 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were stirred evenly according to a mass ratio of 3:7 to obtain a mixed organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) was slowly added to the mixed organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and compound (I-II) were added, and after stirring evenly, an electrolyte was obtained. Among them, the usage amounts of lithium hexafluorophosphate, the mixed organic solvent, FEC, and compound (I-II) are 13 wt%, 84 wt%, 2 wt%, and 1 wt% of the total mass of the electrolyte, respectively.

[0030] Example 3

[0031] This embodiment provides an electrolyte, and its preparation method is as follows: In an argon glove box with water and oxygen content both ≤ 0.1 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are stirred evenly according to a mass ratio of 3:7 to obtain a mixed organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) is slowly added to the mixed organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and compound (I-I) are added, and after stirring evenly, the electrolyte is obtained. Among them, the usage amounts of lithium hexafluorophosphate, the mixed organic solvent, FEC, and compound (I-I) are 13 wt%, 84.5 wt%, 2 wt%, and 0.5 wt% of the total mass of the electrolyte, respectively.

[0032] Example 4

[0033] This embodiment provides an electrolyte, and its preparation method is as follows: In an argon glove box with water and oxygen content both ≤ 0.1 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are stirred evenly according to a mass ratio of 3:7 to obtain a mixed organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) is slowly added to the mixed organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and compound (I-II) are added, and after stirring evenly, the electrolyte is obtained. Among them, the usage amounts of lithium hexafluorophosphate, the mixed organic solvent, FEC, and compound (I-II) are 13 wt%, 84.5 wt%, 2 wt%, and 0.5 wt% of the total mass of the electrolyte, respectively.

[0034] Comparative Example 1 This comparative example provides an electrolyte, and its preparation method is as follows: In an argon glove box with water and oxygen content both ≤ 0.1 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are stirred evenly according to a mass ratio of 3:7 to obtain a mixed organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) is slowly added to the mixed organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) is added, and after stirring evenly, the electrolyte is obtained. Among them, the usage amounts of lithium hexafluorophosphate, the mixed organic solvent, and FEC are 13 wt%, 85 wt%, and 2 wt% of the total mass of the electrolyte, respectively.

[0035] Comparative Example 2 This comparative example provides an electrolyte, and its preparation method is as follows: In an argon glove box with water and oxygen content both ≤ 0.1 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are stirred evenly according to a mass ratio of 3:7 to obtain a mixed organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) is slowly added to the mixed organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and lithium difluorophosphate are added, and after stirring evenly, the electrolyte is obtained. Among them, the usage amounts of lithium hexafluorophosphate, the mixed organic solvent, FEC, and lithium difluorophosphate are 13 wt%, 84 wt%, 2 wt%, and 1 wt% of the total mass of the electrolyte, respectively.

[0036] Comparative Example 3 This comparative example presents an electrolyte solution, and its preparation method is as follows: In an argon glove box with water and oxygen content both ≤ 0.1 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are stirred evenly according to a mass ratio of 3:7 to obtain a mixed organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) is slowly added to the mixed organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and 1,3 - propane sultone (PS) are added, and after stirring evenly, the electrolyte solution is obtained. Among them, the usage amounts of lithium hexafluorophosphate, the mixed organic solvent, FEC, and 1,3 - propane sultone (PS) are 13 wt%, 84 wt%, 2 wt%, and 1 wt% of the total mass of the electrolyte solution respectively.

[0037] Comparative Example 4 This comparative example presents an electrolyte solution, and its preparation method is as follows: In an argon glove box with water and oxygen content both ≤ 0.1 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are stirred evenly according to a mass ratio of 3:7 to obtain a mixed organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) is slowly added to the mixed organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are added, and after stirring evenly, the electrolyte solution is obtained. Among them, the usage amounts of lithium hexafluorophosphate, the mixed organic solvent, FEC, and vinylene carbonate (VC) are 13 wt%, 84 wt%, 2 wt%, and 1 wt% of the total mass of the electrolyte solution respectively.

[0038] Comparative Example 5 This comparative example presents an electrolyte solution, and its preparation method is as follows: In an argon glove box with water and oxygen content both ≤ 0.1 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are stirred evenly according to a mass ratio of 3:7 to obtain a mixed organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) is slowly added to the mixed organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and N,N'-carbonyldiimidazole (CAS No. 530 - 62 - 1) are added, and after stirring evenly, the electrolyte solution is obtained. Among them, the usage amounts of lithium hexafluorophosphate, the mixed organic solvent, FEC, and N,N'-carbonyldiimidazole are 13 wt%, 84 wt%, 2 wt%, and 1 wt% of the total mass of the electrolyte solution respectively.

[0039] Preparation and performance test of soft - package battery The electrolyte solutions in the above Examples 1 - 4 and Comparative Examples 1 - 5 are prepared into soft - package batteries for room - temperature cycle performance test and volume expansion rate test. Table 1 shows the performance test results of soft - package batteries P1 - P4 and DP1 - DP5: The specific steps for preparing the soft - package battery are as follows: (1)Mix the cathode material lithium nickel cobalt manganate (NCM90), conductive agent carbon black (SuperP), and binder polyvinylidene fluoride (PVDF) in a mass ratio of 94:3:3. After mixing, add N-methylpyrrolidone, and then use a vacuum degassing machine to homogenize to obtain a cathode slurry with a solid content of 55%. Uniformly coat the cathode slurry on an aluminum foil with a thickness of 12 μm. After drying, rolling, and cutting, obtain the cathode sheet; (2)Mix the anode material composed of silicon carbon and graphite (specific capacity is about 650 mAh / g), conductive agent SuperP, thickening agent sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) in a mass ratio of 94:1.5:1.5:3. After mixing, add deionized water, and then use a vacuum degassing machine to homogenize to obtain an anode slurry with a solid content of 52%. Uniformly coat the anode slurry on a copper foil with a thickness of 8 μm. After drying, rolling, and cutting, obtain the anode sheet; (3)Fabricate a soft-pack laminated battery in an environment with a dew point temperature below -60°C. Stack the cathode sheet, separator, and anode sheet in sequence, ensuring that the separator completely separates the cathode and anode sheets. Before injecting the electrolyte, bake the moisture content of the battery to below 200 ppm, inject the electrolyte, and then perform sealing, formation, and grading to obtain the experimental battery. Among them, the soft-pack batteries prepared using the electrolytes in Examples 1-4 are denoted as P1-P4, and the soft-pack batteries prepared using the electrolytes in Comparative Examples 1-5 are denoted as DP1-DP5.

[0040] Battery volume expansion rate test: Place the prepared soft-pack batteries P1-P4 and DP1-DP5 in a constant-temperature chamber with an ambient temperature of 25°C, and measure the battery volume V0; after grading, measure the battery volume V1; then charge at a constant current of 1C to a voltage of 4.2V, then charge at a constant voltage of 4.2V until the current is 0.05C, and then discharge at a constant current of 1C to a voltage of 2.8V. Repeat this cycle 100 times, and measure the battery volume V2; calculate the volume expansion rate = (V2 - V1) / V0 × 100% according to the values of V0, V1, and V2.

[0041] Battery room temperature cycle test: In the test environment, place the prepared soft-pack battery in a constant-temperature chamber with an ambient temperature of 25°C, charge at a constant current of 1C to a voltage of 4.2V, then charge at a constant voltage of 4.2V until the current is 0.05C, and then discharge at a constant current of 1C to a voltage of 2.8V. Repeat this cycle 300 times, record the capacity retention rate, and the capacity retention rate (%) in the nth cycle = (discharge capacity in the nth cycle / discharge capacity in the first cycle) × 100%.

[0042] Anode sheet expansion test: In an environment where the dew point temperature is below -40°C, take the soft-pack battery after the above-mentioned normal-temperature cycle test of the battery (25°C, 350 cycles). Disassemble the fully charged battery cell (100% SOC) of the above-mentioned soft-pack battery, take out the middle negative electrode sheet, measure the thickness of the sheet with a micrometer, measure the thickness at three middle points as T1, T2, and T3, and the thickness of the initial negative electrode sheet is T0. Then the electrode sheet expansion rate = {[(T1 + T2 + T3) / 3 - T0] / T0} × 100%.

[0043]

[0044] As can be seen from Table 1 above, compared with DP1-DP5, the volume expansion rate of P1-P4 has decreased significantly, indicating that compound (I-I) and compound (I-II) form a stable SEI film on the electrode surface, inhibiting gas generation during battery cycling; compared with DP1-DP5, the capacity retention rate of P1-P4 is significantly higher, indicating that a simple imidazole ring cannot improve the cycling performance of the battery well, while compound (I-I) or compound (I-II) can effectively improve the cycling performance of the battery; through the data of the electrode sheet expansion rate, it can also be found that the SEI film formed by compound (I-II) has a better effect on inhibiting silicon expansion than compound (I-I).

[0045] As described above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. An imidazole-based additive, characterized in that, The imidazole additives include the compounds shown by Structural Formula I; wherein, R1 is a group containing Si-N group or Si-O group; R2 is an unsaturated group; n is an integer from 1 to 5.

2. The imidazole additive according to claim 1, wherein The Si-N-containing group is any one of the structural formulas 1-3, and the Si-O-containing group is any one of the structural formulas 4-6; 。 3. The imidazole additive according to claim 1 or 2, characterized in that, R2 is one of an alkynyl group, a cyano group or an alkenyl group.

4. The imidazole additive according to claim 1 or 2, characterized in that, The compound shown in Structural Formula I is or .

5. An electrolyte, characterized in that, The electrolyte solution includes the imidazole-based additive described in any one of claims 1-4.

6. The electrolyte according to claim 5, characterized in that, The proportion of the imidazole-based additive in the electrolyte solution is 0.1-5 wt%.

7. The electrolyte according to claim 5 or 6, characterized in that, The electrolyte solution further includes a lithium salt and an organic solvent; The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate or lithium difluoro(oxalato)borate; The organic solvent is at least one of organic esters, C1-C10 alkyl ethers, cyclic ethers, sulfones, dinitriles, ionic liquids.

8. The electrolyte according to claim 7, characterized in that, The proportion of the lithium salt in the electrolyte solution is 8-26 wt%; the proportion of the organic solvent in the electrolyte solution is 72-90 wt%.

9. The electrolyte according to claim 5 or 6, characterized in that, The electrolyte solution further includes a non-imidazole-based film-forming additive, the non-imidazole-based film-forming additive includes fluoroethylene carbonate, and the proportion of the non-imidazole-based film-forming additive in the electrolyte solution is 0-20 wt%.

10. A lithium-ion battery, characterized in that, The lithium ion battery includes the electrolyte solution described in any one of claims 5-9.

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