Electrolyte additive and application thereof
By adding imidazole sulfonate compounds, pentaerythritol bicyclic sulfate and 1,6-hexamethylene diisocyanate as additives to the electrolyte, the problem of insufficient electrolyte stability was solved, and the performance of the secondary battery under high temperature environment, especially the cycle and storage performance, was improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-26
- Publication Date
- 2026-03-27
AI Technical Summary
Existing electrolyte additives have limited effect on improving electrolyte performance, resulting in limited overall performance improvement of secondary batteries, especially poor performance under high temperature environments.
Imidazole sulfonate compounds, pentaerythritol bicyclic sulfate, and 1,6-hexamethylene diisocyanate were used as electrolyte additives. By using these compounds in combination, the generation of free acid in the electrolyte during transportation and storage was suppressed, the stability of the electrolyte was improved, and the film-forming impedance was reduced, thereby improving the high-temperature performance of the secondary battery.
It effectively improves the high-temperature cycle performance and storage performance of secondary batteries, exhibiting excellent high-temperature performance, including lower film-forming impedance and higher capacity retention.
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Abstract
Description
Technical Field
[0001] This invention relates to an electrolyte additive and its application, belonging to the field of energy technology. Background Technology
[0002] During the charging and discharging process of secondary batteries, side reactions can occur between the positive and negative electrode active materials and the electrolyte, easily leading to structural defects and thus deteriorating the battery's performance. Currently, efforts are being made to improve the overall performance of secondary batteries by enhancing the properties of the positive and / or negative electrode materials themselves, and by improving the stability of the electrolyte.
[0003] Existing technologies mainly improve the stability of electrolytes by adding electrolyte additives. However, existing electrolyte additives have limited effect on improving electrolyte performance, which limits the improvement of secondary battery performance. Summary of the Invention
[0004] This invention provides an electrolyte additive that, when used in an electrolyte, can suppress free acid generated during transportation and storage, thereby improving the stability of the electrolyte. Furthermore, when the obtained electrolyte is applied to a secondary battery, it exhibits low film-forming impedance, which is beneficial for improving the high-temperature performance of the secondary battery.
[0005] The present invention provides an electrolyte comprising the above-mentioned electrolyte additives. The electrolyte has a stable acid value before and after storage and has low film-forming impedance when applied to secondary batteries, which can effectively improve the high-temperature performance of secondary batteries.
[0006] The present invention provides a secondary battery comprising the electrolyte described above, and therefore the secondary battery has excellent high-temperature performance.
[0007] The present invention provides an electrolyte additive, wherein the electrolyte additive comprises imidazole sulfonate compounds, pentaerythritol bicyclic sulfate and 1,6-hexamethylene diisocyanate.
[0008] The electrolyte additives described above, wherein the imidazole sulfonate compounds include compounds represented by Formula 1;
[0009]
[0010] In Formula 1, R1 is selected from hydrogen, substituted or unsubstituted C6-C18 aryl, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted thiophene, substituted or unsubstituted imidazolyl, substituted or unsubstituted pyridinyl, and the group shown in Formula 2.
[0011]
[0012] In Formula 2, R2, R3, and R4 are each independently selected from hydrogen, halogen, substituted or unsubstituted C1-C10 alkyl groups.
[0013] In the electrolyte additive described above, R1 is selected from hydrogen, phenyl, thiophene, imidazolyl, pyridinyl, fluorophenyl, fluorothiophene, fluoroimidazolyl, fluoropyridine, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl, 2-butyl, fluoromethyl, fluoroethyl, fluoro-1-propyl, fluoro-2-propyl, fluoro-1-butyl, fluoro-2-methyl-1-propyl, fluoro-2-butyl, vinyl, propenyl, butenyl, fluorovinyl, fluoropropenyl, fluorobutenyl, trimethylsilyl, triethylsilyl, trifluorosilyl, (trifluoromethyl)dimethylsilyl, di(trifluoromethyl)methylsilyl, tri(trifluoromethyl)silyl, silanephenyl.
[0014] The electrolyte additives shown above, wherein the imidazole sulfonate compounds are selected from compounds with the following structures:
[0015]
[0016]
[0017] In the electrolyte additive described above, the mass ratio of the imidazole sulfonate compound to the 1,6-hexamethylene diisocyanate in the electrolyte additive is (0.001–100):1; and / or,
[0018] The electrolyte additive contains pentaerythritol bicyclic sulfate at a mass percentage of 0.3% to 3%.
[0019] The present invention provides an electrolyte comprising the electrolyte additives described above.
[0020] In the electrolyte as described above, the electrolyte additive has a mass percentage content of 0.36% to 18%.
[0021] The electrolyte as described above further includes an electrolyte salt and a solvent;
[0022] The electrolyte comprises, by mass fraction: 7%–18% electrolyte salt, 65%–88% solvent, 0.01%–5% imidazole sulfonate compound, 0.05%–10% 1,6-hexamethylene diisocyanate, and 0.3%–3% pentaerythritol bicyclic sulfate.
[0023] The electrolyte as described above, wherein the electrolyte further includes additives;
[0024] The adjuvant is selected from at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, fluoroethylene carbonate, difluoroethylene carbonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, triphenyl phosphate, triphenyl phosphite, succinic anhydride, dimethylmaleic anhydride, and methanedisulfonate.
[0025] In the electrolyte as described above, the mass percentage of the additive in the electrolyte is ≤5%.
[0026] The electrolyte as described above, wherein the electrolyte comprises, by mass fraction:
[0027] 9%–15% electrolyte salt, 75%–86% solvent, 0.1%–1% imidazole sulfonate compounds, 0.1%–2% 1,6-hexamethylene diisocyanate, 0.3%–1% pentaerythritol bicyclic sulfate, and 0.2%–2% auxiliaries.
[0028] The present invention provides a secondary battery, wherein the electrolyte is as described above.
[0029] The electrolyte additive of the present invention has a simple composition. When applied to electrolytes, it can suppress free acid generated during transportation and storage, improve the stability of the electrolyte, and obtain an electrolyte with low film-forming impedance, which is beneficial to the high-temperature performance of secondary batteries.
[0030] The electrolyte of the present invention includes the above-mentioned electrolyte additives. The electrolyte has a stable acid value before and after storage and has low film-forming impedance when applied to secondary batteries, which can effectively improve the high-temperature performance of secondary batteries.
[0031] The secondary battery of the present invention includes the electrolyte described above, and therefore the secondary battery has excellent high-temperature performance. Detailed Implementation
[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.
[0033] A first aspect of the present invention provides an electrolyte additive comprising imidazole sulfonate compounds, pentaerythritol bicyclic sulfate (TDT), and 1,6-hexamethylene diisocyanate (HDI).
[0034] In this invention, the imidazole ring in the imidazole sulfonate compounds has a high electron cloud density, making them more easily reduced in redox reactions to generate an SEI film that is beneficial for negative electrode protection. Imidazole sulfonate compounds exhibit strong electrophilicity and a high redox film-forming potential, while pentaerythritol bicyclic sulfate has strong nucleophilicity. Under these conditions, imidazole sulfonate compounds more readily attack the carbon atom of 1,6-hexamethylenediisocyanate, preferentially reacting with 1,6-hexamethylenediisocyanate to generate an imidazole-containing film. The sulfonyl isocyanate compounds containing imidazole groups can not only reduce the increase in electrolyte acid value and color caused by electrolyte salt decomposition due to trace moisture (for example, the decomposition of hexafluorophosphate produces HF and PF5, thus increasing the acid value and color of the electrolyte); but also, the sulfonyl isocyanate groups in the sulfonyl isocyanate compounds can significantly reduce the film-forming resistance of pentaerythritol bicyclic sulfate when participating in redox reactions, thereby improving the high-temperature cycle performance and high-temperature storage performance of secondary batteries. Therefore, the addition of the electrolyte in this invention can improve the high-temperature performance of secondary batteries.
[0035] In some embodiments of the present invention, imidazole sulfonates include compounds represented by Formula 1;
[0036]
[0037] In Formula 1, R1 is selected from hydrogen, substituted or unsubstituted C6-C18 aryl, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted thiophene, substituted or unsubstituted imidazolyl, substituted or unsubstituted pyridinyl, and the group shown in Formula 2.
[0038]
[0039] In Formula 2, R2, R3, and R4 are each independently selected from hydrogen, halogen, substituted or unsubstituted C1-C10 alkyl groups.
[0040] Specifically, in Formula 1, R1 is selected from hydrogen, substituted or unsubstituted C6-C18 aryl (e.g., phenyl, substituted phenyl), substituted or unsubstituted C1-C10 alkyl (e.g., the alkyl can be straight-chain alkyl, branched alkyl, cycloalkyl), substituted or unsubstituted C2-C10 alkenyl (e.g., straight-chain alkenyl, cyclic alkenyl (e.g., cyclopentadiene containing heteroatoms or not containing heteroatoms)), substituted or unsubstituted thiophene (e.g., substituted thiophene, thiophene), substituted or unsubstituted imidazolyl (e.g., substituted imidazolyl, imidazolyl), substituted or unsubstituted pyridinyl (e.g., pyridinyl, substituted pyridinyl), and the group shown in Formula 2;
[0041] Specifically, in Formula 2, R2, R3, and R4 are each independently selected from hydrogen, halogens (e.g., F, Cl, Br, I), and substituted or unsubstituted C1-C10 alkyl groups (e.g., the alkyl group can be a straight-chain alkyl group, a branched alkyl group, or a cycloalkyl group).
[0042] The present invention does not limit the types of substituents of alkenyl, alkyl, thiophene, imidazole, pyridyl, and aryl, and can use substituents commonly used in the art, such as at least one of halogen, cyano, ester, nitro, amino, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy, isocyano, isocyanate, and substituted or unsubstituted aryl.
[0043] In this invention, when the imidazole sulfonate compound includes the compound shown in Formula 1, the imidazole sulfonate compound can better bind with the isocyanate group in 1,6-hexamethylene diisocyanate, further neutralize the acid value, and obtain a compound with low film-forming resistance, thereby improving the storage stability of the electrolyte and improving the high-temperature performance of the secondary battery.
[0044] Furthermore, when R1 is selected from hydrogen, phenyl, thienyl, imidazolyl, pyridyl, fluorophenyl, fluorothienyl, fluoroimidazolyl, fluoropyridine, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl, 2-butyl, fluoromethyl, fluoroethyl, fluoro-1-propyl, fluoro-2-propyl, fluoro-1-butyl, fluoro-2-methyl-1-propyl, fluoro-2-butyl, vinyl, propenyl, butenyl, fluorovinyl, fluoropropenyl, fluorobutenyl, trimethylsilyl, triethylsilyl, trifluorosilyl, (trifluoromethyl)dimethylsilyl, di(trifluoromethyl)methylsilyl, tri(trifluoromethyl)silyl, silanephenyl, the high-temperature performance of the secondary battery can be further improved.
[0045] For example, imidazole sulfonates are selected from compounds with the following structures:
[0046]
[0047] The electrolyte additive of the present invention includes imidazole sulfonate compounds, 1,6-hexamethylene diisocyanate, and pentaerythritol dicyclic sulfate. It is understood that the content of imidazole sulfonate compounds, 1,6-hexamethylene diisocyanate, and pentaerythritol dicyclic sulfate has a crucial impact on the performance of the electrolyte additive. Therefore, the present invention can further improve the performance of the electrolyte additive by selecting the content of imidazole sulfonate compounds, 1,6-hexamethylene diisocyanate, and pentaerythritol dicyclic sulfate.
[0048] For example, in some embodiments of the present invention, when the mass ratio of the imidazole sulfonate compound to 1,6-hexamethylene diisocyanate in the electrolyte additive is (0.001 to 100):1, the imidazole sulfonate compound can react more fully with 1,6-hexamethylene diisocyanate to generate sulfonyl isocyanate compounds containing imidazole groups, thereby making the electrolyte system contain more sulfonyl isocyanate groups containing imidazole groups, thereby further improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.
[0049] Furthermore, in the electrolyte additive, the mass ratio of imidazole sulfonate compounds to 1,6-hexamethylene diisocyanate is (0.05–10):1.
[0050] In some embodiments of the present invention, when the mass percentage of pentaerythritol dicyclic sulfate in the electrolyte additive is 0.3% to 3%, the sulfonyl isocyanate group in the sulfonyl isocyanate compound can further reduce the film-forming resistance of pentaerythritol dicyclic sulfate when participating in the redox reaction, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.
[0051] A second aspect of the present invention provides an electrolyte comprising the electrolyte additive of the first aspect.
[0052] The electrolyte of the present invention includes electrolyte additives of the first aspect, so the electrolyte has a stable acid value before and after storage, and when applied to secondary batteries, it has low film-forming impedance, which can effectively improve the high-temperature performance of secondary batteries.
[0053] In some embodiments of the present invention, when the mass percentage of electrolyte additives in the electrolyte is 0.36% to 18%, the role of electrolyte additives can be fully utilized without deteriorating the ion transport performance of the electrolyte, thereby improving the stability of the electrolyte, reducing the film-forming impedance of the electrolyte, and thus improving the high-temperature performance of the secondary battery. Further, the mass percentage of electrolyte additives in the electrolyte is 0.5% to 6%.
[0054] It is understandable that electrolytes also include electrolyte salts and solvents.
[0055] This invention does not specifically limit the electrolyte salt; it can be any commonly used electrolyte salt in the art. The electrolyte salt can be a sodium salt or a lithium salt. When the electrolyte salt is a sodium salt, the obtained electrolyte can be used to prepare a sodium-ion battery; when the electrolyte salt is a lithium salt, the obtained electrolyte can be used to prepare a lithium-ion battery. In some embodiments, the sodium salt may include at least one of sodium hexafluorophosphate, sodium perchlorate, sodium bis(oxalato)borate, sodium difluorooxalatoborate, sodium bis(trifluoromethanesulfonyl)imide, and sodium difluorosulfonylimide; the lithium salt may include at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorosulfonylimide.
[0056] The present invention does not impose any particular limitation on the solvent, and any solvent commonly used in the art can be used. In some embodiments, the solvent can be a non-aqueous organic solvent, which may include carbonate compounds and / or carboxylic acid ester compounds.
[0057] The inventors discovered in their research that by further selecting the content of electrolyte salts, solvents, imidazole sulfonates, pentaerythritol bicyclic sulfate, and 1,6-hexamethylene diisocyanate in the electrolyte, the effects of imidazole sulfonates, pentaerythritol bicyclic sulfate, and 1,6-hexamethylene diisocyanate in the electrolyte additives can be fully utilized, resulting in an electrolyte with superior overall performance.
[0058] For example, in some embodiments of the present invention, when the electrolyte comprises by mass fraction: 7% to 18% electrolyte salt, 65% to 88% solvent, 0.01% to 5% imidazole sulfonate compound, 0.05% to 10% 1,6-hexamethylene diisocyanate, and 0.3% to 3% pentaerythritol bicyclic sulfate, the electrolyte can further improve the high-temperature performance of the secondary battery.
[0059] In some embodiments of the present invention, the electrolyte further includes additives;
[0060] When the additive is selected from at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, fluoroethylene carbonate, difluoroethylene carbonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, triphenyl phosphate, triphenyl phosphite, succinic anhydride, dimethylmaleic anhydride, and methane disulfonate, the high-temperature performance of the secondary battery can be further improved.
[0061] Furthermore, when the additives are selected from 1,3-propanesulfonate lactone and / or fluoroethylene carbonate, the high-temperature performance of the secondary battery will be further improved.
[0062] In some embodiments of the present invention, when the mass percentage of the additive in the electrolyte is ≤5%, the role of the additive can be fully utilized to improve the overall performance of the electrolyte, thereby improving the high-temperature performance of the secondary battery. Further, the mass percentage of the additive in the electrolyte is 0.2% to 2%.
[0063] Furthermore, when the electrolyte comprises, by mass fraction:
[0064] When the electrolyte contains 9%–15% electrolyte salt, 75%–86% solvent, 0.1%–1% imidazole sulfonate compound, 0.1%–2% 1,6-hexamethylene diisocyanate, 0.3%–1% pentaerythritol bicyclic sulfate, and 0.2%–2% additives, the components in the electrolyte can be more fully matched, improving the stability of the electrolyte and reducing the film-forming resistance of the electrolyte, thereby improving the high-temperature performance of the secondary battery.
[0065] A third aspect of the present invention provides a secondary battery comprising the electrolyte of the second aspect.
[0066] It is understood that a secondary battery also includes a positive electrode, a negative electrode, a separator, and an outer packaging. In a specific implementation, the positive electrode, separator, and negative electrode can be stacked sequentially to form a stacked cell, or sequentially wound and then wound to form a wound cell. The cell is then placed in an outer packaging, electrolyte is injected into the outer packaging, and after sealing, a secondary battery is formed.
[0067] The secondary battery of the present invention can be a lithium-ion battery or a sodium-ion battery.
[0068] When the secondary battery is a lithium-ion battery, the operating voltage of the lithium-ion battery can be 2.5-4.5V, and the positive electrode active material in the positive electrode sheet can include LiNi. 1-x-y-z CoxMn y Al z One or more of the following: O2, lithium nickel manganese oxide, lithium cobalt oxide, lithium-rich manganese-based solid solution, lithium manganese oxide, lithium iron phosphate, and lithium manganese iron phosphate, wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, and 0≤x+y+z≤1; the negative electrode active material in the negative electrode sheet may include one or more of the following: artificial graphite, lithium metal, coated natural graphite, silicon-carbon negative electrode, and silicon negative electrode.
[0069] When the secondary battery is a sodium-ion battery, the operating voltage of the sodium-ion battery can be 1.5V to 4.2V, and the positive electrode active material in the positive electrode sheet can include Na. x1 M1O2, Na x2At least one of M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3, and Na2M4(SO4)2·2H2O, wherein: 0 < x1 ≤ 1, M1 includes at least one of Ni, Co, Mn, Fe, and Cu; 0 < x2 < 6, M2 includes at least one of Ni, Fe, and Mn; M3 includes at least one of Fe and Mn; and M4 includes at least one of Fe, Co, Mn, and Cu. The negative electrode active material in the negative electrode sheet may include at least one of soft carbon, hard carbon, sodium titanate, sodium metal, sodium alloy, and metals that can form alloys with sodium.
[0070] The secondary battery of the present invention includes the electrolyte described above, and therefore the secondary battery has excellent high-temperature performance.
[0071] The electrolyte of the present invention and its application are described in detail below through specific embodiments.
[0072] Example 1
[0073] The sodium-ion battery of this embodiment is prepared by a method including the following steps:
[0074] (1) Preparation of positive electrode
[0075] The positive electrode active material Na[Ni 0.33 Fe 0.33 Mn 0.33 O2, conductive carbon black, carbon nanotubes, polyvinylidene fluoride (PVDF), and maleic acid are added to N-methylpyrrolidone (NMP) in a mass ratio of 94.5:2.5:1:1.8:0.2 to prepare a positive electrode slurry.
[0076] The positive electrode slurry is coated on the upper and lower surfaces of the aluminum foil, dried, and then cold-pressed. After cutting, trimming, and slitting, the positive electrode sheet is produced.
[0077] (2) Preparation of negative electrode
[0078] Hard carbon, conductive carbon black, styrene-butadiene rubber (SBR), and thickener (CMC) are mixed in deionized water at a mass ratio of 95:1.5:2:1.5 to prepare a negative electrode slurry. The negative electrode slurry is coated on the upper and lower surfaces of aluminum foil and dried. Then, it is cold-pressed, trimmed, cut into sheets, and slit to produce a negative electrode sheet.
[0079] (3) Preparation of electrolyte
[0080] In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC) were mixed uniformly in a mass ratio of 3:1:1 to obtain 83 g of non-aqueous organic solvent. Then, 0.5 g of imidazole sulfonate compound A1, 0.5 g of 1,6-hexamethylene diisocyanate, and 1 g of pentaerythritol dicyclic sulfate were added as electrolyte additives. 1 g of fluoroethylene carbonate (FEC) and 0.5 g of 1,3-propanesulfonate lactone (PS) were added to obtain a mixed solution.
[0081] After sealing and packaging the mixed solution and freezing it in a freezer (below 0°C) for 2 hours, take it out and slowly add 13.5g of sodium hexafluorophosphate to the mixed solution in a glove box filled with nitrogen (O2 < 1ppm, H2O < 1ppm). After mixing evenly, the electrolyte is prepared. The specific composition of the electrolyte is shown in Table 1.
[0082] (4) Preparation of sodium-ion batteries
[0083] The positive electrode, polyethylene separator, and negative electrode are stacked in sequence and then wound to obtain the battery cell. The tabs are welded on, the battery cell is placed in the outer packaging, electrolyte is injected into the outer packaging, and after encapsulation, standing, formation, and shaping, a sodium-ion battery with a theoretical capacity of 1100mAh is obtained.
[0084] Example 2
[0085] The lithium-ion battery of this embodiment is prepared by a method including the following steps:
[0086] (1) Preparation of positive electrode
[0087] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, conductive agent carbon black, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) in a mass ratio of 96.3:2:0.5:1.2 to prepare a positive electrode slurry;
[0088] The positive electrode slurry is coated on the upper and lower surfaces of the aluminum foil, dried, and then cold-pressed. After cutting, trimming, and slitting, the positive electrode sheet is produced.
[0089] (2) Preparation of negative electrode
[0090] A negative electrode slurry was prepared by mixing graphite with conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener (CMC) in deionized water at a mass ratio of 95:1.5:2:1.5.
[0091] The negative electrode paste is coated on the upper and lower surfaces of the copper foil and dried. Then, it is cold-pressed, trimmed, cut into sheets, and slit to produce the negative electrode sheet.
[0092] (3) Preparation of electrolyte
[0093] In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethylene carbonate (EC) were mixed uniformly in a mass ratio of 5:2:3 to obtain 83 g of non-aqueous organic solvent. Then, 0.5 g of imidazole sulfonate compound A1, 0.5 g of 1,6-hexamethylene diisocyanate, and 1 g of pentaerythritol dicyclic sulfate were added as additives. 1 g of fluoroethylene carbonate (FEC) and 0.5 g of 1,3-propanesulfonate lactone (PS) were added to obtain a mixed solution.
[0094] After sealing and packaging the mixed solution and freezing it in a freezer (below 0°C) for 2 hours, take it out and slowly add 13.5g of lithium hexafluorophosphate to the mixed solution in a glove box filled with nitrogen (O2 < 1ppm, H2O < 1ppm). After mixing evenly, the electrolyte is prepared.
[0095] (4) Preparation of lithium-ion batteries
[0096] The positive electrode, polyethylene separator, and negative electrode are stacked in sequence and then wound to obtain the battery cell. The tabs are welded on, the battery cell is placed in the outer packaging, electrolyte is injected into the outer packaging, and after encapsulation, standing, formation, and shaping, a lithium-ion battery with a theoretical capacity of 1500mAh is obtained.
[0097] Examples 2-28, Comparative Examples 1-3
[0098] The electrolytes of Examples 2-28 and Comparative Examples 1-3 have the same composition as those of Example 1, with the differences shown in Table 1.
[0099] The electrolyte in Example 1 was replaced with the electrolyte in Examples 2-28 and Comparative Examples 1-3, respectively, to obtain the secondary batteries of Examples 2-28 and Comparative Examples 1-3, respectively.
[0100] Table 1
[0101]
[0102]
[0103] Performance testing
[0104] The secondary batteries in the examples and comparative examples were subjected to the following performance tests, and the results are shown in Table 2.
[0105] 1) High-temperature cycling performance test
[0106] Two secondary batteries with their capacities determined by the upper clamping plate were placed in a 45°C environment and charged at a constant current and constant voltage of 1C to the upper limit cutoff voltage. The cutoff current was 0.05C. Then, they were discharged at a constant current of 1C to the lower limit cutoff voltage. This cycle was repeated, and the discharge capacity of the two secondary batteries in the first cycle and the discharge capacity in the 500th cycle were recorded. The capacity retention rate was calculated using the following formula.
[0107] Capacity retention rate = discharge capacity of the 500th cycle / discharge capacity of the first cycle × 100%.
[0108] 2) High-temperature storage test
[0109] One secondary battery with its upper clamp fully sized was removed and placed in a 25°C environment. It was charged at a constant current and constant voltage of 1C to the upper limit cutoff voltage, with a cutoff current of 0.05C. Then, it was discharged at a constant current of 1C to the lower limit cutoff voltage. The discharge capacity at this point was recorded as C0. The cell thickness before high-temperature storage was measured using a cell thickness tester and recorded as D1. The battery cell was then charged again with a constant current and constant voltage of 1C to the upper limit cutoff voltage, with a cutoff current of 0.05C. The fully charged secondary battery was then placed in a 60℃ constant temperature oven for 30 days. After that, the secondary battery was removed, and the cell thickness after high-temperature storage was immediately measured using a cell thickness tester and recorded as D2. Subsequently, the secondary battery was placed in a 25℃ environment for 2 hours, and then discharged at a constant current of 1C to the lower limit cutoff voltage at 25℃. The discharge capacity at this point was recorded as C1. Then, it was charged again with a constant current and constant voltage of 1C to the upper limit cutoff voltage, with a cutoff current of 0.05C, and then discharged at a constant current of 1C to the lower limit cutoff voltage. The discharge capacity at this point was recorded as C2.
[0110] Capacity retention rate = (C1 / C0) × 100%; Capacity recovery rate = (C2 / C0) × 100%.
[0111] Thickness expansion rate = (D2-D1) / D1×100%.
[0112] 3) DC impedance (DCIR) change rate test before and after 30 days of high-temperature storage
[0113] After the secondary battery with the upper clamp has been divided into equal capacity, remove the clamp and place it in an environment of 25°C. Charge it with a constant current and constant voltage of 1C to the upper limit cutoff voltage. The cutoff current is 0.05C. Then discharge it with a constant current of 1C for 30 minutes and record the discharge voltage V0. Place the secondary battery (such as a sodium-ion battery) adjusted to 50% SOC at 25°C for 5 minutes and discharge it with a constant current of 2C for 30 seconds. Record the discharge voltage V1 and the discharge current I*2C during the 2C discharge.
[0114] Before high-temperature storage: The formula for calculating the discharge DC internal resistance at 50% SOC is as follows: DCIR1(mΩ)=(V0-V1) / (I*2C)×1000.
[0115] After 30 days of storage, the secondary battery was removed and placed in an environment of 25°C for 2 hours. Then, it was discharged at a constant current of 1C to the lower cutoff voltage in an environment of 25°C. Then, it was charged at a constant current and constant voltage of 1C to the upper cutoff voltage, with a cutoff current of 0.05C. This cycle was repeated 3 times. After that, it was discharged at a constant current of 1C for 30 minutes, and the discharge voltage V2 was recorded. The secondary battery (such as a sodium-ion battery) adjusted to 50% SOC was placed at 25°C for 5 minutes and discharged at a constant current of 2C for 30 seconds. The discharge voltage V3 was recorded at this time, and the discharge current during the 2C discharge was I1*2C.
[0116] After 30 days of high-temperature storage, the formula for calculating the discharge DC internal resistance at 50% SOC is as follows: DCIR2(mΩ)=(V2-V3) / (I1*2C)×1000.
[0117] The rate of change of DC impedance (DCIR) before and after 30 days of high-temperature storage is calculated as (DCIR2 - DCIR1) / DCIR1 * 100%.
[0118] Table 2
[0119]
[0120]
[0121] As shown in Table 2, compared with the comparative example, the battery of the present invention has better high-temperature cycle capacity retention rate, high-temperature storage capacity retention rate, and high-temperature storage capacity recovery rate, and has lower high-temperature storage thickness expansion rate and high-temperature storage DCIR change rate. This indicates that by including imidazole sulfonate compounds, pentaerythritol bicyclic sulfate and 1,6-hexamethylene diisocyanate as electrolyte additives, the high-temperature cycle performance and high-temperature storage performance of the battery can be improved.
[0122] As can be seen from Examples 1 and 2, when the electrolyte additive of the present invention is applied to sodium-ion batteries, it has better high-temperature cycle performance and high-temperature storage performance. The reason is that, compared with sodium-ion batteries, the upper limit voltage of lithium-ion batteries is too high, which can easily cause the cycle performance and storage performance of the battery to degrade.
[0123] As can be seen from Examples 1 and 3-6, when the imidazole sulfonate compound is A1, the obtained battery has better high-temperature cycling performance and high-temperature storage performance.
[0124] As can be seen from Examples 1, 7-10, 12-15 and 11, by making the mass ratio of imidazole sulfonate compound to 1,6-hexamethylene diisocyanate (0.001-100):1, the high-temperature cycle performance and high-temperature storage performance of the battery can be improved. Furthermore, as can be seen from Examples 1, 7-8, 12-15 and 9-11, by making the mass ratio of imidazole sulfonate compound to 1,6-hexamethylene diisocyanate (0.05-10):1, the high-temperature cycle performance and high-temperature storage performance of the battery can be further improved.
[0125] As can be seen from Examples 19 and 20, by selecting the content of electrolyte additives in the electrolyte, the high-temperature cycle performance and high-temperature storage performance of the battery can be further improved. Furthermore, as can be seen from Examples 8 and 14, when the content of electrolyte additives in the electrolyte is 0.5-6%, the obtained battery has better high-temperature cycle performance and high-temperature storage performance.
[0126] As can be seen from Examples 1, 22-25 and Example 21, and Examples 26 and 27, adding additives to the electrolyte can improve the high-temperature cycle performance and high-temperature storage performance of the battery. Furthermore, as can be seen from Examples 21 and 26, by selecting the content of each component in the electrolyte, the high-temperature cycle performance and high-temperature storage performance of the battery can be further improved.
[0127] Furthermore, as can be seen from Examples 1, 23-24, and 22, when the content of additives in the electrolyte is ≤5%, the high-temperature cycle performance and high-temperature storage performance of the battery can be further improved. As can be seen from Examples 24-25 and 23, when the content of additives in the electrolyte is 0.2-2%, the obtained battery has better high-temperature cycle performance and high-temperature storage performance. As can be seen from Examples 22-25 and 27, by selecting the content of each component in the electrolyte, the high-temperature cycle performance and high-temperature storage performance of the battery can be further improved.
[0128] As can be seen from Examples 1 and 28, when the mass percentage of pentaerythritol dicyclic sulfate in the electrolyte additive is 0.3-3%, the obtained battery has better high-temperature cycle performance and high-temperature storage performance.
[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. An electrolyte additive, characterized in that, The electrolyte additives include imidazole sulfonate compounds, pentaerythritol bicyclic sulfate, and 1,6-hexamethylene diisocyanate.
2. The electrolyte additive according to claim 1, characterized in that, The imidazole sulfonate compounds include those shown in Formula 1; In Formula 1, R1 is selected from hydrogen, substituted or unsubstituted C6-C18 aryl, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted thiophene, substituted or unsubstituted imidazolyl, substituted or unsubstituted pyridinyl, and the group shown in Formula 2. In Formula 2, R2, R3, and R4 are each independently selected from hydrogen, halogen, substituted or unsubstituted C1-C10 alkyl groups.
3. The electrolyte additive according to claim 2, characterized in that, R1 is selected from hydrogen, phenyl, thienyl, imidazolyl, pyridyl, fluorophenyl, fluorothienyl, fluoroimidazolyl, fluoropyridine, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl, 2-butyl, fluoromethyl, fluoroethyl, fluoro-1-propyl, fluoro-2-propyl, fluoro-1-butyl, fluoro-2-methyl-1-propyl, fluoro-2-butyl, vinyl, propenyl, butenyl, fluorovinyl, fluoropropenyl, fluorobutenyl, trimethylsilyl, triethylsilyl, trifluorosilyl, (trifluoromethyl)dimethylsilyl, di(trifluoromethyl)methylsilyl, tri(trifluoromethyl)silyl, silanephenyl.
4. The electrolyte additive according to claim 2 or 3, characterized in that, The imidazole sulfonate compounds are selected from compounds with the following structures:
5. The electrolyte additive according to any one of claims 1-4, characterized in that, In the electrolyte additive, the mass ratio of the imidazole sulfonate compound to the 1,6-hexamethylene diisocyanate is (0.001–100):1; and / or, The electrolyte additive contains pentaerythritol bicyclic sulfate at a mass percentage of 0.3% to 3%.
6. An electrolyte, characterized in that, Includes the electrolyte additive according to any one of claims 1-5.
7. The electrolyte according to claim 6, characterized in that, The electrolyte contains an electrolyte additive at a mass percentage of 0.36% to 18%.
8. The electrolyte according to claim 6 or 7, characterized in that, The electrolyte also includes electrolyte salts and solvents; The electrolyte comprises, by mass percentage: 7%–18% electrolyte salt, 65%–88% solvent, 0.01%–5% imidazole sulfonate compound, 0.05%–10% 1,6-hexamethylene diisocyanate, and 0.3%–3% pentaerythritol bicyclic sulfate.
9. The electrolyte according to any one of claims 6-8, characterized in that, The electrolyte also includes additives; The adjuvant is selected from at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, fluoroethylene carbonate, difluoroethylene carbonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, triphenyl phosphate, triphenyl phosphite, succinic anhydride, dimethylmaleic anhydride, and methanedisulfonate.
10. The electrolyte according to claim 9, characterized in that, The mass percentage of the additive in the electrolyte is ≤5%.
11. The electrolyte according to claim 9 or 10, characterized in that, The electrolyte comprises, by mass percentage: 9%–15% electrolyte salt, 75%–86% solvent, 0.1%–1% imidazole sulfonate compounds, 0.1%–2% 1,6-hexamethylene diisocyanate, 0.3%–1% pentaerythritol bicyclic sulfate, and 0.2%–2% auxiliaries.
12. A secondary battery, characterized in that, Includes the electrolyte according to any one of claims 6-11.