Electrolyte, lithium ion battery and electric device

Abstract

This invention relates to an electrolyte, a lithium-ion battery, and an electrical device. The electrolyte comprises a lithium salt, a solvent, and an additive; wherein the additive comprises a compound having a general structural formula as shown in formula (I): In formula (I), R1, R2, and R3 are each independently selected from hydrogen atoms, substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C1-C6 alkoxy groups, substituted or unsubstituted C3-C6 cycloalkyl groups, substituted or unsubstituted C2-C6 unsaturated hydrocarbon groups, substituted or unsubstituted C1-C6 silyl groups, substituted or unsubstituted C1-C6 ether groups, substituted or unsubstituted C2-C6 carboxylic acid ester groups, fluorine atoms, or cyano groups. The electrolyte provided in this application, on the one hand, allows sulfur and nitrogen atoms in the additive to coordinate with transition metal ions, inhibiting the reactivity of the transition metal ions; on the other hand, the additive can form a surface film on the positive and negative electrode surfaces, improving the cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to an electrolyte, a lithium-ion battery, and an electrical device. Background Technology

[0002] As an electrochemical device, lithium-ion batteries are playing an increasingly important role in fields such as 3C digital products, automotive power supplies, and energy storage systems.

[0003] However, battery performance degradation and lifespan limitations remain pressing issues. Especially under high voltage and high temperature application conditions, transition metal ions in the cathode material are prone to dissolution, leading to damage and corrosion of the cathode structure, as well as oxidative decomposition and gas generation of the electrolyte. These ions then migrate to the negative electrode side, damaging the SEI film and causing rapid capacity degradation. Summary of the Invention

[0004] Therefore, it is necessary to provide an electrolyte, a lithium-ion battery, and an electrical device that can suppress the dissolution of transition metal ions and the damage to the electrode structure, reduce the decomposition and gas generation of the electrolyte, improve the interfacial stability of the positive and negative electrodes, and improve the cycle life of the battery.

[0005] A first aspect of this application provides an electrolyte comprising: a lithium salt, a solvent, and an additive; wherein the additive comprises a compound having a general structural formula as shown in formula (I):

[0006]

[0007]

[0008] In formula (I), R1, R2, and R3 are each independently selected from hydrogen atoms, substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C1-C6 alkoxy groups, substituted or unsubstituted C3-C6 cycloalkyl groups, substituted or unsubstituted C2-C6 unsaturated hydrocarbon groups, substituted or unsubstituted C1-C6 silyl groups, substituted or unsubstituted C1-C6 ether groups, substituted or unsubstituted C2-C6 carboxylic acid ester groups, fluorine atoms, or cyano groups.

[0009] In some embodiments, R1 or R2 is an electron-withdrawing group.

[0010] In some implementations, R3 is an electron-donating group.

[0011] In some embodiments, R1 or R2 is independently selected from fluorine atoms, cyano groups, and C1-C6 carboxylic acid ester groups.

[0012] In some embodiments, R3 is selected from C1-C6 alkyl, C1-C6 alkoxy, C3-C6 cycloalkyl, and C2-C6 unsaturated hydrocarbon groups.

[0013] In some embodiments, the substituents are selected from fluorine atoms or cyano groups.

[0014] In some embodiments, the compound having the general structural formula shown in formula (I) is selected from at least one of the following compounds:

[0015]

[0016]

[0017] In some embodiments, the compound having the general structural formula shown in formula (I) has a mass percentage of 0.5% to 2% in the electrolyte.

[0018] In some embodiments, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)borate, lithium difluorobis(oxalato)phosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium tetrafluorophosphate, potassium bis(fluorosulfonyl)imide, lithium 4,5-dicyano-2-trifluoromethyl-imidazolium, lithium methyl sulfate, lithium ethyl sulfate, and lithium bis(nonafluorobutylsulfonyl)imide.

[0019] In some embodiments, the solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propyl acetate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate, and ethyl butyrate.

[0020] In some embodiments, the additive also includes other additives selected from at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene sulfate, 4-methyl vinyl sulfate, vinyl ethylene carbonate, 4-ethyl vinyl sulfate, lithium difluorophosphate, 1,3-propanesulfonate lactone, vinyl vinyl sulfite, tris(trimethylsilyl)borate, and triallyl isocyanate.

[0021] The second aspect of this application provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and the electrolyte provided in the first aspect.

[0022] In some embodiments, the positive electrode includes a positive electrode active material, which includes at least one of lithium nickel cobalt manganese oxide ternary material, lithium manganese iron phosphate material, lithium manganese oxide material, and lithium manganese iron oxide material.

[0023] A third aspect of this application provides an electrical device comprising the lithium-ion battery provided in the second aspect above.

[0024] Compared with traditional technologies, the present invention has the following advantages:

[0025] The electrolyte provided in this application has two advantages. First, the compound having the general structural formula shown in Formula (I) has a mercapto and pyridine structure, and the sulfur atom on the mercapto and the nitrogen atom on the pyridine ring both have lone pairs of electrons, which can coordinate with transition metal ions in situ, thereby inhibiting the reactivity of transition metal ions, reducing the oxidative decomposition and gas production of the electrolyte, preventing them from migrating to the negative electrode side and damaging the SEI film, and improving the cycle performance of the battery. Second, the compound having the general structural formula shown in Formula (I) preferentially undergoes oxidation and reduction reactions on the electrode, and the multiple structures such as biaromatic rings and ketenes contained in the compound can polymerize on the positive and negative electrode surfaces, forming highly chemically stable surface films rich in Li2CO3 (i.e., CEI film and SEI film) on the positive and negative electrode surfaces, respectively, thereby improving the interfacial stability of the positive and negative electrodes. The formed surface films have high ionic conductivity, thereby improving the cycle performance of the battery. Attached Figure Description

[0026] Figure 1 H is a compound having the structure shown in formula (Ⅰ-1) in one embodiment of this application. 1 NMR test image. Detailed Implementation

[0027] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0028] In this application, unless otherwise defined, all technical terms and jargon not explicitly stated have the same meaning as commonly understood by those skilled in the art and are common knowledge to them. Methods not explicitly stated are all conventional methods known to those skilled in the art. The term "multiple" in this application means at least two, such as two, three, etc., unless otherwise explicitly specified. In this application, technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0029] In this application, numerical ranges are referred to as continuous and, unless otherwise specified, include the minimum and maximum values ​​of the range, and every value between such minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0030] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0031] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0032] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0033] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0034] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0035] "Hydrocarbon group" refers to a group that contains only carbon and hydrogen atoms, including but not limited to alkyl, alkenyl, alkynyl, aryl, etc.

[0036] "Alkyl" refers to a saturated hydrocarbon containing a primary (normal) carbon atom, or a secondary carbon atom, or a tertiary carbon atom, or a quaternary carbon atom, or a combination thereof. Phrases containing this term, such as "C1-C9 alkyl," refer to alkyl groups containing 1 to 9 carbon atoms, and each time it appears, it can independently be C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, or C9 alkyl. Suitable examples include, but are not limited to: methyl (Me, -CH3), ethyl (Et, -CH2CH3), 1-propyl (n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1-butyl (n-Bu, n-butyl, -CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH2CH(CH3)2), 2-butyl (s-Bu, s-butyl, -CH(C H3)CH2CH3), 2-methyl-2-propyl (t-Bu, t-butyl, -C(CH3)3), 1-pentyl (n-pentyl, -CH2CH2CH2CH2CH3), 2-pentyl (-CH(CH3)CH2CH2CH3), 3-pentyl (-CH(CH2CH3)2), 2-methyl-2-butyl (-C(CH3)2CH2CH3), 3-methyl-2-butyl (-CH(CH3)CH(CH3)2), 3-methyl-1-butyl (- CH2CH2CH(CH3)2), 2-methyl-1-butyl(-CH2CH(CH3)CH2CH3), 1-hexyl(-CH2CH2CH2CH2CH2CH3), 2-hexyl(-CH(CH3)CH2CH2CH2CH3), 3-hexyl(-CH(CH2CH3)(CH2CH2CH3)), 2-methyl-2-pentyl(-C(CH3)2CH2CH2CH3), 3-methyl-2-pentyl(-CH(CH3)CH( CH3)CH2CH3), 4-methyl-2-pentyl (-CH(CH3)CH2CH(CH3)2), 3-methyl-3-pentyl (-C(CH3)(CH2CH3)2), 2-methyl-3-pentyl (-CH(CH2CH3)CH(CH3)2), 2,3-dimethyl-2-butyl (-C(CH3)2CH(CH3)2), 3,3-dimethyl-2-butyl (-CH(CH3)C(CH3)3 and octyl (-(CH2)7CH3).

[0037] The term "cycloalkyl" refers to a non-aromatic hydrocarbon containing a ring of carbon atoms, which can be monocycloalkyl, spirocycloalkyl, or bridged cycloalkyl. Phrases containing this term, such as "C3-C9 cycloalkyl," refer to cycloalkyl groups containing 3 to 9 carbon atoms, and each occurrence can independently be C3, C4, C5, C6, C7, C8, or C9 cycloalkyl. Suitable examples include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl. Additionally, "cycloalkyl" may contain one or more double bonds; representative examples of cycloalkyl groups containing double bonds include cyclopentenyl, cyclohexenyl, cyclohexadienyl, and cyclobutadienyl.

[0038] The term "alkoxy" refers to a group having an -O-alkyl group, i.e., an alkyl group as defined above connected to the parent nucleus via an oxygen atom. Phrases containing this term, such as "C1-C9 alkoxy," refer to alkyl moieties containing 1 to 9 carbon atoms, and each time it appears, it can be independently C1 alkoxy, C4 alkoxy, C5 alkoxy, C6 alkoxy, C7 alkoxy, C8 alkoxy, or C9 alkoxy. Suitable examples include, but are not limited to: methoxy (-O-CH3 or -OMe), ethoxy (-O-CH2CH3 or -OEt), and tert-butoxy (-OC(CH3)3 or -OtBu).

[0039] The term "unsaturated hydrocarbon group" refers to a hydrocarbon group containing at least one unsaturated site, such as an alkenyl, alkynyl, or aryl group.

[0040] The term "alkenyl" refers to a compound containing at least one unsaturated site, i.e., a carbon-carbon sp group. 2 Hydrocarbons with a double bond consisting of a positive, secondary, tertiary, or cyclic carbon atom. Phrases containing this term, such as "C2-C9 alkenyl," refer to alkenyl groups containing 2 to 9 carbon atoms, and each occurrence can be independently C2, C3, C4, C5, C6, C7, C8, or C9 alkenyl. Suitable examples include, but are not limited to: vinyl (-CH=CH2), allyl (-CH2CH=CH2), cyclopentenyl (-C5H7), and 5-hexenyl (-CH2CH2CH2CH2CH=CH2).

[0041] The term "alkynyl" refers to a hydrocarbon containing at least one unsaturated carbon atom, namely a carbon-carbon sp triple bond, consisting of a positive, secondary, tertiary, or cyclic carbon atom. Phrases containing this term, such as "C2-C9 alkenyl," refer to alkynyl groups containing 2 to 9 carbon atoms, and each occurrence can be independently C2-alkynyl, C3-alkynyl, C4-alkynyl, C5-alkynyl, C6-alkynyl, C7-alkynyl, C8-alkynyl, or C9-alkynyl. Suitable examples include, but are not limited to, ethynyl (-C≡CH) and propynyl (-CH2C≡CH).

[0042] The term "aryl" refers to an aromatic hydrocarbon group derived from an aromatic ring compound by removing one hydrogen atom. It can be a monocyclic aryl, a fused-ring aryl, or a polycyclic aryl; for polycyclic compounds, at least one ring must be an aromatic ring system. For example, "C5-C..." 20 "Aryl" refers to an aryl group containing 5 to 20 carbon atoms. Each time it appears, it can independently be C5 aryl, C6 aryl, C7 aryl, C8 aryl, C9 ... 10 Aryl, C 14 Aryl, C 18 Aryl or C 20 Aryl group. Suitable examples include, but are not limited to: benzene, biphenyl, naphthalene, anthracene, phenanthrene, dinaphthalene, triphenylene and their derivatives. Understandably, multiple aryl groups may also be interrupted by short non-aromatic units (e.g., <10% non-H atoms, such as C, N or O atoms), specifically acenaphthene, fluorene, or 9,9-diarylfluorene, triarylamines, and diaryl ether systems should also be included in the definition of aryl.

[0043] The term "silyl" refers to the -SiR'3 group, where R' is a straight-chain alkyl, branched-chain alkyl, or cycloalkyl group. Each R' can be the same or different. "C1-C6 silyl" means that the total number of carbon atoms in R' is 1 to 6.

[0044] The term "ether group" refers to the -OR' group or the -R'-OR"- group, where R' and R" are straight-chain alkyl, branched alkyl, or cycloalkyl. "C1-C6 ether group" means that the total number of carbon atoms in R' and R" is 1 to 6.

[0045] The term "carboxylic acid ester group" refers to the R'C(O)O- group or the -C(O)OR' group, where R' is a straight-chain alkyl, branched alkyl, or cycloalkyl group. "C2-C6 carboxylic acid ester group" means that R' has 1 to 5 carbon atoms, and can be, but is not limited to, methyl carboxylic acid ester group, ethyl carboxylic acid ester group, n-propyl carboxylic acid ester group, isopropyl carboxylic acid ester group, n-butyl carboxylic acid ester group, isobutyl carboxylic acid ester group, sec-butyl carboxylic acid ester group, tert-butyl carboxylic acid ester group, n-pentyl carboxylic acid ester group, isopentyl carboxylic acid ester group, tert-pentyl carboxylic acid ester group, and neopentyl carboxylic acid ester group.

[0046] The term "fluorine atom" refers to the -F group.

[0047] The term "cyano" refers to the -CN group.

[0048] A first aspect of this application provides an electrolyte comprising a lithium salt, a solvent, and additives.

[0049] The additives include compounds having the general structural formula shown in formula (I):

[0050]

[0051]

[0052] In formula (I), R1, R2, and R3 are each independently selected from hydrogen atoms, substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C1-C6 alkoxy groups, substituted or unsubstituted C3-C6 cycloalkyl groups, substituted or unsubstituted C2-C6 unsaturated hydrocarbon groups, substituted or unsubstituted C1-C6 silyl groups, substituted or unsubstituted C1-C6 ether groups, substituted or unsubstituted C2-C6 carboxylic acid ester groups, fluorine atoms, or cyano groups.

[0053] The electrolyte provided in this application has two advantages. First, the compound having the general structural formula shown in Formula (I) has a mercapto and pyridine structure, and the sulfur atom on the mercapto and the nitrogen atom on the pyridine ring both have lone pairs of electrons, which can coordinate with transition metal ions in situ, thereby inhibiting the reactivity of transition metal ions, reducing the oxidative decomposition and gas production of the electrolyte, preventing them from migrating to the negative electrode side and damaging the SEI film, and improving the cycle performance of the battery. Second, the compound having the general structural formula shown in Formula (I) preferentially undergoes oxidation and reduction reactions on the electrode, and the multiple structures such as biaromatic rings and ketenes contained in the compound can polymerize on the positive and negative electrode surfaces, forming highly chemically stable surface films rich in Li2CO3 (i.e., CEI film and SEI film) on the positive and negative electrode surfaces, respectively, thereby improving the interfacial stability of the positive and negative electrodes. The formed surface films have high ionic conductivity, thereby improving the cycle performance of the battery.

[0054] It is understandable that the thiol group is polar, and the sulfur atom has a lower electronegativity than the oxygen atom. Therefore, the thiol group has a certain positive charge, which is conducive to the coordination of the sulfur atom with the transition metal. Structurally, it also enhances the aromaticity of the pyridine ring and the benzene ring. The aromaticity of the aromatic ring structure is conducive to the formation of CEI and SEI films on the positive and negative electrode surfaces. Therefore, in compounds with the general structural formula shown in formula (I), there is a synergistic effect between the thiol group and the biaromatic ring structure, which jointly improves the cycle stability of the battery.

[0055] In some embodiments, R1 or R2 is an electron-withdrawing group.

[0056] In some embodiments, R3 is an electron-donating group.

[0057] When R1 or R2 is an electron-withdrawing group, or R3 is an electron-donating group, the positive charge of the mercapto group and the aromaticity of the pyridine and benzene rings are further enhanced, thereby further improving the coordination ability of the sulfur atom to transition metal ions and the ability of the aromatic ring structure to form CEI and SEI films. Therefore, when R1 or R2 is an electron-withdrawing group, or R3 is an electron-donating group, the cycle stability of the battery is further improved.

[0058] In some embodiments, R1 or R2 is independently selected from fluorine atoms, cyano groups, and C1-C6 carboxylic acid ester groups.

[0059] In some embodiments, R3 is selected from C1-C6 alkyl, C1-C6 alkoxy, C3-C6 cycloalkyl, and C2-C6 unsaturated hydrocarbon groups.

[0060] In some of these embodiments, the substituents are selected from fluorine atoms or cyano groups.

[0061] In some embodiments, the compound having the general structural formula shown in formula (I) is selected from at least one of the following compounds:

[0062]

[0063] In some embodiments, the compound having the general structural formula shown in formula (I) has a mass percentage of 0.5% to 2% in the electrolyte, including but not limited to 0.5%, 0.8%, 1%, 1.5%, and 2%. Further, the compound having the general structural formula shown in formula (I) has a mass percentage of 0.5% to 1.5% in the electrolyte.

[0064] In some embodiments, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)borate, lithium difluorobis(oxalato)phosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium tetrafluorophosphate, potassium bis(fluorosulfonyl)imide, lithium 4,5-dicyano-2-trifluoromethyl-imidazolium, lithium methyl sulfate, lithium ethyl sulfate, and lithium bis(nonafluorobutylsulfonyl)imide.

[0065] Furthermore, the lithium salt is selected from a mixture of at least three of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorobis(oxalato)phosphate, lithium difluorosulfonylimide, lithium difluorophosphate, and lithium bis(nonafluorobutylsulfonyl)imide.

[0066] Furthermore, lithium salts include lithium hexafluorophosphate.

[0067] In traditional technologies, when lithium salts include lithium hexafluorophosphate, high temperatures promote the decomposition of LiPF6 and generate HF, leading to the decomposition of CEI / SEI and solvent, which corrodes the cathode and causes the dissolution of transition metal ions, thereby accelerating battery aging.

[0068] The electrolyte provided in this application is particularly suitable for lithium hexafluorophosphate electrolyte systems. Compounds with the general structure shown in formula (I) are more likely to combine with HF than solvents, thereby reducing the generation of free acid in the electrolyte. This can further reduce the oxidative decomposition and gas production of the electrolyte, and further stabilize the interfacial film and inhibit the dissolution of transition metal ions, thereby improving the cycle performance of the battery.

[0069] In some embodiments, the solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propyl acetate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate, and ethyl butyrate.

[0070] In some embodiments, the additives also include other additives selected from at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene sulfate, 4-methyl vinyl sulfate, vinyl ethylene carbonate, 4-ethyl vinyl sulfate, lithium difluorophosphate, 1,3-propanesulfonate lactone, vinyl ethylene sulfite, tris(trimethylsilyl)borate, and triallyl isocyanate.

[0071] Furthermore, the other additives are selected from a mixture of at least two of fluoroethylene carbonate, ethylene sulfate, vinylene carbonate, triallyl isocyanate, and 1,3-propane sulcolone (PS).

[0072] In some embodiments, other additives are present in the electrolyte at a mass percentage of 0.5% to 5%, including but not limited to 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%.

[0073] The second aspect of this application provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and the electrolyte provided in the first aspect.

[0074] In some embodiments, the positive electrode includes a positive electrode active material, which includes at least one of lithium nickel cobalt manganese oxide ternary material, lithium manganese iron phosphate material, lithium manganese oxide material, and lithium manganese iron oxide material.

[0075] It is understood that the transition metal ions in the above-mentioned positive electrode active material are easily dissolved during battery cycling. Therefore, the electrolyte system of this application is particularly suitable for lithium-ion battery systems with the above-mentioned positive electrode active material.

[0076] In some embodiments, the negative electrode includes a negative electrode active material, which includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon, silicon-carbon, silicon oxide, and lithium titanate.

[0077] The lithium-ion battery of this application does not have any particular restrictions on the separator. Any well-known porous structure separator with electrochemical and chemical stability can be selected, such as one or more single-layer or multi-layer films of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride (PVDF).

[0078] It is understood that lithium-ion batteries can be prepared and used according to conventional methods known in the art.

[0079] A third aspect of this application provides an electrical device comprising the lithium-ion battery provided in the second aspect above.

[0080] The electrical device used in this application is not particularly limited and can be any electrical device known in the prior art. For example, the electrical device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0081] The present application will be further described below with reference to specific embodiments and comparative examples.

[0082] The synthetic procedure for compounds having the general structural formula shown in formula (Ⅰ) is as follows:

[0083]

[0084] A method for preparing a compound having the general structural formula shown in formula (Ⅰ) includes the following steps:

[0085] Step (1): Mix thiophenol compounds and 3-(3-pyridine)acrylic acid compounds in acetic acid solvent, add I2 catalyst and stir for 24 h, add cold saturated sodium thiosulfate solution, extract with dichloromethane, then mix with saturated sodium bicarbonate solution to remove unreacted starting material, acidify the aqueous layer, extract with dichloromethane again, combine the organic layers and dry, and evaporate the solvent under reduced pressure to obtain the addition product.

[0086] The structural formulas of thiophenol compounds are as follows:

[0087]

[0088] The structural formula of 3-(3-pyridine)acrylic acid compounds is:

[0089]

[0090] The structural formula of the intermediate is:

[0091]

[0092] Step (2): After cooling the addition product to 0°C, dissolve it in CH3Cl solvent, add concentrated sulfuric acid to carry out the cyclization reaction for 2 hours, quench with ice water, and then extract with dichloromethane. Combine the organic layers, wash them successively with cold water and saturated sodium bicarbonate solution, then wash with brine, dry, concentrate under reduced pressure, and purify by silica gel column chromatography using n-hexane / ethyl acetate as eluent to obtain a compound with the general formula shown in formula (I).

[0093] The structural formula of the compound with the general structural formula shown in formula (Ⅰ) is:

[0094]

[0095] In formulas (I) to (IV), R1, R2, and R3 are each independently selected from hydrogen atoms, substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C1-C6 alkoxy groups, substituted or unsubstituted C3-C6 cycloalkyl groups, substituted or unsubstituted C2-C6 unsaturated hydrocarbon groups, substituted or unsubstituted C1-C6 silyl groups, substituted or unsubstituted C1-C6 ether groups, substituted or unsubstituted C2-C6 carboxylic acid ester groups, fluorine atoms, or cyano groups.

[0096] Taking the compound with the structure shown in formula (I-1) as an example: 15 mol of thiophenol and 10 mol of 3-(3-pyridine)acrylic acid were mixed in 20 mL of acetic acid solvent, and 20 mol% I2 catalyst was added. The mixture was stirred for 24 h. After the reaction was completed, a cold saturated sodium thiosulfate solution was added, and the mixture was extracted with dichloromethane. Then, it was mixed with a saturated sodium bicarbonate solution to remove unreacted starting material. The aqueous layer was acidified and extracted with dichloromethane. The organic layers were combined, dried, and the solvent was evaporated under reduced pressure to obtain the addition product. The obtained addition product was cooled to 0 °C, dissolved in 20 mL of CH3Cl solvent, and concentrated sulfuric acid (10% aq) was added to carry out the cyclization reaction. After reacting for 2 h, the reaction was quenched with ice water and then extracted with dichloromethane. The organic layers were combined, washed successively with cold water and saturated sodium bicarbonate solution, then washed with brine, dried, concentrated under reduced pressure, and finally purified by silica gel column chromatography using n-hexane / ethyl acetate as the eluent to obtain the compound with the structure shown in formula (I-1).

[0097] Characteristic: such as Figure 1 As shown, H 1 NMR(400HZ, CDCl3)3.21-3.41(m,2H,CH2),4.98(ddd,1H,CH),6.97(dd,1H,ArH),7.07(dd ,1H,ArH),7.21(ddd,1H,ArH),7.27-7.31(m,3H,ArH),7.42(ddd,1H,ArH),8.46(dd,1H); 13CNMR(100HZ, CDCl3)39.5,45.5,122.9,121,122.9,125,126.7,129,130.4,133.3,136.4,142.1,148.3,163.4,194.3; m / z 241.6.

[0098] The synthesis methods of the compounds with the structures shown in Formula (I-2), (I-3), (I-4) and (I-5) used in Examples 2-5 below are exactly the same as the synthesis methods of the compounds with the structure shown in Formula (I-1) above, except that the thiophenol and 3-(3-pyridine)acrylic acid are adjusted accordingly.

[0099] Example 1

[0100] Electrolyte:

[0101] S1. In a glove box filled with argon (moisture <10ppm, oxygen <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed evenly in a mass ratio of 30:60:10 to obtain a solvent.

[0102] S2. Lithium hexafluorophosphate (LiPF6) is added to the solvent for dissolution. The concentration of LiPF6 is 1.15 mol / L.

[0103] S3. Add the compound having the structure shown in formula (Ⅰ-1), vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2) and 1,3-propane sulpholol (PS) as additives to the solvent, and stir until homogeneous to obtain the electrolyte.

[0104]

[0105] Among them, the mass percentage of the compound having the structure shown in formula (Ⅰ-1) in the electrolyte is 1.5%, the mass percentage of VC in the electrolyte is 1%, the mass percentage of LiPO2F2 in the electrolyte is 0.5%, and the mass percentage of PS in the electrolyte is 1%.

[0106] Lithium-ion batteries:

[0107] The prepared electrolyte is injected into a fully dried 4.35V NCM622 / graphite soft-pack battery. After processes such as 45°C resting, high-temperature fixture formation, and secondary sealing, the battery is obtained.

[0108] Example 2

[0109] The electrolyte and lithium-ion battery in this embodiment are basically the same as those in Example 1, except that:

[0110] In step S3, the compound having the structure shown in formula (I-1) is replaced with the compound having the structure shown in formula (I-2).

[0111]

[0112] Example 3

[0113] The electrolyte and lithium-ion battery in this embodiment are basically the same as those in Example 1, except that:

[0114] In step S3, the compound having the structure shown in formula (I-1) is replaced with the compound having the structure shown in formula (I-3).

[0115]

[0116] Example 4

[0117] The electrolyte and lithium-ion battery in this embodiment are basically the same as those in Example 1, except that:

[0118] In step S3, the compound having the structure shown in formula (I-1) is replaced with the compound having the structure shown in formula (I-4).

[0119]

[0120] Example 5

[0121] The electrolyte and lithium-ion battery in this embodiment are basically the same as those in Example 1, except that:

[0122] In step S3, the compound having the structure shown in formula (I-1) is replaced with the compound having the structure shown in formula (I-5).

[0123]

[0124] Example 6

[0125] The electrolyte and lithium-ion battery in this embodiment are basically the same as those in Example 1, except that:

[0126] In step S3, the compound having the structure shown in formula (Ⅰ-1) has a mass percentage of 0.5% in the electrolyte.

[0127] Example 7

[0128] The electrolyte and lithium-ion battery in this embodiment are basically the same as those in Example 1, except that:

[0129] In step S3, the mass percentage of the compound having the structure shown in formula (Ⅰ-1) in the electrolyte is 2%.

[0130] Comparative Example 1

[0131] Electrolyte:

[0132] S1. In a glove box filled with argon (moisture <10ppm, oxygen <1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed evenly in a mass ratio of 30:60:10 to obtain a solvent.

[0133] S2. Lithium hexafluorophosphate (LiPF6) is added to the solvent for dissolution. The concentration of LiPF6 is 1.15 mol / L.

[0134] S3. Add vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2), and 1,3-propanesulfonyl lactone (PS) to the solvent as additives, and stir until homogeneous to obtain the electrolyte.

[0135] The electrolyte contains 1% VC by mass, 0.5% LiPO2F2 by mass, and 1% PS by mass.

[0136] Lithium-ion batteries:

[0137] The prepared electrolyte is injected into a fully dried 4.35V NCM622 / graphite soft-pack battery. After processes such as 45°C resting, high-temperature fixture formation, and secondary sealing, the battery is obtained.

[0138] Comparative Example 2

[0139] The electrolyte and lithium-ion battery in this comparative example are basically the same as those in Example 1, except that:

[0140] In step S3, the mass percentage of the compound having the structure shown in formula (Ⅰ-1) in the electrolyte is 0.05%.

[0141] Comparative Example 3

[0142] The electrolyte and lithium-ion battery in this comparative example are basically the same as those in Example 1, except that:

[0143] In step S3, the compound having the structure shown in formula (Ⅰ-1) has a mass percentage of 3% in the electrolyte.

[0144] Comparative Example 4

[0145] The electrolyte and lithium-ion battery in this comparative example are basically the same as those in Example 1, except that:

[0146] In step S3, the compound having the structure shown in formula (I-1) is replaced with the compound having the structure shown in formula (V):

[0147]

[0148] Test case

[0149] (1) Cyclic performance test

[0150] The lithium-ion batteries of the examples and comparative examples were placed in a 45°C constant temperature chamber and left to stand for 30 minutes to allow them to reach a constant temperature. They were then charged at a constant current of 1C until the voltage reached 4.3V, then charged at a constant voltage of 4.35V until the current reached 0.05C, and finally discharged at a constant current of 1C until the voltage reached 2.8V. The first discharge capacity of the battery was recorded as C0. This constitutes one charge-discharge cycle.

[0151] Then, the battery was charged and discharged at 1C / 1C for 500 cycles at 45℃. The discharge capacity was denoted as C1. The capacity retention rate of the lithium-ion battery was calculated using the following formula: Capacity retention rate = (C1 / C0) * 100%. The test results are shown in Table 1.

[0152] (2) High-temperature storage performance test

[0153] At room temperature (25°C), the lithium-ion batteries of the examples and comparative examples were charged to 4.35V at a constant current and constant voltage of 0.5C, and then placed in a 55°C high-temperature chamber for 90 days to test the thickness increase rate of the batteries after storage. The test results are shown in Table 1.

[0154] (3) ICP test

[0155] Weigh out two portions of negative electrode powder (accurate to ±0.0003g) of each example and comparative example, about 0.1g each, and place them in a 100mL beaker. Add a small amount of distilled water to wet the bottom of the beaker, then add 5mL of 12mol / L HCl to dissolve it. Heat on an electric heating plate for 20min, remove and cool, and dilute before testing.

[0156] A series of prepared standard solutions were introduced into an iCAP7000 inductively coupled plasma optically variable instrument (ICP). The intensity of each element in the standard solution was measured at the wavelength of the element to be measured (nickel, cobalt, manganese). The determination could be performed when the linear correlation coefficient r of the working curve was ≥0.9995. The test results are shown in Table 1.

[0157] Table 1

[0158]

[0159] As shown in Table 1, comparing Examples 1-7 and Comparative Examples 1-4, it can be seen that the electrolyte provided in this application, because it includes a compound having a general structure as shown in Formula (I), suppresses the generation of gas in the electrolyte and the damage of transition metal ions to the SEI film on the negative electrode side, and the prepared lithium-ion battery has a better capacity retention rate.

[0160] Comparing Examples 1-5, it can be seen that when R1 or R2 is an electron-withdrawing group, or R3 is an electron-donating group, the positive charge of the thiol group is stronger, and the aromaticity of the pyridine ring is stronger. This further enhances the synergistic effect between the thiol group and the pyridine ring, which is beneficial for coordination with transition metal ions and participation in the reaction at the positive and negative electrode interfaces to form CEI and SEI films, thereby improving the high-temperature cycle performance and high-temperature storage performance of the battery.

[0161] Comparing Examples 1-7 with Comparative Examples 2 and 3, it can be seen that the high-temperature storage and high-temperature cycling performance of the battery is closely related to the amount of compound with the general structure shown in Formula (I). When the amount added is increased to 3%, its high-temperature storage and high-temperature cycling performance decreases. This may be because when the amount added is too large, it does not react completely with the positive and negative electrode interfaces in the early stage of the reaction. In the later cycle, it continuously interacts with the active potential of the positive electrode interface under high SOC state, causing the impedance to continuously increase.

[0162] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0163] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An electrolyte, characterized in that, include: Lithium salts, solvents, and additives; The additives include compounds having the general structural formula shown in formula (I): In formula (I), R1, R2, and R3 are each independently selected from hydrogen atoms, substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C1-C6 alkoxy groups, substituted or unsubstituted C3-C6 cycloalkyl groups, substituted or unsubstituted C2-C6 unsaturated hydrocarbon groups, substituted or unsubstituted C1-C6 silyl groups, substituted or unsubstituted C1-C6 ether groups, substituted or unsubstituted C2-C6 carboxylic acid ester groups, fluorine atoms, or cyano groups.

2. The electrolyte according to claim 1, characterized in that, The R1 or the R2 is an electron-withdrawing group; and / or, R3 is an electron-donating group.

3. The electrolyte according to claim 2, characterized in that, R1 or R2 is each independently selected from fluorine atoms, cyano groups, and C1-C6 carboxylic acid ester groups; and / or, The R3 is selected from C1-C6 alkyl, C1-C6 alkoxy, C3-C6 cycloalkyl and C2-C6 unsaturated hydrocarbon groups.

4. The electrolyte according to claim 1, characterized in that, The substituents are selected from fluorine atoms or cyano groups.

5. The electrolyte according to claim 1, characterized in that, The compound having the general structural formula shown in formula (I) is selected from at least one of the following compounds:

6. The electrolyte according to any one of claims 1 to 5, characterized in that, The compound having the general structural formula shown in formula (I) is present in the electrolyte at a mass percentage of 0.5% to 2%.

7. The electrolyte according to any one of claims 1 to 5, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)borate, lithium difluorobis(oxalato)phosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium tetrafluorophosphate, potassium bis(fluorosulfonyl)imide, lithium 4,5-dicyano-2-trifluoromethyl-imidazolium, lithium methyl sulfate, lithium ethyl sulfate, and lithium bis(nonafluorobutylsulfonyl)imide; and / or, The solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propyl acetate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate, and ethyl butyrate; and / or, The additives also include other additives selected from at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene sulfate, 4-methyl vinyl sulfate, vinyl ethylene carbonate, 4-ethyl vinyl sulfate, lithium difluorophosphate, 1,3-propanesulfonate lactone, vinyl vinyl sulfite, tris(trimethylsilyl)borate, and triallyl isocyanate.

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

9. The lithium-ion battery according to claim 8, characterized in that, The positive electrode includes a positive electrode active material, which includes at least one of lithium nickel cobalt manganese oxide ternary material, lithium manganese iron phosphate material, lithium manganese oxide material, and lithium manganese iron oxide material.

10. An electrical appliance, characterized in that, The electrical device includes the lithium-ion battery as described in claim 8 or 9.

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