Electrolyte additive, electrolyte and lithium ion secondary battery comprising electrolyte additive

Abstract

The invention provides an electrolyte additive, an electrolyte and a lithium ion secondary battery containing the electrolyte additive. The electrolyte additive contains a substance represented by formula (1): # imgabs0 # wherein R1 is present or absent, and in the presence of R1, R1 is any one of halogen, a substituted or unsubstituted alkyl group having 1-5 carbon atoms, a substituted or unsubstituted alkoxy group having 1-5 carbon atoms, an ester group, and a substituted or unsubstituted aryl group; r2 is any one of a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms and a substituted or unsubstituted aryl group; and at least one of R1 and R2 contains a fluorine atom. According to the electrolyte additive, the electrolyte containing the electrolyte additive and the lithium ion secondary battery containing the electrolyte, the cycle performance of the lithium ion secondary battery is improved, and the impedance of the lithium ion secondary battery is reduced.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion secondary batteries, and in particular to an electrolyte additive, an electrolyte containing the electrolyte additive, and a lithium ion secondary battery containing the electrolyte. Background Art

[0002] In recent years, with the continuous development of electronic technology, people's demand for battery devices used to support the energy supply of electronic devices has also been increasing. Nowadays, batteries that can store more electricity and output high power are needed. Traditional lead-acid batteries and nickel-metal hydride batteries can no longer meet the needs of new electronic products such as mobile devices such as smartphones and fixed devices such as power storage systems. Therefore, lithium-ion batteries have attracted widespread attention. In the process of developing lithium-ion batteries, their capacity and performance have been effectively improved.

[0003] Lithium-ion secondary batteries include positive electrodes, negative electrodes and electrolytes. Electrolyte additives for lithium-ion secondary batteries have an important influence on the overall performance of the battery. Electrolyte additives for lithium-ion secondary batteries have been studied. Among them, the high oxidation stability of fluorine-containing organic compounds makes them an ideal choice for lithium-ion secondary battery electrolyte components. The introduction of fluorine into electrolyte salts, solvents (co-solvents) and functional additive molecules is a key method to improve the overall performance and reliability of lithium-ion secondary batteries, which can more effectively form solid electrolyte interphases (SEI) and positive electrode electrolyte interphases (CEI), with better thermal and electrochemical stability and low and high temperature characteristics. Another advantage of fluorine is that it makes the usually flammable electrolyte less flammable. Fluorination of electrolyte components helps to improve the performance of lithium-ion secondary batteries and safety has been widely verified. Fluorinated sulfones are considered to be a very promising electrolyte additive.

[0004] However, in the prior art, in the electrolyte additives of lithium-ion secondary batteries, the selected fluorinated sulfone compounds mainly introduce fluorine substitution on one side of the sulfone structure, and the substituent on the other side is a chain alkane or a benzene ring pyridine group. This type of structure has limited effect on the action of lithium ions, and the impedance increases significantly after film formation on the negative electrode surface, and the cycle performance deteriorates seriously. Summary of the invention

[0005] The main purpose of the present invention is to provide an electrolyte additive, an electrolyte containing the electrolyte additive, and a lithium ion secondary battery containing the electrolyte, so as to solve the problem in the prior art that fluorinated sulfone compounds cause increased impedance and deteriorated cycle performance of lithium ion secondary batteries.

[0006] In order to achieve the above object, according to one aspect of the present invention, there is provided an electrolyte additive, the electrolyte additive comprising a substance represented by the following formula (1):

[0007]

[0008] Among them, R 1 is present or not, in R 1 In the presence of 1 is any one of halogen, substituted or unsubstituted alkyl having 1 to 5 carbon atoms, substituted or unsubstituted alkoxy having 1 to 5 carbon atoms, ester group and substituted or unsubstituted aryl group; R 2 is any one of a substituted or unsubstituted alkyl group and a substituted or unsubstituted aryl group having 1 to 5 carbon atoms; and R 1 and R 2 At least one of the above contains a fluorine atom.

[0009] Furthermore, in the above electrolyte additive, R 1 does not exist, and R 2 is a fluorine-substituted alkyl group having 1 to 5 carbon atoms, preferably, R 2 is a fluorine-substituted alkyl group having 1 to 3 carbon atoms, more preferably, R 2 It is any of monofluoromethyl, difluoromethyl and trifluoromethyl.

[0010] Furthermore, in the above electrolyte additive, R 1 is halogen, preferably, R 1 is fluorine, and R 2 It is a halogen-substituted alkyl group having 1 to 5 carbon atoms.

[0011] Furthermore, in the above electrolyte additive, R 1 is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, and R 2 It is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.

[0012] Furthermore, in the above electrolyte additive, the electrolyte additive comprises any one of the following substances:

[0013]

[0014] as well as

[0015] According to another aspect of the present invention, an electrolyte is provided, comprising an organic solvent, a lithium salt and the electrolyte additive described above.

[0016] Further, in the above electrolyte, based on 100 parts by weight of the organic solvent and the lithium salt, the amount of the electrolyte additive is in the range of 0.01 parts by weight to 3.0 parts by weight, preferably, the amount of the electrolyte additive is in the range of 0.1 parts by weight to 1.0 parts by weight.

[0017] Furthermore, in the above electrolyte, the organic solvent includes linear carbonate, cyclic carbonate or a combination thereof.

[0018] Furthermore, in the above-mentioned electrolyte, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dihexyl carbonate, ethyl methyl carbonate, methylpropyl carbonate and propyl propionate.

[0019] Furthermore, in the above electrolyte, the electrolyte further comprises fluoroethylene carbonate. Preferably, based on 100 parts by weight of the organic solvent and the lithium salt, the amount of the fluoroethylene carbonate is in the range of 1.0 parts by weight to 13.0 parts by weight.

[0020] According to another aspect of the present invention, there is provided a lithium ion secondary battery, comprising: a positive electrode, a negative electrode, a separator, and the electrolyte described above.

[0021] The electrolyte additive, the electrolyte containing the electrolyte additive and the lithium ion secondary battery containing the electrolyte of the present invention improve the cycle performance of the lithium ion secondary battery and reduce the impedance of the lithium ion secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The dQ / dV curves of the batteries in Example 4, Example 9, Example 13 and Comparative Example 1 when charged for the first time are shown.

[0023] Figure 2 The dQ / dV curves of the batteries in Example 1, Example 2 and Comparative Example 2 when charged for the first time are shown.

[0024] Figure 3 The relationship curves between the discharge capacity and coulombic efficiency of the batteries in Example 1, Example 2 and Comparative Example 2 and the number of cycles are shown. DETAILED DESCRIPTION

[0025] It should be noted that, in the absence of conflict, the various embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments. The following embodiments are merely exemplary and are not intended to limit the scope of protection of the present invention.

[0026] As described in the background art, the fluorinated sulfone compounds in the prior art have the problem of increasing the impedance and deteriorating the cycle performance of lithium-ion secondary batteries. In view of the problems in the prior art, a typical embodiment of the present invention provides an electrolyte additive, which includes a substance represented by the following formula (1):

[0027]

[0028] Among them, R 1 is present or not, in R 1 In the presence of 1 is any one of halogen, substituted or unsubstituted alkyl having 1 to 5 carbon atoms, substituted or unsubstituted alkoxy having 1 to 5 carbon atoms, ester group and substituted or unsubstituted aryl group; R 2 is any one of a substituted or unsubstituted alkyl group and a substituted or unsubstituted aryl group having 1 to 5 carbon atoms; and R 1 and R 2 At least one of the above contains a fluorine atom.

[0029] In the electrolyte additive of the present invention, the benzothiazole group and the sulfone group (-SO2-) on the left side of formula (1) are conjugated by electron transfer to achieve the right side R 2 The decomposition reaction activity of the group during the electrochemical reaction, the decomposition product plays a protective role after forming a film on the electrode surface, improving the performance of the lithium-ion secondary battery, and at the same time, the electron pairs of the S and N atoms contained in the benzothiazole group itself can also interact with lithium ions to improve the transmission of lithium ions. The structure shown in formula (1) can provide fluoride ions to form lithium fluoride, and the decomposition product can form a protective film on the electrode surface.

[0030] The electrolyte additive of the present invention comprises a fluorinated sulfone structure substituted by benzothiazole as shown in formula (1), which improves the conductivity of the electrolyte and enhances the cycle stability of the lithium ion secondary battery through good lithium ion solvation, and the sulfone structure will not have a gas production problem. The sulfone structure substituted by benzothiazole introduced into the electrolyte additive of the present invention can enhance the stability of the lithium ionization process and improve the transmission performance of lithium ions due to the increase of the conjugated system and the electron-rich characteristics of the thiazole ring. At the same time, its conjugated system has antioxidant properties, which is conducive to alleviating the degradation and decomposition during high-temperature cycles. Through the electrolyte additive of the present invention, the cycle performance of the lithium ion secondary battery is improved and the impedance of the lithium ion secondary battery is reduced.

[0031] R 1 It can be present or not. 1 In the presence of 1The electronic effect of the benzothiazolyl group and the entire compound plays an important role in improving the performance of lithium-ion secondary batteries. 1 It may be an electron-withdrawing halogen such as fluorine (F), chlorine (Cl), bromine (Br) or iodine (I), or may be a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, or may be a substituted or unsubstituted alkoxy group having 1 to 5 carbon atoms, or may be an ester group having a conjugated effect or a substituted or unsubstituted aryl group, etc. 1 In the case of the above groups, the performance of the lithium ion secondary battery can be improved.

[0032] In some embodiments of the present invention, halogen can be, for example, fluorine (F), chlorine (Cl), bromine (Br) or iodine (I). In some embodiments of the present invention, unsubstituted alkyl can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl, etc.

[0033] In some embodiments of the present invention, in formula (1), R 1 does not exist, and R 2 is a fluorine-substituted alkyl group having 1 to 5 carbon atoms, preferably, R 2 is a fluorine-substituted alkyl group having 1 to 3 carbon atoms, more preferably, R 2 It is any of monofluoromethyl, difluoromethyl and trifluoromethyl.

[0034] In some embodiments of the present invention, in formula (1), R 1 is halogen, preferably, R 1 is fluorine, and R 2 It is a halogen-substituted alkyl group having 1 to 5 carbon atoms.

[0035] In some embodiments of the present invention, in formula (1), R 1 is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, and R 2 It is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.

[0036] In some embodiments of the present invention, in order to further improve the cycle performance of the lithium ion secondary battery and further reduce the impedance of the lithium ion secondary battery, the electrolyte additive includes any one of the following substances:

[0037]

[0038] as well as

[0039] In another typical embodiment of the present invention, an electrolyte is provided, comprising an organic solvent, a lithium salt and the electrolyte additive described above. The electrolyte additive of the present invention comprises a fluorinated sulfone structure substituted by benzothiazole as shown in formula (1), which improves the conductivity of the electrolyte and the cycle stability of the lithium ion secondary battery through good solvation of lithium ions, and the sulfone structure will not have a gas production problem. The sulfone structure substituted by benzothiazole introduced in the electrolyte additive of the present invention can enhance the stability of the lithium ionization process and improve the transmission performance of lithium ions due to the increase of the conjugated system and the electron-rich characteristics of the thiazole ring. At the same time, its conjugated system has antioxidant properties, which is conducive to alleviating the degradation and decomposition during high-temperature cycles. The electrolyte of the present invention is used to improve the cycle performance of lithium ion secondary batteries and reduce the impedance of lithium ion secondary batteries.

[0040] In some embodiments of the present invention, in the electrolyte of the present invention, based on 100 parts by weight of the organic solvent and the lithium salt, the amount of the electrolyte additive is in the range of 0.01 parts by weight to 3.0 parts by weight, preferably, the amount of the electrolyte additive is in the range of 0.1 parts by weight to 1.0 parts by weight. By controlling the amount of the electrolyte additive within the above range, the cycle performance of the lithium ion secondary battery can be improved and the impedance of the lithium ion secondary battery can be reduced.

[0041] Specifically, based on 100 parts by weight of the organic solvent and the lithium salt, the amount of the electrolyte additive can be in the following range: 0.05 parts by weight to 2.95 parts by weight, 0.1 parts by weight to 2.9 parts by weight, 0.15 parts by weight to 2.85 parts by weight, 0.2 parts by weight to 2.8 parts by weight, 0.25 parts by weight to 2.75 parts by weight, 0.3 parts by weight to 2.7 parts by weight, 0.35 parts by weight to 2.65 parts by weight, 0.4 parts by weight to 2.6 parts by weight, 0.45 parts by weight to 2.55 parts by weight, 0.5 parts by weight to 2.5 parts by weight, 0.55 parts by weight to 2.45 parts by weight, 0.6 parts by weight to 2.4 parts by weight, 0.65 parts by weight to 2.35 parts by weight, 0.7 parts by weight to 2.3 parts by weight, 0.75 parts by weight to 2.25 parts by weight, 0.8 parts by weight to 2.2 parts by weight, 0.85 parts by weight to 2. parts by weight, 0.9 parts by weight to 2.15 parts by weight, 0.9 parts by weight to 2.1 parts by weight, 0.95 parts by weight to 2.05 parts by weight, 1.0 parts by weight to 2.0 parts by weight, 1.05 parts by weight to 1.95 parts by weight, 1.1 parts by weight to 1.9 parts by weight, 1.15 parts by weight to 1.85 parts by weight, 1.2 parts by weight to 1.8 parts by weight, 1.25 parts by weight to 1.75 parts by weight, 1.3 parts by weight to 1.7 parts by weight , 1.35 to 1.65 parts by weight, 1.4 to 1.6 parts by weight, 1.45 to 1.55 parts by weight, 0.05 to 0.95 parts by weight, 0.15 to 0.85 parts by weight, 0.25 to 0.75 parts by weight, 0.35 to 0.65 parts by weight, 0.45 to 0.55 parts by weight, 0.50 to 0.55 parts by weight.

[0042] In some embodiments of the present invention, in the electrolyte of the present invention, the organic solvent includes a linear carbonate, a cyclic carbonate or a combination thereof. Preferably, the organic solvent includes a combination of a linear carbonate and a cyclic carbonate. In the case where the electrolyte includes a linear carbonate solvent, a cyclic carbonate solvent, a lithium salt and an additive shown by the above formula (1), the cycle performance of the lithium ion secondary battery can be significantly improved and the impedance of the lithium ion secondary battery can be significantly reduced.

[0043] In the present invention, the organic solvent may be any organic solvent used in the electrolyte to date. Examples of organic solvents include, but are not limited to: linear carbonates and / or cyclic carbonates, such as ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, fluoroethylene carbonate, vinylene carbonate; ethers, such as 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether; sulfones, such as cyclopentane sulfone, methylcyclopentane sulfone; nitriles, such as acetonitrile, propionitrile, acrylonitrile; esters, such as acetate, propionate, butyrate, etc. These organic solvents may be used alone or in combination. In some embodiments of the present invention, in the electrolyte of the present invention, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dihexyl carbonate, ethyl methyl carbonate, methylpropyl carbonate and propyl propionate. In a preferred embodiment, at least one carbonate is used as the organic solvent of the electrolyte of the present invention. In a preferred embodiment, at least one linear carbonate and at least one cyclic carbonate are used together as the organic solvent of the electrolyte of the present invention.

[0044] The present invention has no particular restrictions on the lithium salt contained in the electrolyte, and any lithium salt known in the prior art that can be used in lithium battery electrolytes can be used. Examples of lithium salts may include: one or more of LiCl, LiBr, LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2F)2, LiN(CF3SO2)2, LiC(CF3SO2)3, LiAlCl4, and Li2SiF6.

[0045] In some embodiments of the present invention, in the electrolyte of the present invention, the electrolyte further comprises fluoroethylene carbonate, preferably, based on 100 parts by weight of the organic solvent and the lithium salt, the amount of the fluoroethylene carbonate is in the range of 1.0 parts by weight to 13.0 parts by weight. Fluoroethylene carbonate (FEC) can be used as a negative electrode film-forming additive. By combining the electrolyte additive shown by the above formula (1) with the negative electrode film-forming additive (FEC), a synergistic effect can be produced to jointly improve the performance of the lithium ion secondary battery.

[0046] In another typical embodiment of the present invention, a lithium ion secondary battery is provided, comprising: a positive electrode, a negative electrode, a separator, and the electrolyte described above. Since the lithium ion secondary battery of the present invention uses the electrolyte described above, the lithium ion secondary battery has improved cycle performance and reduced impedance.

[0047] The lithium-ion secondary battery of the present invention can be used in battery packs, electric vehicles, power storage systems, electric tools or electronic devices.

[0048] The positive electrode of the present invention includes a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material. The positive electrode active material layer is formed on both surfaces of the positive electrode current collector. A metal foil such as aluminum foil, nickel foil or stainless steel foil can be used as the positive electrode current collector.

[0049] The positive electrode active material layer contains one or more positive electrode materials capable of inserting and extracting lithium ions as the positive electrode active material, and may contain additional materials such as a positive electrode binder and / or a positive electrode conductive agent if necessary.

[0050] Preferably, the positive electrode material is a lithium-containing compound. Examples of such lithium-containing compounds include lithium-transition metal composite oxides, lithium-transition metal phosphate compounds, and the like. The lithium-transition metal composite oxide is an oxide containing Li and one or more transition metal elements as constituent elements, and the lithium-transition metal phosphate compound is a phosphate compound containing Li and one or more transition metal elements as constituent elements. The transition metal element is advantageously one or more of Co, Ni, Mn, Fe, etc.

[0051] Examples of the lithium-transition metal composite oxide can include, for example, LiCoO2 and LiNiO2, etc. Examples of the lithium-transition metal phosphate compound can include, for example, LiFePO4 and LiFe 1-u Mn u PO4 (0 < u < 1), etc.

[0052] The negative electrode of the present invention includes a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material. The negative electrode active material layer is formed on both surfaces of the negative electrode current collector. A metal foil such as copper (Cu) foil, nickel foil or stainless steel foil can be used as the negative electrode current collector.

[0053] The negative electrode active material layer contains one or more negative electrode materials capable of inserting and extracting lithium ions as the negative electrode active material, and may contain additional materials such as a negative electrode binder and / or a negative electrode conductive agent if necessary.

[0054] The negative electrode active material can be selected from one or more of lithium metal, lithium alloy, carbon material, silicon or tin and their oxides.

[0055] The separator of the present invention is used to separate the positive electrode and the negative electrode in a battery, and allows lithium ions to pass through it while preventing current short - circuit caused by contact between the positive electrode and the negative electrode. The separator is, for example, a porous membrane formed of a synthetic resin or ceramic, and may be a laminated membrane in which two or more porous membranes are laminated. Examples of synthetic resins include, for example, polytetrafluoroethylene, polypropylene, and polyethylene, etc.

[0056] In an embodiment of the present invention, when charging a lithium - ion secondary battery, for example, lithium ions are released from the positive electrode and embedded in the negative electrode through the electrolyte impregnated in the separator. When discharging a lithium - ion secondary battery, for example, lithium ions are released from the negative electrode and embedded in the positive electrode through the electrolyte impregnated in the separator.

[0057] Through the electrolyte additive of the present invention, the electrolyte containing the electrolyte additive, and the lithium - ion secondary battery containing the electrolyte, the cycle performance of the lithium - ion secondary battery is improved and the impedance of the lithium - ion secondary battery is reduced.

[0058] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0059] Examples

[0060] Example 1

[0061] Preparation of the positive electrode

[0062] 95.5 g of lithium nickel cobalt aluminum oxide (NCA) positive - electrode active material, 2.5 g of conductive carbon black, 1.9 g of polyvinylidene fluoride, and 0.1 g of polyvinylpyrrolidone dispersant are mixed to obtain a positive - electrode mixture, and the obtained mixture is dispersed in N - methylpyrrolidone to obtain a positive - electrode mixture slurry. Subsequently, the obtained positive - electrode mixture slurry is uniformly coated on a positive - electrode current collector formed of aluminum foil to obtain a positive - electrode active - material layer, the positive - electrode active - material layer is dried, and a positive - electrode plate is formed using a stamping process.

[0063] Preparation of the negative electrode

[0064] 95.85 g of a silicon suboxide (SiOx, 1 < x < 2) and graphite powder mixture (weight ratio of silicon suboxide to graphite is 1:8), 1.0 g of Super P conductive agent, 3.15 g of CMC (sodium carboxymethyl cellulose) and SBR (styrene - butadiene rubber) binder, and an appropriate amount of water are stirred to prepare a negative - electrode mixture slurry. Then the obtained negative - electrode mixture slurry is uniformly coated on a negative - electrode current collector formed of copper foil to obtain a negative - electrode active - material layer, the negative - electrode active - material layer is dried, and a negative - electrode plate is formed using a stamping process.

[0065] Preparation of the electrolyte

[0066] 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 0.5 g of an electrolyte additive having a structure represented by formula (1-1) and 13.0 g of fluoroethylene carbonate (FEC) were added to the electrolyte, and the mixture was stirred for use.

[0067]

[0068] Battery Assembly

[0069] Assemble CR2016 button cells in a dry laboratory. Use the positive electrode sheet prepared in the above steps as the positive electrode, the negative electrode sheet as the negative electrode, and the electrolyte prepared in Example 1 as the electrolyte. Assemble the positive electrode, the negative electrode, the separator and the battery shell of the button cell. After the battery is assembled, let it stand for 24 hours to age, thereby obtaining a button cell.

[0070] Example 2

[0071] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, 0.5 g of an electrolyte additive having a structure represented by formula (1-2) and 13.0 g of fluoroethylene carbonate (FEC) were added to the electrolyte, and the mixture was stirred evenly and set aside.

[0072]

[0073] Example 3

[0074] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, 0.1 g of an electrolyte additive having a structure represented by formula (1-3) was added to the above electrolyte, and the mixture was stirred evenly for later use.

[0075]

[0076] Example 4

[0077] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 0.5 g of an electrolyte additive having a structure represented by formula (1-3) was added to the above electrolyte, and the mixture was stirred evenly and set aside.

[0078] Example 5

[0079] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, 1.0 g of an electrolyte additive having a structure represented by formula (1-3) was added to the above electrolyte, and the mixture was stirred evenly and set aside.

[0080] Example 6

[0081] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, 0.01 g of an electrolyte additive having a structure represented by formula (1-3) was added to the above electrolyte, and the mixture was stirred evenly for later use.

[0082] Example 7

[0083] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, 3.0 g of an electrolyte additive having a structure represented by formula (1-3) was added to the above electrolyte, and the mixture was stirred evenly and set aside.

[0084] Example 8

[0085] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, 0.1 g of an electrolyte additive having a structure represented by formula (1-2) was added to the above electrolyte, and the mixture was stirred evenly for later use.

[0086] Example 9

[0087] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 0.5 g of an electrolyte additive having a structure represented by formula (1-2) was added to the above electrolyte, and the mixture was stirred evenly and set aside.

[0088] Example 10

[0089] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, 1.0 g of an electrolyte additive having a structure represented by formula (1-2) was added to the above electrolyte, and the mixture was stirred evenly for later use.

[0090] Embodiment 11

[0091] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, 0.01 g of an electrolyte additive having a structure represented by formula (1-2) was added to the above electrolyte, and the mixture was stirred evenly for later use.

[0092] Example 12

[0093] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, 3.0 g of an electrolyte additive having a structure represented by formula (1-2) was added to the above electrolyte, and the mixture was stirred evenly and set aside.

[0094] Example 13

[0095] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 0.5 g of an electrolyte additive having a structure represented by formula (1-1) was added to the above electrolyte, and the mixture was stirred evenly and set aside.

[0096] Embodiment 14

[0097] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, 0.5 g of an electrolyte additive having a structure represented by formula (1-3) and 1.0 g of fluoroethylene carbonate (FEC) were added to the electrolyte, and the mixture was stirred evenly and set aside.

[0098] Comparative Example 1

[0099] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, which was stirred evenly and set aside.

[0100] Comparative Example 2

[0101] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 13.0 g of fluoroethylene carbonate (FEC) was added to the electrolyte, stirred evenly and set aside.

[0102] Comparative Example 3

[0103] A button cell was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.9 g of ethyl methyl carbonate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, 1.0 g of fluoroethylene carbonate (FEC) was added to the electrolyte, and the mixture was stirred evenly for later use.

[0104] Battery performance test method:

[0105] Cycle Test

[0106] The first charge and discharge and cycle test were carried out on a Xinwei charge and discharge instrument. The batteries in Examples 1-14 and Comparative Examples 1-3 were first subjected to a 0.1C cycle test at 23°C for one time, and then subjected to a 0.5C charge and 5C discharge cycle test at 60°C for 100 times.

[0107] The capacity retention rate of the battery after 100 cycles=discharge capacity at the 100th cycle of 5C discharge / discharge capacity at the 1st cycle of 5C discharge×100%.

[0108] Impedance test:

[0109] After 100 cycles, the batteries in Examples 1-14 and Comparative Examples 1-3 were subjected to a 0.5C charging test once. After standing at room temperature for 1 hour, the impedance value of the battery was tested by an electrochemical workstation in a frequency range of (500MHz-50mHz).

[0110] The experimental results are shown in Table 1. Figure 1 , Figure 2 and Figure 3 Shown in.

[0111] Figure 1The dQ / dV curves of the batteries in Example 4, Example 9, Example 13 and Comparative Example 1 when first charged are shown. Figure 1 It can be seen that in the electrolyte of Comparative Example 1, there is only the reduction peak of the solvent ethylene carbonate (EC). After adding the electrolyte additive with the structure shown by formula (1-3), formula (1-2) or formula (1-1) to the electrolyte, an obvious reduction peak appears in the battery, and the reduction potential is significantly lower than the reduction potential of the solvent ethylene carbonate (EC). This shows that the electrolyte additive with the structure shown by formula (1-3), formula (1-2) or formula (1-1) has a lower reduction potential, suggesting that the electrolyte additive with the structure shown by formula (1-3), formula (1-2) or formula (1-1) can react preferentially to ethylene carbonate (EC). This means that the electrolyte additive with the structure shown by formula (1-3), formula (1-2) or formula (1-1) preferentially reacts to form SEI.

[0112] Figure 2 The dQ / dV curves of the batteries in Example 1, Example 2 and Comparative Example 2 when first charged are shown. Figure 2 It can be seen that in the electrolyte of Comparative Example 2, there is only a reduction peak of fluoroethylene carbonate (FEC). After adding the electrolyte additive having a structure shown by formula (1-1) or formula (1-2) to the electrolyte, an obvious reduction peak appears in the battery, and the reduction peak of fluoroethylene carbonate (FEC) is significantly reduced. This shows that the electrolyte additive having a structure shown by formula (1-1) or formula (1-2) has a lower reduction potential, has a higher film-forming property than fluoroethylene carbonate (FEC), and the electrolyte additive having a structure shown by formula (1-1) or formula (1-2) affects the reaction of fluoroethylene carbonate (FEC), and the electrolyte additive and fluoroethylene carbonate (FEC) react synergistically to achieve a better effect.

[0113] Table 1 Battery performance test results

[0114]

[0115]

[0116] In Table 1, both the "amount of electrolyte additive added" and the "amount of film-forming additive added" are weight percentages based on the total weight of the basic electrolyte.

[0117] It can be seen from the above test results that the above embodiments of the present invention achieve the following technical effects:

[0118] By comparing the results of Examples 1-14 with Comparative Example 1, it can be seen that the lithium-ion batteries in Examples 1-14 in which electrolyte additives having structures represented by Formula (1-1), Formula (1-2) or Formula (1-3) are added to the electrolyte have higher capacity retention and lower post-cycle impedance compared to Comparative Example 1 in which no electrolyte additives or film-forming additives are added.

[0119] By comparing the results of Examples 3-5 with those of Examples 6-7, it can be seen that based on 100 parts by weight of organic solvent and lithium salt, when the amount of the electrolyte additive having the structure represented by formula (1-3) is in the range of 0.1 parts by weight to 1.0 parts by weight, the capacity retention rate is further improved and the post-cycle impedance is further reduced.

[0120] By comparing the results of Examples 8-10 with those of Examples 11-12, it can be seen that, based on 100 parts by weight of organic solvent and lithium salt, when the amount of the electrolyte additive having the structure represented by formula (1-2) is in the range of 0.1 parts by weight to 1.0 parts by weight, the capacity retention rate is further improved and the post-cycle impedance is further reduced.

[0121] By comparing the results of Example 1-2 with Comparative Example 2, it can be seen that the lithium ion battery in Example 1-2 in which a combination of an electrolyte additive having a structure represented by Formula (1-1) or Formula (1-2) and fluoroethylene carbonate (FEC) is added to the electrolyte has a higher capacity retention rate and a lower post-cycle impedance than that in Comparative Example 2 in which only fluoroethylene carbonate (FEC) is added.

[0122] By comparing the results of Example 14 with those of Comparative Example 3, it can be seen that the lithium-ion battery in Example 14, in which a combination of an electrolyte additive having a structure represented by formula (1-3) and fluoroethylene carbonate (FEC) is added to the electrolyte, has a higher capacity retention rate and a lower post-cycle impedance than that in Comparative Example 3 in which only fluoroethylene carbonate (FEC) is added.

[0123] By comparing the results of Example 1 with Example 13, it can be seen that the lithium-ion battery in Example 1 in which a combination of an electrolyte additive having a structure represented by formula (1-1) and fluoroethylene carbonate (FEC) is added to the electrolyte has a higher capacity retention rate and a lower post-cycle impedance than that in Example 13 in which only the electrolyte additive having a structure represented by formula (1-1) is added.

[0124] By comparing the results of Example 2 with those of Example 9, it can be seen that the lithium-ion battery in Example 2 in which a combination of an electrolyte additive having a structure represented by formula (1-2) and fluoroethylene carbonate (FEC) is added to the electrolyte has a higher capacity retention rate and a lower post-cycle impedance than that in Example 9 in which only the electrolyte additive having a structure represented by formula (1-2) is added.

[0125] By comparing the results of Example 5 and Example 10 with Comparative Example 3, it can be seen that compared with Comparative Example 3 in which fluoroethylene carbonate (FEC) is added, the lithium ion batteries in Example 5 and Example 10 in which the same amount of electrolyte additive having the structure represented by Formula (1-3) or Formula (1-2) is added to the electrolyte have significantly higher capacity retention rates without changing or increasing the impedance after cycling.

[0126] It can be seen from the above battery performance test results that the electrolyte additive of the present invention effectively improves the cycle performance of the lithium ion secondary battery and reduces the impedance of the lithium ion secondary battery.

[0127] The above description is only the preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An electrolyte additive, characterized in that: The electrolyte additive comprises a substance represented by the following formula (1): Among them, R 1 is present or not, in R 1 In the presence of 1 is any one of halogen, substituted or unsubstituted alkyl having 1 to 5 carbon atoms, substituted or unsubstituted alkoxy having 1 to 5 carbon atoms, ester group and substituted or unsubstituted aryl group; R 2 is any one of a substituted or unsubstituted alkyl group and a substituted or unsubstituted aryl group having 1 to 5 carbon atoms; and R 1 and R 2 At least one of the above contains a fluorine atom.

2. The electrolyte additive according to claim 1, characterized in that: R 1 does not exist, and R 2 is a fluorine-substituted alkyl group having 1 to 5 carbon atoms, preferably, R 2 is a fluorine-substituted alkyl group having 1 to 3 carbon atoms, more preferably, R 2 It is any of monofluoromethyl, difluoromethyl and trifluoromethyl.

3. The electrolyte additive according to claim 1, characterized in that: R 1 is halogen, preferably, R 1 is fluorine, and R 2 It is a halogen-substituted alkyl group having 1 to 5 carbon atoms.

4. The electrolyte additive according to claim 1, characterized in that: R 1 is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, and R 2 It is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.

5. The electrolyte additive according to claim 1, characterized in that: The electrolyte additive comprises any one of the following substances: as well as 6 . An electrolyte comprising an organic solvent, a lithium salt and the electrolyte additive according to any one of claims 1 to 5.

7. The electrolyte according to claim 6, characterized in that Based on 100 parts by weight of the organic solvent and the lithium salt, the amount of the electrolyte additive is in the range of 0.01 parts by weight to 3.0 parts by weight. Preferably, the amount of the electrolyte additive is in the range of 0.1 parts by weight to 1.0 parts by weight.

8. The electrolyte according to claim 6 or 7, characterized in that The organic solvent includes linear carbonate, cyclic carbonate or a combination thereof.

9. The electrolyte according to claim 6 or 7, characterized in that The organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dihexyl carbonate, ethyl methyl carbonate, methylpropyl carbonate and propyl propionate.

10. The electrolyte according to claim 6 or 7, characterized in that: The electrolyte further includes fluoroethylene carbonate. Preferably, based on 100 parts by weight of the organic solvent and the lithium salt, the amount of the fluoroethylene carbonate is in a range of 1.0 parts by weight to 13.0 parts by weight.

11. A lithium ion secondary battery, characterized in that: include: positive electrode, negative electrode, Diaphragm, and The electrolyte according to any one of claims 6 to 10.

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