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 R2 is any one of a substituted or unsubstituted alkyl group having 1-5 carbon atoms, a substituted or unsubstituted phenyl group, and a substituted or unsubstituted heteroaryl group having 1-2 heteroatoms selected from O, S, or N; and R1 is halogen or halogen-substituted alkyl having 1 to 5 carbon atoms. 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 batteries have the advantages of high voltage, high specific energy, environmental protection and no memory effect, and are widely used in digital, military, energy storage and power fields. As a key component of lithium-ion secondary batteries, non-aqueous electrolyte is a bridge connecting the positive and negative electrode materials of lithium-ion secondary batteries. However, during the charging and discharging process, the electrolyte will react with the positive and negative electrodes, resulting in an increase in battery impedance and cycle attenuation.

[0004] Sulfone has excellent oxidation stability, but sulfone has high viscosity, low conductivity and poor compatibility with graphite negative electrode. Fluorination reduces the boiling point, viscosity and ionic conductivity of sulfone, but enhances the wetting ability. The introduction of fluorine into the molecules of electrolyte salts, solvents (co-solvents) and functional additives can more effectively form solid electrolyte interphase (SEI) and positive electrode electrolyte interphase (CEI), with better thermal and electrochemical stability, as well as low and high temperature characteristics. Fluorinated sulfone is considered to be a very promising electrolyte additive.

[0005] However, the SEI formed by the fluorinated sulfone compounds in the prior art at the negative electrode is mainly composed of lithium salts and does not contain organic polymers. Therefore, it is unstable during the charge and discharge process and it is difficult to effectively improve the cycle performance of the battery. Summary of the invention

[0006] 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 are difficult to effectively improve the cycle performance of the battery.

[0007] 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):

[0008]

[0009] Among them, R 2 is any one of a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, a substituted or unsubstituted phenyl group, and a substituted or unsubstituted heteroaryl group containing 1 to 2 heteroatoms selected from O, S or N; and R 1 It is halogen or a halogen-substituted alkyl group having 1 to 5 carbon atoms.

[0010] Furthermore, in the above electrolyte additive, R 2 is any one of an unsubstituted alkyl group having 1 to 5 carbon atoms, an unsubstituted phenyl group, and an unsubstituted heteroaryl group containing 1 to 2 heteroatoms and 4 to 5 carbon atoms, preferably R 2 It is any one of an unsubstituted tert-butyl group, an unsubstituted phenyl group, an unsubstituted pyridyl group, an unsubstituted pyrimidyl group and an unsubstituted furyl group.

[0011] Furthermore, in the above electrolyte additive, R 2 It is any one of a halogen-substituted alkyl group having 1 to 5 carbon atoms, a phenyl group substituted by a halogen or a C1 to C5 alkyl group, and a heteroaryl group containing 1 to 2 hetero atoms and substituted by a C1 to C5 alkyl group.

[0012] Furthermore, in the above electrolyte additive, R 1 is fluorine or a fluorine-substituted alkyl group having 1 to 3 carbon atoms, preferably, R 1 It is any of monofluoromethyl, difluoromethyl and trifluoromethyl.

[0013] Furthermore, in the above electrolyte additive, the electrolyte additive comprises any one of the following substances:

[0014]

[0015] as well as

[0016] 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.

[0017] 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 2.0 parts by weight, preferably in the range of 0.1 parts by weight to 1.0 parts by weight.

[0018] Furthermore, in the above electrolyte, the organic solvent includes linear carbonate, cyclic carbonate or a combination thereof.

[0019] Furthermore, in the above electrolyte, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dihexyl carbonate, ethyl methyl carbonate, methylpropyl carbonate and propyl propionate.

[0020] 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 3.0 parts by weight to 13.0 parts by weight.

[0021] 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.

[0022] 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

[0023] Figure 1 The dQ / dV curves of the batteries in Example 1, Example 2, Example 3 and Comparative Example 2 when charged for the first time are shown.

[0024] Figure 2 The dQ / dV curves of the batteries in Example 5, Example 10, Example 14 and Comparative Example 1 when charged for the first time are shown.

[0025] Figure 3 The cyclic voltammograms of the batteries in Example 16 and Comparative Example 4 at the first cycle are shown.

[0026] Figure 4 Cyclic voltammograms of the battery in Comparative Example 4 at the 1st, 2nd and 5th cycles are shown.

[0027] Figure 5 Cyclic voltammograms of the battery in Example 16 after the 1st, 2nd and 5th cycles are shown. DETAILED DESCRIPTION

[0028] 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.

[0029] As described in the background art, the fluorinated sulfone compounds in the prior art have the problem of being difficult to effectively improve the cycle performance of the battery. 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):

[0030]

[0031] Among them, R 2 is any one of a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, a substituted or unsubstituted phenyl group, and a substituted or unsubstituted heteroaryl group containing 1 to 2 heteroatoms selected from O, S or N; and R 1 It is halogen or a halogen-substituted alkyl group having 1 to 5 carbon atoms.

[0032] The purpose of the present invention is to provide an electrolyte additive that can form a film at both the positive and negative electrodes and significantly improve the performance of lithium-ion secondary batteries in order to overcome the shortcomings of the prior art. The α-position halogenation, especially α-position fluorination, and tetrazole functional group of the substance represented by formula (1) contained in the electrolyte additive of the present invention make the substance represented by formula (1) have a lower reduction potential and are more likely to react at the positive and negative electrodes. The substance represented by formula (1) is more likely to form a film at the positive and negative electrodes, which is beneficial to improving the cycle performance of lithium-ion secondary batteries while reducing the internal resistance of lithium-ion secondary batteries.

[0033] The electrolyte additive of the present invention comprises a sulfone tetrazole compound which is halogenated at the α position, especially fluorinated at the α position. The sulfone group which is halogenated at the α position, especially fluorinated at the α position, provides a low reduction potential, and the tetrazole group ensures that the generated SEI has an organic polymer and has high lithium ion conductivity and thermal stability, thereby ensuring that the lithium ion secondary battery has excellent electrochemical performance.

[0034] The tetrazole group and the sulfone group (-SO2-) in the substance represented by formula (1) contained in the electrolyte additive of the present invention achieve 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 lithium-ion secondary batteries. At the same time, the electron pairs of the N atoms contained in the tetrazole group itself can also interact with lithium ions to improve the transmission of lithium ions.

[0035] The electrolyte additive of the present invention generates redox reactions at the positive and negative electrodes, thereby forming low impedance components at the positive and negative electrodes to reduce the impedance of the lithium ion secondary battery, and inhibiting the dissolution of transition metals to improve the cycle performance of the lithium ion secondary battery.

[0036] In some embodiments of the present invention, heteroaryl can be, for example, a five-membered heteroaryl or a six-membered heteroaryl containing 1-2 heteroatoms, such as pyridyl, pyrimidyl, furyl, thienyl, pyrrolyl, pyranyl or thiopyranyl, etc. In some embodiments of the present invention, halogen can be, for example, fluorine (F), chlorine (Cl), bromine (Br), iodine (I) or astatine (At). In some embodiments of the present invention, alkyl can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl, etc.

[0037] In some embodiments of the present invention, in formula (1), R 2 It can be a substituted or unsubstituted phenyl group or a substituted or unsubstituted heteroaryl group containing 1-2 heteroatoms, wherein the substituted or unsubstituted phenyl group or the substituted or unsubstituted heteroaryl group containing 1-2 heteroatoms has the function of improving the electron density of the conjugated system of the tetrazolyl group and the sulfone group.

[0038] In some embodiments of the present invention, in formula (1), R 2 is any one of an unsubstituted alkyl group having 1 to 5 carbon atoms, an unsubstituted phenyl group, and an unsubstituted heteroaryl group containing 1 to 2 heteroatoms and 4 to 5 carbon atoms, preferably R 2 It is any one of an unsubstituted tert-butyl group, an unsubstituted phenyl group, an unsubstituted pyridyl group, an unsubstituted pyrimidyl group and an unsubstituted furyl group.

[0039] In some embodiments of the present invention, in formula (1), R 2 It is any one of a halogen-substituted alkyl group having 1 to 5 carbon atoms, a phenyl group substituted by a halogen or a C1 to C5 alkyl group, and a heteroaryl group containing 1 to 2 hetero atoms and substituted by a C1 to C5 alkyl group.

[0040] In some embodiments of the present invention, in formula (1), R 1 is fluorine or a fluorine-substituted alkyl group having 1 to 3 carbon atoms, preferably, R 1 It is any of monofluoromethyl, difluoromethyl and trifluoromethyl.

[0041] 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:

[0042]

[0043] as well as

[0044] 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 forms a low-impedance component at the positive and negative electrodes by undergoing a redox reaction at the positive and negative electrodes, thereby reducing the impedance of the lithium-ion secondary battery, and can inhibit the dissolution of transition metals and improve the cycle performance of the lithium-ion secondary battery. The electrolyte of the present invention improves the cycle performance of the lithium-ion secondary battery and reduces the impedance of the lithium-ion secondary battery.

[0045] 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 2.0 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.

[0046] 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 1.95 parts by weight, 0.1 parts by weight to 1.9 parts by weight, 0.15 parts by weight to 1.85 parts by weight, 0.2 parts by weight to 1.8 parts by weight, 0.25 parts by weight to 1.75 parts by weight, 0.3 parts by weight to 1.7 parts by weight, 0.35 parts by weight to 1.65 parts by weight, 0.4 parts by weight to 1.6 parts by weight, 0.45 parts by weight to 1.55 parts by weight, 0.5 parts by weight to 1.5 parts by weight, 0.55 parts by weight to 1.45 parts by weight, 0.6 parts by weight to 1.4 parts by weight. parts by weight, 0.65 to 1.35 parts by weight, 0.7 to 1.3 parts by weight, 0.75 to 1.25 parts by weight, 0.8 to 1.2 parts by weight, 0.85 to 1.15 parts by weight, 0.9 to 1.1 parts by weight, 0.95 to 1.05 parts by weight, 0.9 to 1.0 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.

[0047] 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.

[0048] 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; 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, 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.

[0049] 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.

[0050] 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 3.0 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 in 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.

[0051] 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.

[0052] 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 two 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.

[0053] The positive electrode active material layer contains one or more positive electrode materials capable of intercalating and deintercalating 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.

[0054] 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 two or more transition metal elements as constituent elements, and the lithium-transition metal phosphate compound is a phosphate compound containing Li and one or two or more transition metal elements as constituent elements. The transition metal element is advantageously one or more of Co, Ni, Mn, Fe, etc.

[0055] Examples of the lithium-transition metal composite oxide may include, for example, LiCoO2 and LiNiO2, etc. Examples of the lithium-transition metal phosphate compound may include, for example, LiFePO4 and LiFe 1-u Mn u PO4(0 < u < 1), etc.

[0056] 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 two 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.

[0057] The negative electrode active material layer contains one or more negative electrode materials capable of intercalating and deintercalating 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.

[0058] 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.

[0059] The separator of the present invention is used to separate the positive electrode and the negative electrode in the battery, and allows lithium ions to pass through it while preventing a 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 a ceramic, and may be a laminated membrane in which two or more porous membranes are laminated. Examples of the synthetic resin include, for example, polytetrafluoroethylene, polypropylene, and polyethylene, etc.

[0060] In an embodiment of the present invention, when charging a lithium-ion secondary battery, for example, lithium ions are removed from the positive electrode and embedded in the negative electrode through the electrolyte impregnated in the separator. When discharging the lithium-ion secondary battery, for example, lithium ions are removed from the negative electrode and embedded in the positive electrode through the electrolyte impregnated in the separator.

[0061] 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 can be improved and the impedance of the lithium-ion secondary battery can be reduced.

[0062] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed in the present application.

[0063] Examples

[0064] Example 1

[0065] Preparation of the positive electrode

[0066] 95.5 g of 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 were mixed to obtain a positive electrode mixture, and the obtained mixture was dispersed in N-methylpyrrolidone to obtain a positive electrode mixture slurry. Subsequently, the obtained positive electrode mixture slurry was uniformly coated on the positive electrode current collector formed by aluminum foil to obtain a positive electrode active material layer, the positive electrode active material layer was dried, and a positive electrode plate was formed by a stamping process.

[0067] Preparation of the negative electrode

[0068] 95.85 g of silicon monoxide (SiOx, 1 < x < 2) and graphite powder mixture (weight ratio of silicon monoxide 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 were stirred to prepare a negative electrode mixture slurry. Then the obtained negative electrode mixture slurry was uniformly coated on the negative electrode current collector formed by copper foil to obtain a negative electrode active material layer, the negative electrode active material layer was dried, and a negative electrode plate was formed by a stamping process.

[0069] Preparation of the electrolyte

[0070] 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate, and 18.6 g of lithium hexafluorophosphate were mixed to prepare a base electrolyte. 0.5 g of an electrolyte additive having the structure shown by formula (1-1) and 13.0 g of fluoroethylene carbonate (FEC) were added to the above electrolyte, and after stirring evenly, it was reserved for use.

[0071]

[0072] Battery Assembly

[0073] 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.

[0074] Example 2

[0075] 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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate 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 for later use.

[0076]

[0077] Example 3

[0078] 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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate 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 13.0 g of fluoroethylene carbonate (FEC) were added to the electrolyte, and the mixture was stirred evenly for later use.

[0079]

[0080] Example 4

[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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 0.1 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 for later use.

[0082] Example 5

[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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate 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 for later use.

[0084] Example 6

[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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 1.0 g of an electrolyte additive having a structure represented by formula (1-1) was added to the above electrolyte, stirred evenly and set aside.

[0086] Example 7

[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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 0.01 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 for later use.

[0088] Example 8

[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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 2.0 g of an electrolyte additive having a structure represented by formula (1-1) was added to the above electrolyte, stirred evenly and set aside.

[0090] Example 9

[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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 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 and set aside.

[0092] Example 10

[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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate 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.

[0094] Embodiment 11

[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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 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 for later use.

[0096] Example 12

[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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 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 and set aside.

[0098] Embodiment 13

[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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 2.0 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.

[0100] Embodiment 14

[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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate 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.

[0102] Embodiment 15

[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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate 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 3.0 g of fluoroethylene carbonate (FEC) were added to the electrolyte, and the mixture was stirred evenly for later use.

[0104] Comparative Example 1

[0105] 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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, which was stirred evenly and set aside.

[0106] Comparative Example 2

[0107] 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, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate 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 above electrolyte, stirred evenly and set aside.

[0108] Comparative Example 3

[0109] A button battery was prepared by the same method as in Example 1, except that 20.8 g of ethylene carbonate, 56.7 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, and 1.0 g of fluoroethylene carbonate (FEC) was added to the above electrolyte, stirred evenly and set aside.

[0110] Battery performance test method

[0111] Cycle Test

[0112] The first charge and discharge and cycle test were carried out on a Xinwei charge and discharge instrument. The batteries in Examples 1-15 and Comparative Examples 1-3 were first subjected to a 0.1C cycle test once at 23°C, and then subjected to a 0.5C charge and 5C discharge cycle test 100 times at 60°C.

[0113] The capacity retention rate of the battery after 100 cycles=the discharge capacity at the 100th cycle of 5C discharge / the discharge capacity at the 1st cycle of 5C discharge×100%.

[0114] Impedance test

[0115] After 100 cycles, the batteries in Examples 1-15 and Comparative Examples 1-3 were charged once at 0.5C, and after standing at room temperature for 1 hour, the impedance value of the battery was tested by an electrochemical workstation, with a frequency range of (500MHz-50mHz). Impedance rise rate after cycle = (impedance value after 100 cycles - impedance value after the first charge and discharge) / impedance value after the first charge and discharge × 100%.

[0116] The experimental results are shown in Table 1. Figure 1 and Figure 2 Shown in.

[0117] Figure 2 The dQ / dV curves of the batteries in Example 5, Example 10, Example 14 and Comparative Example 1 when first charged are shown. Figure 2 It can be seen that in the basic 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 (1-1), formula (1-3) or formula (1-2) to the electrolyte, an obvious reduction peak appears in the battery. The electrolyte additive with the structure shown by formula (1-1), formula (1-3) or formula (1-2) reacts preferentially to ethylene carbonate (EC), and the reduction peak of ethylene carbonate (EC) is significantly reduced. This means that the electrolyte additive with the structure shown by formula (1-1), formula (1-3) or formula (1-2) preferentially reacts to form SEI.

[0118] Figure 1 The dQ / dV curves of the batteries in Example 1, Example 2, Example 3 and Comparative Example 2 when first charged are shown. Figure 1 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), formula (1-2) or formula (1-3) to the electrolyte, an obvious reduction peak appears in the battery. The electrolyte additive having a structure shown by formula (1-1), formula (1-2) or formula (1-3) reacts preferentially to fluoroethylene carbonate (FEC), and the reduction peak of fluoroethylene carbonate (FEC) is significantly reduced. This means that the electrolyte additive having a structure shown by formula (1-1), formula (1-2) or formula (1-3) can react synergistically with fluoroethylene carbonate (FEC) to jointly improve the performance of lithium-ion secondary batteries.

[0119] Table 1 Battery performance test results

[0120]

[0121] 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.

[0122] It can be seen from the above test results that the above embodiments of the present invention achieve the following technical effects:

[0123] By comparing the results of Examples 1-15 with Comparative Example 1, it can be seen that the lithium-ion batteries in Examples 1-15 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 impedance rise rate after cycling, compared with Comparative Example 1 in which no electrolyte additives or film-forming additives are added.

[0124] By comparing the results of Examples 4-6 with those of Examples 7-8, 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 (1-1) 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 impedance rise rate after the cycle is further reduced.

[0125] By comparing the results of Examples 9-11 with those of Examples 12-13, 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 impedance rise rate after the cycle is further reduced.

[0126] By comparing the results of Examples 1-3 with Comparative Example 2, it can be seen that the lithium ion batteries in Examples 1-3 in which a combination of an electrolyte additive having a structure represented by Formula (1-1), Formula (1-2) or Formula (1-3) and fluoroethylene carbonate (FEC) are added to the electrolyte have a higher capacity retention rate and a lower impedance rise rate after cycling, compared with Comparative Example 2 in which only fluoroethylene carbonate (FEC) is added.

[0127] By comparing the results of Example 6 and Example 11 with Comparative Example 3, it can be seen that the lithium ion batteries in Example 6 and Example 11 in which the same amount of electrolyte additives having the structure represented by Formula (1-1) or Formula (1-3) are added to the electrolyte have higher capacity retention and lower impedance rise rate after cycling compared with Comparative Example 3 in which fluoroethylene carbonate (FEC) is added.

[0128] Comparative Example 4

[0129] The electrolyte prepared in Comparative Example 1 was used as the electrolyte of the button cell prepared in Comparative Example 4. The button cell was prepared in the same manner as in Comparative Example 1, except that the negative electrode of the battery was replaced with metallic lithium.

[0130] Example 16

[0131] The electrolyte prepared in Example 10 was used as the electrolyte of the button cell prepared in Example 16. The button cell was prepared in the same manner as in Example 10, except that the negative electrode of the battery was replaced with metallic lithium.

[0132] Cyclic voltammetry test

[0133] Cyclic voltammetry was performed on the batteries in Example 16 and Comparative Example 4 on an electrochemical workstation, starting from the open circuit voltage OCV, with a scan rate of 0.1 mV / s, a voltage range of 3-4.3 V, and 5 cycles.

[0134] Figure 3 The cyclic voltammograms of the batteries in Example 16 and Comparative Example 4 at the first cycle are shown. Figure 4 Cyclic voltammograms of the battery in Comparative Example 4 at the 1st, 2nd and 5th cycles are shown. Figure 5 The cyclic voltammetry curves of the battery in Example 16 after the first, second and fifth cycles are shown. The smaller the ΔE, the smaller the polarization and the lower the impedance of the battery. Figures 3 to 5 From the results in Table 2 below, by comparing Comparative Example 4 in which no electrolyte additive is added with Example 16 in which an electrolyte additive having a structure represented by formula (1-3) is added to the electrolyte, it can be seen that the electrolyte additive having a structure represented by formula (1-3) can reduce the impedance of the positive electrode.

[0135] Table 2: Cyclic voltammetry test results of the batteries in Example 16 and Comparative Example 4

[0136]

[0137] 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.

[0138] 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 2 is any one of a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, a substituted or unsubstituted phenyl group, and a substituted or unsubstituted heteroaryl group containing 1 to 2 heteroatoms selected from O, S or N; and R 1 It is halogen or a halogen-substituted alkyl group having 1 to 5 carbon atoms.

2. The electrolyte additive according to claim 1, characterized in that: R 2 is any one of an unsubstituted alkyl group having 1 to 5 carbon atoms, an unsubstituted phenyl group, and an unsubstituted heteroaryl group containing 1 to 2 heteroatoms and 4 to 5 carbon atoms, preferably R 2 It is any one of unsubstituted tert-butyl, unsubstituted phenyl, unsubstituted pyridyl, unsubstituted pyrimidinyl and unsubstituted furyl.

3. The electrolyte additive according to claim 1, characterized in that: R 2 It is any one of a halogen-substituted alkyl group having 1 to 5 carbon atoms, a phenyl group substituted by a halogen or a C1 to C5 alkyl group, and a heteroaryl group containing 1 to 2 hetero atoms and substituted by a C1 to C5 alkyl group.

4. The electrolyte additive according to any one of claims 1 to 3, characterized in that R 1 is fluorine or a fluorine-substituted alkyl group having 1 to 3 carbon atoms, preferably, R 1 It is any of monofluoromethyl, difluoromethyl and trifluoromethyl.

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 2.0 parts by weight, preferably 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, 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 3.0 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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