Nonaqueous electrolyte for lithium secondary battery

Abstract

The nonaqueous electrolyte for lithium secondary batteries according to the present application contains: a lithium salt; an organic solvent; and a first additive, and the first additive includes a compound represented by the following Chemical Formula 1: [Chemical Formula 1] wherein R1 is an unsaturated hydrocarbon group having 2 to 20 carbon atoms with or without a substituent, and R2 is one selected from the group consisting of hydrogen, an alkyl group having 1 to 10 carbon atoms with or without a substituent, and a cycloalkyl group having 3 to 8 carbon atoms with or without a substituent.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2020-0073895, filed on June 8, 2021, the entire contents of which are incorporated herein by reference.

[0002] This invention relates to a non-aqueous electrolyte for lithium secondary batteries and a lithium secondary battery comprising the electrolyte. Background Technology

[0003] Recently, there has been a growing interest in developing energy storage technologies, and efforts are underway to research and develop electrochemical components as applications expand to mobile phones, cameras, laptops, and electric vehicles.

[0004] In electrochemical devices, there is growing interest in the development of secondary batteries, especially lithium secondary batteries developed in the 1990s, which have attracted much attention due to their advantages of high operating voltage and high energy density.

[0005] In the case of lithium-ion secondary battery systems, unlike the early days when lithium metal was directly applied to the system, lithium-containing transition metal oxides are now used as the positive electrode material, and carbon-based materials such as graphite and alloy materials such as silicon are used as the negative electrode materials. This allows for systems where lithium metal is not directly used in the battery.

[0006] Such a lithium-ion secondary battery consists of a positive electrode made of lithium-containing transition metal oxide, a negative electrode capable of storing lithium, an electrolyte for transporting lithium ions, and a separator. Among these, the electrolyte is known to have a significant impact on the battery's stability and safety, and extensive research has been conducted on it.

[0007] The electrolyte for lithium-ion secondary batteries consists of lithium salt, an organic solvent for dissolving the lithium salt, and functional additives. Therefore, it is important to appropriately select these components to improve the electrochemical characteristics of the battery.

[0008] In this respect, with conventional electrolytes, the reductive decomposition stability of the electrolyte solvent is low, leading to shortened lifespan and electrolyte decomposition during storage. The electrolyte decomposition reaction forms an SEI film, which acts as a resistive layer, at the interface between the negative electrode and the electrolyte, while simultaneously generating gas, thus accelerating battery performance degradation.

[0009] Furthermore, when the interface between the negative electrode and the electrolyte is unstable, electrolyte depletion may occur due to electrolyte decomposition. This can lead to battery degradation and malfunction due to lithium or transition metal deposition. Moreover, the deposition of these metal elements acts as a medium that further promotes electrolyte decomposition.

[0010] In particular, for silicon-containing anodes, the SEI film is damaged due to volume changes during charging and discharging, exposing an unstable anode surface, which further promotes electrolyte consumption.

[0011] Therefore, a technology is needed to improve the interfacial stability between the electrolyte and the negative electrode. Summary of the Invention

[0012] [Technical Issues]

[0013] The present invention is believed to solve at least some of the aforementioned problems. For example, one aspect of the present invention provides a non-aqueous electrolyte for lithium secondary batteries, which can reduce electrolyte decomposition during charging and discharging by ensuring the stability of the negative electrode-electrolyte interface, thereby improving life characteristics at room temperature and high temperature.

[0014] [Technical Solution]

[0015] The non-aqueous electrolyte for lithium secondary batteries of the present invention comprises: a lithium salt; an organic solvent; and a first additive, the first additive comprising a compound represented by the following chemical formula 1:

[0016] [Chemical Formula 1]

[0017]

[0018] Wherein, R1 is an unsaturated hydrocarbon group having 2 to 20 carbon atoms with or without a substituent, and R2 is selected from the group consisting of hydrogen, an alkyl group having 1 to 10 carbon atoms with or without a substituent, and a cycloalkyl group having 3 to 8 carbon atoms with or without a substituent.

[0019] In specific instances, R1 can be an alkenyl group with or without a substituent having 2 to 20 carbon atoms, or an alkynyl group with or without a substituent having 2 to 20 carbon atoms.

[0020] More specifically, the first additive may be at least one selected from the group consisting of compounds represented by chemical formula 1a and compounds represented by chemical formula 1b:

[0021] [Chemical Formula 1a]

[0022]

[0023] Wherein, n is a natural number from 1 to 18, and R2 is selected from the group consisting of hydrogen, alkyl groups with or without substituents having 1 to 10 carbon atoms, and cycloalkyl groups with or without substituents having 3 to 8 carbon atoms.

[0024] [Chemical Formula 1b]

[0025]

[0026] Wherein, n is a natural number from 1 to 18, and R2 is selected from the group consisting of hydrogen, alkyl groups with or without substituents having 1 to 10 carbon atoms, and cycloalkyl groups with or without substituents having 3 to 8 carbon atoms.

[0027] More specifically, the first additive may be at least one selected from the group consisting of compounds represented by chemical formula 1c and chemical formula 1d:

[0028] [Chemical Formula 1c]

[0029]

[0030] [Chemical formula 1d]

[0031]

[0032] Furthermore, the first additive may comprise both the compound represented by chemical formula 1a and the compound represented by chemical formula 1b, and the molar ratio of the compound represented by chemical formula 1a to the compound represented by chemical formula 1b may be 2:8 to 8:2.

[0033] In a specific example, the content of the first additive can be 0.01 to 5% by weight of the total weight of the electrolyte.

[0034] More specifically, the content of the first additive may be 0.1 to 3% by weight of the total weight of the electrolyte.

[0035] In addition, the non-aqueous electrolyte of the present invention may further include at least one second additive selected from the group consisting of halogen-substituted or unsubstituted cyclic carbonate compounds, nitrile compounds, phosphate esters / salt compounds, borate esters / salt compounds, sulfonyl lactone compounds, lithium salt compounds and sulfate esters / salt compounds.

[0036] Furthermore, the lithium salt may be at least one selected from the group consisting of LiPF6, LiAsF6, LiN(SO2F)2, LiCF3SO3, LiN(CF3SO2)2, LiBF6, LiSbF6, LiN(C2F5SO2)2, LiAlO4, LiAlCl4, LiSO3CF3, and LiClO4.

[0037] In addition, the organic solvent may comprise chain carbonates, cyclic carbonates, esters, ethers, ketones, or combinations thereof.

[0038] The present invention provides a lithium secondary battery comprising the above-mentioned non-aqueous electrolyte for lithium secondary batteries.

[0039] [Beneficial Effects]

[0040] The non-aqueous electrolyte for lithium secondary batteries of the present invention can improve the stability of the negative electrode-electrolyte interface by forming a carbon-oxygen single or double bond-like film, and improve the life characteristics at room temperature and high temperature by reducing the decomposition of the electrolyte during charging and discharging. Detailed Implementation

[0041] The invention will be described in detail below. The terms and words used in this specification and claims should not be construed as limited to common or dictionary terms; the inventors may appropriately define the concepts of the terms to best describe their invention. The terms and words should be interpreted as having meanings and concepts consistent with the technical concept of the invention.

[0042] In this application, it should be understood that terms such as "comprising" or "having" are intended to indicate that the specification describes features, quantities, steps, operations, components, parts, or combinations thereof, and they do not preclude the possibility of the presence or addition of one or more other features or quantities, steps, operations, components, parts, or combinations thereof. Furthermore, when a portion such as a layer, film, region, or plate is referred to as being "on" another portion, this includes not only the case where the portion is "directly" on the other portion, but also the case where another portion is disposed between them. On the other hand, when a portion such as a layer, film, region, or plate is referred to as being "below" another portion, this includes not only the case where the portion is "directly" below the other portion, but also the case where another portion is disposed between them. Additionally, the term "on" in this application can include both bottom and top locations.

[0043] Furthermore, in this specification, the terms "carbon number a to b" refer to the number of carbon atoms contained in a specific functional group. That is, the functional group can contain a to b carbon atoms. For example, "alkylene with 1 to 5 carbon atoms" refers to alkylene with 1 to 5 carbon atoms, namely, -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2(CH2)CH-, -CH(CH2)CH2-, and -CH(CH2)CH2CH2-, etc.

[0044] The invention will be described in detail below.

[0045] Non-aqueous electrolyte for lithium secondary batteries

[0046] The non-aqueous electrolyte for lithium secondary batteries of the present invention comprises: a lithium salt; an organic solvent; and a first additive, the first additive comprising a compound represented by the following chemical formula 1:

[0047] [Chemical Formula 1]

[0048]

[0049] Wherein, R1 is an unsaturated hydrocarbon group having 2 to 20 carbon atoms, with or without a substituent, and R2 is at least one selected from the group consisting of hydrogen, an alkyl group having 1 to 10 carbon atoms, with or without a substituent, and a cycloalkyl group having 3 to 8 carbon atoms, with or without a substituent.

[0050] (1) Lithium salts

[0051] In the non-aqueous electrolyte for lithium secondary batteries according to embodiments of the present invention, the lithium salt contains LiPF6, and there are no limitations on the use of those commonly used in electrolytes for lithium secondary batteries other than LiPF6. For example, the lithium salt contains Li + As a cation, and may contain F-selected - Cl - ,Br - I - NO3 - N(CN)2 - ClO4 - BF4 - B 10 Cl 10 - PF6 - CF3SO3 - CH3CO2 - CF3CO2 - AsF6 - SbF6 - AlCl4 - AlO4 - CH3SO3 - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - C4F9SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C- (CF3SO2)3C - CF3(CF2)7SO3 - SCN - and (CF3CF2SO2)2N - At least one of the groups constitutes an anion.

[0052] Specifically, lithium salts can contain a variety of compounds selected from LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB. 10 Cl 10 The lithium salt may be one or more combinations of the following: LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, LiAlO4, LiCH3SO3, LiFSI (lithium bis(fluorosulfonyl)imide, LiN(SO2F)2), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, LiN(SO2CF3)2), and LiBETI (lithium bis(perfluoroethanesulfonyl)imide, LiN(SO2C2F5)2). More specifically, the lithium salt may be at least one selected from the group consisting of LiPF6, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiBF6, LiSbF6, LiN(C2F5SO2)2, LiAlO4, LiAlCl4, LiSO3CF3, and LiClO4.

[0053] The lithium salt concentration can be appropriately varied within the generally usable range, but specifically, the electrolyte can contain 0.1M to 3M lithium salt, and more specifically, 0.8M to 2.5M lithium salt. If the lithium salt concentration exceeds 3M, the viscosity of the non-aqueous electrolyte will increase, the lithium-ion transport effect will decrease, and the wettability of the non-aqueous electrolyte will decrease, making it difficult to form an SEI film of uniform thickness on the electrode surface.

[0054] (2) Organic solvents

[0055] The decomposition of organic solvents due to oxidation reactions during the charging / discharging of secondary batteries can be minimized, and there are no restrictions on the type of organic solvent, as long as it can exhibit the desired properties when used with additives. For example, organic solvents can include chain carbonates, cyclic carbonates, esters, ethers, ketones, or combinations thereof.

[0056] Specifically, cyclic carbonate organic solvents may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentene carbonate, 2,3-pentene carbonate, vinylene carbonate, and fluoroethylene carbonate (FEC), and may specifically include a mixture of ethylene carbonate having a high dielectric constant and propylene carbonate having a relatively low melting point compared to ethylene carbonate.

[0057] In addition, the chain carbonate organic solvent is a solvent with low viscosity and low dielectric constant, and may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate, and may specifically include dimethyl carbonate.

[0058] In addition, as an ether-based organic solvent, any one or a mixture of two or more of the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether can be used, but not limited thereto.

[0059] Ester organic solvents may be at least one selected from the group consisting of chain ester organic solvents and cyclic ester organic solvents.

[0060] At this time, as a chain ester organic solvent, one or more mixtures selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate can be used, but the present invention is not limited to these examples.

[0061] As a cyclic ester organic solvent, one or more mixtures selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone can be used, but the present invention is not limited to these examples.

[0062] High-viscosity cyclic carbonate organic solvents, which can readily dissociate lithium salts in the electrolyte due to their high dielectric constant, can be used as organic solvents. Furthermore, to produce electrolytes with higher conductivity, low-viscosity and low-dielectric-constant chain carbonate compounds and chain ester compounds (e.g., dimethyl carbonate and diethyl carbonate) can be mixed with cyclic carbonate organic solvents in appropriate proportions.

[0063] More specifically, the organic solvent can be obtained by mixing a cyclic carbonate compound with a chain carbonate compound, wherein the weight ratio of the cyclic carbonate compound to the chain carbonate compound can be from 10:90 to 70:30.

[0064] (3) First additive

[0065] Furthermore, the non-aqueous electrolyte for secondary batteries of the present invention may also contain a compound represented by the following chemical formula 1 as a first additive.

[0066] [Chemical Formula 1]

[0067]

[0068] Wherein, R1 is an unsaturated hydrocarbon group having 2 to 20 carbon atoms with or without a substituent, and R2 is selected from the group consisting of hydrogen, an alkyl group having 1 to 10 carbon atoms with or without a substituent, and a cycloalkyl group having 3 to 8 carbon atoms with or without a substituent.

[0069] Specifically, R1 can be an alkenyl group having 2 to 20 carbon atoms, with or without a substituent, or an alkynyl group having 2 to 20 carbon atoms, with or without a substituent. Specifically, R1 can be an alkenyl or alkynyl group having 2 to 16, 2 to 12, 2 to 8, or 3 to 5 carbon atoms, and R2 can be an alkyl group having 1 to 8, 1 to 6, 1 to 4, or 1 to 3 carbon atoms, or a cycloalkyl group having 3 to 6 carbon atoms.

[0070] Furthermore, in Formula 1, R1 can be a terminal alkenyl group or a terminal alkynyl group. Here, a terminal alkenyl group refers to a double bond formed at the end of the chain, and a terminal alkynyl group refers to a triple bond formed at the end of the chain.

[0071] Specifically, the first additive may be at least one selected from the group consisting of compounds represented by chemical formula 1a and compounds represented by chemical formula 1b:

[0072] [Chemical Formula 1a]

[0073]

[0074] Wherein, n is a natural number from 1 to 18, and R2 is selected from the group consisting of hydrogen, alkyl groups with or without substituents having 1 to 10 carbon atoms, and cycloalkyl groups with or without substituents having 3 to 8 carbon atoms.

[0075] [Chemical Formula 1b]

[0076]

[0077] Wherein, n is a natural number from 1 to 18, and R2 is selected from the group consisting of hydrogen, alkyl groups with or without substituents having 1 to 10 carbon atoms, and cycloalkyl groups with or without substituents having 3 to 8 carbon atoms.

[0078] In chemical formulas 1a and 1b, n can be 1 to 18, 1 to 14, 1 to 10, 1 to 6, or 1 to 3.

[0079] Non-limiting examples of such compounds include 5-methyl-5-allyloxycarbonyl-1,3-dioxane-2-one (MACBD) represented by formula 1c and 5-methyl-5-propyneoxycarbonyl-1,3-dioxane-2-one (MPCBD) represented by formula 1d.

[0080] [Chemical Formula 1c]

[0081]

[0082] [Chemical formula 1d]

[0083]

[0084] The compound represented by Formula 1 contains ester functional groups and unsaturated hydrocarbon groups in its molecular structure, and forms a film using carbon-oxygen single bonds (CO) or carbon-oxygen double bonds (C=O) as the main components. Furthermore, since the first additive contains unsaturated hydrocarbon functional groups such as allyl and propargyl, it is easily reduced on the negative electrode surface, readily forming a film there. This film exhibits higher stability than the SEI film formed by the general reduction and decomposition of the electrolyte, and its low electronic conductivity suppresses additional electrolyte decomposition reactions, making it less susceptible to damage from volume changes at the negative electrode. In other words, by using a compound like that of Formula 1 as an electrolyte additive, the stability of the interface between the negative electrode and the electrolyte can be ensured.

[0085] At this time, as the first additive, a compound with a terminal alkenyl group, such as chemical formula 1a, or a compound with a terminal alkynyl group, such as chemical formula 1b, can be used alone, or a mixture of the two compounds can be used. Similarly, when the first additive includes both the compound represented by chemical formula 1a and the compound represented by chemical formula 1b, the molar ratio of the compound represented by chemical formula 1a to the compound represented by chemical formula 1b can be 2:8 to 8:2, 3:7 to 7:3, or 4:6 to 6:4.

[0086] Furthermore, in this invention, the content of the first additive can be from 0.01 to 5% by weight of the total weight of the electrolyte, specifically from 0.1 to 3% by weight, and more specifically from 0.5 to 2% by weight. When the content of the first additive is within the above range, a stable film can be formed without increasing the battery resistance.

[0087] When the content of the first additive is less than 0.01% by weight, it is difficult to achieve the desired effect. When the content of the first additive exceeds 5% by weight, the additive decomposes incompletely and may act as a resistor, thereby reducing the performance of the battery.

[0088] (4) Second additive

[0089] Furthermore, the non-aqueous electrolyte for lithium secondary batteries of the present invention may also include a second additive, which can exhibit the effects shown by the mixed additives and act as a supplement. It can form a stable film on the surface of the negative and positive electrodes or inhibit the decomposition caused by the side reactions of the solvent in the non-aqueous electrolyte and improve the mobility of lithium ions without significantly increasing the initial resistance.

[0090] Specifically, the non-aqueous electrolyte of the present invention may further include at least one additive selected from the group consisting of halogen-substituted or unsubstituted cyclic carbonate compounds, nitrile compounds, phosphate esters / salt compounds, borate esters / salt compounds, sulcolone compounds, lithium salt compounds, and sulfate esters / salt compounds.

[0091] Specifically, halogen-substituted or unsubstituted cyclic carbonate compounds can improve battery durability by forming a stable SEI film on the negative electrode surface during battery activation.

[0092] Fluorinated ethylene carbonate (FEC) can be used as halogen-substituted cyclic carbonate compounds. Alternatively, examples of unsubstituted cyclic carbonate compounds may include vinylene carbonate (VC) or vinyl ethylene carbonate (VEC).

[0093] The content of halogen-substituted or unsubstituted cyclic carbonate compounds can be less than 8% by weight of the total weight of the non-aqueous electrolyte, particularly less than 5% by weight. When the content of cyclic carbonate compounds in the non-aqueous electrolyte exceeds 8% by weight, the battery swelling suppression performance and initial resistance may deteriorate.

[0094] When nitrile compounds are used in conjunction with the aforementioned mixed additives, improvements in high-temperature characteristics are expected by stabilizing the positive / negative electrode films. Specifically, it can serve as a supplementary element in the formation of the negative electrode SEI film, suppressing solvent decomposition in the electrolyte and increasing lithium-ion mobility. Examples of nitrile compounds may include at least one selected from the group consisting of succinic anionyl, adiponitrile, acetonitrile, propionitrile, butyronitrile, valerate, octanoic anionyl, heptanoic anionyl, cyclopentaneformitrile, cyclohexaneformitrile, 2-fluorobenzyl nitrile, 4-fluorobenzyl nitrile, difluorobenzyl nitrile, trifluorobenzyl nitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, 1,4-dicyano-2-butene, glutaronitrile, 1,3,6-hexamethylenetrionitrile, and heptanoic anionyl.

[0095] The content of nitrile compounds can be less than 8% by weight of the total weight of the non-aqueous electrolyte, especially less than 5% by weight. When the total content of nitrile compounds in the non-aqueous electrolyte exceeds 8% by weight, the resistance increases due to the increased film formed on the electrode surface, thereby degrading the performance of the battery.

[0096] Furthermore, the battery durability is improved because the phosphate ester / salt compound stabilizes the PF6 anion in the electrolyte and facilitates the formation of the positive and negative electrode films. Some examples of phosphate ester / salt compounds may include at least one selected from the group consisting of lithium difluoro(bis(oxalato)phosphate) (LiDFOP), lithium difluorophosphate (LiDFP, LiPO2F2), lithium tetramethyltrimethylsilyl phosphate, tris(trimethylsilyl) phosphite (TMSPi), tris(trimethylsilyl) phosphate (TMSPa), ethyl di(prop-2-yn-1-yl) phosphate, allyl diphosphate, tris(2,2,2-trifluoroethyl) phosphate (TFEPa), and tris(trifluoroethyl) phosphite, and the content of the phosphate ester / salt compound may be less than 3% by weight, particularly less than 1% by weight, of the total weight of the non-aqueous electrolyte.

[0097] Borate / salt compounds can improve lithium-ion mobility by promoting ion pair separation, reduce the interfacial resistance of the SEI film, and solve problems such as the generation of hydrofluoric acid gas caused by non-separable dissociative substances (e.g., LiF) produced during the battery reaction. As borate / salt compounds, LiBOB, LiB(C2O4)2, lithium oxalyl difluoroborate, or tris(trimethylsilyl)borate (TMSB) can be used, and the content of the borate / salt compound can be less than 3% by weight, particularly less than 1% by weight, of the total weight of the non-aqueous electrolyte.

[0098] As the sulfonyl compound, at least one compound selected from the group consisting of 1,3-propanesulfonyl (PS), 1,4-butanesulfonyl, ethanesulfonyl, 1,3-propenylsulfonyl (PRS), 1,4-butenesulfonyl, and 1-methyl-1,3-propenylsulfonyl can be used, and the content of the sulfonyl compound can be 0.3% to 5% by weight of the total weight of the non-aqueous electrolyte, specifically 1% to 5% by weight. When the content of sulfonyl compounds in the non-aqueous electrolyte exceeds 5% by weight, an excessively thick film may form on the electrode surface, thereby increasing resistance and reducing output. Furthermore, the resistance may increase due to the presence of a large amount of additives in the non-aqueous electrolyte, thus degrading the output characteristics.

[0099] Furthermore, lithium salt compounds are compounds that differ from lithium salts contained in non-aqueous electrolytes. Some examples of lithium salt compounds include one or more selected from the group consisting of lithium methyl sulfate, lithium ethyl sulfate, lithium 2-trifluoromethyl-4,5-dicyanimidazolium, lithium tetrafluorooxalate phosphate, LiODFB, and LiBF4, and the content of lithium salt compounds may be less than 3% by weight, particularly less than 1% by weight, of the total weight of the non-aqueous electrolyte.

[0100] In addition, some examples of sulfate ester / salt compounds may include ethylene sulfate, trimethylene sulfate (TMS) and methyltrimethylamine sulfate (MTMS), and the content of sulfate ester / salt compounds may be less than 3% by weight, particularly less than 1% by weight, of the total weight of the non-aqueous electrolyte.

[0101] More specifically, the second additive may include one or more combinations selected from the group consisting of vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonyl lactone and lithium oxaloyl difluoroborate (ODFB).

[0102] Two or more additives can be used in combination. The content of the second additive can be less than 20% by weight of the total weight of the electrolyte, preferably 0.01% to 15% by weight, and more preferably 0.1% to 10% by weight.

[0103] When the amount of additives added is less than 0.01% by weight, the high-temperature storage characteristics and gas reduction effect that should be achieved by the additives are very weak; when the amount exceeds 20% by weight, excessive side reactions may occur. Especially when a large amount of additives are added, they may not decompose completely and may remain in the electrolyte in a precipitated or unreacted state at room temperature. This increases resistance and may degrade the life characteristics of the secondary battery.

[0104] Lithium secondary batteries

[0105] In another embodiment of the present invention, a lithium secondary battery is provided, which includes the non-aqueous electrolyte for lithium secondary batteries of the present invention.

[0106] The lithium secondary battery of the present invention includes: a positive electrode; a negative electrode; a separator; and the aforementioned non-aqueous electrolyte for lithium secondary batteries. Specifically, the lithium secondary battery can be manufactured by injecting the non-aqueous electrolyte of the present invention into an electrode assembly formed by sequentially stacking a positive electrode, a negative electrode, and a separator placed between the positive and negative electrodes. In this case, the positive electrode, negative electrode, and separator commonly used in the manufacture of lithium secondary batteries can be used as the positive electrode, negative electrode, and separator for forming the electrode assembly.

[0107] Furthermore, the positive and negative electrodes constituting the lithium secondary battery of the present invention can be prepared and used by conventional methods.

[0108] (1) Positive electrode

[0109] First, the positive electrode can be prepared by forming a positive electrode additive layer on the positive electrode current collector. The positive electrode additive layer can be formed by coating a positive electrode slurry containing a positive electrode active material, a binder, a conductive material, and a solvent onto the positive electrode current collector, and then drying the slurry and rolling it onto the positive electrode current collector.

[0110] There are no particular restrictions on the positive electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. Examples of positive electrode current collectors include stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver.

[0111] The positive electrode active material is a compound capable of reversibly inserting and deintercalating lithium, and may specifically include lithium metal oxides comprising lithium and at least one metal such as cobalt, manganese, nickel, or aluminum. Specifically, some examples of lithium metal oxides may include lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni)... p Co q Mn r1 O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1), or Li (Ni p1 Co q1 Mn r2 O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni)O4) (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), or lithium-nickel p2 Co q2 Mn r3 M s2 O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are the atomic fractions of each element, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1, etc.).

[0112] Examples of positive electrode active materials may include Li(Ni) 1 / 3 Mn 1 / 3 Co 1 / 3 O2, Li(Ni) 0.35 Mn 0.28 Co 0.37 O2, Li(Ni) 0.6 Mn 0.2 Co 0.2 O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 O2, Li(Ni) 0.7Mn 0.15 Co 0.15 O2, Li(Ni) 0.8 Mn 0.1 Co 0.1 O2 or Li(Ni) 0.8 Co 0.15 Al 0.05 )O2.

[0113] The content of positive electrode active material can be 90% to 99% by weight of the total weight of solids in the positive electrode slurry, specifically 93% to 98% by weight.

[0114] As a component that facilitates the bonding of active materials with conductive materials and with current collectors, the amount of binder added (based on the total solid weight in the positive electrode slurry) is 1% to 30% by weight. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, sulfonated ethyl-propylene-diene terpolymer, styrene-butadiene rubber, fluororubber, and various copolymers.

[0115] There are no particular limitations on the aforementioned conductive materials, as long as they are conductive and do not cause chemical changes in the battery. Examples include: carbon powder, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or summer black; graphite powder, such as natural graphite, artificial graphite, or graphite with a well-developed crystal structure; conductive fibers, such as carbon fibers and metal fibers; conductive powders, such as fluorinated carbon, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives, etc.

[0116] Based on the total solid weight in the positive electrode slurry, the amount of conductive material added is typically 1% to 30% by weight.

[0117] Furthermore, the solvent may include an organic solvent, such as NMP (N-methyl-2-pyrrolidone), and the amount used may be such that a desired viscosity is obtained when the positive electrode active material and optionally a binder and conductive material are included. For example, the concentration of solids in the positive electrode active material and optionally the slurry containing the binder and conductive material may be 10% to 70% by weight, preferably 20% to 60% by weight.

[0118] (2) Negative electrode

[0119] The negative electrode can be prepared by forming a negative electrode material mixture layer on the negative electrode current collector. The negative electrode can be formed by coating a slurry containing negative electrode active material, binder, conductive material and solvent onto the negative electrode current collector, and then drying and rolling it.

[0120] The negative electrode current collector is usually made to have a thickness of 3 μm to 500 μm. The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. Examples thereof include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or an aluminum-cadmium alloy. In addition, similar to the case of the positive electrode current collector, minute irregularities can be formed on the surface to improve the bonding force of the negative electrode active material, and it can be used in various forms, such as a film, sheet, foil, net, porous body, foam body, and non-woven fabric body.

[0121] In addition, the negative electrode active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly inserting / extracting lithium ions, a metal or an alloy of lithium and a metal, a metal oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0122] Any carbon-based negative electrode active material commonly used in lithium ion secondary batteries can be used as the carbon material capable of reversibly inserting / extracting lithium ions, and representative examples thereof may include crystalline carbon, amorphous carbon, or a combination thereof. Some examples of crystalline carbon may include amorphous, flaky, spherical, or fibrous natural graphite or artificial graphite, and some examples of amorphous carbon may include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0123] A metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or an alloy of lithium and these metals can be used.

[0124] One selected from the group consisting of PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), and Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Groups I, II, and III of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8) can be used as the metal oxide.

[0125] Some examples of the material capable of doping and dedoping lithium may include Si, SiO x(0 < x ≤ 2), Si-Y alloy (Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, and rare earth elements, and is not Si), Sn, SnO2, Sn-Y (Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, and rare earth elements, and is not Sn), and at least one of them can be mixed with SiO2. As the element Y, one selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and their combinations can be used.

[0126] Examples of transition metal oxides include lithium-containing titanium oxides (LTO), vanadium oxides, lithium vanadium oxides, etc.

[0127] Based on the total solid weight in the negative electrode paste, the content of the negative electrode active material can be 80% to 99% by weight.

[0128] In the negative electrode, the binders and conductive materials already used in the above positive electrode can be used.

[0129] The solvent can include organic solvents such as water, NMP, or ethanol, and the usage amount can be such that a desired viscosity is obtained when the negative electrode active material and optionally the binder and conductive material are included. For example, the concentration of the solids in the paste containing the negative electrode active material and optionally the binder and conductive material can be 50% to 75% by weight, preferably 50% to 65% by weight.

[0130] (3) Separator

[0131] As the separator, an organic separator or an organic and inorganic composite separator can be used.

[0132] As the organic separator, a porous polymer membrane prepared from polyolefin polymers (such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers) can be used alone, or a laminate thereof can be used. Alternatively, a conventional porous non-woven fabric (such as a non-woven fabric formed from high melting point glass fibers, polyethylene terephthalate fibers, etc.) can be used as the organic separator.

[0133] The organic / inorganic composite porous safety reinforcing separator (SRS) can be used as an organic and inorganic composite separator, and the SRS is obtained by applying a porous coating containing inorganic particles and a binder polymer on a porous polyolefin-based separator substrate.

[0134] Preferably, inorganic particles having lithium ion transfer ability or a mixture thereof are used as the inorganic particles, and some examples of the inorganic particles include one or more mixtures selected from the group consisting of BaTiO3, BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, where 0 < x < 1, 0 < y < 1), hafnium dioxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiC, and mixtures thereof.

[0135] The shape of the lithium secondary battery of the present invention is not particularly limited, but the lithium secondary battery can be cylindrical, prismatic, pouch-shaped, or coin-shaped using a can.

[0136] Hereinafter, the present invention will be described in more detail with reference to the embodiments. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more fully illustrate the present invention to those skilled in the art.

[0137] Example 1

[0138] <Preparation of non-aqueous electrolyte>

[0139] Ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) are mixed in a weight ratio of 20:10:25:45 to prepare a non-aqueous organic solvent, and LiPF6 is dissolved in the non-aqueous organic solvent to a concentration of 1.0 M. 5-Methyl-5-allyloxycarbonyl-1,3-dioxolan-2-one (MACBD) is added as a first additive based on 0.5% by weight of the total weight of the electrolyte and mixed to prepare a non-aqueous electrolyte.

[0140] <Preparation of electrode>

[0141] The positive electrode active material (Li(Ni 0.6 Mn 0.2 Co 0.2A positive electrode active material slurry (50% wt% solids concentration) is prepared by adding O2, conductive material (carbon black), and binder (polyvinylidene fluoride) in a weight ratio of 90:5:5 to N-methyl-2-pyrrolidone (NMP) as a solvent. The positive electrode active material slurry is then applied to a positive electrode current collector (Al film) with a thickness of 10 μm, and the slurry is dried and rolled onto the positive electrode current collector to manufacture the positive electrode.

[0142] A negative electrode active material slurry (60% wt% solids concentration) is prepared by adding negative electrode active material (artificial graphite), binder (PVDF), and conductive material (carbon black) in a weight ratio of 95:2:3 to NMP as a solvent. The negative electrode active material slurry is then applied onto a negative electrode current collector (Cu film) with a thickness of 8 μm, and the slurry is dried and rolled onto the negative electrode current collector to manufacture the negative electrode.

[0143] <Preparation of Secondary Batteries>

[0144] The positive and negative electrodes manufactured in the above manner are sequentially laminated with a porous polyethylene membrane to produce an electrode assembly. Then, the electrode assembly is placed in a battery case, a non-aqueous electrolyte is injected into the battery case, and the case is sealed to produce a lithium-ion secondary battery.

[0145] Example 2

[0146] The non-aqueous electrolyte and secondary battery were manufactured in the same manner as in Example 1, except that 1.0% by weight of 5-methyl-5-allyloxycarbonyl-1,3-dioxane-2-one (MACBD) was added as a first additive based on the total weight of the electrolyte.

[0147] Example 3

[0148] The non-aqueous electrolyte and secondary battery were manufactured in the same manner as in Example 1, except that 0.5% by weight of 5-methyl-5-propyneoxycarbonyl-1,3-dioxane-2-one (MPCBD) was added as a first additive based on the total weight of the electrolyte.

[0149] Comparative Example 1

[0150] The non-aqueous electrolyte and secondary battery were manufactured in the same manner as in Example 1, except that the first additive was not added to the solvent.

[0151] Comparative Example 2

[0152] Except for the addition of 0.005% by weight of 5-methyl-5-allyloxycarbonyl-1,3-dioxane-2-one (MACBD) as a first additive based on the total weight of the electrolyte, the non-aqueous electrolyte and the secondary battery were manufactured in the same manner as in Example 1.

[0153] Comparative Example 3

[0154] The non-aqueous electrolyte and secondary battery were manufactured in the same manner as in Example 1, except that 7% by weight of 5-methyl-5-allyloxycarbonyl-1,3-dioxane-2-one (MACBD) based on the total weight of the electrolyte was added as a first additive.

[0155] Experimental Example 1: Room Temperature Lifetime Evaluation

[0156] The secondary batteries manufactured in the examples and comparative examples were charged to 4.2V at a constant current / constant voltage rate of 0.5C at room temperature (25°C), and then discharged to 2.5V at a rate of 0.5C. At this point, charging and discharging were performed using a PNE-0506 charge / discharge apparatus (manufacturer: PNESolution Co., Ltd., 5V, 6A), and the measured discharge capacity was defined as the initial discharge capacity.

[0157] The charging and discharging process is set as one cycle, and a total of 200 cycles are performed. Then, the measured initial discharge capacity and the discharge capacity after 200 cycles are substituted into the following formula (1) to measure the capacity retention rate. The results are shown in Table 1 below.

[0158] Equation (1): Capacity retention rate (%) = (Discharge capacity after 200 cycles / Initial discharge capacity) × 100

[0159] In Comparative Example 3, since the additive was not uniformly dissolved in the electrolyte, it could not be evaluated.

[0160] [Table 1]

[0161] Initial capacity (mAh / g) Capacity after 200 cycles (mAh / g) Capacity retention rate (%) Example 1 3220.9 2769.6 86.0 Example 2 3215.7 2593.4 80.6 Example 3 3218.5 2687.9 83.5 Comparative Example 1 3224.1 2243.9 69.6 Comparative Example 2 3221.5 2293.7 71.2 Comparative Example 3 - - -

[0162] Experiment Example 2 – Evaluation of High-Temperature Storage Characteristics

[0163] The secondary batteries manufactured in the examples and comparative examples were charged to 4.2V at a constant current / constant voltage rate of 0.5C at room temperature (25°C), and then discharged to 2.5V at a rate of 0.5C. At this point, charging and discharging were performed using a PNE-0506 charge / discharge apparatus (manufacturer: PNESolution Co., Ltd., 5V, 6A), and the measured discharge capacity was defined as the initial discharge capacity.

[0164] The secondary battery was stored at 60°C for 2 weeks, and then the capacity retention was measured by substituting the discharge capacity, which was determined in the same manner, into the following equation (2). The results are shown in Table 2 below.

[0165] Equation (2): Capacity retention rate (%) = (Discharge capacity after 2 weeks of storage / Initial discharge capacity) × 100

[0166] [Table 2]

[0167] Initial capacity (mAh / g) Capacity (mAh / g) after 2 weeks of storage Capacity retention rate (%) Example 1 3219.9 2879.1 89.4 Example 2 3216.1 2746.3 85.3 Example 3 3219.3 2785.9 86.5 Comparative Example 1 3223.2 2431.5 75.4 Comparative Example 2 3222.6 2484.6 77.1 Comparative Example 3 - - -

[0168] Referring to Tables 1 and 2, when the electrolyte contains additives such as those of Formula 1, specifically, when only additives having the same structure as Formula 1a or 1b are used, or a mixture of both is used, the capacity retention rate after 200 charge-discharge cycles and the capacity retention rate after high-temperature storage are both superior to Comparative Example 1. This is because a stable SEI film is formed through the reductive decomposition of the additives during charge-discharge, thereby improving the stability of the interface between the electrolyte and the negative electrode. Furthermore, in Comparative Examples 1 and 2, where no additives were added or only a very small amount of additives were added, the capacity retention rate decreased compared to the examples. This is because the effect was not obtained due to the small amount of additives, or because the additives acted as resistors due to residual additives.

[0169] The above description is merely an illustration of the technical concept of the present invention. Those skilled in the art can make various modifications and variations without departing from the essential characteristics of the invention. Therefore, the accompanying drawings disclosed in this invention are not intended to limit the technical concept of the invention, but rather to describe it. The scope of the technical concept of the invention is not limited by these drawings. The scope of protection of this invention should be interpreted based on the appended claims, and all technical concepts within their equivalent scope should be interpreted as being included within the scope of this invention.

[0170] On the other hand, this specification uses terms such as up, down, left, right, front, and back to indicate direction, but obviously these terms are only for ease of explanation and may vary depending on the position of the object or the observer's position.

Claims

1. A non-aqueous electrolyte for lithium secondary batteries, said non-aqueous electrolyte comprising: a lithium salt; an organic solvent; and a first additive. in, The first additive comprises a compound represented by the following chemical formula 1: [Chemical Formula 1] ,and Wherein, R1 is an unsaturated hydrocarbon group having 2 to 20 carbon atoms with or without a substituent, and R2 is selected from the group consisting of hydrogen, an alkyl group having 1 to 10 carbon atoms with or without a substituent, and a cycloalkyl group having 3 to 8 carbon atoms with or without a substituent.

2. The non-aqueous electrolyte as described in claim 1, wherein, R1 is an alkenyl group having 2 to 20 carbon atoms, with or without a substituent, or an alkynyl group having 2 to 20 carbon atoms, with or without a substituent.

3. The non-aqueous electrolyte as described in claim 1, wherein, The first additive is at least one selected from the group consisting of compounds represented by chemical formula 1a and compounds represented by chemical formula 1b: [Chemical Formula 1a] ， Wherein, n is a natural number from 1 to 18, and R2 is selected from the group consisting of hydrogen, alkyl groups with or without substituents having 1 to 10 carbon atoms, and cycloalkyl groups with or without substituents having 3 to 8 carbon atoms. [Chemical Formula 1b] ， Wherein, n is a natural number from 1 to 18, and R2 is selected from the group consisting of hydrogen, alkyl groups with or without substituents having 1 to 10 carbon atoms, and cycloalkyl groups with or without substituents having 3 to 8 carbon atoms.

4. The non-aqueous electrolyte as described in claim 3, wherein, The first additive is at least one selected from the group consisting of compounds represented by chemical formula 1c and compounds represented by chemical formula 1d: [Chemical Formula 1c] ,and [Chemical formula 1d] 。 5. The non-aqueous electrolyte as described in claim 3, wherein, The first additive comprises a compound represented by chemical formula 1a and a compound represented by chemical formula 1b, wherein the molar ratio of the compound represented by chemical formula 1a to the compound represented by chemical formula 1b is 2:8 to 8:

2.

6. The non-aqueous electrolyte as described in claim 1, wherein, The content of the first additive is from 0.01% to 5% by weight of the total weight of the non-aqueous electrolyte.

7. The non-aqueous electrolyte as described in claim 1, wherein, The content of the first additive is 0.1% to 3% by weight of the total weight of the non-aqueous electrolyte.

8. The non-aqueous electrolyte of claim 1, further comprising: at least one second additive selected from the group consisting of halogen-substituted or unsubstituted cyclic carbonate compounds, nitrile compounds, phosphate esters / salt compounds, borate esters / salt compounds, sulfonyl lactone compounds, lithium salt compounds, and sulfate esters / salt compounds.

9. The non-aqueous electrolyte as described in claim 1, wherein, The lithium salt is at least one selected from the group consisting of LiPF6, LiAsF6, LiN(SO2F)2, LiCF3SO3, LiN(CF3SO2)2, LiBF6, LiSbF6, LiN(C2F5SO2)2, LiAlO4, LiAlCl4, LiSO3CF3, and LiClO4.

10. The non-aqueous electrolyte as described in claim 1, wherein, The organic solvent comprises esters, ethers, ketones, or combinations thereof.

11. The non-aqueous electrolyte as described in claim 1, wherein, The organic solvent comprises chain carbonates, cyclic carbonates, or combinations thereof.

12. A lithium secondary battery comprising the non-aqueous electrolyte for lithium secondary batteries as described in claim 1.

Images