Electrolyte additive for secondary battery, non-aqueous electrolyte for lithium secondary battery containing the same, and lithium secondary battery containing the same

Abstract

The present invention relates to a new electrolyte additive, a nonaqueous electrolyte for lithium secondary batteries containing this new electrolyte additive, and a lithium secondary battery containing this nonaqueous electrolyte. More specifically, the present invention relates to a nonaqueous electrolyte for lithium secondary batteries containing an additive that can form a stable coating on the electrode surface. The present invention also relates to a lithium secondary battery that contains this nonaqueous electrolyte, which prevents deterioration of the high-temperature life of the lithium secondary battery, prevents increase in resistance when the lithium secondary battery is stored at high temperatures, and improves the ability to suppress expansion of the secondary battery's volume (thickness) when the lithium secondary battery is stored at high temperatures.

Description

[Technical Field]

[0001] The present invention relates to an electrolyte additive for secondary batteries. More specifically, the present invention relates to a nonaqueous electrolyte additive that is effective in removing decomposition products generated from lithium salts, and a nonaqueous electrolyte for lithium secondary batteries containing the same. The present invention relates to a nonaqueous electrolyte additive that can form a strong solid electrolyte interfacial film (SEI) on the surface of a negative electrode, and a nonaqueous electrolyte for lithium secondary batteries containing the same. The present invention also relates to a lithium secondary battery containing such a nonaqueous electrolyte. The lithium secondary battery of the present invention contains the nonaqueous electrolyte, thereby improving the high-temperature performance of the lithium secondary battery. [Background technology]

[0002] Lithium secondary batteries are not only used as portable power sources for mobile phones, laptops, etc., but are also expanding their application to medium- to large-sized power sources such as electric bicycles and electric vehicles (EVs). As their application fields expand, there is a demand for lithium secondary batteries that can maintain excellent performance not only at room temperature but also in harsher external environments such as high and low temperatures.

[0003] Currently widely used lithium secondary batteries typically consist of a carbon-based anode capable of intercalating and deintercalating lithium ions, a lithium-containing transition metal oxide-based cathode, a non-aqueous electrolyte consisting of a lithium salt dissolved in a mixed carbonate organic solvent, and a separator that prevents contact between the cathode and anode. During charging, lithium atoms at the cathode ionize into lithium ions and electrons. The electrons then travel to the anode through an external circuit, and the lithium ions travel to the anode through the non-aqueous electrolyte and separator and intercalate into the carbon anode. During discharge, the electrons travel to the cathode through an external circuit, and simultaneously, the lithium ions deintercalate from the carbon anode and travel to the cathode through the non-aqueous electrolyte and separator, where they reunite to form stable lithium atoms. Lithium secondary batteries generate electrical energy through repeated charging and discharging.

[0004] In lithium secondary batteries, the positive electrode active material can structurally collapse during charge and discharge, causing metal ions to leach from the positive electrode surface. The metal ions leach from the positive electrode can be electrodeposited on the negative electrode, causing the negative electrode to deteriorate. This deterioration of the negative electrode tends to accelerate when the positive electrode potential is high or when the secondary battery is exposed to high temperatures.

[0005] To solve these problems, a method has been proposed in which a compound capable of forming a film (solid electrolyte interphase film, SEI (Solid Electrolyte Interphase)) on the surface of the negative electrode is added to the non-aqueous electrolyte. However, such electrolyte additives cause other side effects such as a reduction in the life performance of the secondary battery and a deterioration in high-temperature safety, and also cause other problems such as a reduction in various performances of the lithium secondary battery.

[0006] LiPF6 is the main lithium salt used in lithium secondary batteries to achieve the appropriate characteristics of the secondary battery. - Anions are highly sensitive to heat, and when secondary batteries are exposed to high temperatures, they thermally decompose to generate Lewis acids such as PF5. The PF5 thus generated not only decomposes organic solvents such as ethylene carbonate, but also generates hydrofluoric acid (HF), accelerating the dissolution of transition metals from the positive electrode active material. The dissolve-in transition metals can be electrodeposited on the positive electrode, causing increased positive electrode resistance, or on the negative electrode, causing self-discharge of the negative electrode. They can also destroy the solid electrolyte interfacial layer (SEI) on the negative electrode, further decomposing the electrolyte and, consequently, increasing the resistance and shortening the lifespan of the secondary battery. These electrolyte decomposition reactions also lead to gas generation within the secondary battery.

[0007] Therefore, when a fully charged lithium secondary battery is stored at high temperatures, the solid electrolyte interfacial layer (SEI) gradually breaks down over time. This breakdown of the solid electrolyte interfacial layer exposes the surface of the anode. The exposed surface of the anode reacts with the carbonate-based solvent in the electrolyte and decomposes, causing a continuous side reaction. This side reaction continuously generates gas.

[0008] Regardless of the type of gas generated in this way, it increases the internal pressure of the lithium secondary battery, acts as a resistive element to lithium migration, expands the volume (thickness) of the secondary battery, creates major problems in reducing the weight of the secondary battery, and deteriorates the performance of the secondary battery.

[0009] In recent years, as the application fields of lithium secondary batteries have expanded, there has been a steady demand for stability and long life characteristics in high-temperature environments. This performance is largely determined by the solid electrolyte interfacial film (SEI film) formed by the initial reaction between the electrode and the electrolyte. Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, in order to improve the high-temperature cycle characteristics and low-temperature output of lithium secondary batteries, there is a constant demand for the development of additives that can suppress side reactions between the positive electrode and the electrolyte and form a strong solid electrolyte interfacial film (SEI film) on the surface of the negative electrode.

[0011] In order to solve the above problems, the present invention provides a non-aqueous electrolyte solution for a lithium secondary battery, which contains an additive capable of forming a stable solid electrolyte interface film (SEI) on the surface of an electrode, particularly on the surface of a negative electrode.

[0012] In addition, in order to solve the above problems, the present invention aims to provide an electrolyte additive for secondary batteries that is effective in forming a strong solid electrolyte interfacial film (SEI) on the surface of an electrode, particularly on the surface of a negative electrode, and in removing decomposition products generated from lithium salts.

[0013] In addition, in order to solve the above-mentioned problems of the prior art, the present invention provides a non-aqueous electrolyte for a lithium secondary battery that can improve high-temperature stability without deteriorating the high-temperature life and performance of the lithium secondary battery, and a lithium secondary battery including the non-aqueous electrolyte for the lithium secondary battery. [Means for solving the problem]

[0014] The nonaqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention comprises:

[0015] Compounds containing imidazole and fluoro groups as additives;

[0016] Lithium salts;

[0017] additional additives; and

[0018] Contains a non-aqueous organic solvent.

[0019] The nonaqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention comprises:

[0020] A compound containing an imidazole group and a fluoro group, represented by the following chemical formula 1, as an additive;

[0021] Lithium salts;

[0022] additional additives; and

[0023] Contains a non-aqueous organic solvent.

[0024] [Chemical formula 1] JPEG2025530042000001.jpg2970

[0025] In one embodiment of the present invention, there is provided a lithium secondary battery including the nonaqueous electrolyte for a lithium secondary battery of the present invention, a positive electrode, a negative electrode, and a separator.

[0026] The negative electrode may include a carbon-based negative electrode active material and a silicon-based negative electrode active material.

[0027] The negative electrode may include a carbon-based negative electrode active material and a silicon-based negative electrode active material in a weight ratio of 97:3 to 50:50.

[0028] The negative electrode may include a carbon-based negative electrode active material and a silicon-based negative electrode active material in a weight ratio of 90:10 to 60:40. [Effects of the Invention]

[0029] The compound containing an imidazole group and a fluoro group, particularly the compound represented by Chemical Formula 1, which is provided as an additive to the nonaqueous electrolyte of the present invention, functions as a Lewis base due to the nitrogen atom of the imidazole group, and can remove Lewis acids such as HF and PF5, which are decomposition products generated by the decomposition of anions when a secondary battery is exposed to high temperatures, from the electrolyte. Therefore, the compound containing an imidazole group and a fluoro group, particularly the compound represented by Chemical Formula 1, which is provided as an additive to the nonaqueous electrolyte of the present invention, can suppress deterioration of the surface insulating film (SEI) of the positive or negative electrode caused by Lewis acids, prevent further electrolyte decomposition in the secondary battery due to destruction of the surface insulating film (SEI), and suppress self-discharge of the secondary battery. The imidazole group also helps form a stable surface insulating film (SEI) on the surface of the negative electrode. The fluoro group of the compound serves to remove CO2 gas generated at the positive electrode and prevent swelling of the secondary battery.

[0030] The additive contained in the nonaqueous electrolyte solution for a secondary battery of the present invention, i.e., the compound containing an imidazole group and a fluoro group, particularly the functional group of the compound represented by Chemical Formula 1, has the effects described above, and prevents the lifespan of a lithium secondary battery from deteriorating even when exposed to high temperatures. It also suppresses an increase in resistance and gas generation during storage at high temperatures, thereby reducing the volume expansion of the secondary battery and enabling the realization of a secondary battery with improved performance. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be described in more detail below with reference to examples. These examples are merely for the purpose of illustrating the present invention, and should not be construed as limiting the scope of the present invention.

[0032] As used herein, terms such as "comprise," "have," and the like should be understood as open-ended terms that encompass the possibility of including other components, unless specifically stated otherwise in the phrase or sentence in which the expression is included.

[0033] As used herein, "%" means % by weight unless expressly indicated otherwise.

[0034] The electrolyte additive for lithium secondary batteries, the nonaqueous electrolyte for lithium secondary batteries, and the lithium secondary battery containing this nonaqueous electrolyte according to the present invention will be specifically described below.

[0035] <Electrolyte additives for lithium secondary batteries>

[0036] The present invention provides a compound containing an imidazole group and a fluoro group, particularly a compound containing an imidazole group and a fluoro group represented by the following Chemical Formula 1, as an additive for an electrolyte solution for a lithium secondary battery.

[0037] [Chemical formula 1]

[0038] JPEG2025530042000002.jpg2970

[0039] <Electrolyte for lithium secondary batteries>

[0040] The present invention

[0041] Compounds containing an imidazole group and a fluoro group;

[0042] additional additives;

[0043] lithium salts; and

[0044] Provided is an electrolyte solution for a lithium secondary battery, which contains a non-aqueous organic solvent.

[0045] The present invention

[0046] a compound containing an imidazole group and a fluoro group, represented by the above chemical formula 1;

[0047] additional additives;

[0048] lithium salts; and

[0049] Provided is an electrolyte solution for a lithium secondary battery, which contains a non-aqueous organic solvent.

[0050] The compound containing an imidazole group and a fluoro group may be included in an amount of 0.05 to 20 wt % based on the total weight of the electrolyte solution for lithium secondary batteries.

[0051] The compound containing an imidazole group and a fluoro group may be contained in an amount of 0.05 to 10 wt % based on the total weight of the electrolyte solution for lithium secondary batteries.

[0052] The compound containing an imidazole group and a fluoro group may be contained in an amount of 0.05 to 5 wt %, 0.05 to 3 wt %, or 0.05 to 2 wt % based on the total weight of the electrolyte solution for lithium secondary batteries.

[0053] The compound containing an imidazole group and a fluoro group may be included in an amount of 0.1 to 20 wt % based on the total weight of the electrolyte solution for lithium secondary batteries.

[0054] The compound containing an imidazole group and a fluoro group may be contained in an amount of 0.1 to 10 wt % based on the total weight of the electrolyte solution for lithium secondary batteries.

[0055] The compound containing an imidazole group and a fluoro group may be contained in an amount of 0.1 to 5 wt %, 0.1 to 3 wt %, or 0.1 to 2 wt % based on the total weight of the electrolyte solution for lithium secondary batteries.

[0056] If the compound containing an imidazole group and a fluoro group is contained in an amount of less than 0.05 wt % relative to the total weight of the electrolyte for a lithium secondary battery, the effect of preventing volume expansion of the lithium secondary battery and the effect of reducing the internal resistance are insufficient. Conversely, if the compound containing an imidazole group and a fluoro group is contained in an amount of more than 20 wt % relative to the total weight of the electrolyte for a lithium secondary battery, the internal resistance and capacity of the secondary battery increase, resulting in problems of reduced high-temperature life characteristics and reduced high-temperature storage characteristics.

[0057] The electrolyte for a lithium secondary battery may further include at least one additional additive selected from the group consisting of halogen-substituted or unsubstituted carbonate-based compounds, nitrile-based compounds, borate-based compounds, lithium salt-based compounds, phosphate-based compounds, sulfite-based compounds, sulfone-based compounds, sulfate-based compounds, and sultone-based compounds.

[0058] Representative examples of the additional additives include lithium difluorophosphate, lithium tetrafluoro(oxalate)phosphate, lithium bis(fluorosulfonyl)imide, 1,3-propane sultone, 1,3-propene sultone, fluoroethylene carbonate, vinylene carbonate, and vinyl ethylene carbonate.

[0059] The additional additive may be included in an amount of 0.05 to 20 wt % based on the total weight of the electrolyte solution for lithium secondary batteries.

[0060] The additional additive may be preferably included in an amount of 0.05 to 10 wt % based on the total weight of the electrolyte solution for lithium secondary batteries.

[0061] The additional additive may be contained in an amount of more preferably 0.05 to 5 wt %, specifically 0.05 to 3 wt %, based on the total weight of the electrolyte solution for lithium secondary batteries.

[0062] If the additional additive is included in an amount less than 0.05 wt % based on the total weight of the electrolyte for a lithium secondary battery, the effect of forming a film on the electrode may be small, and the effect of suppressing side reactions between the electrode and the electrolyte may be reduced. If the electrolyte additive is included in an amount more than 20 wt % based on the total weight of the electrolyte for a lithium secondary battery, an excessively thick film may be formed on the electrode surface, increasing interfacial resistance and resulting in a decrease in capacity.

[0063] The lithium salt may include at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiBF6, LiSbF6, LiAlO4, LiAlCl4, LiClO4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, and LiB(C2O4)2.

[0064] The lithium salt preferably has a large degree of lattice energy dissociation, excellent ionic conductivity, thermal stability, and oxidation resistance, and functions as a path for lithium ions to move within the secondary battery, thereby enabling the basic operation of the lithium secondary battery.

[0065] The concentration of the lithium salt may be 0.1 to 2.5 M (mol / L) based on the total amount of the electrolyte solution for lithium secondary batteries.

[0066] The concentration of the lithium salt may be preferably 0.3 to 2.5 M (mol / L) based on the total amount of the electrolyte for lithium secondary batteries, taking into consideration properties related to electrical conductivity and viscosity related to lithium ion mobility.

[0067] The concentration of the lithium salt may be more preferably 0.7 to 1.6 M (mol / L) in consideration of properties related to electrical conductivity and viscosity related to the mobility of lithium ions.

[0068] If the concentration of the lithium salt is less than 0.1M, the electrical conductivity of the electrolyte for a lithium secondary battery is reduced, and the performance of the non-aqueous electrolyte for rapidly transferring ions between the positive electrode and the negative electrode of the lithium secondary battery is reduced. If the concentration of the lithium salt is more than 2.5M, the viscosity of the electrolyte for a lithium secondary battery is increased, and the mobility of lithium ions is reduced, resulting in a reduction in secondary battery performance at low temperatures.

[0069] The non-aqueous organic solvent may be a linear carbonate solvent, a cyclic carbonate solvent, or a mixture thereof.

[0070] The linear carbonate solvent may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC).

[0071] The cyclic carbonate solvent may contain at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), vinylene carbonate (VC), and fluoroethylene carbonate (FEC).

[0072] It may be desirable to use a mixture of a cyclic, high-dielectric-constant carbonate-based organic solvent having high ionic conductivity that can improve the charge / discharge performance of a secondary battery and a low-viscosity, linear carbonate-based organic solvent that can appropriately adjust the viscosity of the high-dielectric-constant carbonate-based organic solvent.

[0073] Specifically, a high-dielectric-constant carbonate organic solvent selected from the group consisting of cyclic carbonate solvents such as ethylene carbonate (EC), propylene carbonate (PC), and mixtures thereof, can be mixed with a low-viscosity carbonate organic solvent selected from the group consisting of linear carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and mixtures thereof, and the like.

[0074] The cyclic carbonate solvent has high polarity and can dissociate lithium ions sufficiently, but has the disadvantage of high viscosity and low ionic conductivity. Therefore, the characteristics of a lithium secondary battery can be optimized by mixing the cyclic carbonate solvent with a linear carbonate solvent, which has low polarity but low viscosity.

[0075] Therefore, it may be preferable to use a mixture of at least one solvent selected from the cyclic carbonate solvents and at least one solvent selected from the linear carbonate solvents as the non-aqueous organic solvent.

[0076] The mixed solvent of the linear carbonate solvent and the cyclic carbonate solvent can be used by mixing the linear carbonate solvent and the cyclic carbonate solvent in a volume ratio of 9:1 to 1:9.

[0077] From the viewpoint of the life and storage characteristics of the secondary battery, it may be more preferable to use a mixed solvent of the linear carbonate solvent and the cyclic carbonate solvent in a volume ratio of 2:8 to 8:2.

[0078] The non-aqueous organic solvent can include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0079] The non-aqueous organic solvent may contain 5 to 40 wt % of the ethylene carbonate (EC), 5 to 20 wt % of the propylene carbonate (PC), 10 to 70 wt % of the ethyl methyl carbonate (EMC), and 10 to 60 wt % of the diethyl carbonate (DEC).

[0080] Specifically, among the cyclic carbonate solvents, ethylene carbonate (EC) or propylene carbonate (PC), which have a high dielectric constant, can be used. When artificial graphite is used as the negative electrode active material, ethylene carbonate (EC) is preferred. Among the linear carbonate solvents, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC), which have a low viscosity, are preferred.

[0081] The non-aqueous organic solvent may be included in an amount of 5% to 80% of the total amount of the electrolyte solution for lithium secondary batteries, or 5% to 70% of the total amount of the electrolyte solution for lithium secondary batteries.

[0082] <Lithium secondary battery>

[0083] The lithium secondary battery containing the non-aqueous electrolyte does not deteriorate in life characteristics at high temperatures, does not increase in resistance during storage at high temperatures, and has excellent performance in suppressing expansion of the secondary battery volume (thickness).

[0084] The lithium secondary battery of the present invention will be specifically described below.

[0085] The lithium secondary battery of the present invention comprises:

[0086] positive electrode;

[0087] negative electrode;

[0088] Separation membrane; and

[0089] Contains a non-aqueous electrolyte.

[0090] The positive electrode is made of LiCoO2, LiFePO4, LiMnO2, LiMn2O4, or LiNiO 2, or LiNi 1-x-y Co x M y It may contain at least one positive electrode active material selected from the group consisting of lithium metal oxides such as O2 (0≦x≦, 0≦y≦1, 0≦x+y≦1, M is Al, Sr, Mg, Mn or La).

[0091] The negative electrode may contain at least one negative electrode active material selected from the group consisting of silicon, a silicon compound, tin, a tin compound, lithium titanate, crystalline carbon, amorphous carbon, artificial graphite, natural graphite, and a mixture of artificial graphite and natural graphite.

[0092] The separator may be composed of a porous polymer film made of at least one polyolefin polymer selected from ethylene polymer, propylene polymer, ethylene / butene copolymer, and ethylene / hexene copolymer, or a laminate thereof. The separator may include a coating film coated with a ceramic or polymer material.

[0093] The non-aqueous electrolyte solution is a compound containing an imidazole group and a fluoro group, particularly a compound represented by the following formula 1:

[0094] additional additives;

[0095] lithium salts; and

[0096] A non-aqueous organic solvent may be included.

[0097] [Chemical formula 1]

[0098] JPEG2025530042000003.jpg2970

[0099] Examples of the lithium secondary battery include, but are not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0100] More specifically, the positive electrode active material is preferably a composite metal oxide of lithium and one or more materials selected from cobalt, manganese, and nickel. The composite metal oxide may have various solid solubility ratios among the cobalt, manganese, and nickel metals, and may further contain, in addition to the cobalt, manganese, and nickel metals, an element selected from the group consisting of Mg, Al, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Cr, Fe, Sr, V, and rare earth elements.

[0101] Specifically, the positive electrode active material may be LiCoO2, LiFePO4, LiMnO2, LiMn2O4, or LiNiO 2, or LiNi 1-x-y Co x M y Lithium metal oxides such as O2 (0≦x≦1, 0≦y≦1, 0≦x+y≦1, M is Al, Sr, Mg, Mn, or La) or lithium intercalation compounds such as lithium chalcozenide compounds can be used, but are not limited thereto, and any material that can be used as a positive electrode active material in a secondary battery can be used.

[0102] The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer may include a positive electrode active material capable of absorbing and releasing lithium, a binder, a conductive material, and the like.

[0103] The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector. The negative electrode active material layer may include a negative electrode active material capable of inserting and extracting lithium, a binder, a conductive material, etc. The negative electrode active material may be, but is not limited to, crystalline carbon, amorphous carbon, a carbon composite, carbon fiber, lithium metal, a lithium alloy, or a carbon-silicon composite, and any material usable as a negative electrode active material in a secondary battery may be used.

[0104] The positive electrode and / or negative electrode can be manufactured by dispersing an electrode active material, a binder, a conductive material, and optionally a thickener in a solvent to prepare an electrode slurry composition, and then coating the slurry composition on an electrode current collector. The positive electrode current collector is often made of aluminum or an aluminum alloy, and the negative electrode current collector is often made of copper or a copper alloy.

[0105] The positive electrode current collector and the negative electrode current collector may be in the form of a foil or a mesh.

[0106] The binder is a substance that functions to form a paste of the active material, to adhere the active material to one another, to adhere the active material to the current collector, and to buffer the expansion and contraction of the active material, and may be any binder known to those skilled in the art. Examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVdF), polyhexafluoropropylene-polyvinylidene fluoride copolymer (PVdF / HFP), poly(vinyl acetate), alkylated polyethylene oxide, polyvinyl ether, poly(methyl methacrylate), poly(ethyl acrylate), polyacrylonitrile, polyvinylpyridine, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, epoxy resin, and nylon.

[0107] The conductive material is used to impart conductivity to the electrode and can be any conductive material that does not cause chemical changes in the resulting secondary battery. The conductive material can be at least one selected from the group consisting of graphite-based conductive materials, carbon black-based conductive materials, and metal or metal compound-based conductive materials. Examples of graphite-based conductive materials include artificial graphite and natural graphite. Examples of carbon black-based conductive materials include acetylene black, ketjen black, denka black, thermal black, and channel black. Examples of metal or metal compound-based conductive materials include tin, tin oxide, tin phosphate (SnPO), titanium oxide, potassium titanate, and perovskite materials such as LaSrCoO and LaSrMnO. However, the conductive materials are not limited to these.

[0108] The thickener is not particularly limited as long as it serves to adjust the viscosity of the active material slurry, and examples thereof include carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

[0109] The solvent in which the electrode active material, binder, conductive material, etc. are dispersed can be a non-aqueous solvent or an aqueous solvent. Examples of the non-aqueous solvent include N-methyl-2-pyrroledione (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. Examples of the aqueous solvent include water.

[0110] The lithium secondary battery may include a separator that prevents short circuits between the positive and negative electrodes and provides a path for lithium ions to move. The separator may be a polyolefin polymer film such as polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, or polypropylene / polyethylene / polypropylene, or a multilayer film, microporous film, woven fabric, or nonwoven fabric thereof. Alternatively, the separator may be a porous polyolefin film coated with a highly stable resin.

[0111] The lithium secondary battery can be formed into various shapes such as a square shape, a cylindrical shape, a pouch shape, and a coin shape. [Example]

[0112] The present invention will be described in more detail below with reference to examples, which should not be construed as limiting the scope of the present invention.

[0113] <Synthesis Example of 2,2,2-trifluoroethyl 1H-imidazole-1-carboxylate (Compound of Chemical Formula 1)>

[0114] A 500 mL three-neck flask was equipped with an N2 purge line, a dropping funnel, and a thermometer. Then, 0.31 mol of 1,1'-carbonyldiimidazole and 150 mL of dichloromethane were added and stirred. The reactor was filled with nitrogen and cooled from ambient temperature to 10°C. While maintaining the temperature, 0.32 mol of 2,2,2-trifluoroethanol was added dropwise over 30 minutes. After the addition of 2,2,2-trifluoroethanol was completed, the temperature was changed from 10°C to room temperature, and the reaction was continued at the same temperature for 3 hours. After the reaction was completed, 150 mL of water was added to extract the organic layer. This process was repeated twice. The mixture was treated with MgSO4 to remove moisture and then filtered. The filtrate was concentrated to remove the dichloromethane. After drying in a vacuum oven, the final compound, 2,2,2-trifluoroethyl 1H-imidazole-1-carboxylate, was obtained in 75% yield.

[0115] 1 H NMR (Chloroform-d, δ ppm): 1H 8.1ppm, 1H 7.3.ppm, 1H 6.9ppm, 2H 4.7ppm,

[0116] 19 F NMR(Chloroform-d, δ ppm) -74.09 1F, HRMS: C6H5N2O2F3(M+):194.03

[0117] <Production of an electrolyte solution for a lithium secondary battery containing 2,2,2-trifluoroethyl 1H-imidazole-1-carboxylate (compound of chemical formula 1)>

[0118] After dissolving LiPF6 to 1.0 M in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC / EMC = 25 / 75 by volume ratio), 1.0 wt% of fluoroethylene carbonate (FEC), 1.0 wt% of lithium difluorophosphate (LiPO2F2), 0.5 wt% of propane sultone (PS), 0.5 wt% of ethylene sulfate (Esa), and 0.5 wt% of 2,2,2-trifluoroethyl 1H-imidazole-1-carboxylate of the synthesis example represented by Chemical Formula 1 were added to the mixed solution to produce an electrolyte for a lithium secondary battery containing the compound of Chemical Formula 1.

[0119] <Manufacture of a Lithium Secondary Battery Containing an Electrolyte Containing the Compound of Chemical Formula 1>

[0120] Li[Ni x Co 1-x-y Mn y O2 (0 < x < 0.5, 0 < y < 0.5), 94 wt% of an NCM-based positive electrode active material, 3 wt% of a conductive material (Super-P), and 3 wt% of a binder (PVdF) were added to N-methyl-2-pyrrolidone (NMP), an organic solvent, to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to an aluminum thin film as a current collector, dried to manufacture a positive electrode, and then rolled by roll pressing to produce a positive electrode. Also, 96 wt% of a graphite-based negative electrode active material containing silicon oxide (SiOx), 1 wt% of a conductive material (Super-P), 1.5 wt% of a binder SBR, and 1.5 wt% of CMC were mixed to manufacture a negative electrode active material slurry. The negative electrode active material slurry was applied to a copper thin film as a negative electrode current collector and dried to produce a negative electrode.

[0121] The positive electrode and negative electrode manufactured as described above were prepared, and a separator was interposed therebetween. Then, an electrolyte for a lithium secondary battery containing the compound of Chemical Formula 1 was injected between the two electrodes with the separator interposed, and a lithium secondary battery containing the electrolyte and being of an aluminum pouch type (Al-Pouch type) containing the compound of Chemical Formula 1 was manufactured.

[0122] [Comparative Example]

[0123] <Production of electrolyte for lithium secondary batteries containing 1,3-propene sultone (PRS) additive>

[0124] Non-aqueous electrolytes for lithium secondary batteries can contain a sultone-based compound as needed to improve high-temperature stability and suppress battery expansion at high temperatures, since decomposition of the non-aqueous electrolyte can weaken high-temperature stability and cause battery expansion at high temperatures. The sultone-based compound can be, for example, at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone (BS), ethene sultone, 1,3-propene sultone, 1,4-butene sultone, and 1-methyl-1,3-propene sultone. In the comparative example, the commonly used 1,3-propene sultone (PRS) was used.

[0125] LiPF6 was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio of EC / EMC = 25 / 75) to a concentration of 1.0 M, and then 1.0 wt% of fluoroethylene carbonate (FEC), 1.0 wt% of lithium difluorophosphate (LiPO2F2), 0.5 wt% of propane sultone (PS), 0.5 wt% of ethylene sulfate (ESa), and 0.5 wt% of 1,3-propene sultone (PRS) as a comparative example were added to the mixed solution to prepare an electrolyte for a lithium secondary battery.

[0126] <Production of a lithium secondary battery containing an electrolyte solution containing 1,3-propene sultone (PRS) additive>

[0127] A lithium secondary battery containing a 1,3-propene sultone (PRS) electrolyte solution without the compound of Chemical Formula 1 was fabricated in the same manner as in the fabrication of the lithium secondary battery of the above example, except that the 2,2,2-trifluoroethyl 1H-imidazole-1-carboxylate compound represented by Chemical Formula 1 was not added as the electrolyte solution, and a lithium secondary battery electrolyte containing 1,3-propene sultone (PRS) was used.

[0128] The compositions of the electrolyte solutions for lithium secondary batteries of the Examples and Comparative Examples are shown in Table 1 below.

[0129] <Composition of electrolyte for lithium secondary batteries>

[0130] [Table 1]

[0131] [Experimental Example]

[0132] <Experimental Example 1> Measurement of life capacity retention rate at high temperature (45°C)

[0133] Pouch-type lithium secondary batteries fabricated using the lithium secondary battery electrolytes of the Examples and Comparative Examples were charged at a high temperature (45°C) at a 1C-rate up to 4.2 V, then discharged at a 1C-rate down to 2.7 V after a 10-minute rest period, followed by another 10-minute rest period. This process was repeated 500 times, and the battery discharge capacity (mAh) and life capacity retention (%) were measured. The measured discharge capacities and life capacity retentions of the secondary batteries were compared, and the results are shown in Table 2.

[0134] [Table 2]

[0135] As shown in Table 2, the results of the life evaluation at high temperatures showed that the lithium secondary batteries of the Examples had a higher 500-cycle discharge capacity and a higher life capacity retention rate at high temperatures than the lithium secondary batteries of the Comparative Examples.

[0136] Therefore, it was confirmed that the lithium secondary battery of the Example contained an electrolyte solution containing the compound represented by Chemical Formula 1, and thus exhibited a higher life capacity retention rate without deteriorating the high-temperature life performance of the secondary battery compared to the lithium secondary battery of the Comparative Example. That is, the compound additive of Chemical Formula 1 improved the life capacity retention rate at high temperatures without deteriorating performance due to side reactions with other additives.

[0137] <Experimental Example 2> High temperature (60℃) storage characteristics measurement

[0138] The pouch-shaped lithium secondary batteries prepared using the lithium secondary battery electrolytes of the Examples and Comparative Examples were stored at high temperature (60°C) for 6 weeks, and the volume change rate of the secondary batteries was measured. Table 3 below shows the volume change rate of the secondary batteries after 6 weeks of storage at high temperature (60°C) compared to the 0th week.

[0139] [Table 3]

[0140] As shown in Table 3, the volume increase rate of the Examples was lower than that of the Comparative Examples, and it was therefore found that the additive of the present invention is an additive with an excellent effect of suppressing gas generation.

Claims

1. additives; additional additives; lithium salts; and A non-aqueous electrolyte solution for a lithium secondary battery containing a non-aqueous organic solvent, The additive is a compound containing an imidazole group and a fluoro group.

2. 2. The non-aqueous electrolyte for a lithium secondary battery according to claim 1, wherein the additive is a compound of the following formula 1: [Chemical formula 1]

3. 3. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the additive is contained in an amount of 0.05 to 20 wt % based on the total weight of the non-aqueous electrolyte solution for a lithium secondary battery.

4. 3. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the additional additive is at least one compound selected from the group consisting of halogen-substituted or unsubstituted carbonate-based compounds, nitrile-based compounds, borate-based compounds, lithium salt-based compounds, phosphate-based compounds, sulfite-based compounds, sulfone-based compounds, sulfate-based compounds, and sultone-based compounds.

5. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1 or 2; positive electrode; a negative electrode; and A lithium secondary battery including a separator.

6. The lithium secondary battery according to claim 5 , wherein the negative electrode comprises a carbon-based negative electrode active material and a silicon-based negative electrode active material.

7. 7. The lithium secondary battery of claim 6, wherein the carbon-based negative electrode active material and the silicon-based negative electrode active material are contained in a weight ratio of 97:3 to 50:

50.

8. 8. The lithium secondary battery of claim 7, wherein the carbon-based negative electrode active material and the silicon-based negative electrode active material are contained in a weight ratio of 90:10 to 60:40.

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