Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery

Abstract

The present invention relates to a novel electrolyte additive, a non-aqueous electrolyte for a lithium secondary battery comprising the novel electrolyte additive, and a lithium secondary battery comprising the non-aqueous electrolyte. In more detail, the present invention relates to a non-aqueous electrolyte for a lithium secondary battery, which comprises an additive capable of forming a stable coating on the surface of an electrode. The present invention also relates to a lithium secondary battery with improved performance, which comprises the above-mentioned non-aqueous electrolyte, so that the high temperature life of the lithium secondary battery will not deteriorate, and the resistance will not increase when the lithium secondary battery is stored at high temperature. In addition, when the lithium secondary battery is stored at high temperature, the volume (thickness) expansion of the secondary battery can be suppressed.

Description

Technical Field

[0001] The present invention relates to an electrolyte additive for a secondary battery. More specifically, the present invention relates to a non-aqueous electrolyte additive having an excellent effect of removing decomposition products generated by lithium salts and a non-aqueous electrolyte for a lithium secondary battery containing the non-aqueous electrolyte additive. The present invention relates to a non-aqueous electrolyte additive capable of forming a strong solid electrolyte interface film (SEI) on the surface of a negative electrode and a non-aqueous electrolyte for a lithium secondary battery containing the non-aqueous electrolyte additive. The present invention also relates to a lithium secondary battery containing the above-mentioned non-aqueous electrolyte. The lithium secondary battery of the present invention contains the above-mentioned non-aqueous electrolyte, thereby improving the high temperature performance of the lithium secondary battery. Background Art

[0002] Lithium secondary batteries are not only used as portable power sources for mobile phones and laptops, but also for medium and large power sources for electric bicycles, electric vehicles (EVs), etc. With the expansion of such application areas, there is a need for lithium secondary batteries that can maintain excellent performance not only under normal temperature conditions but also in more demanding external environments such as high or low temperature environments.

[0003] At present, widely used lithium secondary batteries are usually composed of a carbon-based negative electrode that can embed and deintercalate lithium ions, a lithium-containing transition metal oxide positive electrode, a non-aqueous electrolyte in which lithium salts are dissolved in a mixed carbonate organic solvent, and a diaphragm for preventing contact between the positive and negative electrodes. When charging a lithium secondary battery, as the lithium atoms at the positive electrode are ionized and generate lithium ions and electrons, the electrons move to the negative electrode through an external circuit, and the lithium ions move to the negative electrode through the non-aqueous electrolyte and the diaphragm, and are intercalated in the carbon negative electrode. When discharging, the electrons move to the positive electrode through the external circuit. At the same time, the lithium ions also deintercalate from the carbon negative electrode and move to the positive electrode through the non-aqueous electrolyte and the diaphragm. As a result, the lithium ions and electrons meet at the positive electrode and become lithium atoms in a stable state. The lithium secondary battery generates electrical energy while repeating this charging and discharging.

[0004] During the charge and discharge process of lithium secondary batteries, as the positive electrode active material breaks in structure, metal ions will also dissolve from the positive electrode surface. The metal ions dissolved from the positive electrode will also be electrodeposited on the negative electrode, causing the negative electrode to deteriorate. When the positive electrode potential is high or the secondary battery is exposed to high temperature, this deterioration of the negative electrode tends to be further accelerated.

[0005] In order to solve this problem, a method of adding a compound that can form a coating (solid electrolyte interphase (SEI)) on the surface of the negative electrode to the non-aqueous electrolyte is proposed. However, these electrolyte additives will produce other side effects, such as: the life performance of the secondary battery is reduced and the high temperature stability is deteriorated, thereby causing other problems such as the overall performance of the lithium secondary battery is reduced.

[0006] LiPF6 is mainly used as the lithium salt of lithium secondary batteries to achieve the appropriate characteristics of secondary batteries. - The heat resistance of anions is poor. When the secondary battery is exposed to high temperature, thermal decomposition will occur, thereby generating Lewis acids such as PF5. The PF5 generated in this way will not only cause the decomposition reaction of organic solvents such as ethylene carbonate, but also generate hydrofluoric acid (HF), thereby accelerating the dissolution of transition metals in the positive electrode active material. The transition metals dissolved in this way will be electrodeposited on the positive electrode and become the cause of increasing the resistance of the positive electrode; or electrodeposited on the negative electrode, causing self-discharge of the negative electrode; or destroying the solid electrolyte interface film (SEI) on the negative electrode, thereby causing further decomposition of the electrolyte and the resulting increase in resistance and life degradation of the secondary battery. This decomposition reaction of the electrolyte will also cause gas to be generated inside the secondary battery.

[0007] For these reasons, if lithium secondary batteries are stored at high temperatures in a fully charged state, the solid electrolyte interface (SEI) gradually breaks down over time. This rupture of the solid electrolyte interface exposes the surface of the negative electrode. The exposed negative electrode surface decomposes while reacting with the carbonate solvent in the electrolyte, causing a continuous side reaction. This side reaction continuously generates gas.

[0008] The gas generated in this way, regardless of its type, will increase the internal pressure of the lithium secondary battery and become a resistance factor to the movement of lithium, causing the volume (thickness) of the secondary battery to expand, and also causing a huge problem in the lightweight of the secondary battery and deteriorating the performance of the secondary battery.

[0009] Recently, as the application fields of lithium secondary batteries are expanding, the requirements for their stability and long life characteristics in high temperature environments continue to emerge. This performance is largely dependent on the above-mentioned solid electrolyte interface film (SEI film) formed by the initial reaction of the electrode and the electrolyte. Summary of the invention

[0010] Problems to be solved by the invention

[0011] Therefore, in order to improve the high temperature cycle characteristics and low temperature output of lithium secondary batteries, it is necessary to continuously develop additives that can inhibit the side reactions between the positive electrode and the electrolyte and form a strong solid electrolyte interface film (SEI film) on the negative electrode surface.

[0012] In order to solve the above problems, the present invention provides a non-aqueous electrolyte for a lithium secondary battery, which contains an additive capable of forming a stable solid electrolyte interface film (SEI film) on the surface of an electrode, in particular, on the surface of a negative electrode.

[0013] In order to solve the above problems, the present invention provides an electrolyte additive for secondary batteries, which can form a strong solid electrolyte interface film on the electrode surface, especially on the negative electrode surface, and has an excellent effect of removing decomposition products generated by lithium salts.

[0014] In addition, in order to solve the problems of the prior art as described above, the present invention provides a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery, which can improve the high temperature stability while not deteriorating the high temperature life and performance of the lithium secondary battery.

[0015] Solutions for solving problems

[0016] A non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention includes: a compound including an imidazole group and a fluorine group as an additive; a lithium salt; an additional additive; and a non-aqueous organic solvent.

[0017] A non-aqueous electrolyte for a lithium secondary battery according to an embodiment of the present invention includes: a compound represented by the following Chemical Formula 1 and including an imidazole group and a fluorine group as an additive; a lithium salt; an additional additive; and a non-aqueous organic solvent.

[0018] Chemical formula 1:

[0019]

[0020] One embodiment of the present invention provides a lithium secondary battery, which includes: the non-aqueous electrolyte for lithium secondary batteries of the present invention, a positive electrode, a negative electrode, and a separator.

[0021] The negative electrode may include a carbon-based negative electrode active material and a silicon-based negative electrode active material.

[0022] The weight ratio of the carbon-based negative electrode active material to the silicon-based negative electrode active material contained in the negative electrode may be 97:3 to 50:50.

[0023] The weight ratio of the carbon-based negative electrode active material to the silicon-based negative electrode active material contained in the negative electrode may be 90:10 to 60:40.

[0024] Effects of the Invention

[0025] The compound containing imidazole and fluorine provided as an additive in the non-aqueous electrolyte of the present invention, in particular, the compound represented by chemical formula 1, can make the nitrogen atom of the imidazole group act as a Lewis base, so that when the secondary battery is exposed to high temperature, the decomposition product HF generated by the decomposition of the anion, such as the Lewis acid of PF5, is removed from the inside of the electrolyte. Therefore, the compound containing imidazole and fluorine provided as an additive in the non-aqueous electrolyte of the present invention, in particular, the compound represented by chemical formula 1, can inhibit the degradation of the surface coating (solid electrolyte interface film (SEI) layer (Solid Electrolyte Interphase Layer)) of the positive or negative electrode caused by Lewis acid, thereby further preventing the decomposition of the electrolyte of the secondary battery caused by the destruction of the coating, and inhibiting the self-discharge of the secondary battery. The above-mentioned imidazole group also has the effect of forming a stable coating on the surface of the negative electrode. The fluorine group of the above-mentioned compound plays a role in removing the CO2 gas generated in the positive electrode, thereby playing a role in preventing the swelling phenomenon (Swelling) of the secondary battery.

[0026] Since the additive contained in the secondary battery non-aqueous electrolyte of the present invention, that is, the compound containing an imidazole group and a fluorine group, in particular, the functional group of the compound represented by Chemical Formula 1 has the effects as described above, it is possible to achieve a secondary battery with improved performance as follows: even when the lithium secondary battery is exposed to a high temperature environment, the life span will not deteriorate, and when stored at high temperature, the phenomenon of resistance increase or gas generation can be suppressed, thereby reducing the volume expansion of the secondary battery. DETAILED DESCRIPTION

[0027] The present invention is described in more detail below by way of examples. These examples are only used to illustrate the present invention, and therefore, these examples should not be interpreted as limiting the scope of the present invention.

[0028] The terms “including”, “having” and the like used in this specification should be understood as open-ended terms covering the possibility of including other components unless otherwise mentioned in a sentence or article including the expression.

[0029] In this specification, "%" means weight percentage unless otherwise clearly indicated.

[0030] Hereinafter, the electrolyte additive for lithium secondary batteries, the nonaqueous electrolyte for lithium secondary batteries, and the lithium secondary battery including the nonaqueous electrolyte of the present invention will be described in detail.

[0031] <Electrolyte Additives for Lithium Secondary Batteries>

[0032] The present invention provides a compound as an additive for an electrolyte for a lithium secondary battery, comprising an imidazole group and a fluorine group, and in particular, provides a compound comprising an imidazole group and a fluorine group represented by the following Chemical Formula 1.

[0033] Chemical formula 1:

[0034]

[0035] <Electrolyte for lithium secondary batteries>

[0036] The present invention provides an electrolyte for a lithium secondary battery, which comprises: a compound containing an imidazole group and a fluorine group; an additional additive; a lithium salt; and a non-aqueous organic solvent.

[0037] The present invention provides an electrolyte for a lithium secondary battery, comprising: a compound containing an imidazole group and a fluorine group represented by the above Chemical Formula 1; an additional additive; a lithium salt; and a non-aqueous organic solvent.

[0038] The electrolyte for lithium secondary batteries may include the compound including an imidazole group and a fluorine group in an amount of 0.05 to 20 weight percent relative to the total weight of the electrolyte.

[0039] Preferably, the electrolyte for lithium secondary batteries may contain 0.05 weight percent to 10 weight percent of the compound containing an imidazole group and a fluorine group, relative to the total weight of the electrolyte.

[0040] More preferably, the compound containing an imidazole group and a fluorine group may be included in an amount of 0.05 to 5 weight percent, 0.05 to 3 weight percent, or 0.05 to 2 weight percent relative to the total weight of the electrolyte for lithium secondary batteries.

[0041] The electrolyte for lithium secondary batteries may include the compound including an imidazole group and a fluorine group in an amount of 0.1 to 20 weight percent relative to the total weight of the electrolyte.

[0042] Preferably, the electrolyte for lithium secondary batteries may contain 0.1 to 10 weight percent of the compound containing an imidazole group and a fluorine group, relative to the total weight of the electrolyte.

[0043] More preferably, the compound containing an imidazole group and a fluorine group may be included in an amount of 0.1 to 5 weight percent, 0.1 to 3 weight percent, or 0.1 to 2 weight percent relative to the total weight of the electrolyte for lithium secondary batteries.

[0044] In a case where the above-mentioned compound containing an imidazole group and a fluorine group is contained in an amount of less than 0.05 weight percent relative to the total weight of the above-mentioned electrolyte for lithium secondary batteries, the volume expansion prevention effect and internal resistance reduction effect of the lithium secondary battery are insufficient. On the contrary, in a case where the above-mentioned compound containing an imidazole group and a fluorine group is contained in an amount of more than 20 weight percent relative to the total weight of the above-mentioned electrolyte for lithium secondary batteries, there will be problems of reduced high-temperature life characteristics and reduced high-temperature storage characteristics caused by increased internal resistance and reduced capacity of the secondary battery.

[0045] The above-mentioned electrolyte for lithium secondary batteries may further contain at least one additional additive selected from the group consisting of halogen-substituted or unsubstituted carbonate compounds, nitrile compounds, borate compounds, lithium salt compounds, phosphate compounds, sulfite compounds, sulfone compounds, sulfate compounds, and sultone compounds.

[0046] Representative examples of the additional additives include lithium difluorophosphate, lithium tetrafluoro(oxalate)phosphate, lithium bis(fluorosulfonyl)imide, 1,3-propane sultone, 1,3-propane sultone, 1,3-propene sultone, fluoroethylene carbonate, vinylene carbonate, and vinyl ethylene carbonate.

[0047] The electrolyte for lithium secondary batteries may contain the additional additive in an amount of 0.05 weight percent to 20 weight percent relative to the total weight of the electrolyte.

[0048] Preferably, the electrolyte for lithium secondary batteries may contain the additional additive in an amount of 0.05 weight percent to 10 weight percent relative to the total weight of the electrolyte.

[0049] More preferably, relative to the total weight of the electrolyte for lithium secondary batteries, the additional additive may be included in an amount of 0.05 to 5 weight percent, specifically 0.05 to 3 weight percent.

[0050] When the above-mentioned additional additives are contained in an amount of less than 0.05 weight percent relative to the total weight of the above-mentioned lithium secondary battery electrolyte, the electrode coating formation effect is very small, and the side reaction inhibition effect of the electrode and the electrolyte will be reduced; and when the above-mentioned electrolyte additives are contained in an amount of more than 20 weight percent relative to the total weight of the above-mentioned lithium secondary battery electrolyte, an excessively thick coating will be formed on the electrode surface, and the interface resistance will increase, thereby reducing the capacity.

[0051] The above-mentioned 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.

[0052] The above lithium salt has a large degree of dissociation of lattice energy, and therefore, preferably a lithium salt having excellent ion conductivity, thermal stability and oxidation resistance is used. The above lithium salt serves as a migration channel for lithium ions in the secondary battery, thereby enabling the basic operation of the lithium secondary battery.

[0053] The concentration of the lithium salt may be 0.1 M (mol / L) to 2.5 M (mol / L) relative to the total amount of the electrolyte for lithium secondary batteries.

[0054] Considering the performance related to conductivity and the viscosity related to the mobility of lithium ions, preferably, the concentration of the lithium salt may be 0.3M (mol / L) to 2.5M (mol / L) relative to the total amount of the electrolyte for the lithium secondary battery.

[0055] Considering the performance related to conductivity and the viscosity related to the mobility of lithium ions, more preferably, the concentration of the lithium salt may be 0.7M (mol / L) to 1.6M (mol / L) relative to the total amount of the electrolyte for lithium secondary batteries.

[0056] If the concentration of the above-mentioned lithium salt is less than 0.1M, the conductivity of the electrolyte for the above-mentioned lithium secondary battery will decrease, thereby reducing the performance of the non-aqueous electrolyte that quickly transfers ions between the positive and negative electrodes of the lithium secondary battery; if the concentration of the above-mentioned lithium salt is greater than 2.5M, the viscosity of the electrolyte for the above-mentioned lithium secondary battery will increase, resulting in a decrease in the mobility of lithium ions and a decrease in the performance of the secondary battery under low temperature conditions.

[0057] The non-aqueous organic solvent may be a linear carbonate solvent, a cyclic carbonate solvent or a mixed solvent thereof.

[0058] The linear carbonate solvent may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylpropyl carbonate (EPC), ethyl methyl carbonate (EMC), and methylpropyl carbonate (MPC).

[0059] In addition, the cyclic carbonate-based solvent may include 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).

[0060] Preferably, a ring-shaped carbonate organic solvent with a high dielectric constant and a linear carbonate organic solvent with a low viscosity are mixed for use. The above-mentioned ring-shaped carbonate organic solvent with a high dielectric constant has a high ionic conductivity that can improve the charge and discharge performance of the secondary battery, and the above-mentioned linear carbonate organic solvent with a low viscosity can appropriately adjust the viscosity of the above-mentioned carbonate organic solvent with a high dielectric constant.

[0061] Specifically, a carbonate organic solvent with a high dielectric constant and a carbonate organic solvent with a low viscosity can be mixed and used, the above-mentioned carbonate organic solvent with a high dielectric constant is used as the above-mentioned cyclic carbonate solvent, and is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and a mixture thereof; the above-mentioned low-viscosity carbonate organic solvent is used as the above-mentioned linear carbonate solvent, and is selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and a mixture thereof.

[0062] The above-mentioned cyclic carbonate solvent has high polarity and can therefore fully dissociate lithium ions. However, due to its high viscosity, its ion conductivity is low. Therefore, by mixing the above-mentioned cyclic carbonate solvent with a linear carbonate solvent having low polarity and low viscosity, the characteristics of the lithium secondary battery can be optimized.

[0063] Therefore, it is preferred that at least one solvent selected from the above-mentioned cyclic carbonate solvents and at least one solvent selected from the above-mentioned linear carbonate solvents be mixed and used as the above-mentioned non-aqueous organic solvent.

[0064] As for the mixed solvent of the linear carbonate-based solvent and the cyclic carbonate-based solvent, the linear carbonate-based solvent and the cyclic carbonate-based solvent may be mixed in a volume ratio of 9:1 to 1:9.

[0065] For the mixed solvent of the linear carbonate solvent and the cyclic carbonate solvent, in consideration of the life and storage characteristics of the secondary battery, the linear carbonate solvent and the cyclic carbonate solvent may be preferably mixed in a volume ratio of 2:8 to 8:2.

[0066] The non-aqueous organic solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC).

[0067] The non-aqueous organic solvent may include: 5 to 40 weight percent of the ethylene carbonate (EC), 5 to 20 weight percent of the propylene carbonate (PC), 10 to 70 weight percent of the ethyl methyl carbonate (EMC), and 10 to 60 weight percent of the diethyl carbonate (DEC).

[0068] Specifically, among the above-mentioned cyclic carbonate solvents, ethylene carbonate (EC) or propylene carbonate (PC) with a high dielectric constant can be used, however, when artificial graphite is used as the negative electrode active material, it is preferred to use the above-mentioned ethylene carbonate (EC), and among the above-mentioned linear carbonate solvents, it is preferred to use dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) or diethyl carbonate (DEC) with a low viscosity.

[0069] The non-aqueous organic solvent may be contained in an amount of 5% to 80% of the total amount of the electrolyte for lithium secondary batteries. The non-aqueous organic solvent may be contained in an amount of 5% to 70% of the total amount of the electrolyte for lithium secondary batteries.

[0070] <Lithium Secondary Battery>

[0071] The life characteristics of the lithium secondary battery containing the above non-aqueous electrolyte will not deteriorate under high temperature conditions, the resistance will not increase when stored at high temperatures, and the performance of suppressing the volume (thickness) expansion of the secondary battery is excellent.

[0072] Hereinafter, the lithium secondary battery of the present invention will be described in detail.

[0073] The lithium secondary battery of the present invention comprises: a positive electrode; a negative electrode; a separator; and a non-aqueous electrolyte.

[0074] The positive electrode may include a material selected from LiCoO2, LiFePO4, LiMnO2, LiMn2O4, LiNiO2 or LiNi 1-x-y Co x M y At least one positive electrode active material selected from the group consisting of lithium metal oxides such as O2 (0≤x≤1, 0≤y≤1, 0≤x+y≤1, M is Al, Sr, Mg, Mn or La).

[0075] The negative electrode may include at least one negative electrode active material selected from the group consisting of silicon, silicon compounds, tin, tin compounds, lithium titanate, crystalline carbon, amorphous carbon, artificial graphite, natural graphite, and a mixture of artificial graphite and natural graphite.

[0076] The above-mentioned diaphragm can be composed of a porous polymer film alone or a laminate thereof, wherein the porous polymer film is prepared from at least one polyolefin polymer selected from ethylene polymer, propylene polymer, ethylene / butene copolymer and ethylene / hexane copolymer. The above-mentioned diaphragm can include a coating film coated with ceramic or polymer material.

[0077] The non-aqueous electrolyte may include: a compound including an imidazole group and a fluorine group, in particular, a compound including an imidazole group and a fluorine group represented by the following Chemical Formula 1; an additional additive; a lithium salt; and a non-aqueous organic solvent.

[0078] Chemical formula 1:

[0079]

[0080] Examples of the lithium secondary battery include, but are not limited to, lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, lithium ion polymer secondary batteries, and the like.

[0081] In more detail, the positive electrode active material is preferably selected from one or more substances selected from cobalt, manganese, nickel and a composite metal oxide with lithium. The solid solubility ratio between the cobalt, manganese and nickel metals of the composite metal oxide can be varied, and in addition to these cobalt, manganese and nickel metals, it can also contain 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.

[0082] Specifically, LiCoO2, LiFePO4, LiMnO2, LiMn2O4, LiNiO2 or LiNi can be used as the positive electrode active material. 1-x-y Co x M y Lithium metal oxides such as lithium sulfide 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 chalcogenide compounds, 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.

[0083] The positive electrode comprises: a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer may comprise a positive electrode active material capable of absorbing and releasing lithium, a binder, a conductive material, and the like.

[0084] 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. As the negative electrode active material, crystalline carbon, amorphous carbon, a carbon composite, carbon fiber, lithium metal, lithium alloy or carbon-silicon composite can be used, but it is not limited thereto, and any material that can be used as a negative electrode active material in a secondary battery can be used.

[0085] The positive electrode and / or negative electrode can be prepared by dispersing an electrode slurry composition in a solvent by using an electrode active material, a binder and a conductive material, and if necessary, a thickener, and then applying the slurry composition to an electrode collector. The positive electrode collector can usually be made of aluminum or an aluminum alloy, and the negative electrode collector can usually be made of copper or a copper alloy.

[0086] The positive electrode current collector and the negative electrode current collector may be in a shape of, for example, foil or mesh.

[0087] The above-mentioned binder is a material that plays the role of gelatinization of active materials, mutual adhesion of active materials, adhesion to collectors, and buffering effects on the expansion and contraction of active materials, etc., as long as it is a binder that ordinary technicians can use. For example, it can be used: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVdF), polyhexafluoropropylene-polyvinylidene fluoride copolymer (PVdF / HFP), polyvinyl acetate, alkylated polyethylene oxide, polyvinyl ether, polymethyl methacrylate, polyethyl acrylate, polyacrylonitrile, polyvinyl pyridine, polyethylene, polypropylene, styrene-butadiene rubber, acrylic styrene-butadiene rubber, nitrile rubber, epoxy resin, nylon, etc., but are not limited to this.

[0088] The above-mentioned conductive material is used to impart conductivity to the electrode. Therefore, for the secondary battery constructed, any conductive material that does not cause chemical changes can be used. The above-mentioned conductive material can use at least one selected from the group consisting of graphite conductive materials, carbon black conductive materials, metal or metal compound conductive materials. Examples of the above-mentioned graphite conductive materials include: artificial graphite, natural graphite, etc.; examples of the above-mentioned carbon black conductive materials include: acetylene black, ketjen black, acetylene carbon black (denka black), thermal black, channel black, etc.; examples of the above-mentioned metal or metal compound conductive materials include: tin, tin oxide, tin phosphate (SnPO4), titanium oxide, potassium titanate, such as LaSrCoO3, LaSrMnO3 and other perovskite substances. However, it is not limited to the above-mentioned conductive materials.

[0089] The thickener is not particularly limited as long as it can adjust the viscosity of the active material slurry. For example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, etc. can be used.

[0090] As the solvent for dispersing the electrode active material, binder, conductive material, etc., a non-aqueous solvent or an aqueous solvent can be used. Examples of the non-aqueous solvent may include: N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethyl-1,3-diaminopropane, ethylene oxide or tetrahydrofuran, etc. Examples of the aqueous solvent may include: water, etc.

[0091] The lithium secondary battery may include a separator disposed between the positive electrode and the negative electrode to prevent short circuit and provide a path for the movement of lithium ions. As the separator, a polyolefin polymer film such as polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, polypropylene / polyethylene / polypropylene or a multilayer film, microporous film, fabric and non-woven fabric thereof may be used. In addition, a film in which a porous polyolefin film is coated with a resin having excellent stability may also be used as the separator.

[0092] In addition, the lithium secondary battery can be prepared into various shapes such as rectangular, cylindrical, pouch or coin.

[0093] Embodiments of the invention

[0094] The present invention is described in more detail below by way of examples, but the scope of the invention should not be construed as being limited to these examples.

[0095] <Synthesis Example of 2,2,2-trifluoroethyl1H-imidazole-1-carboxylate (Compound of Chemical Formula 1)>

[0096] After installing a N2 purge line, a dropping funnel, and a thermometer on a 500mL three-necked flask, 0.31mol of 1,1'-Carbonyldiimidazole and 150mL of dichloromethane were added and stirred. The reactor was filled with nitrogen and the temperature was cooled from room temperature to 10°C. While maintaining the temperature, 0.32mol of 2,2,2-trifluoroethanol was dripped for 30 minutes. After the addition of 2,2,2-trifluoroethanol, the temperature was changed from 10°C to room temperature and reacted at the same temperature for 3 hours. After the reaction was completed, 150mL of water was added, the organic layer was extracted, and the process was repeated twice. In order to remove moisture, the mixture was filtered after treatment with MgSO4, and the filtrate was concentrated to remove dichloromethane from the filtrate. After drying in a vacuum oven, the final compound 2,2,2-trifluoroethyl 1H-imidazole-1-carboxylate was obtained with a yield of 75%.

[0097] 1 H NMR (chloroform-d, δppm): 1H 8.1ppm, 1H 7.3.ppm, 1H 6.9ppm, 2H 4.7ppm,

[0098] 19 F NMR (chloroform-d, δppm) -74.09 1F, HRMS: C6H5N2O2F3 (M+): 194.03

[0099] <Preparation of an electrolyte solution for a lithium secondary battery containing 2,2,2-trifluoroethyl 1H-imidazole-1-carboxylate (compound of Chemical Formula 1)>

[0100] After dissolving LiPF6 in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio: EC / EMC=25 / 75) to a concentration of 1.0 M (mol / L), 1.0 weight percent of fluoroethylene carbonate (FEC), 1.0 weight percent of lithium difluorophosphate (LiPO2F2), 0.5 weight percent of propane sultone (PS), 0.5 weight percent of ethylene sulfate (Esa) and 0.5 weight percent of 2,2,2-trifluoroethyl 1H-imidazole-1-carboxylate of the above synthesis example represented by the above chemical formula 1 were added to the above mixed solution to prepare an electrolyte for a lithium secondary battery containing the compound of chemical formula 1.

[0101] <Prepare a lithium secondary battery including an electrolyte, wherein the electrolyte includes a compound of Chemical Formula 1>

[0102] 94 wt% of a lithium nickel cobalt manganese oxide (NCM) cathode active material containing Li[Ni x Co 1-x-y Mn y O2 (0 < x < 0.5, 0 < y < 0.5), 3 wt% of a conductive material (Super-P), and 3 wt% of a binder (PVdF) were added to an organic solvent N-methyl-2-pyrrolidone (NMP) to prepare a cathode active material slurry. The above cathode active material slurry was coated on an aluminum thin film as a current collector and dried to prepare a cathode, and then the cathode was prepared by rolling with a rolling press. In addition, 96 wt% of a graphite-based anode active material containing silicon oxide (SiOx), 1 wt% of a conductive material (Super-P), 1.5 wt% of a binder styrene-butadiene rubber (SBR), and 1.5 wt% of carboxymethyl cellulose (CMC) were mixed to prepare an anode active material slurry. The above anode active material slurry was coated on a copper thin film as an anode current collector and dried to prepare an anode.

[0103] Prepare the cathode and anode prepared as described above, and interpose a separator therebetween. Then, an electrolyte for a lithium secondary battery containing the compound of Chemical Formula 1 was injected between the two electrodes sandwiching the above separator to prepare an aluminum-pouch type lithium secondary battery including an electrolyte, and the above electrolyte includes the compound of Chemical Formula 1.

[0104] Comparative Example

[0105] <Prepare an electrolyte for a lithium secondary battery including a 1,3-propene sultone (PRS) additive>

[0106] For a non-aqueous electrolyte for a lithium secondary battery, since the non-aqueous electrolyte decomposes to deteriorate the high-temperature stability and causes the phenomenon of battery swelling at high temperatures, in order to improve the high-temperature stability, the effect of suppressing battery swelling at high temperatures, etc., a sultone compound may be included in the non-aqueous electrolyte for a lithium secondary battery as needed. The above sultone compound may be 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, 1,3-propene sultone (PRS) currently commonly used was used.

[0107] LiPF6 was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio: EC / EMC=25 / 75) to a concentration of 1.0 M. Then, 1.0 weight percent of fluoroethylene carbonate, 1.0 weight percent of lithium difluorophosphate (LiPO2F2), 0.5 weight percent of propane sultone (PS), 0.5 weight percent of vinyl sulfate (Esa) and 0.5 weight percent of 1.3-propylene sultone (PRS) additive used as a comparative example were added to the mixed solution to prepare an electrolyte for a lithium secondary battery.

[0108] <Preparation of a lithium secondary battery comprising an electrolyte solution, wherein the electrolyte solution comprises a 1,3-propene sultone additive>

[0109] As the electrolyte, a lithium secondary battery electrolyte containing 1,3-propene sultone (PRS) was used instead of adding the 2,2,2-trifluoroethyl 1H-imidazole-1-carboxylate compound represented by the above Chemical Formula 1. Except for this, a lithium secondary battery containing no compound of Chemical Formula 1 but 1,3-propene sultone electrolyte was prepared by the same method as the lithium secondary battery of the above embodiment.

[0110] The compositions of the electrolyte solutions for lithium secondary batteries in the above-described Examples and Comparative Examples are shown in Table 1 below.

[0111] <Components of electrolyte for lithium secondary battery>

[0112] Table 1

[0113]

[0114] [Experimental example]

[0115] Experimental Example 1: Determination of high temperature (45°C) life capacity retention rate

[0116] Under high temperature (45°C), the pouch-shaped lithium secondary battery prepared using the lithium secondary battery electrolyte of the above embodiment and comparative example was charged to 4.2V at 1C-rate, rested for 10 minutes, and discharged to 2.7V at 1C-rate, and rested for 10 minutes again. The discharge capacity (mAh) and life capacity retention (retention, %) of the battery were determined by repeating the above process 500 times. The discharge capacity and life capacity retention of the measured secondary batteries were compared, and the results are shown in Table 2.

[0117] Table 2

[0118]

[0119] As shown in Table 2 above, the life evaluation results at high temperatures show that the lithium secondary battery of the above embodiment shows higher levels of 500 discharge capacity and life capacity retention rate at high temperatures than the lithium secondary battery of the above comparative example.

[0120] It can be confirmed that since the lithium secondary battery of the above embodiment includes an electrolyte and the electrolyte includes the compound represented by the above chemical formula 1, the high temperature life performance of the secondary battery is not deteriorated and the life capacity retention rate is high compared to the lithium secondary battery of the above comparative example. That is, the compound additive of chemical formula 1 improves the life capacity retention rate at high temperature without having a side reaction with other additives to reduce the performance.

[0121] Experimental Example 2: Determination of high temperature (60°C) storage characteristics

[0122] After the pouch-shaped lithium secondary battery prepared by using the electrolyte for lithium secondary battery of the above-mentioned embodiment and comparative example was stored at high temperature (60°C) for 6 weeks, the volume change rate of the secondary battery was measured. The following Table 3 shows the results of the volume change rate of the secondary battery after 6 weeks of storage at high temperature (60°C) relative to 0 weeks.

[0123] Table 3

[0124] Volume increase rate after storage at 60℃ for 6 weeks (%) Example 1.99 Comparative Example 2.28

[0125] As shown in Table 3, the volume increase rate of the example is smaller than that of the comparative example. This shows that the additive of the present invention is an additive with excellent effect of suppressing gas generation.

Claims

1. A non-aqueous electrolyte for a lithium secondary battery, comprising: Additives; additional additives; lithium salts; and non-aqueous organic solvents, The additive is a compound of the following chemical formula 1: Chemical formula 1: The additional additive is at least one compound selected from the group consisting of halogen-substituted or unsubstituted carbonate compounds, nitrile compounds, borate compounds, lithium salt compounds, phosphate compounds, sulfite compounds, sulfone compounds, sulfate compounds, and sultone compounds. Based on the total weight of the non-aqueous electrolyte for lithium secondary batteries, the additive is contained in an amount of 0.05 weight percent to 20 weight percent.

2. A lithium secondary battery, characterized in that: include: The non-aqueous electrolyte for lithium secondary battery according to claim 1; positive electrode; negative electrode; as well as Diaphragm.

3. The lithium secondary battery according to claim 2, characterized in that: The negative electrode comprises a carbon-based negative electrode active material and a silicon-based negative electrode active material.

4. The lithium secondary battery according to claim 3, characterized in that: The weight ratio of the carbon-based negative electrode active material to the silicon-based negative electrode active material is 97:3 to 50:

50.

5. The lithium secondary battery according to claim 4, characterized in that: The weight ratio of the carbon-based negative electrode active material to the silicon-based negative electrode active material is 90:10 to 60:40.

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