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

Abstract

The present invention relates to a new electrolyte additive, a non-aqueous electrolyte for lithium secondary batteries containing this new electrolyte additive, and a lithium secondary battery containing this non-aqueous electrolyte. More specifically, the present invention relates to a non-aqueous electrolyte for lithium secondary batteries containing an additive that can form a stable film on the electrode surface. The present invention also relates to a lithium secondary battery in which, by containing such a non-aqueous electrolyte, the high-temperature life of the lithium secondary battery does not deteriorate, the resistance when the lithium secondary battery is stored at high temperatures does not increase, and the expansion of the volume (thickness) of the secondary battery when the lithium secondary battery is stored at high temperatures is improved.

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 from a lithium salt, and a non-aqueous electrolyte for a lithium secondary battery containing the same. 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 same. The present invention also relates to a lithium secondary battery containing such a non-aqueous electrolyte. By containing the non-aqueous electrolyte, the high-temperature performance of the lithium secondary battery of the present invention is improved.

Background Art

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

[0003] Currently widely used lithium secondary batteries generally consist of a carbon-based negative electrode capable of inserting and desorbing lithium ions, a transition metal oxide-based positive electrode containing lithium, a non-aqueous electrolyte in which a lithium salt is dissolved in a mixed carbonate-based organic solvent, and a separator for preventing contact between the positive electrode and the negative electrode. When the lithium secondary battery is charged, lithium atoms in the positive electrode are ionized into lithium ions and electrons. The electrons move to the negative electrode through an external circuit, and the lithium ions move through the non-aqueous electrolyte and the separator to the negative electrode and are inserted (intercalated) into the carbon negative electrode. When discharging, the electrons move to the positive electrode through the external circuit, and at the same time, the lithium ions are also desorbed (deintercalated) from the carbon negative electrode, move through the non-aqueous electrolyte and the separator to the positive electrode, and meet with electrons at the positive electrode to become stable lithium atoms. The lithium secondary battery generates electrical energy while repeating such charging and discharging.

[0004] During charging and discharging, lithium-ion batteries can experience structural breakdown of the positive electrode active material, potentially releasing metal ions from the positive electrode surface. These released metal ions can then be electrodeposited onto the negative electrode, causing it to degrade. This degradation of the negative electrode tends to accelerate if the positive electrode potential is high or if the 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) on the negative electrode surface is added to the non-aqueous electrolyte. However, such electrolyte additives cause other side effects such as a decrease in the lifespan of the secondary battery and deterioration of high-temperature safety, while also leading to another problem: a decrease in the overall performance of the lithium secondary battery. LiPF6 is primarily used as the lithium salt in lithium secondary batteries to achieve the appropriate characteristics of the battery. The PF6- anion of LiPF6 is very susceptible to heat, and it is known that when a secondary battery is exposed to high temperatures, it undergoes thermal decomposition, generating Lewis acids such as PF5. The PF5 thus generated not only causes the decomposition reaction of organic solvents such as ethylene carbonate, but also generates hydrofluoric acid (HF), accelerating the leaching of transition metals from the positive electrode active material. These leached transition metals can electrodeposit onto the positive electrode, increasing its resistance, or electrodeposit onto the negative electrode, causing self-discharge of the negative electrode, or destroy the solid electrolyte interface (SEI) on the negative electrode, leading to further decomposition of the electrolyte and consequently increasing the resistance and degrading the lifespan of the secondary battery. Such electrolyte decomposition reactions also lead to gas generation inside the secondary battery.

[0006] Therefore, when lithium secondary batteries are stored at high temperatures in a fully charged state, there is a problem in that the solid electrolyte interface (SEI) gradually breaks down over time. This breakdown of the solid electrolyte interface exposes the surface of the negative electrode. The exposed negative electrode surface decomposes by reacting with the carbonate-based solvent in the electrolyte, causing a continuous side reaction. This side reaction continuously generates gas.

[0007] The gases generated in this way, regardless of their type, increase the internal pressure of the lithium secondary battery, act as a resistive element in lithium movement, expand the volume (thickness) of the secondary battery, create significant problems in reducing the weight of the secondary battery, and degrade the performance of the secondary battery.

[0008] In recent years, as the application fields of lithium-ion batteries have expanded, there has been a steadily growing demand for stability and long lifespan in high-temperature environments. This performance is largely determined by the solid electrolyte interface (SEI) film formed by the initial reaction between the electrode and the electrolyte. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Therefore, in order to improve the high-temperature cycle characteristics and low-temperature output of lithium secondary batteries, there is a constant need for the development of additives that can suppress side reactions between the positive electrode and the electrolyte and form a strong solid electrolyte interface (SEI) film on the surface of the negative electrode.

[0010] To solve the aforementioned problems, the present invention aims to provide a non-aqueous electrolyte for lithium secondary batteries that includes an additive capable of forming a stable solid electrolyte interface (SEI) film on the electrode surface, particularly on the surface of the negative electrode.

[0011] Furthermore, in order to solve the above-mentioned problems, the present invention aims to provide an electrolyte additive for secondary batteries that forms a strong solid electrolyte interface (SEI) on the electrode surface, particularly on the negative electrode surface, and has an excellent effect in removing decomposition products generated from lithium salts.

[0012] Furthermore, in order to solve the problems of the prior art described above, the present invention aims to provide a non-aqueous electrolyte for lithium secondary batteries that can improve high-temperature stability without degradation of the high-temperature life and performance of lithium secondary batteries, and a lithium secondary battery containing this non-aqueous electrolyte for lithium secondary batteries. [Means for solving the problem]

[0013] A non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention comprises a compound containing an imidazole group and a benzene ring as an additive, a lithium salt, an additive, and a non-aqueous organic solvent.

[0014] A non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention comprises, as an additive, a compound containing a methylimidazole group and a benzene ring represented by the following chemical formula 1, a lithium salt, an additive, and a non-aqueous organic solvent.

[0015] [ka]

[0016] One embodiment of the present invention provides a lithium secondary battery comprising a non-aqueous electrolyte for lithium secondary batteries, a positive electrode, a negative electrode, and a separation membrane.

[0017] The anode may include a carbon-based anode active material and a silicon-based anode active material.

[0018] The anode may contain a carbon-based anode active material and a silicon-based anode active material in a weight ratio of 97:3 to 50:50.

[0019] The anode may contain a carbon-based anode active material and a silicon-based anode active material in a weight ratio of 90:10 to 60:40. [Effects of the Invention]

[0020] The compound containing an imidazole group and a benzene ring provided as an additive in the non-aqueous electrolyte of the present invention, particularly the compound represented by Chemical Formula 1, acts as a Lewis base and can remove Lewis acids such as HF and PF5, which are decomposition products generated by the decomposition of anions when the secondary battery is exposed to high temperatures, from inside the electrolyte. Therefore, the compound containing an imidazole group and a benzene ring provided as an additive in the non-aqueous electrolyte of the present invention, particularly the compound represented by Chemical Formula 1, can suppress the deterioration of the surface film (SEI) of the positive electrode or negative electrode caused by Lewis acids, prevent further electrolyte decomposition of the secondary battery due to the destruction of the film (SEI), and also suppress the self-discharge of the secondary battery.

[0021] The functional group of the additive contained in the non-aqueous electrolyte for a secondary battery of the present invention, that is, the compound containing an imidazole group and a benzene ring, particularly the compound represented by Chemical Formula 1, forms a film (SEI layer) with excellent thermal stability due to the passivation effect. The benzene ring of the compound reacts with CO2 to reduce the CO2 concentration. Thereby, an increase in the internal pressure of the secondary battery caused by gas generation is suppressed, the stability of the secondary battery is improved, and the thickness of the secondary battery is maintained constant.

[0022] Due to such effects, even in a situation where a lithium secondary battery is exposed to high temperatures, its lifespan does not deteriorate, an increase in resistance or gas generation during high-temperature storage is suppressed, the volume expansion of the secondary battery is reduced, the self-discharge of the secondary battery is suppressed, and the resistance of the secondary battery can be decreased. Therefore, by using the compound containing an imidazole group and a benzene ring of the present invention, particularly the compound represented by Chemical Formula 1, as an additive for the non-aqueous electrolyte, a secondary battery with improved performance can be realized.

Embodiments for Carrying Out the Invention

[0023] Hereinafter, the present invention will be described in more detail with reference to examples. These examples are merely for illustrating the present invention and should not be construed as limiting the scope of the present invention.

[0024] Terms such as "comprising" and "having" used in this specification should be understood as open-ended terms that encompass the possibility of including other components, unless otherwise specified in the clauses or sentences in which such expressions are included.

[0025] In this specification, "%", unless otherwise explicitly indicated, means weight %.

[0026] Hereinafter, the electrolyte additive for lithium secondary batteries, the non-aqueous electrolyte for lithium secondary batteries, and the lithium secondary battery containing this non-aqueous electrolyte will be specifically described.

[0027] <Electrolyte Additive for Lithium Secondary Batteries> The present invention provides a compound containing an imidazole group and a benzene ring as an additive for an electrolyte of a lithium secondary battery, particularly a compound containing a methylimidazole group and a benzene ring represented by the following Chemical Formula 2.

[0028]

Chemical Formula

[0029] <Non-aqueous Electrolyte for Lithium Secondary Batteries> [[ID=3E]]The present invention provides a non-aqueous electrolyte for lithium secondary batteries, comprising a compound containing an imidazole group and a benzene ring, an additional additive, a lithium salt, and a non-aqueous organic solvent.

[0030] The present invention provides a non-aqueous electrolyte for lithium secondary batteries, comprising a compound containing a methylimidazole group and a benzene ring represented by the above Chemical Formula 2, an additional additive, a lithium salt, and a non-aqueous organic solvent.

[0031] The compound containing an imidazole group and a benzene ring may be contained in an amount of 0.05 to 20% by weight based on the total weight of the non-aqueous electrolyte for lithium secondary batteries.

[0032] The compound containing the imidazole group and the benzene ring may preferably be present in an amount of 0.05 to 10% by weight relative to the total weight of the electrolyte for the lithium secondary battery.

[0033] The compound containing the imidazole group and the benzene ring may more preferably be present in an amount of 0.05 to 5% by weight, 0.05 to 3% by weight, or 0.05 to 2% by weight relative to the total weight of the electrolyte for the lithium secondary battery.

[0034] The compound containing the imidazole group and the benzene ring may be present in an amount of 0.1 to 20% by weight relative to the total weight of the electrolyte for the lithium secondary battery.

[0035] The compound containing the imidazole group and the benzene ring may preferably be present in an amount of 0.1 to 10% by weight relative to the total weight of the electrolyte for the lithium secondary battery.

[0036] The compound containing the imidazole group and the benzene ring may more preferably be present in an amount of 0.1 to 5% by weight, 0.1 to 3% by weight, or 0.1 to 2% by weight relative to the total weight of the electrolyte for the lithium secondary battery.

[0037] If the compound containing the imidazole group and benzene ring is present in an amount of less than 0.05% by weight relative to the total weight of the electrolyte for the lithium secondary battery, the effect of preventing volume expansion and reducing internal resistance of the lithium secondary battery is insufficient. Conversely, if the compound containing the imidazole group and benzene ring is present in an amount exceeding 20% ​​by weight relative to the total weight of the electrolyte for the lithium secondary battery, problems arise such as an increase in the internal resistance and decrease in capacity of the secondary battery, leading to a deterioration in high-temperature life characteristics and high-temperature storage characteristics.

[0038] The electrolyte for the lithium secondary battery may further contain at least one 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.

[0039] Representative examples of the aforementioned 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.

[0040] The aforementioned additive may be present in an amount of 0.05 to 20% by weight relative to the total weight of the electrolyte for the lithium secondary battery.

[0041] The aforementioned additive may preferably be present in an amount of 0.05 to 10% by weight relative to the total weight of the electrolyte for the lithium secondary battery.

[0042] The aforementioned additive may more preferably be present in an amount of 0.05 to 5% by weight, specifically 0.05 to 3% by weight, relative to the total weight of the electrolyte for the lithium secondary battery.

[0043] If the additive is present in an amount of less than 0.05% by weight relative to the total weight of the electrolyte for the lithium secondary battery, the film-forming effect on the electrodes may be minimal, and the effect of suppressing side reactions between the electrodes and the electrolyte may decrease. If the electrolyte additive is present in an amount exceeding 20% ​​by weight relative to the total weight of the electrolyte for the lithium secondary battery, an excessively thick film may be formed on the electrode surface, increasing interfacial resistance and potentially causing a decrease in capacity.

[0044] 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.

[0045] It is preferable to use a lithium salt that has a high degree of lattice energy dissociation, excellent ionic conductivity, and excellent thermal stability and oxidation resistance. The lithium salt functions as a pathway for the movement of lithium ions within the secondary battery, enabling the basic operation of the lithium secondary battery.

[0046] The concentration of the lithium salt may be 0.1 to 2.5 M (mol / L) relative to the total amount of the electrolyte for the lithium secondary battery.

[0047] The concentration of the lithium salt may preferably be 0.3 to 2.5 M (mol / L) relative to the total amount of the electrolyte for the lithium secondary battery, taking into consideration the properties related to electrical conductivity and the viscosity related to the mobility of lithium ions.

[0048] The concentration of the lithium salt may more preferably be 0.7 to 1.6 M (mol / L), taking into consideration the properties related to electrical conductivity and the viscosity related to the mobility of lithium ions.

[0049] If the concentration of the lithium salt is less than 0.1 M, the electrical conductivity of the electrolyte for the lithium secondary battery decreases, and the performance of the non-aqueous electrolyte that rapidly transfers ions between the positive and negative electrodes of the lithium secondary battery deteriorates. If the concentration of the lithium salt exceeds 2.5 M, the viscosity of the electrolyte for the lithium secondary battery increases, the mobility of lithium ions decreases, and the performance of the secondary battery deteriorates at low temperatures.

[0050] The non-aqueous organic solvent may be a linear carbonate solvent, a cyclic carbonate solvent, or a mixture thereof.

[0051] 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).

[0052] Furthermore, the cyclic carbonate 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).

[0053] In some cases, it is desirable to use a mixture of a cyclic, high-dielectric-constant carbonate-based organic solvent with high ionic conductivity that can improve the charge-discharge performance of secondary batteries, and a low-viscosity, linear carbonate-based organic solvent that can appropriately adjust the viscosity of the high-dielectric-constant carbonate-based organic solvent.

[0054] Specifically, a high dielectric constant carbonate-based organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and mixtures thereof, which are cyclic carbonate-based solvents, can be used in combination with a low viscosity carbonate-based organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and mixtures thereof, which are linear carbonate-based solvents.

[0055] While the aforementioned cyclic carbonate solvent has high polarity and can sufficiently dissociate lithium ions, it has the disadvantage of high viscosity and low ionic conductivity. Therefore, by mixing the cyclic carbonate solvent with a linear carbonate solvent, which has low polarity but low viscosity, the characteristics of the lithium secondary battery can be optimized.

[0056] 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.

[0057] 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.

[0058] From the viewpoint of the lifespan and storage characteristics of secondary batteries, 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.

[0059] The non-aqueous organic solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0060] The non-aqueous organic solvent may include 5 to 40% by weight of ethylene carbonate (EC), 5 to 20% by weight of propylene carbonate (PC), 10 to 70% by weight of ethyl methyl carbonate (EMC), and 10 to 60% by weight of diethyl carbonate (DEC).

[0061] Specifically, in the cyclic carbonate solvent, ethylene carbonate (EC) or propylene carbonate (PC), which have high dielectric constants, can be used. When artificial graphite is used as the negative electrode active material, it is preferable to use ethylene carbonate (EC). Among the linear carbonate solvents, it is preferable to use dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC), which have low viscosity.

[0062] The non-aqueous organic solvent may be present in an amount of 5% to 80% of the total amount of the electrolyte for the lithium secondary battery. The non-aqueous organic solvent may be present in an amount of 5% to 70% of the total amount of the electrolyte for the lithium secondary battery.

[0063] <Lithium-ion secondary battery> The lithium secondary battery containing the aforementioned non-aqueous electrolyte exhibits excellent performance in that its lifespan characteristics do not deteriorate at high temperatures, its resistance does not increase during storage at high temperatures, and it suppresses expansion of the secondary battery volume (thickness).

[0064] The lithium secondary battery of the present invention will be described in detail below.

[0065] The lithium secondary battery of the present invention comprises a positive electrode, a negative electrode, a separation membrane, and a non-aqueous electrolyte.

[0066] The positive electrode may contain at least one positive electrode active material selected from the group consisting of lithium metal oxides such as LiCoO2, LiFePO4, LiMnO2, LiMn2O4, LiNiO2, or LiNi1-x-yCoxMyO2 (0≦x≦1, 0≦y≦1, 0≦x+y≦1, M is Al, Sr, Mg, Mn, or La).

[0067] The negative electrode may contain 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 mixtures of artificial and natural graphite.

[0068] The separation membrane may consist solely of a porous polymer film made from at least one polyolefin polymer selected from ethylene polymer, propylene polymer, ethylene / butene copolymer, and ethylene / hexene copolymer, or it may consist of a laminate thereof. The separation membrane may include a coating film coated with ceramic or polymeric material.

[0069] The non-aqueous electrolyte may include a compound containing an imidazole group and a benzene ring, particularly a compound represented by the following chemical formula 3, an additive, a lithium salt, and a non-aqueous organic solvent.

[0070] [ka]

[0071] Examples of the aforementioned lithium secondary batteries include, but are not limited to, lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0072] More specifically, the positive electrode active material is preferably a composite metal oxide of lithium and one or more substances selected from cobalt, manganese, and nickel. The solid solution ratio between the cobalt, manganese, and nickel metals of the composite metal oxide can vary, and in addition to these cobalt, manganese, and nickel metals, it may further contain elements 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.

[0073] Specifically, the positive electrode active material can be a lithium metal oxide such as LiCoO2, LiFePO4, LiMnO2, LiMn2O4, LiNiO2, or a lithium intercalation compound such as a lithium chalcosenide compound, or LiNi1-x-yCoxMyO2 (0≦x≦1, 0≦y≦1, 0≦x+y≦1, M is Al, Sr, Mg, Mn, or La), but is not limited to these, and any material usable as a positive electrode active material in a secondary battery can be used.

[0074] 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, a binder, a conductive material, etc., that can intercalate and release lithium.

[0075] 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, binder, conductive material, etc., that can insert and remove lithium. As the negative electrode active material, crystalline carbon, amorphous carbon, carbon composite, carbon fiber, lithium metal, lithium alloy, or carbon-silicon composite can be used, but are not limited to these, and any material that can be used as a negative electrode active material in a secondary battery can be used.

[0076] 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 produce an electrode slurry composition, and then applying the slurry composition to an electrode current collector. Aluminum or an aluminum alloy can often be used as the positive electrode current collector, and copper or a copper alloy can often be used as the negative electrode current collector.

[0077] Examples of the positive electrode current collector and the negative electrode current collector include foil or mesh forms.

[0078] The binder is a substance that plays a role in pasteuring the active material, bonding the active materials together, bonding to the current collector, and providing a buffering effect against the expansion and contraction of the active material. Any binder that can be used by a person skilled in the art is acceptable. For example, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, 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, acrylicated styrene-butadiene rubber, acrylonitrile-butadiene rubber, epoxy resin, nylon, etc. can be used, but are not limited to these.

[0079] The conductive material is used to impart conductivity to the electrodes, and any conductive material that does not cause a chemical change in the secondary battery that is constructed can be used. As the conductive material, 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 can be used. Examples of graphite-based conductive materials include artificial graphite and natural graphite, while examples of carbon black-based conductive materials include acetylene black, Ketjen black, Denka black, thermal black, and channel black, and examples of metal or metal compound-based conductive materials include perovskite substances such as tin, tin oxide, tin phosphate (SnPO4), titanium oxide, potassium titanate, LaSrCoO3, and LaSrMnO3. However, the conductive material is not limited to those listed above.

[0080] The aforementioned thickening agent is not particularly limited as long as it plays a role in adjusting the viscosity of the active material slurry, and for example, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, etc. can be used.

[0081] 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-pyrrolezidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, or tetrahydrofuran. Examples of the aqueous solvent include water.

[0082] The lithium secondary battery may include a separator that prevents short circuits between the positive and negative electrodes and provides a pathway for lithium ions to move. The separator can be a polyolefin polymer membrane such as polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, or polypropylene / polyethylene / polypropylene, or a multilayer film thereof, a microporous film, a woven fabric, or a nonwoven fabric. Alternatively, a film in which a porous polyolefin film is coated with a resin with excellent stability can be used as the separator.

[0083] Furthermore, the lithium secondary battery can be made into various shapes, such as rectangular, cylindrical, pouch-shaped, or coin-shaped. [Examples]

[0084] The present invention will be described in more detail below with reference to examples. It should not be construed that the scope of the present invention is limited by these examples.

[0085] <Example of synthesis of (2-methyl-1H-imidazol-1-yl)(phenyl)methanone (compound of chemical formula 1)> A 500 mL three-necked flask was fitted with an N2 purge line, a dropping funnel, and a thermometer. 0.71 mol of 2-methylimidazole (MIM) and 200 mL of dichloromethane (MC) were added and stirred. The reactor was kept under a nitrogen atmosphere and stirred at room temperature. Subsequently, 0.36 mol of benzoyl chloride (BC) was added dropwise over approximately 30 minutes. The reaction was then allowed to proceed at room temperature for 6 hours. After the reaction was complete, the mixture was washed twice with 200 mL of 10% by mass sodium bicarbonate solution in deionized water (DIW) for neutralization, followed by one wash with pure deionized water (DIW). The organic layer was then separated. To remove any remaining water, the mixture was treated with MgSO4 and filtered. The filtrate was concentrated to remove dichloromethane, and after drying in a vacuum oven, the final compound, 2-methyl-1H-imidazole-1-yl)(phenyl)methanone, was obtained. The yield was 70%.

[0086] 1 H NMR(Chloroform-d, δ ppm):2H 7.8ppm, 1H 7.7.ppm, 2H 7.5ppm, 1H 7.1ppm, 1H 6.9ppm, 3H 2.7ppm, HRMS:C11H10N2O(M+):186.08

[0087] <Manufacture of electrolyte for lithium secondary batteries containing (2-methyl-1H-imidazol-1-yl)(phenyl)methanone (compound of chemical formula 1)> Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed solvent (EC / EMC = 25 / 75 (volume ratio)), after dissolving LiPF6 to 1.0 M, 1.0 mass% of fluoroethylene carbonate (FEC), 1.0 mass% of lithium difluorophosphate (LiPO2F2), 0.5 mass% of propane sultone (PS), 0.5 mass% of ethylene sulfate (Esa) and 0.5 mass% of the compound of the above synthesis example shown by the above chemical formula 1 ((2-methyl-1H-imidazol-1-yl)(phenyl)methanone) were added to the mixed solution to prepare an electrolyte for a lithium secondary battery containing the compound of chemical formula 1.

[0088] <Manufacture of a lithium secondary battery including an electrolyte containing a compound of chemical formula 1> 94% by weight of an NCM-based positive electrode active material containing Li[NixCo1-x-yMny]O2 (0 < x < 0.5, 0 < y < 0.5), 3% by weight of a conductive material (Super-P), and 3% by weight of a binder (PVdF) were added to N-methyl 2-pyrrolidinone (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 manufacture a final positive electrode. Also, 96% by weight of a graphite-based negative electrode active material containing silicon oxide (SiO x (0 < x < 2)), 1% by weight of a conductive material (Super-P), 1.5% by weight of a binder SBR, and 1.5% by weight 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 manufacture a negative electrode.

[0089] 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 including an electrolyte containing the compound of chemical formula 1 in an aluminum pouch type (Al-Pouch type) was manufactured.

[0090] [Comparative Example] <Manufacturing of electrolyte for lithium secondary batteries containing 1,3-propene sultone (PRS) additive> Non-aqueous electrolytes for lithium secondary batteries may contain sultone compounds as needed to improve high-temperature stability and suppress battery expansion at high temperatures, as the non-aqueous electrolyte decomposes, leading to reduced high-temperature stability and battery expansion suppression. The sultone compound may be at least one selected from the group consisting of, for example, 1,3-propanesultone (PS), 1,4-butanesultone (BS), ethensultone, 1,3-propensultone, 1,4-butensultone, and 1-methyl-1,3-propensultone. In the comparative example, 1,3-propensultone (PRS), which is currently in common use, was used.

[0091] LiPF6 was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC / EMC = 25 / 75 (volume ratio)) to a concentration of 1.0 M. Then, 1.0% by mass of fluoroethylene carbonate (FEC), 1.0% by mass of lithium difluorophosphate (LiPO2F2), 0.5% by mass of propanesultone (PS), 0.5% by mass of ethylene sulfate (Esa), and 0.5% by mass of 1,3-propenesultone (PRS) were added to the mixed solution to prepare an electrolyte for lithium secondary batteries containing the 1,3-propene sultone (PRS) additive.

[0092] <Manufacturing of lithium secondary batteries containing electrolyte with 1,3-propene sultone (PRS) additive> A lithium secondary battery was prepared using the same method as the lithium secondary battery production example described above, except that the electrolyte did not contain the compound of chemical formula 1 but contained the 1,3-propensultone (PRS) additive, while the electrolyte did not contain the (2-methyl-1H-imidazole-1-yl)(phenyl)methanone compound represented by chemical formula 1, and instead contained 1,3-propensultone (PRS), which is the most widely used additive but is expensive and therefore a substitute is needed.

[0093] The composition of the electrolyte for lithium secondary batteries in the above examples and comparative examples is shown in Table 1 below.

[0094] [Table 1]

[0095] [Example of experiment] <Experimental Example 1> Measurement of lifetime capacity retention rate at high temperature (45°C) Lithium secondary batteries in pouch form, prepared using the lithium secondary battery electrolytes of the above-described examples and comparative examples, were charged to 4.2V at a 1C rate in a high-temperature (45°C) environment, given a 10-minute rest period, then discharged to 2.7V at a 1C rate, given another 10-minute rest period. This process was repeated 500 times, and the discharge capacity (mAh) and retention rate (%) of the batteries were measured. The measured discharge capacity and retention rate of the secondary batteries were compared, and the results are shown in Table 2.

[0096] [Table 2]

[0097] As shown in Table 2 above, the life evaluation at high temperatures revealed that the lithium secondary battery of the above example showed a higher level of life capacity retention at high temperatures compared to the lithium secondary battery of the comparative example.

[0098] Therefore, it was confirmed that the lithium secondary battery of the above embodiment, by containing an electrolyte containing the compound represented by chemical formula 1, had a higher lifetime capacity retention rate without deterioration in the high-temperature life performance of the secondary battery compared to the lithium secondary battery of the comparative example. In other words, the compound additive of chemical formula 1 improved the lifetime capacity retention rate at high temperatures without causing performance degradation due to side reactions with other additives.

[0099] <Experimental Example 2> Measurement of Storage Characteristics at High Temperature (60°C) Lithium secondary batteries in pouch form, prepared using the lithium secondary battery electrolytes of the above examples and comparative examples, were stored at a 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 a high temperature (60°C) compared to the state at 0 weeks.

[0100] [Table 3]

[0101] As shown in Table 3, the volume change rate of the secondary battery in the example was lower than that of the secondary battery in the comparative example. This indicates that the additive of the present invention has the effect of suppressing gas generation.

[0102] These results indicate that the additive of the present invention exhibits excellent high-temperature lifetime characteristics at 45°C and suppresses gas generation.

Claims

1. Additives and, Additives and Lithium salts and A non-aqueous electrolyte for lithium secondary batteries comprising a non-aqueous organic solvent, The aforementioned additive is a compound containing an imidazole group and a benzene ring. Nonaqueous electrolyte for lithium secondary batteries.

2. The aforementioned additive is a compound of the following chemical formula 1. The non-aqueous electrolyte for lithium secondary batteries according to claim 1. 【Chemistry 1】

3. The aforementioned additive is contained in an amount of 0.05% to 20% by weight, based on the total weight of the non-aqueous electrolyte for lithium secondary batteries. A non-aqueous electrolyte for a lithium secondary battery according to claim 1 or 2.

4. The 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. A non-aqueous electrolyte for a lithium secondary battery according to claim 1 or 2.

5. A non-aqueous electrolyte for a lithium secondary battery according to claim 1 or 2, Positive electrode and, The negative electrode and, A separation membrane and, Lithium-ion rechargeable battery.

6. The aforementioned negative electrode includes a carbon-based negative electrode active material and a silicon-based negative electrode active material. The lithium secondary battery according to claim 5.

7. The carbon-based anode active material and the silicon-based anode active material are contained in a weight ratio of 97:3 to 50:

50. The lithium secondary battery according to claim 6.

8. The carbon-based anode active material and the silicon-based anode active material are contained in a weight ratio of 90:10 to 60:

40. The lithium secondary battery according to claim 7.

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