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

Abstract

The present invention relates to: a novel electrolyte additive; a non-aqueous electrolyte for a lithium secondary battery, the non-aqueous electrolyte including the novel electrolyte additive; and a lithium secondary battery including the non-aqueous electrolyte. More specifically, the present invention relates to a non-aqueous electrolyte for a lithium secondary battery, the non-aqueous electrolyte including an additive capable of forming a stable film on an electrode surface. Additionally, by incorporating such a non-aqueous electrolyte, the present invention provides a lithium secondary battery with improved performance, including prevention of high-temperature-induced degradation of battery life, suppression of resistance increase during high-temperature storage, and inhibition of volume expansion (thickness increase) of secondary batteries under high-temperature storage conditions.

Description

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

[0001] The present invention relates to an electrolyte additive for secondary batteries. More specifically, the present invention relates to a non-aqueous electrolyte additive having an excellent effect of removing decomposition products generated from lithium salts, and a non-aqueous electrolyte for lithium secondary batteries containing the same. The present invention relates to a non-aqueous electrolyte additive capable of forming a robust solid electrolyte interface (SEI) film on the surface of an anode, and a non-aqueous electrolyte for lithium secondary batteries containing the same. The present invention also relates to a lithium secondary battery containing such a non-aqueous electrolyte. The lithium secondary battery of the present invention has improved high-temperature performance by containing the non-aqueous electrolyte.

[0002] Lithium secondary batteries are not only used as portable power sources for mobile phones, laptops, and other devices, but their applications are also expanding to medium- to large-scale power sources for electric bicycles and electric vehicles (EVs). This expansion of applications is driving the demand for lithium secondary batteries that can maintain superior performance not only at room temperature but also in harsher environments, such as high and low temperatures.

[0003] The lithium secondary batteries widely used today are generally composed of a carbon-based negative electrode that allows the insertion and deintercalation of 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 that prevents contact between the positive and negative electrodes. When a lithium secondary battery is charged, the lithium atoms in the positive electrode are ionized into lithium ions and electrons, and the electrons move to the negative electrode through an external circuit. The lithium ions then cross the non-aqueous electrolyte and the separator to the negative electrode and are intercalated into the carbon negative electrode. When discharging, the electrons move to the positive electrode through an external circuit, and at the same time, the lithium ions are deintercalated from the carbon negative electrode and cross the non-aqueous electrolyte and the separator to the positive electrode, where the lithium ions and electrons meet to form lithium atoms in a stable state. Lithium secondary batteries generate electrical energy by repeating this charging and discharging cycle.

[0004] During charging and discharging of lithium secondary batteries, the cathode active material structurally degrades, causing metal ions to be released from the cathode surface. These released metal ions can then be electrodeposited on the cathode, degrading it. This cathode degradation tends to accelerate when the cathode potential is high or the secondary battery is exposed to high temperatures.

[0005] To address these issues, a method has been proposed in which compounds capable of forming a film (a solid electrolyte interphase, or SEI) on the cathode surface are added to the non-aqueous electrolyte. However, these electrolyte additives cause other side effects, such as reduced lifespan and deteriorated high-temperature safety, leading to another problem: a decline in the overall performance of lithium secondary batteries.

[0006] LiPF6 is mainly used as a lithium salt in lithium secondary batteries to implement the appropriate characteristics of secondary batteries. PF6 of LiPF6 - Anions are known to be highly sensitive to heat, and when secondary batteries are exposed to high temperatures, they undergo thermal decomposition, generating Lewis acids such as PF5. The PF5 thus generated not only causes a decomposition reaction of 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 dissolved transition metals may be deposited on the positive electrode, increasing its resistance, or deposited on the negative electrode, causing self-discharge of the negative electrode, or destroying the solid-electrolyte interface (SEI) film on the negative electrode, which may further decompose the electrolyte, resulting in an increase in the resistance of the secondary battery and a shortened lifespan. This decomposition reaction of the electrolyte also causes gas generation inside the secondary battery.

[0007] For this reason, when lithium secondary batteries are stored at high temperatures in a fully charged state, the solid-electrolyte interface (SEI) gradually collapses over time. This collapse exposes the anode surface. The exposed anode surface decomposes as it reacts with the carbonate solvent in the electrolyte, causing persistent side reactions. These side reactions continuously generate gases.

[0008] Regardless of their type, the gases generated in this way increase the internal pressure of the lithium secondary battery, act as a resistance factor to lithium movement, expand the volume (thickness) of the secondary battery, cause significant problems in reducing the weight of the secondary battery, and deteriorate the performance of the secondary battery.

[0009] As the application areas of lithium secondary batteries have expanded, there has been a steady demand for stability and long lifespan in high-temperature environments. These performance characteristics are largely determined by the solid-electrolyte interface (SEI) film formed by the initial reaction between the electrode and electrolyte.

[0010] Therefore, in order to improve the high-temperature cycle characteristics and low-temperature output of lithium secondary batteries, there is a continuous 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 film (SEI film) on the negative electrode surface.

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

[0012] In addition, in order to solve the above-mentioned problems, the present invention seeks to provide an electrolyte additive for a secondary battery that is excellent in the effect of forming a solid electrolyte interface film (SEI) on an electrode surface, particularly a cathode surface, while simultaneously removing decomposition products generated from a lithium salt.

[0013] In addition, the present invention aims to provide a non-aqueous electrolyte for a lithium secondary battery capable of improving high-temperature stability without deterioration of the high-temperature lifespan and performance of a lithium secondary battery in order to solve the problems of the prior art as described above, and a lithium secondary battery including the non-aqueous electrolyte for a lithium secondary battery.

[0014] A non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention

[0015] A compound containing an imidazole group and a naphthalene group as an additive;

[0016] lithium salt;

[0017] Additional additives; and

[0018] Contains non-aqueous organic solvents.

[0019] A non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention

[0020] A compound containing an imidazole group, an ester group and a naphthalene group as an additive;

[0021] lithium salt;

[0022] Additional additives; and

[0023] Contains non-aqueous organic solvents.

[0024] A non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention

[0025] A compound containing an imidazole group and a naphthalene group represented by the following chemical formula 1 as an additive;

[0026] lithium salt;

[0027] Additional additives; and

[0028] Contains non-aqueous organic solvents.

[0029]

[0030] In one embodiment of the present invention, a lithium secondary battery is provided, which includes a non-aqueous electrolyte, a positive electrode, a negative electrode, and a separator for a lithium secondary battery of the present invention.

[0031] The above negative electrode may include a carbon-based negative electrode active material and a silicon-based negative electrode active material.

[0032] The above 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.

[0033] The above 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.

[0034] The compound containing an imidazole group and a naphthalene group, the compound containing an imidazole group, an ester group, and a naphthalene group, which is provided as an additive in the non-aqueous electrolyte of the present invention, particularly the nitrogen atom of the imidazole group of the compound represented by the 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 the inside of the electrolyte. Therefore, the compound containing an imidazole group and a naphthalene group, the compound containing an imidazole group, an ester group, and a naphthalene group, which is provided as an additive in the non-aqueous electrolyte of the present invention, particularly the compound represented by the chemical formula 1, can suppress the deterioration of the positive or negative electrode surface film (SEI layer [Solid Electrolyte Interphase Layer]) caused by Lewis acids, thereby preventing further electrolyte decomposition of the secondary battery due to destruction of the film (SEI), and can also suppress self-discharge of the secondary battery.

[0035] The functional group of the additive included in the non-aqueous electrolyte of the secondary battery of the present invention, i.e., a compound containing an imidazole group and a naphthalene group, a compound containing an imidazole group, an ester group, and a naphthalene group, and particularly a compound represented by the chemical formula 1, forms a film (SEI layer) with excellent thermal stability on the electrode surface, particularly on the negative electrode surface, due to a passivation effect. The naphthalene group of the compound reacts with CO2 to reduce the CO2 concentration. Therefore, the internal pressure of the secondary battery is not increased due to gas, thereby improving the stability of the secondary battery and maintaining a constant thickness of the secondary battery.

[0036] As a result of the above effects, the lifespan of a lithium secondary battery is not deteriorated even when exposed to high temperatures, and the volume expansion of the secondary battery is reduced by suppressing an increase in resistance or gas generation when stored at high temperatures, suppressing self-discharge of the secondary battery, and lowering the resistance of the secondary battery. Therefore, when the compound containing an imidazole group and a naphthalene group of the present invention, the compound containing an imidazole group, an ester group, and a naphthalene group, and particularly the compound represented by the chemical formula 1, is used as an additive for a non-aqueous electrolyte, a secondary battery with improved performance can be realized.

[0037] Hereinafter, the present invention will be described in more detail through examples. These examples are intended solely to illustrate the present invention, and therefore, the scope of the present invention should not be construed as being limited by these examples.

[0038] The terms "includes" and "has" used in this specification should be understood as open-ended terms that imply the possibility of including other components, unless specifically stated otherwise in the phrase or sentence in which the expression is included.

[0039] In this specification, “%” means weight percent unless explicitly indicated otherwise.

[0040] Hereinafter, the electrolyte additive for a lithium secondary battery, the non-aqueous electrolyte for a lithium secondary battery, and the lithium secondary battery including the non-aqueous electrolyte of the present invention will be described in detail.

[0041] Electrolyte additives for lithium secondary batteries

[0042] The present invention provides a compound containing an imidazole group and a naphthalene group, a compound containing an imidazole group, an ester group and a naphthalene group, and particularly a compound containing an imidazole group and a naphthalene group represented by the following chemical formula 1, as an additive for an electrolyte for a lithium secondary battery.

[0043] [Chemical Formula 1]

[0044]

[0045] Electrolyte for lithium secondary batteries

[0046] The present invention

[0047] A compound containing an imidazole group and a naphthalene group;

[0048] Additional additives;

[0049] lithium salt; and

[0050] An electrolyte for a lithium secondary battery containing a non-aqueous organic solvent is provided.

[0051] The present invention

[0052] A compound containing an imidazole group, an ester group, and a naphthalene group;

[0053] Additional additives;

[0054] lithium salt; and

[0055] An electrolyte for a lithium secondary battery containing a non-aqueous organic solvent is provided.

[0056] The present invention

[0057] A compound comprising an imidazole group and a naphthalene group represented by the above chemical formula 1;

[0058] Additional additives;

[0059] lithium salt; and

[0060] An electrolyte for a lithium secondary battery containing a non-aqueous organic solvent is provided.

[0061] The compound containing the above imidazole group and naphthalene group may be included in an amount of 0.05 to 20 wt% based on the total weight of the electrolyte for the lithium secondary battery.

[0062] The compound containing the above imidazole group and naphthalene group may preferably be included in an amount of 0.05 to 10 wt% based on the total weight of the electrolyte for the lithium secondary battery.

[0063] The compound containing the above imidazole group and naphthalene group may more preferably be included 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 for the lithium secondary battery.

[0064] The compound containing the above imidazole group and naphthalene group may be included in an amount of 0.1 to 20 wt% based on the total weight of the electrolyte for the lithium secondary battery.

[0065] The compound containing the above imidazole group and naphthalene group may preferably be included in an amount of 0.1 to 10 wt% based on the total weight of the electrolyte for the lithium secondary battery.

[0066] The compound including the above imidazole group and naphthalene group may more preferably be included 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 for the lithium secondary battery.

[0067] When the compound including the imidazole group and the naphthalene group is included in an amount of less than 0.05 wt% based on the total weight of the electrolyte for the lithium secondary battery, the effect of preventing volume expansion of the lithium secondary battery and the effect of reducing internal resistance are not sufficient, and conversely, when the compound including the imidazole group and the naphthalene group is included in an amount exceeding 20 wt% based on the total weight of the electrolyte for the lithium secondary battery, the problem of deterioration of high-temperature life characteristics and high-temperature storage characteristics occurs due to an increase in the internal resistance and a decrease in capacity of the secondary battery.

[0068] The above-mentioned electrolyte for a lithium secondary battery may additionally include at least one additional additive selected from the group consisting of a halogen-substituted or unsubstituted carbonate-based compound, a nitrile-based compound, a borate-based compound, a lithium salt-based compound, a phosphate-based compound, a sulfite-based compound, a sulfone-based compound, a sulfate-based compound, and a sultone-based compound.

[0069] Representative examples of the above-mentioned 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.

[0070] The above-mentioned additional additive may be included in an amount of 0.05 to 20 wt% based on the total weight of the electrolyte for the lithium secondary battery.

[0071] The above-mentioned additional additive may preferably be included in an amount of 0.05 to 10 wt% based on the total weight of the electrolyte for the lithium secondary battery.

[0072] The above-mentioned additional additive may more preferably be included in an amount of 0.05 to 5 wt%, specifically 0.05 to 3 wt%, based on the total weight of the electrolyte for the lithium secondary battery.

[0073] If the above-mentioned additional additive is included in an amount of less than 0.05 wt% based on the total weight of the electrolyte for lithium secondary batteries, the effect of forming a film on the electrode is minimal, and thus the effect of suppressing side reactions between the electrode and the electrolyte may be reduced. If the above-mentioned electrolyte additive is included in an amount exceeding 20 wt% based on the total weight of the electrolyte for lithium secondary batteries, an excessively thick film may be formed on the electrode surface, increasing the interfacial resistance and causing problems such as reduced capacity.

[0074] The above lithium salt may include at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiBF6, LiSbF6, LiAl04, LiAlCl4, LiClO4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, and LiB(C2O4)2.

[0075] It is preferable to use a lithium salt having a high lattice energy dissociation degree, excellent ionic conductivity, and superior thermal stability and oxidation resistance. The lithium salt acts as a passage for lithium ions within the secondary battery, thereby enabling the basic operation of the lithium secondary battery.

[0076] The concentration of the lithium salt may be included in a range of 0.1 to 2.5 M (mol / L) based on the total amount of the electrolyte for the lithium secondary battery.

[0077] The concentration of the lithium salt may be preferably included at 0.3 to 2.5 M (mol / L) with respect to the total amount of the electrolyte for the lithium secondary battery, taking into consideration properties related to electrical conductivity and viscosity related to the mobility of lithium ions.

[0078] The concentration of the lithium salt may be more preferably comprised at 0.7 to 1.6 M (mol / L), taking into account properties related to electrical conductivity and viscosity related to mobility of lithium ions.

[0079] 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, thereby reducing the performance of the non-aqueous electrolyte for rapidly transferring ions between the positive and negative electrodes of the lithium secondary battery. If the concentration of the lithium salt exceeds 2.5 M, the viscosity of the electrolyte for the lithium secondary battery increases, thereby reducing the mobility of lithium ions and causing a problem in that the performance of the secondary battery deteriorates at low temperatures.

[0080] The above non-aqueous organic solvent may be a linear carbonate solvent, a cyclic carbonate solvent, or a mixed solvent thereof.

[0081] 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).

[0082] In addition, 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).

[0083] It may be desirable to use a mixture of a high-dielectric constant cyclic carbonate organic solvent having high ionic conductivity that can improve the charge / discharge performance of a secondary battery and a low-viscosity linear carbonate organic solvent that can appropriately control the viscosity of the high-dielectric constant carbonate organic solvent.

[0084] Specifically, a high-dielectric constant carbonate organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and mixtures thereof, which are cyclic carbonate solvents, and a low-viscosity carbonate 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 solvents, can be used in combination.

[0085] The above cyclic carbonate solvent has a large polarity and can sufficiently dissociate lithium ions, but has a large viscosity and thus has a disadvantage of low ion conductivity. Therefore, by mixing and using a linear carbonate solvent with a small polarity but low viscosity with the above cyclic carbonate solvent, the characteristics of a lithium secondary battery can be optimized.

[0086] Therefore, it may be desirable to use a mixture of at least one solvent selected from the cyclic carbonate solvent and at least one solvent selected from the linear carbonate solvent as the non-aqueous organic solvent.

[0087] 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.

[0088] In terms of the life characteristics and storage characteristics of a 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.

[0089] The non-aqueous organic solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0090] The non-aqueous organic solvent may include 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).

[0091] Specifically, among the cyclic carbonate solvents, ethylene carbonate (EC) or propylene carbonate (PC) having a high dielectric constant can be used. When artificial graphite is used as the negative electrode active material, it is preferable to use the ethylene carbonate (EC). Among the linear carbonate solvents, it is preferable to use dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC) having a low viscosity.

[0092] The non-aqueous organic solvent may be included 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 included in an amount of 5% to 70% of the total amount of the electrolyte for the lithium secondary battery.

[0093] Lithium secondary battery

[0094] A lithium secondary battery including the above non-aqueous electrolyte does not deteriorate in life characteristics at high temperatures, does not increase in resistance when stored at high temperatures, and has superior performance in suppressing expansion of the volume (thickness) of the secondary battery.

[0095] Hereinafter, the lithium secondary battery of the present invention will be described in detail.

[0096] The lithium secondary battery of the present invention

[0097] anode;

[0098] cathode;

[0099] membrane;

[0100] and non-aqueous electrolytes.

[0101] The above cathode is LiCoO2, LiFePO4, LiMnO2, LiMn2O4, LiNiO 2, or LiNi 1-x-y Co x M y It may include 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).

[0102] The above 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.

[0103] The above-mentioned separator may be composed solely of a porous polymer film made of at least one polyolefin polymer selected from among ethylene polymers, propylene polymers, ethylene / butene copolymers, and ethylene / hexene copolymers, or may be composed of a laminate thereof. The above-mentioned separator may include a coating film coated with a ceramic or polymer material.

[0104] The above non-aqueous electrolyte is a compound containing an imidazole group and a naphthalene group, a compound containing an imidazole group, an ester group and a naphthalene group, and in particular a compound represented by the following chemical formula 1;

[0105] Additional additives;

[0106] lithium salt; and

[0107] May contain non-aqueous organic solvents.

[0108] [Chemical Formula 1]

[0109]

[0110] Examples of the above 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.

[0111] To explain in more detail, the positive electrode active material is preferably a composite metal oxide of lithium and at least one material selected from cobalt, manganese, and nickel. The solid solution ratio between the cobalt, manganese, and nickel metals in the composite metal oxide can vary, and 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 can be further included.

[0112] Specifically, the positive electrode active materials include LiCoO2, LiFePO4, LiMnO2, LiMn2O4, and LiNiO. 2, or LiNi 1-x-yCo x M y A lithium metal oxide such as O2 (0≤x≤1, 0≤y≤1, 0≤x+y≤1, M is Al, Sr, Mg, Mn or La) or a lithium intercalation compound such as a lithium chalcogenide compound can be used, but is not limited thereto, and any material that can be used as a positive electrode active material in a secondary battery can be used.

[0113] The above 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.

[0114] The above 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 de-inserting lithium, a binder, a conductive material, etc. As the negative electrode active material, crystalline carbon, amorphous carbon, a carbon composite, carbon fiber, lithium metal, a lithium alloy, or a carbon-silicon composite may be used, but is not limited thereto, and any material usable as a negative electrode active material in a secondary battery may be used.

[0115] The above positive and / or negative electrodes can be manufactured by dispersing an electrode active material, a binder, a conductive agent, and, if necessary, a thickener in a solvent to prepare an electrode slurry composition, and then applying the slurry composition to an electrode current collector. Aluminum or an aluminum alloy can commonly be used as the positive current collector, and copper or a copper alloy can commonly be used as the negative current collector.

[0116] Examples of the form of the positive electrode current collector and the negative electrode current collector include foil or mesh forms.

[0117] The above binder is a material that plays a role in pasting the active material, mutual adhesion of the active material, adhesion with the current collector, and cushioning effect for expansion and contraction of the active material, and any binder that can be used by a person skilled in the art can be used. For example, 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), poly(vinylacetate), 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, nylon, etc. can be used, but are not limited thereto.

[0118] The conductive material is used to provide conductivity to the electrode, and any electrically conductive material that does not cause a chemical change in the secondary battery to be formed can be used. The conductive material may include at least one selected from the group consisting of a graphite-based conductive material, a carbon black-based conductive material, and a metal or metal compound-based conductive material. Examples of the graphite-based conductive material include artificial graphite, natural graphite, etc., examples of the carbon black-based conductive material include acetylene black, ketjen black, denka black, thermal black, channel black, etc., and examples of the metal-based or metal compound-based conductive material include perovskite materials such as tin, tin oxide, tin phosphate (SnPO4), titanium oxide, potassium titanate, LaSrCoO3, and LaSrMnO3. However, the present invention is not limited to the conductive materials listed above.

[0119] The above thickener is not particularly limited as long as it can play a role in controlling the viscosity of the active material slurry, and examples thereof include carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

[0120] As a solvent in which the electrode active material, binder, conductive material, etc. are dispersed, a non-aqueous solvent or an aqueous solvent may be used. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, or tetrahydrofuran. Examples of the aqueous solvent include water.

[0121] The above lithium secondary battery may include a separator that prevents short circuits between the positive and negative electrodes and provides a passage for lithium ions to move. As the separator, a polyolefin-based polymer film such as polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, polypropylene / polyethylene / polypropylene, or a multi-film thereof, a microporous film, a woven fabric, or a non-woven fabric may be used. In addition, a film in which a porous polyolefin film is coated with a resin having excellent stability may be used as the separator.

[0122] In addition, the lithium secondary battery can be made into various shapes such as square, cylindrical, pouch or coin shape.

[0123] Hereinafter, the present invention will be described in more detail through examples. The scope of the present invention should not be construed as being limited by these examples.

[0124] <Method for producing a compound of chemical formula 1>

[0125] <Synthesis example of naphthalen-2-yl 1H-imidazole-1-carboxylate (compound of chemical formula 1)>

[0126] A 1,000 mL three-necked flask equipped with an N2 purge line, a dropping funnel, and a thermometer was charged with 0.76 mol of 1,1'-carbonyldiimidazole (CDI) and 400 mL of dichloromethane (MC) and stirred. The reactor was filled with a nitrogen atmosphere and stirred at room temperature. 0.69 mol of 2-naphthol was then added. The reaction was allowed to proceed for 1 hour at room temperature.

[0127] After the reaction was completed, 800 ml of water was used to wash twice to remove impurities. The organic layer was then extracted. After treatment with MgSO4 to remove residual moisture, filtration was performed. Concentration was performed to remove dichloromethane in the filtrate. After concentration, the reaction mixture was purified by recrystallization using toluene and heptane. Afterwards, it was dried in a vacuum oven. The final compound, naphthalen-2-yl 1H-imidazole-1-carboxylate, was obtained. The yield was 60%.

[0128] 1 H NMR (Chloroform-d, δ ppm): 1H 8.4ppm, 1H 8.00.ppm, 2H 7.90ppm, 1H 7.80ppm, 1H 7.62ppm, 2H 7.60ppm, 1H 7.40ppm, 1H 7.20ppm HRMS: C 14 H 10 N2O2(M+):238.07

[0129] [Example]

[0130] <Preparation of an electrolyte for a lithium secondary battery containing naphthalen-2-yl 1H-imidazole-1-carboxylate (compound of chemical formula 1)>

[0131] LiPF6 was dissolved to 1.0 M in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC / EMC=25 / 75 volume ratio), 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 the compound naphthalen-2-yl 1H-imidazole-1-carboxylate of the above-described synthesis example represented by the above-described chemical formula 1 were added to prepare an electrolyte for a lithium secondary battery including the chemical formula 1.

[0132] <Manufacture of a lithium secondary battery comprising an electrolyte containing a compound of chemical formula 1>

[0133] Li[Ni x Co 1-x-y Mn y ]O2(0 <x<0.5, 0<y<0.5)를 포함하는 NCM계 양극 활물질 94 중량%, 도전재(Super-P) 3 중량%, 바인더(PVdF) 3 중량%를 유기용매인 N-메틸 2-피롤리돈(N-methyl 2-pyrrolidinone, NMP)에 첨가하여 양극 활물질 슬러리를 제조하였다. 상기 양극 활물질 슬러리를 집전체인 알루미늄 박막에 도포하고 건조하여 양극을 제조한 후 롤프레스로 압연하여 최종적인 양극을 만들었다. 또한, 실리콘산화물 (SiO x (0 <x<2))을 포함하는 흑연계 음극 활물질 96 중량%, 도전재(Super-P) 1중량%, 바인더 SBR 1.5중량%, CMC 1.5중량%를 혼합하여 음극 활물질 슬러리를 제조하였다. 상기 음극 활물질 슬러리를 음극 집전체인 구리 박막에 도포하고 건조하여 음극을 만들었다.

[0134] The positive and negative electrodes manufactured as described above were prepared, and a separator was interposed between them. Then, an electrolyte for a lithium secondary battery containing the compound of chemical formula 1 was injected between the two electrodes on which the separator was placed, thereby manufacturing a lithium secondary battery containing an electrolyte containing the compound of chemical formula 1 in the form of an aluminum pouch (Al-Pouch type).

[0135] [Comparative example]

[0136] <Manufacture of electrolyte for lithium secondary batteries containing 1,3-propene sultone (PRS) additive>

[0137] The non-aqueous electrolyte for a lithium secondary battery may contain a sultone compound as needed to improve high-temperature stability and suppress battery expansion at high temperatures, as the non-aqueous electrolyte decomposes, weakening high-temperature stability and causing the battery to expand at high temperatures. The sultone compound may 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 a comparative example, 1,3-propene sultone (PRS), which is currently commonly used, was used.

[0138] LiPF6 was dissolved to 1.0 M in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC / EMC=25 / 75 volume ratio), 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) were added to the mixed solution to prepare an electrolyte for a lithium secondary battery containing a 1,3-propene sultone (PRS) additive.

[0139] <Manufacture of a lithium secondary battery containing an electrolyte containing 1,3-propene sultone (PRS) additive>

[0140] A lithium secondary battery including an electrolyte including an additive of 1,3-propene sultone (PRS) that is most widely used as an additive but is expensive and thus requires a substitute, was manufactured using the same method as the lithium secondary battery manufacturing method of the above example, without adding the naphthalen-2-yl 1H-imidazole-1-carboxylate compound represented by the above chemical formula 1 as an electrolyte.

[0141] The composition of the electrolyte for lithium secondary batteries of the above examples and comparative examples is shown in Table 1 below.

[0142] <Composition of electrolyte for lithium secondary batteries>

[0143] Chemical Formula 11,3-Propene Sultone (PRS) Fluoroethylene Carbonate (FEC) Lithium Difluorophosphate (LiPO2F2) 1,3-Propane Sultone (PS) Ethylene Sulfate (Esa) Example OOOOO Comparative Example OOOOO

[0144] [Experimental Example]

[0145] <Experimental Example 1> Measurement of high temperature (45℃) life capacity retention rate

[0146] A pouch-shaped lithium secondary battery manufactured using the electrolyte for lithium secondary batteries of the above examples and comparative examples was charged to 4.2 V at a 1 C rate at a high temperature (45°C), followed by a 10-minute rest period, discharged to 2.7 V at a 1 C rate, and then rested for another 10 minutes. The above process was repeated 500 times, and the discharge capacity (mAh) and life-cycle capacity retention rate (retention, %) of the battery were measured. The measured discharge capacities and life-cycle capacity retention rates of the secondary batteries were compared, and the results are shown in Table 2.

[0147] 1-time discharge capacity (mAh) 500-time discharge capacity (mAh) Life-span capacity retention rate (%) Example 907.2680.575 Comparative example 899.3658.573

[0148] As shown in Table 2 above, the results of the life evaluation at high temperatures showed that the lithium secondary battery of the above example had a higher life capacity retention rate at high temperatures than the lithium secondary battery of the above comparative example.

[0149] Therefore, it was confirmed that the lithium secondary battery of the above example had a high life capacity retention rate without deterioration in high-temperature life performance of the secondary battery compared to the lithium secondary battery of the comparative example by including an electrolyte containing the compound represented by the chemical formula 1. In other words, the compound additive of the chemical formula 1 improved the life capacity retention rate at high temperatures without deterioration in performance due to side reactions with other additives.

[0150] <Experimental Example 2> Measurement of high-temperature (60℃) storage characteristics

[0151] The volume change rate of the secondary battery was measured after storing the pouch-shaped lithium secondary battery manufactured using the electrolyte for the lithium secondary battery of the above examples and comparative examples at a high temperature (60°C) for 6 weeks. Table 3 below shows the results of the volume change rate of the secondary battery after 6 weeks of storage at a high temperature (60°C) compared to the 0th week.

[0152] Volume increase rate (%) after 6 weeks of storage at 60℃ AC-IR change rate (%) after 6 weeks of storage at 60℃ Example 1.7283.19 Comparative example 1.8287.78

[0153] As shown in Table 3, the volume increase rate and AC-IR change rate of the secondary battery of the example were lower than those of the secondary battery of the comparative example. This demonstrates that the additive of the present invention has the effect of suppressing gas generation and improving resistance.

[0154] From this, it can be seen that the additive of the present invention is an additive that has good high-temperature life characteristics at 45°C, suppresses gas generation, and improves resistance.

Claims

1. Additives; Additional additives; lithium salt; and A non-aqueous electrolyte for a lithium secondary battery containing a non-aqueous organic solvent, The above additive is a non-aqueous electrolyte for a lithium secondary battery, which is a compound containing an imidazole group, an ester group, and a naphthalene group.

2. In paragraph 1, the additive is a non-aqueous electrolyte for a lithium secondary battery, which is a compound of the following chemical formula 1. [Chemical Formula 1] 3. A non-aqueous electrolyte for a lithium secondary battery, wherein the additive is contained in an amount of 0.05 wt% to 20 wt% based on the total weight of the non-aqueous electrolyte for a lithium secondary battery, in accordance with paragraph 1 or 2.

4. A non-aqueous electrolyte for a lithium secondary battery according to claim 1 or 2, wherein the additional additive is at least one compound selected from the group consisting of a halogen-substituted or unsubstituted carbonate-based compound, a nitrile-based compound, a borate-based compound, a lithium salt-based compound, a phosphate-based compound, a sulfite-based compound, a sulfone-based compound, a sulfate-based compound, and a sultone-based compound.

5. Non-aqueous electrolyte for lithium secondary batteries according to paragraph 1 or 2; anode; cathode; and A lithium secondary battery including a separator.

6. A lithium secondary battery in accordance with paragraph 5, wherein the negative electrode comprises a carbon-based negative electrode active material and a silicon-based negative electrode active material.

7. A lithium secondary battery in accordance with paragraph 6, wherein the carbon-based negative electrode active material and the silicon-based negative electrode active material are included in a weight ratio of 97:3 to 50:

50.

8. A lithium secondary battery in accordance with paragraph 7, wherein the carbon-based negative electrode active material and the silicon-based negative electrode active material are included in a weight ratio of 90:10 to 60:40.

Images