Nonaqueous electrolyte for lithium secondary battery and lithium secondary battery containing same

Abstract

The present invention provides a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery including the same. Specifically, the non-aqueous electrolyte for a lithium secondary battery of the present invention may include a lithium salt, an organic solvent, and a compound represented by Chemical Formula 1 as a first additive. The present invention also provides a lithium secondary battery including the non-aqueous electrolyte for a lithium secondary battery, which has improved high-temperature storage characteristics and high-temperature cycle characteristics.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0111719, filed September 2, 2022, and Korean Patent Application No. 10-2023-0108612, filed August 18, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery containing the same. [Background technology]

[0003] 2. Description of the Related Art In modern society, as dependency on electrical energy continues to increase, attention is being paid to the development of large-capacity power storage devices that can stably supply power and increase production.

[0004] Lithium-ion batteries have the highest energy density among commercially available power storage devices and are used in a variety of applications, including small electronic devices, electric vehicles (EVs), and power storage devices.

[0005] In particular, lithium ion batteries used in electric vehicles are required to maintain cycle characteristics and performance in a variety of environments and to have high output characteristics.

[0006] Such a lithium-ion battery is composed of a positive electrode made of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, a non-aqueous electrolyte solution containing an organic solvent containing a lithium salt, and a separator.

[0007] Meanwhile, lithium hexafluorophosphate (LiPF6), which is the main lithium salt used, is easily decomposed at high temperatures to produce Lewis acid by-products such as HF and PF5, which react with moisture to produce even more Lewis acid by-products (HF).

[0008] These Lewis acid by-products can erode the passive film formed on the electrode and its surface, potentially causing the elution of transition metal ions from the positive electrode. The eluted transition metal ions can accelerate the decomposition of the electrolyte solvent, accelerating gas generation, or they can be redeposited on the positive electrode, increasing the resistance of the positive electrode. They can also migrate to the negative electrode through the electrolyte and be electrodeposited on the negative electrode, causing self-discharge of the negative electrode, destruction and regeneration of the solid electrolyte interphase (SEI), resulting in additional lithium ion consumption and increased resistance.

[0009] This series of reactions reduces the amount of available lithium ions in the battery, which is the main cause of battery capacity degradation. Furthermore, if the metal ions electrodeposited on the negative electrode grow into dendrites, they can cause an internal short circuit in the battery, which reduces the safety of the battery.

[0010] Therefore, there is a need for the development of a non-aqueous electrolyte that can remove Lewis acid by-products (such as HF and PF5) generated by the thermal decomposition of lithium salts, and that can form a stable coating on the surface of the electrode to suppress the elution of transition metals, or that can suppress the electrodeposition of eluted transition metal ions onto the negative electrode, thereby improving not only safety but also battery performance such as high-rate charge / discharge characteristics. Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide a nonaqueous electrolyte for a lithium secondary battery, which contains an additive that forms a stable coating on the surface of an electrode and is excellent in removing highly reactive Lewis acid by-products formed as decomposition products of salts in the electrolyte and acidic materials.

[0012] Another object of the present invention is to provide a lithium secondary battery containing the nonaqueous electrolyte solution for lithium secondary batteries, which has improved high-temperature storage characteristics and high-temperature cycle characteristics. [Means for solving the problem]

[0013] To achieve the above object, one embodiment of the present invention comprises: a lithium salt, an organic solvent, and a first additive; The first additive provides a non-aqueous electrolyte solution for a lithium secondary battery, comprising a compound represented by the following Chemical Formula 1:

[0014] [ka]

[0015] In the above Chemical Formula 1, Ar is a 5- or 6-membered nitrogen-containing ring; R1 and R2 are each independently an alkyl group having 1 to 8 carbon atoms.

[0016] Yet another embodiment of the present invention is The present invention provides a lithium secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and the nonaqueous electrolyte solution for the lithium secondary battery. [Effects of the Invention]

[0017] The nonaqueous electrolyte for a lithium secondary battery of the present invention contains, as an additive, a compound containing a five- or six-membered nitrogen-containing ring group and a phosphoryl group in its structure, which effectively removes Lewis acid by-products, which are by-products of the electrolyte salt, forms a strong SEI, and has the effect of suppressing metal elution and reducing gas generation by suppressing side reactions between the electrolyte and electrodes, thereby improving battery degradation due to electrode deterioration. Therefore, by using such a nonaqueous electrolyte for a lithium secondary battery, a lithium secondary battery with improved cycle characteristics and high-temperature storage stability can be realized. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will now be described in more detail.

[0019] The terms and phrases used in the specification and claims are used only to describe exemplary embodiments and are not intended to limit the invention.

[0020] For example, in this specification, terms such as "comprises," "comprises," or "has" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and other parts may be added unless "only" is used.

[0021] In addition, in this specification, "%" means % by weight unless otherwise expressly indicated.

[0022] In this specification, unless otherwise defined, the term "substituted" means that at least one hydrogen atom bonded to a carbon atom is substituted with an element other than hydrogen, for example, with an alkyl group having 1 to 5 carbon atoms or a fluorine atom.

[0023] In the past, decomposition products formed by the hydrolysis or thermal decomposition of lithium salts, such as hydrogen fluoride (HF), formed a film on the surface of the electrode, easily dissolving the transition metals that make up the positive electrode into the electrolyte. The dissolved transition metal ions were re-deposited on the positive electrode, causing an increase in the resistance of the positive electrode. Alternatively, transition metals transferred to the negative electrode via the electrolyte were electrodeposited on the negative electrode, causing self-discharge of the negative electrode and destroying the solid electrolyte interphase (SEI) film that provides passivation to the negative electrode, promoting additional electrolyte decomposition reactions and increasing the interfacial resistance of the negative electrode.

[0024] This series of reactions not only reduces the amount of available lithium ions in the battery, resulting in a decrease in battery capacity, but also causes an increase in resistance because it is accompanied by a decomposition reaction of the electrolyte.

[0025] The present invention aims to provide a non-aqueous electrolyte solution for lithium secondary batteries that contains an additive capable of effectively removing decomposition products of the electrolyte salt that cause such deterioration and poor behavior, and that is oxidatively decomposed before organic solvents and can form a strong coating on the surface of the positive electrode, and a lithium secondary battery that contains the same and thereby has improved high-rate charge / discharge performance at high temperatures.

[0026] [Non-aqueous electrolyte for lithium secondary batteries] Specifically, one embodiment of the present invention is a lithium salt, an organic solvent, and a first additive; The non-aqueous electrolyte for a lithium secondary battery includes a compound represented by the following Chemical Formula 1 as the first additive:

[0027] [ka]

[0028] In the above Chemical Formula 1, Ar is a 5- or 6-membered nitrogen-containing ring; R1 and R2 are each independently an alkyl group having 1 to 8 carbon atoms.

[0029] (1) Lithium salt First, in the non-aqueous electrolyte for a lithium secondary battery of the present invention, the lithium salt may be any of those commonly used in electrolytes for lithium secondary batteries, without any limitation. For example, Li + and as an anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO4 - , PF6 - , CF3SO3 - , CH3CO2- , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - , and SCN - Examples include those containing at least one selected from the group consisting of:

[0030] Specifically, the lithium salts include LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10, LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2 (lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethane sulfonyl)imide, LiTFSI). Preferably, the catalyst may comprise a single substance or a mixture of two or more substances selected from the group consisting of LiBF4, LiPF6, LiN(SO2F)2 (LiFSI), LiN(SO2CF2CF3)2 (LiBETI), and LiN(SO2CF3)2 (LiTFSI). In addition to these, lithium salts that are commonly used in electrolytes for lithium secondary batteries can be used without any restrictions.

[0031] The lithium salt can be varied as appropriate within a range that is normally usable, but in order to obtain the optimum effect of forming a corrosion prevention coating on the electrode surface, it may be contained in the electrolyte at a concentration of 0.8 M to 4.0 M, specifically 1.0 M to 3.0 M.

[0032] When the concentration of the lithium salt is within the above range, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, and the mobility of lithium ions can be improved, resulting in improved capacity characteristics and cycle characteristics of the lithium secondary battery.

[0033] (2) Organic solvent The organic solvent will be described below.

[0034] The non-aqueous organic solvent may be any of various organic solvents commonly used in non-aqueous electrolytes, and the type of organic solvent is not limited as long as it minimizes decomposition due to oxidation reactions during the charge / discharge process of the secondary battery and exhibits desired properties together with the additives.

[0035] Specifically, the non-aqueous organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, or a mixture thereof.

[0036] The cyclic carbonate organic solvent is a highly viscous organic solvent that has a high dielectric constant and therefore easily dissociates the lithium salt in the non-aqueous electrolyte solution. Specific examples of the cyclic carbonate organic solvent include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, and particularly, at least one of ethylene carbonate and propylene carbonate.

[0037] The linear carbonate organic solvent is an organic solvent having low viscosity and low dielectric constant, and specific examples thereof may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, and specifically may include one of dimethyl carbonate and ethyl methyl carbonate.

[0038] In the present invention, in order to ensure high ionic conductivity, the cyclic carbonate organic solvent and the linear carbonate organic solvent may be mixed and used. In this case, the cyclic carbonate organic solvent and the linear carbonate organic solvent may be contained in a volume ratio of 10:90 to 50:50, specifically 20:80 to 40:60.

[0039] In addition, in order to produce an electrolyte solution having high ionic conductivity, the organic solvent may further include at least one organic solvent selected from the group consisting of a linear ester organic solvent and a cyclic ester organic solvent, which have a lower melting point and higher stability at high temperatures than the cyclic carbonate organic solvent and / or the linear carbonate organic solvent.

[0040] A representative example of the linear ester-based organic solvent is at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, and specifically, may include at least one of ethyl propionate and propyl propionate.

[0041] The cyclic ester organic solvent may include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0042] On the other hand, in the nonaqueous electrolyte solution of the present invention, the remainder, excluding the lithium salt, the first additive, and the second additive described below, is an organic solvent unless otherwise specified.

[0043] (3) First additive The first additive of the present invention may include a compound represented by the following Chemical Formula 1:

[0044] [ka]

[0045] In the above Chemical Formula 1, Ar is a 5- or 6-membered nitrogen-containing ring; R1 and R2 are each independently an alkyl group having 1 to 8 carbon atoms.

[0046] The five- or six-membered nitrogen-containing ring contained in the structure of the compound represented by Chemical Formula 1 is a functional group that acts as a Lewis base, and the lone electron pair of the nitrogen atom bonds with PF5, suppressing the formation of Lewis acid substances, such as HF, that are generated by the decomposition of PF5. As a result, deterioration behavior due to chemical reactions of the coating on the surface of the positive or negative electrode caused by Lewis acids can be suppressed, preventing further decomposition of the battery electrolyte due to deterioration or destruction of the coating, and further mitigating self-discharge of the secondary battery and improving high-temperature storage characteristics.

[0047] Furthermore, the compound represented by Chemical Formula 1 contains within its structure a phosphoryl group that can form an inorganic coating on the surface of the negative electrode, thereby suppressing side reactions between the electrolyte and the electrode, reducing gas emissions and preventing battery degradation.

[0048] In particular, the compound represented by Chemical Formula 1 forms a passivation film with high passivation ability on the surfaces of the anode and cathode as functional groups such as a nitrogen-containing ring or a phosphoryl group are reductively decomposed. This can prevent a self-discharge reaction of the anode caused by additional reductive decomposition of the electrolyte due to the instability of the SEI film, and can prevent metal ions from being eluted from the cathode and the eluted metal ions from being electrodeposited onto the anode, thereby achieving an effect of improving high-temperature durability such as cycle characteristics and capacity characteristics of a lithium secondary battery.

[0049] Meanwhile, the compound represented by Chemical Formula 1 may be a compound represented by Chemical Formula 1A below.

[0050] [ka]

[0051] In the above Chemical Formula 1A, R1 and R2 are each independently an alkyl group having 1 to 8 carbon atoms.

[0052] In addition, in the above chemical formula 1A, R1 and R2 may each independently be an alkyl group having 1 to 5 carbon atoms.

[0053] In addition, in the above chemical formula 1A, R1 and R2 may each independently be an alkyl group having 1 to 3 carbon atoms.

[0054] Preferably, the compound represented by Chemical Formula 1A may be one of the compounds represented by Chemical Formula 1A-1 or 1A-2 below.

[0055] [ka]

[0056] [ka]

[0057] Meanwhile, the compound of Formula 1 may be included in an amount of 0.5 wt % to 3.0 wt % based on the total weight of the non-aqueous electrolyte.

[0058] When the compound represented by Chemical Formula 1 is contained within the above range, it prevents side reactions caused by additives and forms strong coatings on the anode and cathode, effectively preventing anode degradation during rapid charge and discharge, thereby enabling the production of a secondary battery with improved performance. Specifically, when the content of the compound represented by Chemical Formula 1 is 0.5 wt % or more, it is possible to more stably remove thermal decomposition products of lithium salts such as HF or PF5 and form coatings on the anode and cathode surfaces during battery operation. Furthermore, when the content of the compound represented by Chemical Formula 1 is 3.0 wt % or less, it is possible to control the viscosity of the nonaqueous electrolyte to achieve optimal impregnation, effectively suppress an increase in battery resistance due to additive decomposition, and prevent a decrease in the ionic conductivity of the electrolyte, thereby preventing a decrease in rate performance and low-temperature life characteristics.

[0059] More specifically, the compound represented by Chemical Formula 1 may be contained in an amount of 0.5% by weight to 2.5% by weight, more preferably 0.5% by weight to 2.0% by weight.

[0060] (4) Second additive In addition, the nonaqueous electrolyte for a lithium secondary battery of the present invention may further contain a second additive, as needed, in order to prevent the nonaqueous electrolyte from being decomposed and causing the collapse of the negative electrode in a high-power environment, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery expansion at high temperatures.

[0061] Representative examples of such second additives may include at least one second additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0062] Examples of the cyclic carbonate compounds include vinylene carbonate (VC) and vinylethylene carbonate.

[0063] The halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0064] The sultone compound includes at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0065] Examples of the sulfate-based compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate (MTMS).

[0066] The phosphate-based compound includes one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphate.

[0067] Examples of the borate compounds include tetraphenylborate and lithium oxalyl difluoroborate.

[0068] The nitrile compound may be at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0069] The benzene-based compound may be fluorobenzene, and the amine-based compound may be triethanolamine or ethylenediamine.

[0070] The silane-based compound includes tetravinylsilane.

[0071] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and may be one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bis(oxalato)borate (LiB(C2O4)2)), and LiBF4.

[0072] When the second additive contains at least one of vinylene carbonate, vinylethylene carbonate, and succinonitrile, a stronger SEI coating can be formed on the surface of the negative electrode during the initial activation step of the secondary battery.

[0073] Meanwhile, the second additive may be used in a mixture of two or more types, and may be included in an amount of 50 wt % or less, specifically 0.01 wt % to 10 wt %, and preferably 0.05 wt % to 5.0 wt %, based on the total weight of the nonaqueous electrolyte. If the content of the second additive is less than 0.01 wt %, the effect of improving the low-temperature output of the battery, or the high-temperature storage characteristics and life characteristics of the battery is minimal. If the content of the second additive is more than 50 wt %, excessive side reactions may occur in the electrolyte during battery charge and discharge. In particular, if the SEI film-forming additive is added in an excessive amount, it may not be sufficiently decomposed at high temperatures and may remain unreacted or precipitated in the electrolyte at room temperature. This may result in side reactions that reduce the life or resistance characteristics of the secondary battery.

[0074] [Lithium secondary battery] Another embodiment of the present invention provides a lithium secondary battery including the nonaqueous electrolyte solution for a lithium secondary battery of the present invention.

[0075] The lithium secondary battery of the present invention may be manufactured by a conventional method known in the art. Specifically, the lithium secondary battery may be manufactured by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode are sequentially stacked, housing the electrode assembly in a battery case, and then introducing the nonaqueous electrolyte solution for a lithium secondary battery of the present invention into the battery case.

[0076] Next, each component of the lithium secondary battery of the present invention will be described in more detail.

[0077] (1) Positive electrode The positive electrode according to the present invention includes a positive electrode active material layer containing a positive electrode active material, and optionally, the positive electrode active material layer may further contain a conductive material and / or a binder.

[0078] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it may include a lithium composite metal oxide represented by the following Chemical Formula 2, which contains at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al), and lithium.

[0079] [Chemical Formula 2] Li 1+a Ni x Co y M 1 z M 2 w O2

[0080] In the Chemical Formula 2, M 1 is Mn, Al, or a combination thereof, M 2 is at least one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca, and Sr, and 0 ≦ a ≦ 0.5, 0.55 < x < 1.0, 0 < y ≦ 0.4, 0 < z ≦ 0.4, 0 ≦ w ≦ 0.1.

[0081] The 1 + a represents the atomic fraction of lithium in the lithium transition metal oxide, and 0 ≦ a ≦ 0.5, preferably 0 ≦ a ≦ 0.2, more preferably 0 ≦ a ≦ 0.1.

[0082] The x represents the atomic fraction of nickel among all transition metal elements in the lithium transition metal oxide, and 0.55 < x < 1.0, specifically 0.6 ≦ x ≦ 0.98, more specifically 0.6 ≦ x ≦ 0.95.

[0083] Said y represents the atomic fraction of cobalt among all transition metal elements in the lithium transition metal oxide, and 0 < y ≤ 0.4, specifically 0 < y ≤ 0.3, and more specifically 0.05 ≤ y ≤ 0.3 may be satisfied.

[0084] Said z represents the atomic fraction of element M among all transition metal elements in the lithium transition metal oxide, and 0 < z ≤ 0.4, preferably 0 < z ≤ 0.3, and more preferably 0.01 ≤ z ≤ 0.3 may be satisfied. 1 Said w represents the atomic fraction of element M among all transition metal elements in the lithium transition metal oxide, and 0 < w ≤ 0.1, preferably 0 < w ≤ 0.05, and more preferably 0 < w ≤ 0.02.

[0085] Said w represents the atomic fraction of element M among all transition metal elements in the lithium transition metal oxide, and 0 < w ≤ 0.1, preferably 0 < w ≤ 0.05, and more preferably 0 < w ≤ 0.02. 2 Said w represents the atomic fraction of element M among all transition metal elements in the lithium transition metal oxide, and 0 < w ≤ 0.1, preferably 0 < w ≤ 0.05, and more preferably 0 < w ≤ 0.02.

[0086] Specifically, in order to realize a high-capacity battery, the cathode active material is Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2, or may include a lithium composite transition metal oxide such as Li(Ni 0.90 Mn 0.05 Co 0.05 )O2.

[0087] In addition, according to the application of the secondary battery, the positive electrode active material of the present invention may be used in combination with the lithium composite metal oxide represented by the chemical formula 2, and a lithium-manganese-based oxide (for example, LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (for example, LiCoO2, etc.), a lithium-nickel-based oxide (for example, LiNiO2, etc.), a lithium-nickel-manganese-based oxide (for example, LiNi 1-Y Mn Y O2(0 < Y < 1), LiMn 2-Z Ni Z O4(0 < Z < 2), a lithium-nickel-cobalt-based oxide (for example, LiNi 1-Y1 Co Y1 O2(0 < Y1 < 1), a lithium-manganese-cobalt-based oxide (for example, LiCo 1-Y2 Mn Y2 O2(0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4(0 < Z1 < 2), or Li(Ni p1 Co q1 Mn r2 )O4(0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc. may be used in combination.

[0088] The positive electrode active material may be contained in a content of 80% to 98% by weight, more specifically 85% to 98% by weight, based on the total weight of the positive electrode active material layer. When the positive electrode active material is contained within the above range, excellent capacity characteristics can be exhibited.

[0089] Next, the conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it does not cause chemical changes in the constructed battery and has electronic conductivity. Specific examples include carbon black such as carbon black, acetylene black (or denka black), ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fiber and metal fiber; conductive powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, and the like, and one of these may be used alone or in a mixture of two or more.

[0090] The conductive material may be contained in an amount of 0.1% by weight to 10% by weight, preferably 0.1% by weight to 5% by weight, based on the total weight of the positive electrode active material layer.

[0091] Next, the binder serves to improve adhesion between the positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector.

[0092] Examples of such binders include fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders, which may be used alone or in combination of two or more.

[0093] The binder may be contained in an amount of 0.1% by weight to 15% by weight, preferably 0.1% by weight to 10% by weight, based on the total weight of the positive electrode active material layer.

[0094] The positive electrode of the present invention may be manufactured by a method known in the art, such as by dissolving or dispersing a positive electrode active material, a binder, and / or a conductive material in a solvent to prepare a positive electrode slurry, coating the slurry on a positive electrode current collector, and then drying and rolling the slurry to form a positive electrode active material layer, or by casting the positive electrode active material layer on a separate support, peeling off the support, and laminating the resulting film on a positive electrode current collector.

[0095] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel whose surface has been surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode material. It can be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0096] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is not particularly limited as long as it is sufficient to adjust the viscosity of the cathode composite to an appropriate level, taking into consideration the coating thickness of the cathode composite, production yield, workability, etc.

[0097] (2) Negative electrode Next, the negative electrode will be described.

[0098] The negative electrode according to the present invention includes a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material layer may further include a conductive material and / or a binder, as necessary.

[0099] The negative electrode active material may be any of various negative electrode active materials used in the art, such as a carbon-based negative electrode active material, a silicon-based negative electrode active material, or a mixture thereof.

[0100] According to one embodiment, the negative electrode active material may include a carbon-based negative electrode active material, and the carbon-based negative electrode active material may be any of various carbon-based negative electrode active materials used in the art, such as graphite-based materials such as natural graphite, artificial graphite, and Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-calcined carbon such as petroleum or coal tar pitch-derived cokes; soft carbon; and hard carbon. The shape of the carbon-based negative electrode active material is not particularly limited, and various shapes such as amorphous, plate-like, flake-like, spherical, and fibrous may be used.

[0101] Preferably, the negative electrode active material is at least one carbon-based negative electrode active material selected from natural graphite and artificial graphite. In order to increase the adhesive strength with the current collector and suppress detachment of the active material, both natural graphite and artificial graphite may be used.

[0102] According to another embodiment, the negative electrode active material may include a silicon-based negative electrode active material in addition to the carbon-based negative electrode active material.

[0103] The silicon-based negative electrode active material is, for example, metal silicon (Si), silicon oxide (SiO x, where 0 < x < 2), silicon carbide (SiC), and a Si - Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si) may be included. The element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0104] Since the silicon - based negative electrode active material exhibits higher capacity characteristics compared to the carbon - based negative electrode active material, when the silicon - based negative electrode active material is further included, even more excellent capacity characteristics can be obtained. However, a negative electrode containing a silicon - based negative electrode active material contains more oxygen (O) - rich components in the SEI film compared to a graphite negative electrode. The SEI film containing an O - rich component tends to be more easily decomposed when Lewis acids such as HF or PF5 are present in the electrolyte. Therefore, in order for a negative electrode containing a silicon - based negative electrode active material to maintain a stable SEI film, it is necessary to suppress the generation of Lewis acids such as HF and PF5 in the electrolyte or to remove (or scavenge) the generated Lewis acids. The non - aqueous electrolyte according to the present invention forms stable coatings on the positive and negative electrodes and contains an electrolyte additive with excellent Lewis acid removal effect, so that when using a negative electrode containing a silicon - based active material, the decomposition of the SEI film can be effectively suppressed.

[0105] On the other hand, the mixing ratio of the silicon - based negative electrode active material and the carbon - based negative electrode active material may be 3:97 to 99:1, preferably 5:95 to 15:85 in weight ratio. When the mixing ratio of the silicon - based negative electrode active material and the carbon - based negative electrode active material satisfies the above range, the capacity characteristics can be improved, the volume expansion of the silicon - based negative electrode active material can be suppressed, and excellent cycle performance can be ensured.

[0106] The negative electrode active material may be included in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer. When the content of the negative electrode active material satisfies the above range, excellent capacity characteristics and electrochemical characteristics can be obtained.

[0107] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 10 wt % or less, preferably 5 wt % or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. Examples of such conductive materials include carbon black, such as carbon black, acetylene black (or denka black), ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powder, such as natural graphite, artificial graphite, or graphite, which have a highly developed crystalline structure; conductive fibers, such as carbon fiber and metal fiber; conductive powders, such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives.

[0108] The binder is a component that aids in bonding between the conductive material, active material, and current collector, and is typically added in an amount of 0.1 to 10 wt % based on the total weight of the negative electrode active material layer. Examples of binders include fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders.

[0109] The binder may be included in an amount of 0.1 to 15% by weight, preferably 0.1 to 10% by weight, based on the total weight of the negative electrode active material layer.

[0110] The negative electrode may be manufactured by a method known in the art, for example, by coating a negative electrode slurry prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, on a negative electrode current collector, rolling and drying the resulting slurry to form an active material layer, or by casting the negative electrode active material layer on a separate support, peeling off the support, and laminating the resulting film on the negative electrode current collector.

[0111] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys may be used. The negative electrode current collector typically has a thickness of 3 μm to 500 μm, and, like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0112] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is not particularly limited as long as it is sufficient to adjust the viscosity of the negative electrode slurry to an appropriate level, taking into consideration the coating thickness of the negative electrode composite, production yield, workability, etc.

[0113] (3) Separator The lithium secondary battery according to the present invention includes a separator between the positive electrode and the negative electrode.

[0114] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator that is commonly used as a separator in a lithium secondary battery can be used without any particular limitation. In particular, a separator that has low resistance to the movement of lithium salt ions and has excellent electrolyte humidifying ability is preferred.

[0115] Specifically, the separator may be a porous polymer film, such as a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may also be used, and may be selectively used as a single-layer or multi-layer structure.

[0116] The lithium secondary battery according to the present invention can be usefully used in portable devices such as mobile phones, notebook computers, and digital cameras, and in electric vehicles such as hybrid electric vehicles (HEVs).

[0117] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0118] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also as a unit battery in a medium- to large-sized battery module containing a large number of battery cells.

[0119] [Example] Example 1 (Manufacturing non-aqueous electrolytes for lithium secondary batteries) LiPF6 was dissolved in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 to a concentration of 1.0 M, and then the compound represented by Chemical Formula 1A-1 was added to the solution in an amount of 0.5 wt % and vinylene carbonate (VC) in an amount of 0.5 wt % to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

[0120] (Secondary battery manufacturing) The positive electrode active material (Li(Ni 0.9 Mn 0.03 Co 0.06 Al 0.01 )O2), a conductive material (carbon black), and a binder (polyvinylidene fluoride) were mixed in a weight ratio of 97.6:0.8:1.6 to prepare a positive electrode slurry (solid content 60.0 wt%). The positive electrode slurry was applied to a positive electrode current collector (Al thin film) with a thickness of 13.5 μm, dried, and then roll-pressed to prepare a positive electrode.

[0121] Anode active material (graphite:SiO = 94:6 by weight), binder (SBR-CMC), and conductive material (carbon black) were mixed in a weight ratio of 97.6:0.8:1.6 with water as a solvent to prepare anode slurry (solid content: 60 wt%). The anode slurry was applied to a 6 μm-thick copper (Cu) thin film as anode current collector, dried, and then roll-pressed to prepare anode.

[0122] An electrode assembly was prepared by interposing polypropylene as a porous separator between the positive electrode and the negative electrode, and then housed in a battery case. The non-aqueous electrolyte solution for a lithium secondary battery was then injected into the battery case to prepare a lithium secondary battery.

[0123] Example 2. (Manufacturing non-aqueous electrolytes for lithium secondary batteries) LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.0 M, and then the compound represented by Chemical Formula 1A-1 was added thereto to a concentration of 1.0 wt % and vinylene carbonate (VC) to a concentration of 0.5 wt % to prepare a non-aqueous electrolyte solution for a lithium secondary battery.

[0124] (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery manufactured above was injected instead of the nonaqueous electrolyte solution of Example 1 (see Table 1 below).

[0125] Comparative Example 1 (Manufacturing non-aqueous electrolytes for lithium secondary batteries) LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.0 M, and vinylene carbonate (VC) was added as an additive to a concentration of 0.5 wt % to prepare a non-aqueous electrolyte solution.

[0126] (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery manufactured above was injected instead of the nonaqueous electrolyte solution of Example 1 (see Table 1 below).

[0127] Comparative Example 2 (Manufacturing non-aqueous electrolytes for lithium secondary batteries) LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.0 M, and then a compound represented by the following Chemical Formula 3 was added as an additive in place of the compound represented by Chemical Formula 1A-1 to a concentration of 0.5 wt % and vinylene carbonate (VC) to a concentration of 0.5 wt %, to prepare a non-aqueous electrolyte solution.

[0128] [ka]

[0129] (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery manufactured above was injected instead of the nonaqueous electrolyte solution of Example 1 (see Table 1 below).

[0130] Comparative Example 3. (Manufacturing non-aqueous electrolytes for lithium secondary batteries) LiPF was dissolved in a non-aqueous organic solvent to a concentration of 1.0 M, and then a compound represented by the following Chemical Formula 4 was added as an additive in place of the compound represented by Chemical Formula 1A-1 to a concentration of 0.5 wt % and vinylene carbonate (VC) to a concentration of 0.5 wt %, to prepare a non-aqueous electrolyte solution.

[0131] [ka]

[0132] (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery manufactured above was injected instead of the nonaqueous electrolyte solution of Example 1 (see Table 1 below).

[0133] [Table 1]

[0134] Meanwhile, the abbreviations of the compounds in Table 1 above have the following meanings. EC: Ethylene carbonate EMC: Ethyl methyl carbonate VC: vinylene carbonate

[0135] [Experimental Example] Experimental Example 1: Evaluation of the resistance increase rate after high-temperature storage The lithium secondary batteries prepared in the examples and comparative examples were subjected to an activation process by charging at a 0.1C rate for 3 hours, then charged at a 0.33C rate to 4.2V under constant current / constant voltage conditions (0.05C cut-off) at 25°C until fully charged to 100% SOC, and then stored at high temperature (60°C) for 16 weeks. The batteries were then transferred to a charger / discharger at room temperature (25°C) to measure the resistance, and the resistance increase rate was calculated using the following equation (1). The results are shown in Table 2 below.

[0136] [Formula 1] Resistance increase rate (%) = {(resistance after high-temperature storage - initial resistance) / initial resistance} x 100

[0137] Experimental Example 2: Evaluation of gas generation rate after high-temperature storage The lithium secondary batteries prepared in the examples and comparative examples were subjected to an activation process by charging at a 0.1C rate for 3 hours, and then charged at 25°C under constant current / constant voltage conditions up to 4.2V at a 0.33C rate (0.05C cut-off) until fully charged to 100% SOC. The fully charged batteries were stored at high temperature (60°C) for 16 weeks, and then the amount of gas generated was measured at room temperature (25°C) using GC analysis. The relative amount of gas generated for each battery was calculated as a percentage, with the amount of gas generated measured in Comparative Example 1 being set to 100%, and is shown in Table 2 below.

[0138] Experimental Example 3: Evaluation of capacity retention rate after high-temperature cycling The lithium secondary batteries prepared in the examples and comparative examples were subjected to an activation process by charging at a 0.1 C rate for 3 hours, and then charged at a 0.33 C rate to 4.2 V at 25°C under constant current / constant voltage conditions (0.05 C cut-off) and fully charged to an SOC of 100%. The fully charged batteries were charged at a 0.33 C rate to 4.2 V under constant current / constant voltage conditions at 45°C, and then discharged at a 0.33 C rate to 2.8 V under constant current conditions (1 cycle), and then subjected to 300 cycles. After 300 cycles, the capacity retention rate after 300 cycles was calculated using the following equation 2, and the results are shown in Table 2 below.

[0139] [Formula 2] Capacity retention rate (%) = (capacity after 300 cycles / capacity after 1 cycle) x 100

[0140] [Table 2]

[0141] Referring to Table 2 above, it can be seen that the secondary batteries of Examples 1 and 2 of the present invention have a reduced resistance increase rate (%) and gas generation rate (%), and an improved capacity retention rate (%), compared to the lithium secondary batteries of Comparative Examples 1 to 3.

Claims

1. a lithium salt, an organic solvent, and a first additive; The non-aqueous electrolyte for a lithium secondary battery, wherein the first additive comprises a compound represented by the following Chemical Formula 1: 【Chemical 1】 (In the above Chemical Formula 1, Ar is a 5- or 6-membered nitrogen-containing ring; R １ and R ２ are each independently an alkyl group having 1 to 8 carbon atoms.

2. 2. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the compound represented by Chemical Formula 1 is a compound represented by Chemical Formula 1A below: 【Chemistry 2】 (In the above Chemical Formula 1A, R １ and R ２ are each independently an alkyl group having 1 to 8 carbon atoms.

3. The R １ and R ２ and each independently represent an alkyl group having 1 to 5 carbon atoms.

4. The R １ and R ２ and each independently represent an alkyl group having 1 to 3 carbon atoms.

5. 3. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 2, wherein the compound represented by Chemical Formula 1A is a compound represented by the following Chemical Formula 1A-1 or 1A-2: 【Chemistry 3】 【Chemistry 4】

6. 2. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the compound represented by Chemical Formula 1 is contained in an amount of 0.5 wt % to 3.0 wt % based on the total weight of the non-aqueous electrolyte solution for a lithium secondary battery.

7. 7. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 6, wherein the compound represented by Chemical Formula 1 is contained in an amount of 0.5 wt % to 2.5 wt % based on the total weight of the non-aqueous electrolyte solution for a lithium secondary battery.

8. 2. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, further comprising at least one second additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

9. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; A lithium secondary battery comprising the nonaqueous electrolyte solution for a lithium secondary battery according to claim 1 .

10. 10. The lithium secondary battery according to claim 9, wherein the positive electrode active material contains lithium and at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al).

Images