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

Abstract

The present invention relates to an electrolyte additive for lithium secondary batteries, and a non-aqueous electrolyte for lithium secondary batteries and a lithium secondary battery containing the same. Specifically, the electrolyte additive for lithium secondary batteries of the present invention is a Lewis base-based compound that can effectively suppress the elution of transition metals from a positive electrode by removing by-products generated by decomposition of lithium salts.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0029663 filed on March 8, 2022 and Korean Patent Application No. 10-2023-0029467 filed on March 6, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to an electrolyte additive for lithium secondary batteries that is excellent in removing decomposition products generated from lithium salts, and to a nonaqueous electrolyte for lithium secondary batteries and a lithium secondary battery that contain the same and have improved high-temperature durability. [Background technology]

[0003] As the information society develops, personal IT devices and computer networks become more advanced, and society as a whole becomes more dependent on electrical energy, there is a need to develop technologies for efficiently storing and utilizing electrical energy.

[0004] Of the technologies developed for this purpose, the most suitable for various applications is secondary battery-based technology. Secondary batteries are attracting attention because they can be miniaturized to be used in personal IT devices, electric vehicles, power storage devices, and more.

[0005] Among these secondary battery technologies, lithium-ion batteries have been attracting attention as the battery system with the highest theoretical energy density, and are currently being applied to a variety of devices.

[0006] Lithium-ion batteries consist of a positive electrode made of a lithium-containing transition metal oxide, a negative electrode made of a carbon-based material such as graphite that can store lithium, an electrolyte that acts as a medium for transmitting lithium ions, and a separator. Appropriate selection of these components is important to improve the electrochemical properties of the battery.

[0007] However, lithium-ion batteries have the drawback of increasing resistance and fading capacity during charge / discharge or storage at high temperatures, resulting in performance degradation. One of the causes of these problems is thought to be side reactions caused by the deterioration of the electrolyte at high temperatures, particularly degradation due to the decomposition of lithium salts.

[0008] In particular, in the case of LiPF6, which is mainly used as a lithium salt, the anion PF6 - However, because it is extremely sensitive to heat, it is known to be thermally decomposed when the battery is exposed to high temperatures, producing Lewis acid substances such as PF5.

[0009] Lewis acids degrade the surface structure of the positive and negative electrodes, causing the reduction and decomposition of the solid electrolyte interphase (SEI) on the negative electrode surface and the dissolution of transition metal ions from the surface of the degraded positive electrode. These dissolved transition metal ions are re-deposited on the positive electrode, increasing the positive electrode resistance and causing the loss of redox centers, resulting in capacity fade of the secondary battery. Furthermore, when dissolved metal ions are deposited on the negative electrode, the passivation ability of the SEI formed on the negative electrode surface is reduced, leading to electrolyte decomposition and the consumption of additional electrons and lithium ions to regenerate the SEI, increasing irreversible capacity, fading cell capacity, and potentially causing self-discharge of the negative electrode.

[0010] Therefore, various research and development efforts are being conducted to find methods to remove the by-products generated by the decomposition of lithium salts, thereby maintaining the passivation ability of the SEI film when exposed to heat and eliminating the cause of battery degradation at high temperatures. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made to solve the above problems, and aims to provide an electrolyte additive for a lithium secondary battery that can remove decomposition products generated from a lithium salt inside the electrolyte.

[0012] Another object of the present invention is to provide a non-aqueous electrolyte for a lithium secondary battery, which contains the electrolyte additive for a lithium secondary battery. Another object of the present invention is to provide a lithium secondary battery containing the nonaqueous electrolyte solution for lithium secondary batteries. [Means for solving the problem]

[0013] According to one embodiment, the present invention provides an electrolyte additive for a lithium secondary battery, which is a compound represented by the following Chemical Formula 1:

[0014] [ka]

[0015] In the above Chemical Formula 1, R1 and R2 are each independently an alkyl group having 1 to 10 carbon atoms.

[0016] According to another embodiment, the present invention provides a non-aqueous electrolyte for a lithium secondary battery, comprising a lithium salt, a non-aqueous organic solvent, and the electrolyte additive for a lithium secondary battery.

[0017] According to another embodiment, the present invention provides a lithium secondary battery including the nonaqueous electrolyte solution for lithium secondary batteries. [Effects of the Invention]

[0018] The compound represented by Chemical Formula 1 used as an electrolyte additive for a lithium secondary battery of the present invention contains a nitrogen element having an unshared electron pair as a Lewis base material and easily bonds with a Lewis acid, thereby effectively scavenging decomposition products of lithium salts in the electrolyte.

[0019] When a non-aqueous electrolyte solution for a lithium secondary battery containing such an electrolyte additive for a lithium secondary battery is used, PF5 generated by decomposition of LiPF6 due to high temperature or moisture in the non-aqueous electrolyte solution can be easily removed, thereby realizing a lithium secondary battery with improved cycle performance. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will now be described in more detail. The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best explain his / her invention.

[0021] During initial charge and discharge cycles, lithium secondary batteries develop passivating coatings on the surfaces of the positive and negative electrodes due to the decomposition of the nonaqueous electrolyte, improving high-temperature storage characteristics. However, these coatings can be degraded by acids such as HF and PF5, which are produced by the thermal decomposition of lithium salts (e.g., LiPF6) commonly used in lithium-ion batteries. Furthermore, this acid attack can cause transition metal elements to leach from the positive electrode, resulting in structural changes to the surface, increasing the electrode's surface resistance and eliminating redox center metal elements, resulting in a decrease in theoretical and realized capacity. Furthermore, these leached transition metal ions are electrodeposited on the negative electrode, which reacts in a strong reduction potential zone, consuming electrons and destroying the coating, leading to electrolyte decomposition and the consumption of additional electrons and lithium ions to regenerate the SEI. This results in increased negative electrode resistance, an increase in irreversible capacity, and a persistent decrease in cell capacity.

[0022] Therefore, the present invention provides a non-aqueous electrolyte solution that contains a Lewis base compound capable of forming an SEI as a non-aqueous electrolyte additive component, thereby removing the acid produced by decomposition of a lithium salt and preventing deterioration of the SEI film and elution of transition metals from the positive electrode during high-temperature storage, and a lithium secondary battery containing the same.

[0023] Electrolyte additives for lithium secondary batteries According to one embodiment, the present invention provides a non-aqueous electrolyte additive, which is a compound represented by Chemical Formula 1 below:

[0024] [ka]

[0025] In the above Chemical Formula 1, R1 and R2 are each independently an alkyl group having 1 to 10 carbon atoms.

[0026] The compound represented by Chemical Formula 1 is a Lewis base material, and contains a carbonyl group along with a nitrogen atom having an unshared electron pair in a single molecular structure, resulting in a low electron density at the carbon atom between the nitrogen atoms. The carbon atom attracts the unshared electron pair of the nitrogen atom connected to R1, strengthening the interaction. This action reflexively causes charge localization toward the nitrogen atom that forms a double bond with the carbon atom of the imidazole functional group. This results in a higher bond energy with the Lewis acid material compared to compounds that do not contain a carbonyl group in their structure, such as compounds represented by Chemical Formula 2 or 3 below. Therefore, when the compound represented by Chemical Formula 1 of the present invention is used as an electrolyte additive, it is more effective at scavenging lithium salt decomposition products, such as HF or PF5, within the electrolyte than when the compound represented by Chemical Formula 2 or 3 below is used as an additive, thereby suppressing the leaching of transition metals from the positive electrode due to Lewis acids and the degradation behavior of coatings formed on the positive and negative electrode surfaces due to chemical reactions. In addition, the compound represented by Chemical Formula 1 can suppress the damage to the coating on the surface of the negative electrode and suppress the deterioration behavior, thereby preventing the decomposition of the additional electrolyte in the battery due to the destruction of the coating, and further mitigating the self-discharge of the secondary battery and improving the high-temperature storage characteristics.

[0027] [ka]

[0028] [ka]

[0029] On the other hand, when R1 and R2 are alkyl groups having 10 or more carbon atoms, the degree of charge localization on the functional group of imidazole may be weakened, and the Lewis acid scavenging effect may be relatively reduced. Therefore, in order to secure and / or strengthen the binding energy with Lewis acids such as PF5, it is preferable that R1 and R2 are alkyl groups having 10 or less carbon atoms.

[0030] Specifically, in Chemical Formula 1, R1 and R2 may each independently be an alkyl group having 1 to 7 carbon atoms. Alternatively, R1 and R2 may each independently be an alkyl group having 1 to 5 carbon atoms. Alternatively, R1 may be an alkyl group having 1 to 3 carbon atoms, and R2 may be an alkyl group having 1 to 5 carbon atoms.

[0031] Preferably, the compound represented by Chemical Formula 1 may be at least one of the compounds represented by Chemical Formulas 1a to 1c below.

[0032] [ka]

[0033] [ka]

[0034] [ka]

[0035] Nonaqueous electrolyte for lithium secondary batteries According to another embodiment, the present invention provides a non-aqueous electrolyte for a lithium secondary battery, comprising a lithium salt, an organic solvent, and the electrolyte additive for a lithium secondary battery described above.

[0036] (1) Lithium salt First, the lithium salt will be described as follows. In the non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention, the lithium salt may be any one that is commonly used in electrolytes for lithium secondary batteries, without any limitation. For example, the cation may be Li + and the anion is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4- , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , B 10 Cl 10 - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3(CF3)2CO - , (CF3SO2)2CH - , CH3SO3 - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - Specifically, the lithium salt may be at least one selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10, LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI (LiN(SO2CF2CF3)2). Specifically, the lithium salt may include a single substance or a mixture of two or more substances selected from the group consisting of LiBF4, LiClO4, LiPF6, LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), and LiBETI (LiN(SO2CF2CF3)2), and more specifically, may include LiPF6.

[0037] The lithium salt may 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 3.0 M, specifically 1.0 M to 3.0 M.

[0038] When the concentration of the lithium salt satisfies the above range, the viscosity of the nonaqueous electrolyte can be controlled to achieve optimal impregnation, and the mobility of lithium ions can be improved, thereby improving the capacity characteristics and cycle characteristics of the lithium secondary battery.

[0039] (2) Organic solvent The organic solvent will be described below. The organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, or a mixed organic solvent thereof.

[0040] The cyclic carbonate organic solvent is a highly viscous organic solvent that has a high dielectric constant and effectively 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 among these, ethylene carbonate may be included.

[0041] The linear carbonate organic solvent is an organic solvent having low viscosity and low dielectric constant, and a representative example thereof may be at least one organic solvent 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 ethyl methyl carbonate (EMC).

[0042] In order to produce an electrolyte solution having high ionic conductivity, it is preferable to use a mixed organic solvent of a cyclic carbonate organic solvent and a linear carbonate organic solvent, and the cyclic carbonate organic solvent and the linear carbonate organic solvent may be mixed in a volume ratio of 1:9 to 5:5, specifically 2:8 to 4:6.

[0043] Furthermore, the organic solvent may further contain a linear ester organic solvent and / or a cyclic ester organic solvent in addition to the cyclic carbonate organic solvent and / or the linear carbonate organic solvent, as required.

[0044] Specific examples of such linear ester-based organic solvents include 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.

[0045] The cyclic ester organic solvent may be at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0046] The organic solvent may further include at least one of an ether-based organic solvent, an amide-based organic solvent, and a nitrile-based organic solvent.

[0047] The ether-based organic solvent may be any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a mixture of two or more of these.

[0048] The nitrile solvent may be at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile. On the other hand, in the nonaqueous electrolyte solution of the present invention, the remainder, excluding the lithium salt and the additive, may be entirely an organic solvent.

[0049] (3) Electrolyte additives The non-aqueous electrolyte for a lithium secondary battery of the present invention contains the electrolyte additive for a lithium secondary battery described above, and the electrolyte additive for a lithium secondary battery is a compound represented by Chemical Formula 1 above. Here, the description of the compound represented by Chemical Formula 1 is omitted because it overlaps with the above description.

[0050] Meanwhile, the compound represented by Chemical Formula 1 may be included in the non-aqueous electrolyte in an amount of 0.05 wt % to 5.5 wt % based on the total weight of the non-aqueous electrolyte, taking into consideration the effect of forming a stable coating on the surface of the electrode and the effect of removing thermal decomposition products of the lithium salt.

[0051] When the compound represented by Chemical Formula 1 is contained within the above content range, it can form a strong coating on the surface of the positive electrode, effectively inhibiting the elution of transition metals from the positive electrode active material at high temperatures while minimizing drawbacks such as additive-induced side reactions, capacity loss, and increased resistance. It can also effectively remove thermal decomposition products of lithium salts, thereby achieving excellent high-temperature durability. When the content of the compound represented by Chemical Formula 1 is 0.05 wt % or more, it can more stably maintain the effects of removing thermal decomposition products of lithium salts such as HF or PF5 and protecting the positive electrode from elution of transition metals during battery operation. Furthermore, when the content of the compound represented by Chemical Formula 1 is 5.5 wt % or less, it can control the viscosity of the nonaqueous electrolyte to achieve optimal impregnation, effectively inhibit an increase in battery resistance due to additive decomposition, further enhance ionic conductivity within the battery, and prevent deterioration of rate characteristics and low-temperature life characteristics during high-temperature storage.

[0052] Specifically, the compound represented by Chemical Formula 1 may be contained in an amount of 0.1 to 5.0% by weight, more specifically 0.1 to 3.5% by weight, and preferably 0.3 to 2.5% by weight.

[0053] (4) Other additives Meanwhile, the non-aqueous electrolyte of the present invention may further contain other additives in addition to the compound represented by Chemical Formula 1, as necessary, to prevent the breakdown of the negative electrode due to decomposition of the non-aqueous electrolyte in a high-power environment, and to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery expansion at high temperatures.

[0054] Examples of such other additives include at least one selected from the group consisting of cyclic carbonate-based compounds, halogen-substituted carbonate-based compounds, sultone-based compounds, sulfate-based compounds, phosphate-based or phosphite-based compounds, borate-based compounds, nitrile-based compounds, benzene-based compounds, amine-based compounds, silane-based compounds, and lithium salt-based compounds.

[0055] The cyclic carbonate compound may be, for example, vinylene carbonate (VC) or vinylethylene carbonate. The halogen-substituted carbonate compound may be, for example, fluoroethylene carbonate (FEC).

[0056] 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, ethene sultone, 1-propene-1,3-sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0057] The sulfate compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0058] The phosphate-based or phosphite-based compound may be, for example, one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0059] Examples of the borate-based compounds include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), and lithium bisoxalateborate (LiB(C2O4)2, LiBOB).

[0060] The nitrile compound may be, for example, 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.

[0061] The benzene-based compound may be, for example, fluorobenzene, the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetravinylsilane.

[0062] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples thereof include lithium difluorophosphate (LiDFP, LiPO2F2) and LiBF4.

[0063] Specifically, the other additives may be a mixture of at least two or more compounds selected from vinylene carbonate (VC), 1,3-propane sultone (PS), 1-propene 1,3-sultone (PRS), ethylene sulfate (Esa), lithium tetrafluoroborate (LiBF), and lithium difluorophosphate (LiDFP).

[0064] Meanwhile, the total mixed content of the compound represented by Formula 1 and other additives may be 30 wt % or less, specifically 0.05 wt % to 20 wt %, more specifically 0.05 wt % to 10 wt %, based on the total weight of the non-aqueous electrolyte. When the total content of the additives satisfies the above range, the low-temperature output characteristics of the battery can be improved, and the high-temperature storage characteristics and high-temperature life characteristics can be more effectively improved, and side reactions in the battery due to the additives remaining after the reaction can be prevented.

[0065] 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.

[0066] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode, and the non-aqueous electrolyte solution for lithium secondary batteries described above. More specifically, the lithium secondary battery may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte solution for lithium secondary batteries described above.

[0067] Meanwhile, the lithium secondary battery of the present invention may be manufactured by forming an electrode assembly in which a positive electrode, a separator, and a negative electrode are sequentially stacked, housing the electrode assembly in a battery case, and then adding the nonaqueous electrolyte of the present invention.

[0068] The method for manufacturing the lithium secondary battery of the present invention may be manufactured and applied by a conventional method well known in the art, and will be described in detail below.

[0069] (1) Positive electrode The positive electrode may be prepared by coating a positive electrode current collector with a positive electrode slurry containing a positive electrode active material, a binder, a conductive material, and a solvent, followed by drying and rolling.

[0070] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like may be used.

[0071] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may include a lithium transition metal oxide containing lithium and one or more metals selected from cobalt, manganese, nickel, and aluminum.

[0072] Specifically, the positive electrode active material may include a lithium-manganese oxide or lithium iron phosphate, which have high capacity characteristics and safety of the battery, or a lithium-composite transition metal oxide represented by the following Chemical Formula 4, which has a nickel content of 70 atm % or more in order to achieve high capacity.

[0073] [Chemical formula 4] Li a [Ni b Co c M 1 d M 2 e ]O2

[0074] In the above Chemical Formula 4, M 1 is Mn, Al, or a combination thereof; M 2 are Al, Zr, W, Ti, Mg, Ca, Sr, and Ba, 0.8≦a≦1.2, 0.7≦b<1, 0 <c<0.3、0<d<0.3、0≦e≦0.2である。

[0075] In the chemical formula 4, a represents the atomic fraction of lithium, where 0.8 ≤ a ≤ 1.2, specifically 0.9 ≤ a ≤ 1.1, and more specifically 0.9 ≤ a ≤ 1.05.

[0076] Also, in the chemical formula 4, b represents the atomic fraction of nickel, where 0.7 ≤ b < 1, specifically 0.75 ≤ b ≤ 0.99, more specifically 0.8 ≤ b ≤ 0.95, and even more specifically 0.85 ≤ b ≤ 0.95.

[0077] In the chemical formula 4, c represents the atomic fraction of cobalt, where 0 < c < 0.3, preferably 0.001 < c < 0.3, specifically 0.01 ≤ c < 0.25, more specifically 0.01 ≤ c < 0.20, and even more specifically 0.1 ≤ c < 0.15.

[0078] In the chemical formula 4, d represents the atomic fraction of element M among the transition metals 1 and 0 < d < 0.3, preferably 0.001 < d < 0.25, 0.01 ≤ d < 0.20, more preferably 0.01 ≤ d < 0.20, and more specifically 0.01 ≤ d < 0.15.

[0079] In the chemical formula 4, e represents the atomic fraction of element M among the transition metals 2 and 0 ≤ e ≤ 0.2, specifically 0 ≤ e ≤ 0.1, and preferably 0 ≤ e ≤ 0.05.

[0080] Specifically, examples of the lithium-manganese-based oxide include LiMnO2 or LiMn2O4, and examples of the lithium iron phosphate include LiFePO4.

[0081] Also, the lithium-composite transition metal oxide is Li(Ni 0.7 Mn 0.1 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.8 Mn0.1 Co 0.1 )O2, Li(Ni 0.9 Co 0.05 Mn 0.05 )O2, Li(Ni 0.86 Mn 0.05 Co 0.07 Al 0.02 )O2, and Li(Ni 0.9 Mn 0.03 Co 0.06 Al 0.01 ) O2.

[0082] The positive electrode active material may be included in an amount of 80 wt% to 99 wt%, specifically 90 wt% to 99 wt%, based on the total weight of the solid content in the positive electrode slurry. In this case, if the content of the positive electrode active material is less than 80 wt%, the energy density may be reduced, resulting in a decrease in capacity.

[0083] The binder is a component that aids in bonding the active material and conductive material, etc., and bonding to the current collector, and is typically added in an amount of 1 to 30 wt % based on the total weight of the solids in the positive electrode slurry. 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.

[0084] The conductive material is a substance that does not cause chemical changes in the battery and provides conductivity, and may be added in an amount of 1 wt % to 20 wt % based on the total weight of the solid content in the positive electrode slurry.

[0085] Typical examples of such conductive materials include carbon powders such as carbon black, acetylene black (or denka black), ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powders such as natural graphite, artificial graphite, and graphite with highly developed crystal structures; conductive fibers such as carbon fibers and metal fibers; 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 conductive materials such as polyphenylene derivatives.

[0086] The solvent may also include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a preferred viscosity when the positive electrode active material, and optionally a binder and a conductive material, are contained. For example, the solvent may be contained so that the solids concentration in the positive electrode slurry containing the positive electrode active material, and optionally a binder and a conductive material, is 10 wt % to 60 wt %, preferably 20 wt % to 50 wt %.

[0087] (2) Negative electrode The negative electrode may be manufactured by coating a negative electrode current collector with a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and a solvent, followed by drying and rolling.

[0088] The negative electrode current collector generally has a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity, and examples of such a negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, and the like, and aluminum-cadmium alloys. Similarly to the positive electrode current collector, the surface of the negative electrode current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0089] Further, the negative electrode active material may contain at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and undoping lithium, and a transition metal oxide.

[0090] As the carbon material capable of reversibly intercalating / deintercalating lithium ions, any carbon-based negative electrode active material generally used in lithium-ion secondary batteries can be used without particular limitation. Representative examples thereof include crystalline carbon, amorphous carbon, or a combination of these. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0091] As the metal or an alloy of these metals and lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn or an alloy of these metals and lithium may be used.

[0092] Examples of the metal composite oxide include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3(0≦x≦1), Li x WO2(0≦x≦1), and Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) selected from the group consisting of may be used.

[0093] Examples of the substance capable of doping and undoping lithium include Si, SiO x (0 < x < 2), Si-Y alloy (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and a combination thereof, and is not Si), Sn, SnO2, Sn-Y (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and a combination thereof, and is not Sn), etc. Further, at least one of these may be mixed with SiO2 and used. Examples of 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, 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, Ge, P, As, Sb, Bi, S, Se, Te, Po, and a combination thereof. Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0094] The negative electrode active material may be contained at 80% to 99% by weight based on the total weight of the solid content in the negative electrode slurry. 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 1 to 30 wt % based on the total weight of the solids in the negative electrode slurry. 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. The binder may be the same as or different from the binder contained in the positive electrode.

[0095] 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 1 wt % to 20 wt % based on the total weight of the solids in the negative electrode slurry. 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 powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powders such as natural graphite, artificial graphite, and graphite with highly developed crystalline structures; 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 conductive materials such as polyphenylene derivatives. In this case, the conductive material may be the same as or different from the conductive material contained in the positive electrode.

[0096] The solvent may include water or an organic solvent such as NMP or alcohol, and may be used in an amount that provides a preferred viscosity when the negative electrode active material, and optionally a binder and a conductive material, are contained. For example, the solvent may be contained so that the solids concentration in the slurry containing the negative electrode active material, and optionally a binder and a conductive material, is 50 wt % to 75 wt %, preferably 50 wt % to 65 wt %.

[0097] (3) Separator The separator included in the lithium secondary battery of the present invention may be a commonly used conventional porous polymer film, for example, a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, either alone or in a laminate thereof, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made from a high-melting point glass fiber, a polyethylene terephthalate fiber, or the like, but is not limited thereto.

[0098] 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.

[0099] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples of the present invention may be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0100] Example Example 1 (Production of non-aqueous electrolyte) LiPF was dissolved in a non-aqueous organic solvent containing ethylene carbonate (EC):ethyl methyl carbonate (EMC) in a volume ratio of 30:70 to a concentration of 1.0 M, and then 0.3 wt % of the compound represented by Formula 1a and other additives, including 0.5 wt % of vinylene carbonate (VC), 0.5 wt % of 1,3-propane sultone (PS), 0.2 wt % of 1-propene 1,3-sultone (PRS), 1.0 wt % of ethylene sulfate (ESa), 0.2 wt % of lithium tetrafluoroborate (LiBF), and 0.8 wt % of lithium difluorophosphate (LiDFP), were added to prepare a non-aqueous electrolyte for a lithium secondary battery.

[0101] (Secondary battery manufacturing) Cathode active material (Li(Ni) 0.9 Mn 0.03 Co 0.06 Al 0.01 A cathode slurry (solid content 60 wt%) was prepared by adding 102), a conductive material (carbon black), and a binder (polyvinylidene fluoride) in a weight ratio of 97.6:0.8:1.6 to N-methyl-2-pyrrolidone (NMP) as a solvent. The cathode slurry was applied to one side of an Al cathode current collector with a thickness of 13.5 μm, dried, and roll-pressed to prepare a cathode.

[0102] Anode active material (graphite:SiO = 90:10 weight ratio), conductive material (carbon black), and binder (SBR-CMC) were mixed in a weight ratio of 95.6:1.0:3.4 with deionized water (DI water) (HO) as a solvent to prepare anode slurry (solid content 60 wt%). The anode slurry was applied to one side of a 6 μm-thick Cu anode current collector, dried, and roll-pressed to prepare anode.

[0103] In a dry room, a porous polymer separator was interposed between the positive electrode and negative electrode prepared above, and then the non-aqueous electrolyte (3 g) prepared above was poured into the separator to prepare a secondary battery.

[0104] Example 2 (Production of non-aqueous electrolyte) LiPF was dissolved in a non-aqueous organic solvent containing ethylene carbonate (EC):ethyl methyl carbonate (EMC) in a volume ratio of 30:70 to a concentration of 1.0 M, and then 0.05 wt % of the compound represented by Formula 1a and other additives, including 0.5 wt % of vinylene carbonate (VC), 0.5 wt % of 1,3-propane sultone (PS), 0.2 wt % of 1-propene 1,3-sultone (PRS), 1.0 wt % of ethylene sulfate (ESa), 0.2 wt % of lithium tetrafluoroborate (LiBF), and 0.8 wt % of lithium difluorophosphate (LiDFP), were added to prepare a non-aqueous electrolyte for a lithium secondary battery.

[0105] (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte (3 g) prepared above was injected.

[0106] Example 3 (Production of non-aqueous electrolyte) LiPF was dissolved in a non-aqueous organic solvent containing ethylene carbonate (EC):ethyl methyl carbonate (EMC) in a volume ratio of 30:70 to a concentration of 1.0 M, and then 3.0 wt % of the compound represented by Formula 1a and other additives, including 0.5 wt % of vinylene carbonate (VC), 0.5 wt % of 1,3-propane sultone (PS), 0.2 wt % of 1-propene 1,3-sultone (PRS), 1.0 wt % of ethylene sulfate (ESa), 0.2 wt % of lithium tetrafluoroborate (LiBF), and 0.8 wt % of lithium difluorophosphate (LiDFP), were added to prepare a non-aqueous electrolyte for a lithium secondary battery.

[0107] (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte (3 g) prepared above was injected.

[0108] Example 4 (Production of non-aqueous electrolyte) LiPF was dissolved in a non-aqueous organic solvent containing ethylene carbonate (EC):ethyl methyl carbonate (EMC) in a volume ratio of 30:70 to a concentration of 1.0 M, and then 5.5 wt % of the compound represented by Formula 1a and other additives, including 0.5 wt % of vinylene carbonate (VC), 0.5 wt % of 1,3-propane sultone (PS), 0.2 wt % of 1-propene 1,3-sultone (PRS), 1.0 wt % of ethylene sulfate (ESa), 0.2 wt % of lithium tetrafluoroborate (LiBF), and 0.8 wt % of lithium difluorophosphate (LiDFP), were added to prepare a non-aqueous electrolyte for a lithium secondary battery.

[0109] (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte (3 g) prepared above was injected.

[0110] Example 5 (Production of non-aqueous electrolyte) LiPF was dissolved in a non-aqueous organic solvent containing ethylene carbonate (EC):ethyl methyl carbonate (EMC) in a volume ratio of 30:70 to a concentration of 1.0 M, and then 6.0 wt % of the compound represented by Formula 1a and other additives, including 0.5 wt % of vinylene carbonate (VC), 0.5 wt % of 1,3-propane sultone (PS), 0.2 wt % of 1-propene 1,3-sultone (PRS), 1.0 wt % of ethylene sulfate (ESa), 0.2 wt % of lithium tetrafluoroborate (LiBF), and 0.8 wt % of lithium difluorophosphate (LiDFP), were added to prepare a non-aqueous electrolyte for a lithium secondary battery.

[0111] (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte (3 g) prepared above was injected.

[0112] Comparative Example 1 A non-aqueous electrolyte and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that the compound of Formula 1a was not added during the preparation of the non-aqueous electrolyte.

[0113] Experimental example Experimental example 1: High temperature storage evaluation The lithium secondary batteries prepared in Examples 1 to 5 and the lithium secondary battery prepared in Comparative Example 1 were each charged to 4.2 V at room temperature (25°C) under constant current / constant voltage conditions at a rate of 0.33 C, and then discharged for 10 seconds at a rate of 2.5 C. After that, the initial resistance and initial discharge capacity were measured using a PNE-0506 charger / discharger (manufacturer: PNE solution).

[0114] Next, the battery was again charged to 4.2 V under constant current / constant voltage conditions at a rate of 0.33 C, and then stored for 8 weeks at 60° C. After 8 weeks of high-temperature storage, the resistance and discharge capacity were measured.

[0115] The capacity retention rate (%) and resistance increase rate (%) after high-temperature storage were calculated using the following [Equation 1] and [Equation 2], and the results are shown in Table 1 below.

[0116] [Formula 1] Capacity retention rate (%): (discharge capacity after 8 weeks storage at 60°C / initial discharge capacity) x 100

[0117] [Formula 2] Resistance increase rate (%): {(resistance after 8 weeks storage at 60°C - initial resistance) / initial resistance} x 100

[0118] [Table 1]

[0119] Referring to Table 1, it can be seen that the lithium secondary batteries of Examples 1 to 4, which include the non-aqueous electrolyte solution containing the additive of the present invention, have improved capacity retention rates and significantly improved resistance increase rates after high-temperature storage at 60°C, compared to the secondary battery of Comparative Example 1, which does not include the additive.

[0120] Based on these results, it can be seen that in the case of the lithium secondary batteries of Examples 1 to 4, by introducing a compound having excellent bonding strength with Lewis acids as an electrolyte additive, it is possible to ensure the effect of stabilizing the removal of thermal decomposition products of lithium salts and thereby enhance the durability of the SEI film, and it is also possible to suppress the reaction of additional generation of SEI due to the additional decomposition reaction of the electrolyte, thereby realizing stable operation of the battery.

[0121] On the other hand, in the case of the lithium secondary battery of Example 5, which used a non-aqueous electrolyte containing a slightly higher amount of additive, it can be seen that the capacity retention rate and the resistance increase rate were slightly reduced compared to the secondary batteries of Examples 1 to 4 due to a slight increase in side reactions caused by the additive.

[0122] Experimental Example 2: Gas analysis after high-temperature storage The lithium secondary batteries prepared in Examples 1 to 5 and the lithium secondary battery prepared in Comparative Example 1 were each charged to 4.2 V at room temperature (25° C.) under constant current / constant voltage conditions at a rate of 0.33 C, and then stored at 60° C. for 8 weeks. After 8 weeks of high-temperature storage, the amount of gas generated in the lithium secondary batteries was measured and is shown in Table 2 below.

[0123] [Table 2]

[0124] Referring to the results in Table 2, it can be seen that the secondary batteries of Examples 1 to 4 generated significantly less gas than the secondary battery of Comparative Example 1. That is, in the case of the secondary battery of Example 1, which is provided with a non-aqueous electrolyte solution containing the compound represented by Chemical Formula 1a, it is believed that the amount of gas generated is reduced compared to the secondary battery of Comparative Example 1 by effectively removing Lewis acid inside the non-aqueous electrolyte solution and suppressing the deterioration behavior of the coating.

[0125] On the other hand, in the case of the lithium secondary battery of Example 5, which uses a non-aqueous electrolyte containing a slightly higher content of additives, it can be seen that the amount of gas generated is slightly increased compared to the secondary batteries of Examples 1 to 4 due to a slight increase in side reactions caused by the additives.

Claims

1. An electrolyte additive for a lithium secondary battery, which is a compound represented by the following chemical formula 1: 【Chemical 1】 In the above Chemical Formula 1, R １ and R ２ are each independently an alkyl group having 1 to 10 carbon atoms.

2. The R １ and R ２ and each independently represent an alkyl group having 1 to 7 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 is an alkyl group having 1 to 3 carbon atoms, The R ２ The electrolyte additive for lithium secondary batteries according to claim 1, wherein is an alkyl group having 1 to 5 carbon atoms.

5. The electrolyte additive for a lithium secondary battery according to claim 1, wherein the compound represented by Chemical Formula 1 includes at least one of compounds represented by the following Chemical Formulas 1a to 1c: 【Chemistry 2】 【Chemistry 3】 【Chemistry 4】

6. A non-aqueous electrolyte solution for a lithium secondary battery, comprising a lithium salt, an organic solvent, and the electrolyte additive for a lithium secondary battery according to claim 1 .

7. 7. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 6, wherein the electrolyte additive for a lithium secondary battery is contained in an amount of 0.05 wt % to 5.5 wt % based on the total content of the non-aqueous electrolyte solution for a lithium secondary battery.

8. 7. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 6, wherein the electrolyte additive for a lithium secondary battery is contained in an amount of 0.1 wt % to 5.0 wt % based on the total content of the non-aqueous electrolyte solution for a lithium secondary battery.

9. 7. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 6, wherein the electrolyte additive for a lithium secondary battery is contained in an amount of 0.1 wt % to 3.5 wt % based on the total content of the non-aqueous electrolyte solution for a lithium secondary battery.

10. 7. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 6, further comprising at least one other additive selected from the group consisting of cyclic carbonate-based compounds, halogen-substituted carbonate-based compounds, sultone-based compounds, sulfate-based compounds, phosphate-based compounds, borate-based compounds, nitrile-based compounds, benzene-based compounds, amine-based compounds, silane-based compounds, and lithium salt-based compounds.

11. A lithium secondary battery comprising a positive electrode, a separator, a negative electrode, and the nonaqueous electrolyte solution for a lithium secondary battery according to claim 6.

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