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

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 as part of this specification.

[0002] The present invention relates to an electrolyte additive for lithium secondary batteries that has an excellent effect of removing decomposition products generated from lithium salts, and 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 and personal IT devices and computer networks become more advanced, society as a whole is becoming more dependent on electrical energy, which calls for the development of technologies to efficiently store and utilize 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, and can also be used in electric vehicles and power storage devices.

[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] A lithium-ion battery is composed of a positive electrode made of a transition metal oxide containing lithium, 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. In order to improve the electrochemical properties of the battery, it is important to appropriately select these components.

[0007] On the other hand, lithium-ion batteries have the disadvantage that their performance deteriorates due to an increase in resistance and a decrease in capacity during charging / discharging or storage at high temperatures. One of the causes of these problems is said to be side reactions caused by the deterioration of the electrolyte at high temperatures, particularly the decomposition of lithium salts.

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

[0009] Lewis acid substances deteriorate the surface structure of the film or electrodes formed on the surface of the positive electrode / negative electrode, causing the reduction and decomposition of the solid electrolyte interphase (SEI) on the surface of the negative electrode and the dissolution of transition metal ions from the surface of the deteriorated positive electrode. The dissolved transition metal ions are re-deposited on the positive electrode, increasing the resistance of the positive electrode and causing the loss of redox centers, resulting in the capacity fading of the secondary battery. Furthermore, when the dissolved metal ions are electrodeposited on the negative electrode, the passivation ability of the SEI formed on the surface of the negative electrode is reduced, which causes the decomposition of the electrolyte for regeneration of the SEI and additional consumption of electrons and lithium ions, increasing the irreversible capacity, fading the cell capacity, and causing self-discharge of the negative electrode.

[0010] Therefore, various research and development efforts are being conducted on 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 lithium secondary batteries, which contains the electrolyte additive for lithium secondary batteries. Another object of the present invention is to provide a lithium secondary battery containing the nonaqueous electrolyte 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 each independently represent 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 for lithium secondary batteries. Effect of the Invention

[0018] The compound represented by Chemical Formula 1 used as an additive for the electrolyte for a lithium secondary battery according to the present invention contains a nitrogen element having an unshared electron pair as a Lewis base material and is easily bonded with a Lewis acid, so that it can effectively scavenge decomposition products of lithium salts in the electrolyte.

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

[0020] The present invention will now be described in more detail. The terms and words used in this specification and the claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner 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 describe his / her invention.

[0021] In lithium secondary batteries, a non-aqueous electrolyte is decomposed during initial charging and discharging, forming a coating with passivation ability on the surfaces of the positive and negative electrodes, improving high-temperature storage characteristics. However, this coating can be deteriorated by acids such as HF and PF5, which are generated by thermal decomposition of lithium salts (such as LiPF6) widely used in lithium-ion batteries. In addition, the attack of such acids causes the elution of transition metal elements from the positive electrode, which changes the structure of the surface, increasing the surface resistance of the electrode, and the disappearance of metal elements that act as redox centers, resulting in a decrease in theoretical capacity and realized capacity. In addition, the eluted transition metal ions are electrodeposited on the negative electrode, which reacts in a strong reduction potential zone, consuming electrons and destroying the coating, which causes the decomposition of the electrolyte for regeneration of the SEI and the additional consumption of electrons and lithium ions. As a result, there is a problem that the resistance of the negative electrode increases, the irreversible capacity increases, and the capacity of the cell decreases continuously.

[0022] Therefore, the present invention provides a non-aqueous electrolyte that contains a Lewis base compound capable of forming an SEI as a non-aqueous electrolyte additive component, thereby removing acid produced by decomposition of a lithium salt and preventing deterioration of the SEI film during high-temperature storage and elution of transition metals from the positive electrode, 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 the following Chemical Formula 1:

[0024] [ka]

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

[0026] The compound represented by the formula 1 is a Lewis base material and contains a carbonyl group together with a nitrogen element having an unshared electron pair in one molecular structure, so that the electron density of the carbon atom between the nitrogen elements is low. The carbon element attracts the unshared electron pair of the nitrogen element connected to R1, and the interaction becomes strong. Due to this action, localization of the charge occurs on the nitrogen element side that forms a double bond with the carbon atom of the imidazole functional group reflexively, and the bond energy with the Lewis acid material is higher than that of a compound not containing a carbonyl group in the structure, such as the compound represented by the formula 2 or 3 below. Therefore, when the compound represented by the formula 1 of the present invention is used as an electrolyte additive, the effect of scavenging the decomposition products of lithium salts such as HF or PF5 inside the electrolyte is further improved compared to the case where the compound represented by the formula 2 or 3 below is used as an additive, and the elution of transition metals from the positive electrode caused by Lewis acid and the deterioration behavior due to the chemical reaction of the coating formed on the surface of the positive electrode / negative electrode can be suppressed. In addition, the compound represented by Chemical Formula 1 can suppress damage to the coating on the surface of the negative electrode and suppress deterioration behavior, thereby preventing decomposition of the additional electrolyte of the battery due to destruction of the coating, and further mitigating self-discharge of the secondary battery to improve 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 localization of charge on the functional group of imidazole is weakened, and the effect of removing Lewis acid may be relatively reduced. Therefore, in order to secure and / or strengthen the bond energy with Lewis acid 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. Also, R1 and R2 may each independently be an alkyl group having 1 to 5 carbon atoms. Also, 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 nonaqueous 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 limitations. For example, the cation may be Li + 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 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 appropriately changed within a range that is normally usable, but in order to obtain an optimal effect of forming a corrosion prevention coating on the electrode surface, the lithium salt may be contained in the electrolyte at a concentration of 0.8 M to 3.0 M, specifically, at a concentration of 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 is described as follows. The organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, or a mixture of these organic solvents.

[0040] The cyclic carbonate organic solvent is a high-viscosity organic solvent that has a high dielectric constant and dissociates the lithium salt in the non-aqueous electrolyte well. 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 is 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. 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 necessary.

[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] As the ether-based organic solvent, 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 may be used.

[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 other than the lithium salt and the additive may entirely be 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 since 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 the formula 1 is included within the above content range, it is possible to form a strong coating on the surface of the positive electrode, while suppressing defects such as side reactions, capacity reduction, and resistance increase due to additives to the greatest extent possible, and it is possible to effectively suppress the elution of transition metals in the positive electrode active material at high temperatures, and to effectively remove thermal decomposition products of lithium salts, thereby achieving excellent high-temperature durability. When the content of the compound represented by the formula 1 is 0.05 wt% or more, it is possible to more stably maintain the effect of removing thermal decomposition products of lithium salts such as HF or PF5 and the effect of suppressing the elution of transition metals by protecting the positive electrode during the operation time of the battery. In addition, when the content of the compound represented by the formula 1 is 5.5 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 decomposition of additives, and further increase ion conductivity in the battery, thereby preventing a decrease in rate characteristics and low-temperature life characteristics during high-temperature storage.

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

[0053] (4) Other additives Meanwhile, the nonaqueous electrolyte of the present invention may further contain other additives other than the compound represented by Chemical Formula 1, if necessary, in order to prevent the nonaqueous electrolyte from being decomposed in a high-power environment, which may cause the collapse of the negative electrode, 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 vinyl ethylene 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 or phosphite 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] The borate-based compounds include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), and lithium bis(oxalato)borate (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, for example, triethanolamine or ethylenediamine, and the silane-based compound may be, for example, tetravinylsilane.

[0062] The lithium salt-based compound is a compound different from the lithium salt contained in the nonaqueous electrolyte, and examples of the lithium salt-based compound 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 (LiBF4), 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, the high-temperature storage characteristics and the high-temperature life characteristics can be more effectively improved, and the occurrence of side reactions in the battery due to the additives remaining after the reaction can be prevented.

[0065] Lithium secondary battery Furthermore, another embodiment of the present invention provides a lithium secondary battery including the nonaqueous electrolyte 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 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 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 introducing the nonaqueous electrolyte of the present invention into the battery case.

[0068] The method for manufacturing the lithium secondary battery of the present invention may be 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 including 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 is 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, or aluminum.

[0072] Specifically, the positive electrode active material may include a lithium-manganese oxide having high capacity characteristics and safety of a battery, lithium iron phosphate, or a lithium-composite transition metal oxide represented by the following Chemical Formula 4 having a nickel content of 70 atm % or more in order to realize a 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] 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 the 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 the 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] In addition, 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 80 wt% or less, the energy density may be reduced, and the capacity may be reduced.

[0083] The binder is a component that aids in binding between the active material and the conductive material and between the current collector, and is usually added in an amount of 1% by weight to 30% by weight based on the total weight of the solid content 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 a chemical change in the battery and imparts conductivity, and may be added in an amount of 1% by weight to 20% by weight based on the total weight of the solid content in the positive electrode slurry.

[0085] Representative examples of such conductive materials that may be used 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 contain 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, etc. are contained. For example, the solvent may be contained so that the solid content 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 prepared by coating a negative electrode current collector with a negative electrode slurry including 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 a chemical change in the battery and has high conductivity, and for example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or aluminum-cadmium alloy may be used. In addition, like the positive electrode current collector, fine irregularities may be formed on the surface of the negative electrode current collector to strengthen the binding force of the negative electrode active material, and it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[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, an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and dedoping 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. Typical 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 combinations 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 combinations 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 combinations thereof. Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadate, etc.

[0094] The negative electrode active material may be contained in an amount of 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 helps the conductive material, active material, and current collector to bond together, and is usually added in an amount of 1% by weight to 30% by weight based on the total weight of the solid content 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. In this case, the binder may be the same as or different from the binder included 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% by weight to 20% by weight based on the total weight of the solid content in the negative electrode slurry. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and examples thereof 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 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. 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, etc. are contained. For example, the solvent may be contained so that the solid content concentration in the slurry containing the negative electrode active material, and optionally a binder and a conductive material, is 50% by weight to 75% by weight, preferably 50% by weight to 65% by weight.

[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 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, either alone or in a laminated state, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of 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] The present invention will be described in detail below 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 having ordinary skill in the art.

[0100] Working Example Example 1 (Production of non-aqueous electrolyte) LiPF6 was dissolved in a non-aqueous organic solvent in which ethylene carbonate (EC):ethyl methyl carbonate (EMC) was mixed in a volume ratio of 30:70 to a concentration of 1.0 M, and then 0.3 wt % of the compound represented by Chemical Formula 1a and other additives, such as 0.5 wt % vinylene carbonate (VC), 0.5 wt % 1,3-propane sultone (PS), 0.2 wt % 1-propene 1,3-sultone (PRS), 1.0 wt % ethylene sulfate (Esa), 0.2 wt % lithium tetrafluoroborate (LiBF4), and 0.8 wt % 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 1,2-dichloroethane (1,2,3-tetrafluoroethylene), 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, and then 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 added in a weight ratio of 95.6:1.0:3.4 to deionized water (HO) as a solvent to prepare anode slurry (solid content 60 wt%). The anode slurry was applied to one side of a Cu anode current collector with a thickness of 6 μm, and dried and roll pressed to prepare anode.

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

[0104] Example 2 (Production of non-aqueous electrolyte) LiPF6 was dissolved in a non-aqueous organic solvent in which ethylene carbonate (EC):ethyl methyl carbonate (EMC) was mixed in a volume ratio of 30:70 to a concentration of 1.0 M, and then 0.05 wt % of the compound represented by Chemical Formula 1a and other additives, such as 0.5 wt % vinylene carbonate (VC), 0.5 wt % 1,3-propane sultone (PS), 0.2 wt % 1-propene 1,3-sultone (PRS), 1.0 wt % ethylene sulfate (Esa), 0.2 wt % lithium tetrafluoroborate (LiBF4), and 0.8 wt % 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) LiPF6 was dissolved in a non-aqueous organic solvent in which ethylene carbonate (EC):ethyl methyl carbonate (EMC) was mixed in a volume ratio of 30:70 to a concentration of 1.0 M, and then 3.0 wt % of the compound represented by Chemical Formula 1a and other additives, such as 0.5 wt % vinylene carbonate (VC), 0.5 wt % 1,3-propane sultone (PS), 0.2 wt % 1-propene 1,3-sultone (PRS), 1.0 wt % ethylene sulfate (Esa), 0.2 wt % lithium tetrafluoroborate (LiBF4), and 0.8 wt % lithium difluorophosphate (LiDFP), were added to the solution 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) LiPF6 was dissolved in a non-aqueous organic solvent in which ethylene carbonate (EC):ethyl methyl carbonate (EMC) was mixed in a volume ratio of 30:70 to a concentration of 1.0 M, and then 5.5 wt % of the compound represented by Chemical Formula 1a and other additives, such as 0.5 wt % vinylene carbonate (VC), 0.5 wt % 1,3-propane sultone (PS), 0.2 wt % 1-propene 1,3-sultone (PRS), 1.0 wt % ethylene sulfate (Esa), 0.2 wt % lithium tetrafluoroborate (LiBF4), and 0.8 wt % 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) LiPF6 was dissolved in a non-aqueous organic solvent in which ethylene carbonate (EC):ethyl methyl carbonate (EMC) was mixed in a volume ratio of 30:70 to give a concentration of 1.0 M, and then 6.0 wt % of the compound represented by Chemical Formula 1a and other additives, such as 0.5 wt % vinylene carbonate (VC), 0.5 wt % 1,3-propane sultone (PS), 0.2 wt % 1-propene 1,3-sultone (PRS), 1.0 wt % ethylene sulfate (Esa), 0.2 wt % lithium tetrafluoroborate (LiBF4), and 0.8 wt % 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 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 discharged for 10 seconds at a rate of 2.5 C. Then, the initial resistance and initial discharge capacity were measured using a PNE-0506 charger / discharger (manufacturer: PNE solution).

[0114] Next, the battery was charged again at a rate of 0.33 C under constant current / constant voltage conditions up to 4.2 V, 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 having the nonaqueous electrolyte solution containing the additive of the present invention have improved capacity retention and significantly improved resistance increase rate after high temperature storage at 60° C. compared to the secondary battery of Comparative Example 1 in which the additive is not used.

[0120] In view of these results, in the case of the lithium secondary batteries of Examples 1 to 4, by introducing a compound having excellent binding strength with Lewis acid as an electrolyte additive, it is possible to ensure the effect of stabilizing the removal of thermal decomposition products of lithium salt and thereby enhancing the durability of the SEI film, and it is possible to suppress the reaction of additional generation of SEI due to the additional decomposition reaction of the electrolyte, thereby confirming that stable operation of the battery can be realized.

[0121] On the other hand, in the case of the lithium secondary battery of Example 5 using a nonaqueous electrolyte containing a slightly higher amount of additive, the capacity retention rate and the resistance increase rate were slightly decreased 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 manufactured in Examples 1 to 5 and the lithium secondary battery manufactured 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 stored for 8 weeks at 60° C. 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 much less gas than the secondary battery of Comparative Example 1. That is, in the case of the secondary battery of Example 1 having a nonaqueous electrolyte solution containing the compound represented by Chemical Formula 1a, it is considered that the amount of gas generated is reduced compared to the secondary battery of Comparative Example 1 by effectively removing the Lewis acid inside the nonaqueous 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 using a nonaqueous electrolyte containing a slightly higher content of additive, the amount of gas generated was slightly increased compared to the secondary batteries of Examples 1 to 4 due to a slightly increased side reaction caused by the additive.

Claims

1. An electrolyte additive for a lithium secondary battery, which is a compound represented by the following chemical formula 1: 【Chemistry 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 represents an alkyl group having 1 to 7 carbon atoms.

3. The R １ and R ２ and each independently represents 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 Formula 1 includes at least one of compounds represented by the following Formulas 1a to 1c: 【Chemistry 2】 【Chemistry 3】 【Chemistry 4】

6. 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 according to claim 1 .

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

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

9. The non-aqueous electrolyte 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 to 3.5 wt % based on the total content of the non-aqueous electrolyte for a lithium secondary battery.

10. 7. The nonaqueous 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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