Non-aqueous electrolyte and lithium secondary battery containing the same

Abstract

The present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive includes a compound represented by the following Chemical Formula 1 and lithium difluoro(oxalate)borate (LiODFB), and the organic solvent includes ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP). JPEG2025516290000009.jpg25170(In Chemical Formula 1, n is an integer from 3 to 10.)

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0110317, filed on August 31, 2022, and all the contents disclosed in the documents of the Korean patent application are incorporated herein by reference in their entirety.

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

Background Art

[0003] In recent years, in order to increase the capacity of lithium secondary batteries, attempts have been made to drive secondary batteries at higher voltages.

[0004] However, when driving a secondary battery under high voltage, as charge and discharge proceed, due to side reactions caused by deterioration of the electrolyte, the film formed on the surface of the positive electrode / negative electrode or the surface structure of the electrode deteriorates, and transition metal ions can elute from the surface of the positive electrode. The transition metal ions eluted in this way are electrodeposited on the negative electrode, reducing the passivation ability of the SEI, resulting in a problem that the negative electrode deteriorates.

[0005] Such a deterioration phenomenon of the secondary battery tends to accelerate as the potential of the positive electrode increases or when the battery is exposed to high temperatures, resulting in a problem that the cycle characteristics of the secondary battery deteriorate due to the deterioration phenomenon.

[0006] In addition, when a lithium secondary battery is used continuously for a long time or left at a high temperature, a so-called swelling phenomenon occurs in which gas is generated and the thickness of the battery increases, and the amount of gas generated at this time is known to depend on the state of such SEI.

[0007] Therefore, in order to solve such problems, research and development have been conducted on methods that can suppress the elution of transition metal ions in the positive electrode, reduce the destruction of the SEI film on the negative electrode, reduce the swelling phenomenon of the secondary battery, and enhance the stability at high temperatures.

Summary of the Invention

Problems to be Solved by the Invention

[0008] As a result of conducting comprehensive research to solve the above problems, an object of the present invention is to provide a non-aqueous electrolyte that can suppress the deterioration of the positive electrode and reduce the side reaction between the positive electrode and the electrolyte.

[0009] Another object of the present invention is to provide a lithium secondary battery that includes the non-aqueous electrolyte, thereby improving the high-temperature cycle characteristics and high-temperature storage characteristics and enhancing various performances.

Means for Solving the Problems

[0010] To achieve the above object, the present invention provides a non-aqueous electrolyte containing a lithium salt, an organic solvent, and an additive, wherein the additive includes a compound represented by the following Chemical Formula 1 and lithium difluoro(oxalate)borate (LiODFB), and the organic solvent includes ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP).

[0011]

Chemical Formula

[0012] In Chemical Formula 1, n is an integer from 3 to 10.

Effects of the Invention

[0013] The non-aqueous electrolyte of the present invention contains the compound represented by the above Chemical Formula 1 and lithium difluoro(oxalate)borate (LiODFB), thereby suppressing the decomposition of the lithium salt and suppressing the disintegration of the positive electrode caused by by-products such as HF. Further, it is possible to suppress the decrease in the passivation ability of SEI at high temperatures and prevent the deterioration of the negative electrode.

[0014] Specifically, the combination of the diisocyanate-based compound of Chemical Formula 1 and lithium difluoro(oxalate)borate (LiODFB) can stabilize the electrolyte and suppress the decomposition reaction of the carbonate-based solvent and the propionate-based solvent. Further, in an environment where a stable positive electrode film formed by the combination of the diisocyanate-based compound of Chemical Formula 1 and lithium difluoro(oxalate)borate (LiODFB) is sufficiently formed, the reactivity of ethyl propionate (EP) and propyl propionate (PP) with oxygen desorbed from the positive electrode material is low, so carbon dioxide, which is an oxidation gas, is suppressed. Thereby, the lithium secondary battery containing the non-aqueous electrolyte of the present invention can suppress the generation of gas at high temperatures. That is, when the non-aqueous electrolyte of the present invention is used, elution of transition metals in the positive electrode is suppressed, and by maintaining high high-temperature durability, a lithium secondary battery with improved high-temperature cycle characteristics and high-temperature storage characteristics and improved various performances can be realized.

Embodiments for Carrying Out the Invention

[0015] The terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meaning and concept consistent with the technical idea of the present invention, in accordance with the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0016] In this specification, terms such as "comprising", "including", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and should be understood not to preclude the presence or addition of one or more other features, numbers, steps, components, or combinations thereof in advance.

[0017] Also, in this specification, in the description of "carbon number a to b", "a" and "b" mean the number of carbon atoms contained in a specific functional group. That is, the functional group may contain "a" to "b" carbon atoms. For example, an "alkylene group having 1 to 5 carbon atoms" is an alkylene group containing 1 to 5 carbon atoms, that is, -CH 2 -、-CH 2 CH 2 -、-CH 2 CH 2 CH 2 -、-CH 2 (CH 3 )CH-、-CH(CH 3 )CH 2 -、and -CH(CH 3 )CH 2 CH 2 - and the like.

[0018] Also, in this specification, any alkyl group may or may not be substituted. The above-mentioned "substitution" means that at least one or more hydrogens bonded to carbon are substituted with elements other than hydrogen, unless otherwise defined. For example, it means being substituted with an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, a heterocycloalkyl group having 3 to 12 carbon atoms, a heterocycloalkenyl group having 3 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, a halogen atom, a fluoroalkyl group having 1 to 20 carbon atoms, a nitro group, an aryl group having 6 to 20 carbon atoms, a heteroaryl group having 2 to 20 carbon atoms, a haloaryl group having 6 to 20 carbon atoms, etc.

[0019] Hereinafter, the present invention will be described in more detail.

[0020] [Non-aqueous electrolyte] The non-aqueous electrolyte according to the present invention contains a lithium salt, an organic solvent, and an additive. The additive contains a compound represented by the following Chemical Formula 1 and lithium difluoro(oxalate)borate (LiODFB). The organic solvent may contain ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP).

[0021] [Chemical formula]

[0022] In Chemical Formula 1, n may be an integer from 3 to 10, and preferably, n in Chemical Formula 1 may be an integer from 3 to 8.

[0023] The compound of Chemical Formula 1 is a compound in which an isocyanate group is substituted at the terminal portion. By forming a complex with the lithium salt to stabilize the lithium salt, generation of by-products such as HF can be suppressed. Thereby, elution of transition metals in the positive electrode, particularly elution of cobalt, can be suppressed. When elution of transition metals in the positive electrode is suppressed, deterioration of the positive electrode is suppressed, so that cycle characteristics and storage characteristics can be improved. Since deterioration of the positive electrode becomes more severe as the temperature increases, when the non-aqueous electrolyte of the present invention is used, cycle characteristics and storage characteristics at high temperature can be improved.

[0024] Since the lithium difluoro(oxalate)borate (LiODFB) can stabilize the negative electrode interface by a fast negative electrode reduction reaction, cycle characteristics and storage characteristics at high temperature can be improved.

[0025] In the non-aqueous electrolyte according to the present invention, the compound represented by Chemical Formula 1 may be contained in an amount of 0.1 part by weight to 5 parts by weight, preferably 0.1 part by weight to 3 parts by weight, more preferably 0.1 part by weight to 2 parts by weight, based on 100 parts by weight of the non-aqueous electrolyte. When the content of the compound represented by Chemical Formula 1 satisfies the above range, the effect of suppressing the elution of transition metal in the positive electrode is sufficient, and there is an effect of excellent life characteristics and high-temperature storage characteristics at high temperature.

[0026] In the non-aqueous electrolyte according to the present invention, lithium difluoro(oxalate)borate (LiODFB) may be contained in an amount of 0.1 part by weight to 5 parts by weight, preferably 0.1 part by weight to 3 parts by weight, more preferably 0.1 part by weight to 2 parts by weight, based on 100 parts by weight of the non-aqueous electrolyte. When the content of LiODFB satisfies the above range, in the activation step, the modification change of the negative electrode due to the fast negative electrode reduction decomposition reaction is sufficient, and there is an effect of excellent life characteristics and high-temperature storage characteristics at high temperature.

[0027] In the non-aqueous electrolyte of the present invention, the compound represented by Chemical Formula 1 and lithium difluoro(oxalate)borate (LiODFB) may be contained in a weight ratio of 0.2:1 to 5:1, preferably 1:1 to 5:1, most preferably 1:1 to 3:1. When the additive of Chemical Formula 1 and LiODFB are contained in the above range, the pH of the electrolyte becomes an appropriate range, the decomposition of the lithium salt is appropriately suppressed, and the elution of transition metal during charging at high voltage or at high temperature, particularly the elution of Co, can be suppressed.

[0028] The non-aqueous electrolyte according to the present invention may contain a lithium salt. The lithium salt is used as an electrolyte salt in a lithium secondary battery and is used as a mediator for transmitting ions. Usually, as the lithium salt, for example, it contains Li as a cation + and, as an anion, F - , Cl - , Br - , I - , NO 3 - , N(CN)2 - , BF 4 - , ClO 4 - , B 10 Cl 10 - , AlCl 4 - , AlO 2 - , PF 6 - , CF 3 SO 3 - , CH 3 CO 2 - , CF 3 CO 2 - , AsF 6 - , SbF 6 - , CH 3 SO 3 - , (CF 3 CF 2 SO 2 ) 2 N - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2 N - , BF 2 C 2 O 4 - , BC 4 O 8 - , PF 4 C 2 O 4 - , PF 2 C 4 O 8 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , C 4 F 9 SO 3 - , CF 3 CF 2 SO 3 - , CF 3 CF 2 (CF 3 ) 2 CO - , (CF 3 SO 2 ) 2 CH - , CF 3 (CF 2 ) 7 SO 3 - , and SCN - include at least any one selected from the group consisting of.

[0029] Specifically, the non-aqueous electrolyte of the present invention may contain LiPF 6 as a lithium salt. Additionally, the lithium salt may be LiCl, LiBr, LiI, LiBF 4 , LiClO 4 , LiB 10 Cl 10 , LiAlCl 4 , LiAlO 2 , LiCF 3 SO 3 , LiCH 3 CO 2 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiCH 3 SO 3 , LiN(SO 2 F) 2 (lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO 2 CF 2 CF 3) 2 (Lithium bis(perfluoroethanesulfonyl)imide; LiBETI), and LiN(SO 2 CF 3 ) 2 (Lithium bis(trifluoromethanesulfonyl)imide; LiTFSI), may contain a single substance or a mixture of two or more selected from the group consisting of. In addition to these, lithium salts commonly used in the electrolyte of lithium secondary batteries can be used without limitation.

[0030] The lithium salt can be appropriately changed within the range that can be normally used. However, in order to obtain the effect of forming a coating for preventing corrosion of the optimal electrode surface, in the electrolyte, it may be contained at a concentration of 0.5 M to 5.0 M, preferably 1.0 M to 3.0 M, more preferably 1.2 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics during high-temperature storage of the lithium secondary battery is sufficient, and the viscosity of the non-aqueous electrolyte is appropriate and the electrolyte impregnation property can be improved.

[0031] The non-aqueous electrolyte according to the present invention may contain an organic solvent including ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP). More preferably, the non-aqueous electrolyte according to the present invention may contain an organic solvent consisting of ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP).

[0032] The ethylene carbonate (EC) and propylene carbonate (PC) are high-viscosity organic solvents with a high dielectric constant, which easily dissociate lithium salts in the electrolyte. In an environment where a stable positive electrode film formed by the combination of the diisocyanate-based compound of Chemical Formula 1 and lithium difluoro(oxalate) borate (LiODFB) is sufficiently formed, propyl propionate (PP) has low reactivity with oxygen desorbed from the positive electrode material, so carbon dioxide, which is an oxidation gas, is suppressed. Ethylene propionate (EP) acts together with propyl propionate (PP) and has the effect of increasing lithium ion mobility and improving rapid charging performance.

[0033] The non-aqueous electrolyte of the present invention can provide a non-aqueous electrolyte having sufficient ionic conductivity by including ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP). Thereby, it has the effect of excellent long-term life characteristics. Most preferably, the organic solvent contained in the non-aqueous electrolyte of the present invention may consist of ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP).

[0034] The non-aqueous electrolyte of the present invention may contain, as other organic solvents, at least one or more organic solvents selected from the group consisting of fluoroethylene carbonate (FEC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate.

[0035] On the other hand, the organic solvent may be added and used as needed without being limited to the organic solvents usually used in non-aqueous electrolytes. For example, it may further contain at least one or more organic solvents such as ether-based organic solvents, glyme-based solvents, and nitrile-based organic solvents.

[0036] As the ether-based solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more thereof can be used, but it is not limited thereto.

[0037] The glyme-based solvent has a high dielectric constant and a low surface tension compared to a linear carbonate-based organic solvent, and is a solvent with little reactivity with metals. It may contain at least one selected from the group consisting of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraethylene glycol dimethyl ether (TEGDME), but is not limited thereto.

[0038] The nitrile-based solvent may be one or more 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, but is not limited thereto.

[0039] In addition, in order to prevent the non-aqueous electrolyte from being decomposed in a high-output environment and causing the collapse of the negative electrode, or to further improve the low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, battery expansion suppression effect at high temperature, etc., the non-aqueous electrolyte may further contain a known electrolyte additive as needed.

[0040] Such other electrolyte additives may include, as representative examples thereof, at least one or more additives for forming an SEI film selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0041] Examples of the cyclic carbonate compound include vinylene carbonate (VC) or vinyl ethylene carbonate.

[0042] Examples of the halogen-substituted carbonate compound include fluoroethylene carbonate (FEC).

[0043] Examples of the sultone compound include at least one or more compounds selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0044] Examples of the sulfate compound include ethylene sulfate (Ethylene Sulfate; Esa), trimethylene sulfate (Trimethylene sulfate; TMS), or methyl trimethylene sulfate (Methyl trimethylene sulfate; MTMS).

[0045] Examples of the phosphate compound include one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, trimethylsilyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphite.

[0046] Examples of the borate compound include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), and lithium bis(oxalato)borate (LiBOB). 2 O 4 ) 2 (LiBOB).

[0047] Examples of the nitrile compound include 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.

[0048] Examples of the benzene compound include fluorobenzene, examples of the amine compound include triethanolamine or ethylenediamine, and an example of the silane compound is tetravinylsilane.

[0049] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples include lithium difluorophosphate (LiDFP), LiPO 2 F 2 , or LiBF 4 , etc.

[0050] When such other electrolyte additives further include a combination of vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (Esa), and lithium difluorophosphate (LiDFP), a stronger SEI film can be formed on the surface of the negative electrode during the initial activation process of the secondary battery, the generation of gases that can be generated by the decomposition of the electrolyte at high temperatures can be suppressed, and the high-temperature stability of the secondary battery can be improved.

[0051] On the other hand, two or more of the other electrolyte additives may be used in combination, and may be contained in an amount of 0.050% by weight to 20% by weight, specifically 0.10% by weight to 15% by weight, based on the total weight of the non-aqueous electrolyte, and preferably may be 0.30% by weight to 10% by weight. When the content of the other electrolyte additive satisfies the above range, a more excellent effect of improving ionic conductivity and cycle characteristics can be obtained.

[0052] 〔Lithium secondary battery〕 The present invention also provides a lithium secondary battery containing the non-aqueous electrolyte.

[0053] Specifically, the lithium secondary battery includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and the aforementioned non-aqueous electrolyte.

[0054] At this time, the lithium secondary battery of the present invention can be manufactured by a conventional method known in the art. For example, after forming an electrode assembly in which a positive electrode, a negative electrode, and a separator are sequentially laminated between the positive electrode and the negative electrode, the electrode assembly is inserted into the inside of a battery case, and the non-aqueous electrolyte according to the present invention is injected to manufacture it.

[0055] The lithium secondary battery of the present invention has an upper limit of operating voltage of 4.47 V or more and can be driven at a high voltage. The upper limit voltage of the operating voltage means the charge termination voltage during charging and discharging of the lithium secondary battery, for example, the cut-off voltage under CC-CV charging conditions.

[0056] The lithium secondary battery of the present invention is characterized in that even when driven at a high voltage, the amount of Co elution is small. Specifically, the lithium secondary battery of the present invention can satisfy the following formula (1).

[0057] Formula (1): D t / D 0 <5

[0058] In the formula (1), D tis the amount of Co eluted in the non-aqueous electrolyte measured after storing the lithium secondary battery at 85 °C for 8 hours, and D 0 is the amount of Co eluted in the non-aqueous electrolyte of the lithium secondary battery before high-temperature storage.

[0059] Preferably, the lithium secondary battery of the present invention has D t / D 0 The value can be 1.5 or more and 3.5 or less, and most preferably 1.5 or more and 2.5 or less.

[0060] In addition, the lithium secondary battery of the present invention is characterized in that even when driven at a high voltage, the pH does not become excessively acidic. Specifically, for the lithium secondary battery of the present invention, the pH of the non-aqueous electrolyte measured after storage at 60 °C for 1 week exceeds 4, and preferably the pH can be 4.2 to 5.

[0061] (1) Positive electrode The positive electrode can be manufactured by coating a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive material, a solvent, etc. on a positive electrode current collector.

[0062] 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, fired carbon, or a material obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used.

[0063] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it may include a lithium metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium metal oxide is a lithium-manganese-based oxide (for example, LiMnO 2 、LiMn 2 O 4 etc.), a lithium-cobalt-based oxide (for example, LiCoO 2etc.), lithium-nickel-based oxides (e.g., LiNiO 2 etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-Y Mn Y O 2 (where 0 < Y < 1), LiMn 2-Z Ni Z O 4 (where 0 < Z < 2) etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O 2 (where 0 < Y1 < 1) etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O 2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O 4 (where 0 < Z1 < 2) etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r )O 2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O 4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2) etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O 2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1) etc.), and any one or two or more of these compounds may be included.

[0064] Among them, from the viewpoint of being able to enhance the capacity characteristics and stability of the battery, the lithium metal oxide is LiCoO 2 , LiMnO 2 , LiNiO 2 , lithium nickel manganese cobalt oxide (for example, Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O 2 , Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2 , Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 , Li(Ni 0.7 Mn 0.15 Co 0.15 )O 2 , and Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2 etc.), or lithium nickel cobalt aluminum oxide (for example, Li(Ni 0.8 Co 0.15 Al 0.05 )O 2 etc.), and any one or a mixture of two or more of these may be used.

[0065] Among them, the positive electrode active material may be a lithium cobalt-based oxide represented by the following Chemical Formula 2.

[0066] [Chemical Formula 2] Li a1 Co 1-x1 M 1 x1 O 2+β

[0067] In the Chemical Formula 2, M 1 includes one or more selected from the group consisting of Al, B, Ba, Ca, Zr, Ti, Mg, Ta, Nb, Sr, W, and Mo, and 0.9 < a1 ≤ 1.1, 0 ≤ x1 ≤ 0.2, 0 ≤ β ≤ 0.02 may be satisfied.

[0068] The positive electrode active material may be contained in an amount of 60% to 99% by weight, preferably 70% to 99% by weight, more preferably 80% to 98% by weight, based on the total weight of the solid matter excluding the solvent in the positive electrode mixture slurry.

[0069] The binder is a component that assists in binding the active material and the conductive material, etc., and binding to the current collector.

[0070] Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, various copolymers, and the like.

[0071] Generally, the binder may be contained in an amount of 1% to 20% by weight, preferably 1% to 15% by weight, more preferably 1% to 10% by weight, based on the total weight of the solid content excluding the solvent in the positive electrode mixture slurry.

[0072] 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% to 20% by weight based on the total weight of the solid content in the negative electrode slurry. Such conductive materials are not particularly limited as long as they do not cause a chemical change in the battery and have conductivity. For example, carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; carbon fluoride powders; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used.

[0073] Generally, the conductive material may be contained in an amount of 1% by weight to 20% by weight, preferably 1% by weight to 15% by weight, more preferably 1% by weight to 10% by weight, based on the total weight of the solids excluding the solvent in the positive electrode active material slurry.

[0074] The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a suitable viscosity when the positive electrode active material, and optionally a binder, a conductive material, etc. are included. For example, it may be included such that the concentration of the solid content including the positive electrode active material, and optionally the binder and the conductive material, is 50% by weight to 95% by weight, preferably 70% by weight to 95% by weight, more preferably 70% by weight to 90% by weight.

[0075] (2) Negative electrode The negative electrode can be manufactured, for example, by coating a negative electrode current collector with a negative electrode active material slurry containing a negative electrode active material, a binder, a conductive material, a solvent, etc., or a graphite electrode made of carbon (C) or the metal itself can be used as the negative electrode.

[0076] For example, when manufacturing a negative electrode by coating a negative electrode current collector with a negative electrode active material slurry, 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. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, a surface-treated product of copper or stainless steel with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. may be used. Also, similar to the positive electrode current collector, the binding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0077] 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.

[0078] The carbon material capable of reversibly intercalating / deintercalating lithium ions may be used without particular limitation as long as it is a carbon-based negative electrode active material generally used in lithium ion secondary batteries. Representative examples thereof include crystalline carbon, amorphous carbon, or both of these may be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0079] 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 can be used.

[0080] Examples of the metal composite oxide include PbO, PbO 2 、Pb 2 O 3 、Pb 3 O 4 、Sb 2 O 3 、Sb 2 O 4 、Sb 2 O 5 、GeO, GeO 2 、Bi 2 O 3 、Bi 2 O 4 、Bi 2 O 5 、Li xFe 2 O 3 (0 ≦ x ≦ 1), Li x WO 2 (0 ≦ x ≦ 1), and Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, elements of Group 1, Group 2, Group 3 of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) selected from the group consisting of can be used.

[0081] As the substance capable of doping and undoping the lithium, Si, SiO x (0 < x ≦ 2), Si-Y alloy (wherein 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, SnO 2 , Sn-Y (wherein 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. can be mentioned, and at least one of these and SiO 2 may be mixed and used. 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.

[0082] Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0083] The additive according to the present invention is particularly Si or SiO xIt is effective when (0 < x < 2) is used as the negative electrode active material. Specifically, when using a Si-based negative electrode active material, if a strong SEI layer is not formed on the surface of the negative electrode during initial activation, the life characteristics will be promoted to decline due to intense volume expansion and contraction during the cycle. However, the additive according to the present invention can form a strong SEI layer while having elasticity, so that a secondary battery using a Si-based negative electrode active material can have excellent life characteristics and storage characteristics.

[0084] Among them, the negative electrode active material may be a mixture of graphite and SiO x (0 ≤ x < 2). From the point of increasing the capacity of the lithium secondary battery, the graphite and SiO x (0 ≤ x < 2) may be contained in a weight ratio of 97:3 to 90:10.

[0085] The negative electrode active material may be contained in an amount of 60 to 99% by weight, preferably 70 to 99% by weight, more preferably 80 to 98% by weight, based on the total weight of the solid content in the negative electrode binder slurry.

[0086] Examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluorine rubber, various copolymers thereof, and the like. Specifically, styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC) can be used because of its high thickening property.

[0087] Generally, the binder may be contained in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, more preferably 1 to 10% by weight, based on the total weight of the solid matter excluding the solvent in the negative electrode binder slurry.

[0088] 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 binder 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. For example, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black, etc. carbon powder; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; carbon fluoride powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used.

[0089] The conductive material may be contained in an amount of 1% by weight to 20% by weight, preferably 1% by weight to 15% by weight, more preferably 1% by weight to 10% by weight, based on the total weight of the solids excluding the solvent in the negative electrode binder slurry.

[0090] The solvent may include water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a suitable viscosity when the negative electrode active material, and optionally a binder and a conductive material, etc. are included. For example, it may be included such that the concentration of the solid content including the negative electrode active material, and optionally the binder and the conductive material, is 50% by weight to 95% by weight, preferably 70% by weight to 90% by weight.

[0091] When using the metal itself as the negative electrode, it can be manufactured by methods such as physically bonding, rolling, or vapor depositing the metal on the metal thin film itself or the negative electrode current collector. As the vapor deposition method, a method of electrically vapor depositing or chemically vapor depositing (chemical vapor deposition) the metal can be used.

[0092] For example, the metal film itself or the metal joined / rolled / vapor-deposited on the negative electrode current collector may include one metal selected from the group consisting of lithium (Li), nickel (Ni), tin (Sn), copper (Cu), and indium (In), or an alloy of two metals, etc.

[0093] (3) Separator In addition, as the separator, a normal porous polymer film conventionally used as a separator, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer may be used alone or in a laminated form, or a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used, but it is not limited thereto. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used in a single-layer or multi-layer structure.

[0094] Specifically, as the separator included in the electrode assembly of the present invention, an SRS (safety reinforced separator) separator having a coating layer containing a ceramic component or a polymer substance formed thereon may be used in order to ensure heat resistance or mechanical strength.

[0095] Specifically, the separator included in the electrode assembly of the present invention includes a porous separator substrate and a porous coating layer entirely coated on one or both sides of the separator substrate, and the coating layer may include inorganic particles selected from metal oxides, metalloid oxides, metal fluorides, metal hydroxides, and combinations thereof, and a mixture of binder polymers that connect and fix the inorganic particles to each other.

[0096] The coating layer contains, as inorganic particles, Al 2 O3 , SiO 2 , TiO 2 , SnO 2 , CeO 2 , MgO, NiO, CaO, ZnO, ZrO 2 , Y 2 O 3 , SrTiO 3 , BaTiO 3 , Mg(OH) 2 and may contain one or more selected from MgF. Here, the inorganic particles can improve the thermal stability of the separator. That is, the inorganic particles can prevent the separator from shrinking at high temperatures. And the binder polymer can fix the inorganic particles and also improve the mechanical stability of the separator.

[0097] The outer shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape, a rectangular shape, a pouch shape, or a coin shape using a can, etc.

[0098] Hereinafter, the present invention will be described more specifically with reference to specific examples. However, the following examples are merely illustrative for understanding the present invention and are not intended to limit the scope of the present invention. It is obvious to those skilled in the art that various changes and modifications are possible within the scope of the description and the scope of the technical idea, and it goes without saying that such variations and modifications belong to the scope of the appended claims.

[0099] [Example] Example 1 (Manufacture of non-aqueous electrolyte) Lithium hexafluorophosphate (LiPF 6 was dissolved in an organic solvent (ethylene carbonate (EC): propylene carbonate (PC): ethyl propionate (EP): propyl propionate (PP) = 20:10:25:45 by volume ratio) to a concentration of 1.2 M to produce a non-aqueous solvent. 0.5 g of hexamethylene diisocyanate and 1 g of lithium difluoro(oxalate) borate (LiODFB) were added to 98.5 g of the non-aqueous solvent to produce a non-aqueous electrolyte.

[0100] (Manufacture of Lithium Secondary Battery) The positive electrode active material (LiCoO 2 ) and the conductive material (carbon black) and the binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) which is a solvent at a weight ratio of 97.5:1.3:1.2 to produce a positive electrode slurry (solid content 74% by weight). The positive electrode slurry was applied to one surface of a positive electrode current collector (Al thin film) having a thickness of 15 μm, and dried and roll pressed to produce a positive electrode.

[0101] The negative electrode active material (graphite:SiO = 92:8 weight ratio), the conductive material (carbon black), and the binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) which is a solvent at a weight ratio of 96.8:0.2:3.0 to produce a negative electrode slurry (solid content 62% by weight). The negative electrode slurry was applied to one surface of a negative electrode current collector (Cu thin film) having a thickness of 15 μm, and dried and roll pressed to produce a negative electrode.

[0102] In a dry room, after interposing a polyolefin-based porous separator coated with inorganic particles Al 2 O 3 between the positive electrode and the negative electrode manufactured above, the non-aqueous electrolyte manufactured above was injected to manufacture a secondary battery.

[0103] Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that 1 g of hexamethylene diisocyanate and 1 g of lithium difluoro(oxalate)borate (LiODFB) were added to 98 g of the non-aqueous solvent manufactured in Example 1 to manufacture a non-aqueous electrolyte.

[0104] Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that 2 g of hexamethylene diisocyanate and 1 g of lithium difluoro(oxalate)borate (LiODFB) were added to 97 g of the non-aqueous solvent manufactured in Example 1 to manufacture a non-aqueous electrolyte.

[0105] Example 4 A secondary battery was manufactured in the same manner as in Example 1, except that 0.5 g of hexamethylene diisocyanate and 1 g of lithium difluoro(oxalato)borate (LiODFB) were added to 97.5 g of the non-aqueous solvent manufactured in Example 1 to produce a non-aqueous electrolyte.

[0106] Example 5 A secondary battery was manufactured in the same manner as in Example 1, except that 2 g of hexamethylene diisocyanate and 0.5 g of lithium difluoro(oxalato)borate (LiODFB) were added to 97.5 g of the non-aqueous solvent manufactured in Example 1 to produce a non-aqueous electrolyte.

[0107] Comparative Example 1 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was produced using 100 g of the non-aqueous solvent manufactured in Example 1.

[0108] Comparative Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that 0.5 g of hexamethylene diisocyanate was added to 99.5 g of the non-aqueous solvent manufactured in Example 1 to produce a non-aqueous electrolyte.

[0109] Comparative Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that 1 g of lithium difluoro(oxalato)borate (LiODFB) was added to 99 g of the non-aqueous solvent manufactured in Example 1 to produce a non-aqueous electrolyte.

[0110] Comparative Example 4 In an organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 30:30:40 by volume ratio), LiPF 6It was dissolved to be 1.2 M to produce a non-aqueous solvent. 0.5 g of hexamethylene diisocyanate and 1 g of lithium difluoro(oxalate) borate (LiODFB) were added to 98.5 g of the non-aqueous solvent to produce a non-aqueous electrolyte.

[0111] A secondary battery was produced in the same manner as in Example 1 except that this non-aqueous electrolyte was used.

[0112] 〔Experimental Example 1 - Confirmation of Co elution amount by ICP analysis〕 For each of the secondary batteries produced in Examples 1 to 5 and Comparative Examples 1 to 4, the Co elution amount D 0 was measured, and after storage at 85 °C for 8 hours, the Co elution amount D t was measured.

[0113] Specifically, for each of the batteries produced in Examples 1 to 5 and Comparative Examples 1 to 4, the Co elution amount was analyzed by ICP analysis before and after storage at 85 °C for 8 hours.

[0114]

Table 1

[0115] 〔Experimental Example 2 - Confirmation of pH of electrolyte〕 For each of the secondary batteries produced in Examples 1 to 5 and Comparative Examples 1 to 4, the pH of the non-aqueous electrolyte was measured after storage at 60 °C for 1 week.

[0116]

Table 2

[0117] 〔Experimental Example 3 - Evaluation of high-temperature cycle characteristics〕 For each of the secondary batteries produced in Examples 1 to 5 and Comparative Examples 1 to 4, the cycle characteristics were evaluated.

[0118] Specifically, each of the batteries manufactured in Examples 1 to 5 and Comparative Examples 1 to 4 was charged at a constant current of 0.5C to 4.5V at 45°C, and discharged at a constant current of 0.5C to 3.0V. One cycle was defined as such, and after 200 cycles of charge and discharge, the capacity retention rate with respect to the initial capacity after one cycle was measured. The results are shown in Table 3 below.

[0119]

Table 3

[0120] As shown in Table 3, Examples 1 to 5 using the combination of the diisocyanate-based additive of Chemical Formula 1 and LiODFB had a higher capacity retention rate and better life characteristics compared to the secondary batteries of Comparative Example 1 that contained neither the additive of Chemical Formula 1 nor LiODFB, Comparative Example 2 that did not contain LiODFB, and Comparative Example 3 that did not contain the additive of Chemical Formula 1.

[0121] Also, Examples 1 to 5 using a non-aqueous electrolyte containing organic solvents of ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP) had a higher capacity retention rate and better life characteristics compared to the secondary battery of Comparative Example 4 using a combination of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0122] 〔Experimental Example 4 - Evaluation of High-Temperature Storage Characteristics〕 The high-temperature storage characteristics of each of the secondary batteries manufactured in Examples 1 to 5 and Comparative Examples 1 to 4 were evaluated.

[0123] Specifically, each of the secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 4 was fully charged to 4.5V and then stored at 85°C for 8 hours.

[0124] Before storage, the capacity of the fully charged secondary battery was measured and set as the capacity of the initial secondary battery.

[0125] After 8 hours, the capacity of the stored secondary battery was measured, and the decreased capacity during the storage period was calculated. The percentage of the decreased capacity with respect to the capacity of the initial secondary battery was calculated to derive the capacity retention rate after 8 hours. The results are shown in Table 4 below.

[0126]

Table 4

[0127] As shown in Table 4 above, Examples 1 to 5 using the combination of the diisocyanate-based additive of Chemical Formula 1 and LiODFB had a higher capacity retention rate after high-temperature storage and showed stable performance at high temperature compared to the secondary batteries of Comparative Example 1 that contained neither the additive of Chemical Formula 1 nor LiODFB, Comparative Example 2 that did not contain LiODFB, and Comparative Example 3 that did not contain the additive of Chemical Formula 1.

[0128] Also, Examples 1 to 5 using a non-aqueous electrolyte containing organic solvents of ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) had a higher capacity retention rate after high-temperature storage and showed stable performance at high temperature compared to Comparative Example 4 using a combination of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

Claims

1. A non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive includes a compound represented by the following Chemical Formula 1 and lithium difluoro(oxalato)borate (LiODFB), and the organic solvent includes ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP), the non-aqueous electrolyte. 【Chemical 1】 (In the Chemical Formula 1, n is an integer from 3 to 10.)

2. The non-aqueous electrolyte according to Claim 1, wherein n in the Chemical Formula 1 is an integer from 3 to 8.

3. The lithium salt contains LiPF ６ The non-aqueous electrolyte according to claim 1, which contains ６ .

4. The non-aqueous electrolyte according to Claim 1, comprising 0.1% by weight to 5% by weight of the compound represented by the Chemical Formula 1 based on the total non-aqueous electrolyte.

5. The non-aqueous electrolyte according to Claim 1, comprising 0.1% by weight to 5% by weight of the lithium difluoro(oxalato)borate (LiODFB) based on the total non-aqueous electrolyte.

6. The non-aqueous electrolyte according to Claim 1, wherein the weight ratio of the compound represented by the Chemical Formula 1 to the lithium difluoro(oxalato)borate (LiODFB) is 0.2:1 to 5:

1.

7. a positive electrode, a negative electrode, and a non-aqueous electrolyte according to any one of Claims 1 to 6, a lithium secondary battery, wherein the upper limit of the operating voltage is 4.47 V or more, the lithium secondary battery.

8. The lithium secondary battery according to Claim 7, wherein the positive electrode includes a lithium cobalt-based oxide as a positive electrode active material.

9. The negative electrode uses graphite and SiO as negative electrode active materials ｘ The lithium secondary battery according to claim 7, comprising (0 ≤ x < 2).

10. The lithium secondary battery according to Claim 7, wherein the lithium secondary battery satisfies the following formula (1). Formula (1): D ｔ / D ０ < 5 (In the above formula (1), D ｔ is the amount of Co eluted in the non-aqueous electrolyte measured after storing the lithium secondary battery at 85 °C for 8 hours, and D ０ is the amount of Co eluted in the non-aqueous electrolyte of the lithium secondary battery before high-temperature storage.)

11. The lithium secondary battery according to Claim 7, wherein the pH of the non-aqueous electrolyte measured after storing the lithium secondary battery at 60 °C for one week exceeds 4.

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