Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery containing the same

Abstract

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery, which contains a lithium salt, an organic solvent, and a compound represented by Chemical Formula 1, and a lithium secondary battery containing the same. JPEG2024520516000026.jpg38170In the above Chemical Formula 1, R1 is an alkyl group having 1 to 10 carbon atoms; R2 is an alkylene group having 1 to 10 carbon atoms; L is a direct bond, -O-, -COO-, -RO-, or -R'COO-; R and R' each independently represent an alkylene group having 1 to 10 carbon atoms, m is an integer of 0 to 5.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0131937, filed on October 5, 2021, and Korean Patent Application No. 10-2022-0115214, filed on September 13, 2022, and all the contents disclosed in the documents of the Korean patent applications are incorporated herein by reference in their entirety.

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

Background Art

[0003] A lithium secondary battery is generally manufactured by forming an electrode assembly with a separator interposed between a positive electrode including a positive electrode active material made of a transition metal oxide containing lithium and a negative electrode including a negative electrode active material capable of storing lithium ions, inserting the electrode assembly into a battery case, and then injecting a non-aqueous electrolyte serving as a medium for transmitting lithium ions and sealing it.

[0004] Lithium secondary batteries can be miniaturized and have high energy density and operating voltage, so they are applied in various fields such as mobile devices, electronic products, and electric vehicles. As the application fields of lithium secondary batteries diversify, the required physical property conditions are becoming increasingly high. In particular, there is a demand for the development of lithium secondary batteries that can be stably driven even under high voltage and high temperature conditions and have long-life characteristics.

[0005] On the other hand, when a lithium secondary battery is driven under high voltage and / or high temperature conditions, PF6 is released from a lithium salt such as LiPF6 contained in the electrolyte. -The anion may be thermally decomposed to generate a Lewis acid such as PF5, which reacts with moisture to produce HF. Such decomposition products as PF5 and HF may not only destroy the film formed on the surface of the electrode, but also cause a decomposition reaction of the organic solvent. In addition, the electrolytic solution decomposition products may react with the decomposition products of the positive electrode active material to elute transition metal ions, and the eluted transition metal ions may be electrodeposited on the negative electrode, possibly destroying the film formed on the surface of the negative electrode.

[0006] If the decomposition reaction of the electrolyte continues on the film thus destroyed, the performance of the battery will further deteriorate. Therefore, there is a demand for the development of a secondary battery that can maintain excellent performance even under high voltage and high temperature conditions.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention is for solving the above problems, and by including a compound having a structure in which a propargyl group is bonded to coumarin, it is an object to provide a non-aqueous electrolyte that can suppress the decomposition reaction of the electrolyte and form a strengthened film on the electrode, and a lithium secondary battery containing the same.

Means for Solving the Problems

[0009] According to one embodiment, the present invention provides a non-aqueous electrolyte for a lithium secondary battery, which includes a lithium salt, an organic solvent, and a compound represented by the following Chemical Formula 1.

[0010]

Chem.

[0011] In the chemical formula 1, R1 is an alkyl group having 1 to 10 carbon atoms, R2 is an alkylene group having 1 to 10 carbon atoms, L is a direct bond, -O-, -COO-, -RO-, or -R'COO-, The R and R' are each independently an alkylene group having 1 to 10 carbon atoms, m is any integer from 0 to 5.

[0012] According to another embodiment, the present invention provides a lithium secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte for the lithium secondary battery.

Effects of the Invention

[0013] The non-aqueous electrolyte according to the present invention contains a compound having a structure in which a propargyl group, which is advantageous for forming a film on the surface of the negative electrode by reacting with active oxygen in the positive electrode and effectively suppressing the decomposition of the positive electrode due to the coumarin structure. Therefore, not only can a highly durable film be formed on the electrode, but also the decomposition reaction of the electrolyte can be suppressed, and the gas generation rate of a battery containing a high-nickel positive electrode active material can be reduced. Further, thereby, a lithium secondary battery having fundamentally improved electrochemical characteristics can be provided.

Modes for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described in more detail.

[0015] Generally, anions contained in lithium salts such as LiPF6 widely used in electrolytes for lithium secondary batteries form decomposition products such as hydrogen fluoride (HF) and PF5 due to thermal decomposition or moisture. Such decomposition products have acidic properties and deteriorate the surface of the film or the electrode in the battery.

[0016] Due to the decomposition products of the electrolyte and the structural changes of the positive electrode caused by repeated charge and discharge, transition metals in the positive electrode are likely to dissolve into the electrolyte. The dissolved transition metals are further re-deposited on the positive electrode, increasing the resistance of the positive electrode. Furthermore, when the dissolved transition metals move to the negative electrode through the electrolyte, they are electrodeposited on the negative electrode, causing the destruction of the SEI (solid electrolyte interphase) film and further electrolyte decomposition reactions, resulting in problems such as the consumption of lithium ions and an increase in resistance.

[0017] Also, during the initial activation of the battery, protective films are formed on the positive and negative electrodes due to electrolyte reactions. However, if the films become unstable for the above reasons, further decomposition of the electrolyte occurs during charge and discharge or high-temperature exposure, accelerating the deterioration of the battery and generating gas.

[0018] In particular, batteries containing a positive electrode active material with a high nickel content have improved initial capacity characteristics. However, when charge and discharge are repeated, side reactions may increase the amount of lithium by-products and gas generation, and the decomposition reaction of the electrolyte may become intense.

[0019] To solve such problems, the inventors have found that by including a compound represented by the following Chemical Formula 1, having a structure in which a propargyl group is bonded to coumarin, in a non-aqueous electrolyte, the decomposition reaction of the electrolyte can be reduced, and the dissolution of transition metals and the generation of gas can be suppressed. In particular, when the non-aqueous electrolyte according to the present invention is included, it has been confirmed that not only the initial capacity of a battery containing a high-nickel positive electrode active material but also the durability during high-temperature storage and cycle progress are improved.

[0020] Hereinafter, each component constituting the present invention will be described in more detail.

[0021] Non-aqueous electrolyte The present invention provides a non-aqueous electrolyte for a lithium secondary battery, comprising a lithium salt, an organic solvent, and a compound represented by Chemical Formula 1.

[0022] The following will specifically describe each component.

[0023] (1) Compound represented by Chemical Formula 1 The non-aqueous electrolyte of the present invention contains a compound represented by the following Chemical Formula 1.

[0024] [Chemical Formula]

[0025] In the above Chemical Formula 1, R1 is an alkyl group having 1 to 10 carbon atoms, R2 is an alkylene group having 1 to 10 carbon atoms, L is a direct bond, -O-, -COO-, -RO-, or -R'COO-, The above R and R' are each independently an alkylene group having 1 to 10 carbon atoms, m is any one integer from 0 to 5.

[0026] When the charge and discharge of the lithium secondary battery are continued, active oxygen such as singlet oxygen and superoxide is generated at the positive electrode, which causes a decrease in the performance of the battery. The coumarin contained in the compound represented by Chemical Formula 1 has a higher reactivity with active oxygen than an electrolyte solvent such as ethylene carbonate, and thus can react with active oxygen prior to the electrolyte solvent, thereby suppressing the decomposition of the electrolyte by active oxygen. Further, since the compound represented by Chemical Formula 1 contains a propargyl functional group that is easily reduced, a passive film with enhanced durability can be formed while being reductively decomposed on the surface of the negative electrode. That is, since a stable film can be formed at the interfaces of the positive electrode, the negative electrode, and the electrolyte, even when a high-nickel positive electrode active material is used, side reactions can be suppressed and stability can be ensured. Therefore, not only the initial performance of the lithium secondary battery but also the high-temperature durability and long-term life can be effectively improved.

[0027] In one embodiment of the present invention, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of a compound represented by the following Chemical Formula 1-1 and a compound represented by the following Chemical Formula 2-1.

[0028]

Chem.

[0029]

Chem.

[0030] In Chemical Formula 1-1 and Chemical Formula 2-1, R1, R2, L, and m are as defined in Chemical Formula 1.

[0031] Preferably, the compound represented by Chemical Formula 1 may include the compound represented by Chemical Formula 1-1. When the propargyl group is substituted at the 3-position as in Chemical Formula 1-1, it is preferable because it has the effect of stabilizing the radicals at the 3- and 4-positions and increasing the reactivity.

[0032] In one embodiment of the present invention, L in Chemical Formula 1 may be -O- or -COO-.

[0033] In one embodiment of the present invention, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of a compound represented by the following Chemical Formula 1-2, a compound represented by the following Chemical Formula 1-3, a compound represented by the following Chemical Formula 2-2, and a compound represented by the following Chemical Formula 2-3. Preferably, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of a compound represented by the following Chemical Formula 1-2 and a compound represented by the following Chemical Formula 1-3.

[0034]

Chem.

[0035] [Chemistry]

[0036] [Chemistry]

[0037] [Chemistry]

[0038] In the chemical formula 1-2, the chemical formula 1-3, the chemical formula 2-2, and the chemical formula 2-3, R1, R2, and m are as defined in the chemical formula 1. In one embodiment of the present invention, m in the chemical formula 1 may be 0, and R2 may be an alkylene group having 1 to 5 carbon atoms, preferably an alkylene group having 1 to 3 carbon atoms, more preferably a methylene group.

[0039] In one embodiment of the present invention, the compound represented by the chemical formula 1 may include at least one selected from the group consisting of the compound represented by the following chemical formula 1A, the compound represented by the following chemical formula 1B, the compound represented by the following chemical formula 2A, and the compound represented by the following chemical formula 2B. Preferably, the compound represented by the chemical formula 1 may include at least one selected from the group consisting of the compound represented by the following chemical formula 1A and the compound represented by the following chemical formula 1B.

[0040] [Chemistry]

[0041] [Chemistry]

[0042] [Chemistry]

[0043] [Chemical formula]

[0044] In one embodiment of the present invention, the content of the compound represented by Chemical Formula 1 may be 0.1% by weight to 5% by weight, preferably 0.1% by weight to 1% by weight, more preferably 0.2% by weight to 0.8% by weight, based on the total weight of the non-aqueous electrolyte.

[0045] When the content of the compound represented by Chemical Formula 1 is 0.1% by weight or more, it is preferable from the viewpoint of obtaining the effect of suppressing the decomposition of metal ions in the positive electrode, which is to be obtained in the present invention. When it is 5% by weight or less, it is preferable because it is possible to prevent the battery performance from deteriorating due to an increase in resistance.

[0046] (2) Additive The non-aqueous electrolyte of the present invention may further selectively contain the following additives as necessary to prevent the electrolyte from being decomposed in a high-voltage environment and causing the collapse of the electrode, or to further improve effects such as low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and suppression of battery swelling at high temperatures.

[0047] The additive may be one or more selected from cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate or phosphite compounds, borate compounds, nitrile compounds, amine compounds, silane compounds, benzene compounds, and lithium salt compounds.

[0048] The cyclic carbonate compound may be one or more selected from vinylene carbonate (VC) and vinyl ethylene carbonate (VEC), and specifically, it may be vinylene carbonate.

[0049] The halogen-substituted carbonate compound may be fluoroethylene carbonate (FEC).

[0050] The above-mentioned sultone compound is a substance capable of forming a stable SEI film by a reduction reaction on the surface of the negative electrode, and may be one or more compounds selected from 1,3-propanesultone (PS), 1,4-butanesultone, ethenesultone, 1,3-propenesultone (PRS), 1,4-butenesultone, and 1-methyl-1,3-propenesultone. Specifically, it may be 1,3-propanesultone (PS).

[0051] The above-mentioned sulfate compound is a substance capable of being electrically decomposed on the surface of the negative electrode to form a stable SEI film that does not crack even during high-temperature storage, and may be one or more selected from ethylene sulfate (Ethylene Sulfate; Esa), trimethylene sulfate (Trimethylene sulfate; TMS), or methyl trimethylene sulfate (Methyl trimethylene sulfate; MTMS).

[0052] The above-mentioned phosphate or phosphite compound may be one or more selected from lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0053] The above-mentioned borate compound may be lithium tetraphenylborate.

[0054] The nitrile compound may be at least one selected from succinonitrile (SN), adiponitrile (ADN), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, ethylene glycol bis(2-cyanoethyl) ether (ASA3), 1,3,6-hexanetricarbonitrile (HTCN), 1,4-dicyano-2-butene (DCB), and 1,2,3-tris(2-cyanoethyl)propane (TCEP).

[0055] The amine compound may be at least one selected from triethanolamine and ethylenediamine, and the silane compound may be tetravinylsilane.

[0056] The benzene compound may be at least one selected from monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene.

[0057] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and may be at least one compound selected from lithium difluorophosphate (LiDFP; LiPO2F2), lithium bis(oxalato)borate (LiBOB; LiB(C2O4)2), lithium tetrafluoroborate (LiBF4), and lithium difluoro(bis(oxalato))phosphate (LiDFOP).

[0058] Preferably, the non-aqueous electrolyte according to an embodiment of the present invention may further contain one or more additives selected from vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,3 - propane sultone (PS), 1,3 - propene sultone (PRS), ethylene sulfate (ESa), succinonitrile (SN), adiponitrile (ADN), ethylene glycol bis(2 - cyanoethyl) ether (ASA3), 1,3,6 - hexanetricarbonitrile (HTCN), 1,4 - dicyano - 2 - butene (DCB), 1,2,3 - tris(2 - cyanoethyl) propane (TCEP), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium difluoro(bisoxalato) phosphate (LiDFOP), and lithium difluorophosphate (LiDFP).

[0059] More preferably, the non-aqueous electrolyte according to an embodiment of the present invention may further contain one or more additives selected from vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3 - propane sultone (PS), ethylene sulfate (ESa), lithium difluorooxalate borate (LiODFB), and lithium difluorophosphate (LiDFP).

[0060] On the other hand, the content of the additive may be 0.1% by weight to 10% by weight, preferably 0.3% by weight to 5% by weight, based on the total weight of the non-aqueous electrolyte. When the content of the additive is within the above range, the effect of suppressing side reactions by forming a film on the positive electrode and the negative electrode can be obtained.

[0061] (3) Organic solvent The non-aqueous electrolyte of the present invention contains an organic solvent.

[0062] As the organic solvent, various organic solvents commonly used in lithium electrolytes can be used without limitation. For example, the organic solvent may be a cyclic carbonate solvent, a linear carbonate solvent, a linear ester solvent, a cyclic ester solvent, a nitrile solvent, or a mixture thereof, and preferably may include a mixture of a cyclic carbonate solvent and a linear carbonate solvent.

[0063] The cyclic carbonate solvent is a high-viscosity organic solvent and has a high dielectric constant, so it can well dissociate lithium salts in the electrolyte. It may be one or more 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 preferably may include ethylene carbonate (EC) or propylene carbonate (PC).

[0064] Also, the linear carbonate solvent is an organic solvent having low viscosity and low dielectric constant, and may be one or more 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 preferably may include ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or diethyl carbonate (DEC).

[0065] In order to produce an electrolyte solution having high ionic conductivity, it is preferable to use a mixture of a cyclic carbonate solvent and a linear carbonate solvent as the organic solvent.

[0066] The linear ester solvent may be one or more selected from methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, and preferably may be methyl propionate, ethyl propionate, or propyl propionate.

[0067] The cyclic ester solvent may be one or more selected from γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0068] The nitrile solvent may be one or more selected from succinonitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, and preferably may be succinonitrile.

[0069] In the total weight of the non-aqueous electrolyte, unless otherwise specified, the remainder excluding the contents of other components excluding the organic solvent, such as the compound represented by Chemical Formula 1, the additive, and the lithium salt, is all organic solvent.

[0070] (4) Lithium salt The non-aqueous electrolyte of the present invention contains a lithium salt.

[0071] The lithium salt can be used without limitation such as those commonly used in electrolytes for lithium secondary batteries. Specifically, the lithium salt contains Li as a cation + and, as an anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2- , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO4 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , BF2C2O4CHF - , PF4C2O4 - , PF2C4O8 - , PO2F2 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - , and SCN - may contain any one or more selected from

[0072] Specifically, the lithium salt may be one or more selected from LiPF6, LiClO4, LiBF4, LiN(FSO2)2 (LiFSI), LiN(SO2CF3)2 (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), LiSO3CF3, LiPO2F2, lithium bis(oxalate)borate (LiBOB), lithium difluoro(oxalate)borate (LiFOB), lithium difluoro(bisoxalato) phosphate (LiDFOP), lithium tetrafluoro(oxalate)phosphate (LiTFOP), and lithium fluoromalonato(difluoro)borate (LiFMDFB), and preferably, it may be LiPF6.

[0073] In one embodiment of the present invention, the concentration of the lithium salt in the non-aqueous organic solution containing the lithium salt and the organic solvent may be 0.5 to 4.0 M, specifically 0.5 M to 3.0 M, and more specifically 0.8 M to 2.0 M. When the concentration of the lithium salt is within the above range, the effects of improving low-temperature output and cycle characteristics can be sufficiently ensured, while preventing the viscosity and surface tension from becoming excessively high, and appropriate electrolyte impregnation properties can be obtained.

[0074] Lithium secondary battery Next, the lithium secondary battery according to the present invention will be described.

[0075] The lithium secondary battery according to the present invention 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 a non-aqueous electrolyte. At this time, the non-aqueous electrolyte is the non-aqueous electrolyte according to the present invention described above. Since the non-aqueous electrolyte is as described above, the description thereof is omitted, and other components will be described below.

[0076] (1) Positive electrode The positive electrode according to the present invention contains a positive electrode active material, and can be manufactured by coating a positive electrode slurry containing a positive electrode active material, a binder, a conductive material, a solvent, etc. on a positive electrode current collector, and then drying and rolling.

[0077] 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 those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used.

[0078] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium.

[0079] More specifically, the positive electrode active material is a lithium-cobalt-based oxide (for example, LiCoO2, etc.), a lithium-manganese-based oxide (for example, LiMnO2, LiMn2O4, etc.), a lithium-nickel-based oxide (for example, LiNiO2, etc.), a lithium-nickel-manganese-based oxide (for example, LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (for example, LiNi 1-Y1 Co Y1O2 (where 0 < Y1 < 1, etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2, etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) and Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2, etc.), lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M s2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, Ti, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, respectively, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1)) may include one or more of them. Among them, from the viewpoint of being able to improve the capacity characteristics and stability of the battery, the positive electrode active material may include at least one selected from the group consisting of lithium-cobalt oxide, lithium-manganese-based oxide, lithium-nickel-manganese-cobalt-based oxide, and lithium-nickel-cobalt-transition metal (M) oxide, and preferably includes at least one selected from lithium-nickel-manganese-cobalt-based oxide with a nickel content of 55 atm% or more and lithium-nickel-cobalt-transition metal (M) oxide with a nickel content of 55 atm% or more.

[0080] As a representative example, Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2)O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2、 and Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2, and at least one selected from the group consisting of, preferably, Li(Ni 0.86 Co 0.057 Mn 0.07 Al 0.02 )O2 may be included.

[0081] In addition, the positive electrode active material according to an embodiment of the present invention may include a lithium composite transition metal oxide represented by the following Chemical Formula 3.

[0082] [Chemical Formula 3] Li 1+x (Ni a Co b Mn c M d )O2

[0083] In the Chemical Formula 3, M is one or more selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, 1 + x, a, b, c, and d are atomic fractions of independent elements, specifically, atomic fractions of Li, Ni, Co, Mn, and M, respectively, 0 ≦ x ≦ 0.2, 0.50 ≦ a < 1, 0 < b ≦ 0.25, 0 < c ≦ 0.25, 0 ≦ d ≦ 0.1, and a + b + c + d = 1.

[0084] Preferably, a, b, c, and d may be 0.70 ≦ a ≦ 0.95, 0.025 ≦ b ≦ 0.20, 0.025 ≦ c ≦ 0.20, and 0 ≦ d ≦ 0.05, respectively.

[0085] Further, each of a, b, c, and d may be 0.80 ≦ a ≦ 0.95, 0.025 ≦ b ≦ 0.15, 0.025 ≦ c ≦ 0.15, and 0 ≦ d ≦ 0.05.

[0086] Further, each of a, b, c, and d may be 0.85 ≦ a ≦ 0.90, 0.05 ≦ b ≦ 0.10, 0.05 ≦ c ≦ 0.10, and 0 ≦ d ≦ 0.03.

[0087] The positive electrode active material may be contained in an amount of 80% to 99% by weight, specifically 90% to 99% by weight, based on the total weight of the solid content in the positive electrode slurry. Here, when the content of the positive electrode active material is 80% by weight or less, there is a risk that the energy density will be low and the capacity will decrease.

[0088] The binder is a component that assists in binding the active material and the conductive material, etc., and binding to the current collector, and is usually added in an amount of 1% to 30% by weight based on the total weight of the solid content in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, or various copolymers thereof.

[0089] Further, the conductive material is a substance that imparts conductivity without causing a chemical change to the battery, and may be added in an amount of 0.5% to 20% by weight based on the total weight of the solid content in the positive electrode slurry.

[0090] Examples of the conductive material may include carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powders such as natural graphite, artificial graphite, carbon nanotubes, and graphite; 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.

[0091] Further, the solvent of the positive electrode slurry may contain an organic solvent such as NMP (N-methyl-2-pyrrolidone), and can be used in an amount that provides a suitable viscosity when containing the positive electrode active material, binder, conductive material, and the like. For example, it may be contained such that the concentration of the solid content in the positive electrode slurry containing the positive electrode active material, binder, and conductive material is 40% by weight to 90% by weight, preferably 50% by weight to 80% by weight.

[0092] (2) Negative electrode The negative electrode according to the present invention contains a negative electrode active material, and can be manufactured by coating a negative electrode slurry containing the negative electrode active material, binder, conductive material, solvent, etc. on a negative electrode current collector, followed by drying and rolling.

[0093] 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; those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel; or 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, sheet, foil, net, porous body, foam, non-woven fabric body, etc.

[0094] Further, the negative electrode active material may include one or more selected from carbon materials capable of reversibly intercalating / deintercalating lithium ions; metals or alloys of these metals and lithium; metal composite oxides; substances capable of doping and dedoping lithium; lithium metal; and transition metal oxides.

[0095] The carbon material capable of reversibly intercalating / deintercalating lithium ions is not particularly limited as long as it is a carbon-based negative electrode active material generally used in lithium ion secondary batteries, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination of these. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, and calcined coke.

[0096] As the metal or the 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.

[0097] 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, elements of Group 1, Group 2, Group 3 of the periodic table, halogen; 0<x≦1; 1≦y≦3; 1≦z≦8), and one or more selected from this group can be used.

[0098] Examples of the substance capable of doping and undoping lithium include 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, SnO2, 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. Further, at least one of these may be mixed with SiO2 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 (dubnium), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0099] Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadate, etc.

[0100] 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.

[0101] The binder is a component that aids in the binding between the conductive material, the active material, and the current collector, and may usually be added in an amount of 1% to 30% by weight based on the total weight of the solid content in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluorine rubber, or various copolymers thereof.

[0102] 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 0.5% 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. For example, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, carbon nanotubes, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives may be used.

[0103] The solvent of the negative electrode slurry may contain water; or organic solvents such as NMP and alcohol, and may be used in an amount that provides a suitable viscosity when containing the negative electrode active material, binder, conductive material, etc. For example, it may be contained such that the concentration of the solid content in the slurry containing the negative electrode active material, binder, and conductive material is 30% to 80% by weight, preferably 40% to 70% by weight.

[0104] (3) Separator The lithium secondary battery according to the present invention includes a separator between the positive electrode and the negative electrode.

[0105] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. It is not particularly limited as long as it is usually used as a separator in a lithium secondary battery, and in particular, it is preferably one that has low resistance to the migration of ions in the electrolytic solution and has excellent electrolytic solution impregnation ability and safety.

[0106] Specifically, as the separator, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a homopolymer of ethylene, a homopolymer of propylene, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer; or a laminate structure of two or more layers thereof can be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high melting point glass fibers, polyethylene terephthalate fibers, etc. may be used. 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 used in a single-layer or multi-layer structure.

[0107] The lithium secondary battery according to the present invention as described above can be usefully used in portable devices such as mobile phones, notebook computers, digital cameras, etc.; and in the field of electric vehicles such as hybrid electric vehicles (HEV).

[0108] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same are provided.

[0109] The battery module or battery pack can be used as a power source for any one or more of medium and large-sized devices, including power tools, electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); and power storage systems.

[0110] Although the outer shape of the lithium secondary battery of the present invention is not particularly limited, it may be, for example, a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0111] The lithium secondary battery according to the present invention can be used not only as a battery cell for a small device but also preferably as a unit cell in a medium and large-sized battery module including a large number of battery cells.

[0112] Hereinafter, the present invention will be specifically described with reference to specific examples.

[0113] <Example> Example 1. (Manufacture of non-aqueous electrolyte) Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 30:70, and then LiPF6 was dissolved to a concentration of 1.0 M to produce a non-aqueous organic solution. 0.5 wt% of the compound represented by Chemical Formula 1A (Cas No. 119827-21-3), 0.5 wt% of vinylene carbonate (VC), 0.5 wt% of 1,3-propane sultone (PS), and the balance of the non-aqueous organic solution were mixed to produce 100 wt% of a non-aqueous electrolyte.

[0114] (Manufacture of lithium secondary battery) Positive electrode active material (LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03Oxygen (O2), a conductive material (carbon nanotubes), and a binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent at a weight ratio of 98.0:0.7:1.3 to produce a positive electrode mixture slurry (solid content: 76.5% by weight). The positive electrode mixture slurry was applied to one side of a positive electrode current collector (Al thin film) with a thickness of 12 μm, followed by drying and roll pressing to produce a positive electrode.

[0115] Anode active material (artificial graphite), a conductive material (carbon black), and a binder (styrene-butadiene rubber) were added to distilled water as a solvent at a weight ratio of 96.5:1.5:2.0 to produce a negative electrode mixture slurry (solid content: 50% by weight). The negative electrode mixture slurry was applied to one side of a negative electrode current collector (Cu thin film) with a thickness of 8 μm, followed by drying and roll pressing to produce a negative electrode.

[0116] In a dry room, a polyethylene porous film separator was interposed between the positive electrode and the negative electrode produced above, and then the non-aqueous electrolyte produced above was injected to manufacture a secondary battery.

[0117] Example 2. A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by Chemical Formula 1B (Cas No. 71387-23-0) was used instead of the compound represented by Chemical Formula 1A during the production of the non-aqueous electrolyte.

[0118] Example 3. A lithium secondary battery was manufactured in the same manner as in Example 1, except that VC and PS were not added during the production of the non-aqueous electrolyte.

[0119] Example 4. During the production of the positive electrode, a lithium secondary battery was manufactured in the same manner as in Example 1, except that LiCoO2 was used instead of LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03 O2.

[0120] Example 5 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the compound represented by Chemical Formula 2A was used instead of the compound represented by Chemical Formula 1A (Cas No. 119827-21-3) during the production of the non-aqueous electrolyte.

[0121] Example 6 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 2, except that the compound represented by Chemical Formula 2B was used instead of the compound represented by Chemical Formula 1B (Cas No. 71387-23-0) during the production of the non-aqueous electrolyte.

[0122] Comparative Example 1. A lithium secondary battery was produced in the same manner as in Example 1, except that the compound represented by Chemical Formula 1A was not added during the production of the non-aqueous electrolyte.

[0123] Comparative Example 2. A lithium secondary battery was produced in the same manner as in Example 1, except that coumarin was used instead of the compound represented by Chemical Formula 1A during the production of the non-aqueous electrolyte.

[0124] Comparative Example 3. A lithium secondary battery was produced in the same manner as in Comparative Example 2, except that VC and PS were not added during the production of the non-aqueous electrolyte.

[0125] Comparative Example 4. During the production of the positive electrode, a lithium secondary battery was produced in the same manner as in Comparative Example 1, except that LiCoO2 was used instead of LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03 O2.

[0126] Experimental Example 1. High-temperature life evaluation For each of the lithium secondary batteries manufactured in the above Examples and Comparative Examples, after performing an activation (formation) process at a rate of 0.2C at 25°C, the gas inside the battery was removed by a degassing process. For the lithium secondary battery from which the gas was removed, at a temperature of 45°C, constant current / constant voltage (CC / CV) charging up to 4.2V at a rate of 0.33C and 0.05C cut off charging were performed, and constant current (CC) discharging up to 2.5V at a rate of 0.33C was performed.

[0127] Performing the above charge / discharge once each was defined as one cycle, and the results of measuring the discharge capacity in the initial state (one cycle) were described as the initial capacity in Table 1 below. After repeating the same charge / discharge 200 times, the discharge capacity was measured, the retention rate with respect to the initial capacity was calculated, and it was described as the capacity retention rate in Table 1 below.

[0128] Experimental Example 2. High-temperature storage evaluation For each of the lithium secondary batteries manufactured in the above Examples and Comparative Examples, after performing an activation (formation) process at a rate of 0.2C at 25°C, the gas inside the battery was removed by a degassing process. Then, at room temperature (25°C), charging under constant current / constant voltage conditions up to 4.2V at a rate of 0.33C and 0.05C cut off charging were performed, and discharging was carried out to 2.5V at 0.33C. The discharge capacity measured at this time was described as the initial capacity in Table 1 below.

[0129] Thereafter, after storing the lithium secondary battery at 60°C for 4 weeks, it was transferred to a charger at room temperature (25°C), and then charging under constant current / constant voltage conditions up to 4.2V at a rate of 0.33C and 0.05C cut off charging were performed, and discharging was carried out to 2.5V at 0.33C. The discharge capacity measured at this time and the retention rate with respect to the initial capacity were described in Table 1 below.

[0130]

Table 1

[0131] From the results in Table 1 above, it can be confirmed that the batteries of Examples 1, 2, 5, and 6 manufactured using the electrolyte containing the compound represented by Chemical Formula 1 of the present application are superior in both high-temperature life characteristics and high-temperature storage characteristics compared to the battery of Comparative Example 1 manufactured using the electrolyte not containing the compound represented by Chemical Formula 1, and the battery of Comparative Example 2 manufactured using the electrolyte containing coumarin instead of the compound represented by Chemical Formula 1.

[0132] Even when comparing the batteries of Example 3 and Comparative Example 3 manufactured using the electrolyte not containing VC and PS, it can be seen that the battery of Example 3 containing the compound represented by the chemical formula 1 is superior in high-temperature life characteristics and high-temperature storage characteristics.

[0133] Also, even when the positive electrode material is changed to LCO, by comparing the results of Example 4 and Comparative Example 4, it can be confirmed that by including the compound represented by Chemical Formula 1 in the electrolyte, the high-temperature life characteristics and high-temperature storage characteristics can be improved.

Claims

1. A non-aqueous electrolyte for a lithium secondary battery, comprising a lithium salt, an organic solvent, and a compound represented by the following Chemical Formula 1, wherein the organic solvent includes a mixture of a cyclic carbonate solvent and a linear carbonate solvent: 【Chemical 1】 (In the above Chemical Formula 1, R1 is an alkyl group having 1 to 10 carbon atoms, R2 is an alkylene group having 1 to 10 carbon atoms, L is a direct bond, -O-, -COO-, -RO-, or -R'COO-, wherein R and R' are each independently an alkylene group having 1 to 10 carbon atoms, and m is any integer from 0 to 5.)

2. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, wherein the compound represented by Chemical Formula 1 includes at least one selected from the group consisting of a compound represented by the following Chemical Formula 1-1 and a compound represented by the following Chemical Formula 2-1: 【Chemical 2】 [Chemical Formula 3] (In Chemical Formula 1-1 and Chemical Formula 2-1, R1, R2, L, and m are as defined in Chemical Formula 1 above.)

3. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, wherein L in Chemical Formula 1 is -O- or -COO-.

4. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, wherein the compound represented by Chemical Formula 1 includes at least one selected from the group consisting of a compound represented by the following Chemical Formula 1-2, a compound represented by the following Chemical Formula 1-3, a compound represented by the following Chemical Formula 2-2, and a compound represented by the following Chemical Formula 2-3: 【Chemical Formula 4】 【Chemical Formula 5】 [[Chemical Formula 6]] 【Chemical Formula 7】 (In Chemical Formula 1-2, Chemical Formula 1-3, Chemical Formula 2-2, and Chemical Formula 2-3, R1, R2, and m are as defined in Chemical Formula 1 above.)

5. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, wherein the compound represented by Chemical Formula 1 includes at least one selected from the group consisting of a compound represented by the following Chemical Formula 1A, a compound represented by the following Chemical Formula 1B, a compound represented by the following Chemical Formula 2A, and a compound represented by the following Chemical Formula 2B: [Chemical Formula 8] 【Chemical Formula 9】 【Chemical Formula 10】 【Chemical Formula 11】

6. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, wherein the content of the compound represented by Chemical Formula 1 is 0.1% by weight to 5% by weight based on the total weight of the non-aqueous electrolyte.

7. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, wherein the content of the compound represented by Chemical Formula 1 is 0.1% by weight to 1% by weight based on the total weight of the non-aqueous electrolyte.

8. The non-aqueous electrolyte for a lithium secondary battery according to claim 1, further comprising one or more additives selected from vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, ethylene sulfate, lithium difluorooxalate borate, and lithium difluorophosphate.

9. 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, A lithium secondary battery comprising the non-aqueous electrolyte according to any one of claims 1 to 8.

10. The lithium secondary battery according to claim 9, wherein the positive electrode active material contains a lithium composite transition metal oxide represented by the following chemical formula 3: [Chemical formula 3] Li １＋ｘ (Ni ａ Co ｂ Mn ｃ M ｄ )O ２ (In the above chemical formula 3, M is one or more selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, 1 + x, a, b, c, and d are the atomic fractions of Li, Ni, Co, Mn, and M, respectively, 0 ≦ x ≦ 0.2, 0.50 ≦ a < 1, 0 < b ≦ 0.25, 0 < c ≦ 0.25, 0 ≦ d ≦ 0.1, and a + b + c + d = 1.)

11. The lithium secondary battery according to claim 10, wherein a, b, c, and d in the chemical formula 3 are 0.80 ≦ a ≦ 0.95, 0.025 ≦ b ≦ 0.15, 0.025 ≦ c ≦ 0.15, and 0 ≦ d ≦ 0.05, respectively.

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