Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery including a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte includes a lithium salt, a non-aqueous organic solvent, a first additive which is a compound represented by the following Chemical Formula 1, and one or more second additives selected from the group consisting of vinylene carbonate and vinyl ethylene carbonate, the positive electrode includes a positive electrode active material represented by the following Chemical Formula 2 as a positive electrode active material, and the negative electrode includes a carbon material capable of reversibly intercalating / deintercalating lithium ions as a negative electrode active material. JPEG2024524976000010.jpg32170 (In the above Chemical Formula 1, R1 may be hydrogen or an alkyl group having 1 to 5 carbon atoms, and n may be an integer of 3 to 8.) [Chemical formula 2] Li x Ni a Co b M 1 c M 2 d O2 (In the above Chemical Formula 2, M 1 is one or more selected from Mn and Al, 2 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.90≦x≦1.1, 0.80≦a<1.0, 0

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0014469, filed on February 3, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

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

[0003] In recent years, the development of the information society has led to the development of personal IT devices and computer networks, which has increased society's overall dependence on electrical energy. This has led to a demand for the development of battery technology that can efficiently store and utilize electrical energy.

[0004] In particular, with growing interest in solving environmental problems and realizing a sustainable recycling-based society, research into electricity storage devices such as lithium-ion batteries and electric double-layer capacitors is being conducted extensively.

[0005] Among energy storage devices, lithium-ion batteries have been attracting attention as the battery system with the highest theoretical energy density.

[0006] The lithium-ion battery is mainly composed of a positive electrode made of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte serving as a medium for transferring lithium ions, and a separator. Of these, the electrolyte is known to be a component that has a significant impact on the stability and safety of the battery, and much research into this topic is currently underway.

[0007] However, as lithium secondary batteries are charged and discharged, the positive electrode active material may structurally collapse due to decomposition products of lithium salts contained in the electrolyte, which may result in a decrease in positive electrode performance. Furthermore, when the positive electrode structure collapses, transition metal ions may leach out from the surface of the positive electrode. These leachable transition metal ions are electro-deposited on the positive or negative electrode, increasing the resistance of the positive electrode or degrading the negative electrode, and destroying the solid electrolyte interphase (SEI), leading to further electrolyte decomposition and resulting in increased battery resistance and reduced battery life.

[0008] Such a deterioration in battery performance tends to be accelerated when the potential of the positive electrode increases or when the battery is exposed to high temperatures.

[0009] Therefore, there is an urgent need to research electrolytes that can form a stable SEI film on the surface of the electrode in order to suppress the elution of transition metal ions from the positive electrode or prevent the deterioration of the negative electrode. Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a lithium secondary battery containing a non-aqueous electrolyte having a composition that allows the formation of a coating film on the surface of an electrode that is stable even at high temperatures and has low resistance.

[0011] That is, an object of the present invention is to provide a lithium secondary battery containing the nonaqueous electrolyte for lithium secondary batteries, which has improved high-temperature stability, battery flame retardancy, and high-temperature performance. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention provides a lithium secondary battery including a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte includes a lithium salt, a non-aqueous organic solvent, a first additive which is a compound represented by the following Chemical Formula 1, and one or more second additives selected from the group consisting of vinylene carbonate and vinyl ethylene carbonate, the positive electrode includes a positive electrode active material represented by the following Chemical Formula 2 as a positive electrode active material, and the negative electrode includes a carbon material capable of reversibly intercalating / deintercalating lithium ions as a negative electrode active material.

[0013] [ka]

[0014] In the above chemical formula 1, R1 may be hydrogen or an alkyl group having 1 to 5 carbon atoms, and n may be an integer of 3 to 8.

[0015] [Chemical formula 2] Li x Ni a Co b M 1 c M 2 d O2

[0016] In the above chemical formula 2, M 1 is one or more selected from Mn and Al, and M 2 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.90≦x≦1.1, 0.80≦a<1.0, 0 <b<0.2、0<c<0.2、0≦d≦0.1である。 [Effects of the Invention]

[0017] The compound of the present invention represented by Chemical Formula 1 contains an acrylate group and a fluorine-substituted alkyl group having 3 or more carbon atoms in its structure, and thus can form a strong SEI coating containing elemental fluorine on the surface of an electrode.

[0018] Specifically, the compound represented by Chemical Formula 1 of the present invention is electrochemically decomposed on the surface of the electrode prior to vinylene carbonate and / or vinylethylene carbonate to form a stable coating, and can also promote the additional coating formation reaction of vinylene carbonate and / or vinylethylene carbonate.

[0019] Furthermore, in the nonaqueous electrolyte of the present invention, the compound represented by Chemical Formula 1 contains, in its molecular structure, an alkyl group substituted with fluorine, which has excellent flame retardancy and non-flammability, and which acts as a scavenger of radicals resulting from fluorine, while also ensuring excellent oxidation resistance.

[0020] Furthermore, the present invention provides a lithium secondary battery using a high-nickel positive electrode active material and a carbon material capable of reversibly intercalating / deintercalating lithium ions in combination with a first additive and a second additive. This allows for the easy suppression of radicals formed due to the structural instability of the high-nickel positive electrode active material, thereby improving the flame retardancy and oxidation resistance of the lithium secondary battery. Furthermore, after the reduction reaction of the first additive, which is reduced at a higher potential, the reduction reaction of the second additive proceeds in stages, forming a coating derived from the second additive on top of the coating derived from the first additive, thereby forming a coating with excellent durability. As a result, a lithium secondary battery with excellent high-temperature stability, battery flame retardancy, and high-temperature performance can be realized. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will now be described in more detail.

[0022] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0023] On the other hand, in this specification, the terms "comprise," "include," "comprise," or "have" 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 possibility of addition of one or more other features, numbers, steps, components, or combinations thereof.

[0024] Before describing the present invention, it is important to note that in the description of "number of carbon atoms a to b" in the specification, "a" and "b" refer to 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 "alkyl group having 1 to 5 carbon atoms" refers to an alkyl group containing 1 to 5 carbon atoms, i.e., -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3)CH3, and -CH(CH3)CH2CH3.

[0025] In this specification, both the alkyl group and the alkylene group may be substituted or unsubstituted. Unless otherwise defined, the term "substituted" means that at least one hydrogen atom bonded to a carbon atom is substituted with an element other than hydrogen, such as 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, a nitrile group, an aryl group having 6 to 20 carbon atoms, a heteroaryl group having 2 to 20 carbon atoms, or a haloaryl group having 6 to 20 carbon atoms.

[0026] non-aqueous electrolyte The non-aqueous electrolyte for a lithium secondary battery according to the present invention may include a lithium salt, a non-aqueous organic solvent, a first additive which is a compound represented by the following Chemical Formula 1, and one or more second additives selected from the group consisting of vinylene carbonate and vinyl ethylene carbonate:

[0027] [ka]

[0028] In the above chemical formula 1, R1 may be hydrogen or an alkyl group having 1 to 5 carbon atoms, and n may be an integer of 3 to 8.

[0029] (1) Lithium salt First, the lithium salt will be described as follows.

[0030] The lithium salt may be any of those commonly used in non-aqueous electrolytes for lithium secondary batteries, without any particular limitation. For example, a lithium salt having a cation of Li + and as an anion, F - , Cl - , Br - , I -, NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO4 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , (PO2F2) - , (FSO2)(POF2)N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - , and SCN - It may include at least one selected from the group consisting of:

[0031] Specifically, the lithium salts include LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10, LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO2CF2CF3)2 (lithium bis(perfluoroethanesulfonyl)imide; LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI). In addition to these, any lithium salt commonly used in the electrolyte of a lithium secondary battery can be used without any limitation.

[0032] The lithium salt can be varied as appropriate within a range that is normally usable, but to obtain the optimum effect of forming a corrosion-preventing coating on the electrode surface, it may be contained in the electrolyte at a concentration of 0.1 M to 4.0 M, preferably 0.5 M to 3.0 M, and most preferably 0.5 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the viscosity of the nonaqueous electrolyte can be controlled to achieve optimum impregnation, the mobility of lithium ions can be improved, and the capacity characteristics and cycle characteristics of the lithium secondary battery can be improved.

[0033] (2) Non-aqueous organic solvent The non-aqueous organic solvent may be any of various organic solvents commonly used in non-aqueous electrolytes, and may be any type that can minimize decomposition due to oxidation reactions during the charge / discharge process of the secondary battery and exhibit desired properties together with the additives.

[0034] Specifically, the non-aqueous organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, a linear ester organic solvent, or a mixture thereof.

[0035] The cyclic carbonate organic solvent is a highly viscous organic solvent that has a high dielectric constant and therefore easily dissociates the lithium salt in the non-aqueous electrolyte. Specific examples of the cyclic carbonate organic solvent include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate, and among these, ethylene carbonate may be included.

[0036] The linear carbonate organic solvent is an organic solvent having low viscosity and low dielectric constant, and specific examples thereof may include at least one organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, and specifically may include ethyl methyl carbonate (EMC).

[0037] Linear ester-based organic solvents are solvents that are relatively more stable at high temperatures and during high-voltage operation than cyclic carbonate-based organic solvents, and can improve the drawback of cyclic carbonate-based organic solvents, which cause gas generation during high-temperature operation, while also achieving high ionic conductivity.

[0038] Specific examples of the linear ester organic solvent include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, and specifically, at least one of ethyl propionate and propyl propionate.

[0039] Furthermore, the non-aqueous electrolyte of the present invention may further contain a cyclic ester organic solvent, if necessary.

[0040] The cyclic ester organic solvent may contain at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0041] (3) First additive The non-aqueous electrolyte according to the present invention may contain a compound represented by the following chemical formula 1 as a first additive.

[0042] [ka]

[0043] In the above chemical formula 1, R1 may be hydrogen or an alkyl group having 1 to 5 carbon atoms, and preferably, R1 may be hydrogen.

[0044] In Chemical Formula 1, n may be an integer of 3 to 8, preferably an integer of 4 to 8, and more preferably an integer of 5 to 8. When the integer n satisfies the above range, the thermal properties of the compound itself can be improved, and the stability of the coating formed therefrom can be expected. When n is less than 3 in Chemical Formula 1, the molecule becomes smaller and the fluorine content decreases, resulting in a lower boiling point, reduced flame retardancy, and weaker electrochemical decomposition, resulting in reduced high-temperature durability. As a result, gas generation and deterioration of swelling properties may occur during high-temperature storage. Furthermore, when n is more than 8 in Chemical Formula 1, the fluorine content is excessive, which increases the viscosity and non-polarity of the material and reduces its solubility in the electrolyte, potentially resulting in deterioration of battery performance.

[0045] Specifically, the compound represented by Chemical Formula 1 may include at least one of compounds represented by the following Chemical Formula 1-1 and Chemical Formula 1-2.

[0046] [ka]

[0047] [ka]

[0048] The compound represented by Chemical Formula 1 has a double bond (C=C) functional group contained in its molecular structure that undergoes an electrochemical reaction during electrochemical decomposition, forming a strong SEI film containing elemental fluorine on the surface of the negative electrode. Furthermore, the fluorine-substituted alkyl group contained in the molecular structure, which has excellent flame retardancy and non-flammability, can form a passivation film on the surface of the positive electrode that acts as a scavenger for radicals originating from elemental fluorine and ensures excellent oxidation resistance. As a result, side reactions between the electrode and the electrolyte are suppressed, providing a lithium secondary battery with improved life characteristics at room temperature and low temperatures.

[0049] In particular, the compound represented by Chemical Formula 1 of the present invention contains an ethylene group (-CH2-CH2-) between the acrylate functional group and the terminal fluorine-substituted alkyl group, and therefore has increased flexibility due to the increased molecular chain length of the linking group compared to compounds such as 2,2,3,3,4,4,4-heptafluorobutyl acrylate, which contain a methylene group (-CH2-) between the acrylate functional group and the terminal fluorine-substituted alkyl group. As a result, a coating derived from such a compound can be formed on the surface of a negative electrode with improved durability.

[0050] Vinylene carbonate and / or vinylethylene carbonate are used as electrolyte additives because they form a stable coating during battery operation. However, when a compound containing three or more oxygen atoms in its unit structure, such as vinylene carbonate and / or vinylethylene carbonate, forms an electrode coating during the initial battery operation, oxidation stability is reduced and many side reactions occur on the electrode surface. In contrast, the compound represented by Chemical Formula 1 of the present invention is electrochemically decomposed before vinylene carbonate and / or vinylethylene carbonate at the electrode, forming a stable coating on the electrode surface, thereby suppressing side reactions on the electrode surface. That is, as described above, the compound represented by Chemical Formula 1 of the present invention has a structural feature in which two oxygen atoms are contained in its molecular structure and an acrylate functional group and a terminal fluorine-substituted alkyl group are linked (bonded) via an ethylene group (—CH2-CH2-). This allows a low-resistance and strong SEI to be formed on the surface of the electrode before side reactions occur, thereby suppressing not only an increase in interfacial resistance but also preventing the electrode surface from being exposed and suppressing side reactions between the electrode and the electrolyte. As a result, the SEI film is strengthened at the anode, and at the cathode, the elution of transition metals from the cathode is effectively controlled, improving high-temperature stability. This allows for the realization of a lithium secondary battery with excellent high-temperature storage properties and high-temperature cycle properties, as well as reduced battery swelling.

[0051] The first additive may be included in an amount of 0.1 wt % to 5 wt %, preferably 0.1 wt % to 4 wt %, and more preferably 2 wt % to 4 wt %, based on the total weight of the non-aqueous electrolyte. When the content of the first additive satisfies the above range, a stable coating is formed, effectively preventing transition metals from leaching from the positive electrode at high temperatures, thereby achieving excellent high-temperature durability. That is, when the first additive is included in the non-aqueous electrolyte at 0.1 wt % or more, the coating formation effect is improved, and a stable SEI film is formed even during high-temperature storage. This prevents resistance increases and capacity decreases even after high-temperature storage, thereby improving various performances. Furthermore, when the first additive is included in an amount of 5 wt % or less, formation of an excessively thick coating during initial charging can be prevented, thereby preventing resistance increases, thereby preventing a decrease in the initial capacity and output characteristics of the secondary battery.

[0052] (4) Second additive The nonaqueous electrolyte of the present invention may contain, as a second additive, one or more selected from the group consisting of vinylene carbonate and vinyl ethylene carbonate. Preferably, the second additives contain both vinylene carbonate and vinyl ethylene carbonate, which can maximize high-temperature stability.

[0053] The second additive, vinylene carbonate and / or vinylethylene carbonate, is a substance capable of forming a stable SEI film during battery operation, and in particular, when used in combination with the compound represented by Chemical Formula 1 of the present invention, it can promote an enhanced film formation reaction.

[0054] The second additive may be included in an amount of 0.01 wt % to 3 wt %, preferably 0.10 wt % to 1.5 wt %, and more preferably 0.1 wt % to 1 wt %, based on the total weight of the non-aqueous electrolyte. When the content of the second additive satisfies the above range, stable coatings are formed on the negative and positive electrodes, which can help improve the life of the secondary battery.

[0055] Meanwhile, in the nonaqueous electrolyte for a lithium secondary battery of the present invention, the weight ratio of the first additive to the second additive may be 1:0.002 to 1:30, preferably 1:0.1 to 1:15, and more preferably 1:0.2 to 1:10.

[0056] When the weight ratio of the first additive to the second additive is within the above range, the reduction reaction of the first additive not only forms a coating film on the negative electrode alone, but also promotes the reduction reaction of the second additive, which helps form a coating film with excellent durability. In addition, the effect of suppressing the generation of radicals caused by the fluorine component of the additive can impart flame retardancy and high-temperature stability.

[0057] (5) Third additive In addition, the non-aqueous electrolyte of the present invention may further contain other third additives to prevent the non-aqueous electrolyte from being decomposed in a high-power environment, which may cause the collapse of the negative electrode, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery expansion at high temperatures.

[0058] Examples of such third additives include at least one selected from the group consisting of halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate or phosphite compounds, borate compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0059] Examples of the halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0060] The sultone compound may be, for example, at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0061] The sulfate-based compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), methyl trimethylene sulfate (MTMS), or the like.

[0062] The phosphate- or phosphite-based compound may be, for example, one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0063] Examples of the borate-based compounds include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB) which can form a coating on the surface of the negative electrode, and lithium bisoxalateborate (LiB(C2O4)2, LiBOB).

[0064] The benzene-based compound may be fluorobenzene, the amine-based compound may be triethanolamine, ethylenediamine, or the like, and the silane-based compound may be tetravinylsilane, or the like.

[0065] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples thereof include LiPO2F2 and LiBF4.

[0066] Among such third additives, in order to form a stronger SEI coating on the surface of the negative electrode during the initial activation step, the third additive may contain a third additive that has an excellent effect of forming a coating on the surface of the negative electrode, specifically, at least one selected from the group consisting of propene sultone, ethylene sulfate, fluoroethylene carbonate (FEC), LiBF4, and lithium oxalyl difluoroborate (LiODFB).

[0067] The third additive may be a mixture of two or more compounds, and may be contained in an amount of 0.01 wt % to 20 wt %, specifically 0.01 wt % to 10 wt %, based on the total weight of the non-aqueous electrolyte.

[0068] When the third additive is contained in the above range, a secondary battery with further improved performance can be manufactured. For example, when the third additive is contained in an amount of 0.01 wt % or more, the durability of the SEI layer can be improved while minimizing the increase in resistance. When the third additive is contained in an amount of 20 wt % or less, the SEI layer can be maintained for a long period of time while maintaining an acceptable increase in resistance.

[0069] Lithium secondary battery The present invention provides a lithium secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte of the present invention.

[0070] The lithium secondary battery of the present invention may be manufactured by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode are sequentially stacked, housing the electrode assembly in a battery case, and then injecting the nonaqueous electrolyte of the present invention into the battery case.

[0071] The method for manufacturing the lithium secondary battery of the present invention may be manufactured and applied by a conventional method known in the art, as will be described in detail below.

[0072] (1) Positive electrode The positive electrode according to the present invention includes a positive electrode active material layer containing a positive electrode active material, and the positive electrode active material layer may further include a conductive material and / or a binder, as necessary.

[0073] The positive electrode according to the present invention may include a lithium-nickel-manganese-cobalt-based oxide represented by the following Chemical Formula 2 as a positive electrode active material. In particular, when the positive electrode active material of a lithium secondary battery includes a combination of a first additive and a second additive along with a high-nickel positive electrode active material such as that represented by Chemical Formula 2, radicals formed due to the structural instability of the high-nickel positive electrode active material can be easily suppressed. This has the effect of improving the flame retardancy and oxidation resistance of the lithium secondary battery.

[0074] [Chemical formula 2] Li x Ni a Co b M 1 c M 2 d O2

[0075] In the above Chemical Formula 2, the M 1 is one or more selected from Mn and Al, and may be preferably Mn or a combination of Mn and Al.

[0076] M 2 may be one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S.

[0077] The x represents the atomic fraction of lithium in the lithium transition metal oxide, and may be 0.90≦x≦1.1, preferably 0.95≦x≦1.08, and more preferably 1.0≦x≦1.08.

[0078] The a represents the atomic fraction of nickel among the metal elements excluding lithium in the lithium transition metal oxide, and may be 0.80≦a<1.0, preferably 0.80≦a≦0.95, and more preferably 0.80≦a≦0.90. When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0079] Said b represents the atomic fraction of cobalt among the metal elements excluding lithium in the lithium transition metal oxide, and may be 0 < b < 0.2, 0 < b ≤ 0.15, or 0.01 ≤ b ≤ 0.10.

[0080] Said c represents the atomic fraction of M among the metal elements excluding lithium in the lithium transition metal oxide, and may be 0 < c < 0.2, 0 < c ≤ 0.15, or 0.01 ≤ c ≤ 0.10. 1

[0081] Said d represents the atomic fraction of M among the metal elements excluding lithium in the lithium transition metal oxide, and may be 0 ≤ d ≤ 0.1 or 0 ≤ d ≤ 0.05. 2

[0082] The positive electrode active material may further contain, as a compound capable of additional reversible intercalation and deintercalation of lithium, specifically, 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 (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., 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 (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-manganese-cobalt-based oxide (e.g., Li(Ni p Co q Mnr )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (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, p2 + q2 + r2 + s2 = 1), etc.), lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (where M contains any one or two or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X contains any one or two or more elements selected from the group consisting of F, S, and N, -0.5 ≦ a ≦ 0.5, 0 ≦ b ≦ 0.1, 0 ≦ x ≦ 0.5), etc., and any one or two or more of these compounds may be included.

[0083] Among them, from the point of being able to enhance the capacity characteristics and stability of the battery, the additional positive electrode active material may contain at least one selected from the group consisting of lithium-cobalt-based oxide, lithium-manganese-based oxide, lithium-nickel-manganese-cobalt-based oxide, and lithium-nickel-cobalt-transition metal (M) oxide.

[0084] The positive electrode active material may be included in an amount of 80 wt% to 99 wt%, specifically 90 wt% to 99 wt%, based on the total weight of the solid content in the positive electrode slurry. In this case, if the content of the positive electrode active material is 80 wt% or less, the energy density may be reduced, resulting in a decrease in capacity.

[0085] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and examples thereof include carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powders such as natural graphite, artificial graphite, and graphite with highly developed crystal structures; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0086] The conductive material is usually added in an amount of 1% by weight to 30% by weight based on the total weight of the solid content in the positive electrode active material layer.

[0087] The binder is a component that functions to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector, and is typically added in an amount of 1 to 30 wt % based on the total weight of the solids in the positive electrode active material layer. Examples of such binders include fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders.

[0088] The positive electrode of the present invention as described above may be manufactured by a method known in the art. For example, the positive electrode may be manufactured by dissolving or dispersing a positive electrode active material, a binder, and / or a conductive material in a solvent to prepare a positive electrode slurry, which is then coated on a positive electrode current collector, followed by drying and rolling to form a positive electrode active material layer, or by casting the positive electrode active material layer on a separate support, peeling off the support, and laminating the resulting film on a positive electrode current collector.

[0089] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like may be used.

[0090] 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 and a conductive material, are contained. For example, the solvent may be contained so that the solids concentration in the active material slurry containing the positive electrode active material, and optionally a binder and a conductive material, is 10 wt % to 90 wt %, preferably 30 wt % to 80 wt %.

[0091] (2) Negative electrode The negative electrode according to the present invention includes a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material layer may further include a conductive material and / or a binder, as necessary.

[0092] The negative electrode according to the present invention may include, as the negative electrode active material, a carbon material capable of reversibly intercalating / deintercalating lithium ions. In particular, when the negative electrode active material of a lithium secondary battery includes a combination of a first additive and a second additive, the reduction reaction of the second additive proceeds stepwise after the reduction reaction of the first additive, which is reduced at a higher potential, and a coating due to the second additive is formed on the coating due to the first additive, resulting in the formation of a strong coating with excellent durability. This facilitates the insertion and extraction of lithium into and extraction from the negative electrode active material, and the formed coating can withstand the expansion and contraction of the negative electrode active material, resulting in a secondary battery with excellent safety and high-temperature durability.

[0093] As the carbon material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative electrode active material generally used in lithium ion secondary batteries can be used without particular limitation. Representative examples thereof include crystalline carbon, amorphous carbon, or these may be used together. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon (low-temperature fired carbon) or hard carbon, mesophase pitch carbide, fired coke, and the like. The negative electrode according to the present invention most preferably may contain graphite (graphite) as the negative electrode active material.

[0094] The negative electrode active material may further contain at least one selected from the group consisting of lithium metal, a metal or an alloy of a metal and lithium, a metal composite oxide, a substance capable of doping and undoping lithium, and a transition metal oxide, if necessary.

[0095] As the metal or the alloy of a metal 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.

[0096] 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) can be used.

[0097] Examples of the substance capable of doping and undoping lithium include Si, SiO x (0 < x ≤ 2), Si-Y alloy (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), Sn, SnO2, Sn-Y (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn), etc. Further, at least one of these may be mixed with SiO2 and used. 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.

[0098] Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0099] The negative electrode active material may be contained at 80% to 99% by weight based on the total weight of the solid content in the negative electrode active material layer.

[0100] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 1 wt % to 20 wt % based on the total weight of the solid content in the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powder such as aluminum 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.

[0101] The binder is a component that aids in bonding between the conductive material, active material, and current collector, and is typically added in an amount of 1 to 30 wt % based on the total weight of the solids in the negative electrode active material layer. Examples of such binders include fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders.

[0102] The negative electrode may be manufactured by a method known in the art, for example, by coating a negative electrode active material slurry prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent onto a negative electrode current collector, rolling and drying the resulting slurry to form a negative electrode active material layer, or by casting the negative electrode active material layer onto a separate support, peeling off the support, and laminating the resulting film onto the negative electrode current collector.

[0103] The negative electrode current collector generally has a thickness of 3 μm to 500 μm. There are no particular limitations on the negative electrode current collector, so long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. Furthermore, as with the positive electrode current collector, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and the negative electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0104] The solvent may include water or an organic solvent such as NMP or alcohol, and may be used in an amount that provides a suitable viscosity when containing the negative electrode active material, and optionally a binder, a conductive material, etc. For example, the solvent may be included so that the solids concentration in the active material slurry containing the negative electrode active material, and optionally a binder and a conductive material, is 50 wt % to 75 wt %, preferably 40 wt % to 70 wt %.

[0105] (3) Separator The separator included in the lithium secondary battery of the present invention may be a commonly used porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, either alone or in a laminate thereof. Alternatively, a commonly used porous nonwoven fabric, for example, a nonwoven fabric made of a high-melting-point glass fiber, a polyethylene terephthalate fiber, or the like, may be used, but is not limited thereto.

[0106] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0107] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0108] Example Example 1 (Production of non-aqueous electrolyte) A non-aqueous solvent was prepared by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 30:70 volume ratio) to a concentration of 1M. 3 g of a compound (first additive) in which R1 is H and n is 5 in the compound of Formula 1, and 0.5 g of vinylene carbonate (VC) (second additive) were added to 96.5 g of the non-aqueous solvent to prepare a non-aqueous electrolyte.

[0109] (Secondary battery manufacturing) Cathode active material (LiNi 0.8 Mn 0.1 Co 0.1A cathode active material slurry (solid concentration 60 wt%) was prepared by adding 02), a conductive material (carbon black), and a binder (polyvinylidene fluoride) in a weight ratio of 97.5:1:1.5 to a solvent, N-methyl-2-pyrrolidone (NMP). The cathode active material slurry was applied to a cathode current collector (Al thin film) with a thickness of 15 μm, dried, and then roll-pressed to prepare a cathode.

[0110] A negative electrode active material slurry (solid content concentration 50 wt%) was prepared by adding a negative electrode active material (graphite), a conductive material (carbon black), and a binder (polyvinylidene fluoride) to distilled water in a weight ratio of 96:0.5:3.5. The negative electrode active material slurry was applied to a negative electrode current collector (Cu thin film) with a thickness of 8 μm, dried, and then roll-pressed to prepare a negative electrode.

[0111] The positive and negative electrodes prepared by the above method were laminated together with a polyethylene porous film separator to prepare an electrode assembly, which was then placed in a battery case, and 150 μL of the non-aqueous electrolyte was poured into the battery case, which was then sealed to prepare a pouch-type lithium secondary battery (battery capacity: 50 mAh).

[0112] Example 2 A non-aqueous solvent was prepared by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 30:70 volume ratio) to a concentration of 1 M, and 3 g of a compound (first additive) in which R1 is H and n is 5 in the compound of Chemical Formula 1, and 0.5 g of vinyl ethylene carbonate (VEC) (second additive) were added to 96.5 g of the non-aqueous solvent to prepare a non-aqueous electrolyte. A secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was used to prepare a secondary battery.

[0113] Example 3 A non-aqueous solvent was prepared by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 30:70 volume ratio) to a concentration of 1 M, and 3 g of a compound (first additive) in which R1 is H and n is 5 in the compound of Chemical Formula 1, 0.5 g of vinylene carbonate (VC) (second additive), and 0.5 g of vinyl ethylene carbonate (VEC) (second additive) were added to 96.0 g of the non-aqueous solvent to prepare a non-aqueous electrolyte. A secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was used to prepare a secondary battery.

[0114] Comparative Example 1 A non-aqueous solvent was prepared by dissolving LiPF in an organic solvent (ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 30:70 volume ratio) to a concentration of 1 M, and 0.5 g of vinylene carbonate (VC) was added to 99.5 g of the non-aqueous solvent to prepare a non-aqueous electrolyte. A secondary battery was prepared in the same manner as in Example 1, except that a secondary battery was prepared using this.

[0115] Comparative Example 2 A non-aqueous solvent was prepared by dissolving LiPF in an organic solvent (ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 30:70 volume ratio) to a concentration of 1 M, and 0.5 g of vinyl ethylene carbonate (VEC) (second additive) was added to 99.5 g of the non-aqueous solvent to prepare a non-aqueous electrolyte. A secondary battery was prepared in the same manner as in Example 1, except that a secondary battery was prepared using this.

[0116] Comparative Example 3 A non-aqueous solvent was prepared by dissolving LiPF in an organic solvent (ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 30:70 volume ratio) to a concentration of 1 M, and 0.5 g of vinylene carbonate (VC) and 0.5 g of vinyl ethylene carbonate (VEC) were added to 99.0 g of the non-aqueous solvent to prepare a non-aqueous electrolyte. A secondary battery was prepared in the same manner as in Example 1, except that a secondary battery was prepared using this.

[0117] Comparative Example 4 A non-aqueous solvent was prepared by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 30:70 volume ratio) to a concentration of 1 M, and 3 g of the compound of Formula 1, in which R1 is H and n is 5, was added to 97.0 g of the non-aqueous solvent to prepare a non-aqueous electrolyte. A secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was used to prepare a secondary battery.

[0118] Experimental example - Evaluation of high temperature stability Each of the secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 was activated at 0.1 C / C.

[0119] Thereafter, the temperature of each of the lithium secondary batteries was increased from 30°C to 300°C at a rate of 0.2K / min, and the heat generation initiation temperature and total heat generation amount of the lithium secondary batteries were measured using a multiple module calorimeter.

[0120] [Table 1]

[0121] As shown in Table 1, Examples 1 to 3 have a smaller total calorific value than Comparative Examples 1 to 4, and are therefore superior in high-temperature stability.

Claims

1. A lithium secondary battery including a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte, The non-aqueous electrolyte includes a lithium salt, a non-aqueous organic solvent, a first additive that is a compound represented by the following Chemical Formula 1, and one or more second additives selected from the group consisting of vinylene carbonate and vinyl ethylene carbonate: 【Chemical 1】 In the above Chemical Formula 1, R １ is hydrogen or an alkyl group having 1 to 5 carbon atoms, n is an integer from 3 to 8, the weight ratio of the first additive to the second additive is 1:0.1 to 1:15; The positive electrode includes a positive electrode active material represented by the following Chemical Formula 2: [Chemical formula 2] Li ｘ Ni ａ Co ｂ M １ ｃ M ２ ｄ O ２ (In the above chemical formula 2, M １ is one or more selected from Mn and Al, and M ２ is one or more elements selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.90≦x≦1.1, 0.80≦a<1.0, 0<b<0.2, 0<c<0.2, 0≦d≦0.1; The negative electrode of the lithium secondary battery contains, as a negative electrode active material, a carbon material capable of reversibly intercalating / deintercalating lithium ions.

2. In the above formula 1, R １ The lithium secondary battery according to claim 1 , wherein is hydrogen.

3. 2. The lithium secondary battery of claim 1, wherein the first additive is selected from the group consisting of compounds represented by the following Formula 1-1 and Formula 1-2: 【Chemistry 2】

4. 2. The lithium secondary battery of claim 1, wherein the first additive is contained in an amount of 0.1 wt % to 5 wt % based on the total weight of the non-aqueous electrolyte for the lithium secondary battery.

5. 5. The lithium secondary battery according to claim 1, wherein the second additive is contained in an amount of 0.01 wt % to 3 wt % based on the total weight of the non-aqueous electrolyte for the lithium secondary battery.

6. 2. The lithium secondary battery according to claim 1, wherein the weight ratio of the first additive to the second additive is 1:0.2 to 1:

10.

7. 2. The lithium secondary battery according to claim 1, wherein the lithium salt is contained at a concentration of 0.1M to 4M.

8. 2. The lithium secondary battery of claim 1, wherein the non-aqueous electrolyte further comprises at least one third additive selected from the group consisting of halogen-substituted carbonate-based compounds, sultone-based compounds, sulfate-based compounds, phosphate-based or phosphite-based compounds, borate-based compounds, benzene-based compounds, amine-based compounds, silane-based compounds, and lithium salt-based compounds.

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