Lithium secondary battery

Abstract

To provide a lithium secondary battery capable of suppressing an avalanche of a positive electrode construction by reducing a leakage of a transition metal under a high voltage and a high temperature condition by combining an electrolyte that can effectively protects a positive electrode containing a cobalt-free lithium nickel manganese system oxide as well as using the positive electrode containing the cobalt-free lithium nickel manganese system oxide, and improving a high voltage characteristic and a high temperature characteristic of a battery.SOLUTION: A lithium secondary battery contains: an electrolyte containing a non-aqueous organic solvent, a lithium salt, and an additive agent; a positive electrode containing a positive electrode active material; and a negative electrode containing a negative electrode active material. The non-aqueous organic solvent contains an ethylene carbonate that is less than 5 weight% on the basis of a total weight of the non-aqueous organic solvent. The positive electrode active material contains a lithium nickel manganese system oxide. The additive agent is expressed by a chemical formula 1. The chemical formula 1 is as being defined in a specification.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present description relates to lithium secondary batteries. [Background technology]

[0002] Lithium secondary batteries are rechargeable and have an energy density per unit weight that is more than three times higher than conventional lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and nickel-zinc batteries, and they can be charged quickly. As a result, they have been commercialized for use in laptops, mobile phones, power tools, and electric bicycles, and research and development is being actively conducted to further improve their energy density.

[0003] In particular, as IT devices become increasingly sophisticated, there is a demand for higher-capacity batteries. By expanding the voltage range to achieve higher capacity, the energy density can be increased. However, there is a problem in that the electrolyte is oxidized in the high-voltage range, deteriorating the performance of the positive electrode.

[0004] In particular, cobalt-free lithium nickel manganese oxide as a positive electrode active material is a positive electrode active material that does not contain cobalt in its composition and is composed mainly of nickel, manganese, etc., and positive electrodes containing this are economical and can achieve high energy density, so it is attracting attention as a next-generation positive electrode active material.

[0005] However, when a positive electrode containing a cobalt-free lithium nickel manganese oxide is used in a high voltage environment, the positive electrode structure collapses, causing the elution of transition metals, which can lead to problems such as gas generation inside the cell and capacity reduction. This transition metal elution phenomenon tends to become more severe in high temperature environments, and the eluted transition metals can be precipitated on the surface of the negative electrode and induce side reactions, which can lead to an increase in battery resistance and a decrease in battery life and output characteristics.

[0006] For this reason, there is a demand for an electrolyte that can be used even under high voltage and high temperature conditions when using a positive electrode containing a cobalt-free lithium nickel manganese oxide. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of one embodiment is to provide a lithium secondary battery having improved high voltage and high temperature characteristics by using a positive electrode containing a cobalt-free lithium nickel manganese-based oxide in combination with an electrolyte that can effectively protect the positive electrode containing a cobalt-free lithium nickel manganese-based oxide to reduce the elution of transition metals under high voltage and high temperature conditions, thereby suppressing the collapse of the positive electrode structure. [Means for solving the problem]

[0008] One embodiment of the present invention includes an electrolyte solution including a non-aqueous organic solvent, a lithium salt, and an additive; a positive electrode including a positive electrode active material; and a negative electrode including a negative electrode active material, the non-aqueous organic solvent comprises less than 5 wt. % ethylene carbonate based on the total weight of the non-aqueous organic solvent; The positive electrode active material includes a lithium nickel manganese oxide, The additive provides a lithium secondary battery, comprising a compound represented by the following Chemical Formula 1: [ka] In the above Chemical Formula 1, Ring A is a substituted or unsubstituted C3-C6 heteroaryl group containing at least one nitrogen atom, or a substituted or unsubstituted C3-C6 heterocyclic group containing at least one nitrogen atom; L 1 is a substituted or unsubstituted C1-C3 alkylene group, R 1 is hydrogen or a substituted or unsubstituted C1 to C10 alkyl group.

[0009] The non-aqueous organic solvent may be composed only of a chain carbonate.

[0010] The chain carbonate may be represented by the following chemical formula 2. [ka] In the above Chemical Formula 2 R 2 and R 3 are each independently a substituted or unsubstituted C1 to C20 alkyl group.

[0011] The non-aqueous organic solvent can be at least two of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and ethyl methyl carbonate (EMC).

[0012] The non-aqueous organic solvent may contain ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 0:100 to 50:50.

[0013] Ring A in Chemical Formula 1 can be a substituted or unsubstituted imidazolyl group, a substituted or unsubstituted pyrrolyl group, a substituted or unsubstituted pyrazolyl group, a substituted or unsubstituted triazolyl group, a substituted or unsubstituted pyrrolidinyl group, a substituted or unsubstituted pyridyl group, a substituted or unsubstituted pyrimidinyl group, a substituted or unsubstituted pyrazinyl group, a substituted or unsubstituted triazinyl group, a substituted or unsubstituted piperidinyl group, or a substituted or unsubstituted piperazinyl group.

[0014] Ring A in Formula 1 may contain at least one double bond.

[0015] The formula 1 may be represented by any one of the following formulas 1A to 1O. [ka] [ka] [ka] [ka] In the above Chemical Formula 1A to Chemical Formula 1O, L 1 is a substituted or unsubstituted C1-C3 alkylene group, R 1 and R 4 ~R 8 are each independently a hydrogen atom or a substituted or unsubstituted C1 to C10 alkyl group, m1 is an integer from 1 to 4; m2 is an integer from 1 to 3; m3 is an integer of 1 or 2, m4 is an integer from 1 to 6.

[0016] The compound represented by Chemical Formula 1 may be selected from the compounds listed in Group 1 below. [ka]

[0017] The compound represented by Formula 1 may be included in an amount of 0.05 to 5.0 parts by weight based on 100 parts by weight of the total electrolyte solution for lithium secondary batteries.

[0018] The electrolyte may further include at least one other additive selected from the group consisting of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), and 2-fluorobiphenyl (2-FBP).

[0019] The lithium nickel manganese-based oxide may include a cobalt-free lithium composite oxide represented by the following Chemical Formula 4. [Chemical formula 4] Li a Ni x Mn y M 1 z M 2 w O 2±b X c In the above Chemical Formula 4, 0.5≦a<1.8, 0≦b≦0.1, 0≦c≦0.1, 0≦w<0.1, 0.6≦x<1.0, 0 <y<0.4、0<z<0.1、w+x+y+z=1であり、 M 1 and M. 2 are each independently one or more elements selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Si, Ba, Ca, Ce, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

[0020] The formula 4 may be represented by the following formula 4-1. [Chemical formula 4-1] Li a Ni x1 Mn y1 Alz1 M 2 w1 O 2±b X c In the above Chemical Formula 4-1, 0.5≦a<1.8, 0≦b≦0.1, 0≦c≦0.1, 0≦w1<0.1, 0.6≦x1<1.0, 0 <y1<0.4、0<z1<0.1、w1+x1+y1+z1=1であり、 M 2 are each independently one or more elements selected from Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Si, Ba, Ca, Ce, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

[0021] In the formula 4-1, x1 may be 0.6≦x1≦0.79, y1 may be 0.2≦y1≦0.39, and z1 may be 0.01≦z1<0.1.

[0022] The negative electrode active material may include at least one of graphite and a Si composite.

[0023] The lithium secondary battery may have an upper limit charging voltage of 4.35 V or higher. Effect of the Invention

[0024] In one embodiment, a positive electrode including a cobalt-free lithium nickel manganese-based oxide is combined with an electrolyte capable of effectively protecting the positive electrode to ensure the safety of the phase transition of the positive electrode even in a high temperature and high voltage environment. The electrolyte decomposition and side reactions with the electrode are suppressed to reduce gas generation and simultaneously suppress an increase in the internal resistance of the battery, thereby realizing a lithium secondary battery with improved battery stability and life characteristics. [Brief description of the drawings]

[0025] [Figure 1] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, a lithium secondary battery according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings, which are given by way of example only and are not intended to limit the present invention, but are defined only by the scope of the claims that follow.

[0027] In this specification, unless otherwise defined, "substituted" means that at least one hydrogen atom in a substituent or compound is replaced with deuterium, a halogen group, a hydroxyl group, an amino group, a substituted or unsubstituted C1 to C30 amine group, a nitro group, a substituted or unsubstituted C1 to C40 silyl group, a C1 to C30 alkyl group, a C1 to C10 alkylsilyl group, a C6 to C30 arylsilyl group, a C3 to C30 cycloalkyl group, a C3 to C30 heterocycloalkyl group, a C6 to C30 aryl group, a C2 to C30 heteroaryl group, a C1 to C20 alkoxy group, a C1 to C10 fluoroalkyl group, a cyano group, or a combination thereof.

[0028] In one embodiment of the present invention, "substitution" means that at least one hydrogen of a substituent or compound is replaced with deuterium, a halogen group, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C10 fluoroalkyl group, or a cyano group. In one specific embodiment of the present invention, "substitution" means that at least one hydrogen of a substituent or compound is replaced with deuterium, a halogen group, a C1-C20 alkyl group, a C6-C30 aryl group, a C1-C10 fluoroalkyl group, or a cyano group. In one specific embodiment of the present invention, "substitution" means that at least one hydrogen of a substituent or compound is replaced with deuterium, a halogen group, a C1-C5 alkyl group, a C6-C18 aryl group, a C1-C5 fluoroalkyl group, or a cyano group. In addition, in a specific example of the present invention, "substituted" means that at least one hydrogen of a substituent or compound is replaced with deuterium, a cyano group, a halogen group, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0029] Lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, into cylindrical, square, coin, pouch, and other types depending on the shape, and into bulk and thin film types depending on the size. The structures and manufacturing methods of these batteries are widely known in the art, so detailed description will be omitted.

[0030] Here, a cylindrical lithium secondary battery will be described as an example of the lithium secondary battery. Fig. 1 is a schematic diagram showing a structure of a lithium secondary battery according to an embodiment. Referring to Fig. 1, the lithium secondary battery 100 according to an embodiment includes a battery cell including a positive electrode 114, a negative electrode 112 facing the positive electrode 114, a separator 113 disposed between the positive electrode 114 and the negative electrode 112, and an electrolyte (not shown) impregnating the positive electrode 114, the negative electrode 112, and the separator 113, a battery container 120 including the battery cell, and a sealing member 140 sealing the battery container 120.

[0031] The configuration of the lithium secondary battery 100 according to one embodiment of the present invention will now be described in more detail.

[0032] A lithium secondary battery according to one embodiment of the present invention includes an electrolyte, a positive electrode, and a negative electrode.

[0033] The electrolyte solution includes a non-aqueous organic solvent, a lithium salt, and an additive, the non-aqueous organic solvent includes less than 5 wt % ethylene carbonate based on the total weight of the non-aqueous organic solvent, and the additive can include a compound represented by the following Chemical Formula 1: [ka] In the above Chemical Formula 1, Ring A is a substituted or unsubstituted C3-C6 heteroaryl group containing at least one nitrogen atom, or a substituted or unsubstituted C3-C6 heterocyclic group containing at least one nitrogen atom; L 1 is a substituted or unsubstituted C1-C3 alkylene group, R 1 is hydrogen or a substituted or unsubstituted C1 to C10 alkyl group.

[0034] The positive electrode may include a positive electrode active material including a lithium nickel manganese-based oxide.

[0035] In the case of positive electrode active materials containing lithium nickel manganese oxides, particularly cobalt-free lithium nickel manganese oxides, the structural instability is strong under high voltage conditions, leading to solvent decomposition and dissolution of transition metals, particularly Ni.

[0036] The degradation and short circuit caused by the elution of such transition metals reduces the battery life capacity and causes a sudden increase in resistance.

[0037] However, when the above-mentioned electrolyte is used together, the decrease in the life capacity of the battery and the sudden increase in resistance can be mitigated.

[0038] In particular, by using a positive electrode containing a cobalt-free lithium nickel manganese oxide in an electrolyte containing less than 5 wt % ethylene carbonate based on the total weight of the nonaqueous organic solvent, it is possible to effectively reduce the elution of transition metals under high voltage and high temperature conditions, thereby suppressing the structural collapse of the positive electrode and improving the high voltage and high temperature characteristics of the battery.

[0039] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0040] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent.

[0041] Examples of the carbonate-based solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of the ester-based solvent include methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, caprolactone, etc. Examples of the ether-based solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. The ketone solvent may be cyclohexanone, etc. The alcohol solvent may be ethyl alcohol, isopropyl alcohol, etc., and the aprotic solvent may be nitriles such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc.

[0042] The non-aqueous organic solvent may be used alone or in combination of two or more thereof. When two or more thereof are used in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance, which is widely understood by those skilled in the art.

[0043] As an example, the non-aqueous organic solvent may contain less than 5% by weight of ethylene carbonate based on the total weight of the non-aqueous organic solvent.

[0044] When the content of ethylene carbonate is 5% by weight or more within the above-mentioned range, the activity of Ni increases during high voltage operation, and the oxidation number of Ni tends to be reduced from 4 to 2, and ethylene carbonate, which has low oxidation stability, is oxidized and decomposed, resulting in Ni being dissolved and deposited on the negative electrode.

[0045] As a specific example, the non-aqueous organic solvent may be composed of only a chain carbonate, in which case the resistance increase rate during high temperature storage is significantly reduced, thereby achieving excellent high temperature storage characteristics.

[0046] In this specification, the term "composed only of chain carbonate" means that the organic solvent belonging to the category of chain carbonate is not mixed with a cyclic carbonate or the like and is used alone or in combination.

[0047] In one embodiment, the chain carbonate may be represented by the following chemical formula 2: [ka] In the above Chemical Formula 2 R 2 and R 3 are each independently a substituted or unsubstituted C1 to C20 alkyl group.

[0048] As an example, R 2 and R 3 may each independently be a substituted or unsubstituted C1 to C10 alkyl group, for example, 2 and R 3 may each independently be a substituted or unsubstituted C1 to C5 alkyl group.

[0049] In one embodiment, R 2 and R 3may each independently be a substituted or unsubstituted methyl group, a substituted or unsubstituted ethyl group, a substituted or unsubstituted n-propyl group, a substituted or unsubstituted n-butyl group, a substituted or unsubstituted n-pentyl group, a substituted or unsubstituted iso-butyl group, or a substituted or unsubstituted neo-pentyl group.

[0050] For example, the non-aqueous organic solvent according to one specific embodiment can be at least two of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and ethyl methyl carbonate (EMC).

[0051] The non-aqueous organic solvent according to a most specific embodiment may be a mixed solvent of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC).

[0052] The non-aqueous organic solvent may contain ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 0:100 to 50:50.

[0053] The non-aqueous organic solvent may be more advantageous in terms of improving battery characteristics if it contains more than 50% by volume of dimethyl carbonate (DMC).

[0054] For example, the non-aqueous organic solvent may contain ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 0:100 to 40:60, 0:100 to 30:70, 10:90 to 40:60, or 10:90 to 30:70.

[0055] The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent in addition to the carbonate-based solvent, and the carbonate-based solvent and the aromatic hydrocarbon-based solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0056] As the aromatic hydrocarbon solvent, an aromatic hydrocarbon compound represented by the following formula 3 can be used. [ka] In the above formula 3, R 11 ~R 16 are the same or different and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group having 1 to 10 carbon atoms, and combinations thereof.

[0057] Specific examples of the aromatic hydrocarbon solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorobenzene ... and combinations thereof.

[0058] The lithium salt is a material that is dissolved in a non-aqueous organic solvent and acts as a lithium ion source in a battery to enable basic lithium secondary battery operation and promote the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts include LiPF6, LiBF4, lithium difluoro(oxalate)borate (LiDFOB), LiPO2F2, LiSbF6, LiAsF6, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 and LiB(C2O4)2 (lithium bis(oxalato) borate: LiBOB).

[0059] The lithium salt is preferably used at a concentration within the range of 0.1 M to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, and therefore can exhibit excellent electrolyte performance and can effectively migrate lithium ions.

[0060] Ring A in Chemical Formula 1 can be a substituted or unsubstituted imidazolyl group, a substituted or unsubstituted pyrrolyl group, a substituted or unsubstituted pyrazolyl group, a substituted or unsubstituted triazolyl group, a substituted or unsubstituted pyrrolidinyl group, a substituted or unsubstituted pyridyl group, a substituted or unsubstituted pyrimidinyl group, a substituted or unsubstituted pyrazinyl group, a substituted or unsubstituted triazinyl group, a substituted or unsubstituted piperidinyl group, or a substituted or unsubstituted piperazinyl group.

[0061] Ring A in Formula 1 may contain at least one double bond.

[0062] The formula 1 may be represented by any one of the following formulas 1A to 1O. [ka] [ka] [ka] [ka] In the above Chemical Formula 1A to Chemical Formula 1O, L 1 is a substituted or unsubstituted C1-C3 alkylene group, R 1 and R 4 ~R 8 are each independently a hydrogen atom or a substituted or unsubstituted C1 to C10 alkyl group, m1 is an integer from 1 to 4; m2 is an integer from 1 to 3; m3 is an integer of 1 or 2, m4 is an integer from 1 to 6.

[0063] The compound represented by Chemical Formula 1 may be selected from the compounds listed in Group 1 below. [ka]

[0064] The additive may be included in an amount of 0.05 to 5.0 parts by weight based on 100 parts by weight of the total electrolyte solution (lithium salt + non-aqueous organic solvent) excluding the additive.

[0065] For example, the additive may be included in an amount of 0.05 to 3.0 parts by weight based on 100 parts by weight of the total electrolyte solution (lithium salt+non-aqueous organic solvent) excluding the additive.

[0066] For example, the additive may be included in an amount of 0.1 to 3.0 parts by weight, 0.3 to 3.0 parts by weight, 0.5 to 3.0 parts by weight, or 0.5 to 2.0 parts by weight, based on 100 parts by weight of the entire electrolyte solution excluding the additive (lithium salt + non-aqueous organic solvent).

[0067] When the content of the additive is within the above range, an increase in resistance at high temperatures can be prevented, thereby realizing a lithium secondary battery having improved life characteristics and output characteristics.

[0068] Meanwhile, the electrolyte may further include at least one other additive selected from the group consisting of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), and 2-fluorobiphenyl (2-FBP).

[0069] By further including the other additives, the life span can be further improved and gas generated at the positive and negative electrodes during high temperature storage can be effectively controlled.

[0070] The other additives may be included in an amount of 0.2 to 20 parts by weight, specifically 0.2 to 15 parts by weight, for example 0.2 to 10 parts by weight, based on 100 parts by weight of the total electrolyte solution for lithium secondary batteries.

[0071] When the content of the other additives is within the above range, the increase in film resistance can be minimized, thereby contributing to improved battery performance.

[0072] The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0073] The positive electrode active material may include a lithium nickel manganese oxide.

[0074] For example, the lithium nickel manganese-based oxide may include at least one of cobalt-free lithium composite oxides represented by the following Chemical Formula 4. [Chemical formula 4] Li a Ni x Mn y M 1 z M 2 w O 2±b X c In the above Chemical Formula 4, 0.5≦a<1.8, 0≦b≦0.1, 0≦c≦0.1, 0≦w<0.1, 0.6≦x<1.0, 0 <y<0.4、0<z<0.1、w+x+y+z=1であり、 M 1 and M. 2 are each independently one or more elements selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Si, Ba, Ca, Ce, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

[0075] In this specification, the cobalt-free lithium nickel manganese oxide as the positive electrode active material means a positive electrode active material that does not contain cobalt in its composition and is composed mainly of nickel, manganese, etc.

[0076] Of course, the lithium composite oxide may have a coating layer on its surface, or the lithium composite oxide may be mixed with a compound having a coating layer. The coating layer may include at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds forming the coating layer may be amorphous or crystalline. The coating elements included in the coating layer may include Mg, Al, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer forming process may use any coating method as long as the compound can be coated with such elements in a manner that does not adversely affect the physical properties of the positive electrode active material (e.g., spray coating, immersion method, etc.), and this is well understood by those skilled in the art, so a detailed description will be omitted.

[0077] As an example, Formula 4 may be represented by Formula 4-1 below. [Chemical formula 4-1] Li a Ni x1 Mn y1 Al z1 M 2 w1 O 2±b X c In the above Chemical Formula 4-1, 0.5≦a<1.8, 0≦b≦0.1, 0≦c≦0.1, 0≦w1<0.1, 0.6≦x1<1.0, 0 <y1<0.4、0<z1<0.1、w1+x1+y1+z1=1であり、 M 2 are each independently one or more elements selected from Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Si, Ba, Ca, Ce, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

[0078] In one embodiment, in Chemical Formula 4-1, 0.6 ≦ x1 ≦ 0.9, 0.1 ≦ y1 < 0.4, and 0 < z1 < 0.1, and it can be 0.6 ≦ x1 ≦ 0.8, 0.2 ≦ y1 < 0.4, and 0 < z1 < 0.1.

[0079] For example, x1 of Chemical Formula 4-1 can be 0.6 ≦ x1 ≦ 0.79, y1 can be 0.2 ≦ y1 ≦ 0.39, and z1 can be 0.01 ≦ z1 < 0.1.

[0080] The content of the positive electrode active material can be 90% by weight to 98% by weight based on the total weight of the positive electrode active material layer.

[0081] In one embodiment of the present invention, the positive electrode active material layer can contain a binder. At this time, the content of the binder can be 1% by weight to 5% by weight based on the total weight of the positive electrode active material layer.

[0082] The binder serves to make the positive electrode active material particles adhere well to each other and also make the positive electrode active material adhere well to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0083] As the positive electrode current collector, Al can be used, but is not limited thereto.

[0084] The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector and containing a negative electrode active material.

[0085] The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0086] As the material capable of reversibly inserting / desorbing the lithium ions, a carbon material can be used, and any carbon-based negative electrode active material generally used in a lithium secondary battery can be used. Representative examples thereof include crystalline carbon, amorphous carbon, or these can 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 or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0087] As the alloy of lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0088] As the material capable of doping and undoping lithium, Si, Si-C composite, SiOx (0 < x ≤ 2), Si-Q alloy (where Q is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element excluding Si, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof), Sn, SnOx (0 < x ≤ 2), Sn-R 11 (where R 11 is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element excluding Sn, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof), and the like can be mentioned, and at least one of these can also be used by mixing with SiO2.

[0089] The elements Q and R 11Examples include those selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0090] Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

[0091] In a specific embodiment, the negative electrode active material can include at least one of graphite and an Si composite.

[0092] The Si composite includes a core containing Si-based particles and an amorphous carbon coating layer. For example, the Si-based particles can include one or more of silicon particles, Si-C composites, SiO x (0 < x ≦ 2) and Si alloy.

[0093] As an example, the core containing the Si-based particles includes voids at the center, the radius of the center corresponds to 30% to 50% of the radius of the negative electrode active material, and the average particle size of the Si-based particles can be 10 nm to 200 nm.

[0094] In this specification, the average particle size can be the particle size (D50) at 50% by volume in the cumulative size-distribution curve.

[0095] When the average particle size of the Si-based particles is within the above range, volume expansion occurring during charge and discharge can be suppressed, and disconnection of the conductive path due to particle crushing during charge and discharge can be prevented.

[0096] The core including the Si-based particle may further include amorphous carbon, and in this case, the center portion may not include amorphous carbon, and the amorphous carbon may be present only in the surface portion of the negative electrode active material.

[0097] In this case, the surface portion means the region from the outermost surface of the center portion to the outermost surface of the negative electrode active material.

[0098] Furthermore, the Si-based particles are contained substantially uniformly throughout the Si composite, that is, they can be present at a substantially uniform concentration in the center and surface portions.

[0099] The amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonized, calcined coke, or a combination thereof.

[0100] For example, the Si-C composite can include silicon particles and crystalline carbon.

[0101] The silicon particles may be included in an amount of 1 to 60 wt %, for example 3 to 60 wt %, based on the total weight of the Si-C composite.

[0102] The crystalline carbon may be, for example, graphite, and in particular may be natural graphite, artificial graphite, or a combination thereof.

[0103] The average particle size of the crystalline carbon may be from 5 μm to 30 μm.

[0104] When the negative electrode active material contains both graphite and a Si complex, the graphite and the Si complex may be contained in the form of a mixture, and in this case, the graphite and the Si complex may be contained in a weight ratio of 99:1 to 50:50.

[0105] More specifically, the graphite and the Si complex may be contained in a weight ratio of 97:3 to 80:20, or 95:5 to 80:20.

[0106] The amorphous carbon precursor may be coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or a polymer resin such as a phenol resin, a furan resin, or a polyimide resin.

[0107] The content of the negative electrode active material in the negative electrode active material layer may be 95% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

[0108] In one embodiment of the present invention, the negative electrode active material layer includes a binder, and may optionally further include a conductive material. The content of the binder in the negative electrode active material layer may be 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer. When the negative electrode active material layer further includes a conductive material, the negative electrode active material may be 90 wt% to 98 wt%, the binder may be 1 wt% to 5 wt%, and the conductive material may be 1 wt% to 5 wt%.

[0109] The binder serves to effectively adhere the negative active material particles to each other and to the current collector. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0110] The non-water-soluble binder may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0111] The water-soluble binder may be a rubber-based binder or a polymeric resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymeric resin binder may be selected from polytetrafluoroethylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0112] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included as a thickener. As the cellulose-based compound, one or more of carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K, or Li may be used. The content of such a thickener may be 0.1 to 3 parts by weight per 100 parts by weight of the negative electrode active material.

[0113] The conductive material is used to impart conductivity to the electrodes, and any electronically conductive material that does not undergo chemical changes in the battery that is constructed can be used. Examples of the conductive material that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fibers; metal-based materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures of these.

[0114] The negative electrode current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0115] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multi-layer film of two or more layers of these may be used, and it is of course possible to use a mixed multi-layer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator.

[0116] The lithium secondary battery may have an upper limit charging voltage of 4.35 V or more. For example, the upper limit charging voltage may be 4.35 V to 4.55 V.

[0117] Examples of the present invention and comparative examples are described below. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0118] Fabrication of lithium secondary batteries Example 1 LiNi as the positive electrode active material 0.75 Mn 0.23 Al 0.02 O2, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed in a weight ratio of 96:3:1, and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0119] The positive electrode active material slurry was coated on an aluminum foil having a thickness of 15 μm, dried at 100° C., and pressed to prepare a positive electrode.

[0120] A mixture of artificial graphite and Si composite in a weight ratio of 93:7 was used as the negative active material, and the negative active material was mixed with a styrene-butadiene rubber binder and carboxymethyl cellulose in a weight ratio of 98:1:1, respectively, and dispersed in distilled water to prepare a negative active material slurry.

[0121] The Si composite used had a core containing artificial graphite and silicon particles, and the surface of the core was coated with coal-based pitch.

[0122] The negative electrode active material slurry was coated on a copper foil having a thickness of 10 μm, dried at 100° C., and pressed to prepare a negative electrode.

[0123] The prepared positive and negative electrodes were assembled with a 10 μm thick polyethylene separator to prepare an electrode assembly, and an electrolyte was injected to prepare a lithium secondary battery. The composition of the electrolyte is as follows:

[0124] (Electrolyte composition) Lithium salt: LiPF61.5M Non-aqueous organic solvent: ethyl methyl carbonate: dimethyl carbonate (EMC:DMC=20:80 volume ratio) Additive: 1 part by weight of the compound represented by the following chemical formula 1-1 (additive alone) [ka] (However, in the composition of the electrolyte, "parts by weight" refers to the relative weight of the additive to 100 parts by weight of the entire electrolyte (lithium salt + non-aqueous organic solvent) excluding the additive.)

[0125] Comparative Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by Formula 1-1 was not added to the electrolyte solution.

[0126] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte solution contained 20 wt % ethylene carbonate based on the total weight of the non-aqueous organic solvent.

[0127] Comparative Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1 part by weight of fluoroethylene carbonate (FEC) was added instead of the compound represented by Chemical Formula 1-1 in the composition of the electrolyte solution.

[0128] Example 2 A lithium secondary battery was produced in the same manner as in Example 1, except that the non-aqueous organic solvent was changed to 100 volumetric ratio of dimethyl carbonate.

[0129] Example 3 A lithium secondary battery was produced in the same manner as in Example 1, except that the mixing ratio of ethyl methyl carbonate and dimethyl carbonate was changed to a volume ratio of 40:60, respectively.

[0130] Comparative Examples 4 to 6 Lithium secondary batteries were fabricated in the same manner as in Example 1 and Comparative Examples 1 and 2, except that the positive electrode active material was changed to LiCoO2.

[0131] Comparative Examples 7 to 9 The positive electrode active material is LiNi 0.5 Co 0.2 Al 0.3 Except for changing to O2, lithium secondary batteries were fabricated in the same manner as in Example 1 and Comparative Examples 1 and 2.

[0132] Comparative Examples 10 to 12 The positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 Except for changing to O2, lithium secondary batteries were fabricated in the same manner as in Example 1 and Comparative Examples 1 and 2.

[0133] Evaluation 1: Evaluation of high-temperature storage characteristics For the lithium secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 12, the initial direct current resistance (DCIR) was measured in terms of ΔV / ΔI (change in voltage / change in current) value, and then the maximum energy state inside the battery was made to be a fully charged state (SOC 100%). In this state, the battery was stored at high temperature (60° C.) for 30 days, after which the direct current resistance was measured and the DCIR increase rate (%) was calculated according to the following formula 1. The results are shown in Table 1 below. [Formula 1] DCIR increase rate = {(DCIR after 30 days) / (initial DCIR)}X100

[0134] Evaluation 2: Evaluation of high temperature life characteristics The lithium secondary batteries produced in Examples 1 to 3 and Comparative Examples 1 to 12 were charged and discharged once at 0.2 C to measure the charge and discharge capacity.

[0135] In addition, the lithium secondary batteries produced in Examples 1 to 3 and Comparative Examples 1 to 12 were charged at an upper charge voltage limit of 4.4 V, and then discharged at a constant current of 0.2 C to 2.5 V to measure the initial discharge capacity.

[0136] The discharge capacity was measured again by performing 200 charge / discharge cycles at 0.33 C charge (CC / CV, 4.4 V, 0.025 C cut-off) / 1.0 C discharge (CC, 2.5 V cut-off) at 45° C. The discharge capacity ratio to the initial discharge capacity is shown in Table 2 below as the capacity recovery rate (%, recovery).

[0137] Evaluation 3: Measurement of gas generation amount after high temperature storage The lithium secondary batteries according to Example 1 and Comparative Examples 1 to 12 were left at 60° C. for 7 days, and the amount of gas generated (ml) on the first and seventh days was measured using a refinery gas analyzer (RGA). The increase rate was calculated, and the results are shown in Table 3 below.

[0138] The increase rate was calculated according to the following formula 2. [Formula 2] Increase rate = {(gas generation amount on day 7) / (gas generation amount on day 1)} x 100

[0139] [Table 1]

[0140] [Table 2]

[0141] [Table 3]

[0142] Referring to Tables 1 to 3, it can be seen that in the composition in which the electrolyte solution and the positive electrode active material according to the present invention are combined, the DCIR increase rate is reduced, and both the high temperature storage characteristics and the high temperature charge / discharge characteristics are improved.

[0143] Also, it can be seen that the amount of gas generated after high temperature storage is significantly reduced in the lithium secondary batteries according to the examples.

[0144] Although a preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and can be embodied in various modified forms within the scope of the claims, the detailed description of the invention, and the attached drawings, which of course also fall within the scope of the present invention. [Explanation of symbols]

[0145] 100: Lithium secondary battery 112: Negative electrode 113: Separator 114: Positive electrode 120:Battery container 140: Sealing member

Claims

1. an electrolyte solution comprising a non-aqueous organic solvent, a lithium salt and an additive; a positive electrode comprising a positive electrode active material; and a negative electrode including a negative electrode active material; the non-aqueous organic solvent comprises less than 5% by weight of ethylene carbonate based on the total weight of the non-aqueous organic solvent; The positive electrode active material includes a lithium nickel manganese oxide, The additive comprises a compound represented by the following Chemical Formula 1: 【Chemistry 1】 (In the above Chemical Formula 1, Ring A is a substituted or unsubstituted C3-C6 heteroaryl group containing at least one nitrogen atom, or a substituted or unsubstituted C3-C6 heterocyclic group containing at least one nitrogen atom; L １ is a substituted or unsubstituted C1-C3 alkylene group, R １ is hydrogen or a substituted or unsubstituted C1 to C10 alkyl group.

2. 2. The lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent is composed only of a chain carbonate.

3. The lithium secondary battery according to claim 2 , wherein the chain carbonate is represented by the following chemical formula 2: 【Chemistry 2】 (In the above formula 2, R ２ and R ３ are each independently a substituted or unsubstituted C1 to C20 alkyl group.

4. 2. The lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent is at least two of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and ethyl methyl carbonate (EMC).

5. 2. The lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent comprises ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 0:100 to 50:

50.

6. 2. The lithium secondary battery of claim 1, wherein ring A in Chemical Formula 1 is a substituted or unsubstituted imidazolyl group, a substituted or unsubstituted pyrrolyl group, a substituted or unsubstituted pyrazolyl group, a substituted or unsubstituted triazolyl group, a substituted or unsubstituted pyrrolidinyl group, a substituted or unsubstituted pyridyl group, a substituted or unsubstituted pyrimidinyl group, a substituted or unsubstituted pyrazinyl group, a substituted or unsubstituted triazinyl group, a substituted or unsubstituted piperidinyl group, or a substituted or unsubstituted piperazinyl group.

7. The lithium secondary battery according to claim 1 , wherein the ring A in the formula (1) contains at least one double bond.

8. The lithium secondary battery of claim 1, wherein the formula 1 is represented by any one of the following formulas 1A to 1O. 【Chemistry 3】 【Chemistry 4】 【Chemistry 5】 【Chemistry 6】 (In the above Chemical Formula 1A to Chemical Formula 1O, L １ is a substituted or unsubstituted C1-C3 alkylene group, R １ and R ４ ~R ８ are each independently hydrogen or a substituted or unsubstituted C1-C10 alkyl group; m1 is an integer from 1 to 4; m2 is an integer from 1 to 3; m3 is an integer of 1 or 2, m4 is an integer from 1 to 6.

9. 2. The lithium secondary battery of claim 1, wherein the compound represented by Formula 1 is one selected from the compounds listed in Group 1 below: 【Chemistry 7】

10. The compound represented by Chemical Formula 1 is contained in an amount of 0.05 to 5.0 parts by weight based on 100 parts by weight of the total electrolyte solution (lithium salt + non-aqueous organic solvent) excluding additives. The lithium secondary battery of claim 1.

11. The electrolyte may be any of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF ４ ), lithium difluorophosphate (LiPO ２ F ２ 2. The lithium secondary battery according to claim 1, further comprising at least one other additive selected from the group consisting of 2-fluorobiphenyl (2-FBP) and 2-fluorobiphenyl (2-FBP).

12. 2. The lithium secondary battery of claim 1, wherein the lithium nickel manganese-based oxide comprises a cobalt-free lithium composite oxide represented by the following Chemical Formula 4: [Chemical formula 4] Li ａ Ni ｘ Mn ｙ M １ ｚ M ２ ｗ O ２±ｂ X ｃ (In the above Chemical Formula 4, 0.5≦a<1.8, 0≦b≦0.1, 0≦c≦0.1, 0≦w<0.1, 0.6≦x<1.0, 0<y<0.4, 0<z<0.1, and w+x+y+z=1; M １ and M. ２ are each independently one or more elements selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Si, Ba, Ca, Ce, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

13. The lithium secondary battery according to claim 12, wherein the chemical formula 4 is represented by the following chemical formula 4-1: [Chemical formula 4-1] Li ａ Ni ｘ１ Mn ｙ１ Al ｚ１ M ２ ｗ１ O ２±ｂ X ｃ (In the above Chemical Formula 4-1, 0.5≦a<1.8, 0≦b≦0.1, 0≦c≦0.1, 0≦w1<0.1, 0.6≦x1<1.0, 0<y1<0.4, 0<z1<0.1, and w1+x1+y1+z1=1, M ２ are each independently one or more elements selected from Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Si, Ba, Ca, Ce, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

14. 14. The lithium secondary battery according to claim 13, wherein x1 in the formula 4-1 is 0.6≦x1≦0.79, y1 is 0.2≦y1≦0.39, and z1 is 0.01≦z1<0.

1.

15. The lithium secondary battery according to claim 1 , wherein the negative electrode active material comprises at least one of graphite and a Si composite.

16. 2. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has an upper limit charging voltage of 4.35 V or higher.

Images