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 actively underway to further improve their energy density.

[0003] In particular, as IT devices become increasingly sophisticated, there is a demand for high-capacity batteries. While achieving high capacity through an expansion of the voltage range can increase energy density, 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 oxides as positive electrode active materials are positive electrode active materials that do not contain cobalt in their composition and are composed mainly of nickel, manganese, etc. Positive electrodes containing these are economical and can achieve high energy density, so they are attracting attention as next-generation positive electrode active materials.

[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 transition metal leaching, which can lead to problems such as gas generation inside the cell and capacity reduction. This transition metal leaching phenomenon tends to intensify in high-temperature environments, and the leached transition metals can precipitate on the surface of the negative electrode and induce side reactions, resulting in increased battery resistance and reduced battery life and output characteristics.

[0006] Therefore, when using a positive electrode containing a cobalt-free lithium nickel manganese oxide, an electrolyte that can be used under high voltage and high temperature conditions is required. 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 the cobalt-free lithium nickel manganese-based oxide, thereby reducing the elution of transition metals under high-voltage and high-temperature conditions and 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, which includes 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 solely of a chain carbonate.

[0010] The chain carbonate may be represented by the following chemical formula 2. [ka] In the above 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 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.

[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 Chemical 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 (LiBF), lithium difluorophosphate (LiPOF), 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 can 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. [Effects of the Invention]

[0024] In one embodiment, a cobalt-free lithium nickel manganese-based oxide is used in combination with an electrolyte that can effectively protect the positive electrode, thereby ensuring the safety of the phase transition of the positive electrode even in a high-temperature, high-voltage environment. The decomposition of the electrolyte and side reactions with the electrode are suppressed, thereby reducing gas generation and simultaneously suppressing an increase in the internal resistance of the battery, thereby realizing a lithium secondary battery with improved battery stability and life characteristics. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[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 scope of the present invention, which is defined only by the scope of the claims that follow.

[0027] Unless otherwise defined, the term "substituted" used herein means that at least one hydrogen atom in a substituent or compound has been replaced with deuterium, a halogen group, a hydroxyl group, an amino group, a substituted or unsubstituted C1-C30 amine group, a nitro group, a substituted or unsubstituted C1-C40 silyl 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-C20 alkoxy group, a C1-C10 fluoroalkyl group, a cyano group, or a combination thereof.

[0028] In one embodiment of the present invention, "substituted" means that at least one hydrogen atom in 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 another specific embodiment of the present invention, "substituted" means that at least one hydrogen atom in 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 another specific embodiment of the present invention, "substituted" means that at least one hydrogen atom in 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 atom of a substituent or compound is substituted 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, prismatic, 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 a lithium secondary battery. Figure 1 illustrates a schematic structure of a lithium secondary battery according to an embodiment. Referring to Figure 1, a 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 be described in more detail below.

[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, wherein the non-aqueous organic solvent includes less than 5 wt % of ethylene carbonate based on the total weight of the non-aqueous organic solvent, and the additive may 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 oxide, especially cobalt-free lithium nickel manganese oxide, the structural instability is strong under high voltage conditions, resulting in solvent decomposition and leaching of transition metals, especially Ni.

[0036] The degradation and short circuit caused by the elution of such transition metals reduces the life capacity of the battery 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 alleviated.

[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 non-aqueous organic solvent, it is possible to effectively reduce the elution of transition metals under high voltage and high temperature conditions, thereby suppressing 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 migrate.

[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 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), and butylene carbonate (BC). Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, and caprolactone. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. The ketone solvent may be cyclohexanone, etc. The alcohol solvent may be ethyl alcohol, isopropyl alcohol, etc. The aprotic solvent may be nitriles such as R-CN (R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc.

[0042] The non-aqueous organic solvents 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 well 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] If the ethylene carbonate content is 5 wt % or more of the above-mentioned range, the activity of Ni increases during high-voltage operation, and the oxidation state of Ni tends to be reduced from tetravalent to divalent. As a result, ethylene carbonate, which has low oxidation stability, is oxidatively decomposed, and Ni is eluted and deposited on the negative electrode.

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

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

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

[0048] As an example, R in Formula 2 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 in Formula 2 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 may 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 containing more than 50% by volume of dimethyl carbonate (DMC) can be more advantageous in terms of improving battery characteristics.

[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] The aromatic hydrocarbon solvent may be an aromatic hydrocarbon compound represented by the following formula 3: [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, alkyl groups having 1 to 10 carbon atoms, haloalkyl groups 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, fluoroisopropyl ether ... and combinations thereof.

[0058] The lithium salt is dissolved in a non-aqueous organic solvent and serves as a lithium ion source in the battery, enabling basic lithium secondary battery operation and promoting 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 SO2) (wherein x and y are integers of 1 to 20), LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalato)borate: LiBOB).

[0059] The concentration of the lithium salt is preferably within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[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 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.

[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 with improved life 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 (LiBF), lithium difluorophosphate (LiPOF), 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 other additives is within the above range, it is possible to minimize the increase in film resistance and contribute to improving 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-based 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 a positive electrode active material refers to 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 the coating elements, hydroxides of the coating elements, oxyhydroxides of the coating elements, oxycarbonates of the coating elements, and hydroxycarbonates of the coating elements. The compounds forming the coating layer may be amorphous or crystalline. The coating element contained in the coating layer may be Mg, Al, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating layer formation process may be performed using any coating method (e.g., spray coating, dipping, etc.) that does not adversely affect the physical properties of the positive electrode active material, as this is well understood by those skilled in the art and will not be described in detail.

[0077] For 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 may be 0.6 ≦ x1 ≦ 0.8, 0.2 ≦ y1 < 0.4, and 0 < z1 < 0.1.

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

[0080] The content of the positive electrode active material may be 90% 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 may contain a binder. At this time, the content of the binder may be 1% 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 both of these can be used. 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 the 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, a Si-C composite, SiOx (0 < x ≦ 2), a 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 mixed with SiO2 and used.

[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, lithium titanium oxide, and the like.

[0091] In a specific embodiment, the negative electrode active material can include at least one of graphite and a 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% in volume ratio 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 interruption 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 the central portion may be free of amorphous carbon, with amorphous carbon being 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 charcoal, 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 % of the total weight of the Si—C composite, for example, 3 to 60 wt %.

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

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

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

[0105] More specifically, the graphite and the Si composite 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 used in an amount of 90 wt % to 98 wt %, the binder in an amount of 1 wt % to 5 wt %, and the conductive material in an amount of 1 wt % to 5 wt %.

[0109] The binder serves to effectively adhere the negative electrode 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 polymer 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 polymer 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. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be Na, K, or Li. The amount of the thickener used 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 electron-conductive material that does not undergo chemical change in the battery that is constructed can be used. Examples of conductive materials that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based materials such as metal powder or metal fiber 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 and negative electrodes. Such a separator may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more of these materials. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[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. These examples are merely examples of the present invention, and the present invention is not limited to these 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 then 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 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 then 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 solution 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 solution, "parts by weight" refers to the relative weight of the additive to 100 parts by weight of the entire electrolyte solution (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 fabricated in the same manner as in Example 1, except that the electrolyte solution contained 20 wt % of 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 fabricated in the same manner as in Example 1, except that the non-aqueous organic solvent was changed to 100% dimethyl carbonate by volume.

[0129] Example 3 A lithium secondary battery was fabricated 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 fabricated in Examples 1 to 3 and Comparative Examples 1 to 12, the initial DC resistance (DCIR) was measured using the ΔV / ΔI (change in voltage / change in current) value, and then the maximum energy state inside the battery was set to a fully charged state (SOC 100%). After storing the battery in this state at high temperature (60°C) for 30 days, the DC resistance was measured and the DCIR increase rate (%) was calculated using the following formula 1, and the results are shown in Table 1 below. [Formula 1] DCIR increase rate = {(DCIR after 30 days) / (initial DCIR)} x 100

[0134] Evaluation 2: Evaluation of high temperature life characteristics The lithium secondary batteries fabricated 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] Furthermore, 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 cutoff) / 1.0 C discharge (CC, 2.5 V cutoff) 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 rate of increase was calculated, and the results are shown in Table 3 below.

[0138] The rate of increase was calculated using the following formula 2. [Formula 2] Growth 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] It is also apparent that the lithium secondary batteries according to the examples exhibit a significant reduction in the amount of gas generated after storage at high temperatures.

[0144] Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is to be understood that these modifications 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 from 0% to less than 5% by weight of ethylene carbonate based on the total weight of the non-aqueous organic solvent; the non-aqueous organic solvent comprises dimethyl carbonate (DMC); The non-aqueous organic solvent contains dimethyl carbonate (DMC) in an amount of 70% by volume or more and 90% by volume or less, the positive electrode active material includes a cobalt-free 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-C10 alkyl group.

2. 2. The lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent is composed solely of a chain carbonate containing dimethyl carbonate (DMC).

3. The lithium secondary battery according to claim 2 , wherein the chain carbonate containing dimethyl carbonate (DMC) is represented by the following chemical formula 2: 【Chemistry 2】 In the above Chemical Formula 2 R ２ and R ３ are each independently a substituted or unsubstituted C1 to C20 alkyl group, and the dimethyl carbonate (DMC) corresponds to a linear carbonate in which R 2 and R 3 in Chemical Formula 2 are both unsubstituted C1 alkyl groups.

4. 2. The lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent further comprises one or more selected from the group consisting of 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 further contains ethyl methyl carbonate (EMC), and the ethyl methyl carbonate (EMC) and the dimethyl carbonate (DMC) are contained in a volume ratio of 10:90 to 30:

70.

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 ring A in Formula 1 contains at least one double bond.

8. 2. The lithium secondary battery of claim 1, wherein the formula 1 is represented by any one of the following formulas 1A to 1O: 【Transformation 3】 【Chemistry 4】 【Transformation 5】 【Transformation 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 Chemical Formula 1 is one selected from the compounds listed in Group 1 below: 【Transformation 7】

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

11. The electrolyte may be selected from 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. The lithium secondary battery of claim 1 , wherein the cobalt-free 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 satisfies 0.6≦x1≦0.79, y1 satisfies 0.2≦y1≦0.39, and z1 satisfies 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 upper limit charging voltage of the lithium secondary battery is 4.35 V or higher.

Images