Lithium secondary battery

Abstract

To provide a lithium secondary battery in which the collapse of a positive electrode structure is suppressed by reducing elution of transition metal under a high-voltage and high-temperature condition using a layered positive electrode active material including cobalt-free lithium nickel manganese oxide in combination with an electrolyte solution capable of protecting effectively a positive electrode including the positive electrode active material, so that the high-voltage characteristic and the high-temperature characteristic of the battery are improved.SOLUTION: A lithium secondary battery in an embodiment includes: an electrolyte solution including a nonaqueous 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 nonaqueous organic solvent contains less than 5 wt% of ethylene carbonate. The additive contains a compound expressed by Chemical Formula 1. The positive electrode active material is expressed by Chemical Formula 2. Chemical Formula 1 and Chemical Formula 2 are defined in the specification.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This description relates to a lithium secondary battery.

Background Art

[0002] Lithium secondary batteries are rechargeable and have an energy density per unit weight that is more than three times higher and can be fast-charged compared to conventional lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, etc., and thus have been commercialized for use in notebook computers, mobile phones, power tools, and electric bicycles. Research and development for further improving the energy density are actively underway.

[0003] In particular, as IT devices are gradually becoming more high-performance, there is a situation where high-capacity batteries are required. By expanding the voltage range to increase the capacity, the energy density can be increased. However, in the high-voltage range, there is a problem that the electrolyte oxidizes and the performance of the positive electrode deteriorates.

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

[0005] However, when a positive electrode containing cobalt-free lithium nickel manganese-based oxide is used in a high-voltage environment, transition metal elution may occur due to the collapse of the positive electrode structure, which may cause problems such as gas generation inside the cell and a decrease in capacity. Such a transition metal elution phenomenon tends to deepen in a high-temperature environment, and the eluted transition metal may be deposited on the surface of the negative electrode to induce side reactions, resulting in an increase in the resistance of the battery, a decrease in the battery life, and a decrease in the output characteristics.

[0006] Accordingly, when using a positive electrode containing cobalt-free lithium nickel manganese-based oxide, an electrolyte that is applicable even under high-voltage and high-temperature conditions is required.

Summary of the Invention

Problems to be Solved by the Invention

[0007] One embodiment is to provide a lithium secondary battery in which a transition metal elution is reduced under high voltage and high temperature conditions by combining the use of a layered cathode active material containing a cobalt-free lithium nickel manganese-based oxide and an electrolyte capable of effectively protecting the cathode containing the cathode active material, thereby suppressing the collapse of the cathode structure and improving the high voltage characteristics and high temperature characteristics of the battery.

Means for Solving the Problems

[0008] One embodiment of the present invention includes an electrolyte containing a non-aqueous organic solvent, a lithium salt, and an additive; a cathode containing a cathode active material; and an anode containing an anode active material, the non-aqueous organic solvent contains less than 5% by weight of ethylene carbonate, the additive contains a compound represented by the following Chemical Formula 1, the cathode active material is represented by the following Chemical Formula 2, to provide a lithium secondary battery.

[0009]

Chem.

[0010] In the above Chemical Formula 1, R 1 ~R 4 are each independently hydrogen, a halogen, a cyano group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, or a substituted or unsubstituted heterocyclic group having 2 to 30 carbon atoms; [Chemical Formula 2] Li a Ni x Mn 1-x-y A y O 2±b X c In the above Chemical Formula 2, 0.9 ≦ a ≦ 1.2, 0 ≦ b ≦ 0.1, 0 ≦ c ≦ 0.1, 0.5 ≦ x ≦ 0.95, and 0 ≦ y < 0.3, A is one or more elements selected from the group consisting of B, Na, Mg, Al, Ti, and Si, X is one or more elements selected from S, F, P, and Cl.

[0011] The non-aqueous organic solvent may be composed of only chain carbonates. The chain carbonate can be represented by the following Chemical Formula 3.

[0012]

Chemical Formula

[0013] In the above Chemical Formula 3, R 5 and R 6 are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms.

[0014] The non-aqueous organic solvent 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).

[0015] The non-aqueous organic solvent can contain ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a weight ratio of 0:100 to 50:50.

[0016] At least one of R 1 ~R 4 in Chemical Formula 1 may be a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, or a substituted or unsubstituted heterocyclic group having 2 to 30 carbon atoms substituted with an electron-withdrawing group.

[0017] The electron-withdrawing group may be at least one selected from halogen, isocyanate group (-NCO), isothiocyanate group (-NCS), cyanate group (-OCN), thiocyanate group (-SCN), cyano group (-CN), isocyano group (-NC), -N=C=N- group, -N=S=N- group, nitro group (NO2), trifluoromethane (CF3) group, pentafluoroethane (C2F5) group, trifluoromethanesulfonyl (SO2CF3) group, pentafluoroethanesulfonyl (SO2C2F5) group, trifluoromethanesulfonate (SO3CF3) group, pentafluoroethanesulfonate (SO3C2F5) group, pentafluorophenyl (C6F5) group, acetyl (COCH3) group, ethyl ketone (COC2H5) group, propyl ketone (COC3H7) group, butyl ketone (COC4H9) group, pentyl ketone (COC5H 11 ) group, hexyl ketone (COC6H 13 ) group, ethanolate (CO2CH3) group, propanoate (CO2C2H5) group, butanoate (CO2C3H7) group, pentanoate (CO2C4H9) group, hexanoate (CO2C5H 11 ) group.

[0018] At least one of R 2 and R 3 in Chemical Formula 1 may be hydrogen. Both R 2 and R 3 in Chemical Formula 1 may be hydrogen. The compound represented by Chemical Formula 1 can be selected from the compounds listed in Group 1 below.

[0019]

Chemical Formula

[0020] The compound represented by Chemical Formula 1 may be contained in an amount of 0.01 to 5.0 parts by weight based on 100 parts by weight of the entire electrolyte for a lithium secondary battery.

[0021] The electrolytic solution can further contain at least one other additive among vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinyl ethylene 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).

[0022] X in the chemical formula 2 may satisfy 0.8 ≤ x ≤ 0.95. The positive electrode active material is LiNi 0.75 Mn 0.25 O2, LiNi 0.80 Mn 0.20 O2, LiNi 0.85 Mn 0.15 O2, LiNi 0.90 Mn 0.10 O2 or LiNi 0.95 Mn 0.05 O2 and solid solutions thereof can be included. The negative electrode active material can include at least one of graphite and Si composite. The lithium secondary battery may have a charge upper limit voltage of 4.35 V or more.

Advantages of the Invention

[0023] One embodiment can realize a lithium secondary battery with improved battery stability and life characteristics by using in combination an electrolytic solution that can effectively protect a positive electrode including a layered positive electrode active material containing a cobalt - free lithium nickel manganese - based oxide, ensuring the phase transition safety of the positive electrode even in a high - temperature and high - voltage environment, suppressing the decomposition of the electrolytic solution and side reactions with the electrodes, reducing gas generation, and simultaneously suppressing an increase in the internal resistance of the battery.

Brief Description of the Drawings

[0024]

Figure 1

Modes for Carrying Out the Invention

[0025] Hereinafter, a lithium secondary battery according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, this is presented by way of example and the present invention is not limited thereby, and the present invention is only defined by the scope of the claims described later.

[0026] In this specification, “substitution” means that, unless otherwise defined, at least one hydrogen in a substituent or compound is substituted with deuterium, a halogen group, a hydroxyl group, an amino group, an amine group having 1 to 30 carbon atoms, a nitro group, a silyl group having 1 to 40 carbon atoms, an alkyl group having 1 to 30 carbon atoms, an alkylsilyl group having 1 to 10 carbon atoms, an arylsilyl group having 6 to 30 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, a heterocycloalkyl group having 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, a heteroaryl group having 2 to 30 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, a trifluoroalkyl group having 1 to 10 carbon atoms, an isocyanate group (-NCO), an isothiocyanate group (-NCS), a cyanate group (-OCN), a thiocyanate group (-SCN), a cyano group (-CN), an isocyano group (-NC), or a combination thereof.

[0027] In an example of the present invention, "substituted" means that at least one hydrogen in a substituent or a compound is substituted with deuterium, a halogen group, an alkyl group having 1 to 30 carbon atoms, an alkylsilyl group having 1 to 10 carbon atoms, an arylsilyl group having 6 to 30 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, a heterocycloalkyl group having 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, a heteroaryl group having 2 to 30 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a cyano group. Further, in a specific example of the present invention, "substituted" means that at least one hydrogen in a substituent or a compound is substituted with deuterium, a halogen group, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 30 carbon atoms, a trifluoroalkyl group having 1 to 10 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a cyano group. Further, in a specific example of the present invention, "substituted" means that at least one hydrogen in a substituent or a compound is substituted with deuterium, a halogen group, an alkyl group having 1 to 5 carbon atoms, an aryl group having 6 to 18 carbon atoms, a trifluoroalkyl group having 1 to 5 carbon atoms, a fluoroalkyl group having 1 to 5 carbon atoms, or a cyano group. Further, in a specific example of the present invention, "substituted" means that at least one hydrogen in a substituent or a 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.

[0028] Lithium secondary batteries can be classified into lithium-ion batteries, lithium-ion polymer batteries, lithium polymer batteries, etc. according to the types of separation membranes and electrolytes used, and can be classified into cylindrical, square, coin-type, pouch-type, etc. according to their forms, and can be divided into bulk type and thin film type according to their sizes. Since the structures and manufacturing methods of these batteries are widely known in this field, detailed descriptions are omitted.

[0029] Here, a cylindrical lithium secondary battery will be exemplarily described as an example of a lithium secondary battery. FIG. 1 schematically shows the structure of a lithium secondary battery according to an embodiment. Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment includes a positive electrode 114, a negative electrode 112 positioned opposite to the positive electrode 114, a separator 113 disposed between the positive electrode 114 and the negative electrode 112, and a battery cell including an electrolytic solution (not shown) that impregnates the positive electrode 114, the negative electrode 112, and the separator 113, a battery container 120 in which the battery cell is contained, and an encapsulating member 140 that seals the battery container 120.

[0030] Hereinafter, a more detailed configuration of the lithium secondary battery 100 according to an embodiment of the present invention will be described.

[0031] A lithium secondary battery according to an embodiment of the present invention includes an electrolytic solution, a positive electrode, and a negative electrode. The electrolytic solution includes a non-aqueous organic solvent, a lithium salt, and an additive. The non-aqueous organic solvent contains less than 5% by weight of ethylene carbonate, and the additive can include a compound represented by the following Chemical Formula 1.

[0032]

Chemical formula

[0033] The positive electrode can include a positive electrode active material including a lithium nickel manganese-based oxide represented by the following Chemical Formula 2. The lithium nickel manganese oxide represented by Chemical Formula 2 is a cobalt-free lithium nickel manganese oxide and may be a layered cathode active material. In the case of a cathode active material containing a cobalt-free lithium nickel manganese oxide, structural instability is strong under high voltage conditions, and solvent decomposition and elution of transition metals, particularly Ni, occur.

[0034] Such elution of transition metals causes deterioration and short circuits, resulting in a decrease in the life capacity of the battery and an increase in resistance.

[0035] However, when using the above-mentioned electrolytes together, a decrease in the life capacity of the battery and an increase in resistance can be alleviated.

[0036] In particular, by using the above-mentioned cathode active material in an electrolyte containing less than 5% by weight of ethylene carbonate, elution of transition metals can be effectively reduced under high voltage and high temperature conditions, thereby suppressing cathode structure collapse and improving the high voltage characteristics and high temperature characteristics of the battery.

[0037] The non-aqueous organic solvent plays a role as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0038] As the non-aqueous organic solvent, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents can be used.

[0039] As the carbonate solvent, 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. can be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, caprolactone, etc. can be used. As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. can be used. Further, as the ketone solvent, cyclohexanone, etc. can be used. Further, as the alcohol solvent, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvent, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and can contain a double bond, an aromatic ring, or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolane, etc. can be used. The non-aqueous organic solvent can be used alone or in admixture of one or more, and when used in admixture of one or more, the mixing ratio can be appropriately adjusted according to the intended battery performance, which should be widely understood by those skilled in the art.

[0040] As an example, the non-aqueous organic solvent can contain less than 5% by weight of ethylene carbonate.

[0041] When the content of ethylene carbonate is 5% by weight or more within the aforementioned range, the activity of Ni increases during high-voltage driving, and the oxidation number of Ni tends to be strongly reduced from tetravalent to divalent. As a result, ethylene carbonate with low oxidation stability is oxidatively decomposed, and Ni is eluted and deposited on the negative electrode.

[0042] As a specific example, the non-aqueous organic solvent may be composed of only chain carbonates. In this case, excellent high-temperature storage characteristics can be realized by significantly relaxing the resistance increase rate during high-temperature storage.

[0043] In this specification, the meaning of being composed of only chain carbonates means including, alone or in combination, organic solvents belonging to the category of chain carbonates without being mixed with cyclic carbonates or the like. In one embodiment, the chain carbonate can be represented by the following Chemical Formula 3.

[0044]

Chemical Formula

[0045] In the above Chemical Formula 3, R 5 and R 6 are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms.

[0046] As an example, R 5 and R 6 in the above Chemical Formula 3 may each independently be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms. For example, R 5 and R 6 may each independently be a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.

[0047] In one embodiment, R 5 and R 6may 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.

[0048] For example, the non-aqueous organic solvent according to a 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).

[0049] The non-aqueous organic solvent according to the most specific embodiment may be a mixed solvent of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). The non-aqueous organic solvent may contain ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a weight ratio of 0:100 to 50:50. It may be more advantageous from the aspect of improving battery characteristics that the non-aqueous organic solvent contains dimethyl carbonate (DMC) in an amount exceeding 50% by weight.

[0050] For example, the non-aqueous organic solvent may contain ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a weight ratio of 0:100 to 40:60, 0:100 to 30:70, 10:90 to 40:60, or 10:90 to 30:70.

[0051] The non-aqueous organic solvent may further contain an aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. At this time, the carbonate-based solvent and the aromatic hydrocarbon-based solvent can be mixed in a volume ratio of 1:1 to 30:1.

[0052] As the aromatic hydrocarbon-based solvent, the aromatic hydrocarbon-based compound of the following Chemical Formula 4 can be used.

[0053] [Chemical formula]

[0054] In the above chemical formula 4, R 11 ~R 16 are the same as or different from each other, 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.

[0055] 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, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0056] The lithium salt is dissolved in a non-aqueous organic solvent, acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in 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) (where x and y are integers from 1 to 20), LiCl, LiI, and one or more selected from the group consisting of LiB(C2O4)2 (lithium bis(oxalato) borate; LiBOB).

[0057] The concentration of the lithium salt is preferably used in the range of 0.1 M to 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0058] At least one of R 1 ~R 4 in Chemical Formula 1 may be an alkyl group having 1 to 20 carbon atoms which is unsubstituted or substituted with an electron-withdrawing group, an aryl group having 6 to 20 carbon atoms which is unsubstituted or substituted with an electron-withdrawing group, or a heterocyclic group having 2 to 30 carbon atoms which is unsubstituted or substituted with an electron-withdrawing group.

[0059] The electron-withdrawing group may be at least one selected from halogen, isocyanate group (-NCO), isothiocyanate group (-NCS), cyanate group (-OCN), thiocyanate group (-SCN), cyano group (-CN), isocyano group (-NC), -N=C=N- group, -N=S=N- group, nitro group (NO2), trifluoromethane (CF3) group, pentafluoroethane (C2F5) group, trifluoromethanesulfonyl (SO2CF3) group, pentafluoroethanesulfonyl (SO2C2F5) group, trifluoromethanesulfonate (SO3CF3) group, pentafluoroethanesulfonate (SO3C2F5) group, pentafluorophenyl (C6F5) group, acetyl (COCH3) group, ethyl ketone (COC2H5) group, propyl ketone (COC3H7) group, butyl ketone (COC4H9) group, pentyl ketone (COC5H 11 ) group, hexyl ketone (COC6H 13 ) group, ethanolate (CO2CH3) group, propanoate (CO2C2H5) group, butanoate (CO2C3H7) group, pentanoate (CO2C4H9) group, hexanoate (CO2C5H 11 ) group.

[0060] At least one of R 2 and R 3 in Chemical Formula 1 may be hydrogen. Both R 2 and R 3 in Chemical Formula 1 may be hydrogen.

[0061] The compound represented by Chemical Formula 1 can be selected from the compounds listed in Group 1 below.

[0062]

Chemical Formula

[0063] The additive may be contained in an amount of 0.01 to 5.0 parts by weight based on 100 parts by weight of the whole electrolyte for a lithium secondary battery. As an example, the additive may be contained in an amount of 0.01 to 3.0 parts by weight based on 100 parts by weight of the entire electrolyte for a lithium secondary battery. For example, the additive may be contained 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 for a lithium secondary battery.

[0064] When the content range of the additive is as described above, a lithium secondary battery with improved life characteristics and output characteristics can be realized by preventing an increase in resistance at high temperatures. On the other hand, the electrolyte may further contain at least one other additive such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinyl ethylene 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).

[0065] By further containing the other additive, the life can be further improved or the gas generated from the positive electrode and the negative electrode during high - temperature storage can be effectively controlled.

[0066] The other additive may be contained 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 entire electrolyte for the lithium secondary battery. When the content of the other additive is as described above, it can contribute to improving battery performance by minimizing the increase in film resistance.

[0067] 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 contains a positive electrode active material.

[0068] The positive electrode active material can include a cobalt-free lithium nickel manganese-based oxide represented by the following Chemical Formula 2. [Chemical Formula 2] Li a Ni x Mn 1-x-y A y O 2±b X c In the above Chemical Formula 2, 0.9 ≦ a ≦ 1.2, 0 ≦ b ≦ 0.1, 0 ≦ c ≦ 0.1, 0.5 ≦ x ≦ 0.95, and 0 ≦ y < 0.3, A is one or more elements selected from the group consisting of B, Na, Mg, Al, Ti, and Si, X is one or more elements selected from S, F, P, and Cl. Of course, those having a coating layer on the surface of the lithium composite oxide can also be used, or the lithium composite oxide and a compound having a coating layer can be mixed and used. This coating layer can contain at least one coating element compound selected from the group consisting of an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, and a hydroxycarbonate of the coating element. The compounds forming these coating layers may be amorphous or crystalline. As the coating elements contained in the coating layer, Mg, Al, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof can be used. The coating layer forming step may use any coating method as long as such elements are used for the compound and the physical properties of the positive electrode active material are not adversely affected (for example, spray coating, dipping method, etc.). Since this is well understood by those skilled in the art, a detailed description thereof is omitted.

[0069] As an example, x in the chemical formula 2 may be 0.8 ≦ x ≦ 0.95. For example, the positive electrode active material is LiNi 0.75 Mn 0.25 O2, LiNi 0.80 Mn 0.20 O2, LiNi 0.85 Mn 0.15 O2, LiNi 0.90 Mn 0.10 O2 or LiNi 0.95 Mn 0.05 O2, and solid solutions thereof can be included.

[0070] 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. 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.

[0071] The binder plays a role of well adhering the positive electrode active material particles to each other and well adhering the positive electrode active material to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer 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.

[0072] Al can be used as the positive electrode current collector, but is not limited thereto.

[0073] 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.

[0074] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material dopable and dedopable with lithium, or a transition metal oxide.

[0075] As the material capable of reversibly intercalating / deintercalating lithium ions, any of the carbon-based negative electrode active materials generally used in lithium secondary batteries can be used. Typical examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. 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, hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0076] 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.

[0077] As the material dopable and dedopable with lithium, Si, Si-C composite, SiO x (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, SnO2, 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), etc. can be mentioned, and at least one of these can also be used in mixture with SiO2.

[0078] The elements Q and R11 Examples of such materials 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.

[0079] Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, lithium titanium oxide, and the like.

[0080] In a specific embodiment, the negative electrode active material can include at least one of graphite and an Si composite. The Si composite includes a core containing Si-based particles and an amorphous carbon coating layer. For example, the Si-based particles can include silicon particles, an Si-C composite, SiO x (0 < x ≦ 2), and one or more of Si alloys. As an example, the core containing the Si-based particles contains voids at the center. The radius of the center corresponds to 30% to 50% of the radius of the Si composite. The average particle size of the Si composite is 5 μm to 20 μm, and the average particle size of the Si-based particles may be 10 nm to 200 nm.

[0081] In this specification, the average particle size may be the particle size (D50) at 50% as the volume ratio in the cumulative size-distribution curve. 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.

[0082] The core containing the Si-based particles additionally contains amorphous carbon. At this time, the center portion does not contain amorphous carbon, and the amorphous carbon exists only on the surface portion of the Si composite. At this time, the surface part means the region from the outermost surface of the central part to the outermost surface of the Si composite. Also, the Si-based particles are substantially uniformly contained in the Si composite as a whole, that is, they exist at a substantially uniform concentration in the central part and the surface part.

[0083] The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or a combination thereof. For example, the Si-C composite can contain silicon particles and crystalline carbon.

[0084] The silicon particles may be contained in an amount of 1 to 60% by weight, for example 3 to 60% by weight, based on the total weight of the Si-C composite.

[0085] The crystalline carbon may be, for example, graphite, and specifically, it may be natural graphite, artificial graphite, or a combination thereof. The average particle size of the crystalline carbon may be 5 μm to 30 μm.

[0086] When the negative electrode active material contains both graphite and an 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. More specifically, the graphite and the Si composite may be contained in a weight ratio of 97:3 to 80:20, 95:5 to 80:20.

[0087] As the amorphous carbon precursor, coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or polymer resins such as phenolic resin, furan resin, and polyimide resin can be used.

[0088] In the negative electrode active material layer, the content of the negative electrode active material may be 95% to 99% by weight based on the total weight of the negative electrode active material layer.

[0089] In one embodiment of the present invention, the negative electrode active material layer contains a binder and may further selectively contain a conductive material. In the negative electrode active material layer, the content of the binder may be 1% to 5% by weight based on the total weight of the negative electrode active material layer. When further containing a conductive material, 90% to 98% by weight of the negative electrode active material, 1% to 5% by weight of the binder, and 1% to 5% by weight of the conductive material can be used.

[0090] The binder serves to make the negative electrode active material particles adhere well to each other and also make the negative electrode active material adhere well to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof can be used.

[0091] Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0092] Examples of the water-soluble binder include 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, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0093] When using a water-soluble binder as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included as a thickener. As such cellulose-based compounds, carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof, etc., can be used by mixing one or more of them. As the alkali metal, Na, K, or Li can be used. The content of such a thickener used may be 0.1 to 3 parts by weight with respect to 100 parts by weight of the negative electrode active material.

[0094] The conductive material is used to impart conductivity to the electrode, and in the configured battery, any material can be used as long as it is an electron conductive material that does not cause a chemical change. Examples thereof 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 powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or a conductive material containing a mixture thereof can be used.

[0095] As the negative electrode current collector, one 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 can be used.

[0096] Depending on the type of lithium secondary battery, a separator may exist between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used, and of course, a mixed multilayer film such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, a three-layer separator of polypropylene / polyethylene / polypropylene, etc. can be used.

[0097] The lithium secondary battery may have a charge upper limit voltage of 4.35 V or more. For example, the charge upper limit voltage may be 4.35 V to 4.55 V.

[0098] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

Examples

[0099] Fabrication of Lithium Secondary Battery Example 1 As the positive electrode active material, LiNi 0.75 Mn 0.23 Al 0.02 O2, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed at a weight ratio of 96:3:1, respectively, and dispersed in N-methylpyrrolidone to produce a positive electrode active material slurry. The positive electrode active material slurry was coated on an aluminum foil with a thickness of 15 μm, dried at 100 °C, and then rolled (press) to produce a positive electrode.

[0100] As the negative electrode active material, a mixture in which artificial graphite and Si composite were mixed at a weight ratio of 93:7 was used, and the negative electrode active material, styrene-butadiene rubber binder, and carboxymethyl cellulose were mixed at a weight ratio of 98:1:1, respectively, and dispersed in distilled water to produce a negative electrode active material slurry.

[0101] As the Si-C composite, a core containing artificial graphite and silicon particles and a coal-based pitch coated on the surface of the core was used. The negative electrode active material slurry was coated on a copper foil with a thickness of 10 μm, dried at 100 °C, and then rolled (press) to produce a negative electrode. The manufactured positive electrode and negative electrode and a separator made of a 10-μm-thick polyethylene material were assembled to manufacture an electrode assembly, and an electrolytic solution was injected to manufacture a lithium secondary battery.

[0102] The electrolyte composition is as follows. (Electrolyte composition) Lithium salt: LiPF6 1.5 M Non-aqueous organic solvent: Ethyl methyl carbonate: Dimethyl carbonate (EMC:DMC = 20:80 by weight ratio) Additive: 0.25 parts by weight of the compound represented by the following Chemical Formula 1-1 / 10 parts by weight of fluoroethylene carbonate (FEC) / 0.5 parts by weight of succinonitrile (SN)

Chemical formula

[0103] Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1 except that 0.5 parts by weight of the compound represented by Chemical Formula 1-1 was changed and added.

[0104] Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1 except that dimethyl carbonate (DMC) was used alone as the non-aqueous organic solvent.

[0105] Example 4 A lithium secondary battery was manufactured in the same manner as in Example 1 except that 0.5 parts by weight of the compound represented by Chemical Formula 1-1 was changed and added and dimethyl carbonate (DMC) was used alone as the non-aqueous organic solvent.

[0106] Example 5 A lithium secondary battery was manufactured in the same manner as in Example 1 except that 0.5 parts by weight of the compound represented by Chemical Formula 1-2 was used instead of the compound of Chemical Formula 1-1.

Chem.

[0107] Example 6 A lithium secondary battery was manufactured in the same manner as in Example 1 except that 0.5 part by weight of the compound represented by Chemical Formula 1-3 below was used instead of the compound of Chemical Formula 1-1 in the electrolyte composition.

Chem.

[0108] Comparative Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1 except that the compound represented by Chemical Formula 1-1 was not added to the electrolyte composition.

[0109] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1 except that ethylene carbonate:ethyl methyl carbonate:dimethyl carbonate (EC:EMC:DMC = 20:10:70 by weight ratio) was used as the non-aqueous organic solvent in the electrolyte composition.

[0110] Evaluation 1: Evaluation of charge-discharge cycle characteristics at room temperature After charging and discharging the lithium secondary batteries according to Examples 1 to 6 and Comparative Examples 1 and 2 under the following conditions, the cycle characteristics were evaluated, and the results are shown in Table 1. After 200 cycles of charge and discharge under the conditions of 25°C, 0.33C charge (CC / CV, 4.45V, 0.025C Cut-off) / 1.0C discharge (CC, 2.5V Cut-off), the capacity retention rate and the change in direct current internal resistance (DC-IR) were measured.

[0111] DC-IR was calculated by the following Formulas 1 and 2 based on the voltage changed while discharging by applying a current of SOC 50C for 30 seconds, and the results are shown in Table 2 below. [Formula 1] Capacity retention rate = (Capacity after 200 cycles / Capacity after 1 cycle) * 100 [Formula 2] Change in DC internal resistance = { (DC-IR after 200 cycles) / (DC-IR after 1 cycle)} * 100

[0112] [Table 1]

[0113] Referring to Table 1, it can be confirmed that when the additive according to the present invention is used, the room temperature life characteristics are improved.

[0114] Evaluation 2: High temperature (45°C) life characteristic evaluation The lithium secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 to 2 were charged and discharged 200 cycles under the conditions of charging at 45°C, 0.33C (CC / CV, 4.45V, 0.025C Cut-off) / discharging at 1.0C (CC, 2.5V Cut-off), and the capacity retention rate and the change in the direct current internal resistance (DC-IR: Direct current internal resistance) were measured.

[0115] The DC-IR was calculated by the above Formulas 1 and 2 based on the voltage changed while discharging by applying a current of SOC 50C for 30 seconds, and the results are shown in Table 2 below.

[0116] [Table 2]

[0117] Referring to Table 2, it can be confirmed that when the additive according to the present invention is used, the characteristics of the high temperature life are improved.

[0118] Evaluation 3: High temperature storage characteristic evaluation (capacity retention rate / capacity recovery rate / DC-IR) The charge-discharge capacity was measured by performing one charge-discharge cycle at 0.33C on the lithium secondary batteries fabricated in Examples 1 to 6 and Comparative Examples 1 and 2 (before high-temperature storage). Also, after charging the lithium secondary batteries fabricated in Examples 1 to 6 and Comparative Examples 1 and 2 to SOC 100% (the state of being charged to 100% of the total charge capacity of the battery), storing them at 60°C for 30 days, and then discharging them under constant current conditions up to 3.0V at 0.33C, the initial discharge capacity was measured.

[0119] Again, the battery was recharged under the conditions of constant current up to 4.3V at 0.33C and constant voltage with 0.02C as the end current, and then discharged under constant current conditions up to 3.0V at 0.33C to measure the discharge capacity for two cycles. The ratio of the first discharge capacity to the initial discharge capacity was defined as the retention capacity, and the second discharge capacity was defined as the recovery capacity.

[0120] The initial DC resistance (DCIR) was measured for the lithium secondary batteries fabricated in Examples 1 to 6 and Comparative Examples 1 and 2 using the ΔV / ΔI (change in voltage / change in current) value. After setting the maximum energy state inside the battery to the fully charged state (SOC 100%), storing it at a high temperature (60°C) for 30 days in this state, the DC resistance was measured, and the DCIR increase rate (%) was calculated using the following formula 3, and the results are shown in Table 3 below. [Formula 3] DC-IR increase rate = (DCIR after 30 days / initial DCIR) * 100

[0121]

Table 3

[0122] Referring to Table 3 above, it can be seen that the lithium secondary batteries according to Examples 1 to 6 have improved retention capacity and recovery capacity during high-temperature storage and suppressed resistance change rate compared to Comparative Examples 1 and 2.

[0123] The preferred embodiments of the present invention have been described above. However, the present invention is not limited thereto, and various modifications can be made and implemented within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that these also belong to the scope of the present invention.

Explanation of Reference Signs

[0124] 100: Lithium secondary battery 112: Negative electrode 113: Separator 114: Positive electrode 120: Battery container 140: Encapsulating member

Claims

1. An electrolytic solution containing a non-aqueous organic solvent, a lithium salt, and an additive; A positive electrode containing a positive electrode active material; and A negative electrode containing a negative electrode active material, wherein the non-aqueous organic solvent contains ethylene carbonate and a chain carbonate contained in an amount of less than 5% by weight based on the total amount of the electrolytic solution, the chain carbonate contains ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a weight ratio of 0:100 to 50:50, the additive contains a compound represented by the following Chemical Formula 1, the positive electrode active material is one represented by the following Chemical Formula 2, a lithium secondary battery: 【Chemical 1】 In the above Chemical Formula 1, R １ to R ４ each independently represents hydrogen, halogen, a cyano group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, or a substituted or unsubstituted heterocyclic group having 2 to 30 carbon atoms; [Chemical Formula 2] Li ａ Ni ｘ Mn １－ｘ－ｙ A ｙ O ２±ｂ X ｃ In the above Chemical Formula 2, 0.9 ≦ a ≦ 1.2, 0 ≦ b ≦ 0.1, 0 ≦ c ≦ 0.1, 0.5 ≦ x ≦ 0.95, and 0 ≦ y < 0.3, A is one or more elements selected from the group consisting of B, Na, Mg, Al, Ti, and Si, X is one or more elements selected from S, F, P, and Cl.

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

3. The lithium secondary battery according to Claim 1, wherein the chain carbonate further contains at least one of diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

4. R in Chemical Formula 1 １ ~R ４ At least one of which is an alkyl group having 1 to 20 carbon atoms which is substituted or unsubstituted with an electron-withdrawing group, an aryl group having 6 to 20 carbon atoms which is substituted or unsubstituted with an electron-withdrawing group, or a heterocyclic group having 2 to 30 carbon atoms which is substituted or unsubstituted with an electron-withdrawing group. The lithium secondary battery according to claim 1.

5. The electron-withdrawing group is at least one selected from the group consisting of halogen, isocyanate group (-NCO), isothiocyanate group (-NCS), cyanate group (-OCN), thiocyanate group (-SCN), cyano group (-CN), isocyano group (-NC), -N = C = N- group, -N = S = N- group, nitro group (NO2), trifluoromethane (CF ３ ), pentafluoroethane (C ２ F ５ ), trifluoromethanesulfonyl (SO ２ CF ３ ), pentafluoroethanesulfonyl (SO ２ C ２ F ５ ), trifluoromethanesulfonate (SO ３ CF ３ ), pentafluoroethanesulfonate (SO ３ C ２ F ５ ), pentafluorophenyl (C ６ F ５ ), acetyl (COCH ３ ), ethyl ketone (COC ２ H ５ ), propyl ketone (COC ３ H ７ ), butyl ketone (COC ４ H ９ ), pentyl ketone (COC ５ H １１ ), hexyl ketone (COC ６ H １３ ), ethanoate (CO ２ CH ３ ), propanoate (CO ２ C ２ H ５ ), butanoate (CO ２ C ３ H ７ ), pentanoate (CO ２ C ４ H ９ ), hexanoate (CO ２ C ５ H １１ ), and the lithium secondary battery according to claim 4.

6. R in the chemical formula (1) ２ and R ３ The lithium secondary battery according to claim 1, wherein at least one of them is hydrogen.

7. R in the chemical formula (1) ２ and R ３ are each hydrogen. The lithium secondary battery according to claim 1.

8. The lithium secondary battery according to Claim 1, wherein the compound represented by Chemical Formula 1 is one selected from the compounds listed in the following Group 1: [Chemical 2] 。

9. The lithium secondary battery according to Claim 1, wherein the compound represented by Chemical Formula 1 is contained in an amount of 0.01 to 5.0 parts by weight based on 100 parts by weight of the total electrolytic solution for the lithium secondary battery.

10. The electrolyte further contains at least one other additive among vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinyl ethylene 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 ), and 2 - fluorobiphenyl (2 - FBP). The lithium secondary battery according to claim 1.

11. The lithium secondary battery according to Claim 1, wherein x in Chemical Formula 2 is 0.8 ≦ x ≦ 0.

95.

12. The positive electrode active material is LiNi ０．７５ Mn ０．２５ O ２ 、LiNi ０．８０ Mn ０．２０ O ２ 、LiNi ０．８５ Mn ０．１５ O ２ 、LiNi ０．９０ Mn ０．１０ O ２ or LiNi ０．９５ Mn ０．０５ O ２ and a solid solution thereof, the lithium secondary battery according to claim 1.

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

14. The lithium secondary battery according to Claim 1, wherein the lithium secondary battery has a charging upper limit voltage of 4.35 V or more.

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