Additive and lithium secondary battery electrolyte and lithium secondary battery comprising the same

Abstract

Provided are an additive represented by Chemical Formula 1, an electrolyte for a lithium secondary battery including the same, and a lithium secondary battery. Details of Chemical Formula 1 are the same as those described in the specification.

Description

Technical Field

[0001] This disclosure relates to additives, electrolytes, and lithium secondary batteries for use in lithium secondary batteries. Background Technology

[0002] Lithium-ion batteries are rechargeable and have three or more times the energy density per unit weight of traditional lead-acid, nickel-cadmium, nickel-metal hydride, and nickel-zinc batteries. They can also be charged at high rates. Therefore, they are commercially manufactured for use in laptops, cell phones, power tools, electric bicycles, etc., and research on further improving their energy density is being actively conducted.

[0003] This lithium secondary battery is manufactured by injecting an electrolyte into a battery cell, the battery cell comprising: a positive electrode including a positive electrode active material capable of intercalating / deintercalating lithium ions and a negative electrode active material including a negative electrode active material capable of intercalating / deintercalating lithium ions.

[0004] In particular, the electrolyte uses an organic solvent in which lithium salts are dissolved, and this electrolyte is important in determining the stability and performance of lithium secondary batteries.

[0005] LiPF6, the most commonly used lithium salt as an electrolyte, has the problem of accelerating solvent consumption and generating large amounts of gas through reaction with the electrolyte's organic solvent. When LiPF6 decomposes, it produces LiF and PF5, which cause electrolyte depletion in the battery, leading to high-temperature performance degradation and poor safety.

[0006] Accordingly, electrolytes that offer improved safety and do not degrade in performance, even under high-temperature conditions, are required. Summary of the Invention

[0007] Technical issues

[0008] The implementation provides an additive with improved thermal stability.

[0009] Another embodiment provides a lithium secondary battery with improved cycle life characteristics, high-temperature safety and high-temperature reliability by applying additives, and in particular, a lithium secondary battery with improved high-temperature storage characteristics and puncture safety by reducing gas generation and resistance increase rate during high-temperature storage.

[0010] Another embodiment provides a lithium secondary battery including an electrolyte for a lithium secondary battery.

[0011] Technical solution

[0012] Embodiments of the present invention provide an additive represented by chemical formula 1.

[0013] [Chemical Formula 1]

[0014]

[0015] In chemical formula 1,

[0016] A, B, and C are each independently a substituted or unsubstituted nitrogen-containing heterocyclic group.

[0017] The nitrogen in A, B, and C is each linked to a P=O group via a σ bond.

[0018] A, B, and C can each be independently a substituted or unsubstituted nitrogen-containing aromatic heterocyclic group or a substituted or unsubstituted nitrogen-containing non-aromatic heterocyclic group.

[0019] The substituted or unsubstituted nitrogen-containing aromatic heterocyclic group may be a substituted or unsubstituted pyrrole group, a substituted or unsubstituted pyrazol group, a substituted or unsubstituted imidazolyl group, a substituted or unsubstituted triazolyl group, a substituted or unsubstituted oxazinyl group, a substituted or unsubstituted thiazinyl group, a substituted or unsubstituted benzimidazolyl group, a substituted or unsubstituted indolyl group, a substituted or unsubstituted isoindolyl group, a substituted or unsubstituted benzoxazinyl group, a substituted or unsubstituted benzothiazinyl group, a substituted or unsubstituted phenothiazinyl group, or a substituted or unsubstituted phenothiazinyl group.

[0020] The substituted or unsubstituted nitrogen-containing non-aromatic heterocyclic group may be substituted or unsubstituted 2-pyrrolinyl, substituted or unsubstituted 3-pyrrolinyl, substituted or unsubstituted pyrrolidinyl, substituted or unsubstituted pyrazolyl, substituted or unsubstituted imidazolidinyl, substituted or unsubstituted piperidinyl, substituted or unsubstituted piperazinyl, substituted or unsubstituted morpholinyl, substituted or unsubstituted thiomorpholinyl, substituted or unsubstituted dithiazinyl, substituted or unsubstituted indololinyl, or substituted or unsubstituted isoindololinyl.

[0021] A, B, and C can each independently be a substituted or unsubstituted pyrrolidinyl, a substituted or unsubstituted piperidinyl, a substituted or unsubstituted pyrrolidinyl, a substituted or unsubstituted pyrazolyl, a substituted or unsubstituted imidazolyl, or a substituted or unsubstituted benzimidazolyl.

[0022] A, B, and C can each be independently selected from the substituents listed in Group 1.

[0023] [Group 1]

[0024]

[0025] Another embodiment of the present invention provides an electrolyte for lithium secondary batteries, comprising a non-aqueous organic solvent, a lithium salt, and the aforementioned additives.

[0026] The amount of additives included may be from 0.1 wt% to 10 wt%, depending on the total weight of the electrolyte used in the lithium secondary battery.

[0027] The amount of additives included may be from 0.1 wt% to 5.0 wt% based on the total weight of the electrolyte used in lithium secondary batteries.

[0028] The amount of additives included may be from 0.1 wt% to 3.0 wt% based on the total weight of the electrolyte used in lithium secondary batteries.

[0029] Another embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0030] The active material for the positive electrode can be a lithium composite oxide represented by chemical formula 4.

[0031] [Chemical Formula 4]

[0032] Li x M 1 1-y-z M 2 y M 3 z O2

[0033] In chemical formula 4,

[0034] 0.5≤x≤1.8, 0≤y≤1, 0≤z≤1, 0≤y+z<1 and M 1 M 2 and M 3 Each can be any one of metals selected from, such as Ni, Co, Mn, Al, Sr, Mg, or La, and combinations thereof.

[0035] For example, the positive electrode active material may be a lithium composite oxide represented by at least one of chemical formulas 4-1 to 4-3.

[0036] [Chemical Formula 4-1]

[0037] Li x1 Ni y1 Co z1 Al 1-y1-z1 O2

[0038] In chemical formula 4-1,

[0039] 1≤x1≤1.2, 0<y1<1 and 0<z1<1.

[0040] [Chemical Formula 4-2]

[0041] Li x2 Niy2 Co z2 Mn 1-y2-z2 O2

[0042] In chemical formula 4-2,

[0043] 1≤x²≤1.2, 0<y²<1 and 0<z²<1.

[0044] [Chemical Formula 4-3]

[0045] Li x3 CoO2

[0046] In chemical formula 4-3,

[0047] 0.5 < x3 ≤ 1.

[0048] Beneficial effects

[0049] By applying additives that improve thermal safety, the increase in internal resistance, gas generation, and voltage drop after placement at high temperatures can be prevented, thus enabling the implementation of lithium secondary batteries with improved high-temperature characteristics and puncture safety. Attached Figure Description

[0050] Figure 1 This is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention.

[0051] Figure 2 For compounds with chemical formula a 1 H-NMR spectrum.

[0052] Figure 3 For compounds with chemical formula a 13 C-NMR spectrum.

[0053] Figure 4 For compounds with chemical formula a 31 P-NMR image.

[0054] Figure 5 To show the temperature and voltage changes of lithium secondary battery cells according to Examples 1 to 3 and Comparative Examples 1 and 2 based on thermal exposure.

[0055] Figure 6 The graphs show the changes in cell surface temperature and cell voltage of lithium secondary battery cells of Examples 1 to 3, and Comparative Examples 1 and 2 after puncture at 150 mm / s.

[0056] Figure 7 A graph measuring the CID (current cut-off device) operation time of lithium secondary battery cells according to Examples 1 to 3 and Comparative Examples 1 and 2.

[0057] Figure 8 A graph showing the room temperature charge and discharge cycle characteristics of the lithium secondary battery cells according to Examples 1 to 3 and Comparative Examples 1 and 2.

[0058] Figure 9 To show the resistance increase rate and capacity recovery rate of the lithium secondary battery cells according to Examples 1 to 3 and Comparative Examples 1 and 2 after being placed at 60°C for 30 days.

[0059] <Explanation of reference numerals in the attached drawings>

[0060] 100: Lithium secondary battery

[0061] 112: Negative electrode

[0062] 113: Diaphragm

[0063] 114: Positive electrode

[0064] 120: Battery casing

[0065] 140: Sealing component Detailed Implementation

[0066] The following describes in detail, with reference to the accompanying drawings, a lithium secondary battery according to embodiments of the present invention. However, these embodiments are exemplary, and the invention is not limited thereto; rather, the invention is defined by the scope of the claims.

[0067] Depending on the type of separator and electrolyte, lithium secondary batteries can be classified as lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries. Depending on shape, they can also be classified as cylindrical, prismatic, coin-shaped, pouch-shaped, etc. Furthermore, depending on size, they can be block-shaped or thin-film type. The structures and manufacturing methods for lithium-ion batteries disclosed herein are well known in the art.

[0068] Here, a cylindrical lithium secondary battery will be described as an example of a lithium secondary battery. Figure 1 The structure of a lithium secondary battery according to an embodiment is illustrated schematically.

[0069] refer to Figure 1 The lithium secondary battery 100 according to the embodiment includes: a battery cell including a positive electrode 114, a negative electrode 112 facing the positive electrode 114, and a separator 113 between the positive electrode 114 and the negative electrode 112; an electrolyte (not shown) impregnating the positive electrode 114, the negative electrode 112 and the separator 113; a battery container 120 containing the battery cell; and a sealing member 140 for sealing the container 120.

[0070] In this specification, unless otherwise defined, “substitution” means that at least one hydrogen atom in a substituent or compound is replaced by: deuterium, halogen, hydroxyl, amino, substituted or unsubstituted C1 to C30 amino, nitro, substituted or unsubstituted C1 to C40 silyl, C1 to C30 alkyl, C1 to C10 alkylsilyl, C6 to C30 arylsilyl, C3 to C30 cycloalkyl, C3 to C30 heterocycloalkyl, C6 to C30 aryl, C2 to C30 heteroaryl, C1 to C20 alkoxy, C1 to C10 trifluoroalkyl, cyano, or combinations thereof.

[0071] In one embodiment of the invention, "substitution" means that at least one hydrogen atom in the substituent or compound is replaced by: deuterium, C1 to C30 alkyl, C1 to C10 alkylsilyl, C6 to C30 arylsilyl, C3 to C30 cycloalkyl, C3 to C30 heterocycloalkyl, C6 to C30 aryl, or C2 to C30 heteroaryl. In another embodiment of the invention, "substitution" means that at least one hydrogen atom in the substituent or compound is replaced by: deuterium, C1 to C20 alkyl, or C6 to C30 aryl. In another embodiment of the invention, "substitution" means that at least one hydrogen atom in the substituent or compound is replaced by: deuterium, C1 to C5 alkyl, or C6 to C18 aryl. In another embodiment of the invention, "substitution" means that at least one hydrogen atom in the substituent or compound is replaced by: deuterium, methyl, ethyl, propyl, butyl, phenyl, biphenyl, terphenyl, or naphthyl.

[0072] In this specification, unless otherwise defined, “heteroatom” means that a functional group includes 1 to 3 heteroatoms selected from N, O, S, P and Si and the remainder is carbon.

[0073] In this specification, "heterocyclic group" has the general concept of aromatic heterocyclic group and non-aromatic heterocyclic group, and may include at least one heteroatom selected from N, O, S, P and Si to replace carbon (C) in cyclic compounds such as aryl, cycloalkyl, their fused rings or combinations thereof. When the heterocyclic group is fused ring, the entire ring or each ring of the heterocyclic group may include one or more heteroatoms.

[0074] For example, "aromatic heterocyclic group" refers to an aryl group that includes at least one heteroatom selected from N, O, S, P, and Si. Two or more heteroaryl groups are directly connected by σ bonds, or when the heteroaryl group includes two or more rings, the two or more rings may be fused. When the heteroaryl group is a fused ring, each ring may include 1 to 3 heteroatoms.

[0075] In this specification, a "σ bond" refers to a bond in which orbitals formed along the axis bonded to the atomic nucleus overlap each other to form a strong bond. In other words, it means a single bond formed directly between atoms.

[0076] The additives according to the embodiments will be described below.

[0077] The additive according to an embodiment of the present invention is represented by chemical formula 1.

[0078] [Chemical Formula 1]

[0079]

[0080] In chemical formula 1,

[0081] A, B, and C are each independently a substituted or unsubstituted nitrogen-containing heterocyclic group.

[0082] The nitrogen in A, B, and C is each linked to a P=O group via a σ bond.

[0083] The additive according to an embodiment of the invention has a structure in which three nitrogen-containing heterocycles containing N are substituted in the 'P' of the phosphine oxide group (P=O), wherein the 'P' and 'N' are connected by σ bonds.

[0084] The 'N' on the 'P' of the phosphine oxide group (P=O) attached by a σ bond has a lone pair of electrons, and since the lone pair of electrons can chelate during exposure to high temperatures, it can chelate HF to capture HF, and in addition, it can chelate PF5, a strong Lewis acid that is a decomposition product of lithium salts, to stabilize it, thereby suppressing other side reactions.

[0085] Furthermore, lone pairs of electrons help stabilize the surface of the positive electrode by chelating the transition metal of the active material of the positive electrode.

[0086] During formation, the additives form a film on the surfaces of both the positive and negative electrodes, thereby suppressing the increase in electrode / electrolyte interfacial resistance during high-temperature storage and also suppressing gases generated due to additional side reactions of the electrolyte at high temperatures. Furthermore, during exposure to high temperatures, the additives remaining in the electrolyte without forming a film form an additional insulating film on the surface of the positive electrode, thus exhibiting improved thermal safety characteristics. In particular, these structures form a thick insulating film on the negative electrode during formation, which can prevent the escape of electrons accumulated in the negative electrode even when the battery is punctured, thereby suppressing fires caused by battery short circuits.

[0087] For example, A, B, and C can each be independently a substituted or unsubstituted nitrogen-containing aromatic heterocyclic group or a substituted or unsubstituted nitrogen-containing non-aromatic heterocyclic group.

[0088] For example, the substituted or unsubstituted nitrogen-containing aromatic heterocyclic group may be a substituted or unsubstituted pyrrole group, a substituted or unsubstituted pyrazol group, a substituted or unsubstituted imidazolyl group, a substituted or unsubstituted triazolyl group, a substituted or unsubstituted oxazinyl group, a substituted or unsubstituted thiazinyl group, a substituted or unsubstituted benzimidazolyl group, a substituted or unsubstituted indolyl group, a substituted or unsubstituted isoindolyl group, a substituted or unsubstituted benzoxazinyl group, a substituted or unsubstituted benzothiazinyl group, a substituted or unsubstituted phenothiazinyl group, or a substituted or unsubstituted phenothiazinyl group.

[0089] For example, the substituted or unsubstituted nitrogen-containing non-aromatic heterocyclic group may be a substituted or unsubstituted 2-pyrrolinyl, a substituted or unsubstituted 3-pyrrolinyl, a substituted or unsubstituted pyrrolidinyl, a substituted or unsubstituted pyrazolyl, a substituted or unsubstituted imidazolidinyl, a substituted or unsubstituted piperidinyl, a substituted or unsubstituted piperazinyl, a substituted or unsubstituted morpholinyl, a substituted or unsubstituted thiomorpholinyl, a substituted or unsubstituted dithiazinyl, a substituted or unsubstituted indololinyl, or a substituted or unsubstituted isoindololinyl.

[0090] For example, A, B, and C can each independently be a substituted or unsubstituted pyrrolidinyl, a substituted or unsubstituted piperidinyl, a substituted or unsubstituted pyrrolidinyl, a substituted or unsubstituted pyrazolyl, a substituted or unsubstituted imidazolyl, or a substituted or unsubstituted benzimidazolyl.

[0091] As a specific example, A, B, and C can each be independently selected from the substituents listed in Group 1.

[0092] [Group 1]

[0093]

[0094] A, B, and C may be the same as or different from each other.

[0095] For example, each of A, B, and C can be a substituted or unsubstituted imidazole group.

[0096] According to the most specific implementation method, the additive can be represented by chemical formula a.

[0097] [Chemical formula a]

[0098]

[0099] An electrolyte for a lithium secondary battery according to another embodiment of the present invention comprises a non-aqueous organic solvent, a lithium salt, and the aforementioned additives.

[0100] Based on the total weight of the electrolyte used in lithium secondary batteries, the amount of additives included can be from 0.1 wt% to 10 wt%, specifically, from 0.1 wt% to 5.0 wt%, and more specifically, from 0.1 wt% to 3.0 wt%.

[0101] When the included additives are within the specified content range, lithium secondary batteries with improved puncture safety and high-temperature reliability can be achieved by suppressing the increase in resistance at high temperatures.

[0102] In other words, when the amount of additives included is less than 0.1 wt%, there is a problem of deterioration in high-temperature storage characteristics, and when the amount of additives included is greater than 10 wt%, there is another problem of deterioration in cycle life due to increased interfacial resistance.

[0103] Non-aqueous organic solvents are used as media for transporting ions that participate in the electrochemical reactions of the battery.

[0104] Non-aqueous organic solvents can be carbonates, esters, ethers, ketones, alcohols, or aprotic solvents.

[0105] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolactone, mevalonolactone, caprolactone, etc.

[0106] Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran, etc. Additionally, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol and isopropanol, etc., and aprotic solvents may include nitriles (such as R-CN (where R is a hydrocarbon group having a C2 to C20 straight-chain, branched, or cyclic structure, and may include double bonds, aromatic rings, or ether bonds), dioxolane (such as 1,3-dioxolane), and sulfolane.

[0107] Non-aqueous organic solvents can be used alone or in mixtures of one or more, and when one or more are used in mixture, the mixing ratio can be appropriately adjusted according to the desired battery performance, as is widely understood by those skilled in the art.

[0108] Carbonate solvents are prepared by mixing cyclic and linear carbonates. In this case, the electrolyte exhibits excellent performance when the cyclic and linear carbonates are mixed in a volume ratio of 1:1 to 1:9.

[0109] In addition to carbonate solvents, non-aqueous organic solvents may further include aromatic hydrocarbon solvents. In this case, carbonate solvents and aromatic hydrocarbon solvents may be mixed in a volume ratio of 1:1 to 30:1.

[0110] Aromatic hydrocarbon solvents can be aromatic hydrocarbon compounds represented by chemical formula 2.

[0111] [Chemical Formula 2]

[0112]

[0113] In chemical formula 2, R 201 To R 206 They may be the same or different, and are selected from hydrogen, halogens, C1 to C10 alkyl groups, haloalkyl groups and combinations thereof.

[0114] Specific examples of aromatic hydrocarbon organic solvents may be selected from 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, and fluoromethylbenzene. Benzene, 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.

[0115] The electrolyte may further include vinylene carbonate, vinyl ethylene carbonate, or ethylene carbonate compounds represented by Formula 3, in order to improve the cycle life of the battery.

[0116] [Chemical Formula 3]

[0117]

[0118] In chemical formula 3, R 207 and R 208 Identical or different, and selected from hydrogen, halogen, cyano (CN), nitro (NO2), and fluorinated C1 to C5 alkyl groups, provided that R 207 and R 208 At least one of them is a halogen, a cyano (CN), a nitro (NO2), and a fluorinated C11 to C5 alkyl group, and R 207 and R 208 They are not both hydrogen.

[0119] Examples of ethylene carbonate compounds may be difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, brominated ethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of additives used to improve cycle life may be used within appropriate limits.

[0120] Lithium salts dissolve in non-aqueous organic solvents and act as a source of lithium ions in the battery, ensuring the basic operation of the lithium secondary battery and facilitating the movement of lithium ions between the positive and negative electrodes. Examples of lithium salts may include at least one selected from the following: LiPF6, LiBF4, lithium difluoro(oxalate)borate (LiDFOB), LiPO2F2, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, 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 natural numbers, for example, integers ranging from 1 to 20), LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalate)borate: LiBOB). Lithium salts can be used at concentrations ranging from 0.1M to 2.0M. When lithium salts are included in the above concentration range, the electrolyte can exhibit excellent performance and lithium-ion mobility due to optimal electrolyte conductivity and viscosity.

[0121] Another embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0122] 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.

[0123] Positive electrode active materials may include lithiated intercalation compounds that can reversibly insert and deintercalate lithium ions.

[0124] Specifically, lithium and at least one of a composite oxide of metals selected from cobalt, manganese, nickel and combinations thereof may be used.

[0125] Of course, lithium composite oxides with a coating on their surface can be used, or mixtures of composite oxides and coating compounds can be used. The coating may include at least one coating element compound selected from oxides, hydroxides, hydroxy oxides, oxycarbonates, and hydroxycarbonates of the coating element. The compound used for the coating may be amorphous or crystalline. Coating elements included in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. By using these elements in the compound, the coating can be formed in a method that does not adversely affect the properties of the positive electrode active material; for example, the method may include any coating method (e.g., spraying, dipping, etc.), but not described in more detail as this is well known to those skilled in the art.

[0126] The positive electrode active material may be, for example, at least one of lithium composite oxides represented by chemical formula 4.

[0127] [Chemical Formula 4]

[0128] Li x M 1 1-y-z M 2 y M 3 z O2

[0129] In chemical formula 4,

[0130] 0.5≤x≤1.8, 0≤y<1, 0≤z<1, 0≤y+z<1, and M 1 M 2 and M 3 Each is independently selected from any one of metals such as Ni, Co, Mn, Al, Sr, Mg or La, and combinations thereof.

[0131] In the implementation, M 1 It can be a metal such as Co, Mn, Al, Sr, Mg, or La, and M 2 and M 3 They can be Ni or Co, each independently.

[0132] In a specific implementation, M 1 It can be Mn or Al, and M 2 and M 3 They can be Ni or Co independently, but they are not limited to these.

[0133] In a more specific embodiment, the positive electrode active material may be a lithium composite oxide represented by at least one of chemical formulas 4-1 to 4-3.

[0134] [Chemical Formula 4-1]

[0135] Li x1 Ni y1 Co z1 Al 1-y1-z1 O2

[0136] In chemical formula 4-1, 1≤x1≤1.2, 0<y1<1 and 0<z1<1.

[0137] [Chemical Formula 4-2]

[0138] Li x2 Ni y2 Co z2 Mn 1-y2-z2 O2

[0139] In chemical formula 4-2,

[0140] 1≤x²≤1.2, 0<y²<1 and 0<z²<1.

[0141] [Chemical Formula 4-3]

[0142] Li x3 CoO2

[0143] In chemical formula 4-3,

[0144] 0.5 < x3 ≤ 1.

[0145] For example, in chemical formula 4-1, 1≤x1≤1.2, 0.5≤y1<1 and 0<z1≤0.5.

[0146] As a specific example, in chemical formula 4-1, 1≤x1≤1.2, 0.6≤y1<1 and 0<z1≤0.5.

[0147] As a more specific example, in chemical formula 4-1, 1≤x1≤1.2, 0.7≤y1<1 and 0<z1≤0.5.

[0148] For example, in chemical formula 4-1, 1≤x1≤1.2, 0.8≤y1<1 and 0<z1≤0.5.

[0149] For example, in chemical formula 4-2, 1≤x2≤1.2, 0.3≤y2<1 and 0.3≤z2<1.

[0150] As a specific example, in chemical formula 4-2, 1≤x²≤1.2, 0.6≤y²<1 and 0.3≤z²<1.

[0151] As a more specific example, in chemical formula 4-2, 1 ≤ x² ≤ 1.2, 0.7 ≤ y² < 1, and 0.3 ≤ z² < 1.

[0152] For example, in chemical formula 4-2, 1≤x2≤1.2, 0.8≤y2<1 and 0.3≤z2<1.

[0153] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be from 90 wt% to 98 wt%.

[0154] In embodiments of the present invention, the positive electrode active material layer may optionally include a conductive material and a binder. In this case, the binder content may be from 1 wt% to 5 wt% based on the total weight of the positive electrode active material layer.

[0155] Based on the total weight of the positive electrode active material layer, the respective contents of the conductive material and the binder can be from 1 wt% to 5 wt%.

[0156] Conductive materials are used to impart conductivity to the positive electrode and can be used as long as they are electronically conductive materials without causing chemical changes in the battery. Examples of conductive materials may include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metallic materials including metal powders or metal fibers such as copper, nickel, aluminum and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0157] The binder improves the adhesion properties between the positive electrode active material particles and between the positive electrode active material particles and the current collector, and examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin and nylon, etc., but are not limited thereto.

[0158] The positive electrode current collector may include, but is not limited to, Al.

[0159] The negative electrode includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes negative electrode active material formed on the negative electrode current collector.

[0160] The negative electrode active material may include materials that can reversibly insert / deintercalate lithium ions, lithium metal, lithium metal alloys, materials that can be doped / dedoped with lithium, or transition metal oxides.

[0161] Materials that can reversibly insert / deintercalate lithium ions may include carbon materials, which can be any commonly used carbon-based negative electrode active material in lithium secondary ion batteries, and examples may be crystalline carbon, amorphous carbon, or mixtures thereof. Crystalline carbon may be amorphous, or in the form of flakes, sheets, spheres, or fibers, natural or artificial graphite, and amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0162] Lithium metal alloys include alloys of lithium with metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0163] Materials capable of being doped / dedoped with lithium include Si, Si-C composites, and SiO. x (0 < x < 2), Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements and combinations thereof, but not Si), Sn, SnO2 and Sn-R (where R is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements and combinations thereof, but not Sn), etc., and at least one of these materials can be mixed with SiO2.

[0164] Elements Q and R can be selected from 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.

[0165] Transition metal oxides can be vanadium oxides, lithium vanadium oxides, or lithium titanium oxides.

[0166] In a specific implementation, the negative electrode active material may be a Si-C composite comprising Si-based active material and carbon-based active material.

[0167] The average particle size of the Si-based active material in the Si-C composite can be from 50 nm to 200 nm.

[0168] When the average particle size of the Si-based active material is within the above range, volume expansion during charging and discharging can be suppressed, and breakage of the conductive path due to particle breakage during charging and discharging can be prevented.

[0169] Based on the total weight of the Si-C composite, the amount of Si-based active material included can be from 1 wt% to 60 wt%, for example, from 3 wt% to 60 wt%.

[0170] In another specific embodiment, the negative electrode active material may further include crystalline carbon together with the aforementioned Si-C composite.

[0171] When the negative electrode active material comprises both a Si-C complex and crystalline carbon, the Si-C complex and crystalline carbon may be included in a mixture, and in this case, the weight ratio of the included Si-C complex to the crystalline carbon may be from 1:99 to 50:50. More specifically, the weight ratio of the included Si-C complex to the crystalline carbon may be from 5:95 to 20:80.

[0172] Crystalline carbon can be, for example, graphite, and more specifically, natural graphite, artificial graphite, or mixtures thereof.

[0173] The average particle size of crystalline carbon can range from 5 μm to 30 μm.

[0174] In this specification, the average particle size may be the particle size at 50% of the volume in the cumulative size-distribution curve (D50).

[0175] The Si-C composite may further include a shell surrounding the surface of the Si-C composite, and the shell may include amorphous carbon.

[0176] Amorphous carbon may include soft carbon, hard carbon, products of mesophase pitch carbonization, calcined coke, or mixtures thereof.

[0177] Based on 100 parts by weight of carbon-based active material, the amount of amorphous carbon included may be from 1 part by weight to 50 parts by weight, for example, from 5 parts by weight to 50 parts by weight, or from 10 parts by weight to 50 parts by weight.

[0178] In the negative electrode active material layer, the amount of negative electrode active material included, based on the total weight of the negative electrode active material layer, can be from 95 wt% to 99 wt%.

[0179] In embodiments of the present invention, the negative electrode active material layer includes a binder and optionally includes a conductive material. In the negative electrode active material layer, the binder content may be from 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer. When the negative electrode active material layer includes a conductive material, the negative electrode active material layer comprises 90 wt% to 98 wt% of negative electrode active material, 1 wt% to 5 wt% of binder, and 1 wt% to 5 wt% of conductive material.

[0180] Binders improve the adhesion properties between the active material particles of the negative electrode and between the active material particles of the negative electrode and the current collector. Binders include non-water-soluble binders, water-soluble binders, or combinations thereof.

[0181] The non-water-soluble adhesive may be selected from polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0182] Water-soluble adhesives can be rubber-based adhesives or polymer resin adhesives. Rubber-based adhesives can be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. Polymer resin adhesives can be selected from polytetrafluoroethylene, ethylene-propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0183] When a water-soluble binder is used as a negative electrode binder, a cellulose compound can be further used to provide viscosity. Cellulose compounds include one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts. The alkali metal can be Na, K, or Li. Based on 100 parts by weight of the negative electrode active material, the amount of this thickener can be from 0.1 parts by weight to 3 parts by weight.

[0184] Includes conductive materials to provide electrode conductivity, and any conductive material may be used as a conductive material unless it causes a chemical change, and examples of conductive materials may include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metallic materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0185] The negative electrode current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0186] Depending on the type of lithium secondary battery, a separator can be present between the positive and negative electrodes. The separator can be a porous substrate or a composite porous substrate.

[0187] The porous substrate can be a substrate including pores through which lithium ions can move. Porous substrates include, for example, polyethylene, polypropylene, polyvinylidene fluoride, or multiples thereof, such as polyethylene / polypropylene bilayer membranes, polyethylene / polypropylene / polyethylene trilayer membranes, polypropylene / polyethylene / polypropylene trilayer membranes, etc.

[0188] The composite porous substrate may take the form of a porous substrate and a functional layer on the porous substrate. From the perspective of ensuring additional functionality, the functional layer may be, for example, at least one of a heat-resistant layer and an adhesive layer. For example, the heat-resistant layer may include a heat-resistant resin and optionally a filler.

[0189] Additionally, the adhesive layer may include an adhesive resin and selective fillers.

[0190] The packing material can be organic or inorganic.

[0191] refer to Figure 1 The lithium secondary battery 100 according to the embodiment includes a battery cell: the battery cell includes a negative electrode 112, a positive electrode 114 facing the negative electrode 112, a separator 113 between the negative electrode 112 and the positive electrode 114, and an electrolyte (not shown) impregnating the negative electrode 112, the positive electrode 114 and the separator 113; a battery casing 120 for housing the battery cell; and a sealing member 140 for sealing the battery casing 120.

[0192] The following describes embodiments and comparative examples of the present invention. However, these embodiments are in no way intended to limit the scope of the invention.

[0193] Synthesis of additives

[0194] Synthesis example: Compounds with chemical formula a

[0195] [Reaction Scheme 1]

[0196]

[0197] From the basis Figures 2 to 4 NMR analysis data confirmed the compound with chemical formula a.

[0198] Figure 2 For compounds with chemical formula a 1 H-NMR spectrum.

[0199] Figure 3 For compounds with chemical formula a 13 C-NMR spectrum.

[0200] Figure 4 For compounds with chemical formula a 31 P-NMR image.

[0201] Manufacturing of lithium secondary battery cells

[0202] Example 1

[0203] By using LiNi as the positive electrode active material in a weight ratio of 97:2:1 0.91 Mno 0.07 Al0.02 O2, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material are mixed and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0204] A slurry of positive electrode active material was coated onto a 14 μm thick Al foil, dried at 110 °C, and pressed to manufacture the positive electrode.

[0205] The negative electrode active material was prepared by mixing artificial graphite and Si-C composite in a weight ratio of 93:7. Then, the negative electrode active material, styrene-butadiene rubber binder and carboxymethyl cellulose in a weight ratio of 97:1:2 were mixed and dispersed in distilled water to prepare a negative electrode active material slurry.

[0206] The Si-C composite comprises a core consisting of artificial graphite and silicon particles, and coal pitch coated on the surface of the core.

[0207] A negative electrode active material slurry was coated onto a 10 μm thick Cu foil, dried at 100 °C, and pressed to manufacture the negative electrode.

[0208] Electrode assemblies are manufactured by assembling positive and negative electrodes and a separator made of polyethylene with a thickness of 25 μm, and electrolyte is injected to manufacture lithium secondary battery cells.

[0209] Electrolytes have the following composition.

[0210] (Composition of electrolytes)

[0211] Salt: 1.5M LiPF6

[0212] Solvent: Ethylene carbonate: Ethyl methyl carbonate: Dimethyl carbonate (EC:EMC:DMC = 20:10:70 by volume)

[0213] Additives: comprising 0.5 wt% of a compound of chemical formula a according to the synthesis example.

[0214] (In the composition of electrolytes, "wt%" is based on the total content of electrolytes (lithium salt + non-aqueous organic solvent + additives))

[0215] Example 2

[0216] The lithium secondary battery cell was manufactured in the same manner as in Example 1, except that a compound represented by chemical formula a was added in an amount of 1.0 wt%.

[0217] Example 3

[0218] The lithium secondary battery cell was manufactured in the same manner as in Example 1, except that a compound represented by chemical formula a was added in an amount of 2.0 wt%.

[0219] Comparative Example 1

[0220] The lithium secondary battery cell was manufactured in the same manner as in Example 1, except that an electrolyte without additives was used.

[0221] Comparative Example 2

[0222]

[0223] The lithium secondary battery cell was manufactured in the same manner as in Example 1, except that triphenylphosphine oxide (CAS No. 791-28-6) manufactured by Sigma-Aldrich Corp was used in an amount of 1.0 wt%.

[0224] Assessment 1: Heat Exposure Assessment

[0225] The lithium secondary battery cells of Examples 1 to 3, Comparative Examples 1 and 2 were charged at a charging rate of 0.5C under a discharge state of 3.0V under a cutoff condition of 4.2V / 3hr, and then thermal exposure was evaluated.

[0226] Lithium-ion battery cells according to Examples 1 to 3, and Comparative Examples 1 and 2, were placed in a chamber and heated from room temperature to 140°C at a rate of 5°C / min, then held at that temperature for 1 hour. Changes were then examined, and the results were... Figure 5 As shown in the diagram. In this case, the dashed line represents the change of voltage over time, and the solid line represents the change of temperature over time.

[0227] Figure 5 To show the temperature and voltage changes of lithium secondary battery cells according to Examples 1 to 3 and Comparative Examples 1 and 2 based on thermal exposure.

[0228] refer to Figure 5 A sharp voltage drop was observed in the lithium secondary battery cells according to Examples 1 to 3, and Comparative Examples 1 and 2. When the cylindrical battery is rapidly exposed to high temperatures, gas is generated, thus increasing the internal pressure. This may cause the battery protection circuit (CID) to operate, making it unable to read the voltage. The sharp voltage drop in the lithium secondary battery cells according to Examples 1 to 3, and Comparative Examples 1 and 2 is caused by the protection circuit operating due to the gas generated by exposure to high temperatures.

[0229] However, even when the lithium secondary battery cells according to Examples 1 to 3 were exposed to a temperature of 140°C, the cells did not experience thermal runaway and maintained a temperature of 140°C. However, when the lithium secondary battery cells of Comparative Example 1 and Comparative Example 2 were exposed to a temperature of 140°C, the cells appeared to maintain a temperature of 140°C, but experienced rapid thermal runaway to 240°C (78 minutes) and 200°C (42 minutes), respectively. Accordingly, the lithium secondary battery cells of Comparative Example 1 and Comparative Example 2 not only generated gas but also experienced thermal runaway, resulting in explosions.

[0230] Accordingly, the lithium secondary battery cells according to Examples 1 to 3 exhibited higher thermal stability compared to the lithium secondary battery cells of Comparative Examples 1 and 2.

[0231] Assessment 2: Assessment of puncture safety

[0232] The permeation characteristics of lithium secondary battery cells according to Examples 1 to 3, and Comparative Examples 1 and 2 were evaluated using the following methods, and the results were... Figure 6 As shown in the image.

[0233] The puncture limit was assessed by charging the cells to SOC (State of Charge) 50 (capacity equivalent to half of the total capacity of 100) at 150 mm / s using a 2.5π nail, and attaching temperature and voltage sensors to the cell surface to obtain voltage or temperature profiles during puncture.

[0234] Figure 6 The graphs show the changes in cell surface temperature and cell voltage of lithium secondary battery cells of Examples 1 to 3, and Comparative Examples 1 and 2 after puncture at 150 mm / s.

[0235] In the lithium secondary battery cells of Examples 1 to 3 and Comparative Examples 1 and 2, the voltage dropped to 0V, indicating that the puncture caused a short circuit between the positive and negative electrodes. In this text, due to the short circuit, the cell generated a spark and was highly likely to ignite. When the positive / negative electrodes came into contact with each other due to puncture and thus a short circuit occurred, the lithium secondary battery cells of Comparative Examples 1 and 2 generated a spark and ignited, raising the battery temperature to 480°C or higher. However, the lithium secondary battery cells of Examples 1 to 3 generated a spark due to the short circuit, but maintained a temperature below 300°C without ignition. In other words, even when the positive and negative electrodes came into contact with each other and a short circuit occurred, the lithium secondary battery cells of the examples did not ignite, indicating that the cells have excellent thermal stability.

[0236] Assessment 3: Measurement of CID operation time points

[0237] The lithium secondary battery cells of Examples 1 to 3, as well as Comparative Examples 1 and 2, were charged for 3 hours at a charge / discharge rate of 0.5C in 4.35V CC / CV mode, and then the CID (current cut-off device) time point was measured after being placed in a chamber at 90°C for 20 hours.

[0238] In this paper, CID (Current Interruption Device) refers to a component in the art that detects pressure changes (i.e., an increase in pressure within a sealing device) and interrupts current at a predetermined pressure or higher, and therefore will not be elaborated upon here. Measurement results are shown in... Figure 7 middle.

[0239] Figure 7 A graph measuring the CID (current cut-off device) operation time of lithium secondary battery cells according to Examples 1 to 3 and Comparative Examples 1 and 2.

[0240] The high-temperature storage characteristics of lithium-ion batteries can be evaluated by measuring the CID operation time point.

[0241] refer to Figure 7 When stored at a high temperature of 90°C, Comparative Examples 1 and 2 exhibited a sharp voltage drop before approximately 8 hours. However, in the embodiment including the additive according to an exemplary embodiment of the present invention, the voltage drop was delayed by at least 10 hours or longer. This delayed electrolyte decomposition and reduced resistance persistence, effectively delaying OCV decline. In other words, the lithium secondary battery cell according to the present invention exhibits excellent gas suppression effects when stored at high temperatures.

[0242] Evaluation 4: Evaluation of room temperature charge and discharge cycle characteristics

[0243] The lithium secondary battery cells according to Examples 1 to 3, as well as Comparative Examples 1 and 2, were charged and discharged. Their cycle characteristics were then evaluated, and the results were... Figure 8 As shown in the image.

[0244] When charged and discharged 250 times at a rate of 0.5C within a voltage range of 2.5V to 4.2V at 25°C, the changes in discharge capacity and DC-IR (DC internal resistance) of the individual cells were examined, and the results were... Figure 8 As shown in the image.

[0245] Figure 8 A graph showing the room temperature charge and discharge cycle characteristics of the lithium secondary battery cells according to Examples 1 to 3 and Comparative Examples 1 and 2.

[0246] refer to Figure 8Examples 1 to 3 exhibited better cycle life characteristics than Comparative Examples 1 and 2, and the degree of increase in internal resistance was also improved.

[0247] Assessment 5: Evaluation of Storage Characteristics at High Temperatures

[0248] The lithium secondary battery cells according to Examples 1 to 3, and Comparative Examples 1 and 2 were stored under the following conditions, and their internal resistance and capacity retention were measured. The results were as follows: Figure 9 As shown in the image.

[0249] After being stored at high temperature (60°C) for 10 days, the DC internal resistance (DC-IR) was measured at SOC 50 under a 0.5C discharge rate.

[0250] In addition, the discharge capacity was measured for each of the lithium secondary battery cells manufactured according to Examples 1 to 3 and Comparative Examples 1 and 2. Subsequently, after being stored at a high temperature of 60°C at 10-day intervals, the cells were charged and discharged twice at 0.2C, and the discharge capacity was measured twice. The ratio of the discharge capacity after storage at high temperature to the discharge capacity before storage at high temperature was calculated, wherein the first discharge capacity ratio was obtained as the capacity retention rate, and the second discharge capacity ratio was obtained as the recovery capacity.

[0251] Figure 9 To show the resistance increase rate and capacity recovery rate of the lithium secondary battery cells according to Examples 1 to 3 and Comparative Examples 1 and 2 after being placed at 60°C for 30 days.

[0252] refer to Figure 9 In the cases of Examples 1 to 3, the high-temperature storage characteristics were further improved compared with Comparative Examples 1 and 2.

[0253] Although the invention has been described in conjunction with exemplary embodiments now considered to be practices, it should be understood that the invention is not limited to the disclosed embodiments, but rather is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. An electrolyte for lithium secondary batteries, comprising: Non-aqueous organic solvents Lithium salts, and Additives represented by chemical formula 1: [Chemical Formula 1] In chemical formula 1, A, B, and C are each independently a substituted or unsubstituted imidazole group or a substituted or unsubstituted benzimidazole group, and The nitrogen in A, B, and C is each linked to a P=O group via a σ bond. The amount of the additives included is from 0.1 wt% to 10 wt% based on the total weight of the electrolyte used in the lithium secondary battery.

2. The electrolyte for lithium secondary batteries according to claim 1, wherein... A, B, and C are each independently selected from the substituents listed in Group 1: Group 1 。 3. The electrolyte for lithium secondary batteries according to claim 1, wherein... Based on the total weight of the electrolyte for the lithium secondary battery, the amount of the additives included is from 0.1 wt% to 5.0 wt%.

4. The electrolyte for a lithium secondary battery according to claim 1, wherein... Based on the total weight of the electrolyte for the lithium secondary battery, the amount of the additives included is from 0.1 wt% to 3.0 wt%.

5. A lithium secondary battery, comprising: A positive electrode, including the positive electrode active material; A negative electrode, including the negative electrode active material; The electrolyte according to any one of claims 1 to 4.

6. The lithium secondary battery according to claim 5, wherein... The active material of the positive electrode is represented by chemical formula 4: [Chemical Formula 4] Li x M 1 1-y-z M 2 y M 3 z O2 in, In chemical formula 4, 0.5≤x≤1.8, 0≤y≤1, 0≤z≤1, 0≤y+z<1, and M 1 M 2 and M 3 Each is independently selected from any one of the metals, Ni, Co, Mn, Al, Sr, Mg or La, and combinations thereof.

7. The lithium secondary battery according to claim 5, wherein... The positive electrode active material is a lithium composite oxide represented by at least one of chemical formulas 4-1 to 4-3: [Chemical Formula 4-1] Li x1 Ni y1 Co z1 Al 1-y1-z1 O2 in, In chemical formula 4-1, 1 ≤ x1 ≤ 1.2, 0 < y1 < 1 and 0 < z1 < 1, [Chemical Formula 4-2] Li x2 Ni y2 Co z2 Mr 1-y2-z2 O2 In chemical formula 4-2, 1 ≤ x² ≤ 1.2, 0 < y² < 1 and 0 < z² < 1, [Chemical Formula 4-3] Li x3 CoO2 In chemical formula 4-3, 0.5＜ x3 ≤1。

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