Additive, electrolyte for lithium secondary battery containing the same, and lithium secondary battery

Abstract

The present invention provides an additive represented by Chemical Formula 1, an electrolyte for a lithium secondary battery containing the additive, and a lithium secondary battery. Details regarding Chemical Formula 1 are as described in the specification.

Description

Technical Field

[0001] This description relates to an additive, an electrolyte for a lithium secondary battery containing the same, and 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 than that of conventional lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, etc., and can be rapidly charged. Therefore, they have been commercialized for use in notebook computers, mobile phones, power tools, and electric bicycles, and research and development for further improving the energy density is actively underway.

[0003] Such a lithium secondary battery is used by injecting an electrolyte into a battery cell including a positive electrode containing a positive electrode active material capable of inserting (intercalating) and desorbing (deintercalating) lithium, and a negative electrode containing a negative electrode active material capable of inserting and desorbing lithium.

[0004] In particular, the electrolyte uses an organic solvent in which a lithium salt is dissolved, and such an electrolyte is important for determining the stability and performance of a lithium secondary battery.

[0005] LiPF, which is most frequently used as the lithium salt of the electrolyte 6 has a problem that it reacts with the organic solvent of the electrolyte to promote the depletion of the solvent and generate a large amount of gas. When LiPF 6 is decomposed, LiF and PF 5 are generated, which causes the depletion of the electrolyte in the battery and results in deteriorated high-temperature performance and vulnerability to safety.

[0006] Therefore, there is a demand for an electrolyte that does not deteriorate in performance even under high-temperature conditions and has improved safety.

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of one embodiment is to provide an additive having improved thermal stability.

[0008] Another object of one embodiment is to improve the life characteristics, high-temperature safety, and high-temperature reliability by applying the additive, and in particular, to improve the high-temperature storage characteristics and through-safety by reducing the gas generation amount and the resistance increase rate during high-temperature storage, and to provide an electrolyte for a lithium secondary battery.

[0009] Still another object of one embodiment is to provide a lithium secondary battery including the electrolyte for a lithium secondary battery.

Means for Solving the Problems

[0010] One embodiment of the present invention provides an additive represented by the following Chemical Formula 1.

Chem.

[0011] A, B, and C may each independently be a substituted or unsubstituted nitrogen-containing aromatic heterocycle or a substituted or unsubstituted nitrogen-containing non-aromatic heterocycle.

[0012] The substituted or unsubstituted nitrogen-containing aromatic heterocycle can be a substituted or unsubstituted pyrrolyl group, a substituted or unsubstituted pyrazolyl group, a substituted or unsubstituted imidazolyl group, a substituted or unsubstituted triazolyl group, a substituted or unsubstituted oxazine group, a substituted or unsubstituted thiazine 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 phenoxazinyl group.

[0013] The substituted or unsubstituted nitrogen-containing non-aromatic heterocycle can be a substituted or unsubstituted 2-pyrroline group, a substituted or unsubstituted 3-pyrroline group, a substituted or unsubstituted pyrrolidine group, a substituted or unsubstituted pyrazolidine group, a substituted or unsubstituted imidazolidine group, a substituted or unsubstituted piperidine group, a substituted or unsubstituted piperazine group, a substituted or unsubstituted morpholine group, a substituted or unsubstituted thiomorpholine group, a substituted or unsubstituted dithiazine group, a substituted or unsubstituted indoline group, or a substituted or unsubstituted isoindoline group.

[0014] A, B, and C can each independently be a substituted or unsubstituted pyrrolidine group, a substituted or unsubstituted piperidine group, a substituted or unsubstituted pyrrolyl group, a substituted or unsubstituted pyrazolyl group, a substituted or unsubstituted imidazolyl group, or a substituted or unsubstituted benzimidazolyl group.

[0015] A, B, and C can each independently be selected, for example, from among the substituents listed in Group 1 below.

Chemical formula

[0016] Another embodiment of the present invention provides an electrolyte for a lithium secondary battery containing a non-aqueous organic solvent, a lithium salt, and the aforementioned additive.

[0017] The additive may be contained in a content of 0.1% by weight to 10% by weight based on the total weight of the electrolyte for the lithium secondary battery.

[0018] The additive may be contained in a content of 0.1% by weight to 5.0% by weight based on the total weight of the electrolyte for the lithium secondary battery.

[0019] The additive may be contained in a content of 0.1% by weight to 3.0% by weight based on the total weight of the electrolyte for the lithium secondary battery.

[0020] Another embodiment of the present invention provides a lithium secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and the above-described electrolyte.

[0021] The positive electrode active material may be a lithium composite oxide represented by the following Chemical Formula 4. [Chemical Formula 4] Li x M 1 1-y-z M 2 y M 3 z O 2 (In the above 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 may each independently be any one selected from metals such as Ni, Co, Mn, Al, Sr, Mg, or La and combinations thereof.)

[0022] As an example, the positive electrode active material may be a lithium composite oxide represented by at least one of the following Chemical Formulas 4-1 to 4-3: [Chemical Formula 4-1] Li x1 Ni y1 Co z1 Al 1-y1-z1 O 2 (In the 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 Mn 1-y2-z2 O 2 (In the chemical formula 4-2, 1 ≦ x2 ≦ 1.2, 0 < y2 < 1, and 0 < z2 < 1); [Chemical formula 4-3] Li x3 CoO 2 (In the chemical formula 4-3, 0.5 < x3 ≦ 1).

Advantages of the Invention

[0023] By applying an additive with improved thermal safety, an increase in the internal resistance of the battery and gas generation after high-temperature storage are suppressed, a voltage drop is suppressed, and a lithium secondary battery with improved high-temperature characteristics and through-safety can be realized.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode 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 as an example, and the present invention is not limited thereby, and the present invention is defined only by the scope of the claims described later.

[0026] Lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, lithium polymer batteries, etc. according to the types of the separator and the electrolyte used, can be classified into cylindrical, square, coin-type, pouch-type, etc. according to the form, and can be classified into bulk type and thin film type according to the size. Since the structures and manufacturing methods of these batteries are widely known in the art, detailed descriptions thereof are omitted.

[0027] Here, a cylindrical lithium secondary battery will be 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 containing an electrolyte (not shown) that impregnates the positive electrode 114, the negative electrode 112, and the separator 113, a battery container 120 that houses the battery cell, and a sealing member 140 that seals the battery container 120.

[0028] As used herein, unless otherwise defined, "substituted" means that at least one hydrogen in a substituent or a compound is substituted with deuterium, a halogen group, a hydroxyl group, an amino group, a substituted or unsubstituted C1-C30 amine group, a nitro group, a substituted or unsubstituted C1-C40 silyl group, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C20 alkoxy group, a C1-C10 trifluoroalkyl group, a cyano group, or a combination thereof.

[0029] In one example of the present invention, "substituted" means that at least one hydrogen in a substituent or a compound is substituted with deuterium, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, or a C2-C30 heteroaryl group. 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 C1-C20 alkyl group, or a C6-C30 aryl group. 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 C1-C5 alkyl group, or a C6-C18 aryl group. 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 methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, or a naphthyl group.

[0030] As used herein, unless otherwise defined, "hetero" means containing 1 to 3 heteroatoms selected from the group consisting of N, O, S, P, and Si in one functional group, and the remainder being carbon.

[0031] As used herein, the term "heterocyclic group" is a generic term encompassing aromatic heterocyclic rings and non-aromatic heterocyclic rings, and refers to a ring containing at least one heteroatom selected from the group consisting of N, O, S, P, and Si in place of carbon (C) within a ring compound such as an aryl group, a cycloalkyl group, a fused ring thereof, or a combination thereof. When the heterocyclic group is a fused ring, the entire heterocyclic group or each individual ring thereof can contain one or more heteroatoms.

[0032] As an example, an "aromatic heterocyclic group" means containing at least one heteroatom selected from the group consisting of N, O, S, P, and Si within an aryl group. Two or more heteroaryl groups can be directly linked through a sigma bond, or when the heteroaryl group contains two or more rings, the two or more rings can be fused to each other. When the heteroaryl group is a fused ring, each individual ring can contain 1 to 3 of the heteroatoms.

[0033] As used herein, the term "sigma bond" means a bond formed by the parallel overlap of orbitals formed along the axis connecting the nuclei of atoms, thereby forming a strong bond. That is, it means directly forming a single bond between atoms.

[0034] Hereinafter, an additive according to an embodiment will be described.

[0035] An additive according to an embodiment of the present invention is represented by the following Chemical Formula 1: [Chemical Formula] (In Chemical Formula 1, A, B, and C are each independently a substituted or unsubstituted nitrogen-containing heterocyclic ring, and the nitrogen contained in A, B, and C is each linked to a P=O group by a sigma bond).

[0036] The additive according to one embodiment of the present invention has a structure in which three nitrogen-containing heterocycles in which N is contained in the "P" of the phosphine oxide group (P=O) are substituted, and the "P" and "N" are linked by a sigma bond.

[0037] N linked to "P" of the phosphine oxide group (P=O) by a sigma bond has a lone pair of electrons, and since the lone pair of electrons can be chelated, HF can be trapped by chelating with HF during high-temperature exposure. It can chelate with PF, which is a strong Lewis acid and a decomposition product of lithium salts, to suppress additional side reactions. 5 Additional side reactions can be suppressed by chelating and stabilizing it.

[0038] In addition, the lone pair of electrons also helps to stabilize the surface of the positive electrode by chelating with the transition metal of the positive electrode active material.

[0039] Such a structure forms a film on the surfaces of the positive electrode and the negative electrode during chelation, thereby suppressing an increase in the interfacial resistance between the electrode and the electrolyte during high-temperature storage and suppressing gas generation due to additional electrolyte side reactions at high temperatures. In addition, the additive remaining in the electrolyte without forming a film forms an additional insulating film on the surface of the positive electrode during high-temperature exposure, thereby having the effect of improving thermal safety characteristics. This structure, in particular, forms a thick insulating film on the negative electrode during chelation, which prevents electrons accumulated on the negative electrode from escaping even in a situation where the battery is penetrated, thereby suppressing ignition due to battery short circuit.

[0040] As an example, A, B, and C can each independently be a substituted or unsubstituted nitrogen-containing aromatic heterocycle or a substituted or unsubstituted nitrogen-containing non-aromatic heterocycle.

[0041] For example, the substituted or unsubstituted nitrogen-containing aromatic heterocycle may be a substituted or unsubstituted pyrrolyl group, a substituted or unsubstituted pyrazolyl group, a substituted or unsubstituted imidazolyl group, a substituted or unsubstituted triazolyl group, a substituted or unsubstituted oxazine group, a substituted or unsubstituted thiazine 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 phenoxazinyl group.

[0042] For example, the substituted or unsubstituted nitrogen-containing non-aromatic heterocycle may be a substituted or unsubstituted 2-pyrroline group, a substituted or unsubstituted 3-pyrroline group, a substituted or unsubstituted pyrrolidine group, a substituted or unsubstituted pyrazolidine group, a substituted or unsubstituted imidazolidine group, a substituted or unsubstituted piperidine group, a substituted or unsubstituted piperazine group, a substituted or unsubstituted morpholine group, a substituted or unsubstituted thiomorpholine group, a substituted or unsubstituted dithiazine group, a substituted or unsubstituted indoline group, or a substituted or unsubstituted isoindoline group.

[0043] As an example, A, B, and C may each independently be a substituted or unsubstituted pyrrolidine group, a substituted or unsubstituted piperidine group, a substituted or unsubstituted pyrrolyl group, a substituted or unsubstituted pyrazolyl group, a substituted or unsubstituted imidazolyl group, or a substituted or unsubstituted benzimidazolyl group.

[0044] As a specific example, A, B, and C may each independently be selected from the substituents listed in Group 1 below.

Chemical formula

[0045] A, B, and C may be the same as or different from each other.

[0046] For example, each of the above A, B, and C may be a substituted or unsubstituted imidazolyl group.

[0047] According to a most specific embodiment, the additive may be represented by the following chemical formula a.

Chemical formula

[0048] An electrolyte for a lithium secondary battery according to another embodiment of the present invention includes a non-aqueous organic solvent, a lithium salt, and the aforementioned additive.

[0049] The additive may be included in a content of 0.1% by weight to 10% by weight, specifically 0.1% by weight to 5.0% by weight, and more specifically 0.1% by weight to 3.0% by weight based on the total weight of the electrolyte for the lithium secondary battery.

[0050] When the content range of the additive is as described above, it is possible to prevent an increase in resistance at high temperatures, reduce the amount of gas generation, and realize a lithium secondary battery with improved through-safety and high-temperature reliability.

[0051] That is, when the content of the additive is less than 0.1% by weight, there is a problem that the high-temperature storage characteristics deteriorate, and when it exceeds 10% by weight, there is a problem that the life is reduced due to an increase in interfacial resistance.

[0052] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0053] As the non-aqueous organic solvent, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents can be used.

[0054] As the carbonate solvent, 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), 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. Also, 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, ring, or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolane, etc. can be used.

[0055] The non-aqueous organic solvent can be used alone or in combination of one or more. When used in combination of one or more, the mixing ratio can be appropriately adjusted according to the intended battery performance, which can be widely understood by those skilled in the art.

[0056] In addition, in the case of the carbonate solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, the cyclic carbonate and the chain carbonate may be used in a volume ratio of 1:1 to 1:9 so that the performance of the electrolyte may be excellent.

[0057] 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 may be mixed at a volume ratio of 1:1 to 30:1.

[0058] As the aromatic hydrocarbon-based solvent, an aromatic hydrocarbon-based compound represented by the following Chemical Formula 2 can be used:

Chemical Formula

[0059] Specific examples of the aromatic hydrocarbon-based 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 selected from the group consisting of these.

[0060] The electrolyte may further contain vinylene carbonate, vinyl ethylene carbonate, or an ethylene carbonate compound represented by the following Chemical Formula 3 as a life improvement additive to improve battery life: [Chemical formula] (In the above Chemical Formula 3, R 207 and R 208 are the same as or different from each other and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO 2 ), and a fluorinated alkyl group having 1 to 5 carbon atoms. At least one of the said R 207 and R 208 is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO 2 ), and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that R 207 and R 208 are not simultaneously hydrogen).

[0061] Typical examples of the ethylene carbonate compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. When such a life improvement additive is further used, its usage amount can be appropriately adjusted.

[0062] The lithium salt is dissolved in a non-aqueous organic solvent and 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. Typical examples of such a lithium salt include LiPF 6 , LiBF 4 , LiDFOP, LiDFOB, LiPO 2 F 2 , LiSbF 6 , LiAsF6 , LiN(SO 2 C 2 F 5 ) 2 , Li(CF 3 SO 2 ) 2 , LiN(SO 3 C 2 F 5 ) 2 , Li(FSO 2 ) 2 N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC 4 F 9 SO 3 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 )(where x and y are natural numbers, for example, integers from 1 to 20), LiCl, LiI, and LiB(C 2 O 4 ) 2 (lithium bis(oxalato) borate: LiBOB). One or more selected from the group consisting of these are mentioned. 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 included in the above range, since the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance can be shown, and lithium ions can move effectively.

[0063] Another embodiment of the present invention provides a lithium secondary battery including a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; and the electrolyte described above.

[0064] The positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer contains a positive electrode active material.

[0065] As the positive electrode active material, a compound (lithiated insertion compound) capable of reversible insertion and desorption of lithium can be used.

[0066] Specifically, at least one of composite oxides of metals selected from cobalt, manganese, nickel and combinations thereof and lithium can be used.

[0067] Of course, those having a coating layer on the surface of the composite oxide can also be used, or the composite oxide and the composite oxide 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 oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements and hydroxycarbonates of coating elements. The compounds forming these coating layers can be amorphous or crystalline. As the coating elements contained in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or mixtures 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 it does not adversely affect the physical properties of the positive electrode active material (for example, spray coating, dipping method, etc.). Since this is a content well understood by those skilled in the art, detailed description is omitted.

[0068] The positive electrode active material can be, for example, one or more of lithium composite oxides represented by the following Chemical Formula 4: [Chemical Formula 4] Li x M 1 1-y-z M 2 y M 3 z O 2 (In the above Chemical Formula 4, 0.5 ≦ x ≦ 1.8, 0 ≦ y < 1, 0 ≦ z < 1, 0 ≦ y + z < 1, M 1 , M 2 and M 3 can each independently be any one selected from metals such as Ni, Co, Mn, Al, Sr, Mg or La and combinations thereof).

[0069] In one embodiment, the M 1 can be a metal such as Co, Mn, Al, Sr, Mg or La, and the M 2 and M 3 can each independently be Ni or Co.

[0070] In a specific embodiment, the M 1 can be Mn or Al, and the M 2 and M 3 can each independently be Ni or Co, but is not limited thereto.

[0071] In a more specific embodiment, the positive electrode active material can be a lithium composite oxide represented by at least one of the following Chemical Formulas 4-1 to 4-3: [Chemical Formula 4-1] Li x1 Ni y1 Co z1 Al 1-y1-z1 O 2 (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 Mn 1-y2-z2 O 2 (In Chemical Formula 4-2, 1 ≦ x2 ≦ 1.2, 0 < y2 < 1, and 0 < z2 < 1); [Chemical Formula 4-3] Li x3 CoO 2 (In Chemical Formula 4-3, 0.5 < x3 ≦ 1).

[0072] As an example, in the chemical formula 4-1, 1 ≦ x1 ≦ 1.2, 0.5 ≦ y1 < 1, and 0 < z1 ≦ 0.5 can be satisfied.

[0073] As a specific example, in the chemical formula 4-1, 1 ≦ x1 ≦ 1.2, 0.6 ≦ y1 < 1, and 0 < z1 ≦ 0.5 can be satisfied.

[0074] As a more specific example, in the chemical formula 4-1, 1 ≦ x1 ≦ 1.2, 0.7 ≦ y1 < 1, and 0 < z1 ≦ 0.5 can be satisfied.

[0075] For example, in the chemical formula 4-1, 1 ≦ x1 ≦ 1.2, 0.8 ≦ y1 < 1, and 0 < z1 ≦ 0.5 can be satisfied.

[0076] As an example, in the chemical formula 4-2, 1 ≦ x2 ≦ 1.2, 0.3 ≦ y2 < 1, and 0.3 ≦ z2 < 1 can be satisfied.

[0077] As a specific example, in the chemical formula 4-2, 1 ≦ x2 ≦ 1.2, 0.6 ≦ y2 < 1, and 0.3 ≦ z2 < 1 can be satisfied.

[0078] As a more specific example, in the chemical formula 4-2, 1 ≦ x2 ≦ 1.2, 0.7 ≦ y2 < 1, and 0.3 ≦ z2 < 1 can be satisfied.

[0079] For example, in the chemical formula 4-2, 1 ≦ x2 ≦ 1.2, 0.8 ≦ y2 < 1, and 0.3 ≦ z2 < 1 can be satisfied.

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

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

[0082] The content of the conductive material and the binder may each be 1 wt% to 5 wt% based on the total weight of the positive electrode active material layer.

[0083] The conductive material is used to impart conductivity to the positive electrode, and any electron conductive material that does not cause a chemical change in the configured battery can be used. 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.

[0084] The binder plays a role in causing the positive electrode active material particles to adhere well to each other and causing the positive electrode active material to adhere well to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, 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.

[0085] As the positive electrode current collector, Al can be used, but is not limited thereto.

[0086] 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.

[0087] The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material dopable and dedopable with lithium, or a transition metal oxide.

[0088] As the substance capable of reversibly inserting / desorbing the lithium ions, carbonaceous substances can be used, and any carbonaceous negative electrode active material generally used in lithium secondary batteries can be used. Representative 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.

[0089] As the alloy of the lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0090] As the substance capable of doping and dedoping lithium, Si, Si-C composite, SiOx (0 < x < 2), Si-Q alloy (wherein 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, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), Sn, SnO 2 , Sn-R (wherein R is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn), and the like can be mentioned. Also, at least one of these can be mixed with SiO 2 and used.

[0091] As the elements Q and R, 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 can be used.

[0092] Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, or lithium titanate.

[0093] In a specific embodiment, the negative electrode active material can be a Si-C composite including a Si-based active material and a carbon-based active material.

[0094] The average particle size of the Si-based active material in the Si-C composite can be 50 nm to 200 nm.

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

[0096] The Si-based active material can 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.

[0097] In another specific embodiment, the negative electrode active material can further include crystalline carbon together with the above-described Si-C composite.

[0098] When the negative electrode active material contains the Si-C composite and crystalline carbon, the Si-C composite and crystalline carbon can be contained in the form of a mixture, and in this case, the Si-C composite and crystalline carbon can be contained in a weight ratio of 1:99 to 50:50. More specifically, the Si-C composite and crystalline carbon can be contained in a weight ratio of 5:95 to 20:80.

[0099] The crystalline carbon can include, for example, graphite, and more specifically, can include natural graphite, artificial graphite, or a mixture thereof.

[0100] The average particle size of the crystalline carbon can be 5 μm to 30 μm.

[0101] In this specification, the average particle size can be the particle size (D50) at 50% by volume in the cumulative size-distribution curve.

[0102] The Si-C composite can further include a shell surrounding the surface of the Si-C composite, and the shell can include amorphous carbon.

[0103] The amorphous carbon can include soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or a mixture thereof.

[0104] The amorphous carbon can be included in an amount of 1 to 50 parts by weight, for example, 5 to 50 parts by weight, or 10 to 50 parts by weight based on 100 parts by weight of the carbon-based active material.

[0105] In the negative electrode active material layer, the content of the negative electrode active material can be 95% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

[0106] In one embodiment of the present invention, the negative electrode active material layer includes a binder and can optionally further include a conductive material. The content of the binder in the negative electrode active material layer can be 1% by weight to 5% by weight based on the total weight of the negative electrode active material layer. When further including a conductive material, 90% by weight to 98% by weight of the negative electrode active material, 1% by weight to 5% by weight of the binder, and 1% by weight to 5% by weight of the conductive material can be used.

[0107] 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.

[0108] 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.

[0109] Examples of the water-soluble binder include a rubber-based binder or a polymer resin binder. The rubber-based binder can 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 can 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.

[0110] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included. Examples of this cellulose-based compound include carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof, and one or more of them can be mixed and used. As the alkali metal, Na, K, or Li can be used. The content of such a thickener used can be 0.1 part by weight to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0111] The conductive material is used to impart conductivity to the electrode, and in the battery being configured, 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.

[0112] As the negative electrode current collector, those 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.

[0113] Depending on the type of the lithium secondary battery, a separator may also be present between the positive electrode and the negative electrode. Such a separator can be a porous substrate or a composite porous substrate.

[0114] The porous substrate, as a substrate containing voids, allows lithium ions to move through the voids. For the porous substrate, for example, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used, and it goes without saying that a mixed multilayer film such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, or a three-layer separator of polypropylene / polyethylene / polypropylene can be used.

[0115] The composite porous substrate can be in a form including a porous substrate and a functional layer located on the porous substrate. From the viewpoint of enabling additional function addition, the functional layer can be, for example, at least one of a heat-resistant layer and an adhesive layer. For example, the heat-resistant layer can contain a heat-resistant resin and optionally a filler.

[0116] Further, the adhesive layer can contain an adhesive resin and optionally a filler.

[0117] The filler can be an organic filler or an inorganic filler.

[0118] Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment includes a battery cell including a negative electrode 112, a positive electrode 114 positioned opposite to the negative electrode 112, a separator 113 disposed between the negative electrode 112 and the positive electrode 114, and an electrolytic solution (not shown) impregnating the negative electrode 112, the positive electrode 114, and the separator 113, a battery container 120 housing the battery cell, and a sealing member 140 sealing the battery container 120.

Examples

[0119] Hereinafter, examples and comparative examples of the present invention will be described. Such following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0120] Synthesis of Additive Synthesis Example: Compound of Chemical Formula a

Chemical formula

[0121] Fabrication of Lithium Secondary Battery Example 1 LiNi as a positive electrode active material 0.91 Co 0.07 Al 0.02 O 2, polyvinylidene fluoride as a binder and Ketjen black as a conductive material were mixed at a weight ratio of 97:2:1 respectively, dispersed in N-methylpyrrolidone to produce a positive electrode active material slurry.

[0122] The positive electrode active material slurry was coated on an aluminum foil with a thickness of 14 μm, dried at 110 °C, and then rolled (press) to produce a positive electrode.

[0123] A mixture in which graphite and a Si-C composite were mixed at a weight ratio of 93:7 was used as the negative electrode active material. The negative electrode active material, styrene-butadiene rubber binder, and carboxymethyl cellulose were mixed at a weight ratio of 97:1:2 respectively, and dispersed in distilled water to produce a negative electrode active material slurry.

[0124] The Si-C composite is one in which a core containing artificial graphite and silicon particles is coated with coal-based pitch on the surface of the core.

[0125] 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.

[0126] The manufactured positive electrode and negative electrode were assembled with a separator made of a 25-μm-thick polyethylene material to produce an electrode assembly, and an electrolyte was injected to fabricate a lithium secondary battery.

[0127] The electrolyte composition is as follows. (Electrolyte composition) Salt: LiPF 6 1.5M Solvent: Ethylene carbonate: Ethyl methyl carbonate: Dimethyl carbonate (EC: EMC: DMC = 20:10:70 by volume ratio) Additive: A composition containing 0.5% by weight of the compound of Chemical Formula a according to the above synthesis example (However, the "wt%" in the electrolyte composition is a value based on the total content of the electrolyte (lithium salt + non-aqueous organic solvent + additive).)

[0128] Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that 1.0% by weight of the compound of Chemical Formula a was added.

[0129] Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that 2.0% by weight of the compound of Chemical Formula a was added.

[0130] Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that an electrolyte solution not containing an additive was used.

[0131] Comparative Example 2 [Chemical Formula] A lithium secondary battery was fabricated in the same manner as in Example 1, except that 1.0% by weight of the commercially available triphenylphosphine oxide (CAS No. 791-28-6) from Sigma-Aldrich was added.

[0132] Evaluation 1: Evaluation of Thermal Exposure After charging the lithium secondary batteries according to Examples 1 to 3, Comparative Examples 1 and 2 at a charging rate of 0.5C under a cut-off condition of 4.2V / 3hr in a 3.0V discharged state, an evaluation was carried out when thermal exposure occurred. After placing the lithium secondary batteries according to Examples 1 to 3, Comparative Examples 1 and 2 in a chamber, the temperature was increased from room temperature to 140°C at a rate of 5°C per minute, and the changes in the lithium secondary batteries were observed while maintaining at the said temperature for about 1 hour. The results are shown in FIG. 5. At this time, the dotted line indicates the voltage change over time, and the solid line indicates the temperature change over time.

[0133] FIG. 5 is a graph showing the temperature and voltage changes due to thermal exposure for the lithium secondary batteries according to Examples 1 to 3, Comparative Examples 1 and 2.

[0134] Referring to FIG. 5, a sudden voltage drop was observed in the lithium secondary batteries according to Examples 1 to 3, Comparative Examples 1 and 2. When the cylindrical battery is suddenly exposed to a high temperature, gas is generated and the internal pressure increases, causing the battery protection circuit (CID) to operate and making it impossible to read the voltage. From the appearance of the sudden voltage drop, it can be seen that in the lithium secondary batteries according to Examples 1 to 3, Comparative Examples 1 and 2, the protection circuit was activated due to gas generation caused by high temperature exposure.

[0135] However, even when the lithium secondary batteries according to Examples 1 to 3 are exposed to a temperature of 140° C., thermal runaway does not occur while maintaining the temperature of 140° C. On the contrary, when the lithium secondary batteries according to Comparative Examples 1 and 2 are exposed to a temperature of 140° C., although the temperature seems to be maintained at 140° C., it can be confirmed that sudden thermal runaway appears up to 240° C. (at the 78-minute mark) and 200° C. (at the 42-minute mark), respectively. From this, it can be seen that the lithium secondary batteries according to Comparative Examples 1 and 2 not only generated simple gas but also underwent thermal runaway and the battery exploded.

[0136] Therefore, it can be seen that the lithium secondary batteries according to Examples 1 to 3 have higher thermal stability than the lithium secondary batteries according to Comparative Examples 1 and 2.

[0137] Evaluation 2: Evaluation of Through-Safety The through characteristics of the lithium secondary batteries according to Examples 1 to 3, Comparative Examples 1 and 2 were evaluated by the following method, and the results are shown in FIG. 6. For the through-limit evaluation, after charging to SOC (state of charge) 50 (the capacity corresponding to half of the total capacity of 100), the through evaluation was carried out at 150 mm / s using 2.5 nails, and temperature sensors and voltage sensors were attached to the cell surface to obtain the voltage or temperature profile during penetration.

[0138] FIG. 6 is a graph showing the temperature change on the cell surface and the voltage change of the cell after penetration at 150 mm / s for the lithium secondary batteries of Examples 1 to 3, Comparative Examples 1 and 2.

[0139] In the lithium secondary batteries of Examples 1 to 3, Comparative Examples 1 and 2, when the voltage dropped to 0 V, it means that a positive electrode / negative electrode short circuit occurred due to penetration. At this time, since a flame is generated due to the short circuit, the risk of ignition is high. When the positive electrode / negative electrode came into contact with each other due to penetration and a short circuit occurred, the lithium secondary batteries according to Comparative Examples 1 and 2 caught fire after the flame was generated, and the battery temperature rose to 480 °C or higher. On the other hand, it can be seen that the lithium secondary batteries according to Examples 1 to 3 generate a flame due to the short circuit, but the temperature is maintained below 300 °C and the battery does not catch fire. That is, it can be seen that the lithium secondary batteries according to the examples are excellent in thermal stability because they do not catch fire even when the positive electrode / negative electrode comes into contact and a short circuit occurs.

[0140] Evaluation 3: Measurement of the CID activation point The lithium secondary batteries of Examples 1 to 3, Comparative Examples 1 and 2 were charged at a 0.5C charge-discharge rate in a 4.35V CC / CV method for 3 hours, and then left in a 90 °C chamber for 20 hours to measure the CID (Current Interrupt Device) activation point. The CID (Current Interrupt Device) is an element that senses a pressure change, that is, a pressure increase, inside a sealed element and cuts off the current by itself when the pressure exceeds a certain level. Since this is self-evident in the industry, the description thereof is omitted. The measurement results are shown in FIG. 7.

[0141] FIG. 7 is a graph measuring the CID (Current Interrupt Device) activation points of the lithium secondary batteries according to Examples 1 to 3, Comparative Examples 1 and 2.

[0142] The high-temperature storage characteristics of the lithium secondary battery can be evaluated by measuring the CID activation point.

[0143] Referring to Fig. 7, Comparative Examples 1 and 2 show a rapid voltage drop about 8 hours before storage at a high temperature of 90°C. However, the Examples containing the additive according to one embodiment of the present invention show that the time for the voltage drop is at least 10 hours or more, delaying the electrolyte decomposition, thereby reducing the increase in resistance and showing the effect of delaying the OCV drop. That is, the lithium secondary battery according to the present invention is excellent in the effect of suppressing gas generation during high-temperature storage.

[0144] Evaluation 4: Evaluation of charge and discharge cycle characteristics at room temperature The lithium secondary batteries according to Examples 1 to 3, Comparative Examples 1 and 2 were evaluated for cycle characteristics after charge and discharge under the following conditions, and the results are shown in Fig. 8. While performing 250-cycle charge and discharge at a C-rate of 0.5C at 25°C between 2.5V and 4.2V, the change in discharge capacity and the change in direct current internal resistance (DC-IR) were measured, and the results are both shown in Fig. 8.

[0145] Fig. 8 is a graph showing the charge and discharge cycle characteristics at room temperature of the lithium secondary batteries according to Examples 1 to 3, Comparative Examples 1 and 2.

[0146] Referring to Fig. 8, in the case of Examples 1 to 3, it can be seen that the life characteristics are more excellent and the degree of increase in internal resistance is also improved compared with Comparative Examples 1 and 2.

[0147] Evaluation 5: Evaluation of high-temperature storage characteristics The internal resistance and capacity retention rate of the lithium secondary batteries according to Examples 1 to 3, Comparative Examples 1 and 2 were measured after storage under the following conditions, and the results are shown in Fig. 9. After storage at a high temperature (60°C) at 10-day intervals, the direct current internal resistance (DC-IR) was measured at SOC 50 under the condition of 0.5C rate-limiting discharge.

[0148] In addition, the discharge capacities of each of the lithium secondary batteries produced in Examples 1 to 3, Comparative Examples 1 and 2 were measured. Next, after high-temperature storage at 10-day intervals (60 °C), charge and discharge were performed twice at 0.2C, and the discharge capacities of the two times were measured. The discharge capacity ratio after high-temperature storage with respect to the discharge capacity before high-temperature storage was determined, and the first discharge capacity was indicated as the retention capacity, and the second discharge capacity was indicated as the recovery capacity.

[0149] FIG. 9 is a graph showing the measurement results of the resistance increase rate and the battery capacity recovery rate after leaving the lithium secondary batteries according to Examples 1 to 3, Comparative Examples 1 and 2 at 60 °C for 30 days.

[0150] Referring to FIG. 9, it can be seen that in the case of Examples 1 to 3, the high-temperature storage characteristics are more excellent than those of Comparative Examples 1 and 2.

[0151] Although the preferred embodiments of the present invention have been described above, 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 this also belongs to the scope of the present invention.

Explanation of Reference Numerals

[0152] 100 ··· Lithium secondary battery 112 ··· Negative electrode 113 ··· Separator 114 ··· Positive electrode 120 ··· Battery container 140 ··· Sealing member

Claims

1. An additive represented by the following Chemical Formula 1 for an electrolyte for a lithium secondary battery: 【Chemical 1】 (In the Chemical Formula 1, A, B, and C are each independently a substituted or unsubstituted pyrrolyl group, a substituted or unsubstituted imidazolyl group, or a substituted or unsubstituted benzimidazolyl group, and in A, B, and C, one of the nitrogen atoms contained in each is linked to a P=O group by a sigma bond, respectively).

2. The additive according to Claim 1, wherein A, B, and C are unsubstituted imidazolyl groups.

3. A non-aqueous organic solvent, a lithium salt, and the additive according to Claim 1 or 2 An electrolyte for a lithium secondary battery containing the same.

4. The electrolyte for a lithium secondary battery according to Claim 3, wherein the additive is contained in a content of 0.1% by weight to 10% by weight based on the total weight of the electrolyte for the lithium secondary battery.

5. The electrolyte for a lithium secondary battery according to Claim 3, wherein the additive is contained in a content of 0.1% by weight to 5.0% by weight based on the total weight of the electrolyte for the lithium secondary battery.

6. The electrolyte for a lithium secondary battery according to Claim 3, wherein the additive is contained in a content of 0.1% by weight to 3.0% by weight based on the total weight of the electrolyte for the lithium secondary battery.

7. A positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; and the electrolyte according to Claim 3 A lithium secondary battery containing the same.

8. The lithium secondary battery according to Claim 7, wherein the positive electrode active material is represented by the following Chemical Formula 4: [Chemical Formula 4] Li ｘ M １ １－ｙ－ｚ M ２ ｙ M ３ ｚ O ２ (In the 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 can each independently be any one selected from Ni, Co, Mn, Al, Sr, Mg or La metals and combinations thereof).

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