Organic electrolyte and secondary battery containing the same

Abstract

The present application relates to an organic electrolyte and a secondary battery including the same. The organic electrolyte includes one or more cyclic nitrile compounds; and one or more chain nitrile compounds.

Description

Technical Field

[0001] The present invention relates to an organic electrolyte and a secondary battery including the same. Background Art

[0002] Lithium batteries are used as driving power sources for portable electronic devices including camcorders, mobile phones and laptop computers. Lithium secondary batteries can be recharged at a high rate and have a high energy density per unit weight, which is about three times the energy density per unit weight of conventional lead storage batteries, nickel-cadmium batteries, nickel-hydrogen batteries and nickel-zinc batteries.

[0003] Lithium batteries operate at high driving voltages, and therefore cannot use aqueous electrolytes that are highly reactive with lithium. For lithium batteries, non-aqueous electrolytes, such as organic electrolytes, are typically used. Organic electrolytes are prepared by dissolving lithium salts in organic solvents. Suitable organic solvents for organic electrolytes can be stable at high voltages and have high ionic conductivity, high dielectric constant, and low viscosity.

[0004] Meanwhile, lithium secondary batteries have high capacity and high voltage, and thus the expansion caused by the decomposition of organic electrolytes brings about an increasing importance of stability. In addition, organic electrolytes are made of organic materials, which means that organic electrolytes are easily decomposed at high temperatures and high voltages, thus adversely affecting battery performance. Therefore, research has been conducted in overcoming these limitations.

[0005] In particular, there is a continuing need for the development of an organic electrolyte suitable for use in the manufacture of lithium secondary batteries that exhibits excellent capacity retention under high voltage settings and has excellent storage characteristics at high temperatures. Summary of the invention

[0006] Technical issues

[0007] In one aspect, an organic electrolyte of novel composition is provided.

[0008] Another aspect provides a secondary battery including the organic electrolyte.

[0009] Technical Solution

[0010] In one aspect, an organic electrolyte of novel composition is provided.

[0011] Another aspect provides a secondary battery including the organic electrolyte.

[0012] Disclosure of beneficial effects

[0013] An organic electrolyte according to one aspect includes at least one cyclic nitrile compound and at least one chain nitrile compound, thereby improving high-temperature life characteristics and high-temperature storage characteristics of a secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic diagram showing the structure of a lithium secondary battery according to an embodiment;

[0015] FIG. 2A to FIG. 2D A graph showing the results of measuring cyclic voltammetry characteristics of the positive electrode half-cells manufactured in Reference Examples 1 to 4 for 5 cycles at 3V to 4.55V;

[0016] FIG. 3A to FIG. 3D A graph showing the results of measuring cyclic voltammetry characteristics of the negative electrode half-cells manufactured in Reference Examples 5 to 8 for 5 cycles from 3V to 0V;

[0017] Figure 4 A graph showing the evaluation of room temperature (25° C.) life characteristics of lithium batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 7;

[0018] Figure 5 A graph showing evaluation of high temperature (45° C.) life characteristics of lithium batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 7;

[0019] FIG. 6A to FIG. 6C is a graph showing the expansion characteristics, capacity retention rate, and capacity recovery rate measured when the lithium batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 7 were stored at high temperature (60° C.) for 4 weeks; and

[0020] FIG. 7A to FIG. 7C Graphs showing EIS measured when the lithium batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 7 were stored at a high temperature (at 60° C.) for 4 weeks.

[0021] <Numbering of major components in the drawings>

[0022] 1: Lithium battery 2: Negative electrode

[0023] 3: positive electrode 4: separator

[0024] 5: Battery housing 6: Cover assembly DETAILED DESCRIPTION

[0025] The inventive concept described below can be modified in various forms and has multiple embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, the inventive concept should not be interpreted as being limited to specific embodiments, but should be understood to cover all modifications, equivalents or alternatives included within the technical scope of the inventive concept.

[0026] The terms used herein are only for the purpose of explaining specific embodiments and are not intended to limit the inventive concept. The singular form also includes the plural form, unless the context clearly indicates otherwise. It should be further understood that when the terms "include" or "comprise" are used herein, the specified features, numbers, steps, operations, elements, parts, components, materials or combinations thereof are specified, but the presence or addition of one or more other features, numbers, steps, operations, elements, parts, components, materials or combinations thereof are not excluded. The " / " used hereinafter can be interpreted as "and" or "or" according to the context.

[0027] In the accompanying drawings, for clear explanation, the diameter, length and thickness of the elements, layers and regions are enlarged or reduced. The same reference numerals refer to similar elements throughout the text. When a layer, film, region or plate, etc. is referred to as being "on" another component, it may be directly on another component, or there may be an intermediate component. The terms "first" and "second" etc. may be used to describe various elements throughout the text, but the elements are not limited by these terms. These terms are only used to distinguish one element from another element. Some elements may be omitted in the accompanying drawings, but this is only to help understand the features of the present invention, and is not intended to exclude the omitted elements.

[0028] Hereinafter, an organic electrolyte and a secondary battery including the same according to an example embodiment will be described in detail.

[0029] The organic electrolyte according to the embodiment includes at least one cyclic nitrile compound represented by the following Formula 1; and at least one chain nitrile compound:

[0030] <Formula 1>

[0031]

[0032] Among them, in the above formula 1,

[0033] CY1 is C5-C 20 Carbocyclic groups,

[0034] R1 is selected from hydrogen, deuterium, -F, -Cl, -Br, -I, hydroxy, nitro, amino, amidino, substituted or unsubstituted C1-C 20 Alkyl, substituted or unsubstituted C2-C 20 Alkenyl, substituted or unsubstituted C2-C 20 Alkynyl, substituted or unsubstituted C1-C 20 Alkoxy and substituted or unsubstituted C3-C 10 Cycloalkyl,

[0035] m is an integer selected from 0 to 39, and when m is 2 or more, two or more R1 are the same as or different from each other,

[0036] n is an integer selected from 1 to 40;

[0037] 6≤m+n≤40.

[0038] Chain nitrile compounds form a SEI film with good reversibility on the surface of the positive electrode, but this SEI film is not stable enough at high temperatures. Therefore, it is necessary to use an organic electrolyte containing straight-chain nitrile compounds to improve the high-temperature life and high-temperature storage characteristics of secondary batteries.

[0039] Therefore, the present inventors unexpectedly found that when a cyclic nitrile compound is added to a chain nitrile compound, high-temperature life characteristics and high-temperature storage characteristics of a secondary battery are enhanced, and thus, the present invention was completed.

[0040] In a secondary battery including an organic electrolyte containing a cyclic nitrile compound represented by the above formula 1, the cyclic nitrile compound forms a passivation film (solid electrolyte interface (SEI) film) on the surface of the positive electrode, and this SEI film is stable at high temperatures, thereby preventing the degradation of the active material. As a result, the high temperature life characteristics and high temperature storage characteristics of the secondary battery are enhanced. Without wishing to be bound by theory, the boiling point of the cyclic nitrile compound is substantially higher than that of the chain nitrile compound, and the nitrile group present in the cyclic nitrile compound is firmly bound to the ring through a σ bond, and the SEI film is formed by the lone pair of electrons of the nitrile group. Therefore, it is believed that a stable SEI film can be formed even at high temperatures.

[0041] Cyclic nitrile compounds form a stable SEI film that can be used as a resistance layer for Li ions, but when cyclic nitrile compounds are combined with chain nitrile compounds, an SEI film with improved reversibility and stability at high temperatures can be obtained. Therefore, by using a combination of suitable amounts of cyclic nitrile compounds and chain nitrile compounds, an electrolyte that forms a stable SEI film at high temperatures and has minimal resistance increase can be developed. In high-temperature long-term life evaluations, it prevents the decomposition of the positive electrode and minimizes the collapse of the positive electrode structure, resulting in improved capacity and charge / discharge efficiency characteristics, and in high-temperature storage evaluations, gas generation is reduced, resulting in improved expansion characteristics.

[0042] According to an embodiment, in the above formula 1, CY1 may be C5-C 20 An aliphatic cyclic group, and may be 10≤m+n≤40.

[0043] In the above formula 1, CY1 can be selected from cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl, cyclododecyl, cyclotridecyl, cyclotetradecyl, cyclopentadecyl, cyclohexadecyl, cycloheptadecyl, cyclooctadecyl, cyclononadecyl and cycloeicosyl.

[0044] For example, in the above Formula 1, CY1 may be selected from cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, and cyclodecyl, but is not limited thereto, and CY1 may include a monocyclic ring and a condensed ring formed of carbon.

[0045] For example, in the above formula 1, CY1 may be a cyclopentyl group, a cyclohexyl group, or a cycloheptyl group. For example, in the above formula 1, CY1 may be a cyclohexyl group.

[0046] R1 can be selected from:

[0047] hydrogen, deuterium, -F, -Cl, -Br, -I, hydroxy, nitro, amino, amidino, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, sec-pentyl, 3-pentyl, and sec-isopentyl; and

[0048] methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, sec-pentyl, 3-pentyl and sec-isopentyl, each substituted with at least one of the following: deuterium, -F, -Cl, -Br, -I, hydroxy, nitro, amino and amidino.

[0049] For example, R1 can be selected from: hydrogen, deuterium, -F, -Cl, -Br, -I, hydroxyl, nitro, amino, amidino, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl; and

[0050] methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, each substituted with at least one of the following: deuterium, -F, -Cl, -Br, -I, hydroxy, nitro, amino and amidino.

[0051] For example, R1 may be selected from hydrogen, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl.

[0052] For example, R1 may be hydrogen.

[0053] An organic electrolyte, wherein the above Formula 1 is represented by any one selected from Formulas 1-1 to 1-36:

[0054]

[0055]

[0056] In the above formulas 1-1 to 1-36,

[0057] R 11a To R 17a and R 11b To R 17b Refer to the above description of R1 respectively.

[0058] For example, in the above formulas 1-1 to 1-36,

[0059] R 11a To R 17a and R 11b To R 17b Can be independently selected from:

[0060] hydrogen, deuterium, -F, -Cl, -Br, -I, hydroxy, nitro, amino, amidino, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, sec-pentyl, 3-pentyl, and sec-isopentyl; and

[0061] methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, sec-pentyl, 3-pentyl and sec-isopentyl, each substituted with at least one of the following: deuterium, -F, -Cl, -Br, -I, hydroxy, nitro, amino and amidino.

[0062] For example, R 11a To R 17a and R 11b To R 17b may be independently selected from: hydrogen, deuterium, -F, -Cl, -Br, -I, hydroxyl, nitro, amino, amidino, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl; and

[0063] methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, each substituted with at least one of the following: deuterium, -F, -Cl, -Br, -I, hydroxy, nitro, amino and amidino.

[0064] For example, R 11a To R 17a and R 11b To R 17b Each may be independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl.

[0065] For example, R 11a To R 17a and R 11b To R 17b Each may be hydrogen.

[0066] The cyclic nitrile compound may be included in an amount of 1 wt % to 2 wt % relative to the total weight of the organic electrolyte.

[0067] For example, the content of the cyclic nitrile compound may be 1 wt % relative to the total weight of the organic electrolyte. For example, the content of the cyclic nitrile compound may be 2 wt % relative to the total weight of the organic electrolyte.

[0068] When the amount of the cyclic nitrile compound satisfies the above range, a stable SEI film is formed on the electrode surface, thereby improving high temperature life and high temperature storage characteristics of the secondary battery.

[0069] The chain nitrile compound can be represented by the following formula 2.

[0070] <Formula 2>

[0071] X1-R-X2

[0072] In the above formula 2,

[0073] R is selected from substituted or unsubstituted C1-C 20 Alkylene,

[0074] X1 and X2 are each independently selected from hydrogen, deuterium, -F, -Cl, -Br, -I, hydroxyl, cyano, nitro, amidino, substituted or unsubstituted C1-C 20 Alkyl, substituted or unsubstituted C2-C 20 Alkenyl, substituted or unsubstituted C2-C 20 Alkynyl, substituted or unsubstituted C1-C 20 Alkoxy and substituted or unsubstituted C3-C 10 cycloalkyl, and

[0075] At least one of X1 and X2 is a cyano group.

[0076] An organic electrolyte, wherein in the above formula 2, R is selected from the following formulas 2-1 to 2-5:

[0077]

[0078] In the above formulas 2-1 to 2-5,

[0079] p is each independently an integer selected from 1 to 20,

[0080] r and s are each independently an integer selected from 1 to 10,

[0081] 2≤r+s≤19, and

[0082] * and *' are binding sites with X1 and X2 in Formula 2, respectively.

[0083] In the above formula 2, X1 and X2 are both cyano groups.

[0084] The chain nitrile compound may include a chain nitrile compound containing two cyano groups and a chain nitrile compound containing three cyano groups.

[0085] The chain nitrile compound containing two cyano groups may include at least one compound selected from the group consisting of malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid, sebacononitrile, and undecanedinitrile, but is not limited thereto.

[0086] The chain nitrile compound containing three cyano groups may include at least one compound selected from 1,2,3-hexanitrile, 1,2,4-hexanitrile, 1,2,5-hexanitrile, 1,2,6-hexanitrile, 1,3,4-hexanitrile, 1,3,5-hexanitrile, 1,3,6-hexanitrile and 1,4,5-hexanitrile, but is not limited thereto.

[0087] The content of the chain nitrile compound may be 3 wt % to 7 wt % relative to the total weight of the organic electrolyte. For example, the content of the chain nitrile compound may be 3 wt % to 6 wt %, 3 wt % to 5 wt %, 4 wt % to 7 wt %, or 5 wt % to 7 wt % relative to the total weight of the organic electrolyte.

[0088] When the amount of the chain nitrile compound satisfies the above range, the reversibility of the SEI film formed on the electrode interface may be enhanced, thereby improving the charge / discharge characteristics and battery performance of the secondary battery.

[0089] The weight ratio of the chain nitrile compound containing two cyano groups to the chain nitrile compound containing three cyano groups may be 3:2.

[0090] The organic electrolyte further includes a lithium salt. The concentration of the lithium salt in the organic electrolyte may be about 0.01 M to 2.0 M, but is not necessarily limited to this range, and the lithium salt may be used within an appropriate concentration range that does not deteriorate battery performance. Further improved battery characteristics may be obtained within the above concentration range.

[0091] There is no particular limitation on the lithium salt used in the organic electrolyte, and any lithium salt used as a lithium salt in the art can be used. For example, the lithium salt may include at least one selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(2≤x≤20, 2≤y≤20), LiCl, LiI, lithium bis(oxalato)borate (LiBOB) and LiPO2F2.

[0092] The organic electrolyte may include an organic solvent. The organic solvent may include at least one selected from the group consisting of dialkyl carbonates, cyclic carbonates, linear or cyclic esters, linear or cyclic amides, aliphatic nitriles, linear or cyclic ethers, and derivatives thereof.

[0093] Specifically, the organic solvent may include at least one selected from the group consisting of ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), butylene carbonate, ethyl propionate (EP), propyl propionate (PP), ethyl butyrate, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, γ-valerolactone, γ-butyrolactone and tetrahydrofuran, but is not limited thereto, and any organic solvent that can be used for organic electrolytes in the art can be used.

[0094] In some cases, for the purpose of improving battery life characteristics, preventing battery capacity reduction, and increasing the discharge capacity of the battery, the organic electrolyte may include at least one of propyl sulfone (PS), vinylene carbonate (VC), or vinyl ethylene carbonate (VEC), but is not limited thereto, and any material that can be added to the organic electrolyte in the art may be used.

[0095] The organic electrolyte may be a liquid or a gel. The organic electrolyte may be prepared by adding a lithium salt, a cyclic nitrile compound, and a chain nitrile compound to the above-mentioned organic solvent.

[0096] As used herein, the term "C5-C 20 The "carbocyclic group" refers to a monocyclic or polycyclic group having 5 to 20 carbon atoms including only carbon as a ring-constituting atom, and examples of the carbocyclic group include cyclopentane, cyclohexane, cycloheptane and benzene.

[0097] As used herein, the term "C1-C 20 The "alkyl group" refers to a linear or branched aliphatic monovalent hydrocarbon group having 1 to 20 carbon atoms, and examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl and hexyl.

[0098] As used herein, the term "C2-C 20 The "alkenyl group" refers to a linear or branched monovalent hydrocarbon group having 2 to 20 carbon atoms including at least one double bond, and examples of the alkenyl group include ethenyl, propenyl and butenyl.

[0099] As used herein, the term "C2-C 20The term "alkynyl group" refers to a linear or branched monovalent hydrocarbon group having 2 to 20 carbon atoms including at least one triple bond, and examples of the alkynyl group include ethynyl, propynyl and butynyl.

[0100] As used herein, the term "C1-C 20 "Alkoxy" refers to a group consisting of the formula -OR2 (wherein R2 is C1-C 20 An alkoxy group is a monovalent group represented by an alkyl group, and examples of the alkoxy group include a methoxy group, an ethoxy group, and a propoxy group.

[0101] As used herein, the term "C3-C 10 The "cycloalkyl group" refers to a monovalent saturated cyclic hydrocarbon group having 3 to 10 carbon atoms, and examples of the cycloalkyl group include cyclopropyl, cyclobutyl and cyclopentyl.

[0102] In this specification, substituted C1-C 20 Alkyl, substituted C2-C 20 Alkenyl, substituted C2-C 20 Alkynyl, substituted C1-C 20 Alkoxy and substituted C3-C 10 At least one substituent in the cycloalkyl group is selected from:

[0103] Deuterium (-D), -F, -Cl, -Br, -I, hydroxyl, nitro, amidino, hydrazine, hydrazone, C1-C 20 Alkyl, C2-C 20 Alkenyl, C2-C 20 Alkynyl and C1-C 20 Alkoxy;

[0104] C1-C 20 Alkyl, C2-C 20 Alkenyl, C2-C 20 Alkynyl and C1-C 20 Alkoxy: deuterium (-D), -F, -Cl, -Br, -I, hydroxyl, nitro, amidino, hydrazine, hydrazone, C1-C 20 Alkyl, C2-C 20 Alkenyl, C2-C 20 Alkynyl and C1-C 20 Alkoxy;

[0105] C3-C 10 Cycloalkyl; and

[0106] C3-C substituted with at least one of the following 10 Cycloalkyl: deuterium (-D), -F, -Cl, -Br, -I, hydroxyl, nitro, amidino, hydrazine, hydrazone, C1-C 20 Alkyl, C2-C 20Alkenyl, C2-C 20 Alkynyl, C1-C 20 Alkoxy and C3-C 10 Cycloalkyl.

[0107] A secondary battery according to another aspect includes a positive electrode; a negative electrode; and the above-mentioned organic electrolyte. The secondary battery may be a lithium secondary battery. There is no particular limitation on the form of the lithium secondary battery, and includes lithium secondary batteries such as lithium ion batteries, lithium ion polymer batteries, lithium sulfur batteries, and lithium air batteries, as well as lithium primary batteries.

[0108] The capacity retention rate of the lithium secondary battery may be 88% or more after 300 cycles of charge / discharge at 45° C. For example, the capacity retention rate of the lithium secondary battery may be 89% or more after 300 cycles of charge / discharge at 45° C.

[0109] For example, the secondary battery can be manufactured by the following method.

[0110] First, prepare the positive electrode.

[0111] For example, a positive electrode active material composition in which a positive electrode active material, a conductive material, a binder and a solvent are mixed is prepared. The positive electrode active material composition is directly applied to a metal current collector to prepare a positive electrode plate. Alternatively, the positive electrode active material composition may be cast on a separate carrier to form a film, which may then be separated from the carrier and laminated on a metal current collector to prepare a positive electrode plate. The positive electrode is not limited to the forms listed above, but may have a form different from the above forms.

[0112] The positive electrode active material is a lithium-containing metal oxide, and any one commonly used in the art can be used without limitation. For example, at least one composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and a combination thereof can be used. Specific examples of the positive electrode active material may be a compound represented by any one of the following formulas: Li a A 1-b B b D2 (where 0.90≤a≤1.8 and 0≤b≤0.5); Li a E 1-b B b O 2-c D c (where 0.90≤a≤1.8, 0≤b≤0.5 and 0≤c≤0.05); LiE 2-b B b O 4-c D c (where 0≤b≤0.5 and 0≤c≤0.05); Li a Ni 1-b-c Co b B c Dα (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α≤2); Li a Ni 1-b-c Co b B c O 2-α F α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α<2); Li a Ni 1-b- c Co b B c O 2-α F2 (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α<2); Li a Ni 1-b-c Mn b B c D α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α≤2); Li a Ni 1-b-c Mn b B c O 2-α F α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α<2); Li a Ni 1-b-c Mn b B c O 2-α F2 (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α<2); Li a Ni b E c G d O2 (where 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5 and 0.001≤d≤0.1); Li a Ni b Co c Mn d GeO2 (where 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5 and 0.001≤e≤0.1); Li a NeG b O2 (where 0.90≤a≤1.8 and 0.001≤b≤0.1); Li a CoG b O2 (where 0.90≤a≤1.8 and 0.001≤b≤0.1); Li aMnG b O2 (where 0.90≤a≤1.8 and 0.001≤b≤0.10); Li a Mn b O4 (where 0.90≤a≤1.8 and 0.001≤b≤0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(where 0≤f≤2);Li (3-f) Fe2(PO4)3 (where 0≤f≤2); and LiFePO4.

[0113] In the above formula, A is Ni, Co, Mn or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; F is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0114] For example, it may be LiCoO2, LiMn x O 2x (x=1、2)、LiNi 1-x Mn x O 2x (0 <x<1)、LiNi 1-x-y Co x Mn y O2(0≤x≤0.5, 0≤y≤0.5), LiFePO4, etc.

[0115] A compound having a coating on its surface can be used, and a mixture of the compound and the compound having the coating can be used. The coating may include a coating element compound, such as an oxide, a hydroxide, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a hydroxycarbonate of the coating element. The compound forming the coating may be amorphous or crystalline. The coating element contained in the coating may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating may be formed by any method (e.g., spraying, dipping, etc.) that does not adversely affect the physical properties of the positive active material, and the elements in the compound and the coating method can be well understood by those of ordinary skill in the art, and therefore, a detailed description thereof will be omitted.

[0116] As the conductive material, carbon black, graphite particles, etc. may be used, but the embodiment is not limited thereto, and any conductive material that can be used as a conductive material in the art may be used.

[0117] Examples of the binder may include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene and mixtures thereof, or styrene butadiene rubber-based polymers, but are not limited thereto, and any binder usable as a binder in the art may be used.

[0118] As the solvent, N-methylpyrrolidone (NMP), acetone, water, etc. may be used, but the embodiment is not limited thereto and any solvent used in the art may be used.

[0119] The positive electrode active material, the conductive material, the binder and the solvent are the contents generally used in lithium batteries. Depending on the use and configuration of the lithium battery, at least one of the conductive material, the binder and the solvent may be omitted.

[0120] Next, a negative electrode was prepared.

[0121] For example, a negative electrode active material composition in which a negative electrode active material, a conductive material, a binder and a solvent are mixed is prepared. The negative electrode active material composition may be directly applied to a metal current collector and dried to prepare a negative electrode plate. Alternatively, the negative electrode active material composition may be cast on a separate carrier to form a film, which may then be separated from the carrier and laminated on a metal current collector to prepare a negative electrode plate.

[0122] The negative electrode active material may be any material that can be used as a negative electrode active material for a lithium battery in the art. For example, the negative electrode active material may include at least one selected from the group consisting of lithium metal, metals that can form alloys with lithium, transition metal oxides, non-transition metal oxides, and carbon materials.

[0123] For example, the metal that can form an alloy with lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb, Si-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, or a combination of their elements, but not Si), Sn-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, or a combination of their elements, but not Sn), etc. The element Y may be 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, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po or a combination thereof.

[0124] For example, the transition metal oxide may be lithium titanate oxide, vanadium oxide, lithium vanadium oxide, etc.

[0125] For example, the non-transition metal oxide may be SnO2, SiO x (0 < x < 2), etc.

[0126] The carbonaceous material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite, such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and the amorphous carbon is soft carbon (low-temperature fired carbon) or hard carbon, mesophase carbonized pitch, fired coke, etc.

[0127] In the negative electrode active material composition, the conductive material and the binder may be the same as those in the positive electrode active material composition.

[0128] The negative electrode active material, the conductive material, the binder, and the solvent are in the contents commonly used in lithium batteries. Depending on the use and configuration of the lithium battery, at least one of the conductive material, the binder, and the solvent may be omitted.

[0129] Next, a separator inserted between the positive electrode and the negative electrode is prepared.

[0130] The separator may be any separator commonly used in lithium batteries. A separator having low resistance to ion migration of the electrolyte and excellent electrolyte wettability may be used. For example, the separator may be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of non-woven or fabric. For example, a wound separator such as polyethylene and polypropylene may be used for lithium-ion batteries, and a separator having excellent organic electrolyte solution retention ability may be used for lithium-ion polymer batteries. For example, the separator may be prepared by the following method.

[0131] A polymer resin, a filler, and a solvent are mixed to prepare a separator composition. The separator composition may be directly applied to the electrode and dried to form a separator. Alternatively, the separator composition may be cast on a carrier and then dried to form a separator film, and then it may be separated from the carrier and laminated on the electrode to form a separator.

[0132] There is no particular limitation on the polymer resin used in forming the separator, and it may be any of various materials used as an electrode plate binder. Examples of the polymer resin may include a vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or a mixture thereof.

[0133] Next, the above-mentioned organic electrolyte is prepared.

[0134] As Figure 1As shown in FIG. 1 , a lithium battery 1 includes a positive electrode 3, a negative electrode 2, and a separator 4. The positive electrode 3, the negative electrode 2, and the separator 4 are wound or folded to be placed in a battery case 5. Then, the battery case 5 is filled with an organic electrolyte and sealed with a cap assembly 6, thereby completing the manufacture of the lithium battery 1. The battery case 5 may be a cylindrical type, a rectangular type, or a thin film type. For example, the lithium battery may be a large thin film type battery. The lithium battery may be a lithium ion battery.

[0135] The separator is located between the positive electrode and the negative electrode to form a battery assembly. Several battery assemblies can be stacked to form a bi-cell structure and then impregnated with an organic electrolyte, and the resulting product is placed in a bag and then sealed to complete the manufacture of a lithium ion polymer battery.

[0136] In addition, multiple battery modules can be stacked to form a battery pack, and the battery pack can be used for any high-capacity and high-output device. For example, the battery pack can be used for laptop computers, smartphones, or electric vehicles.

[0137] In addition, lithium batteries can be used in electric vehicles (EVs) due to their life characteristics and high rate characteristics. For example, lithium batteries can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, lithium batteries can be used in areas that require large amounts of power storage. In addition, lithium batteries can be used in electric bicycles, power tools, etc.

[0138] The following examples and comparative examples are used for a more detailed description of the present invention. However, the examples are only for the illustrative purpose of describing the present invention and are not intended to limit the scope of the present invention.

[0139] (Preparation of organic electrolyte)

[0140] Preparation Example 1

[0141] 1.3M LiPF6 as a lithium salt, 1 wt% of 1,3,5-cyclohexanetricarbonitrile as a cyclic nitrile compound, 3 wt% of 1,3,6-hexanetricarbonitrile as a chain nitrile compound, and 2 wt% of succinonitrile were added to a mixed solution of EC / PC / EP / PP (volume ratio: EC / PC / EP / PP=15 / 15 / 25 / 45) to prepare an organic electrolyte.

[0142] Preparation Example 2

[0143] An organic electrolyte was prepared in the same manner as in Preparation Example 1, except that 1,3,5-cyclohexanetricarbonitrile was added in an amount of 2 wt % instead of 1 wt %.

[0144] Preparation Example 3

[0145] 1.3 M LiPF6 as a lithium salt was added to a mixed solution of EC / PC / EP / PP (volume ratio: EC / PC / EP / PP=15 / 15 / 25 / 45) to prepare an organic electrolyte.

[0146] Preparation Example 4

[0147] 1.3 M LiPF6 as a lithium salt and 1 wt% of 1,3,5-cyclohexanetricarbonitrile were added to a mixed solution of EC / PC / EP / PP (volume ratio: EC / PC / EP / PP=15 / 15 / 25 / 45) to prepare an organic electrolyte.

[0148] Preparation Example 5

[0149] 1.3 M LiPF6 as a lithium salt and 3 wt% of 1,3,6-hexanitrile were added to a mixed solution of EC / PC / EP / PP (volume ratio: EC / PC / EP / PP=15 / 15 / 25 / 45) to prepare an organic electrolyte.

[0150] Preparation Example 6

[0151] 1.3 M LiPF6 as a lithium salt and 2 wt% of succinonitrile were added to a mixed solution of EC / PC / EP / PP (volume ratio: EC / PC / EP / PP=15 / 15 / 25 / 45) to prepare an organic electrolyte.

[0152] Preparation Example 7

[0153] 1.3 M LiPF6 as a lithium salt, 3 wt% of 1,3,6-hexanetricarbonitrile and 2 wt% of succinonitrile as chain nitrile compounds were added to a mixed solution of EC / PC / EP / PP (volume ratio: EC / PC / EP / PP=15 / 15 / 25 / 45) to prepare an organic electrolyte.

[0154] Preparation Example 8

[0155] An organic electrolyte was prepared in the same manner as in Preparation Example 7, except that succinonitrile was added in an amount of 3 wt % instead of 2 wt %.

[0156] Preparation Example 9

[0157] An organic electrolyte was prepared in the same manner as in Preparation Example 7, except that succinonitrile was added in an amount of 4 wt % instead of 2 wt %.

[0158] Preparation Example 10

[0159] An organic electrolyte was prepared in the same manner as in Preparation Example 7, except that succinonitrile was added in an amount of 5 wt % instead of 2 wt %.

[0160] Preparation Example 11

[0161] An organic electrolyte was prepared in the same manner as in Preparation Example 1, except that 1,3,6-hexanetricarbonitrile was added in an amount of 5 wt % instead of 3 wt %.

[0162] Preparation Example 12

[0163] 1.3 M LiPF6 as a lithium salt and 0.5 wt% of a cyclobutane 1,2-carbonitrile compound as a cyclic nitrile compound were added to a mixed solution of EC / PC / EP / PP (volume ratio: EC / PC / EP / PP=15 / 15 / 25 / 45) to prepare an organic electrolyte.

[0164] Preparation Example 13

[0165] 1.3 M LiPF6 as a lithium salt, 3 wt% of 1,3,6-hexanetricarbonitrile as a chain nitrile compound, and 1 wt% of a divinyl sulfone compound as an additive were added to a mixed solution of EC / PC / EP / PP (volume ratio: EC / PC / EP / PP=15 / 15 / 25 / 45) to prepare an organic electrolyte.

[0166] (Preparation of positive electrode half-cell)

[0167] Reference Example 1

[0168] A positive electrode half-cell was prepared by using a positive electrode containing lithium cobalt oxide and a lithium foil as a counter electrode, placing a porous polyethylene film as a separator between the positive electrode and the counter electrode, and injecting the organic electrolyte obtained in Preparation Example 3.

[0169] Reference Examples 2 to 4

[0170] A positive electrode half-cell was prepared in the same manner as in Reference Example 1, except that the organic electrolytes obtained in Preparation Examples 4 to 6 were respectively used instead of the organic electrolyte obtained in Preparation Example 3.

[0171] (Preparation of negative electrode half-cell)

[0172] Reference Example 5

[0173] A negative electrode half-cell was prepared by using a negative electrode containing graphite and lithium metal as a counter electrode, placing a porous polyethylene film as a separator between the negative electrode and the counter electrode, and injecting the organic electrolyte obtained in Preparation Example 3, thereby preparing a negative electrode half-cell.

[0174] Reference 6 to 8

[0175] A negative electrode half-cell was prepared in the same manner as in Reference Example 5, except that the organic electrolytes obtained in Preparation Examples 4 to 6 were respectively used instead of the organic electrolyte obtained in Preparation Example 3.

[0176] Evaluation Example 1: Electrochemical Decomposition Evaluation of Positive Half-Cell

[0177] The positive electrode half-cells prepared in Reference Examples 1 to 4 were used to evaluate the cyclic voltammetry characteristics of 5 cycles from 3V to 4.55V. FIG. 2A to FIG. 2D The results are shown in .

[0178] See also FIG. 2A to FIG. 2D It can be seen that the 1,3,5-cyclohexanetricarbonitrile ( Figure 2B ) than the organic electrolyte containing 1,3,6-hexanitrile ( Figure 2C ) or succinonitrile ( Figure 2D ) has low positive electrode oxidation-reduction reaction reversibility. In particular, see Figure 2B It can be seen that in the organic electrolyte containing 1,3,5-cyclohexanetricarbonitrile, the initial reduction reaction is difficult to occur at 4 V. This is considered to be because the organic electrolyte containing 1,3,5-cyclohexanetricarbonitrile forms a film on the surface of the positive electrode, thereby increasing the resistance.

[0179] Evaluation Example 2: Electrochemical Decomposition Evaluation of Negative Electrode Half-Cell

[0180] The negative electrode half-cells prepared in Reference Examples 5 to 8 were used to evaluate the cyclic voltammetry characteristics of 5 cycles from 3V to 0V. FIG. 3A to FIG. 3D The results are shown in .

[0181] See also FIG. 3A to FIG. 3D , considering Figure 3A The initial reduction peak in FIG. 3B to FIG. 3D There is no significant difference between the initial reduction peaks in , which can be explained by the fact that the cyclic and chain nitrile compounds do not directly form a film on the negative electrode. In addition, considering Figure 3B and Figure 3C The peak intensity in the organic solvent-only Figure 3A The peak intensity in the is high, and it can be seen that the addition of 1,3,5-cyclohexanetricarbonitrile ( Figure 3B ) or 1,3,6-hexanitrile ( Figure 3C ) contributes to the reversibility of the negative electrode.

[0182] (Preparation of full battery)

[0183] Example 1

[0184] (Preparation of negative electrode)

[0185] 98wt% of artificial graphite (BSG-L, Tianjin BTR New Energy Technology Co., Ltd.), 1.0wt% of styrene-butadiene rubber (SBR) binder (ZEON) and 1.0wt% of carboxymethyl cellulose (CMC, NIPPONA&L) were mixed and the mixture was added to distilled water and stirred for 60 minutes using a mechanical stirrer to prepare a negative active material slurry. The slurry was applied to a 10μm thick copper collector using a scraper with a thickness of about 60μm, dried at 100°C for 0.5 hours in a hot air dryer, dried at 120°C for another 4 hours under vacuum, and then rolled to prepare a negative plate.

[0186] (Preparation of positive electrode)

[0187] 97.45wt% LiNi 1 / 3 Co 1 / 3 Al 1 / 3 O2, 0.5wt% of artificial graphite (SFG6, Timcal) powder as a conductive material, 0.7wt% of carbon black (Ketjen black, ECP), 0.25wt% of modified acrylonitrile rubber (BM-720H, Zeon Corporation), 0.9wt% of polyvinylidene fluoride (PVdF, S6020, Solvay), 0.2wt% of polyvinylidene fluoride (PVdF, S5130, Solvay) were mixed, and the mixture was added to N-methyl-2-pyrrolidone solvent and stirred for 30 minutes using a mechanical stirrer to prepare a positive active material slurry. The slurry was applied to a 20μm thick aluminum collector using a scraper with a thickness of about 60μm, dried at 100°C for 0.5 hours in a hot air dryer, dried at 120°C for another 4 hours under vacuum, and then rolled to prepare a positive plate.

[0188] A lithium battery was manufactured using a 14 μm thick polyethylene separator coated with ceramic on the positive electrode side as a separator and the organic electrolyte prepared in Preparation Example 1 as an electrolyte.

[0189] Example 2

[0190] A lithium battery was manufactured in the same manner as in Example 1, except that the organic electrolyte prepared in Preparation Example 2 was used instead of the organic electrolyte prepared in Preparation Example 1.

[0191] Comparative Examples 1 to 7

[0192] Lithium batteries were manufactured in the same manner as in Example 1, except that the organic electrolytes prepared in Preparation Examples 7 to 13 were respectively used instead of the organic electrolyte prepared in Preparation Example 1.

[0193] Evaluation Example 3: Evaluation of initial DC resistance (DC-IR) at room temperature (25°C)

[0194] The lithium batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 7 were charged at a constant current of 0.7C rate to 4.47V (vs.Li) at 25°C, and charged at a current cutoff of 25C rate while maintaining the voltage at 4.47V in a constant voltage mode. Then, they were discharged at a constant current of 0.2C rate to 3V (vs.Li), and the standard capacity was measured during discharge.

[0195] The standard capacity refers to the capacity obtained when constant current charging is performed at a rate of 0.7C to reach 4.47V, and charging is performed at a current cutoff of 0.025C rate while maintaining a voltage of 4.47V in a constant voltage mode, and then discharging at a rate of 0.2C cutoff to 3V.

[0196] Then, charging was performed under the same conditions as the standard capacity, and discharging was performed at a constant current of 0.1 C rate to reach 3.4 V (vs. Li) during discharge. Thereafter, direct current internal resistance (DC-IR) was measured by the following method.

[0197] Based on the capacity used, constant current charging was performed at a rate of 0.7C to reach 4.47V, and then charging was performed at a current cutoff rate of 0.025C while maintaining a voltage of 4.47V in constant voltage mode. Thereafter, discharge was performed at a rate of 0.1C for 3 hours, 5 hours, and 1 hour based on the capacity used, and discharge was performed at a current rate of 1C for 1 second based on the standard capacity at SOCs of 70%, 20%, and 10%, respectively. The current applied during the 1-second discharge at a rate of 1C and the voltage change at that point were measured, and the DC-IR was calculated based on Equation 1 below.

[0198] <Equation 1>

[0199] DC-IR=(V2-V1) / I

[0200] V1 is the final voltage during the 1 second discharge at the standard capacity 1C rate, V2 is the voltage before the start of the 1 second discharge at the standard capacity 1C rate, and I is the current difference between the standard capacity 1C rate and the used capacity 0.1C rate.

[0201] Evaluation Example 4: Evaluation of charge / discharge characteristics at room temperature (25°C)

[0202] The lithium batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 7 were charged at a constant current of 0.7C at 25°C to 4.47V (vs. Li), and the charging was cut off at a current of 0.025C while maintaining the voltage at 4.47V in a constant voltage mode. Afterwards, the discharge was performed at a constant current of 0.2C to 3V (vs. Li), thereby completing the formation process.

[0203] The lithium battery that has undergone the formation process was charged at 25°C at a constant current of 0.7C rate to 4.47V (vs.Li), and the charging was stopped at a current of 0.025C rate while maintaining the voltage at 4.47V in the constant voltage mode. After that, the battery was discharged at a constant current of 1.0C rate to 3V (vs.Li). This charge / discharge cycle was repeated 300 times.

[0204] A rest period of 10 minutes was given after one charge / discharge cycle in all of the above charge / discharge cycles.

[0205] Table 1 and Figure 4 The results of the charge / discharge experiment are shown in . The capacity retention rate at the 300th cycle is defined by the following Equation 2.

[0206] <Equation 2>

[0207] Capacity retention rate = (discharge capacity at the 300th cycle / discharge capacity at the 1st cycle) × 100

[0208] Along with the charge / discharge characteristics at room temperature, the thickness change of the lithium battery cell after 300 charge / discharge cycles was also measured to calculate the swelling ratio. The swelling ratio indicates the thickness change of the lithium battery after 300 charge / discharge cycles compared to the thickness of the initial lithium battery.

[0209] See Table 1 and Figure 4 , Examples 1 and 2 showed higher discharge capacity retention than Comparative Examples 2 to 7, and exhibited better expansion characteristics than Comparative Example 1.

[0210] Evaluation Example 5: Charge / discharge characteristics at high temperature (45°C)

[0211] The lithium batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 7 were charged at a constant current of 0.7C at 45°C to 4.47V (vs. Li), and the charging was cut off at a current of 0.025C while maintaining the voltage at 4.47V in a constant voltage mode. Then, the discharge was performed at a constant current of 0.2C to 3V (vs. Li), thereby completing the formation process.

[0212] The lithium battery after the formation process was charged at 25°C with a current rate of 0.7C to 4.47V (vs.Li), and the charging was stopped at a current rate of 0.025C while the voltage was maintained at 4.47V in a constant voltage mode. Then, the battery was discharged at a constant current rate of 1.0C to 3V (vs.Li). This charge / discharge cycle was repeated 300 times.

[0213] A rest period of 10 minutes was given after one charge / discharge cycle in all of the above charge / discharge cycles.

[0214] Table 1 and Figure 5 The results of the charge / discharge experiments are shown in FIG.

[0215] Along with the charge / discharge characteristics at high temperature, the thickness change of the lithium battery cell after 300 cycles of charge / discharge was also measured to calculate the swelling ratio.

[0216] See Table 1 and Figure 5 , it can be seen that Examples 1 and 2 are the best in terms of discharge capacity and life trend at high temperature. There is no significant difference in swelling characteristics. Unlike the room temperature life evaluation, in the high temperature life evaluation, Examples 1 and 2 have better discharge capacity and life trend than Comparative Examples 1 to 7, and it is believed that this is because the high temperature life is mainly affected by the degradation of the active material and the film properties. That is, the cyclic nitrile compounds added in Examples 1 and 2 form a stable film on the positive electrode at high temperature to inhibit the degradation of the active material, so it is believed that Examples 1 and 2 have better discharge capacity and high temperature life trend than Comparative Examples 1 to 7.

[0217] Evaluation Example 6: Stability evaluation at high temperature (60°C)

[0218] The lithium ion batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 7 were charged at a constant current of 0.7C at 45°C to 4.47V (vs. Li), and the charging was cut off at a current of 0.025C while maintaining the voltage at 4.47V in a constant voltage mode. Then, the discharge was performed at a constant current of 0.2C to 3V (vs. Li), thereby completing the formation process.

[0219] At the 2nd cycle, constant current charging was performed at a rate of 0.7 C to 4.47 V, and then constant voltage charging was performed at 0.025 C while maintaining the voltage at 4.47 V, and constant current discharging was performed at a rate of 0.2 C to 3 V. The discharge capacity at the 2nd cycle was regarded as the standard capacity.

[0220] At the 3rd cycle, constant current charging was performed at a rate of 0.7 C to reach 4.47 V, and then constant voltage charging was performed while maintaining the voltage at 4.47 V to reach 0.025 C.

[0221] The charged lithium battery was stored in a 60°C oven for 4 weeks and then taken out and discharged at a rate of 0.2C to 3V at the third cycle.

[0222] At the 4th cycle, constant current charging was performed at a rate of 0.7C to reach 4.47V, and then constant voltage charging was performed to reach 0.025CV while maintaining the voltage at 4.47, and constant current discharging was performed at a rate of 0.2C to reach 3V.

[0223] Table 1 and FIG. 6A to FIG. 6C The results of the charge / discharge evaluation are shown in . The capacity retention rate after high temperature storage is defined by the following equation 3. In addition, the capacity recovery rate was calculated by the 4th charge / discharge cycle after 4 weeks of high temperature storage. The capacity recovery rate is defined by the following equation 4.

[0224] <Equation 3>

[0225] Capacity retention rate [%] = [discharge capacity after the third cycle at high temperature / standard capacity] × 100 (standard capacity is the discharge capacity at the second cycle)

[0226] <Equation 4>

[0227] Capacity recovery rate = (discharge capacity at the 4th cycle / discharge capacity after the 3rd cycle at high temperature) × 100

[0228] See Table 1 and FIG. 6A to FIG. 6C , it can be seen that after 4 weeks of storage at high temperature, the expansion characteristics of Examples 1 and 2 are the best. In particular, considering that Example 2 has improved expansion characteristics than Example 1, it is believed that the expansion characteristics will improve as the content of the cyclic nitrile compound increases. In addition, in the examples and the comparative examples, the capacity retention rate and the capacity recovery rate after high temperature storage show similar values, and considering that Example 1 has a higher capacity retention rate than Example 2, it is believed that the capacity retention rate will increase as the content of the cyclic nitrile compound increases.

[0229] Evaluation Example 7: Stability evaluation after storage at high temperature (60°C)

[0230] The lithium batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 7 were charged at a constant current rate of 0.7C to 4.47V (vs. Li) at 25°C, and were charged at a rate of 0.025C while maintaining the voltage at 4.47V in a constant voltage mode until a state of charge (SOC) of 100%.

[0231] Direct current internal resistance (DC-IR) evaluation of the charged lithium battery and high temperature storage EIS evaluation of the charged lithium battery stored in a 60°C oven for 1 week and 4 weeks and then taken out.

[0232] FIG. 7A to FIG. 7C The results are shown in .

[0233] See also Fig. 7A , it was confirmed that Examples 1 and 2 had initial Rct values ​​(ΔR) similar to or greater than those of Comparative Examples 1 to 7, which indicates that the cyclic nitrile compound was decomposed to form a film on the surface of the positive electrode. Figure 7B and Figure 7C , it can be seen that for the batteries taken out after storage at high temperature for 4 weeks, the change in Rct value of Examples 1 and 2 is smaller than that of Comparative Examples 1 to 7. That is, because the film present on the surface of the positive electrode suppresses the degradation of the active material, the increase in resistance after high temperature storage in Examples 1 and 2 is less than that in Comparative Examples 1 to 7.

[0234]

Table 1

[0235]

[0236] The embodiments disclosed in the inventive concept are not intended to limit the technical spirit of the inventive concept but to help understand that the scope of the invention is defined by the appended claims and all technical spirits of equivalents of the invention should be interpreted as being included in the scope of the invention.

Claims

1. An organic electrolyte comprising at least one cyclic nitrile compound represented by the following formula 1; and a chain nitrile compound: <Formula 1> In the above formula 1, CY1 is C5-C 20 Carbocyclic groups, R1 is selected from hydrogen, deuterium, -F, -Cl, -Br, -I, hydroxy, nitro, amino, amidino, substituted or unsubstituted C1-C 20 Alkyl, substituted or unsubstituted C2-C 20 Alkenyl, substituted or unsubstituted C2-C 20 Alkynyl, substituted or unsubstituted C1-C 20 Alkoxy and substituted or unsubstituted C3-C 10 Cycloalkyl, m is an integer selected from 0 to 39, and when m is 2 or more, two or more R1 are the same as or different from each other, n is an integer selected from 1 to 40; 6≤m+n≤40, The chain nitrile compound includes a chain nitrile compound containing two cyano groups and a chain nitrile compound containing three cyano groups, and The content of the chain nitrile compound is 3 wt % to 7 wt % relative to the total weight of the organic electrolyte.

2. The organic electrolyte according to claim 1, wherein In the above formula 1, CY1 is selected from cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl, cyclododecyl, cyclotridecyl, cyclotetradecyl, cyclopentadecyl, cyclohexadecyl, cycloheptadecyl, cyclooctadecyl, cyclononadecyl and cycloeicosyl.

3. The organic electrolyte according to claim 1, wherein R1 is selected from: hydrogen, deuterium, -F, -Cl, -Br, -I, hydroxy, nitro, amino, amidino, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, sec-pentyl, 3-pentyl, and sec-isopentyl; and methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, sec-pentyl, 3-pentyl and sec-isopentyl, each substituted with at least one of deuterium, -F, -Cl, -Br, -I, hydroxyl, nitro, amino and amidino.

4. The organic electrolyte according to claim 1, wherein The above formula 1 is represented by any one selected from formula 1-1 to formula 1-36: in, In the above formulas 1-1 to 1-36, R 11a To R 17a and R 11b To R 17b They are the same as the description of R1 in claim 1 respectively.

5. The organic electrolyte according to claim 4, wherein In the above formulas 1-1 to 1-36, R 11a To R 17a and R 11b To R 17b Each independently selected from: hydrogen, deuterium, -F, -Cl, -Br, -I, hydroxy, nitro, amino, amidino, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, sec-pentyl, 3-pentyl, and sec-isopentyl; and methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, sec-pentyl, 3-pentyl and sec-isopentyl, each substituted with at least one of deuterium, -F, -Cl, -Br, -I, hydroxyl, nitro, amino and amidino.

6. The organic electrolyte according to claim 4, wherein In the above formulas 1-1 to 1-36, R 11a To R 17a and R 11b To R 17b Each is hydrogen.

7. The organic electrolyte according to claim 1, wherein The content of the cyclic nitrile compound is 1 wt % to 2 wt % relative to the total weight of the organic electrolyte.

8. The organic electrolyte according to claim 1, wherein The chain nitrile compound is represented by the following formula 2: <Formula 2> X1—R—X2 in, In the above formula 2, R is selected from substituted or unsubstituted C1-C 20 Alkylene, X1 and X2 are each independently selected from hydrogen, deuterium, -F, -Cl, -Br, -I, hydroxyl, cyano, nitro, amidino, substituted or unsubstituted C1-C 20 Alkyl, substituted or unsubstituted C2-C 20 Alkenyl, substituted or unsubstituted C2-C 20 Alkynyl, substituted or unsubstituted C1-C 20 Alkoxy and substituted or unsubstituted C3-C 10 a cycloalkyl group, and At least one of X1 and X2 is a cyano group.

9. The organic electrolyte according to claim 8, wherein In the above formula 2, R is selected from the following formulas 2-1 to 2-5: in, In the above formulas 2-1 to 2-5, p is an integer selected from 1 to 20, r and s are each independently an integer selected from 1 to 10, 2≤r+s≤19, and * and *' are binding sites with X1 and X2 in Formula 2, respectively.

10. The organic electrolyte according to claim 8, wherein X1 and X2 are both cyano groups.

11. The organic electrolyte according to claim 10, wherein The chain nitrile compound containing two cyano groups includes at least one compound selected from malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid, sebacononitrile and undecane dinitrile.

12. The organic electrolyte according to claim 10, wherein The chain nitrile compound containing three cyano groups includes at least one compound selected from 1,2,3-hexanetrinitrile, 1,2,4-hexanetrinitrile, 1,2,5-hexanetrinitrile, 1,2,6-hexanetrinitrile, 1,3,4-hexanetrinitrile, 1,3,5-hexanetrinitrile, 1,3,6-hexanetrinitrile and 1,4,5-hexanetrinitrile.

13. The organic electrolyte according to claim 1, wherein The weight ratio of the cyclic nitrile compound to the chain nitrile compound is 1:5 to 2:

5.

14. A secondary battery comprising: positive electrode; negative electrode; and An organic electrolyte according to any one of claims 1 to 13.

15. The secondary battery according to claim 14, wherein After 300 cycles of charge / discharge at 45° C., the capacity retention rate was 88% or more.

16. The secondary battery according to claim 14, wherein The secondary battery is a lithium ion polymer battery.

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