Non-aqueous electrolytes and lithium secondary batteries containing them

Abstract

The present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive includes a compound represented by the following Chemical Formula 1 and lithium difluoro(oxalate)borate (LiODFB), and the organic solvent includes ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP). JPEG2025516290000009.jpg25170(In Chemical Formula 1, n is an integer from 3 to 10.)

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2022-0110317, filed on 31 August 2022, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] This invention relates to a non-aqueous electrolyte and a lithium secondary battery containing the same. [Background technology]

[0003] In recent years, attempts have been made to increase the capacity of lithium-ion batteries by driving them at higher voltages.

[0004] However, when a secondary battery is driven under high voltage, as charging and discharging progress, side reactions caused by electrolyte degradation can degrade the coating or surface structure of the positive / negative electrode, potentially leading to the elution of transition metal ions from the positive electrode surface. These eluted transition metal ions are then electrodeposited onto the negative electrode, reducing the passivation capacity of the SEI, thus causing the negative electrode to degrade.

[0005] This degradation phenomenon in secondary batteries tends to accelerate as the potential of the positive electrode increases, or when the battery is exposed to high temperatures, and this degradation phenomenon leads to the problem of deterioration in the cycle characteristics of the secondary battery.

[0006] Furthermore, when lithium secondary batteries are used continuously for long periods or left at high temperatures, a phenomenon known as swelling occurs, in which gas is generated and the thickness of the battery increases. It is known that the amount of gas generated at this time depends on the state of the SEI (Single Energy Intake).

[0007] Therefore, research and development efforts are underway to develop methods that can suppress the elution of transition metal ions at the positive electrode, reduce the breakdown of the SEI film at the negative electrode, reduce the swelling phenomenon of secondary batteries, and improve stability at high temperatures in order to solve these problems. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] As a result of conducting multifaceted research to solve the above problems, the present invention aims to provide a non-aqueous electrolyte that can suppress the degradation of the positive electrode and reduce side reactions between the positive electrode and the electrolyte.

[0009] Furthermore, the present invention aims to provide a lithium secondary battery in which high-temperature cycling characteristics and high-temperature storage characteristics are improved, and various other performance characteristics are enhanced, by including the non-aqueous electrolyte. [Means for solving the problem]

[0010] To achieve the above objectives, the present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises a compound represented by the following chemical formula 1 and lithium difluoro(oxalate) borate (LiODFB), and the organic solvent comprises ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP).

[0011] [ka]

[0012] In the above chemical formula 1, n is an integer between 3 and 10. [Effects of the Invention]

[0013] The non-aqueous electrolyte of the present invention, by containing the compound represented by chemical formula 1 and lithium difluoro(oxalate) borate (LiODFB), can suppress the decomposition of lithium salts and prevent the collapse of the positive electrode caused by by-products such as HF. Furthermore, it can suppress the decrease in the passivation capacity of SEI at high temperatures and prevent the deterioration of the negative electrode.

[0014] Specifically, the combination of the diisocyanate compound of chemical formula 1 and lithium difluoro(oxalate) borate (LiODFB) stabilizes the electrolyte and suppresses the decomposition reactions of carbonate and propionate solvents. Furthermore, in an environment where a stable positive electrode film formed by the combination of the diisocyanate compound of chemical formula 1 and lithium difluoro(oxalate) borate (LiODFB) is sufficiently formed, the reactivity between ethyl propionate (EP) and propyl propionate (PP) and oxygen desorbed from the positive electrode material is low, thus suppressing the generation of carbon dioxide, an oxidizing gas. As a result, the lithium secondary battery containing the non-aqueous electrolyte of the present invention can suppress gas generation at high temperatures. In other words, by using the non-aqueous electrolyte of the present invention, the elution of transition metals in the positive electrode is suppressed, and high-temperature durability is maintained, thereby improving high-temperature cycle characteristics and high-temperature storage characteristics, and realizing a lithium secondary battery with improved performance in various aspects. [Modes for carrying out the invention]

[0015] The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0016] In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the presence of implemented features, figures, steps, components, or combinations thereof, and should be understood not to preemptively exclude the presence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0017] Furthermore, in this specification, when "a to b carbon atoms" is mentioned, "a" and "b" refer to the number of carbon atoms contained in a specific functional group. That is, the functional group may contain "a" to "b" carbon atoms. For example, "alkylene group with 1 to 5 carbon atoms" means an alkylene group containing 1 to 5 carbon atoms, i.e., -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2(CH3)CH-, -CH(CH3)CH2-, and -CH(CH3)CH2CH2-, etc.

[0018] Furthermore, in this specification, alkyl groups may be substituted or not. Unless otherwise defined, "substituted" means that at least one hydrogen bonded to a carbon is replaced by an element other than hydrogen, for example, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, a heterocycloalkyl group having 3 to 12 carbon atoms, a heterocycloalkenyl group having 3 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, a halogen atom, a fluoroalkyl group having 1 to 20 carbon atoms, a nitro group having 6 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a heteroaryl group having 2 to 20 carbon atoms, a haloaryl group having 6 to 20 carbon atoms, etc.

[0019] The present invention will be described in more detail below.

[0020] [Non-aqueous electrolytes] The non-aqueous electrolyte according to the present invention comprises a lithium salt, an organic solvent, and an additive, wherein the additive comprises a compound represented by the following chemical formula 1 and lithium difluoro(oxalate) borate (LiODFB), and the organic solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP).

[0021] [ka]

[0022] In the aforementioned chemical formula 1, n may be an integer between 3 and 10, and preferably, n in the aforementioned chemical formula 1 may be an integer between 3 and 8.

[0023] The compound of chemical formula 1 is a compound in which an isocyanate group is substituted at the terminal end, and by forming a complex with a lithium salt and stabilizing the lithium salt, the generation of by-products such as HF can be suppressed. This can suppress the leaching of transition metals at the positive electrode, in particular the leaching of cobalt. Since the leaching of transition metals at the positive electrode is suppressed, the degradation of the positive electrode is suppressed, and thus the cycle characteristics and storage characteristics can be improved. Since the degradation of the positive electrode becomes more severe as the temperature increases, using the non-aqueous electrolyte of the present invention can improve the cycle characteristics and storage characteristics at high temperatures.

[0024] The lithium difluoro(oxalate) borate (LiODFB) can stabilize the anode interface through a rapid anode reduction reaction, thereby improving its high-temperature cycling and storage characteristics.

[0025] In the non-aqueous electrolyte according to the present invention, the compound represented by chemical formula 1 may be present in an amount of 0.1 to 5 parts by weight, preferably 0.1 to 3 parts by weight, and more preferably 0.1 to 2 parts by weight, per 100 parts by weight of the non-aqueous electrolyte. When the content of the compound represented by chemical formula 1 satisfies the above range, the effect of suppressing the dissolution of transition metals at the positive electrode is sufficient, and the effect of excellent high-temperature life characteristics and high-temperature storage characteristics is obtained.

[0026] In the non-aqueous electrolyte according to the present invention, lithium difluoro(oxalate) borate (LiODFB) may be present in an amount of 0.1 to 5 parts by weight, preferably 0.1 to 3 parts by weight, and more preferably 0.1 to 2 parts by weight, per 100 parts by weight of the non-aqueous electrolyte. When the content of LiODFB satisfies the above range, the negative electrode modification change by a rapid negative electrode reductive decomposition reaction in the activation step is sufficient, resulting in excellent high-temperature life characteristics and high-temperature storage characteristics.

[0027] In the non-aqueous electrolyte of the present invention, the compound represented by chemical formula 1 and lithium difluoro(oxalate) borate (LiODFB) may be included in a weight ratio of 0.2:1 to 5:1, preferably 1:1 to 5:1, and most preferably 1:1 to 3:1. When the additive of chemical formula 1 and LiODFB are included within the above range, the pH of the electrolyte becomes within an appropriate range, the decomposition of lithium salts is appropriately suppressed, and the elution of transition metals, particularly Co, during high-voltage charging or at high temperatures can be suppressed.

[0028] The non-aqueous electrolyte according to the present invention may contain a lithium salt. The lithium salt is used as an electrolyte salt in a lithium secondary battery and is used as a medium for transferring ions. Typically, the lithium salt is, for example, Li as a cation. + It includes, as an anion, F - Cl - , Br - , I - NO3 - , N(CN)2 -, BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - , and SCN - Those containing at least any one selected from the group consisting of

[0029] Specifically, the non-aqueous electrolyte of the present invention may contain LiPF6 as a lithium salt. Additionally, the lithium salt may be LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10The electrolyte may contain a single substance or a mixture of two or more substances selected from the group consisting of LiAlCl4, LiAlO2, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO2CF2CF3)2 (lithium bis(perfluoroethanesulfonyl)imide; LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI). In addition to these, lithium salts commonly used as electrolytes in lithium secondary batteries can be used without restriction.

[0030] The lithium salt may be appropriately changed within a range of normal use, but in order to obtain the optimal effect of forming a corrosion-preventive film on the electrode surface, it may be included in the electrolyte at a concentration of 0.5 M to 5.0 M, preferably 1.0 M to 3.0 M, and more preferably 1.2 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics during high-temperature storage of the lithium secondary battery is sufficient, and the viscosity of the non-aqueous electrolyte is appropriate, improving electrolyte impregnation.

[0031] The non-aqueous electrolyte according to the present invention may contain an organic solvent comprising ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP). More preferably, the non-aqueous electrolyte according to the present invention may contain an organic solvent comprising ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP).

[0032] The aforementioned ethylene carbonate (EC) and propylene carbonate (PC) are highly viscous organic solvents with high dielectric constants, which facilitate the dissociation of lithium salts in the electrolyte. In an environment where a stable positive electrode film formed by the combination of the diisocyanate compound of chemical formula 1 and lithium difluoro(oxalate) borate (LiODFB) is sufficiently formed, propyl propionate (PP) has low reactivity with oxygen released from the positive electrode material, thus suppressing the production of carbon dioxide, an oxidizing gas. Ethylene propionate (EP) acts together with propyl propionate (PP) to increase lithium ion mobility and improve rapid charging performance.

[0033] The non-aqueous electrolyte of the present invention, by containing ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP), can provide a non-aqueous electrolyte with sufficient ionic conductivity. This results in the effect of excellent long-term lifespan characteristics. Most preferably, the organic solvent contained in the non-aqueous electrolyte of the present invention may consist of ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP).

[0034] The non-aqueous electrolyte of the present invention may contain, as other organic solvents, at least one organic solvent selected from the group consisting of fluoroethylene carbonate (FEC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate.

[0035] On the other hand, the organic solvent may be further used with any organic solvent commonly used for non-aqueous electrolytes, without limitation, as needed. For example, it may further contain at least one or more organic solvents such as ether-based organic solvents, glyme-based solvents, and nitrile-based organic solvents.

[0036] The ether-based solvent can be any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more of these, but is not limited to these.

[0037] The aforementioned glyme-based solvent has a higher dielectric constant and lower surface tension compared to linear carbonate-based organic solvents, and is a solvent with low reactivity with metals. It may include, but is not limited to, at least one selected from the group consisting of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME).

[0038] The nitrile solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited to these.

[0039] Furthermore, the non-aqueous electrolyte of the present invention may, if necessary, further contain known electrolyte additives in order to prevent the non-aqueous electrolyte from decomposing in a high-power environment, which can cause the collapse of the negative electrode, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery swelling at high temperatures.

[0040] Such other electrolyte additives may include, as representative examples, at least one SEI film-forming additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0041] Examples of the aforementioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate.

[0042] Examples of halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0043] Examples of the sultone compounds include at least one compound selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethensultone, 1,3-propensultone (PRS), 1,4-butensultone, and 1-methyl-1,3-propensultone.

[0044] Examples of the sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0045] Examples of the phosphate compounds include one or more compounds selected from the group consisting of lithium difluoro(bisoxalato) phosphate, lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, trimethylsilyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphate.

[0046] Examples of the borate compounds include tetraphenyl borate, lithium oxalyl difluoroborate (LiODFB), and lithium bisoxalate borate (LiB(C2O4)2, LiBOB).

[0047] Examples of the nitrile compounds include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0048] Examples of the benzene-based compound include fluorobenzene, examples of the amine-based compound include triethanolamine or ethylenediamine, and examples of the silane-based compound include tetravinylsilane.

[0049] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples include lithium difluorophosphate (LiDFP), LiPO2F2, or LiBF4.

[0050] If the other electrolyte additives further include a combination of vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (Esa), and lithium difluorophosphate (LiDFP), an even stronger SEI film can be formed on the surface of the negative electrode during the initial activation process of the secondary battery, thereby suppressing the generation of gases that may be produced by the decomposition of the electrolyte at high temperatures and improving the high-temperature stability of the secondary battery.

[0051] On the other hand, the other electrolyte additives may be used in a mixture of two or more types, and may be present in an amount of 0.050% to 20% by weight, specifically 0.10% to 15% by weight, based on the total weight of the nonaqueous electrolyte, and preferably 0.30% to 10% by weight. When the content of the other electrolyte additives satisfies the above range, a better improvement in ionic conductivity and cycle characteristics can be obtained.

[0052] [Lithium-ion secondary battery] The present invention also provides a lithium secondary battery comprising the non-aqueous electrolyte.

[0053] Specifically, the lithium secondary battery includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and the aforementioned non-aqueous electrolyte.

[0054] In this case, the lithium secondary battery of the present invention can be manufactured by conventional methods known in the art. For example, it can be manufactured by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator between the positive and negative electrodes are sequentially stacked, inserting the electrode assembly into a battery case, and injecting the non-aqueous electrolyte according to the present invention.

[0055] The lithium secondary battery of the present invention has an upper limit of operating voltage of 4.47V or higher and can be driven at high voltage. The upper limit of the operating voltage refers to the charge termination voltage during charging and discharging of the lithium secondary battery, for example, the cutoff voltage under CC-CV charging conditions.

[0056] The lithium secondary battery of the present invention is characterized by low Co leaching even when driven at high voltage. Specifically, the lithium secondary battery of the present invention can satisfy the following formula (1).

[0057] Formula (1):D t / D0<5

[0058] In the above formula (1), D tD0 represents the amount of Co leached from the non-aqueous electrolyte after high-temperature storage of the lithium secondary battery at 85°C for 8 hours, while D0 represents the amount of Co leached from the non-aqueous electrolyte of the lithium secondary battery before high-temperature storage.

[0059] Preferably, the lithium secondary battery of the present invention is D t The / D0 value can be between 1.5 and 3.5, most preferably between 1.5 and 2.5.

[0060] Furthermore, the lithium secondary battery of the present invention is characterized in that its pH does not become excessively acidic even when driven at high voltage. Specifically, the non-aqueous electrolyte of the lithium secondary battery of the present invention, measured after being stored at 60°C for one week, has a pH greater than 4, preferably between 4.2 and 5.

[0061] (1) Positive electrode The positive electrode can be manufactured by coating a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive material, and a solvent onto a positive electrode current collector.

[0062] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used.

[0063] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may specifically include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium metal oxide may be a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn YO2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1), etc.), and any one or two or more of these compounds may be included.

[0064] Among them, from the point of view of being able to improve the capacity characteristics and stability of the battery, the lithium metal oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 (For example, O2) and other similar substances may be used, and one or more of these may be used as a mixture.

[0065] In particular, the positive electrode active material may be a lithium cobalt-based oxide represented by the following chemical formula 2.

[0066] [Chemical formula 2] Li a1 Co 1-x1 M 1 x1 O 2+β

[0067] In the above chemical formula 2, M 1 It contains one or more elements selected from the group consisting of Al, B, Ba, Ca, Zr, Ti, Mg, Ta, Nb, Sr, W, and Mo, and 0.9 <a1≦1.1、0≦x1≦0.2、0≦β≦0.02であってよい。

[0068] The positive electrode active material may be present in an amount of 60% to 99% by weight, preferably 70% to 99% by weight, and more preferably 80% to 98% by weight, based on the total weight of the solid matter in the positive electrode mixture slurry excluding the solvent.

[0069] The aforementioned binder is a component that assists in the bonding of the active material to the conductive material and to the current collector.

[0070] Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers.

[0071] Typically, the binder may be present in an amount of 1% to 20% by weight, preferably 1% to 15% by weight, and more preferably 1% to 10% by weight, based on the total weight of the solids in the positive electrode mixture slurry excluding the solvent.

[0072] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 1% to 20% by weight based on the total weight of the solid content in the negative electrode slurry. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and may be used, for example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a well-developed crystalline structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0073] Typically, the conductive material may be included in an amount of 1% to 20% by weight, preferably 1% to 15% by weight, and more preferably 1% to 10% by weight, based on the total weight of the solid matter in the positive electrode mixture slurry excluding the solvent.

[0074] The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone) and may be used in an amount that results in a suitable viscosity when the positive electrode active material and selectively include a binder and conductive material are present. For example, the concentration of the solid content containing the positive electrode active material and selectively including the binder and conductive material may be 50% to 95% by weight, preferably 70% to 95% by weight, and more preferably 70% to 90% by weight.

[0075] (2) Negative electrode The negative electrode can be manufactured, for example, by coating a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and a solvent onto a negative electrode current collector, or by using a graphite electrode made of carbon (C) or the metal itself as the negative electrode.

[0076] For example, when a negative electrode is manufactured by coating a negative electrode mixture slurry onto the negative electrode current collector, the negative electrode current collector generally has a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. Also, similar to the positive electrode current collector, the bonding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0077] Furthermore, the negative electrode active material may include at least one selected from the group consisting of lithium metal, carbon material capable of reversibly intercalating / deintercalating lithium ions, metal or alloys of these metals with lithium, metal composite oxides, materials capable of doping and dedoping lithium, and transition metal oxides.

[0078] As the carbon material capable of reversibly intercalating / deintercalating the lithium ions, any carbonaceous negative electrode active material generally used in a lithium ion secondary battery can be used without particular limitation, and representative examples thereof include crystalline carbon, amorphous carbon, or these may be used together. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0079] As the metal or an alloy of these metals with lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or an alloy of these metals with lithium can be used.

[0080] Examples of the metal composite oxide include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), and Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, elements of Group 1, Group 2, Group 3 of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) can be selected from the group consisting of those used.

[0081] As the substance capable of doping and undoping lithium, Si, SiO x(0 < x ≤ 2), Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO₂, Sn-Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), etc. may be mentioned, and at least one of these may be mixed with SiO₂ and used. The element Y may be 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, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0082] Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0083] The additive according to the present invention is particularly effective when Si or SiO x (0 < x < 2) is used as the negative electrode active material. Specifically, when using a Si-based negative electrode active material, if a strong SEI layer is not formed on the surface of the negative electrode during initial activation, the life characteristics will be promoted to decline due to intense volume expansion and contraction during the progress of the cycle. However, the additive according to the present invention can form a strong SEI layer while having elasticity, so that a secondary battery using a Si-based negative electrode active material can have excellent life characteristics and storage characteristics.

[0084] Among them, the negative electrode active material may be a mixture of graphite and SiO x (0 ≤ x < 2). From the point of increasing the capacity of the lithium secondary battery, the graphite and SiO x (0 ≤ x < 2) may be contained in a weight ratio of 97:3 to 90:10.

[0085] The negative electrode active material may be present in an amount of 60 to 99% by weight, preferably 70 to 99% by weight, and more preferably 80 to 98% by weight, based on the total weight of solids in the negative electrode mixture slurry.

[0086] Examples of the aforementioned binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof. Specifically, styrene-butadiene rubber (SBR)-carboxymethylcellulose (CMC) can be used due to its high viscosity.

[0087] Typically, the binder may be present in an amount of 1% to 20% by weight, preferably 1% to 15% by weight, and more preferably 1% to 10% by weight, based on the total weight of the solid matter in the negative electrode mixture slurry excluding the solvent.

[0088] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 1% to 20% by weight based on the total weight of the solid content in the negative electrode mixture slurry. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and may be used, for example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a well-developed crystalline structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0089] The conductive material may be present in an amount of 1% to 20% by weight, preferably 1% to 15% by weight, and more preferably 1% to 10% by weight, based on the total weight of the solid matter in the negative electrode mixture slurry excluding the solvent.

[0090] The solvent may include water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that results in a suitable viscosity when the negative electrode active material and selectively include a binder and conductive material. For example, the concentration of the solid content containing the negative electrode active material and selectively including the binder and conductive material may be 50% to 95% by weight, preferably 70% to 90% by weight.

[0091] When a metal itself is used as the negative electrode, it can be manufactured by physically joining, rolling, or vapor-depositing the metal onto the metal thin film itself or onto the negative electrode current collector. As for the vapor deposition method, electro-deposit or chemical vapor deposition of the metal can be used.

[0092] For example, the metal bonded / rolled / deposited onto the metal thin film itself or the negative electrode current collector may include one metal or an alloy of two metals selected from the group consisting of lithium (Li), nickel (Ni), tin (Sn), copper (Cu), and indium (In).

[0093] (3) Separator Furthermore, the separator may be a conventional porous polymer film, such as a porous polymer film made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, used alone or in a laminated configuration. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used, but is not limited to these. In addition, a coated separator containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used as a single-layer or multi-layer structure.

[0094] Specifically, as the separator included in the electrode assembly of the present invention, an SRS (safety reinforced separator) separator may be used, which has a coating layer containing ceramic components or polymer substances formed on it in order to ensure heat resistance or mechanical strength.

[0095] Specifically, the separator included in the electrode assembly of the present invention comprises a porous separator substrate and a porous coating layer that is applied to one or both sides of the separator substrate, wherein the coating layer may contain a mixture of inorganic particles selected from metal oxides, metalloid oxides, metal fluorides, metal hydroxides, and combinations thereof, and a binder polymer that connects and fixes the inorganic particles to each other.

[0096] The coating layer may contain one or more inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, and MgF. Here, the inorganic particles can improve the thermal stability of the separator. That is, the inorganic particles can prevent the separator from shrinking at high temperatures. Furthermore, the binder polymer can fix the inorganic particles and improve the mechanical stability of the separator.

[0097] The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, rectangular, pouch-shaped, or coin-shaped, using a can.

[0098] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative for understanding the present invention and are not intended to limit the scope of the invention. It will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the described concept and technical idea, and it goes without saying that such variations and modifications fall within the scope of the appended claims.

[0099] [Examples] Example 1 (Manufacturing of non-aqueous electrolytes) A non-aqueous solvent was prepared by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC): propylene carbonate (PC): ethylene propionate (EP): propyl propionate (PP) = 20:10:25:45 by volume) to a concentration of 1.2 M. A non-aqueous electrolyte was prepared by adding 0.5 g of hexamethylene diisocyanate and 1 g of lithium difluoro(oxalate) borate (LiODFB) to 98.5 g of the non-aqueous solvent.

[0100] (Manufacturing of lithium-ion batteries) A positive electrode slurry (74% solids by weight) was prepared by adding a positive electrode active material (LiCoO2), a conductive material (carbon black), and a binder (polyvinylidene fluoride) in a weight ratio of 97.5:1.3:1.2 to the solvent N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was applied to one surface of a 15 μm thick positive electrode current collector (a thin Al film), and the positive electrode was manufactured by drying and roll pressing.

[0101] A negative electrode slurry (62% solids by weight) was prepared by adding a negative electrode active material (graphite:SiO=92:8 by weight ratio), a conductive material (carbon black), and a binder (polyvinylidene fluoride) in a weight ratio of 96.8:0.2:3.0 to the solvent N-methyl-2-pyrrolidone (NMP). The negative electrode slurry was applied to one surface of a 15 μm thick negative electrode current collector (Cu thin film), and the negative electrode was manufactured by drying and roll pressing.

[0102] In a dry room, a polyolefin-based porous separator coated with inorganic Al2O3 particles was interposed between the positive and negative electrodes manufactured as described above, and then the non-aqueous electrolyte manufactured as described above was injected to produce a secondary battery.

[0103] Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that 1 g of hexamethylene diisocyanate and 1 g of lithium difluoro(oxalate) borate (LiODFB) were added to 98 g of the non-aqueous solvent prepared in Example 1 to produce a non-aqueous electrolyte.

[0104] Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 2 g of hexamethylene diisocyanate and 1 g of lithium difluoro(oxalate) borate (LiODFB) to 97 g of the non-aqueous solvent prepared in Example 1.

[0105] Example 4 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 0.5 g of hexamethylene diisocyanate and 1 g of lithium difluoro(oxalate) borate (LiODFB) to 97.5 g of the non-aqueous solvent prepared in Example 1.

[0106] Example 5 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 2 g of hexamethylene diisocyanate and 0.5 g of lithium difluoro(oxalate) borate (LiODFB) to 97.5 g of the non-aqueous solvent prepared in Example 1.

[0107] Comparative Example 1 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared using 100 g of the non-aqueous solvent prepared in Example 1.

[0108] Comparative Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that 0.5 g of hexamethylene diisocyanate was added to 99.5 g of the nonaqueous solvent prepared in Example 1 to produce a nonaqueous electrolyte.

[0109] Comparative Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that 1 g of lithium difluoro(oxalate) borate (LiODFB) was added to 99 g of the non-aqueous solvent prepared in Example 1 to produce a non-aqueous electrolyte.

[0110] Comparative Example 4 A non-aqueous solvent was prepared by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) in a volume ratio of 30:30:40) to a concentration of 1.2 M. A non-aqueous electrolyte was prepared by adding 0.5 g of hexamethylene diisocyanate and 1 g of lithium difluoro(oxalate) borate (LiODFB) to 98.5 g of the non-aqueous solvent.

[0111] A secondary battery was manufactured in the same manner as in Example 1, except that this non-aqueous electrolyte was used.

[0112] [Experimental Example 1 - Confirmation of Co elution amount by ICP analysis] For each secondary battery produced in Examples 1-5 and Comparative Examples 1-4, the amount of Co elution D0 was measured, and after storage at 85°C for 8 hours, the amount of Co elution D0 was measured. t We measured it.

[0113] Specifically, the amount of Co eluted from each battery produced in Examples 1-5 and Comparative Examples 1-4 was analyzed by ICP analysis before and after storage at 85°C for 8 hours.

[0114] [Table 1]

[0115] [Experimental Example 2 - Confirmation of Electrolyte pH] The pH of the non-aqueous electrolyte was measured for each secondary battery produced in Examples 1-5 and Comparative Examples 1-4 after storage at 60°C for one week.

[0116] [Table 2]

[0117] [Experimental Example 3 - Evaluation of High-Temperature Cycle Characteristics] The cycle characteristics of each secondary battery manufactured in Examples 1-5 and Comparative Examples 1-4 were evaluated.

[0118] Specifically, each battery manufactured in Examples 1-5 and Comparative Examples 1-4 was charged to 4.5V at 45°C with a constant current of 0.5C, and then discharged to 3.0V with a constant current of 0.5C. This constituted one cycle. After 200 charge-discharge cycles, the capacity retention rate relative to the initial capacity after one cycle was measured. The results are shown in Table 3 below.

[0119] [Table 3]

[0120] As shown in Table 3, Examples 1 to 5, which used a combination of the diisocyanate additive of chemical formula 1 and LiODFB, showed higher capacity retention and superior lifespan characteristics compared to the secondary batteries of Comparative Example 1 (which did not contain either the additive of chemical formula 1 or LiODFB), Comparative Example 2 (which did not contain LiODFB), and Comparative Example 3 (which did not contain the additive of chemical formula 1).

[0121] Furthermore, Examples 1-5, which used non-aqueous electrolytes containing organic solvents of ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP), showed higher capacity retention and superior lifespan characteristics compared to the secondary battery of Comparative Example 4, which used a combination of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0122] [Experimental Example 4 - Evaluation of High-Temperature Storage Characteristics] The high-temperature storage characteristics were evaluated for each secondary battery manufactured in Examples 1-5 and Comparative Examples 1-4.

[0123] Specifically, after fully charging each of the secondary batteries in Examples 1-5 and Comparative Examples 1-4 to 4.5V, they were stored at 85°C for 8 hours.

[0124] Before saving, the capacity of the fully charged rechargeable battery was measured and set as the initial capacity of the rechargeable battery.

[0125] After 8 hours, the capacity of the stored secondary battery was measured, and the capacity reduction during the storage period was calculated. The capacity retention rate after 8 hours was derived by calculating the percentage of the reduced capacity relative to the initial capacity of the secondary battery. The results are shown in Table 4 below.

[0126] [Table 4]

[0127] As shown in Table 4 above, Examples 1 to 5, which used a combination of the diisocyanate additive of chemical formula 1 and LiODFB, showed higher capacity retention after high-temperature storage and more stable performance at high temperatures compared to the secondary batteries of Comparative Example 1, Comparative Example 2, which did not contain LiODFB, and Comparative Example 3, which did not contain the additive of chemical formula 1, respectively.

[0128] Furthermore, Examples 1-5, which used non-aqueous electrolytes containing organic solvents of ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP), showed higher volume retention after high-temperature storage and more stable performance at high temperatures compared to Comparative Example 4, which used a combination of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

Claims

1. A non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, The aforementioned additive comprises a compound represented by the following chemical formula 1 and lithium difluoro(oxalate) borate (LiODFB), The aforementioned organic solvent is a non-aqueous electrolyte for lithium secondary batteries, comprising ethylene carbonate (EC), propylene carbonate (PC), ethylene propionate (EP), and propyl propionate (PP). 【Chemistry 1】 (In the above chemical formula 1, n is an integer between 3 and 10.)

2. The non-aqueous electrolyte according to claim 1, wherein n in the chemical formula 1 is an integer from 3 to 8.

3. The lithium salt is LiPF ６ A non-aqueous electrolyte according to claim 1, comprising:

4. The nonaqueous electrolyte according to claim 1, comprising 0.1% to 5% by weight of the compound represented by chemical formula 1 based on the total nonaqueous electrolyte.

5. The non-aqueous electrolyte according to claim 1, comprising 0.1% to 5% by weight of lithium difluoro(oxalate) borate (LiODFB) relative to the total non-aqueous electrolyte.

6. The non-aqueous electrolyte according to claim 1, wherein the weight ratio of the compound represented by chemical formula 1 to the lithium difluoro(oxalate) borate (LiODFB) is 0.2:1 to 5:

1.

7. Positive electrode and, The negative electrode and, A lithium secondary battery comprising a non-aqueous electrolyte according to any one of claims 1 to 6, A lithium-ion secondary battery with an upper limit of 4.47V or higher operating voltage.

8. The lithium secondary battery according to claim 7, wherein the positive electrode contains a lithium cobalt-based oxide as the positive electrode active material.

9. The negative electrode consists of graphite and SiO as negative electrode active materials. ｘ A lithium secondary battery according to claim 7, including (0 ≤ x < 2).

10. The lithium secondary battery according to claim 7, wherein the lithium secondary battery satisfies the following formula (1). Equation (1): D ｔ / D ０ <5 (In the above formula (1), D ｔ This is the amount of Co eluted from the non-aqueous electrolyte after storing a lithium secondary battery at a high temperature of 85°C for 8 hours, and D ０ This represents the amount of Co leached from the non-aqueous electrolyte of lithium secondary batteries before high-temperature storage.

11. The lithium secondary battery according to claim 7, wherein the pH of the non-aqueous electrolyte measured after storing the lithium secondary battery at 60°C for one week is greater than 4.

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