Additive for non-aqueous electrolyte, and non-aqueous electrolyte and lithium secondary battery including the same

Abstract

This disclosure relates to an additive for a non-aqueous electrolyte, a non-aqueous electrolyte comprising the additive, and a lithium secondary battery. The additive comprises a compound represented by Formula 1, which is capable of improving the life characteristics of the lithium secondary battery by forming an electrode-electrolyte interface that is stable and has low resistance even at high temperatures.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2021-0143853, filed on October 26, 2021, and Korean Patent Application No. 10-2022-0138354, filed on October 25, 2022, the disclosures of which are incorporated herein by reference. Technical Field

[0004] This disclosure relates to an additive for a non-aqueous electrolyte, a non-aqueous electrolyte including the additive, and a lithium secondary battery. Background Technology

[0005] With the development of the information society, personal IT devices and computer networks have been developed, and the entire society's dependence on electricity has also increased. Therefore, it is necessary to develop technologies for the effective storage and utilization of electrical energy.

[0006] In particular, with the rise of interest in solving environmental problems and achieving a sustainable circular society, research on lithium-ion batteries, which are attracting much attention as a clean energy source with low carbon dioxide emissions, has been extensively carried out.

[0007] Because lithium-ion batteries not only have the highest theoretical energy density among energy storage devices, but can also be miniaturized for personal IT devices and have high operating voltages, they are attracting much attention as power sources for energy storage, electric vehicles, and laptops and mobile phones.

[0008] Lithium-ion batteries mainly consist of a positive electrode formed by a transition metal oxide containing lithium, a negative electrode that can store lithium, an electrolyte that serves as a medium for transferring lithium ions, and a separator. Among these components, the electrolyte is known to have a significant impact on the stability or safety of the battery, and a great deal of research has been conducted on electrolytes.

[0009] As lithium-ion batteries are charged and discharged, the positive electrode active material undergoes structural collapse due to the decomposition products of lithium salts included in the electrolyte. This collapse causes a decrease in the performance of the positive electrode, and during this collapse, transition metal ions dissolve from the positive electrode surface. These dissolved transition metal ions then electrodeposit on either the positive or negative electrode, increasing the resistance of the positive electrode, degrading the negative electrode, or disrupting the solid electrolyte interphase (SEI). This results in further electrolyte decomposition, leading to battery life degradation and increased resistance.

[0010] This battery performance degradation tends to accelerate further when the potential of the positive electrode increases or when the battery is exposed to high temperatures.

[0011] Therefore, in order to suppress the dissolution of transition metal ions from the positive electrode or prevent the degradation of the negative electrode, it is urgent to study an electrolyte composition that can form a stable SEI film on the surface of the electrode. Summary of the Invention

[0012] Technical issues

[0013] One aspect of this disclosure is to provide an additive for non-aqueous electrolytes that can form a stable and low-resistance film on the surface of an electrode even at high temperatures.

[0014] Another aspect of this disclosure provides a non-aqueous electrolyte for lithium secondary batteries and a lithium secondary battery comprising the non-aqueous electrolyte, wherein the non-aqueous electrolyte can improve low-temperature capacity characteristics and high-temperature durability by forming a robust film on the surface of the electrode through the inclusion of the additives for the non-aqueous electrolyte.

[0015] Technical solution

[0016] According to one aspect of this disclosure,

[0017] An additive for non-aqueous electrolytes is provided, the additive comprising a compound represented by Formula 1:

[0018] [Formula 1]

[0019]

[0020] In Equation 1,

[0021] n is an integer from 2 to 20.

[0022] According to another aspect of this disclosure, a non-aqueous electrolyte for lithium secondary batteries is provided, the non-aqueous electrolyte comprising a lithium salt, a non-aqueous organic solvent, and the additives for the non-aqueous electrolyte.

[0023] The additives used for non-aqueous electrolytes are present in an amount of 9.0% by weight or less based on the total weight of the non-aqueous electrolytes used in lithium secondary batteries.

[0024] According to another aspect of this disclosure, a lithium secondary battery including the non-aqueous electrolyte for a lithium secondary battery is provided.

[0025] Beneficial effects

[0026] Because the compound represented by Formula 1 of this disclosure includes fluorine-substituted alkyl groups and propynyl groups in its structure, which have excellent antioxidant and flame-retardant properties, a robust film containing fluorine can be formed on the surface of the electrode. Therefore, if this compound is included as an additive, a non-aqueous electrolyte capable of forming an electrode-electrolyte interface with low resistance, high flame retardancy, and high-temperature durability can be provided. Furthermore, because the output characteristics of the battery can be improved, heat generation and expansion caused by additional reactions between electrolytes when exposed to high temperatures can be reduced, and performance at low temperatures can be improved by including the non-aqueous electrolyte, lithium secondary batteries with excellent storage and cycle characteristics at both low and high temperatures can be achieved. The non-aqueous electrolyte of this disclosure is particularly suitable for high-output batteries that use high-capacity active materials such as high-nickel-based cathode active materials. Attached Figure Description

[0027] The following accompanying drawings illustrate preferred embodiments of the present disclosure by way of example, and the technical concept of the present disclosure can be further understood in conjunction with the following detailed description of the invention. Therefore, the present disclosure should not be interpreted solely by the matters shown in these drawings.

[0028] Figure 1 It is a compound represented by formula 1-1. 1 H-NMR spectrum. Detailed Implementation

[0029] The contents of this disclosure will be described in more detail below.

[0030] It will be understood that the words or terms used in this specification and claims should not be construed as having the meanings defined in common dictionaries. It will be further understood that, based on the principle that the inventors may appropriately define the meanings of words or terms to best interpret the invention, these words or terms should be interpreted as having meanings consistent with the technical concept of the invention and the context of related art.

[0031] Furthermore, the terminology used in this specification is for describing exemplary embodiments only and is not intended to limit the invention. Unless otherwise stated, singular terms may include plural forms.

[0032] Before describing this disclosure, it will be further understood that the terms “comprising,” “including,” or “having” in this specification specify the presence of the stated features, numbers, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements, or combinations thereof.

[0033] In this specification, the terms "a to b carbon atoms" refer to the number of carbon atoms included in a specific functional group. That is, a functional group can include carbon atoms "a" to "b". For example, the expression "alkane group having 1 to 5 carbon atoms" refers to alkane groups containing 1 to 5 carbon atoms, namely -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2(CH3)CH-, -CH(CH3)CH2-, and -CH(CH3)CH2CH2-.

[0034] The term "alkyl" refers to a branched or unbranched divalent unsaturated hydrocarbon group. In embodiments, the alkyl group can be substituted or unsubstituted. Alkyl groups may include methyl, ethylene, propane, isopropane, butane, isobutane, tert-butyl, pentane, and 3-pentane.

[0035] Furthermore, unless otherwise defined in this specification, the term "substitution" means that at least one hydrogen atom bonded to a carbon atom is substituted by an element other than hydrogen, such as an alkyl group having 1 to 6 carbon atoms or fluorine.

[0036] Additives for non-aqueous electrolytes

[0037] The additives for non-aqueous electrolytes according to embodiments of this disclosure include compounds represented by Formula 1.

[0038] [Formula 1]

[0039]

[0040] In Equation 1,

[0041] n is an integer from 2 to 20.

[0042] The compound represented by Formula 1 can form a robust solid electrolyte interface (SEI) film containing fluorine on the surface of the negative electrode, while the triple bond (-C≡C-), i.e., the propyne group, included in its molecular structure, induces electrochemical reactions during electrochemical decomposition. Furthermore, the fluorine-substituted alkyl groups in the molecular structure, possessing excellent flame retardancy and non-flammability, can act as free radical scavengers induced by fluorine, and can simultaneously form a passivation film on the surface of the positive electrode, ensuring excellent oxidation resistance. If a stable film is formed on the electrode surface as described above, lithium secondary batteries with improved room temperature and low temperature life characteristics can be provided because side reactions between the electrode and the electrolyte solution are controlled.

[0043] In particular, because the compounds of Formula 1 of this disclosure contain an ethylene group (-CH2-CH2-) as a linker between the acrylate functional group and the terminal fluorinated alkyl group, structural flexibility is improved by increasing the molecular chain length. Therefore, compared with other compounds in which the fluorinated alkyl group is directly bonded to the acrylate functional group or contains an ethylene group (-CH2-) between the acrylate functional group and the terminal fluorinated alkyl group, the compounds of this disclosure are able to form films with improved durability on the surface of the negative electrode.

[0044] Furthermore, since the compound represented by Formula 1 includes two oxygen elements in its molecular structure, its oxidative safety is improved compared to compounds that include three or more oxygen elements, and thus its high-pressure stability and electrolyte durability are improved.

[0045] As described above, when a compound represented by Formula 1, whose molecular structure includes two oxygen elements, a propynyl group, and an ethylene group (-CH2-CH2-) as a linking group between an acrylate functional group and a terminal fluorine-substituted alkyl group, is used as an electrolyte additive, an electrode-electrolyte interface film with low resistance, high flame retardancy, high-temperature durability, and flexibility even at low temperatures can be formed. Therefore, since a non-aqueous electrolyte that improves output characteristics and reduces exothermic reactions caused by additional side reactions when exposed to high-temperature conditions such as thermal abuse can be prepared, a lithium secondary battery that reduces battery swelling and exhibits excellent storage and cycle characteristics at both low and high temperatures can be realized.

[0046] Specifically, in Equation 1, n can be an integer from 3 to 15, and more specifically, n can be an integer from 4 to 10.

[0047] If n is an integer satisfying the above range, the stability of the film formed from the compound can be expected because the thermal properties of the compound itself can be improved. In particular, in Equation 1, when n is 16 or greater, and more particularly when n is greater than 20, the excessive inclusion of fluorine increases the viscosity and nonpolarity of the material, thereby reducing its solubility in the electrolyte and resulting in a decrease in ionic conductivity and deterioration of battery performance.

[0048] Preferably, the compound represented by Formula 1 may include at least one of the compounds represented by Formulas 1-1 to 1-3.

[0049] [Equation 1-1]

[0050]

[0051] [Equation 1-2]

[0052]

[0053] [Equation 1-3]

[0054]

[0055] Non-aqueous electrolyte for lithium secondary batteries

[0056] Furthermore, the non-aqueous electrolyte according to embodiments of this disclosure includes the additives for the non-aqueous electrolyte, which include compounds represented by Formula 1.

[0057] Non-aqueous electrolytes may further include lithium salts, non-aqueous organic solvents, and other electrolyte additives.

[0058] (1) Additives for non-aqueous electrolytes

[0059] Since the description of the compound represented by Formula 1 overlaps with the above description, its description will be omitted.

[0060] According to embodiments of this disclosure, the additive for the non-aqueous electrolyte may be present in an amount of 9.0% by weight or less, specifically from 0.1% to 7.0% by weight, based on the total weight of the non-aqueous electrolyte.

[0061] When the amount of additives used in the non-aqueous electrolyte meets the above range, excellent high-temperature durability can be achieved because the dissolution of transition metals from the positive electrode at high temperatures can be effectively suppressed by forming a stable film. That is, if the additives used in the non-aqueous electrolyte are present in the non-aqueous electrolyte at 0.1 wt% or more, the film-forming effect of a stable SEI film is improved even during high-temperature storage, thus preventing an increase in resistance and a decrease in capacity even after high-temperature storage, and therefore improving overall performance. Furthermore, if the additives used in the non-aqueous electrolyte are present in 7.0 wt% or less, an increase in resistance can be prevented by preventing the formation of an excessively thick film during initial charging, while controlling the viscosity of the electrolyte so that the lithium salt can dissolve easily, thus preventing the degradation of the secondary battery's output characteristics and initial capacity.

[0062] Specifically, the additives for the non-aqueous electrolytes may be present in an amount of 0.1% to 5% by weight, more specifically 0.5% to 3% by weight, based on the total weight of the non-aqueous electrolytes.

[0063] (2) Lithium salts

[0064] Any lithium salt commonly used in the electrolyte for lithium secondary batteries can be used without limitation, and, for example, the lithium salt may include Li +As a cation, and may include F selected from - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - B 10 Cl 10 - AlCl4 - AlO4 - 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 - At least one of the groups constituted is an anion.

[0065] Specifically, lithium salts can include a single material selected from the group consisting of: LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10The lithium salt may include, but is not limited to, LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2 (lithium bis(pentafluoroethane sulfonyl)imide, LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), or a mixture of two or more thereof. As a representative example, the lithium salt may include at least one selected from the group consisting of: LiBF4, LiClO4, LiPF6, LiN(SO2F)2, LiN(SO2CF2CF3)2, and LiN(SO2CF3)2.

[0066] The lithium salt can be appropriately varied within the generally available range, but it can be included in the electrolyte at a concentration of 0.8M to 3.0M, specifically 1.0M to 3.0M, to achieve the best effect of forming a film to prevent surface corrosion of the electrode.

[0067] If the concentration of lithium salt is less than 0.8 M, the capacity characteristics may be reduced due to the decreased mobility of lithium ions. Furthermore, if the concentration of lithium salt is greater than 3.0 M, the impregnation properties of the electrolyte may be reduced due to the excessive increase in the viscosity of the non-aqueous electrolyte, which may also reduce the film-forming effect.

[0068] (3) Non-aqueous organic solvents

[0069] Various non-aqueous organic solvents commonly used in non-aqueous electrolytes for lithium secondary batteries can be used without restriction as non-aqueous organic solvents. Specifically, their types are not limited, as long as decomposition caused by oxidation reactions during the charging and discharging of the secondary battery can be minimized and the desired performance can be exhibited together with additives.

[0070] For example, highly viscous cyclic carbonate-based organic solvents, which can readily dissociate lithium salts in electrolytes due to their high dielectric constant, can be used as non-aqueous organic solvents. Furthermore, to prepare electrolytes with high ionic conductivity, cyclic carbonate-based organic solvents can be mixed in appropriate proportions with at least one of linear carbonate-based organic solvents and / or linear ester-based organic solvents, and used as non-aqueous organic solvents.

[0071] Specifically, in order to prepare an electrolyte with high ionic conductivity, at least one of (i) cyclic carbonate-based organic solvents and (ii) linear carbonate-based organic solvents and linear ester-based organic solvents can be mixed in a volume ratio of 10:90 to 80:20, specifically 30:70 to 50:50, and used as the non-aqueous organic solvent of this disclosure.

[0072] Cyclic carbonate-based organic solvents are high-viscosity organic solvents that can readily dissociate lithium salts in electrolytes due to their high dielectric constant. Specific examples of cyclic carbonate-based organic solvents include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butenyl carbonate, 2,3-butenyl carbonate, 1,2-pentenyl carbonate, 2,3-pentenyl carbonate, and vinylene carbonate, and wherein the cyclic carbonate-based organic solvent may include at least one of ethylene carbonate and propylene carbonate.

[0073] Furthermore, linear carbonate-based organic solvents are organic solvents with low viscosity and low dielectric constant. As a representative example, at least one organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate can be used, and linear carbonate-based organic solvents may specifically include ethyl methyl carbonate (EMC).

[0074] Furthermore, specific examples of linear ester-based organic solvents may be at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate (PP), and butyl propionate, wherein the linear ester-based organic solvent may include at least one of ethyl propionate and propyl propionate.

[0075] If necessary, the organic solvents of this disclosure may further include at least one cyclic ester-based organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0076] Unless otherwise stated, the residues in the non-aqueous electrolyte of this disclosure that do not include components other than organic solvents (e.g., additives, lithium salts and other additives used in the non-aqueous electrolyte of this disclosure) may be non-aqueous organic solvents.

[0077] (4) Other additives

[0078] The non-aqueous electrolyte according to embodiments of this disclosure may further include other additives that can form a stable film on the surfaces of the negative and positive electrodes by being used together with the additives without significantly increasing the initial resistance, or can act as a complementary agent to suppress the decomposition of the solvent in the non-aqueous electrolyte and improve the mobility of lithium ions.

[0079] These other additives are not particularly restricted, as long as they can form a stable film on the surfaces of the positive and negative electrodes.

[0080] Specifically, as a representative example, other additives may include at least one additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, nitrile compounds, phosphate compounds, borate compounds, and lithium salt compounds.

[0081] Specifically, during battery activation, cyclic carbonate-based compounds can improve battery durability by forming a stable SEI film primarily on the surface of the negative electrode. Cyclic carbonate-based compounds may include vinylene carbonate (VC) or vinyl ethylene carbonate, and may be present in an amount of 3% by weight or less based on the total weight of the non-aqueous electrolyte. When the amount of cyclic carbonate-based compounds in the non-aqueous electrolyte exceeds 3% by weight, the battery's swelling suppression performance and initial resistance decrease.

[0082] Halogen-substituted carbonate compounds may include fluoroethylene carbonate (FEC) and may be present in an amount of 5% by weight or less based on the total weight of the non-aqueous electrolyte. When the amount of halogen-substituted carbonate compounds exceeds 5% by weight, the battery swelling suppression performance decreases.

[0083] In addition, nitrile compounds may include at least one compound selected from the group consisting of succinic anion, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valerate, decanonitrile, heptanonitrile, cyclovalerate, cyclohexanenitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0084] Nitrile compounds can act as complementary agents to form the SEI film on the negative electrode, inhibiting the decomposition of the solvent in the electrolyte and improving the mobility of lithium ions. Nitrile compounds can be present in an amount of 8% by weight or less based on the total weight of the non-aqueous electrolyte. When the amount of nitrile compounds in the non-aqueous electrolyte exceeds 8% by weight, the increased film formation on the electrode surface leads to increased resistance, thus degrading battery performance.

[0085] Furthermore, the battery durability can be improved because the phosphate ester-based compound stabilizes the PF6 anion in the electrolyte and facilitates the formation of positive and negative electrode films. The phosphate ester-based compound may include at least one compound selected from the group consisting of lithium difluoro(bis(oxalato)phosphate) (LiDFOP), LiPO2F2, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite, and may be present in an amount of 3% by weight or less based on the total weight of the non-aqueous electrolyte.

[0086] Boronate compounds can improve lithium-ion mobility by promoting ion-pair separation of lithium salts, reduce interfacial resistance of SEI films, and address issues such as hydrofluoric acid gas generation by dissociating materials that form during battery reactions and cannot be well separated (such as LiF). Boronate compounds can include lithium bis(oxalate)borate (LiBOB, LiB(C2O4)2), lithium difluoroborate oxalate, or lithium tetramethyltrimethylsilylborate (TMSB), and can be present in an amount of 3% by weight or less based on the total weight of the non-aqueous electrolyte.

[0087] Furthermore, the lithium salt-based compound is a compound that differs from the lithium salt included in the non-aqueous electrolyte, wherein the lithium salt-based compound may include at least one compound selected from the group consisting of LiODFB and LiBF4, and may be present in an amount of 3% by weight or less based on the total weight of the non-aqueous electrolyte.

[0088] Two or more other additives may be mixed and used, and the other additives may be present in an amount of 10% by weight or less, particularly 0.01% by weight to 10% by weight, and preferably 0.1% by weight to 5.0% by weight, based on the total weight of the non-aqueous electrolytes.

[0089] If the amount of other additives is less than 0.01% by weight, the high-temperature storage characteristics and gas reduction effect achievable by the additives are not significant. Furthermore, if the amount of other additives is greater than 10% by weight, excessive side reactions may occur in the electrolyte during battery charging and discharging. In particular, since other additives may not be fully decomposed when excessive amounts are added, they may exist in the electrolyte as unreacted material or precipitates at room temperature. Therefore, the life characteristics of the secondary battery will be reduced due to increased resistance.

[0090] Lithium secondary batteries

[0091] Next, a lithium secondary battery according to this disclosure will be described.

[0092] The lithium secondary battery according to the present disclosure includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. In this case, the non-aqueous electrolyte is the non-aqueous electrolyte according to the present disclosure. Since the non-aqueous electrolyte has been described above, its description will be omitted, and other components will be described below.

[0093] (1) Positive electrode

[0094] The positive electrode according to the present disclosure may include a positive electrode active material layer containing a positive electrode active material, and if necessary, the positive electrode active material layer may further include a conductive agent and / or a binder.

[0095] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and specifically, the positive electrode active material may include a lithium composite metal oxide containing lithium and at least one metal such as cobalt, manganese, nickel or aluminum (for example, Li(Ni x Co y Mn z )O2, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1), and more specifically, in terms of improving the capacity characteristics and stability of the battery, it may include a lithium nickel manganese cobalt-based oxide represented by the following formula 2.

[0096] [Formula 2]

[0097] Li(Ni a Co b Mn c M d )O2

[0098] In formula 2,

[0099] M is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B or Mo, and

[0100] a, b, c and d are the atomic fractions of each independent element,

[0101] where 0.55 ≤ a < 1, 0 < b ≤ 0.3, 0 < c ≤ 0.3, 0 ≤ d ≤ 0.1, and a + b + c + d = 1.

[0102] a, b, c and d may respectively satisfy 0.60 ≤ a ≤ 0.95, 0.01 ≤ b ≤ 0.20, 0.01 ≤ c ≤ 0.20, and 0 ≤ d ≤ 0.05.

[0103] Specifically, the lithium nickel manganese cobalt-based oxide may be a lithium composite transition metal oxide in which the nickel content in the transition metal is 55 atm% or higher, preferably 60 atm% or higher, and representative examples thereof may be selected from the group consisting of Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.5 Mn 0.2 Co 0.3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, and Li(Ni 0.9 Co 0.06 Mn 0.03 Al[[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

[0105] The positive electrode active material may be included in an amount of 90% to 99% by weight, particularly 93% to 98% by weight, based on the total weight of the solid content in the positive electrode active material layer.

[0106] The conductive agent is not particularly limited, as long as it is conductive and will not cause adverse chemical changes in the battery. For example, conductive materials such as: carbon black 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 good crystal structure; conductive fibers, such as carbon fibers or metal fibers; conductive powders, such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or derivatives of polyphenylene.

[0107] Conductive agents are typically added in amounts ranging from 1% to 30% by weight of the total weight of the solids content in the positive electrode active material layer.

[0108] Adhesives are components used to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector, wherein the adhesive is typically added in an amount of 1% to 30% by weight based on the total weight of the solid content in the positive electrode active material layer. Examples of adhesives can be: fluoropolymer adhesives, including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based adhesives, including styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, or styrene isoprene rubber; cellulose-based adhesives, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol-based adhesives, including polyvinyl alcohol; polyolefin-based adhesives, including polyethylene or polypropylene; polyimide-based adhesives; polyester-based adhesives; and silane-based adhesives.

[0109] The positive electrode of this disclosure can be prepared by methods known in the art for preparing positive electrodes. For example, the positive electrode can be prepared by coating a positive electrode slurry, obtained by dissolving or dispersing a positive electrode active material, a binder, and / or a conductive agent in a solvent, onto a positive electrode current collector, drying it, and then rolling it to form a positive electrode active material layer; or the positive electrode can be prepared by casting the positive electrode active material layer onto a separate support, and then pressing a film layer separated from the support onto the positive electrode current collector.

[0110] The positive current collector is not particularly restricted, as long as it is conductive and will not cause adverse chemical changes in the battery, and, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel that has been surface-treated with one of carbon, nickel, titanium, silver or the like can be used.

[0111] The solvent may include organic solvents such as N-methyl-2-pyrrolidone (NMP) and may be used in an amount such that a desired viscosity is obtained when the positive electrode active material is included, as well as selectively including binders and conductive agents. For example, the solvent may be included in an amount such that the concentration of the solid content in the active material slurry, including the positive electrode active material and selectively including binders and conductive agents, is in the range of 10% to 70% by weight, preferably 20% to 60% by weight.

[0112] (2) Negative electrode

[0113] Next, the negative electrode will be described.

[0114] The negative electrode according to this disclosure includes a negative electrode active material layer containing a negative electrode active material, and, if necessary, the negative electrode active material layer may further include a conductive agent and / or a binder.

[0115] The negative electrode active material may include at least one selected from the group consisting of lithium metal, carbon material capable of reversibly inserting / deintercalating lithium ions, metal or lithium alloy with the metal, metal composite oxide, lithium-doped and undoped materials, and transition metal oxides. In particular, lithium metal, lithium material capable of reversibly inserting / deintercalating lithium ions, or a mixture of lithium-doped and undoped carbon material and silicon-based material may be used.

[0116] As a carbon material capable of reversibly inserting / deintercalating lithium ions, carbon-based anode active materials commonly used in lithium-ion secondary batteries can be used without particular limitation, and, as typical examples, crystalline carbon, amorphous carbon, or both can be used. Examples of crystalline carbon can be graphite, such as irregular, planar, flake, spherical, or fibrous natural or artificial graphite, while examples of amorphous carbon can be soft carbon (low-temperature sintered carbon) or hard carbon, mesophase pitch carbides, and calcined coke.

[0117] As a metal or an alloy of lithium with that metal, 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 lithium with that metal, may be used.

[0118] One kind selected from the group consisting of the following can be used as the metal composite oxide: 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, or Ge; Me': Al, B, P, Si, Group I, II, III elements of the periodic table, or halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8).

[0119] Doped and undoped lithium-containing materials can include 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 Y is not Si), Sn, SnO2, and 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 Y is not Sn), and mixtures of SiO2 with at least one of them can also be used. Element Y can be selected from the group consisting of: Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), 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, and combinations thereof.

[0120] Transition metal oxides can include lithium titanium composite oxide (LTO), vanadium oxides, and lithium vanadium oxides.

[0121] The negative electrode active material can be included in an amount of 80% to 99% by weight based on the total weight of the solid content in the negative electrode active material layer.

[0122] A conductive agent is a component that further enhances the conductivity of the negative electrode active material, wherein the conductive agent can be added in an amount of 1% to 20% by weight based on the total weight of the solid content in the negative electrode active material layer. The conductive agent is not particularly limited, as long as it is conductive and does not cause adverse chemical changes in the battery, and, for example, conductive materials such as: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers or metal fibers; metal powders, such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or derivatives of polyphenylene.

[0123] Adhesives are components that facilitate bonding between conductive agents, active materials, and current collectors, and are typically added in amounts ranging from 1% to 30% by weight of the total weight based on the solid content in the negative electrode active material layer. Examples of adhesives can be: fluoropolymer adhesives, including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based adhesives, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose-based adhesives, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol-based adhesives, including polyvinyl alcohol; polyolefin-based adhesives, including polyethylene or polypropylene; polyimide-based adhesives; polyester-based adhesives; and silane-based adhesives.

[0124] The negative electrode can be prepared according to methods known in the art for preparing negative electrodes. For example, the negative electrode can be prepared by coating a negative electrode active material slurry, obtained by dissolving or dispersing the negative electrode active material, along with a selective binder and conductive agent, onto a negative electrode current collector, rolling and drying to form a negative electrode active material layer; or the negative electrode can be prepared by casting the negative electrode active material layer onto a separate support, and then pressing the film layer separated from the support onto the negative electrode current collector.

[0125] Negative electrode current collectors typically have a thickness of approximately 3 μm to 500 μm. There are no particular limitations on the negative electrode current collector, as long as it has high conductivity without causing adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys can be used. Furthermore, similar to positive electrode current collectors, negative electrode current collectors can have fine surface roughness to improve the adhesion strength to the negative electrode active material. Negative electrode current collectors can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0126] The solvent may include water or organic solvents such as NMP and ethanol, and may be used in an amount such that a desired viscosity is obtained when the negative electrode active material is included, and selectively including binders and conductive agents. For example, the solvent may be included in an amount such that the concentration of the solid content, including the negative electrode active material and selectively including binders and conductive agents, is in the range of 50% to 75% by weight, preferably 50% to 65% by weight.

[0127] (3) partition

[0128] The lithium secondary battery according to this disclosure includes a separator between the positive and negative electrodes.

[0129] The separator separates the negative and positive electrodes and provides a path for the movement of lithium ions. Any separator can be used without particular limitation, as long as it is commonly used in lithium secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to the transfer of electrolyte ions can be used.

[0130] Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin-based polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures having two or more layers of these. Additionally, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, coated separators incorporating ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can optionally be used.

[0131] As described above, the lithium secondary batteries according to this disclosure can be suitably used in portable devices such as mobile phones, laptops and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0132] Therefore, according to another embodiment of the present disclosure, a battery module including the lithium secondary battery as a unit battery and a battery pack including the battery module are provided.

[0133] Battery modules or battery packs can be used as power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or as a power source for at least one medium to large device in an energy storage system.

[0134] The shape of the lithium secondary battery disclosed herein is not particularly limited, but cylindrical, prismatic, pouch, or coin-shaped containers are all acceptable.

[0135] The lithium secondary battery according to this disclosure can be used not only as a battery cell for use as a power source in small devices, but also as a unit battery in medium and large battery modules that include multiple battery cells.

[0136] The present disclosure will be described in detail below with reference to embodiments.

[0137] In this context, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these exemplary embodiments are provided so that the description will be thorough and complete and will fully convey the scope of this disclosure to those skilled in the art.

[0138] Example

[0139] I. Synthesis of Non-Aqueous Electrolyte Additives

[0140] Synthesis Example 1. Synthesis of the compound represented by Formula 1-1

[0141] 500 mL of ethyl acetate was added to the reactor, which was maintained at 10 °C. After dissolving 52.82 g (0.2 mol) of 2-(perfluorobutyl)ethanol (manufactured by Sigma-Aldrich) and 24.3 g (0.24 mol) of trimethylamine (manufactured by Samchun Chemical Co., Ltd.), 22.20 g of propionyl chloride (0.24 mol, manufactured by TCL) was slowly added dropwise while stirring.

[0142] Then, the reactants were stirred for another 2 hours at room temperature, and after the reaction was complete, 500 mL of water was added to separate the water and organic layers to obtain the organic layer.

[0143] After washing the obtained organic layer twice with distilled water, the solvent was vacuum distilled to obtain the compound of formula 1-1 (yield: 75%). The compound of formula 1-1... 1 The H-NMR spectrum (500MHz NMR, Aglient DD1) is shown in Figure 1 middle.

[0144]

[0145] Synthesis Example 2. Synthesis of compounds represented by formula 1-2

[0146] The compounds represented by Formulas 1-2 were obtained in the same manner as in Example 1, except that 2-(perfluorohexyl)ethanol (manufactured by Sigma-Aldrich) was used instead of 2-(perfluorobutyl)ethanol (manufactured by Sigma-Aldrich) (yield: 74%).

[0147] Synthesis Example 3. Synthesis of compounds represented by formulas 1-3

[0148] Compounds represented by Formulas 1-3 were obtained in the same manner as in Example 1, except that 2-(perfluorononyl)ethanol (manufactured by Sigma-Aldrich) was used instead of 2-(perfluorobutyl)ethanol (manufactured by Sigma-Aldrich) (yield: 73%).

[0149] II. Secondary Battery Preparation

[0150] Example 1.

[0151] (Preparation of non-aqueous electrolytes)

[0152] LiPF6 was dissolved in a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) in a volume ratio of 30:20:30:20 to achieve a LiPF6 concentration of 1.0 M. Then, a non-aqueous electrolyte was prepared by adding 0.5% by weight of the compound represented by Formula 1-1 obtained in Synthesis Example 1 as an additive (see Table 1 below).

[0153] (Positive electrode preparation)

[0154] A positive electrode active material (LiCoO2), a conductive agent (carbon black), and a binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 97.5:1:1.5 to prepare a positive electrode active material slurry (60% by weight solids). A 15 μm thick positive electrode current collector (Al film) was coated with this positive electrode active material slurry, dried, and then rolled to prepare the positive electrode.

[0155] (Anode preparation)

[0156] A negative electrode active material (graphite), a conductive agent (carbon black), and a binder (polyvinylidene fluoride) were added to distilled water in a weight ratio of 96:0.5:3.5 to prepare a negative electrode active material slurry (solid content concentration 50% by weight). An 8 μm thick negative electrode current collector (Cu film) was coated with this slurry, dried, and then rolled to prepare the negative electrode.

[0157] (Preparation of secondary batteries)

[0158] After preparing an electrode assembly by stacking a polyethylene porous membrane as a separator with the positive and negative electrodes prepared by the above method, the electrode assembly is placed in a battery casing, more than 5 mL of the non-aqueous electrolyte is injected into it, and the battery casing is sealed to prepare a pouch-type lithium secondary battery (battery capacity 6.24 mAh).

[0159] Example 2.

[0160] The pouch-type lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by adding the compounds represented by Formula 1-2 obtained in Synthesis Example 2 instead of the compounds represented by Formula 1-1 as additives (see Table 1 below).

[0161] Example 3.

[0162] The pouch-type lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by adding the compounds represented by Formulas 1-3 obtained in Synthesis Example 3 instead of the compounds represented by Formulas 1-1 as additives (see Table 1 below).

[0163] Example 4.

[0164] The pouch-type lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by dissolving LiPF6 in a non-aqueous organic solvent at a concentration of 1.0 M and then adding 1.0 wt% of a compound represented by Formula 1-1 as an additive (see Table 1 below).

[0165] Example 5.

[0166] The pouch-type lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by dissolving LiPF6 in a non-aqueous organic solvent at a concentration of 1.0 M and then adding 5.0 wt% of a compound represented by Formula 1-1 as an additive (see Table 1 below).

[0167] Comparative Example 1.

[0168] The lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by dissolving LiPF6 in a non-aqueous organic solvent at a concentration of 1.0 M and then without adding any additives (see Table 1 below).

[0169] Compare Example 2.

[0170] The lithium secondary battery was prepared in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding a compound represented by Formula 3 (a = 25) instead of a compound represented by Formula 1-1 (see Table 1 below).

[0171] [Formula 3]

[0172]

[0173] Comparative Example 3.

[0174] The lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by dissolving LiPF6 in a non-aqueous organic solvent at a concentration of 1.0 M and then adding 0.05% by weight of a compound represented by Formula 1-1 as an additive (see Table 1 below).

[0175] Comparative Example 4.

[0176] The lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by dissolving LiPF6 in a non-aqueous organic solvent at a concentration of 1.0 M and then adding 8.0 wt% of a compound represented by Formula 1-1 as an additive (see Table 1 below).

[0177] Comparative Example 5.

[0178] The lithium secondary battery was prepared in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding a compound represented by Formula 4 instead of a compound represented by Formula 1-1 (see Table 1 below).

[0179] [Formula 4]

[0180]

[0181] Comparative Example 6.

[0182] The lithium secondary battery was prepared in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding a compound represented by Formula 5 instead of a compound represented by Formula 1-1 (see Table 1 below).

[0183] [Formula 5]

[0184]

[0185] Compare Example 7.

[0186] The lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by dissolving LiPF6 in a non-aqueous organic solvent at a concentration of 1.0 M and then adding 10.0 wt% of a compound represented by Formula 1-1 as an additive (see Table 1 below).

[0187] In this case, it is impossible to prepare a non-aqueous electrolyte because lithium salts cannot be dissolved by a considerable amount of additives.

[0188] [Table 1]

[0189]

[0190] [Experimental Example]

[0191] Experimental Example 1. Initial Capacity Assessment

[0192] The lithium secondary batteries prepared in Examples 1 to 5 and the lithium secondary batteries prepared in Comparative Examples 1 to 6 were activated at 0.1C CC. Subsequently, using a PESC05-0.5 charge / discharge apparatus (manufacturer: PNE SOLUTION Co., Ltd., 5V, 500mA), each lithium secondary battery was charged to 4.45V at 0.33C CC under constant current-constant voltage (CC-CV) charging conditions at 25°C, followed by a 0.05C current cutoff and discharge to 2.5V at 0.33C CC conditions. After defining the above charge and discharge as one cycle and performing three cycles, the capacity of the third cycle was summarized as the initial capacity, as shown in Table 2 below.

[0193] Experimental Example 2. Initial Resistance Evaluation

[0194] The lithium secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 6 were activated at 0.1C CC. Subsequently, using a PESC05-0.5 charge / discharge apparatus (manufacturer: PNE SOLUTION Co., Ltd., 5V, 500mA), each lithium secondary battery was charged to 4.45V at 0.33C CC under constant current-constant voltage (CC-CV) charging conditions at 25°C, followed by a 0.05C current cutoff and discharge to 2.5V at 0.33C CC conditions. After defining the above charge and discharge as one cycle and performing three cycles, each lithium secondary battery was discharged at 2.5C for 10 seconds to 50% state of charge (SOC), and the initial resistance (DC-IR) was calculated using the measured voltage difference. The results are shown in Table 2 below.

[0195] [Table 2]

[0196]

[0197] As shown in Table 2, it is understood that the initial resistance and initial capacity of the secondary batteries prepared in Examples 1 to 5 are improved compared with those prepared in Comparative Examples 1 to 6.

[0198] Test Example 3. Low Temperature Resistance (-10℃) Evaluation

[0199] The lithium secondary batteries prepared in Examples 1 to 5 and the lithium secondary batteries prepared in Comparative Examples 1 to 6 were activated at 0.1C CC. Subsequently, after each lithium secondary battery was set to 35% SOC and then stored in a chamber at -10°C for 24 hours, the low-temperature storage resistance (DC-IR) was calculated using the voltage difference measured by discharging the lithium secondary battery at a current of 2.5C for 10 seconds. The results are shown in Table 3 below.

[0200] Experimental Example 4. Low Temperature (-10℃) Capacity Assessment

[0201] The lithium secondary batteries prepared in Examples 1 to 5 and the lithium secondary batteries prepared in Comparative Examples 1 to 6 were activated at 0.1C CC. Subsequently, after each lithium secondary battery was set to 10% SOC and stored in a chamber at -10°C for 24 hours, the capacity measured when the lithium secondary battery was discharged at a current of 0.05C to SOC 0 (V cutoff = 2.5C) is shown in Table 3 below.

[0202] [Table 3]

[0203]

[0204] As shown in Table 3, it is understood that the low-temperature resistance and low-temperature capacity of the secondary batteries prepared in Examples 1 to 5 are improved compared with those prepared in Comparative Examples 1 to 6.

Claims

1. An additive for non-aqueous electrolytes, said additive comprising a compound represented by Formula 1: [Formula 1] in, In Equation 1, n is an integer from 2 to 20.

2. The additive for non-aqueous electrolytes as described in claim 1, wherein, In Equation 1, n is an integer from 3 to 15.

3. The additive for non-aqueous electrolytes as described in claim 1, wherein, In Equation 1, n is an integer from 4 to 10.

4. The additive for non-aqueous electrolytes as claimed in claim 1, wherein the compound represented by formula 1 is at least one of the compounds represented by formulas 1-1 to 1-3: [Equation 1-1] [Equation 1-2] [Equation 1-3] 5. A non-aqueous electrolyte for lithium secondary batteries, said non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive for the non-aqueous electrolyte as described in claim 1; The additive for the non-aqueous electrolyte is present in an amount of 9.0% by weight or less based on the total weight of the non-aqueous electrolyte for the lithium secondary battery.

6. The non-aqueous electrolyte for a lithium secondary battery as claimed in claim 5, wherein the additive for the non-aqueous electrolyte is present in an amount of 0.1% to 7.0% by weight based on the total weight of the non-aqueous electrolyte for the lithium secondary battery.

7. The non-aqueous electrolyte for lithium secondary batteries as claimed in claim 5, wherein the additive for the non-aqueous electrolyte is present in an amount of 0.1% to 5.0% by weight based on the total weight of the non-aqueous electrolyte for lithium secondary batteries.

8. The non-aqueous electrolyte for lithium secondary batteries as claimed in claim 5, further comprising at least one other additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, nitrile compounds, phosphate compounds, borate compounds, and lithium salt compounds.

9. A lithium secondary battery, comprising: a positive electrode; a negative electrode; a separator disposed between the negative electrode and the positive electrode; and The non-aqueous electrolyte for lithium secondary batteries as described in claim 5.

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