Electrolyte for secondary battery and secondary battery comprising same

Abstract

An electrolyte for a secondary battery according to the present disclosure comprises a lithium salt, an organic solvent, a first additive represented by chemical formula 1, and a second additive comprising a nitrogen-carbon multiple-bond compound.

Description

Electrolyte for secondary batteries and secondary batteries including the same

[0001] The present disclosure provides an electrolyte for a secondary battery and a lithium secondary battery comprising the same.

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged, and are used as power sources for small electronic devices such as mobile phones and laptop PCs.

[0003] In particular, lithium-ion batteries offer high operating voltage, energy density, and charging speed, as well as advantages in terms of weight reduction. Accordingly, lithium-ion batteries are being applied as a power source for electric vehicles as well as small electronic devices.

[0004] For example, for lithium secondary batteries to be used as a power source for electric vehicles, they must be equipped with superior output and lifespan characteristics.

[0005] Meanwhile, a lithium secondary battery may include a negative electrode comprising a negative electrode active material (e.g., graphite); a positive electrode comprising a positive electrode active material (e.g., lithium transition metal oxide particles); and a non-aqueous electrolyte comprising a lithium salt and an organic solvent.

[0006] For example, in a lithium secondary battery, charging and discharging can proceed as the process of lithium ions being inserted and extracted from lithium transition metal oxide particles and graphite is repeated.

[0007] For example, the output characteristics and lifespan characteristics of a lithium secondary battery can be improved by varying the composition of the electrolyte. For example, the output characteristics of a lithium secondary battery can be improved by enhancing the conductivity of lithium ions. In addition, the lifespan characteristics of a lithium secondary battery can be improved by firmly forming a solid electrolyte interface (SEI) on the negative electrode.

[0008] One objective of the present disclosure is to provide an electrolyte for a secondary battery having improved electrochemical properties.

[0009] One objective of the present disclosure is to provide a lithium secondary battery comprising the above electrolyte.

[0010] The electrolyte for a secondary battery according to the present disclosure comprises a lithium salt, an organic solvent, a first additive represented by Formula 1, and a second additive comprising a nitrogen-carbon multiple bond compound.

[0011] [Chemical Formula 1]

[0012]

[0013] In Formula 1, R1 is a substituted or unsubstituted C1-C6 alkyl group; a substituted or unsubstituted C2-C6 alkenyl group; a substituted or unsubstituted C2-C6 alkynyl group; a substituted or unsubstituted C3-C7 cycloalkyl group; a substituted or unsubstituted C3-C7 cycloalkenyl group; or a substituted or unsubstituted C1-C6 alkoxy group, and R2 to R5 are independently a halogen; or a substituted or unsubstituted C1-C6 alkyl group, M is an alkali metal, and Y + is a monovalent cation.

[0014] According to exemplary embodiments, the content of the first additive may be 0.01% to 10% by weight of the total weight of the electrolyte.

[0015] According to exemplary embodiments, the content of the second additive may be 0.01% to 10% by weight of the total weight of the electrolyte.

[0016] According to exemplary embodiments, the ratio of the content of the second additive to the content of the first additive in the total weight of the electrolyte may be 0.1 to 2.

[0017] According to exemplary embodiments, the second additive may include an isocyanate compound; a nitrile compound; or an isocyanate compound and a nitrile compound.

[0018] According to exemplary embodiments, the isocyanate compound may include one to three isocyanate groups.

[0019] According to exemplary embodiments, the isocyanate compound may comprise at least one selected from the group consisting of cyclopentyl isocyanate, phenyl isocyanate, hexamethylene diisocyanate, ethyl isocyanate, fluorophenyl isocyanate, furfuryl isocyanate, (trimethylsilyl)isocyanate, benzenesulfonyl isocyanate, p-toluenesulfonyl isocyanate, cyclohexanemethyl isocyanate, benzoyl isocyanate, benzyl isocyanate, 3-(triethoxysilyl)propyl isocyanate, cyclohexyl isocyanate, methyl isocyanate, toluene diisocyanate, and 4,4'-methylene bis(phenyl isocyanate).

[0020] According to exemplary embodiments, the nitrile compound may include one to three nitrile groups.

[0021] According to exemplary embodiments, the nitrile compound may comprise at least one selected from the group consisting of succinonitrile, adiponitrile, fumaronitrile, 1,3,6-hexanedricarbonitrile, 1,4-dicyano-2-butene, malononitrile, glutaronitrile, heptanedinitrile, hexanedinitrile, benzonitrile, propionitrile, methoxypropionitrile, maleonitrile, 3-butenenitrile, 3,3,3-trifluoropropionitrile, 4-(fluorodimethylsilyl)butanitrile, and 3-(difluoromethylsilyl)propanenitrile.

[0022] According to exemplary embodiments, the organic solvent may comprise at least one selected from the group consisting of linear carbonate-based solvents, cyclic carbonate-based solvents, ester-based solvents, and ether-based solvents.

[0023] According to exemplary embodiments, the compound may further include an auxiliary additive comprising at least one of a fluorine-containing cyclic carbonate compound, an unsaturated group-containing cyclic carbonate compound, a sulfate compound, a sulfone compound, a lithium phosphate compound, a lithium borate compound, an organic acid compound, and a lactone compound.

[0024] In exemplary embodiments, the content of the auxiliary additive may be 0.01% to 5% by weight of the total weight of the electrolyte.

[0025] In exemplary embodiments, the ratio of the content of the auxiliary additive to the content of the first additive in the total weight of the electrolyte may be 0.1 to 1.

[0026] A lithium secondary battery according to the present disclosure comprises a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte for the secondary battery.

[0027] The electrolyte for a secondary battery according to the exemplary embodiments of the present disclosure can increase the capacity retention rate of the battery during repeated charging and discharging and can improve output characteristics.

[0028] The electrolyte for a secondary battery according to the exemplary embodiments of the present disclosure can improve the storage characteristics and lifespan characteristics of the battery in a high-temperature environment.

[0029] A lithium secondary battery according to exemplary embodiments of the present disclosure may have improved lifespan characteristics and output characteristics.

[0030] FIGS. 1 and FIGS. 2 are a planar perspective view and a cross-sectional view, respectively, schematically illustrating a lithium secondary battery according to exemplary embodiments.

[0031] The electrolyte for a secondary battery according to the present disclosure comprises a lithium salt, an organic solvent, and two or more different additives. Additionally, the lithium secondary battery according to the present disclosure comprises the electrolyte.

[0032] In this specification, "X-type compound" may mean a compound containing an X unit in a parent group, a side group, or a substituent.

[0033] In this specification, "Ca-Cb" may mean "a to b number of carbon atoms." Additionally, "a 5-7 ring" may mean "a ring having 5 to 7 atoms."

[0034] An electrolyte for a secondary battery according to exemplary embodiments (hereinafter abbreviated as electrolyte) may include a first additive represented by the following chemical formula 1.

[0035] [Chemical Formula 1]

[0036]

[0037] In Chemical Formula 1, R1 may be a substituted or unsubstituted C1-C6 alkyl group; a substituted or unsubstituted C2-C6 alkenyl group; a substituted or unsubstituted C2-C6 alkynyl group; a substituted or unsubstituted C3-C7 cycloalkyl group; a substituted or unsubstituted C3-C7 cycloalkenyl group; or a substituted or unsubstituted C1-C6 alkoxy group.

[0038] In one embodiment, R1 may be a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group.

[0039] In some embodiments, R1 may be a substituted or unsubstituted C2-C6 alkenyl group. In some embodiments, R1 may be an unsubstituted C2-C6 alkenyl group.

[0040] In this specification, the meaning of "substituted" may be that a hydrogen atom is substituted with any substituent and any substituent is further bonded.

[0041] For example, any of the above substituents may be a halogen, a C1-C6 alkyl group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, a C1-C6 alkoxy group, a nitro group, a cyano group, etc. In some embodiments, any of the above substituents may be a halogen or a C1-C6 alkyl group.

[0042] In Chemical Formula 1, R2 to R5 may independently be a halogen; or a substituted or unsubstituted C1-C6 alkyl group.

[0043] In one embodiment, at least one of R2 to R5 is a halogen (e.g., F, Cl, Br, or I). In some embodiments, at least one of R2 to R5 may be F.

[0044] In one embodiment, R2 to R5 may all be halogens. In some embodiments, R2 to R5 may all be F.

[0045] In Chemical Formula 1, M may be an alkali metal. In one embodiment, M may be Li, Na, or K.

[0046] In Chemical Formula 1, Y + is a monovalent cation. In one embodiment, Y + It may be an alkali metal ion; an ammonium ion; or a primary to quaternary ammonium ion.

[0047] In some embodiments, Y + is N + RaRbRcRd or ReRfN + = It could be Rg.

[0048] Ra to Rd may independently be hydrogen; a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group. Additionally, at least two of Ra to Rd may be bonded to each other to form a 5-7-membered heterocyclic ring.

[0049] Re to Rg may independently be hydrogen; a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group. Additionally, at least two of Re to Rg may be bonded to each other to form a 5-7-membered heterocyclic ring.

[0050] In some embodiments, Y + is N + RaRbRcRd, where at least one of Ra to Rd is hydrogen, and the remainder is a substituted or unsubstituted C1-C6 alkyl group; it may be a substituted or unsubstituted C2-C6 alkenyl group. In some embodiments, Y + is N + RaRbRcRd, where Ra is hydrogen, and Rb to Rd can be C1-C3 alkyl groups independently of each other.

[0051] According to exemplary embodiments, the first additive may include a compound represented by the following chemical formula 1-1.

[0052] [Chemical Formula 1-1]

[0053]

[0054] According to exemplary embodiments, the content of the first additive may be 0.01% to 10% by weight of the total weight of the electrolyte. According to some embodiments, the content of the first additive may be 0.1% to 5% by weight, 0.2% to 2% by weight, 0.5% to 1.5% by weight, or 0.5% to 1% by weight of the total weight of the electrolyte. Within these ranges, side reactions of the electrolyte can be further prevented.

[0055] The electrolyte for a secondary battery according to exemplary embodiments comprises a second additive different from the first additive. The second additive comprises a nitrogen-carbon multiple bond compound. For example, the second additive may comprise a nitrogen-carbon double bond compound or a nitrogen-carbon triple bond compound.

[0056] Nitrogen-carbon multiple bonds have high reactivity. Accordingly, they can easily react with reactive chemical species, such as radicals, formed by side reactions between the battery and the electrolyte that may occur during battery operation, and can prevent chain side reactions.

[0057] In addition, by-products formed by the decomposition of lithium salts during battery operation, such as HF, can be removed (scavenged), and the electrode-electrolyte interface can be stabilized. Accordingly, the dissolution of the anode transition metal can be suppressed through the formation of a stable CEI (Cathode-Electrolyte Interface).

[0058] According to exemplary embodiments, the second additive may include an isocyanate-based compound and / or a nitrile-based compound.

[0059] According to some embodiments, the second additive may include an isocyanate-based compound and a nitrile-based compound. Accordingly, the rate of increase in resistance of the battery after high-temperature storage can be further reduced, and the capacity efficiency of the battery during rapid charging can be further improved.

[0060] According to exemplary embodiments, the isocyanate compound may comprise one to three isocyanate groups. According to some embodiments, the isocyanate compound may be a monofunctional or difunctional isocyanate compound.

[0061] According to exemplary embodiments, the isocyanate compound may include a cyclic substituent. For example, the isocyanate compound may include a cycloalkyl group having 3 to 10 carbon atoms or an aryl group having 6 to 20 carbon atoms. The cycloalkyl group and the aryl group may each be independently substituted with a halogen, a hydroxyl group, a carboxyl group, an alkyl group having 1 to 10 carbon atoms, etc.

[0062] According to exemplary embodiments, the isocyanate compound may be a chain-type compound that does not include a ring structure. For example, the isocyanate compound may include a structure in which any carbon of a straight or branched hydrocarbon chain is an isocyanate group.

[0063] According to exemplary embodiments, the isocyanate compounds may include cyclopentyl isocyanate, phenyl isocyanate, hexamethylene diisocyanate, ethyl isocyanate, fluorophenyl isocyanate, furfuryl isocyanate, (trimethylsilyl)isocyanate, benzenesulfonyl isocyanate, p-toluenesulfonyl isocyanate, cyclohexanemethyl isocyanate, benzoyl isocyanate, benzyl isocyanate, 3-(triethoxysilyl)propyl isocyanate, cyclohexyl isocyanate, methyl isocyanate, toluene diisocyanate, 4,4'-methylene bis(phenyl isocyanate), etc. These may be used alone or in combination of two or more.

[0064] According to exemplary embodiments, the nitrile compound may comprise one to three nitrile groups. According to some embodiments, the nitrile compound may be a difunctional or trifunctional nitrile compound.

[0065] According to exemplary embodiments, the nitrile-based compound may not contain unsaturated bonds. Accordingly, the action of the nitrile group may not be inhibited, and side reactions may not occur.

[0066] According to exemplary embodiments, the nitrile-based compounds may include succinonitrile, adiponitrile, fumaronitrile, 1,3,6-hexanedricarbonitrile, 1,4-dicyano-2-butene, malononitrile, glutaronitrile, heptanedinitrile, hexanedinitrile, benzonitrile, propionitrile, methoxypropionitrile, maleonitrile, 3-butenenitrile, 3,3,3-trifluoropropionitrile, 4-(fluorodimethylsilyl)butanitrile, 3-(difluoromethylsilyl)propanenitrile, etc. These may be used alone or in combination of two or more.

[0067] According to exemplary embodiments, the content of the second additive may be 0.01% to 10% by weight of the total weight of the electrolyte. According to some embodiments, the content of the second additive may be 0.05% to 5% by weight, 0.1% to 2% by weight, 0.1% to 1.5% by weight, or 0.2% to 1% by weight of the total weight of the electrolyte. Within these ranges, side reactions between the positive electrode active material and the electrolyte may be further reduced, and the stability and high-temperature storage characteristics of the battery may be improved.

[0068] According to exemplary embodiments, the ratio of the content of the second additive to the content of the first additive in the total weight of the electrolyte may be 0.1 to 2. According to some embodiments, the ratio of the content of the second additive to the content of the first additive in the total weight of the electrolyte may be 0.4 to 1.

[0069] Within the above range, the content ratio of the first additive and the second additive is appropriate so that a highly stable film can be formed on the surface of the positive electrode active material. Accordingly, the crystal structure of the positive electrode active material may collapse less even during repeated charging and discharging of the battery, and battery stability may be improved.

[0070] When the second additive comprises an isocyanate compound and a nitrile compound, the weight ratio of the nitrile compound to the weight of the isocyanate compound may be 0.5 to 2. According to some embodiments, the weight ratio of the nitrile compound to the weight of the isocyanate compound may be 0.8 to 1.2.

[0071] The electrolyte according to exemplary embodiments comprises an organic solvent. The organic solvent may be a non-aqueous solvent. The organic solvent may be a dispersion medium or solvent for the first additive, the second additive, and the lithium salt, and may have sufficient solubility for them.

[0072] According to exemplary embodiments, the organic solvent may include an ester-based (carboxylate-based) solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, an aprotic solvent, a carbonate-based solvent, etc.

[0073] The above carbonate-based solvent may include linear carbonate-based solvents and cyclic carbonate-based solvents.

[0074] For example, the above linear carbonate-based solvent may include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, etc.

[0075] For example, the above-mentioned cyclic carbonate-based solvent may include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, etc.

[0076] In some embodiments, the content of the linear carbonate-based solvent in the total volume of the organic solvent may be 50 volume% to 90 volume% or 60 volume% to 85 volume%. In some embodiments, where the linear carbonate-based solvent comprises two different linear carbonate-based compounds, the content of each linear carbonate-based compound may be 25 volume% to 45 volume%.

[0077] In some embodiments, the content of the cyclic carbonate-based solvent in the total volume of the organic solvent may be 10 volume% to 50 volume% or 15 volume% to 40 volume%.

[0078] In exemplary embodiments, the content of the linear carbonate-based solvent in the total volume of the organic solvent may be greater than the content of the cyclic carbonate-based solvent.

[0079] For example, among the organic solvents, the volume ratio of the linear carbonate-based solvent to the cyclic carbonate-based solvent may be 1 to 9 or 1.5 to 4.

[0080] The above ester-based solvent is a solvent containing an ester group (-OCO-) distinct from a carbonate group (-OCOO-) and may be a concept parallel to a carbonate-based solvent. In some embodiments, the above ester-based solvent may include a linear ester-based solvent and a cyclic ester-based solvent.

[0081] For example, the above linear ester-based solvent may include methyl propionate, ethyl propionate, propyl acetate, butyl acetate, ethyl acetate, etc.

[0082] For example, the above-mentioned cyclic ester solvent may include butyrolactone, caprolactone, valerolactone, etc.

[0083] For example, the above ether-based solvent may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), and 2-methyltetrahydrofuran.

[0084] For example, the above ketone-based solvent may include cyclohexanone, etc.

[0085] For example, the above alcohol-based solvent may include at least one of ethyl alcohol and isopropyl alcohol.

[0086] For example, the aprotic solvent may include at least one of an amide-based solvent (e.g., dimethylformamide), a dioxolane-based solvent (e.g., 1,3-dioxolane), and a sulfolane-based solvent.

[0087] The electrolyte according to exemplary embodiments comprises a lithium salt. The lithium salt may be different from the first additive and the second additive.

[0088] For example, the above lithium salt is Li + X - It can be expressed as. In one embodiment, the anion (X) of the lithium salt - ) is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4- , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It could be the back.

[0089] In some embodiments, the lithium salt may be LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, LiN(CF3SO2)2, CF3SO3Li, LiC(CF3SO2)3, etc.

[0090] In some embodiments, the content of the lithium salt may be 0.01 to 2 M. In some embodiments, the content of the lithium salt may be 0.1 to 1.5 M. Within the concentration range, lithium ions and / or electrons can be smoothly moved during the charging and discharging of the battery.

[0091] In one embodiment, the electrolyte for the lithium secondary battery may further include an auxiliary additive to further improve the lifespan characteristics and output characteristics of the lithium secondary battery, or to improve high-temperature storage characteristics, etc.

[0092] In exemplary embodiments, the auxiliary additive may include a fluorine-containing cyclic carbonate compound, an unsaturated group-containing cyclic carbonate compound, a sulfate compound, a sulfone compound, a lithium phosphate compound, a lithium borate compound, an organic acid compound, a lactone compound, etc.

[0093] For example, the above fluorine-containing cyclic carbonate compound may have a cyclic structure of 5 to 7 members. For example, the above fluorine-containing cyclic carbonate compound may have a fluorine atom directly bonded to the ring, or a fluorine-substituted alkyl group (e.g., -CF3, etc.) bonded to the ring.

[0094] In some embodiments, the fluorine-containing cyclic carbonate compound may include fluoroethylene carbonate (FEC), etc.

[0095] In some embodiments, the unsaturated group-containing cyclic carbonate compound may include vinyl ethylene carbonate (VEC), vinylene carbonate (VC), etc.

[0096] In some embodiments, the sulfate compound may include a cyclic sulfate compound or a linear sulfate compound.

[0097] For example, the cyclic sulfate compound may have a 5- to 7-membered cyclic structure. In some embodiments, the cyclic sulfate compound may include ethylene sulfate (ESA), trimethylene sulfate (TMS), methyltrimethylene sulfate (MTMS), 1,3-propanediol cyclic sulfate, etc.

[0098] For example, linear sulfate compounds may include 2,4,8,10-tetraoxa-3,9-dithiaspiro[5.5]undecane 3,3,9,9-tetraoxide, 4,4'-bi(1,3,2-dioxathiolan)] 2,2,2',2'-tetraoxide, etc.

[0099] For example, the sulfonate compound may have a cyclic structure of 5 to 7 members. In some embodiments, the sulfonate compound may include at least one of an alkyl sulfonate compound and an alkenyl sulfonate compound. For example, the alkyl sulfonate compound may have only saturated bonds within the ring, and the alkenyl sulfonate compound may include double bonds within the ring.

[0100] In some embodiments, the alkyl sulfone compound may include 1,3-propane sulfone (PS), 1,4-butane sulfone, etc. Additionally, the alkenyl sulfone compound may include ethene sulfone, 1,3-propene sulfone (PRS), 1,4-butene sulfone, 1-methyl-1,3-propene sulfone, etc.

[0101] In some embodiments, the lithium phosphate-based compound may include lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, etc.

[0102] In some embodiments, the lithium borate-based compound may include lithium tetraphenylborate, lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiFOB), etc.

[0103] In some embodiments, the organic acid compound may include succinic acid or its anhydride, maleic acid or its anhydride, etc.

[0104] In some embodiments, the lactone compound may include at least one of a linear lactone compound and a lactone compound containing a double bond within a ring. In some embodiments, the lactone compound may include a muconic lactone, etc.

[0105] In exemplary embodiments, the content of the auxiliary additive may be 0.01% to 5% by weight of the total weight of the electrolyte. In some embodiments, the content of the auxiliary additive may be 0.1% to 3% by weight of the total weight of the electrolyte. Within this range, the life characteristics, output characteristics, high-temperature storage characteristics, etc., of the lithium secondary battery may be further improved.

[0106] In exemplary embodiments, the ratio of the content of the auxiliary additive to the content of the first additive in the total weight of the electrolyte may be 0.1 to 1.

[0107] A lithium secondary battery according to the present disclosure comprises a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte for the secondary battery.

[0108] In exemplary embodiments, the anode comprises an anode active material, and the anode active material may comprise a lithium transition metal oxide or a lithium iron phosphate compound.

[0109] According to exemplary embodiments of the present invention, a lithium secondary battery comprising the electrolyte for the lithium secondary battery is provided.

[0110] Hereinafter, a lithium secondary battery according to exemplary embodiments will be described in more detail with reference to the drawings. FIGS. 1 and 2 are a schematic plan perspective view and a cross-sectional view, respectively, showing a lithium secondary battery according to exemplary embodiments.

[0111] Referring to FIGS. 1 and 2, a lithium secondary battery may include a positive electrode (100) and a negative electrode (130) facing the positive electrode (100).

[0112] The positive electrode (100) may include a positive electrode current collector (105) and a positive electrode active material layer (110) on the positive electrode current collector (105).

[0113] For example, the positive active material layer (110) may include a positive active material. Additionally, the positive active material layer (110) may further include a positive binder and a conductive material.

[0114] For example, the anode (100) can be manufactured by mixing and stirring an anode active material, an anode binder, a conductive material, a dispersion medium, etc. to produce an anode slurry, and then applying, drying, and rolling the anode slurry onto an anode current collector (105).

[0115] For example, the positive current collector (105) may include stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof.

[0116] For example, the positive electrode active material may include lithium transition metal oxide particles or lithium iron phosphate compound particles capable of reversible insertion and extraction of lithium ions.

[0117] In one embodiment, the lithium transition metal oxide particles may contain nickel, cobalt, manganese, aluminum, etc.

[0118] In some embodiments, the lithium transition metal oxide particles contain nickel, and the nickel content among the lithium transition metal oxide particles may be 80 mol% or more of the total elements excluding lithium and oxygen.

[0119] In some embodiments, the lithium transition metal oxide particles may be represented by LiNiO2, LiCoO2, LiMnO2, LiMn2O4, or the following chemical formula 2.

[0120] [Chemical Formula 2]

[0121] Li x Ni (1-a-b) Co a M b O y

[0122] In Chemical Formula 2, M is at least one of Al, Zr, Ti, Cr, B, Mg, Mn, Ba, Si, Y, W, and Sr, and 0.9≤x≤1.2, 1.9≤y≤2.1, and 0≤a+b≤0.5.

[0123] In Chemical Formula 2, 0 <a+b≤0.4, 0<a+b≤0.3, 0<a+b≤0.2 또는 0<a+b≤0.1을 만족할 수 있다.

[0124] In some embodiments, the lithium iron phosphate particles may include a compound represented by the following chemical formula 3.

[0125] [Chemical Formula 3]

[0126] Li x Fe 1-y M y (PO 4-z )X z

[0127] In Chemical Formula 3, M may include at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y. For example, M may include Al, Mg, Co, or Mn.

[0128] In Chemical Formula 3, X may include at least one element selected from the group consisting of F, S, and N. For example, X may include F.

[0129] In Chemical Formula 3, 0.5≤x≤1.5, 0≤y≤0.1, and 0≤z≤0.5. In some embodiments, 0.8≤x≤1.2, 0≤y≤0.05, and 0≤z≤0.1.

[0130] In some embodiments, the lithium iron phosphate may include LiFePO4 with an olivine crystal structure.

[0131] For example, the anode binder may include organic binders such as polyvinylidenefluoride (PVDF), vinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile, and polymethylmethacrylate; and water-based binders such as styrene-butadiene rubber (SBR). Additionally, for example, the anode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0132] For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes; and metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0133] The cathode (130) may include a cathode current collector (125) and a cathode active material layer (120) on the cathode current collector (125).

[0134] For example, the negative electrode active material layer (120) may include a negative electrode active material, a negative electrode binder and a conductive material as needed.

[0135] For example, the cathode (130) can be manufactured by mixing and stirring a cathode active material, a cathode binder, a conductive material, a solvent, etc. to produce a cathode slurry, and then applying, drying, and rolling the cathode slurry onto a cathode current collector (125).

[0136] For example, the negative current collector (125) may include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably may include copper or a copper alloy.

[0137] For example, the above-mentioned negative electrode active material may be a material capable of absorbing and extracting lithium ions. For example, the above-mentioned negative electrode active material may include a lithium alloy, a carbon-based active material, a silicon-based active material, etc.

[0138] For example, the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0139] For example, the carbon-based active material may include crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.

[0140] For example, the amorphous carbon may include hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500°C or lower, mesophase pitch-based carbon fiber (MPCF), etc. For example, the crystalline carbon may include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0141] In one embodiment, the negative electrode active material may include a silicon-based active material. For example, the silicon-based active material may be Si, SiO x (0 <x<2), Si / C, SiO / C, Si-Metal 등을 포함할 수 있다.

[0142] The above-described cathode binder and conductive material may be materials substantially identical or similar to the anode binder and conductive material described above. For example, the cathode binder may be a water-based binder such as styrene-butadiene rubber (SBR). Additionally, for example, the cathode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0143] In one embodiment, a separator (140) may be interposed between the anode (100) and the cathode (130).

[0144] In some embodiments, the area of ​​the negative electrode (130) may be larger than the area of ​​the positive electrode (100). In this case, lithium ions generated from the positive electrode (100) can move smoothly to the negative electrode (130) without precipitating in the middle.

[0145] For example, the separator (140) may include a porous polymer film made of a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc. Additionally, for example, the separator (140) may include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0146] For example, an electrode cell may be formed including an anode (100), a cathode (130), and a separator (140).

[0147] For example, a plurality of electrode cells may be stacked to form an electrode assembly (150) (however, for convenience, only one electrode cell is shown in FIG. 3).

[0148] For example, an electrode assembly (150) can be formed by winding, lamination, zigzag-folding, etc. of a separator (140).

[0149] A lithium secondary battery according to exemplary embodiments may include a positive electrode lead (107) connected to a positive electrode (100) and protruding outside of a case (160); and a negative electrode lead (127) connected to a negative electrode (130) and protruding outside of a case (160).

[0150] For example, the positive electrode (100) and the positive electrode lead (107) may be electrically connected. Likewise, the negative electrode (130) and the negative electrode lead (127) may be electrically connected.

[0151] For example, the positive lead (107) can be electrically connected to the positive current collector (105). Additionally, the negative lead (130) can be electrically connected to the negative current collector (125).

[0152] For example, the positive current collector (105) may include a protrusion (positive tab, 106) on one side. A positive active material layer (110) may not be formed on the positive tab (106). The positive tab (106) may be integral with the positive current collector (105) or connected by welding or the like. The positive current collector (105) and the positive lead (107) may be electrically connected through the positive tab (106).

[0153] Likewise, the negative current collector (125) may include a protrusion (negative tab, 126) on one side. A negative active material layer (120) may not be formed on the negative tab. The negative tab (126) may be integral with the negative current collector (125) or connected by welding or the like. The negative current collector (125) and the negative lead (127) may be electrically connected through the negative tab (126).

[0154] In one embodiment, the electrode assembly (150) may include a plurality of positive electrodes and a plurality of negative electrodes. For example, the plurality of positive electrodes and the plurality of negative electrodes may be arranged alternately with respect to each other, and a separator may be interposed between the positive electrodes and the negative electrodes. Accordingly, a lithium secondary battery according to one embodiment of the present invention may include a plurality of positive electrode tabs and a plurality of negative electrode tabs protruding from each of the plurality of positive electrodes and the plurality of negative electrodes.

[0155] In one embodiment, the positive tabs (or negative tabs) may be laminated, pressed, and welded to form a positive tab laminate (or negative tab laminate). The positive tab laminate may be electrically connected to a positive lead (107). Additionally, the negative tab laminate may be electrically connected to a negative lead (127).

[0156] For example, the electrode assembly (150) and the above-described electrolyte can be housed together in a case (160) to form a lithium secondary battery.

[0157] The above lithium secondary battery can be manufactured in, for example, cylindrical, prismatic, pouch, or coin types.

[0158] In the following, embodiments of the present invention are further described with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are merely illustrative of the present invention and are not intended to limit the appended claims. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and spirit of the present invention, and that such variations and modifications fall within the scope of the appended claims.

[0159] Preparation Example

[0160] 1,000 g of a solvent mixed with ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7 and 50 g of lithium difluorophosphate (LiPO2F2) were added to a reactor and stirred, and 97 g of triethylammonium ethenesulfonate was added.

[0161] The mixture in the reactor was stirred at room temperature for about 7 hours to carry out the reaction. After the reaction was finished, the resulting crystals were filtered, washed with DMC, and vacuum dried to obtain a white compound represented by Chemical Formula 1-1 (yield about 90%).

[0162]

[0163] Examples and Comparative Examples

[0164] Preparation of electrolyte

[0165] A 1.0 M LiPF6 solution was prepared by dissolving LiPF6 in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a 3:7 (v / v) ratio.

[0166] The electrolytes of the examples and comparative examples were prepared by adding each additive to the above LiPF6 solution according to the type and content (weight% of the total weight of the electrolyte) as shown in Table 1 below.

[0167] Manufacturing of lithium secondary batteries

[0168] Li(Ni) 0.8 Co 0.1 Mn 0.1 An anode slurry was prepared by dispersing O2, polyvinylidene fluoride (PVdF), and carbon black in N-methyl-2-pyrrolidone (NMP) in a weight ratio of 92:4:4.

[0169] The above anode slurry was applied onto an aluminum foil (thickness: 20 μm) having a protrusion on one side (hereinafter, anode tab) (excluding the protrusion portion), and an anode was manufactured by drying and rolling.

[0170] A cathode slurry was prepared by dispersing crystalline artificial graphite, acetylene black, and PVDF in NMP in a weight ratio of 92:1:7.

[0171] The above cathode slurry was applied onto a copper foil (thickness: 15 μm) having a protrusion on one side (hereinafter, cathode tab) (excluding the protrusion portion), and the cathode was manufactured by drying and rolling.

[0172] A cell was formed by interposing a polyethylene separator (thickness: 20 μm) between the anode and the cathode. An anode lead and a cathode lead were welded and connected to the anode tab and the cathode tab, respectively.

[0173] The cell was housed inside a pouch such that a portion of the positive lead and the negative lead were exposed to the outside. An electrolyte was injected into the pouch, and the pouch was sealed to manufacture a lithium secondary battery.

[0174] Mars charge / discharge

[0175] The lithium secondary batteries of the examples and comparative examples were subjected to a phosphating charge / discharge (charge / discharge conditions: charged in 0.2C CC / CV mode (4.2V, 0.05C cut-off) and then discharged in 0.2C CC mode (2.5V cut-off), and a standard charge / discharge (charge / discharge conditions: charged in 0.5C CC / CV mode (4.2V, 0.05C cut-off), then discharged in 0.5C CC mode (2.5V cut-off), and then charged in 0.5C CC / CV mode (4.2V, 0.05C cut-off). After that, 1C CC / CV charging (4.2V CUT-OFF) was performed.

[0176] 1st Additive 2nd Additive Content (Weight%) Type Content (Weight%) Example 10.5A-10.2 Example 20.5A-20.2 Example 30.5A-30.2 Example 40.5B-10.2 Example 50.5B-20.2 Example 60.5B-30.2 Example 70.5B-40.2 Example 80.5A-10.1B-10.1 Comparative Example 1---Comparative Example 20.25--Comparative Example 30.5--Comparative Example 41--Comparative Example 5-A-10.2 Comparative Example 6-A-20.2 Comparative Example 7-A-30.2 Comparative Example 8-B-10.2 Comparative Example 9-B-20.2 Comparative Example 10-B-30.2 Comparative Example 11-B-40.2

[0177] First additive: Compound represented by Chemical Formula 1-1 of the preparation example

[0178] A-1: Cyclopentyl isocyanate

[0179] A-2: Phenyl isocyanate

[0180] A-3: Hexamethylene diisocyanate

[0181] B-1: Succinonitrile

[0182] B-2: Adiponitrile

[0183] B-3: Fumaronitrile

[0184] B-4: 1,3,6-hexanetricarbonitrile

[0185]

[0186] Experimental Example

[0187] The physical properties of the batteries of the examples and comparative examples were evaluated by the following method, and the results are shown in Table 2.

[0188] (1) Evaluation of high-temperature life characteristics

[0189] The batteries of the examples and comparative examples were charged and discharged at a rate of 1C / 1C in a voltage range of 3-4.2V for 500 cycles at a temperature of 45℃. The discharge capacity after 500 cycles relative to the initial discharge capacity was calculated as a percentage and evaluated as the capacity retention rate.

[0190] (2) Evaluation of high-temperature storage characteristics

[0191] The batteries of the examples and comparative examples were charged to 4.2 V at 1C and then discharged to SOC 50. Afterward, the initial DC resistance was measured by discharging for 10 seconds at each of the four C-Rates (0.5C, 1C, 2C, 4C), and then fully charged to 4.2 V again and stored at a high temperature (70℃) for one week. Subsequently, the DC resistance after high-temperature storage relative to the initial DC resistance was calculated as a percentage and evaluated as the resistance increase rate.

[0192] (3) Rapid charging evaluation

[0193] The capacity of the batteries of the examples and comparative examples was measured after charging to 4.2V with 1C, discharged to 3V with 1C, and then charged to 4.2V with 4C constant current (CC) to check the efficiency (%) of the 4C charging capacity relative to the initial 1C charging capacity.

[0194] (4) Metal leaching evaluation

[0195] The batteries of the examples and comparative examples were charged and discharged at a rate of 1C / 1C in a voltage range of 3-4.2V for 100 cycles at a temperature of 45℃. After the final discharge, the batteries were disassembled, and the metal content eluted onto the surface of the negative electrode was analyzed by ICP-OES. The analyzed metals were Al, which is the positive current collector, and Ni, Co, and Mn, which are the components of the positive active material, and the measured values ​​were confirmed in ppm units.

[0196]

[0197] 45℃, 500 cycle Capacity retention rate (%) Resistance increase rate after storage at 70℃ (%) Rapid charging capacity efficiency (%) 45℃, 100 cycle Metal leaching amount on cathode (ppm) NiCoMnAl Example. 197.53 0.28 2.03 6.59 2.70 2.16 6.30 Example. 295.63 8.98 2.53 2.66 0.75 2.21 9.13 Example. 390.23 5.67 9.72 9.25 0.01 3.41 7.91 Example. 495.14 0.78 3.52 0.701 2.20 2.50 7.12 Example. 591.24 2.48 0.72 3.6 01.123.117.11 Example.692.742.178.926.800.501.806.55 Example.791.843.283.328.661.362.005.88 Example.896.728.785.221.751.832.056.22 Comparative Example.167.888.735.698.207.8014.5038.72 Comparative Example.285.745.268.797 .514.7810.7020.88Comparative Example.388.850.573.593.343.308.7018.78Comparative Example.483.662.069.586.662.806.5016.55Comparative Example.572.183.555.375.906.2010.8025.77Comparative Example.670.590.252.277.507.0011.2530.67Comparative Example.773.578 .753.667.627.7012.8736.25Comparative Example.871.589.749.862.776.2513.8920.74Comparative Example.976.892.138.765.806.6611.5523.45Comparative Example.1075.091.142.857.806.8710.8019.52Comparative Example.1168.580.750.569.517.1214.1218.99

[0198] Referring to Table 2 above, the batteries of the examples contained an electrolyte containing a first additive and a second additive. Accordingly, the battery had a small increase in resistance even after being stored for a long time in a high-temperature environment, and had a high capacity retention rate and high capacity efficiency during rapid charging. In addition, the amount of metal leaching from the anode was low, which is a result of the second additive stabilizing the CEI on the surface of the anode.

[0199] On the other hand, in the batteries of the comparative examples, an electrolyte that does not contain the first additive or the second additive was used. Consequently, the internal resistance of the battery increased significantly during high-temperature storage, or the amount of metal leaching from the anode increased during repeated charge and discharge cycles at high temperatures, resulting in an excessive decrease in battery capacity.

[0200] The above description is merely an example of applying the principles of the present disclosure, and other configurations may be included without departing from the scope of the present invention.

[0201] [Explanation of the symbol]

[0202] 100: Anode

[0203] 105: Positive current collector

[0204] 106: Positive tab

[0205] 107: Positive lead

[0206] 110: Positive active material layer

[0207] 120: Cathode active material layer

[0208] 125: Cathode current collector

[0209] 126: Cathode tab

[0210] 127: Cathode lead

[0211] 130: Cathode

[0212] 140: Separator

[0213] 150: Electrode assembly

[0214] 160: Case

Claims

1. Lithium salt; Organic solvent; A first additive represented by Chemical Formula 1; and Electrolyte for a secondary battery comprising a second additive comprising a nitrogen-carbon multiple bond compound: [Chemical Formula 1] (In Chemical Formula 1, R1 is a substituted or unsubstituted C1-C6 alkyl group; a substituted or unsubstituted C2-C6 alkenyl group; a substituted or unsubstituted C2-C6 alkynyl group; a substituted or unsubstituted C3-C7 cycloalkyl group; a substituted or unsubstituted C3-C7 cycloalkenyl group; or a substituted or unsubstituted C1-C6 alkoxy group, and R2 to R5 are independently a halogen; or a substituted or unsubstituted C1-C6 alkyl group, M is an alkali metal, and Y + is a monovalent cation).

2. An electrolyte for a secondary battery according to claim 1, wherein the content of the first additive is 0.01% to 10% by weight of the total weight of the electrolyte.

3. An electrolyte for a secondary battery according to claim 1, wherein the content of the second additive is 0.01% to 10% by weight of the total weight of the electrolyte.

4. An electrolyte for a secondary battery according to claim 1, wherein the ratio of the content of the second additive to the content of the first additive in the total weight of the electrolyte is 0.1 to 2.

5. An electrolyte for a secondary battery according to claim 1, wherein the second additive comprises an isocyanate-based compound; a nitrile-based compound; or an isocyanate-based compound and a nitrile-based compound.

6. In claim 5, the electrolyte for a secondary battery, wherein the isocyanate-based compound comprises one to three isocyanate groups.

7. An electrolyte for a secondary battery according to claim 5, wherein the isocyanate compound comprises at least one selected from the group consisting of cyclopentyl isocyanate, phenyl isocyanate, hexamethylene diisocyanate, ethyl isocyanate, fluorophenyl isocyanate, furfuryl isocyanate, (trimethylsilyl)isocyanate, benzenesulfonyl isocyanate, p-toluenesulfonyl isocyanate, cyclohexanemethyl isocyanate, benzoyl isocyanate, benzyl isocyanate, 3-(triethoxysilyl)propyl isocyanate, cyclohexyl isocyanate, methyl isocyanate, toluene diisocyanate, and 4,4'-methylene bis(phenyl isocyanate).

8. An electrolyte for a secondary battery according to claim 5, wherein the nitrile-based compound comprises 1 to 3 nitrile groups.

9. An electrolyte for a secondary battery according to claim 5, wherein the nitrile-based compound comprises at least one selected from the group consisting of succinonitrile, adiponitrile, fumaronitrile, 1,3,6-hexanedricarbonitrile, 1,4-dicyano-2-butene, malononitrile, glutaronitrile, heptanedinitrile, hexanedinitrile, benzonitrile, propionitrile, methoxypropionitrile, maleonitrile, 3-butenenitrile, 3,3,3-trifluoropropionitrile, 4-(fluorodimethylsilyl)butanitrile, and 3-(difluoromethylsilyl)propanenitrile.

10. An electrolyte for a secondary battery according to claim 1, wherein the organic solvent comprises at least one selected from the group consisting of a linear carbonate-based solvent, a cyclic carbonate-based solvent, an ester-based solvent, and an ether-based solvent.

11. An electrolyte for a secondary battery according to claim 1, further comprising an auxiliary additive including at least one of a fluorine-containing cyclic carbonate-based compound, an unsaturated group-containing cyclic carbonate-based compound, a sulfate-based compound, a sulfone-based compound, a lithium phosphate-based compound, a lithium borate-based compound, an organic acid-based compound, and a lactone-based compound.

12. An electrolyte for a secondary battery according to claim 11, wherein the content of the auxiliary additive is 0.01% to 5% by weight of the total weight of the electrolyte.

13. An electrolyte for a secondary battery according to claim 11, wherein the ratio of the content of the auxiliary additive to the content of the first additive in the total weight of the electrolyte is 0.1 to 1.

14. Anode; A negative electrode facing the above positive electrode; A separator interposed between the anode and the cathode; and A lithium secondary battery comprising an electrolyte for a secondary battery according to claim 1.

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