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, a solvent, a first additive including a sulfonylmorpholine-based compound, and a second additive including an unsaturated carbonate-based compound or a fluorine-containing carbonate-based compound.

Description

Electrolyte for secondary batteries and secondary batteries containing the same

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

[0002]

[0003] Secondary batteries are batteries that can be repeatedly charged and discharged, and are used as a power source for small electronic devices such as cell phones and laptop PCs.

[0004] In particular, lithium secondary batteries offer the advantages of high operating voltage, high energy density, high charging speed, and lightweight design. Accordingly, lithium secondary batteries are being used as a power source for not only small electronic devices but also electric vehicles.

[0005] For example, in order for lithium secondary batteries to be used as a power source for electric vehicles, they must have better output characteristics and lifespan characteristics.

[0006] Meanwhile, a lithium secondary battery may include a negative electrode including a negative electrode active material (e.g., graphite, silicon); a positive electrode including a positive electrode active material (e.g., lithium transition metal oxide particles); and a non-aqueous electrolyte including a lithium salt and an organic solvent.

[0007] For example, a lithium secondary battery can be charged and discharged by repeating the process of lithium ions being inserted and removed from lithium transition metal oxide particles and graphite.

[0008] For example, by varying the composition of the electrolyte, the output characteristics and lifespan characteristics of a lithium secondary battery can be improved. For example, by improving lithium ion conductivity, the output characteristics of a lithium secondary battery can be improved. Furthermore, by firmly forming a solid electrolyte interface (SEI) on the negative electrode, the lifespan characteristics of a lithium secondary battery can be improved.

[0009]

[0010] An object of the present disclosure is to provide an electrolyte for a secondary battery having improved electrochemical properties.

[0011] One object of the present disclosure is to provide a lithium secondary battery including the above electrolyte.

[0012]

[0013] An electrolyte for a secondary battery according to the present disclosure comprises a lithium salt, a solvent, a first additive including a sulfonylmorpholine compound, and a second additive including an unsaturated carbonate compound or a fluorine-containing carbonate compound.

[0014] According to exemplary embodiments, the sulfonylmorpholine compound may include an alkylsulfonyl group bonded to the nitrogen of the morpholine ring.

[0015] According to exemplary embodiments, the sulfonylmorpholine compound may be represented by the following chemical formula 1.

[0016] [Chemical Formula 1]

[0017]

[0018] In the above chemical formula 1, R1 and R2 are each independently an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 1 to 10 carbon atoms, and n may be 0 or an integer of 1 to 4.

[0019] According to exemplary embodiments, in the above chemical formula 1, R1 and R2 may be methyl groups, and n may be 2.

[0020] According to exemplary embodiments, the content of the first additive may be 0.01 wt% to 5 wt% of the total weight of the electrolyte.

[0021] According to exemplary embodiments, the unsaturated carbonate compound may include vinylene carbonate or vinylethylene carbonate.

[0022] According to exemplary embodiments, the halogen-containing carbonate compound may include fluoroethylene carbonate.

[0023] According to exemplary embodiments, the content of the second additive may be from 0.01 wt% to 5 wt% of the total weight of the electrolyte.

[0024] 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 0.5 to 15.

[0025] According to exemplary embodiments, at least one auxiliary additive selected from the group consisting of a compound represented by the following chemical formula 2, a sulfate-based compound, a sultone-based compound, a fluorine-containing lithium phosphate-based compound, a lithium borate-based compound, and a lactone-based compound may be further included.

[0026] [Chemical Formula 2]

[0027]

[0028] In Chemical Formula 2, 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, R2 to R5 are each independently a halogen; or a substituted or unsubstituted C1-C6 alkyl group, M is an alkali metal, and Y + can be a monovalent cation.

[0029] According to exemplary embodiments, the content of the auxiliary additive may be 0.01 wt% to 10 wt% of the total weight of the electrolyte.

[0030] A lithium secondary battery according to the present disclosure includes a positive electrode, a negative electrode opposite to the positive electrode, and an electrolyte impregnating the positive electrode and the negative electrode.

[0031]

[0032] The electrolyte for a secondary battery according to exemplary embodiments of the present disclosure can increase the capacity retention rate of a battery during repeated charge / discharge cycles and improve output characteristics. In addition, the high-temperature storage characteristics of a battery containing the electrolyte can be improved.

[0033] Lithium secondary batteries according to exemplary embodiments of the present disclosure may have improved life characteristics, high temperature characteristics, and output characteristics.

[0034]

[0035] FIG. 1 and FIG. 2 are a plan perspective view and a cross-sectional view, respectively, schematically illustrating a lithium secondary battery according to exemplary embodiments.

[0036]

[0037] An electrolyte for a secondary battery according to the present disclosure comprises a lithium salt, an organic solvent, and two or more different additives. In addition, a lithium secondary battery according to the present disclosure comprises the electrolyte.

[0038] In this specification, “X-based compound” may mean a compound that contains an X unit in a parent group, side group, or substituent.

[0039] In this specification, "Ca-Cb" may mean "the number of carbon atoms a to b." Additionally, "5-7 membered ring" may mean "the number of atoms in the ring is 5 to 7."

[0040] An electrolyte for a secondary battery according to exemplary embodiments (hereinafter, abbreviated as an electrolyte) may include a first additive including a sulfonylmorpholine compound.

[0041] The above sulfonylmorpholine compound may have a sulfonyl group bonded to a morpholine ring, and the sulfonyl group may be an alkyl sulfonyl group. The alkyl sulfonyl group may be bonded to nitrogen or carbon of the morpholine ring, for example, may be bonded to nitrogen.

[0042] According to exemplary embodiments, the sulfonylmorpholine compound may be represented by the following chemical formula 1.

[0043] [Chemical Formula 1]

[0044]

[0045] In the above chemical formula 1, R1 and R2 can each independently be an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 1 to 10 carbon atoms. In some embodiments, R1 and R2 can each independently be an alkyl group having 1 to 4 carbon atoms. For example, R1 and R2 can be a methyl group.

[0046] In the above chemical formula 1, n may be 0 or an integer from 1 to 4. For example, n may be 0 or 2. When n is an integer from 2 to 4, multiple R2s may be the same or different from each other.

[0047] According to exemplary embodiments, the sulfonylmorpholine compound may be represented by the following chemical formula 1-1 or 1-2.

[0048] [Chemical Formula 1-1]

[0049]

[0050] [Chemical Formula 1-2]

[0051]

[0052] According to exemplary embodiments, the content of the first additive may be 0.01 wt% to 5 wt% of the total weight of the electrolyte. In some embodiments, the content of the first additive may be 0.1 wt% to 3 wt% or 0.5 wt% to 1 wt% of the total weight of the electrolyte.

[0053] Within the above range, the high-temperature storage characteristics of the battery can be further improved, and the discharge capacity may not be significantly reduced even after repeated charge and discharge.

[0054] According to exemplary embodiments, the electrolyte comprises a second additive comprising an unsaturated carbonate compound or a fluorine-containing carbonate compound. The second additive is a carbonate compound containing an unsaturated functional group or fluorine, and can reduce side reactions that occur when the battery is stored at high temperatures. In addition, the second additive can interact with the first additive to improve the lifespan characteristics of the battery.

[0055] According to exemplary embodiments, the unsaturated carbonate compound may include vinylene carbonate or vinylethylene carbonate.

[0056] According to exemplary embodiments, the halogen-containing carbonate compound may include fluoroethylene carbonate.

[0057] According to exemplary embodiments, the content of the second additive may be 0.01 wt% to 5 wt% of the total weight of the electrolyte. According to some embodiments, the content of the second additive may be 0.1 wt% to 3 wt%, 0.5 wt% to 1.5 wt%, or 0.8 wt% to 1.2 wt% of the total weight of the electrolyte.

[0058] Within the above range, the high-temperature storage characteristics of the battery can be further improved, and the discharge capacity may not be significantly reduced even after repeated charge and discharge.

[0059] 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 0.5 to 3. 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 1 to 2.

[0060] Within the above range, the content ratio of the first additive and the second additive can be appropriately adjusted so that the efficiency of the battery can be improved while reducing the occurrence of side reactions in a high-temperature environment.

[0061] 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 therein.

[0062] 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, and the like.

[0063] The above carbonate solvent may include a linear carbonate solvent and a cyclic carbonate solvent.

[0064] For example, the linear carbonate solvent may include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, etc.

[0065] For example, the cyclic carbonate solvent may include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, etc.

[0066] In some embodiments, the content of the linear carbonate solvent in the total volume of the organic solvent may be 50% to 90% by volume or 60% to 85% by volume. In some embodiments, when the linear carbonate solvent includes two different linear carbonate compounds, the content of each linear carbonate compound may be 25% to 45% by volume.

[0067] In some embodiments, the content of the cyclic carbonate solvent in the total volume of the organic solvent may be 10% to 50% by volume or 15% to 40% by volume.

[0068] In exemplary embodiments, the content of the linear carbonate solvent in the total volume of the organic solvent may be greater than the content of the cyclic carbonate solvent.

[0069] For example, among the organic solvents, the volume ratio of the linear carbonate solvent to the cyclic carbonate solvent may be 1 to 9 or 1.5 to 4.

[0070] The above ester solvent is a solvent containing an ester group (-OCO-) that is distinct from a carbonate group (-OCOO-), and may be a parallel concept to a carbonate solvent. In some embodiments, the ester solvent may include a linear ester solvent and a cyclic ester solvent.

[0071] For example, the linear ester solvent may include methyl propionate, ethyl propionate, propyl acetate, butyl acetate, ethyl acetate, and the like.

[0072] For example, the cyclic ester solvent may include butyrolactone, caprolactone, valerolactone, etc.

[0073] For example, the ether 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.

[0074] For example, the ketone solvent may include cyclohexanone, etc.

[0075] For example, the alcohol solvent may include at least one of ethyl alcohol and isopropyl alcohol.

[0076] For example, the aprotic solvent may include at least one of a nitrile solvent, an amide solvent (e.g., dimethylformamide), a dioxolane solvent (e.g., 1,3-dioxolane), and a sulfolane solvent.

[0077] An electrolyte according to exemplary embodiments comprises a lithium salt. The lithium salt may be different from the first additive and the second additive.

[0078] For example, the lithium salt is Li + X - 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.

[0079] In some embodiments, the lithium salt may be LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, LiN(CF3SO2)2, CF3SO3Li, LiC(CF3SO2)3, etc.

[0080] 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 above concentration range, lithium ions and / or electrons may move smoothly during charging and discharging of the battery.

[0081] In one embodiment, the electrolyte for the lithium secondary battery may further include an auxiliary additive to further improve the life characteristics and output characteristics of the lithium secondary battery, or to improve high-temperature storage characteristics, etc.

[0082] In exemplary embodiments, the auxiliary additive may include a compound represented by the following chemical formula 2, a sulfate-based compound, a sultone-based compound, a fluorine-containing lithium phosphate-based compound, a lithium borate-based compound, a lactone-based compound, etc.

[0083] [Chemical Formula 2]

[0084]

[0085] In chemical formula 2, 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.

[0086] In one embodiment, R1 can be a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group.

[0087] In some embodiments, R1 can be a substituted or unsubstituted C2-C6 alkenyl group. In some embodiments, R1 can be an unsubstituted C2-C6 alkenyl group.

[0088] In this specification, the meaning of "substituted" may mean that a hydrogen atom is substituted with any substituent and any substituent is further bonded.

[0089] For example, the optional substituent 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, the optional substituent may be a halogen or a C1-C6 alkyl group.

[0090] In chemical formula 2, R2 to R5 may each independently be a halogen; or a substituted or unsubstituted C1-C6 alkyl group.

[0091] 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 can be F.

[0092] In one embodiment, all of R2 to R5 can be halogen. In some embodiments, all of R2 to R5 can be F.

[0093] In Chemical Formula 2, M may be an alkali metal. In one embodiment, M may be Li, Na, or K.

[0094] In chemical formula 2, Y + is a monovalent cation. In one embodiment, Y + may be an alkali metal ion; an ammonium ion; or a primary to quaternary ammonium ion.

[0095] In some embodiments, Y + is N + RaRbRcRd or ReRfN + =Rg may be.

[0096] Ra to Rd may independently be hydrogen; a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group. In addition, at least two of Ra to Rd may be combined with each other to form a 5-7 membered heterocycle.

[0097] Re to Rg may be, independently, hydrogen; a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group. In addition, at least two of Re to Rg may be combined with each other to form a 5-7 membered heterocycle.

[0098] In some embodiments, Y + is N + RaRbRcRd, and at least one of Ra to Rd is hydrogen, and the others may be substituted or unsubstituted C1-C6 alkyl groups; substituted or unsubstituted C2-C6 alkenyl groups. In some embodiments, Y+ is N + RaRbRcRd, where Ra is hydrogen, and Rb to Rd can be independently C1-C3 alkyl groups.

[0099] According to exemplary embodiments, the second additive may include a compound represented by the following chemical formula 2-1.

[0100] [Chemical Formula 2-1]

[0101]

[0102] In some embodiments, the sulfate compound may comprise a cyclic sulfate compound or a linear sulfate compound.

[0103] For example, the cyclic sulfate compound may have a 5-7 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, and the like.

[0104] 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-dioxathiolane)] 2,2,2',2'-tetraoxide, etc.

[0105] For example, the sultone compound may have a 5-7 membered cyclic structure. In some embodiments, the sultone compound may include at least one of an alkyl sultone compound and an alkenyl sultone compound. For example, the alkyl sultone compound may have only saturated bonds within the ring, and the alkenyl sultone compound may include a double bond within the ring.

[0106] In some embodiments, the alkyl sultone compound may include 1,3-propane sultone (PS), 1,4-butane sultone, and the like. Additionally, the alkenyl sultone compound may include ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, 1-methyl-1,3-propene sultone, and the like.

[0107] In some embodiments, the fluorine-containing lithium phosphate compound may include lithium difluorophosphate, lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, and the like.

[0108] In some embodiments, the lithium borate compound may include lithium tetraphenylborate, lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiFOB), or the like.

[0109] In some embodiments, the lactone compound may include at least one of a linear lactone compound and a lactone compound including a double bond in a ring. In some embodiments, the lactone compound may include a muconic lactone, etc.

[0110] According to exemplary embodiments, the content of the auxiliary additive may be 0.01 wt% to 10 wt% of the total weight of the electrolyte. According to some embodiments, the content of the auxiliary additive may be 0.1 wt% to 5 wt% or 0.5 wt% to 2 wt% of the total weight of the electrolyte.

[0111] According to exemplary embodiments of the present invention, a lithium secondary battery including the electrolyte for the lithium secondary battery is provided.

[0112] Hereinafter, a lithium secondary battery according to exemplary embodiments will be described in more detail with reference to the drawings. Figures 1 and 2 are schematic plan perspective views and cross-sectional views, respectively, showing lithium secondary batteries according to exemplary embodiments.

[0113] Referring to FIGS. 1 and 2, a lithium secondary battery may include a positive electrode (100) and a negative electrode (130) opposite to the positive electrode (100).

[0114] 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).

[0115] For example, the positive electrode active material layer (110) may include a positive electrode active material. In addition, the positive electrode active material layer (110) may further include a positive electrode binder and a conductive material.

[0116] For example, the positive electrode (100) can be manufactured by mixing and stirring a positive electrode active material, a positive electrode binder, a conductive agent, a dispersion medium, etc. to manufacture a positive electrode slurry, and then applying, drying, and rolling the positive electrode slurry onto a positive electrode current collector (105).

[0117] For example, the positive electrode collector (105) may include stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof.

[0118] 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 de-insertion of lithium ions.

[0119] In one embodiment, the lithium transition metal oxide particles may contain nickel, cobalt, manganese, aluminum, iron, or the like.

[0120] In some embodiments, the lithium transition metal oxide particles contain nickel, and the content of nickel in the lithium transition metal oxide particles may be 80 mol% or more of the total elements excluding lithium and oxygen.

[0121] In some embodiments, the lithium transition metal oxide particles may be represented by LiNiO2, LiCoO2, LiMnO2, LiMn2O4, or the following chemical formula 3.

[0122] [Chemical Formula 3]

[0123] Li x Ni (1-a-b) Co a M b O y

[0124] In chemical formula 3, 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, 0≤a+b≤0.5.

[0125] In chemical formula 3, 0 <a+b≤0.4, 0<a+b≤0.3, 0<a+b≤0.2 또는 0<a+b≤0.1을 만족할 수 있다.

[0126] In some embodiments, the lithium iron phosphate particles may comprise a compound represented by the following chemical formula 4.

[0127] [Chemical Formula 4]

[0128] Li x Fe 1-y M y (PO 4-z )X z

[0129] In chemical formula 4, 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.

[0130] In chemical formula 4, X may include at least one element selected from the group consisting of F, S, and N. For example, X may include F.

[0131] In Chemical Formula 4, 0.5≤x≤1.5, 0≤y≤0.1, 0≤z≤0.5. In some embodiments, 0.8≤x≤1.2, 0≤y≤0.05, 0≤z≤0.1.

[0132] In some embodiments, the lithium iron phosphate may comprise LiFePO4 having an olivine crystal structure.

[0133] For example, the positive electrode binder may include an organic binder such as polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile, polymethylmethacrylate, or an aqueous binder such as styrene-butadiene rubber (SBR). In addition, for example, the positive electrode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0134] For example, the conductive material may include a carbon-based conductive material such as graphite, carbon black, graphene, carbon nanotubes, etc.; a metal-based conductive material such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc.

[0135] The negative electrode (130) may include a negative electrode current collector (125) and a negative electrode active material layer (120) on the negative electrode current collector (125).

[0136] For example, the negative electrode active material layer (120) may include a negative electrode active material, a negative electrode binder, and a conductive material, if necessary.

[0137] For example, the negative electrode (130) can be manufactured by mixing and stirring a negative electrode active material, a negative electrode binder, a conductive material, a solvent, etc. to manufacture a negative electrode slurry, and then applying, drying, and rolling the negative electrode slurry onto a negative electrode current collector (125).

[0138] For example, the negative electrode 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.

[0139] For example, the negative electrode active material may be a material capable of absorbing and desorbing lithium ions. For example, the negative electrode active material may include a lithium alloy, a carbon-based active material, a silicon-based active material, and the like.

[0140] For example, the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, and the like.

[0141] For example, the carbon-based active material may include crystalline carbon, amorphous carbon, carbon composite, carbon fiber, etc.

[0142] For example, the amorphous carbon may include hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500°C or lower, mesophase pitch-based carbon fibers (MPCF), etc. For example, the crystalline carbon may include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0143] In one embodiment, the negative active material may include a silicon-based active material. For example, the silicon-based active material may include Si, SiO. x (0 <x<2), Si / C, SiO / C, Si-Metal 등을 포함할 수 있다.

[0144] The above-described negative electrode binder and conductive material may be substantially the same or similar materials as the above-described positive electrode binder and conductive material. For example, the negative electrode binder may be an aqueous binder such as styrene-butadiene rubber (SBR). Furthermore, for example, the negative electrode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0145] In one embodiment, a separator (140) may be interposed between the anode (100) and the cathode (130).

[0146] 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) may smoothly move to the negative electrode (130) without being precipitated in the middle.

[0147] For example, the separator (140) may include a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc. In addition, for example, the separator (140) may include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0148] For example, an electrode cell can be formed including an anode (100), a cathode (130), and a separator (140).

[0149] For example, a plurality of electrode cells can be stacked to form an electrode assembly (150) (however, for convenience, one electrode cell is illustrated in FIG. 2).

[0150] For example, an electrode assembly (150) can be formed by winding, lamination, z-folding, etc. of a separator (140).

[0151] A lithium secondary battery according to exemplary embodiments may include a positive electrode lead (107) connected to a positive electrode (100) and protruding outward from a case (160); and a negative electrode lead (127) connected to a negative electrode (130) and protruding outward from a case (160).

[0152] For example, the positive electrode (100) and the positive electrode lead (107) may be electrically connected. Similarly, the negative electrode (130) and the negative electrode lead (127) may be electrically connected.

[0153] For example, the positive electrode lead (107) may be electrically connected to the positive electrode collector (105). Additionally, the negative electrode lead (130) may be electrically connected to the negative electrode collector (125).

[0154] For example, the positive electrode current collector (105) may include a protrusion (positive electrode tab, 106) on one side. The positive electrode active material layer (110) may not be formed on the positive electrode tab (106). The positive electrode tab (106) may be integral with the positive electrode current collector (105) or may be connected by welding or the like. The positive electrode current collector (105) and the positive electrode lead (107) may be electrically connected through the positive electrode tab (106).

[0155] Likewise, the negative electrode collector (125) may include a protrusion (negative electrode tab, 126) on one side. The negative electrode active material layer (120) may not be formed on the negative electrode tab. The negative electrode tab (126) may be integral with the negative electrode collector (125) or may be connected by welding or the like. The negative electrode collector (125) and the negative electrode lead (127) may be electrically connected through the negative electrode tab (126).

[0156] 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 alternately arranged, 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.

[0157] 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 the positive lead (107). Additionally, the negative tab laminate may be electrically connected to the negative lead (127).

[0158] For example, the electrode assembly (150) and the above-described electrolyte may be housed together in a case (160) to form a lithium secondary battery.

[0159] The above lithium secondary battery can be manufactured in, for example, a cylindrical shape, a square shape, a pouch shape, or a coin shape.

[0160] Hereinafter, embodiments of the present invention will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present invention and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various modifications and variations of the examples are possible within the scope and technical spirit of the present invention, and it is also natural that such modifications and variations fall within the scope of the appended claims.

[0161]

[0162] Examples and Comparative Examples

[0163] Preparation of electrolyte

[0164] A 1.0 M LiPF6 solution was prepared by dissolving LiPF6 in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at a ratio of 2:4:4 (v / v).

[0165] To the above LiPF6 solution, each additive was added in the type and content (weight % of the total weight of the electrolyte) according to Table 1 below to prepare electrolytes of examples and comparative examples.

[0166] Manufacturing of lithium secondary batteries

[0167] Li(Ni) 0.8 Co 0.1 Mn 0.1 )O2, polyvinylidene fluoride (PVdF), and carbon black were dispersed in N-methyl-2-pyrrolidone (NMP) at a weight ratio of 92:4:4 to prepare a cathode slurry.

[0168] The above positive electrode slurry was applied onto an aluminum foil (thickness: 20 μm) having a protrusion (hereinafter, positive electrode tab) on one side (excluding the protrusion portion), dried, and rolled to manufacture a positive electrode.

[0169] A cathode slurry was prepared by dispersing crystalline artificial graphite, acetylene black, and PVDF in NMP at a weight ratio of 92:1:7.

[0170] The above cathode slurry was applied onto a copper foil (thickness: 15 μm) having a protrusion (hereinafter, cathode tab) on one side (excluding the protrusion portion), dried, and rolled to manufacture a cathode.

[0171] A cell was formed by interposing a polyethylene separator (thickness: 20 μm) between the positive and negative electrodes. The positive and negative electrode leads were connected by welding to the positive and negative tabs, respectively.

[0172] The cell was housed inside a pouch so that some areas of the positive and negative leads were exposed to the outside. An electrolyte was injected into the pouch, and the pouch was sealed and sealed to manufacture a lithium secondary battery.

[0173] Mars charging and discharging

[0174] The lithium secondary batteries of the examples and comparative examples were subjected to a chemical charge / discharge (charge / discharge conditions: charged in 0.2C CC / CV mode (4.2 V, 0.05 C cut-off) and then discharged in 0.2C CC mode (2.5 V cut-off)) and a standard charge / discharge (charge / discharge conditions: charged in 0.5C CC / CV mode (4.2 V, 0.05 C cut-off) and then discharged in 0.5C CC mode (2.5 V cut-off) and then charged in 0.5C CC / CV mode (4.2 V, 0.05 C cut-off)). After that, 1C CC / CV charging (4.2 V cut-off) was performed.

[0175] First additiveSecond additiveAuxiliary additiveType Content (weight%)Type Content (weight%)Type Content (weight%)Example 1A-10.5B-11--Example 2A-11B-11--Example 3A-20.5B-11--Example 4A-21B-11--Example 5A-11B-21--Example 6A-11B-31--Example 7A-11B-315--Example 8A-11B-11C-11Example 9A-11B-11C-21Example 10A-11B-11C-31Example 11A-11B-11C-41Example 12A-11B-11C-51Example 13A-11B-11C-61 Example 14A-11B-11C-71 Comparative Example 1A-11----Comparative Example 2A-21----Comparative Example 3--B-11--Comparative Example 4--B-21--Comparative Example 5--B-31--Comparative Example 6--B-315--Comparative Example 7------

[0176]

[0177] A-1: A compound represented by the following chemical formula 1-1

[0178] [Chemical Formula 1-1]

[0179]

[0180] A-2: A compound represented by the following chemical formula 1-2

[0181] [Chemical Formula 1-2]

[0182]

[0183] B-1: Vinylene carbonate

[0184] B-2: Vinyl ethylene carbonate

[0185] B-3: Fluoroethylene carbonate

[0186] C-1: 1,3-propanesultone

[0187] C-2: 1,3-propenesultone

[0188] C-3: Lithium difluoro(oxalate)borate (LiDFOB)

[0189] C-4: A compound represented by the following chemical formula 2-1

[0190] [Chemical Formula 2-1]

[0191]

[0192] C-5: Lithium difluorophosphate (LiPO2F2)

[0193] C-6: Ethylene sulfate (ESA)

[0194] C-7: 1,3-propanediol cyclic sulfate

[0195]

[0196] Experimental Example 1: Evaluation of High-Temperature Storage Characteristics

[0197] (1) Evaluation of battery thickness increase rate

[0198] The batteries of the examples and comparative examples were stored at 70°C for 7 days after being charged at 1C to 4.2 V, and the thickness of the cells was measured. The increased thickness value was calculated as a percentage of the initial thickness value to calculate the thickness increase rate.

[0199] (2) Capacity maintenance rate and capacity recovery rate evaluation

[0200] The batteries of the examples and comparative examples were stored at a high temperature (70°C) for 7 days after being charged at 1C to 4.2V, discharged at 1C twice after being charged at 1C to 4.2V, and stored at 70°C for 7 days. The retention capacity was measured, and the recovery capacity (discharge capacity) was measured by charging and discharging in the same manner as when the initial capacity was measured, and the capacity retention rate and capacity recovery rate were calculated as a percentage of the initial capacity.

[0201] In addition, the increase rate of the internal resistance of the batteries of some embodiments and comparative examples before and after storage at 70°C for 7 days was calculated.

[0202] The evaluation results are shown in Table 2.

[0203] Thickness Increase Rate (%)Retention Capacity (mAh)Recovery Capacity (mAh)Resistance Increase Rate Before and After Storage (%)Example 175.46834.7886.3132.17Example 278.77840.9891.7137.24Example 380.14810.7856.4134.15Example 478.63824.3878.7129.26Example 572.64794.0837.5131.26Example 685.39768.2805.3125.13Example 7232.83726.1748.9-Example 837.55855.8889.1113.14Example 959.47860.3894.7125.25Example 1072.13837.3868.1117.56Example 1161.57842.7884.3127.63Example 1269.42843.9876.893.23Example 1353.25838.27879.25108.72Example 1441.25831.27875.25112.34Example 1581.04829.26865.41131.27Example 1682.39823.21859.48139.65Comparative Example 185.07811.3841.8148.76Comparative Example 288.46807.6828.2144.42Comparative Example 395.12822.1849.8152.78Comparative Example 4101.77801.4819.6159.45Comparative Example 5110.64752.4784.7178.26Comparative Example 6298.44670.3701.8-Comparative Example 7124.79742.17769.4183.48

[0204]

[0205] Referring to Table 2 above, the batteries of the examples had a lower thickness increase rate, a higher recovery capacity, and a lower resistance increase rate after high-temperature storage than the batteries of the comparative examples.

[0206] In particular, the electrolytes of Examples 12 to 14 further included a cyclic sulfate-based compound or a fluorine-containing lithium phosphate-based compound as an auxiliary additive. Accordingly, the thickness increase rate was much lower than that of the batteries of the comparative examples, and gas generation inside the batteries was significantly reduced.

[0207] In addition, the batteries of Examples 12 to 14 had a lower resistance increase rate than the batteries of Comparative Examples 1 and 3, so that the internal resistance of the batteries did not increase significantly even when left in a high-temperature environment for a long time.

[0208]

[0209] Experimental Example 2: Life Characteristics Evaluation

[0210] The batteries of some examples and comparative examples were charged at 1C CC / CV (4.2V CUT-OFF) at a temperature of 45°C and discharged at 1C CC (3V CUT-OFF) to measure the initial discharge capacity C1.

[0211] For the lithium secondary batteries of the examples and comparative examples, the above charging and discharging process was repeated 900 times at a temperature of 45°C, and the 900th discharge capacity C2 was measured.

[0212] The capacity retention rate was calculated as a percentage of C2 compared to C1, as follows.

[0213] Capacity retention rate (%) = C2 / C1 × 100 (%)

[0214] The 900-cycle discharge capacity and capacity retention rate are shown in Table 3, and the capacity retention rate graph of the lithium secondary batteries of Example 2, Example 11, and Comparative Example 1 according to the number of cycles is shown in Fig. 3.

[0215] Discharge capacity (mAh) Capacity retention rate (%) Example 2814.887.5 Example 4810.487.0 Example 11824.689.6 Example 12820.388.1 Comparative example 1801.684.6 Comparative example 2798.781.3 Comparative example 3802.483.5

[0216] Referring to Table 3 and Figure 3, the batteries of the examples maintain a high discharge capacity even after repeated charge and discharge of the batteries, and the life characteristics are improved.

[0217] On the other hand, in the batteries of the comparative examples, the capacity rapidly decreased with repeated charging and discharging of the batteries, and the batteries had low discharge capacities.

[0218] 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.

Claims

1. Lithium salt; menstruum; A first additive comprising a sulfonylmorpholine compound; and An electrolyte for a secondary battery comprising a second additive comprising an unsaturated carbonate compound or a fluorine-containing carbonate compound.

2. An electrolyte for a secondary battery, wherein the sulfonylmorpholine compound in paragraph 1 contains an alkylsulfonyl group bonded to nitrogen of a morpholine ring.

3. In the first paragraph, the sulfonylmorpholine compound is an electrolyte for a secondary battery represented by the following chemical formula 1: [Chemical Formula 1] (In the above chemical formula 1, R1 and R2 are each independently an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 1 to 10 carbon atoms, and n is 0 or an integer of 1 to 4).

4. An electrolyte for a secondary battery in the third paragraph, wherein in the chemical formula 1, R1 and R2 are methyl groups and n is 2.

5. An electrolyte for a secondary battery, wherein the content of the first additive in the first paragraph is 0.01 wt% to 5 wt% of the total weight of the electrolyte.

6. An electrolyte for a secondary battery, wherein the unsaturated carbonate compound in the first paragraph comprises vinylene carbonate or vinylethylene carbonate.

7. An electrolyte for a secondary battery according to claim 1, wherein the halogen-containing carbonate compound comprises fluoroethylene carbonate.

8. An electrolyte for a secondary battery, wherein the content of the second additive in the first paragraph is 0.01 wt% to 5 wt% of the total weight of the electrolyte.

9. An electrolyte for a secondary battery, 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 0.5 to 15.

10. An electrolyte for a secondary battery, further comprising at least one auxiliary additive selected from the group consisting of a compound represented by the following chemical formula 2, a sulfate-based compound, a sultone-based compound, a fluorine-containing lithium phosphate-based compound, a lithium borate-based compound, and a lactone-based compound: [Chemical Formula 2] (In Chemical Formula 2, 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 each independently a halogen; or a substituted or unsubstituted C1-C6 alkyl group, M is an alkali metal, and Y + is a monovalent cation).

11. An electrolyte for a secondary battery, wherein the content of the auxiliary additive in the 10th paragraph is 0.01 wt% to 10 wt% of the total weight of the electrolyte.

12. A lithium secondary battery comprising a positive electrode, a negative electrode opposite to the positive electrode, and an electrolyte according to claim 1 that impregnates the positive electrode and the negative electrode.

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