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 nitrile-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 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 nitrile-based compound.

[0011] [Chemical Formula 1]

[0012]

[0013] 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.

[0014] 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.

[0015] 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 2.5.

[0016] According to exemplary embodiments, the nitrile compound may include one to three nitrile groups.

[0017] 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.

[0018] According to exemplary embodiments, the organic solvent may include a linear carbonate-based solvent and a cyclic carbonate-based solvent.

[0019] 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.

[0020] In exemplary embodiments, the content of the auxiliary additive may be 0.01% to 5% by weight of the total weight of the electrolyte.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] A lithium secondary battery according to exemplary embodiments of the present disclosure may have improved lifespan characteristics and output characteristics.

[0026] 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.

[0027] 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.

[0028] In this specification, "X-type compound" may mean a compound containing an X unit in a parent group, a side group, or a substituent.

[0029] 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."

[0030] 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.

[0031] [Chemical Formula 1]

[0032]

[0033] The compound represented by Chemical Formula 1 above is a phosphonic anhydride and can remove moisture from the electrolyte. Accordingly, gas generation inside the battery can be suppressed, and decomposition of the electrolyte or side reactions between the electrode and the electrolyte due to an increase in moisture content can be suppressed.

[0034] 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 0.05% to 5% by weight, 0.1% to 2% by weight, 0.1% to 1% 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.

[0035] The electrolyte for a secondary battery according to exemplary embodiments comprises a second additive different from the first additive. The second additive comprises a nitrile-based compound.

[0036] The nitrogen-carbon triple bond has high reactivity. Accordingly, it 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.

[0037] 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).

[0038] 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.

[0039] According to exemplary embodiments, the nitrile compound may not contain unsaturated bonds. Accordingly, the action of the nitrile group may not be inhibited, and side reactions may not occur.

[0040] 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.

[0041] 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.

[0042] 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 2.5. 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 0.2 to 2.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] The above carbonate-based solvent may include linear carbonate-based solvents and cyclic carbonate-based solvents.

[0047] 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.

[0048] For example, the above-mentioned cyclic carbonate-based solvent may include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, etc.

[0049] 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%.

[0050] 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%.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] For example, the above linear ester-based solvent may include methyl propionate, ethyl propionate, propyl acetate, butyl acetate, ethyl acetate, etc.

[0055] For example, the above-mentioned cyclic ester solvent may include butyrolactone, caprolactone, valerolactone, etc.

[0056] 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.

[0057] For example, the above ketone-based solvent may include cyclohexanone, etc.

[0058] For example, the above alcohol-based solvent may include at least one of ethyl alcohol and isopropyl alcohol.

[0059] 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.

[0060] The electrolyte according to exemplary embodiments comprises a lithium salt. The lithium salt may be different from the first additive and the second additive.

[0061] 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.

[0062] In some embodiments, the lithium salt may be LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, LiN(CF3SO2)2, CF3SO3Li, LiC(CF3SO2)3, etc.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] In some embodiments, the fluorine-containing cyclic carbonate compound may include fluoroethylene carbonate (FEC), etc.

[0068] In some embodiments, the unsaturated group-containing cyclic carbonate compound may include vinyl ethylene carbonate (VEC), vinylene carbonate (VC), etc.

[0069] In some embodiments, the sulfate compound may include a cyclic sulfate compound or a linear sulfate compound.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] In some embodiments, the lithium phosphate-based compound may include lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, etc.

[0075] In some embodiments, the lithium borate-based compound may include lithium tetraphenylborate, lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiFOB), etc.

[0076] In some embodiments, the organic acid compound may include succinic acid or its anhydride, maleic acid or its anhydride, etc.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] According to exemplary embodiments of the present invention, a lithium secondary battery comprising the electrolyte for the lithium secondary battery is provided.

[0083] 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.

[0084] 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).

[0085] 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).

[0086] 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.

[0087] 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).

[0088] For example, the positive current collector (105) may include stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof.

[0089] 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.

[0090] In one embodiment, the lithium transition metal oxide particles may contain nickel, cobalt, manganese, aluminum, etc.

[0091] 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.

[0092] In some embodiments, the lithium transition metal oxide particles may be represented by LiNiO2, LiCoO2, LiMnO2, LiMn2O4, or the following chemical formula 2.

[0093] [Chemical Formula 2]

[0094] Li x Ni (1-a-b) Co a M b O y

[0095] 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.

[0096] 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.

[0097] In some embodiments, the lithium iron phosphate particles may include a compound represented by the following chemical formula 3.

[0098] [Chemical Formula 3]

[0099] Li x Fe 1-y M y (PO 4-z )X z

[0100] 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.

[0101] 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.

[0102] 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.

[0103] In some embodiments, the lithium iron phosphate may include LiFePO4 with an olivine crystal structure.

[0104] 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).

[0105] 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.

[0106] The cathode (130) may include a cathode current collector (125) and a cathode active material layer (120) on the cathode current collector (125).

[0107] 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.

[0108] 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).

[0109] 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.

[0110] 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.

[0111] For example, the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0112] For example, the carbon-based active material may include crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.

[0113] 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.

[0114] 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.

[0115] 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).

[0116] In one embodiment, a separator (140) may be interposed between the anode (100) and the cathode (130).

[0117] 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.

[0118] 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.

[0119] For example, an electrode cell may be formed including an anode (100), a cathode (130), and a separator (140).

[0120] 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).

[0121] For example, an electrode assembly (150) can be formed by winding, lamination, zigzag-folding, etc. of a separator (140).

[0122] 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).

[0123] 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.

[0124] 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).

[0125] 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).

[0126] 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).

[0127] 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.

[0128] 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).

[0129] 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.

[0130] The above lithium secondary battery can be manufactured in, for example, cylindrical, prismatic, pouch, or coin types.

[0131] 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.

[0132] Examples and Comparative Examples

[0133] Preparation of electrolyte

[0134] 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) mixed in a ratio of 2:4:4 (v / v).

[0135] 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.

[0136] manufacturing of lithium secondary batteries

[0137] 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.

[0138] 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.

[0139] A cathode slurry was prepared by dispersing crystalline artificial graphite, acetylene black, and PVDF in NMP in a weight ratio of 92:1:7.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] Mars charge / discharge

[0144] 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.

[0145] First Additive Second Additive Auxiliary Additive (VC) Content (Weight%) Type Content (Weight%) Content (Weight%) Example 10.1A-10.21 Example 20.5A-10.21 Example 31A-10.21 Example 41A-10.2- Example 50.5A-10.2- Example 61A-10.2- Example 71A-20.2- Example 81A-30.2- Comparative Example 1---- Comparative Example 20.1--- Comparative Example 30.5--- Comparative Example 41--- Comparative Example 5---1 Comparative Example 6-A-10.2- Comparative Example 7-A-20.2- Comparative Example 8-A-30.2- Comparative Example 90.1--1 Comparative Example 100.5--1 Comparative Example 111--1

[0146]

[0147] First additive: A compound represented by Chemical Formula 1

[0148] A-1: Succinonitrile

[0149] A-2: Adiponitrile

[0150] A-3: 1,3,6-Hexanetricarbonitrile

[0151] VC: Vinylene carbonate

[0152]

[0153] Experimental Example

[0154] 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.

[0155] (1) Evaluation of high-temperature storage characteristics

[0156] 1) Thickness increase rate: After charging the batteries of the examples and comparative examples to 4.2V at 1C, they were stored at a high temperature (70℃) for one week, and the thickness increase rate was evaluated by calculating the ratio of the battery thickness to the initial thickness as a percentage.

[0157] 2) Resistance increase rate: The batteries of the examples and comparative examples were charged at 1C to 4.2V and then discharged to SOC50. Afterward, the initial DC resistance was measured by discharging at 0.5C, 1C, 2C, and 4C for 10 seconds each, and then fully charged to 4.2V. Afterward, the DC resistance was measured after high-temperature storage (70℃) for one week in the same way as the initial DC resistance method, and the DC-IR increase rate (%) after one week of high-temperature storage compared to the initial DC-IR was confirmed.

[0158] 3) Capacity retention rate and capacity recovery rate: The capacity retention rate was measured by storing the batteries of the examples and comparative examples at a high temperature (70°C) for one week and then discharging them at 1°C, and calculating the result as a percentage by dividing the discharged capacity measured before storage. Subsequently, the capacity recovery rate was measured by charging them at 1°C and then discharging them, and dividing the result by the initial capacity.

[0159] (2) Evaluation of moisture content at room temperature

[0160] The initial moisture content of the electrolytes in the examples and comparative examples, and the moisture content after leaving the electrolytes at room temperature for one week were measured.

[0161] Moisture content was measured using the Karl Fischer titration method, and Hydranal-Coulomat AK was used as the anode solution and Hydranal-Coulomat CG-K as the cathode solution.

[0162] Thickness Increase Rate (%) DC-IR Increase Rate (%) Capacity Retention Rate (%) Capacity Recovery Rate (%) Moisture Content (ppm) After Initial 1 Week Storage Example 1 27.8 48.1 79.18 4.8 2.2 30.91 Example 2 23.6 46.68 1.98 6.92.3 40.57 Example 3 20.4 45.58 1.68 7.52.4 30.32 Example 4 30.05 5.976.68 1.02 651.17 Example 5 27.25 3.178.18 2.13.04 1.01 Example 6 23.55 2.277.68 4.22.6 20.68 Example 7 24.65 4.576.48 1.42 990.76 Example 824.255.277.682.12.810.79 Comparative Example 144.065.665.170.24.992.42 Comparative Example 230.762.568.372.23.361.89 Comparative Example 326.259.371.675.43.211.44 Comparative Example 422.358.173.274.73.221.16 Comparative Example 537.960.773.378.54.752.15 Comparative Example 640.758.968.173.74.252.27 Comparative Example 741.859.367.673.04.802.56 Comparative Example 840.360.968.573.23.912.13 Comparative Example 929.060.173.976.03.021.64 Comparative Example 1027.058.377.681.02.821.33 Comparative Example 1125.157.176.681.02.691.26

[0163] Referring to Table 2 above, the batteries of the examples contained an electrolyte containing a first additive and a second additive. Accordingly, even after the battery was stored for a long time in a high-temperature environment, the increase in resistance and the increase in thickness were small, and the capacity retention rate was high. In addition, the moisture content in the electrolyte was significantly reduced even after being left at room temperature.

[0164] 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, during high-temperature storage, the internal resistance and thickness of the battery increased significantly, or the lifespan characteristics deteriorated.

[0165] When Examples 1 to 3 were compared with Comparative Examples 9 to 11, Examples 4 to 6 were compared with Comparative Examples 2 to 4, and Examples 6 to 8 were compared with Comparative Examples 6 to 8, the high-temperature storage characteristics, high-temperature life characteristics, and moisture reduction characteristics of the batteries in the examples were further improved.

[0166] 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.

[0167] [Explanation of the symbol]

[0168] 100: Anode

[0169] 105: Positive current collector

[0170] 106: Positive tab

[0171] 107: Positive lead

[0172] 110: Positive active material layer

[0173] 120: Cathode active material layer

[0174] 125: Cathode current collector

[0175] 126: Cathode tab

[0176] 127: Cathode lead

[0177] 130: Cathode

[0178] 140: Separator

[0179] 150: Electrode assembly

[0180] 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 nitrile-based compound: [Chemical Formula 1] .

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.

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

6. An electrolyte for a secondary battery according to claim 1, 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.

7. An electrolyte for a secondary battery according to claim 1, wherein the organic solvent comprises a linear carbonate-based solvent and a cyclic carbonate-based solvent.

8. 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.

9. An electrolyte for a secondary battery according to claim 8, wherein the content of the auxiliary additive is 0.01% to 5% by weight of the total weight of the electrolyte.

10. An electrolyte for a secondary battery according to claim 8, 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.

11. 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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