Electrolyte for lithium secondary battery and lithium secondary battery comprising same

Abstract

According to an exemplary embodiment, there may be provided an electrolyte solution for a lithium secondary battery, the electrolyte solution for a lithium secondary battery comprising: an additive comprising a compound represented by a specific chemical formula; an organic solvent; and a lithium salt. Therefore, a lithium secondary battery including the electrolyte solution for a lithium secondary battery can provide excellent high-temperature characteristics and other properties (e.g., initial resistance, fast charging performance, normal-temperature capacity characteristics, etc.

Description

Technical Field

[0001] The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the electrolyte. More specifically, the present invention relates to an electrolyte for a lithium secondary battery comprising a solvent and an electrolyte salt and a lithium secondary battery including the electrolyte. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged, and are widely used as a power source for portable electronic devices such as mobile phones and laptop computers.

[0003] Lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and lightness, and therefore are being actively developed and applied.

[0004] For example, a lithium secondary battery may include: an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; and an electrolyte impregnating the electrode assembly.

[0005] As the positive electrode active material of the lithium secondary battery, a lithium metal oxide can be used. Examples of the lithium metal oxide include nickel-based lithium metal oxide.

[0006] As the application range of lithium secondary batteries expands, longer life, high capacity, and operational stability are required. Therefore, lithium secondary batteries that provide uniform power and capacity even when repeatedly charged and discharged are preferred.

[0007] However, with repeated charge and discharge, for example, due to surface damage of the nickel-based lithium metal oxide used as a positive electrode active material, power and capacity may be reduced, and side reactions between the nickel-based lithium metal oxide and the electrolyte may also be caused. In particular, lithium secondary batteries are in a high temperature environment during repeated charge and discharge and overcharge. In this case, the above problems are accelerated, thereby causing battery expansion (gas is generated inside the battery, and the battery thickness increases), an increase in the internal resistance of the battery, and a reduction in the life characteristics of the battery. Summary of the invention

[0008] 1. Technical issues to be resolved

[0009] A technical problem of the present invention is to provide an electrolyte for a lithium secondary battery having excellent high temperature characteristics and other properties (eg, initial resistance, rapid charging performance, room temperature capacity characteristics, etc.).

[0010] A technical problem of the present invention is to provide a lithium secondary battery having excellent high temperature characteristics and other properties (eg, initial resistance, rapid charging performance, normal temperature capacity characteristics, etc.).

[0011] (II) Technical solution

[0012] An electrolyte for a lithium secondary battery according to an exemplary embodiment may include: an additive including a compound represented by Chemical Formula 1; an organic solvent; and a lithium salt.

[0013] [Chemical formula 1]

[0014]

[0015] In Chemical Formula 1, R 1 and R 2 may be independently a substituted or unsubstituted C2-C8 cyclic ether group, L 1 and L 2 Each independently may be a substituted or unsubstituted C1-C5 alkylene group.

[0016] In one embodiment, the R 1 and R 2 may be independently an unsubstituted C2-C5 cyclic ether group, wherein L 1 and L 2 Each may independently be an unsubstituted C1-C3 alkylene group.

[0017] In one embodiment, the R 1 and R 2 may be independently an unsubstituted C4 cyclic ether group, wherein L 1 and L 2 Each may independently be an unsubstituted C1 alkylene group.

[0018] In one embodiment, the content of the additive may be 0.1-5 wt % relative to the total weight of the electrolyte.

[0019] In one embodiment, the content of the additive may be 0.2-2 wt % relative to the total weight of the electrolyte.

[0020] In one embodiment, the organic solvent may include a linear carbonate-based solvent and a cyclic carbonate-based solvent.

[0021] In one embodiment, the electrolyte may further include at least one auxiliary additive selected from the group consisting of cyclic carbonate-based compounds, fluorine-substituted carbonate-based compounds, sultone-based compounds, cyclic sulfate-based compounds, and phosphate-based compounds.

[0022] In one embodiment, the auxiliary additive may be contained in an amount of 0.05-10 wt % relative to the total weight of the electrolyte.

[0023] In one embodiment, the auxiliary additive may be contained in an amount of 0.1-5 wt % relative to the total weight of the electrolyte.

[0024] In one embodiment, in the electrolyte, the ratio of the weight of the auxiliary additive to the weight of the additive may be 0.1 to 10.

[0025] A lithium secondary battery according to an exemplary embodiment may include: an electrode assembly in which a plurality of positive electrodes and a plurality of negative electrodes are repeatedly stacked; a case accommodating the electrode assembly; and an electrolyte for the lithium secondary battery accommodated in the case together with the electrode assembly.

[0026] (III) Beneficial effects

[0027] The electrolyte including the electrolyte additive for a lithium secondary battery according to the exemplary embodiment may form a strong solid electrolyte interphase (SEI) on the surface of an electrode.

[0028] Therefore, a lithium secondary battery having improved high-temperature storage characteristics (eg, capacity retention rate of the battery at high temperature, effects of preventing resistance increase and thickness increase) can be realized.

[0029] The electrolyte for a lithium secondary battery according to the exemplary embodiment can realize a lithium secondary battery in which other characteristics (for example, effects of reducing initial resistance, improving fast charge life capacity retention rate, improving low temperature capacity and life capacity retention rate at 25° C.) are also improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic plan view showing a lithium secondary battery according to an exemplary embodiment.

[0031] Figure 2 is a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment.

[0032] Figure 3 is a graph showing H-NMR results of the additive represented by Chemical Formula 1-1 according to one embodiment. DETAILED DESCRIPTION

[0033] In the present specification, "-based compound" may refer to a compound having "-based compound" and a derivative of the compound.

[0034] In this manual, “C a -C b ” may refer to “the number of carbon (C) atoms from a to b”.

[0035] <Electrolyte for lithium secondary batteries>

[0036] An electrolyte for a lithium secondary battery according to an exemplary embodiment may include: a lithium salt; an organic solvent; and an additive including a compound represented by Chemical Formula 1.

[0037] The electrolyte for a lithium secondary battery according to the exemplary embodiment may realize a lithium secondary battery having excellent high temperature characteristics and other characteristics.

[0038] Hereinafter, the constituent elements of the present invention will be described in more detail.

[0039] additive

[0040] The electrolyte for a lithium secondary battery according to the exemplary embodiment may include an additive including a compound represented by Chemical Formula 1.

[0041] [Chemical formula 1]

[0042]

[0043] In Formula 1, each R 1 and R 2 can be independent of each other and can be the same or different from each other.

[0044] For example, R 1 It may be a substituted or unsubstituted C2-C8 cyclic ether group. 1 Preferably, it is an unsubstituted C2-C5 cyclic ether group, and more preferably, it is an unsubstituted C4 cyclic ether group.

[0045] For example, R 2 It may be a substituted or unsubstituted C2-C8 cyclic ether group. 1 Preferably, it is an unsubstituted C2-C5 cyclic ether group, and more preferably, it is an unsubstituted C4 cyclic ether group.

[0046] For example, R 1 and R 2 may be independent of each other and may be the same or different.

[0047] For example, L 1 It can be a substituted or unsubstituted C1-C5 alkylene group, L 1 Preferably, it may be an unsubstituted C1-C3 alkylene group, L 1 More preferably, it may be an unsubstituted C1 alkylene group.

[0048] For example, the cyclic ether group may refer to a heterocyclic compound including an ether bond in a ring composed of an alkyl group.

[0049] For example, the alkyl group may refer to an alkane (C n H 2n+2 ) is the portion of a structure that remains when one hydrogen atom is removed. For example, CH3-CH2-CH2- can refer to propyl.

[0050] For example, the alkylene group may refer to an alkane (—C n H 2n -) is a group in which one hydrogen atom is separated from each of the carbon atoms at both ends. For example, -CH2-CH2-CH2- can refer to propylene.

[0051] For example, the ether may refer to a compound in which two carbon atoms are bonded to the same oxygen atom. For example, CH3-O-CH3 may refer to dimethyl ether.

[0052] For example, "substituted" may mean that the hydrogen atoms of the alkylene group are replaced by substituents, so that the substituents may be further bonded to the carbon atoms of the alkylene group. For example, the substituents may be at least one of halogen, C1-C6 alkyl, C2-C6 alkenyl, amino, C1-C6 alkoxy, C3-C7 cycloalkyl, and 5- to 7-membered heterocycloalkyl. In some embodiments, the substituents may be halogen or C1-C6 alkyl.

[0053] When an additive containing a compound represented by the chemical formula 1 is included in the electrolyte for a secondary battery, for example, a film with relatively low resistance can be formed on the electrode by a decomposition reaction of a cyclic ether group. Preferably, SEI can be formed on the negative electrode. Therefore, the decomposition of the organic solvent can be effectively prevented, and the generation of gas and the increase in battery thickness can be significantly reduced. In addition, the film with relatively low resistance can prevent the increase in initial resistance, which can significantly improve the fast charging performance by increasing the mobility of lithium ion ions. In other words, when an additive containing a compound represented by the chemical formula 1 is included in the electrolyte for a secondary battery, high temperature storage characteristics, normal temperature characteristics and initial resistance characteristics can be improved simultaneously.

[0054] In one embodiment, the compound represented by the chemical formula 1 may include bis((tetrahydrofuran-2-yl)methyl)sulfite. For example, bis((tetrahydrofuran-2-yl)methyl)sulfite may be represented by chemical formula 1-1.

[0055] [Chemical formula 1-1]

[0056]

[0057] For example, when bis((tetrahydrofuran-2-yl)methyl)sulfite is included as an electrolyte additive for a secondary battery, a stable SEI film can be formed on the negative electrode through the sulfite group, thereby realizing a lithium secondary battery with improved high temperature storage characteristics. In addition, the decomposition of the electrolyte caused by the reaction between the electrolyte and the negative electrode can be suppressed, thereby reducing the generation of gas.

[0058] In particular, by inducing the formation of a film with relatively reduced resistance through the decomposition reaction of the cyclic ether group, it is possible to simultaneously improve the initial resistance value, fast charging characteristics, and other characteristics such as normal temperature life and low temperature characteristics compared to existing additives that provide high temperature storage characteristics.

[0059] In one embodiment, considering the formation of sufficient passivation and stable SEI film, the content of the additive can be adjusted to 0.1% by weight or more, 0.2% by weight or more, 0.3% by weight or more, 0.4% by weight or more, 0.5% by weight or more, or 1% by weight or more relative to the total weight of the electrolyte. In addition, considering the lithium ion migration in the electrolyte and the activity of the active material, the content of the additive can be adjusted to 10% by weight or less, 9% by weight or less, 7% by weight or less, 6% by weight or less, 5% by weight or less, 4.5% by weight or less, 4% by weight or less, 3.5% by weight or less, 3% by weight or less, or 2% by weight or less relative to the total weight of the electrolyte.

[0060] In a preferred embodiment, the content of the additive may be 0.1-5% by weight, more preferably 0.2-2% by weight. Within the above range, the passivation of the negative electrode can be fully achieved without excessively hindering the migration of lithium ions and the activity of the positive electrode active material, and the excellent capacity retention rate at high temperature and the effect of preventing the thickness and resistance of the battery from increasing can be improved.

[0061] Auxiliary additives

[0062] The electrolyte for a lithium secondary battery according to the exemplary embodiment may further include auxiliary additives while including the above-mentioned additives.

[0063] In one embodiment, the auxiliary additive may include, for example, a cyclic carbonate-based compound, a fluorine-substituted carbonate-based compound, a sultone-based compound, a cyclic sulfate-based compound, and a phosphate-based compound.

[0064] In one embodiment, in consideration of the effect with the main additive comprising the compound represented by Chemical Formula 1, the content of the auxiliary additive can be adjusted to, for example, 10 wt % or less, 9 wt % or less, 8 wt % or less, 7 wt % or less, 6 wt % or less, 5 wt % or less, 4 wt % or less, 3 wt % or less, 2 wt % or less, 1 wt % or less in the total weight of the non-aqueous electrolyte. In addition, in consideration of the stabilization of the SEI film, the content of the auxiliary additive can be adjusted to 0.01 wt % or more, 0.02 wt % or more, 0.03 wt % or more, 0.05 wt % or more, 0.1 wt % or more, 0.2 wt % or more, 0.3 wt % or more, 0.4 wt % or more, or 0.5 wt % or more.

[0065] The content of the auxiliary additive in the total weight of the non-aqueous electrolyte is preferably about 0.05-10 wt %, more preferably 0.1-5 wt %. Within the above range, the durability of the electrode protective film can be enhanced without hindering the effect of the main additive, and it can help improve high temperature storage characteristics and other characteristics.

[0066] In one embodiment, in the electrolyte, the ratio of the weight of the auxiliary additive to the weight of the additive may be 0.1 to 10, more than 1 and less than 10, or 5 to less than 10. In this case, through the interaction of the main additive and the auxiliary additive, a lithium secondary battery with further improved high temperature storage characteristics and cycle characteristics can be achieved.

[0067] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and the like.

[0068] The fluorine-substituted cyclic carbonate-based compound may include fluoroethylene carbonate (FEC).

[0069] The sultone-based compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, and the like.

[0070] The cyclic sulfate-based compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, and the like.

[0071] The phosphate-based compound may be an oxalatophosphate-based compound, and may include lithium bis(oxalo)phosphate.

[0072] In a preferred embodiment, as the auxiliary additive, a fluorine-substituted cyclic carbonate-based compound, a sultone-based compound, a cyclic sulfate-based compound, and an oxalatophosphate-based compound may be used simultaneously.

[0073] By adding the auxiliary additive, the durability and stability of the electrode can be further enhanced. The auxiliary additive can be contained in an appropriate content within a range that does not hinder the migration of lithium ions in the electrolyte.

[0074] Organic solvents and lithium salts

[0075] The organic solvent may include, for example, an organic compound that has sufficient solubility for the lithium salt, the additive, and the auxiliary additive and is not reactive in the battery.

[0076] For example, the organic solvent may include at least one of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent.

[0077] In one embodiment, the organic solvent may include a carbonate-based solvent.

[0078] In some embodiments, the carbonate-based solvent may include a linear carbonate-based solvent and a cyclic carbonate-based solvent.

[0079] For example, the linear carbonate-based solvent may include at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and dipropyl carbonate.

[0080] For example, the cyclic carbonate-based solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate.

[0081] In some embodiments, the organic solvent may include more of the linear carbonate-based solvent than the cyclic carbonate-based solvent on a volume basis.

[0082] For example, the mixing volume ratio of the linear carbonate-based solvent to the cyclic carbonate-based solvent may be 1:1 to 9:1, and preferably 1.5:1 to 4:1.

[0083] For example, the ester-based solvent may include at least one of methyl acetate (MA), ethylacetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), and ethylpropionate (EP).

[0084] For example, the 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.

[0085] For example, the ketone-based solvent may include cyclohexanone.

[0086] For example, the alcohol-based solvent may include at least one of ethyl alcohol and isopropyl alcohol.

[0087] For example, the aprotic solvent may include at least one of a nitrile-based solvent, an amide-based solvent (eg, dimethylformamide), a dioxolane-based solvent (eg, 1,3-dioxolane), and a sulfolane-based solvent.

[0088] The electrolyte may include a lithium salt, and the lithium salt may be composed of Li + X - express.

[0089] For example, the anion (X - ) may be selected from 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 - Any of the above.

[0090] In some embodiments, the lithium salt may include at least one of LiBF4 and LiPF6.

[0091] In one embodiment, the lithium salt may be included at a concentration of 0.01-5 M relative to the organic solvent, more preferably 0.01-2 M. Within the above concentration range, lithium ions and / or electrons may migrate smoothly during charge and discharge of the battery.

[0092] <Lithium Secondary Battery>

[0093] A lithium secondary battery according to an exemplary embodiment may include: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte including an organic solvent and a lithium salt.

[0094] Hereinafter, a lithium secondary battery according to an exemplary embodiment will be described in more detail with reference to the accompanying drawings. Figure 1 and Figure 2 1 and 2 are respectively a schematic plan view and a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. Figure 2 is along Figure 1 A cross-sectional view taken along line I-I'.

[0095] Reference Figure 1 and Figure 2 The lithium secondary battery may include a positive electrode 100 and a negative electrode 130 disposed opposite to the positive electrode 100 .

[0096] For example, the positive electrode 100 may include a positive electrode collector 105 and a positive electrode active material layer 110 on the positive electrode collector 105 .

[0097] For example, the positive electrode active material layer 110 may include a positive electrode active material, and may include a positive electrode binder and a conductive material as needed.

[0098] For example, the positive electrode 100 may be manufactured by mixing and stirring a positive active material, a positive binder, a conductive material, a dispersion medium, etc. to prepare a positive electrode slurry, and then coating the positive electrode slurry on the positive electrode collector 105 and performing drying and rolling.

[0099] For example, the positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof.

[0100] For example, the positive active material may include lithium metal oxide particles that can reversibly intercalate and deintercalate lithium ions.

[0101] In one embodiment, the positive active material may include lithium metal oxide particles containing nickel.

[0102] In some embodiments, in the lithium metal oxide particles, the content of nickel may be 80 mol % or more relative to the total molar number of all elements except lithium and oxygen. In this case, a lithium secondary battery with high capacity may be realized.

[0103] In some embodiments, in the lithium metal oxide particles, the content of nickel may be 83 mol % or more, 85 mol % or more, 90 mol % or more, or 95 mol % or more relative to the total moles of all elements except lithium and oxygen.

[0104] In some embodiments, the lithium metal oxide particles may further include at least one of cobalt and manganese.

[0105] In some embodiments, the lithium metal oxide particles may further include cobalt and manganese. In this case, a lithium secondary battery having excellent power characteristics and penetration stability, etc. may be realized.

[0106] In one embodiment, the lithium metal oxide particles may be represented by Chemical Formula 2 below.

[0107] [Chemical formula 2]

[0108] Li x Ni (1-a-b)Co a M b O y

[0109] For example, in Chemical Formula 2, M may be at least one of Al, Zr, Ti, Cr, B, Mg, Mn, Ba, Si, Y, W, and Sr, and may be 0.9≤x≤1.2, 1.9≤y≤2.1, and 0≤a+b≤0.5.

[0110] In some embodiments, a+b can be 0 <a+b≤0.4、0<a+b≤0.3、0<a+b≤0.2、0<a+b≤0.17、0<a+b≤0.15、0<a+b≤0.12、0<a+b≤0.1。

[0111] In one embodiment, the lithium metal oxide particles may further include a coating element or a doping element. For example, the coating element or the doping element may include Al, Ti, Ba, Zr, Si, B, Mg, P, Sr, W, La, or an alloy thereof or an oxide thereof. In this case, a lithium secondary battery with further improved life characteristics can be achieved.

[0112] For example, the positive electrode binder may include organic binders such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile, polymethyl methacrylate, etc.; water-based binders such as styrene-butadiene rubber (SBR), etc. In addition, for example, the positive electrode binder may also be used together with a thickener such as carboxymethyl cellulose (CMC).

[0113] For example, the conductive material may include: carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes; tin, tin oxide, titanium oxide; metal-based conductive materials such as perovskite materials such as LaSrCoO3 and LaSrMnO3.

[0114] For example, the negative electrode 130 may include a negative electrode collector 125 and a negative electrode active material layer 120 on the negative electrode collector 125 .

[0115] For example, the negative electrode active material layer 120 may include a negative electrode active material, and may include a negative electrode binder and a conductive material as needed.

[0116] 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 prepare a negative electrode paste, and then coating the negative electrode paste on the negative electrode current collector 125 and drying and calendering it.

[0117] For example, the negative electrode current collector 125 can include gold, stainless steel, nickel, aluminum, titanium, copper, or their alloys. More preferably, it can include copper or a copper alloy.

[0118] For example, the negative electrode active material can be a material that allows lithium ions to be inserted and extracted. For example, the negative electrode active material can include a lithium alloy, a carbon-based material, a silicon-based material, etc.

[0119] For example, the lithium alloy can include metal elements such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0120] For example, the carbon-based material can include crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.

[0121] For example, the amorphous carbon can be hard carbon, coke, mesocarbon microbead (MCMB) calcined at a temperature below 1500 °C, mesophase pitch-based carbon fiber (MPCF), etc. The crystalline carbon can be, for example, natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0122] In one embodiment, the negative electrode active material can include a silicon-based material. For example, the silicon-based material can include Si, SiO x (0 < x < 2), Si / C, SiO / C, Si-Metal, etc. In this case, a lithium secondary battery with high capacity can be achieved.

[0123] For example, when the negative electrode active material includes a silicon-based material, there may be a problem of an increase in the battery thickness during repeated charge and discharge. The lithium secondary battery according to an exemplary embodiment can alleviate the rate of increase in the battery thickness by including the above electrolyte.

[0124] In some embodiments, the content of the silicon active material in the negative electrode active material can be 1-20 wt%, 1-15 wt%, or 1-10 wt%.

[0125] The negative electrode binder and the conductive material can be substantially the same or similar materials as the above positive electrode binder and conductive material. For example, the negative electrode binder can be an aqueous binder such as styrene-butadiene rubber (SBR). In addition, for example, the negative electrode binder can be used together with a thickener such as carboxymethyl cellulose (CMC).

[0126] For example, the separator 140 may be interposed between the positive electrode 100 and the negative electrode 130 .

[0127] In some embodiments, the area of ​​the negative electrode 130 may be greater than that of the positive electrode 100. In this case, lithium ions generated from the positive electrode 100 may smoothly migrate to the negative electrode 130 without being precipitated in the middle.

[0128] For example, the separator 140 may include a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. In addition, for example, the separator 140 may include a non-woven fabric formed of high melting point glass fiber, polyethylene terephthalate fiber, etc.

[0129] For example, the electrode unit may be formed by including the positive electrode 100 , the negative electrode 130 , and the separator 140 .

[0130] For example, a plurality of electrode units may be stacked to form the electrode assembly 150. For example, the electrode assembly 150 may be formed by winding, laminating, z-folding, etc., of the separator 140.

[0131] The lithium secondary battery according to the exemplary embodiment may include a positive electrode lead 107 connected to the positive electrode 100 and protruding to the outside of the case 160 , and a negative electrode lead 127 connected to the negative electrode 130 and protruding to the outside of the case 160 .

[0132] 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.

[0133] For example, the positive electrode lead 107 may be electrically connected to the positive electrode collector 105. In addition, the negative electrode lead 130 may be electrically connected to the negative electrode collector 125.

[0134] For example, the positive electrode current collector 105 may include a protrusion (positive electrode tab, not shown) on one side. The positive electrode tab may not be formed with the positive electrode active material layer 110. The positive electrode tab may be formed integrally 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.

[0135] Similarly, the negative electrode current collector 125 may include a protrusion (negative electrode tab, not shown) on one side. The negative electrode tab may not be formed with the negative electrode active material layer 120. The negative electrode tab may be formed integrally with the negative electrode current collector 125, or may be connected by welding or the like. The negative electrode current collector 125 and the negative electrode lead 127 may be electrically connected through the negative electrode tab.

[0136] In one embodiment, the electrode assembly 150 may include a plurality of positive electrodes and a plurality of negative electrodes. For example, a plurality of positive electrodes and negative electrodes may be arranged alternately with each other, and a separator may be inserted between the positive electrodes and the negative electrodes. Therefore, a lithium secondary battery according to an embodiment of the present invention may include a plurality of positive electrode tabs and a plurality of negative electrode tabs protruding from the plurality of positive electrodes and the plurality of negative electrodes, respectively.

[0137] In one embodiment, the positive electrode tabs (or negative electrode tabs) may be stacked, pressed, and welded to form a positive electrode tab stack (or negative electrode tab stack). The positive electrode tab stack may be electrically connected to the positive electrode lead 107. In addition, the negative electrode tab stack may be electrically connected to the negative electrode lead 127.

[0138] For example, the electrode assembly 150 and the above-mentioned electrolyte may be accommodated together in the case 160 to form a lithium secondary battery.

[0139] The lithium secondary battery may be manufactured in a cylindrical, prismatic, pouch, or coin shape, for example.

[0140] Preferred examples and comparative examples of the present invention are described below. However, the following examples are merely preferred examples of the present invention, and the present invention is not limited to the following examples.

[0141] <Examples and Comparative Examples>

[0142] (1) Synthesis example of additive (chemical formula 1-1)

[0143] Dichloromethane (100 mL), tetrahydrofurfuryl alcohol (25.7 g, 252 mmol) and triethylamine (25.6 g, 253 mmol) were added to a round-bottom flask in sequence and then cooled to 0°C. Thionyl chloride (9.15 mL, 126 mmol) was slowly added to the mixture for 2 hours. After the addition was completed, the mixture was heated to room temperature and further stirred for 2 hours. After the reaction was completed, the reaction mixture was slowly added dropwise to 50 mL of saturated aqueous ammonium chloride solution to separate the organic layer, and further washed twice with 50 mL of distilled water. The solvent of the organic layer from which moisture was removed by treatment with sodium sulfate was dried and then purified by a silica gel column to obtain 24 g of a light yellow liquid (bis((tetrahydrofuran-2-yl)methyl)sulfite) (yield of 76%). The H-NMR results for it are as follows, and the H-NMR results for it are shown in Figure 3 middle.

[0144] 1H-NMR(CDCl3, 600MHz): 4.11(m, 2H), 4.07(d, 1H), 3.98(d, 2H), 3.85(m,3H), 3.77(q, 2H), 1.98(m, 2H), 1.88(m, 4H), 1.66(m, 2H)

[0145] (2) Preparation of electrolyte

[0146] Prepare 1 M LiPF6 solution (EC / EMC mixed solvent with a volume ratio of 25:75).

[0147] Based on the total weight of the electrolyte, additives and auxiliary additives were added to the LiPF6 solution in the amounts (weight %) listed in Table 1 below and mixed to prepare electrolytes of Examples and Comparative Examples.

[0148] (3) Production of lithium secondary battery samples

[0149] Will Li[Ni 0.8 Co 0.1 Mn 0.1 ]O2, carbon black and polyvinylidene fluoride (PVDF) were dispersed in N-methylpyrrolidone (NMP) in a weight ratio of 98:1:1 to prepare a positive electrode slurry.

[0150] The positive electrode slurry was uniformly coated on an aluminum foil having a thickness of 12 μm, and dried and rolled to manufacture a positive electrode.

[0151] A negative electrode slurry was prepared by dispersing a negative electrode active material prepared by mixing artificial graphite and natural graphite at a weight ratio of 7:3, a conductive material, styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) at a weight ratio of 96:3:1:1 in water. The negative electrode slurry was uniformly coated on a copper foil having a thickness of 8 μm, and dried and rolled to manufacture a negative electrode.

[0152] The prepared positive electrodes and negative electrodes were alternately stacked repeatedly, and a separator (thickness of 13 μm, polyethylene film) was interposed between the positive electrodes and the negative electrodes, thereby manufacturing an electrode assembly.

[0153] The electrode assembly was housed in a soft package, the electrolyte prepared in (2) was injected and sealed, and immersed for 12 hours, thereby manufacturing a lithium secondary battery sample.

[0154] [Table 1]

[0155]

[0156] The components described in Table 1 are as follows.

[0157] BHFSi: bis((tetrahydrofuran-2-yl)methyl)sulfite

[0158] FEC: Fluorinated Ethylene Carbonate

[0159] PS: 1,3-propane sultone

[0160] PRS: Prop-1-ene-1,3-sultone

[0161] <Experimental example>

[0162] (1) High temperature storage characteristics

[0163] (1-1) After high temperature storage, measure the capacity retention rate (Ret)

[0164] At 25°C, the lithium secondary batteries of the embodiments and comparative examples were repeatedly subjected to 0.5C CC / CV charging (4.2V, 0.05C cut-off (CUT-OFF)) and 0.5C CC discharge (2.7V cut-off) for 3 times, and the third discharge capacity C1 was measured. The charged lithium secondary battery was stored at 60°C for 12 weeks, and then further placed at room temperature for 30 minutes and subjected to 0.5C CC discharge (2.75V cut-off), and the discharge capacity C2 was measured. The capacity retention rate was calculated as follows and recorded in Table 2 below.

[0165] Capacity retention rate (%) = C2 / C1×100 (%)

[0166] (1-2) After high temperature storage, measure the increase rate of internal resistance (DCIR)

[0167] At room temperature, the lithium secondary batteries of the embodiments and comparative examples were charged at 0.5C CC / CV at 25°C (4.2V0.05C cut-off), and then discharged at 0.5C CC to SOC 60. At SOC 60, the C-rate was changed to 0.2C, 0.5C, 1C, 1.5C, 2C, 2.5C, and the discharge and supplementary charge were respectively 10 seconds, and the DCIR R1 was measured. The charged lithium secondary batteries of the embodiments and comparative examples were placed under conditions of exposure to an atmosphere at 60°C for 12 weeks, and then further placed at room temperature for 30 minutes, and the DCIR R2 was measured in the same manner as described above. The internal resistance increase rate was calculated as follows, and the resulting values ​​are recorded in Table 2 below.

[0168] Internal resistance increase rate (%) = (R2-R1) / R1×100 (%)

[0169] (1-3) Measuring the thickness of the battery after high temperature storage

[0170] The lithium secondary batteries of the examples and comparative examples were subjected to 0.5C CC / CV charging (4.2V 0.05C cutoff) at 25°C, and then the battery thickness T1 was measured.

[0171] The charged lithium secondary batteries of the embodiment and the comparative example were placed (using a constant temperature device) under the condition of being exposed to an atmosphere of 60°C for 12 weeks, and then the battery thickness T2 was measured. The battery thickness was measured using a flat plate thickness measuring device (Mitutoyo, 543-490B). The battery thickness increase rate was calculated as follows, and the result values ​​are recorded in the following Table 2.

[0172] Battery thickness increase rate (%) = (T2-T1) / T1×100 (%)

[0173] (2) Initial resistance

[0174] At room temperature, the lithium secondary batteries of the embodiments and comparative examples were charged at 0.5C CC / CV (4.2V0.05C cut-off) at 25°C, and then discharged at 0.5C CC to SOC 60. At SOC 60, the C-rate was changed to 0.2C, 0.5C, 1C, 1.5C, 2C, 2.5C, and discharged and supplemented for 10 seconds, respectively, and the initial DCIR was measured and shown in Table 3 below.

[0175] (3) Fast charge life capacity retention rate

[0176] The lithium secondary batteries of the embodiments and comparative examples were charged at 0.33C to a state of charge (SOC) of 8%, charged in stages at 2.5C-2.25C-2C-1.75C-1.5C-1.0C in the SOC 8-80% range, charged again at 0.33C in the SOC 80-100% range (4.2V, 0.05C cutoff), and then CC discharged at 0.33C to 2.7V.

[0177] The first discharge capacity A1 was measured, the charge and discharge were repeated 100 times, and the 100th discharge capacity A2 was measured.

[0178] The fast charge capacity retention rate was calculated according to the following formula and is shown in Table 3 below.

[0179] Fast charge capacity retention rate (%) = A2 / A1×100 (%)

[0180] (4) Low temperature capacity

[0181] The lithium secondary batteries of the Examples and Comparative Examples were charged at 0.5C CC / CV (4.2V, 0.05C cutoff) at 25°C and then discharged at 0.5C CC (2.7V cutoff) at -10°C for 4 hours. The discharge capacity (mAh) was measured and shown in Table 3 below.

[0182] (5) Lifetime capacity retention at 25°C

[0183] At 25° C., the lithium secondary batteries of the embodiments and comparative examples were repeatedly subjected to 0.5C CC / CV charging (4.2V, 0.05C cutoff) and 0.5C CC discharging (2.7V cutoff) 500 times. At this time, the first discharge capacity was set as C, and the capacity retention rate during life was measured by dividing the 500th discharge capacity by the first discharge capacity, and is shown in Table 3 below.

[0184] [Table 2]

[0185]

[0186] [Table 3]

[0187]

[0188] As can be confirmed from Table 2, the lithium secondary batteries of Examples show excellent result values ​​in the high-temperature storage evaluation (capacity retention rate, resistance increase rate, and thickness increase rate).

[0189] It can be confirmed from Table 3 that the lithium secondary batteries of the examples show good results in other properties (initial resistance, rapid charge life capacity retention rate, low temperature capacity, and normal temperature life capacity retention rate).

[0190] In addition, when comparing Comparative Example 1 and Comparative Example 2, it can be seen that the inclusion of PRS improves high temperature characteristics, but other properties are poor. However, it can be confirmed that the examples can improve both high temperature storage properties and other properties.

Claims

1. An electrolyte for a lithium secondary battery, comprising: An additive comprising a compound represented by Chemical Formula 1; organic solvents; and Lithium salts, [Chemical formula 1] In Chemical Formula 1, R 1 and R 2 are each independently a substituted or unsubstituted C2-C8 cyclic ether group, L 1 and L 2 Each is independently a substituted or unsubstituted C1-C5 alkylene group.

2. The electrolyte for lithium secondary battery according to claim 1, wherein The R 1 and R 2 are each independently an unsubstituted C2-C5 cyclic ether group, wherein L 1 and L 2 Each is independently an unsubstituted C1-C3 alkylene group.

3. The electrolyte for lithium secondary battery according to claim 1, wherein The R 1 and R 2 are each independently an unsubstituted C4 cyclic ether group, said L 1 and L 2 Each is independently an unsubstituted C1 alkylene group.

4. The electrolyte for lithium secondary battery according to claim 1, wherein The content of the additive is 0.1-5 wt % relative to the total weight of the electrolyte.

5. The electrolyte for lithium secondary battery according to claim 1, wherein The content of the additive is 0.2-2 wt % relative to the total weight of the electrolyte.

6. The electrolyte for lithium secondary battery according to claim 1, wherein The organic solvent includes a linear carbonate-based solvent and a cyclic carbonate-based solvent.

7. The electrolyte for lithium secondary battery according to claim 1, wherein The electrolyte further comprises at least one auxiliary additive selected from the group consisting of a cyclic carbonate-based compound, a fluorine-substituted carbonate-based compound, a sultone-based compound, a cyclic sulfate-based compound, and a phosphate-based compound.

8. The electrolyte for lithium secondary battery according to claim 7, wherein The content of the auxiliary additive is 0.05-10 wt % relative to the total weight of the electrolyte.

9. The electrolyte for lithium secondary battery according to claim 7, wherein The content of the auxiliary additive is 0.1-5 wt % relative to the total weight of the electrolyte.

10. The electrolyte for lithium secondary battery according to claim 7, wherein In the electrolyte, the ratio of the weight of the auxiliary additive to the weight of the additive is 0.1 to 10.

11. A lithium secondary battery comprising: An electrode assembly, wherein a plurality of positive electrodes and a plurality of negative electrodes are repeatedly stacked; a housing for accommodating the electrode assembly; as well as The electrolyte for a lithium secondary battery according to claim 1, wherein the electrolyte for a lithium secondary battery is contained in the casing together with the electrode assembly.

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