Electrolyte solution for a lithium secondary battery and lithium secondary battery containing this

Abstract

An electrolyte solution for a lithium secondary battery and a lithium secondary battery containing the electrolyte solution are provided. The electrolyte solution contains an additive comprising a compound with a specific structure, an organic solvent, and a lithium salt. Consequently, the lithium secondary battery containing the electrolyte solution exhibits improved fast-charging performance, as well as enhanced lifespan and high-temperature storage characteristics.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an electrolyte solution for a lithium secondary battery and a lithium secondary battery containing the same. More specifically, the present disclosure relates to an electrolyte solution for a lithium secondary battery containing a solvent and an electrolyte salt, and a lithium secondary battery containing the same. BACKGROUND

[0002] A secondary battery that can be repeatedly charged and discharged is often used as a power source for mobile electronic devices such as camcorders, mobile phones, and laptops.

[0003] For example, lithium secondary batteries are widely developed and used due to their high operating voltage and energy density per unit weight, high charging speed, compact dimensions, etc.

[0004] The lithium secondary battery may, for example, include an electrode assembly with a cathode, an anode, and a separator, as well as an electrolyte solution in which the electrode assembly is immersed. The lithium secondary battery may also include an outer casing, for example, in the form of a bag, for containing the electrode assembly and the electrolyte solution.

[0005] The cathode of the lithium secondary battery can be manufactured, for example, by coating, drying and pressing a cathode slurry, which may contain an active cathode material and a binder, optionally with a conductive material, onto a cathode current collector.

[0006] The active cathode material can be a material that can reversibly intercalate and deintercalate lithium ions. For example, the active cathode material can be a lithium metal oxide containing a metal element such as nickel (Ni), cobalt (Co), manganese (Mn), etc.

[0007] As the application range of lithium secondary batteries expands, improved cycle life characteristics, high capacity, and operational stability are required. Accordingly, the development of a lithium secondary battery that delivers consistent performance and capacity even during repeated charging and discharging is necessary. SUMMARY

[0008] According to one aspect of the present disclosure, an electrolyte solution for a lithium secondary battery with improved chemical stability is provided.

[0009] According to one aspect of the present invention, a lithium secondary battery with improved fast charging, cycle life and high temperature storage characteristics is provided.

[0010] An electrolyte solution for a secondary battery contains an additive comprising a compound having a structure represented by chemical formula 1, an organic solvent, and a lithium salt.

[0011] In chemical formula 1, R 1 to R 4 each independently of one another represents a C1 to C10 alkyl group in which at least one hydrogen atom is substituted by a halogen atom, and M + is a cesium, potassium, lithium, sodium or rubidium cation.

[0012] In some embodiments, R 1 to R 4 each independently be a C1 to C10 alkyl group in which all hydrogen atoms are substituted by halogen atoms.

[0013] In some embodiments, the halogen atom may be a fluorine atom, and M + can be the cesium or potassium cation.

[0014] In some embodiments, R 1 to R 4 each independently be a C1 to C10 alkyl group in which all hydrogen atoms are substituted by fluorine atoms.

[0015] In some embodiments, the compound having the structure represented by Chemical Formula 1 may include a compound having the structure represented by Chemical Formula 2-1 or Chemical Formula 2-2.

[0016] In some embodiments, the organic solvent may include at least one selected from the group consisting of a carbonate-based organic solvent, an ester-based organic solvent, an ether-based organic solvent, a ketone-based organic solvent, and an aprotic organic solvent.

[0017] In some embodiments, the organic solvent may include a cyclic carbonate-based solvent and a linear carbonate-based solvent.

[0018] In some embodiments, the volume ratio between the cyclic carbonate-based solvent and the linear carbonate-based solvent in the organic solvent may be in a range of 1 / 9 to 1.

[0019] In some embodiments, the content of the additive may be in a range of 0.1 wt% to 10 wt% based on the total weight of the electrolyte solution.

[0020] In some embodiments, the electrolyte solution may further contain at least one auxiliary additive selected from the group consisting of a fluorine-containing carbonate-based compound, a lithium phosphate-based compound, a sultone-based compound, and a sulfate-based compound.

[0021] In some embodiments, the content of the auxiliary additive may be in a range of 0.01 wt% to 10 wt% based on the total weight of the electrolyte solution.

[0022] In some embodiments, the weight ratio of the auxiliary additive relative to the additive in the electrolyte solution may be in the range of 0.1 to 5.

[0023] A lithium secondary battery includes an electrode assembly containing repeatedly stacked cathodes and anodes and the above-described electrolyte solution for a lithium secondary battery impregnating the electrode assembly.

[0024] The electrolyte solution for a lithium secondary battery according to embodiments of the present disclosure can form a uniform solid electrolyte interphase (SEI) having a high ionic conductivity on an electrode surface.

[0025] The lithium secondary battery according to embodiments of the present disclosure contains the electrolyte solution to have improved fast charging performance and cycle life and improved high-temperature storage properties

[0026] The electrolyte solution of the present disclosure can be used in a wide range of green technologies, such as electric vehicles, battery charging stations, solar power generation, wind power generation, etc. using a battery, etc. The lithium secondary battery according to the present disclosure can be used for green electric vehicles and hybrid vehicles to prevent climate change by suppressing air pollution and greenhouse gas emissions, etc. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic plan view showing a lithium secondary battery according to embodiments. Fig. 2 is a schematic cross-sectional view showing a lithium secondary battery according to embodiments. Fig.3 is a graph showing peaks appearing in a Cs-1s spectrum in an XPS measurement of anodes of a lithium secondary battery according to Example 1 and Comparative Example 1. Fig. 4 is a graph showing peaks in a B-1s spectrum in an XPS measurement of anodes of a lithium secondary battery according to Example 1 and Comparative Example 1. Fig. 5 is a graph showing a voltage change of a lithium secondary battery according to Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The electrolyte solution for a lithium secondary battery according to embodiments of the present disclosure contains an additive containing a compound having a specific structure, an organic solvent, and a lithium salt.

[0028] Furthermore, a lithium secondary battery according to embodiments includes an electrode assembly including repeatedly stacked cathodes and anodes, and the electrolyte solution for a lithium secondary battery impregnating the electrode assembly.

[0029] Accordingly, the fast charging performance, service life and high-temperature storage properties of the lithium secondary battery can be improved.

[0030] As used herein, the term “A-based compound” may refer to a compound containing A and a derivative of that compound.

[0031] Embodiments of the present disclosure will be described in more detail below with reference to detailed examples and drawings. However, the present inventive concepts are not limited to the specific embodiments disclosed herein. <Elektrolytlösung für eine Lithium-Sekundärbatterie>

[0032] An electrolytic solution for a lithium secondary battery (hereinafter abbreviated as electrolytic solution) according to embodiments of the present disclosure may contain an additive containing a compound having a structure represented by Chemical Formula 1, an organic solvent, and a lithium salt. Additive

[0033] The electrolyte solution for a lithium secondary battery according to embodiments may contain an additive containing a compound having a structure represented by Chemical Formula 1.

[0034] In the chemical formula 1, R 1 to R 4 each independently of one another is a C1 to C10 alkyl group in which at least one hydrogen atom is substituted by a halogen atom, and M + can be a cesium cation, a potassium cation, a lithium cation, a sodium cation or a rubidium cation.

[0035] For example, R 1to R 4 each independently of one another be a C1 to C8 alkyl group in which at least one hydrogen atom is substituted by the halogen atom, a C1 to C5 alkyl group in which at least one hydrogen atom is substituted by the halogen atom, or a C1 to C3 alkyl group in which at least one hydrogen atom is substituted by the halogen atom.

[0036] The halogen atom can be, for example, a fluorine atom, a chlorine atom, a bromine atom or an iodine atom.

[0037] In one embodiment, the halogen atom may be a fluorine atom.

[0038] M + can be, for example, the cesium or potassium cation.

[0039] In some embodiments, R 1 to R 4 each independently be a C1 to C10 alkyl group in which all hydrogen atoms are substituted by halogen atoms.

[0040] For example, R 1 to R 4each independently of one another be a C1 to C8 alkyl group in which all hydrogen atoms are substituted by halogen atoms, a C1 to C5 alkyl group in which all hydrogen atoms are substituted by halogen atoms, or a C1 to C3 alkyl group in which all hydrogen atoms are substituted by halogen atoms.

[0041] For example, R 1 to R 4 each independently of one another be a C1 to C10 alkyl group in which all hydrogen atoms are substituted by fluorine atoms, a C1 to C8 alkyl group in which all hydrogen atoms are substituted by fluorine atoms, a C1 to C5 alkyl group in which all hydrogen atoms are substituted by fluorine atoms, or a C1 to C3 alkyl group in which all hydrogen atoms are substituted by fluorine atoms.

[0042] In one embodiment, R 1 to R 4 all be a trifluoromethyl group.

[0043] In some embodiments, the compound having the structure represented by Chemical Formula 1 may include a compound having a structure represented by Chemical Formula 2-1 or 2-2.

[0044] For example, the additive containing the compound having the structure represented by Chemical Formula 1 can be introduced into the electrolyte solution, and a uniform and highly ion-conductive solid electrolyte interphase (SEI) film can be formed on an electrode surface.

[0045] For example, a film with BO bonding exhibits high ionic conductivity, which reduces battery resistance and improves fast charging performance.

[0046] For example, an alkali metal cation such as the cesium cation contained in the compound must not be reduced in order to prevent the formation of a lithium dendrite and thus form a uniform and low-resistance film.

[0047] This can improve the fast charging performance, service life and high-temperature storage properties of the lithium secondary battery.

[0048] In some embodiments, the content of the additive may range from 0.1 weight percent (wt%) to 10 wt% based on the total weight of the electrolyte solution.

[0049] The content of the additive may, for example, be in a range from 0.2 to 8 wt%, from 0.3 to 5 wt%, from 0.4 to 3 wt%, from 0.5 to 2 wt% or from 0.1 to 2 wt%, based on the total weight of the electrolyte solution.

[0050] In the above range, the SEI film with uniform and high ionic conductivity can be formed, and the mobility of lithium ions and the activity of the cathode active material cannot be hindered. Auxiliary additive

[0051] The electrolyte solution for a lithium secondary battery according to embodiments may further contain an auxiliary additive containing a carbonate-based cyclic compound, a fluorine-containing carbonate-based compound, a sultone-based compound, a sulfate-based compound, a sulfite-based cyclic compound, a lithium phosphate-based compound, and / or a borate-based compound.

[0052] In some embodiments, the electrolyte solution may further contain the auxiliary additive containing the fluorine-containing carbonate-based compound, the lithium phosphate-based compound, the sultone-based compound, and / or the sulfate-based compound.

[0053] The additive described above can be used together with the auxiliary additive, so that the lithium secondary battery with further improved high-temperature storage properties can be efficiently realized.

[0054] The carbonate-based cyclic compound may include, for example, vinylene carbonate (VC), vinylethylene carbonate (VEC), etc.

[0055] For example, the fluorine-containing carbonate-based compound may contain a fluorine atom or a substituent having a fluorine atom bonded to at least one carbon atom of the carbonate-based compound (for example, a fluorine-substituted alkyl group such as -CF3).

[0056] In some embodiments, the fluorine-containing carbonate-based compound may include a fluorine-containing cyclic carbonate-based compound having a cyclic structure. For example, the fluorine-containing cyclic carbonate-based compound may have a cyclic structure with 5 to 7 members.

[0057] The fluorine-containing cyclic carbonate-based compound may, for example, contain fluoroethylene carbonate (FEC).

[0058] In some embodiments, the lithium phosphate-based compound may include a fluorine-containing lithium phosphate-based compound.

[0059] For example, the fluorine-containing lithium phosphate-based compound may contain a fluorine atom or a substituent group having a fluorine atom (for example, a fluorine-substituted alkyl group such as CF3) bonded to a phosphorus atom of the lithium phosphate-based compound.

[0060] In some embodiments, the fluorine-containing lithium phosphate-based compound may include lithium difluorophosphate (LiPO2F2), lithium difluoro(bisoxalato)phosphate, etc. For example, the fluorine-containing lithium phosphate-based compound may include lithium difluorophosphate (LiPO2F2).

[0061] In some embodiments, the sultone-based compound may contain at least one compound selected from the group consisting of an alkyl sultone-based compound and an alkenyl sultone-based compound.

[0062] In some embodiments, the sultone-based compound may contain both the alkyl sultone-based compound and the alkenyl sultone-based compound.

[0063] The alkyl sultone-based compound may contain, for example, 1,3-propane sultone (PS) and 1,4-butane sultone.

[0064] The alkenyl sultone-based compounds include, for example, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone and 1-methyl-1,3-propene sultone.

[0065] In some embodiments, the sulfate-based compound may include a cyclic sulfate-based compound having a cyclic structure. The cyclic sulfate-based compound may have a 5- to 7-membered cyclic structure.

[0066] The cyclic sulfate-based compounds include, for example, 1,2-ethylene sulfate (ESA), trimethylene sulfate (TMS), 1,2-propylene sulfate and methyltrimethylene sulfate (MTMS).

[0067] The cyclic sulfite-based compounds may contain, for example, ethylene sulfite, butylene sulfite, etc.

[0068] The borate-based compound may, for example, contain lithium bis(oxalato)borate.

[0069] In one embodiment, the content of the auxiliary additive may be in a range of 0.01 wt% to 10 wt% based on the total weight of the electrolyte solution.

[0070] The content of the auxiliary additive may, for example, be in a range from 0.05 wt% to 9 wt%, from 0.5 wt% to 8 wt%, from 0.8 wt% to 7 wt%, from 1.0 wt% to 6 wt% or from 1.5 wt% to 5 wt%, based on the total weight of the electrolyte solution.

[0071] In the above-mentioned range, the durability of the SEI can be improved even without the effect of the additive.

[0072] In some embodiments, the weight ratio between the auxiliary additive and the additive in the electrolyte solution may be in a range of 0.1 to 5.

[0073] The weight ratio can, for example, be in a range of 0.2 to 4.8, 0.3 to 4.5, 0.4 to 4.0, or 0.5 to 3.5. Within the above range, the high-temperature storage and cycle life characteristics of the lithium secondary battery can be further improved.

[0074] In one embodiment, the auxiliary additive may contain the fluorine-containing carbonate-based compound, the lithium phosphate-based compound, the sultone-based compound, and the sulfate-based compound together.

[0075] In some embodiments, the auxiliary additive may further include at least one compound selected from the group consisting of a borate-based compound, a nitrile-based compound, an amine-based compound, a silane-based compound, and a benzene-based compound.

[0076] The borate-based compound may, for example, contain at least one compound from the group consisting of lithium tetraphenylborate and lithium difluoro(oxalato)borate (LiODFB).

[0077] The nitrile-based compound may include, for example, succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, etc. These can be used alone or in a combination of two or more of them.

[0078] The amine-based compound may contain, for example, triethanolamine, ethylenediamine, etc.

[0079] The silane-based compound may, for example, contain tetravinylsilane.

[0080] For example, the benzene-based compound may contain at least one compound selected from the group consisting of monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene. Organic solvent and lithium salt

[0081] The organic solvent may, for example, contain an organic compound that has sufficient solubility for the lithium salt, the additive and the auxiliary additive and must not be reactive in the lithium secondary battery.

[0082] In some embodiments, the organic solvent may include a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and / or an aprotic solvent.

[0083] In some embodiments, the organic solvent may include the carbonate-based solvent, and the carbonate-based solvent may include a linear carbonate-based solvent and a cyclic carbonate-based solvent.

[0084] The linear carbonate-based solvent includes, for example, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, etc.

[0085] The cyclic carbonate-based solvent may include, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, etc.

[0086] In some embodiments, the amount of linear carbonate-based solvent may be greater than or equal to the amount of cyclic carbonate-based solvent based on the total volume of organic solvent.

[0087] In some embodiments, the volume ratio between the volume of the cyclic carbonate-based solvent and that of the linear carbonate-based solvent in the organic solvent may be in the range of 1 / 9 to 1. For example, the volume ratio may be 1 / 9 to 1, 1 / 9 to 2 / 3, 1 / 6 to 2 / 3, or 1 / 4 to 2 / 3. Within the above range, the high-temperature storage properties of the lithium secondary battery can be further improved.

[0088] The ester-based solvent may, for example, contain at least one of methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), γ-butyrolactone (GBL), decanolide, valerolactone, mevalonolactone, and caprolactone.

[0089] The ether-based solvent may, for example, contain at least one of dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), and 2-methyltetrahydrofuran.

[0090] The ketone-based solvent may contain, for example, cyclohexanone.

[0091] The alcohol-based solvent may, for example, contain at least one of ethyl alcohol or isopropyl alcohol.

[0092] The aprotic solvent may, for example, include a nitrile-based solvent, an amide-based solvent (for example, dimethylformamide), a dioxolane-based solvent (for example, 1,3-dioxolane) and / or a sulfolane-based solvent.

[0093] In some embodiments, the electrolyte solution may contain the lithium salt.

[0094] The lithium salt can be replaced by Li + X -An anion of the lithium salt X - can 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 - , (CF3CF2SO2)2N - , etc.

[0095] In some embodiments, the lithium salt may contain at least one of LiBF4 and LiPF6.

[0096] In some embodiments, the lithium salt may be present at a concentration of 0.01 M to 5 M, 0.01 M to 4 M, 0.5 M to 3 M, or 0.5 M to 2 M, based on the organic solvent. In the above-mentioned concentration range, the mobility of lithium ions and / or electrons during charging and discharging of the lithium secondary battery may be facilitated. <Lithium-Sekundärbatterie>

[0097] Fig. 1 and Fig. 2 are a schematic plan view and a cross-sectional view showing a lithium secondary battery according to embodiments. Fig. 2 is a cross-sectional view along line II' of Fig. 1.

[0098] With reference to Fig. 1 and Fig. 2, the lithium secondary battery may include an electrode assembly 150 having a cathode 100, an anode 130, and a separator 140 disposed between the cathode and the anode.

[0099] For example, the electrode assembly 150 may include the cathode 100 and the anode 130 repeatedly stacked on top of each other, and the electrode assembly 150 may contain the electrolyte solution according to the embodiments described above in a case 160 to be soaked therein in the case 160.

[0100] The cathode 100 may include a cathode current collector 105 and a cathode active material layer 110 disposed on at least one surface of the cathode current collector 105.

[0101] The cathode current collector 105 may, for example, contain stainless steel, nickel, aluminum, titanium, or an alloy thereof. The cathode current collector 105 may include a surface treated with carbon, nickel, titanium, silver, etc., made of aluminum or stainless steel. The thickness of the cathode current collector 105 may, for example, be in a range of 10 µm to 50 µm.

[0102] The cathode active material may contain a compound capable of reversibly intercalating and deintercalating lithium ions.

[0103] In embodiments, the cathode active material may contain a lithium nickel metal oxide. The lithium nickel metal oxide may also contain at least one of the elements cobalt (Co), manganese (Mn), and aluminum (Al).

[0104] In some embodiments, the cathode active material or the lithium nickel metal oxide may include a layered structure or a crystal structure according to Chemical Formula 3 below. Li x Ni a M b O 2+z [Chemical Formula 3]

[0105] In chemical formula 3, 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b≤0.4, and -0.5≤z≤0.1. As described above, M may contain Co, Mn, and / or Al.

[0106] The chemical structure represented by Chemical Formula 3 represents a bonding relationship contained in the layered structure or crystal structure of the cathode active material or lithium-transition nickel metal oxide particle, and does not exclude other additional elements. For example, M contains Co and / or Mn, and Co and / or Mn can serve as the main active element of the cathode active material together with Ni. Chemical Formula 3 is used to express the bonding relationship of the main active element and should be understood as a formula that includes the introduction and substitution of additional elements.

[0107] In one embodiment, in addition to the main active element, an auxiliary element may be included to improve the chemical stability of the cathode active material or the layered / crystal structure. The auxiliary element may be incorporated into the layered / crystal structure to form a bond, and this case is understood to fall within the scope of the chemical structure represented by Chemical Formula 3.

[0108] The auxiliary element may, for example, contain at least one of the following elements: Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P and Zr. The auxiliary element may serve as an active auxiliary element, such as Al, which together with Co or Mn contributes to the capacity / power activity of the cathode active material.

[0109] For example, the cathode active material or the lithium transition metal oxide particle may contain a layered structure or a crystal structure of the chemical formula 3-1. Li x Ni a M1 b1 M2 b2 O 2+z [Chemical Formula 3-1]

[0110] In Chemical Formula 3-1, M1 may contain Co, Mn, and / or Al. M2 may contain the auxiliary element described above. In Chemical Formula 3-1, 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b1+b2≤0.4, and -0.5≤z≤0.1.

[0111] The cathode active material described above may further contain a doping element. For example, elements that are substantially identical or similar to the auxiliary elements described above may be used as the doping element. For example, the elements described above may be used alone or in a combination of two or more of them.

[0112] The doping element may be present on a surface of the lithium transition metal oxide particle or may penetrate through the surface of the lithium transition metal oxide particle to be contained in the bonding structure represented by Chemical Formula 3 or Chemical Formula 3-1.

[0113] The cathode active material can contain a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content can be used.

[0114] Ni can be considered as a transition metal with respect to the performance and capacity of the lithium secondary battery. Thus, as described above, a high-capacity cathode and a high-capacity lithium secondary battery can be realized by using a high-Ni composition in the cathode active material.

[0115] However, with increasing Ni content, the long-term storage stability and lifetime of the cathode or secondary battery may deteriorate relatively, and side reactions with an electrolyte may also increase. However, according to embodiments, lifetime stability and capacity retention characteristics can be improved using Mn while maintaining electrical conductivity with Co.

[0116] The Ni content in the NCM-based lithium oxide (e.g., a mole fraction of nickel relative to the total moles of nickel, cobalt, and manganese) may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content may be in a range from 0.8 to 0.95, from 0.82 to 0.95, from 0.83 to 0.95, from 0.84 to 0.95, from 0.85 to 0.95, or from 0.88 to 0.95.

[0117] In some embodiments, the cathode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0118] In some embodiments, the cathode active material may include, for example, a Mn-rich active material having a chemical structure or a crystal structure represented by Chemical Formula 4, a Li-rich layered oxide (LLO) / OLO (Over-Lithiated Oxide)-based active material, a Co-free (Co-less)-based active material, etc. p[L 12 MnO3]·(1-p)[Li q JO2] [Chemical Formula 4]

[0119] In chemical formula 4: 0 <p<1, 0,9≤q≤1,2, und J kann mindestens ein Element aus Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg und B enthalten.

[0120] For example, a cathode mixture can be prepared by dispersing the active cathode material in a solvent. The cathode mixture can be coated onto the cathode current collector 105 and then dried and pressed to form the cathode 100. The coating process can include gravure coating, slot die coating, multi-layer simultaneous coating, embossing, doctor blade coating, dip coating, bar coating, casting, etc.

[0121] The cathode mixture may also contain a binder and optionally a conductive material, a thickener, etc.

[0122] Non-limiting examples of the solvent in the preparation of the cathode mixture are N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0123] The binder may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethyl methacrylate, acrylonitrile-butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PVDF-based binder may be used as the cathode binder.

[0124] The conductive material can be added to improve the conductivity of the cathode mixture layer and / or the mobility of lithium ions or electrons. The conductive material can, for example, include a carbon-based conductive material such as graphite, carbon black, acetylene black, Ketjen black, graphene, a carbon nanotube, a VGCF (vapor-grown carbon fiber), a carbon fiber, etc., and / or a metal-based conductive material such as tin, tin oxide, titanium oxide, a perovskite material including LaSrCoO3, LaSrMnO3, etc.

[0125] Carboxymethylcellulose (CMC), for example, can be used as a thickener.

[0126] The anode 130 may include an anode current collector 125 and an anode active material layer 120 disposed on at least one surface of the anode current collector 125.

[0127] Non-limiting examples of the anode current collector 125 may include, for example, a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, etc. The thickness of the anode current collector 135 may, for example, be in a range of 10 µm to 50 µm.

[0128] The anode active material layer 120 may contain an anode active material. A material capable of adsorbing and desorbing lithium ions may be used as the anode active material. The anode active material may include, for example, a carbon-based material such as crystalline carbon, amorphous carbon, a carbon composite, carbon fiber, etc.; a lithium metal; a lithium alloy; a silicon (Si)-containing material; or tin (Sn)-containing materials, etc.

[0129] The amorphous carbon may include, for example, hard carbon, soft carbon, coke, a mesocarbon microbead (MCMB), a mesophase pitch-based carbon fiber (MPCF), etc.

[0130] The crystalline carbon may include, for example, natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0131] The lithium metal may include pure lithium metal or a lithium metal with a protective layer formed thereon to prevent dendrite growth. In one embodiment, a lithium metal-containing layer deposited or coated on an anode current collector may be used as the anode active material layer 120. In one embodiment, a lithium thin-film layer may be used as the anode active material layer.

[0132] An element that may be contained in the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0133] The silicon-containing material can provide increased capacity. The silicon-containing material can be Si, a SiOx (0 <x<2), metalldotiertes Silikat oder SiOx (0<x<2), einen Silizium-Kohlenstoff-Verbundstoff usw. enthalten. Das Metall kann Lithium und / oder Magnesium enthalten.

[0134] For example, an anode mixture can be prepared by mixing the anode active material in a solvent. The anode mixture can be coated / deposited onto the anode current collector and then dried and pressed to form the anode. The coating process can include gravure coating, slot die coating, multi-layer simultaneous coating, embossing, doctor blade coating, dip coating, bar coating, casting, etc.

[0135] The anode mixture may also contain a binder and, if appropriate, a conductive material, a thickener, etc.

[0136] Non-limiting examples of the solvent for the anode mixture include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc.

[0137] The materials described above that can be used in the manufacture of the cathode can also be used as binders, conductive materials and thickeners.

[0138] In some embodiments, the anode binder may include a styrene-butadiene rubber (SBR)-based binder, carboxymethylcellulose (CMC), a polyacrylic acid-based binder, a poly(3,4-ethylenedioxythiophene) (PEDOT)-based binder, etc.

[0139] In some embodiments, a separator 140 may be disposed between the cathode 100 and the anode 130. The separator may prevent an electrical short circuit between the cathode 100 and the anode 130 while maintaining ion flow. The thickness of the separator may be, for example, 10 µm to 20 µm.

[0140] The separator 140 may, for example, include a porous polymer film or a porous nonwoven fabric. The porous polymer film may include a polyolefin-based polymer such as an ethylene polymer, a propylene polymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc.

[0141] The porous nonwoven fabric may contain a high melting point glass fiber, a polyethylene terephthalate fiber, etc.

[0142] The separator 140 may contain a ceramic-based material. For example, inorganic particles may be coated onto the polymer film or dispersed within the polymer film to improve heat resistance.

[0143] The separator 140 may have a single- or multi-layer structure containing the polymer film and / or nonwoven fabric described above.

[0144] In embodiments, the cathode 100, the anode 130, and the separator 140 may be repeatedly arranged to form the electrode assembly 150. In some embodiments, the electrode assembly 150 may be formed by winding, stacking, Z-folding, or stack-folding the separator 140.

[0145] In one embodiment, the electrode assembly 150 may be in the form of a jelly roll formed by winding the cathode 100, the anode 130, and the separator 140 together. In one embodiment, the electrode assembly 150 may be in the form of a jelly roll in which notched anodes and cathodes are arranged in a space formed by repeatedly Z-folding the separator 140.

[0146] In one embodiment, the electrode assembly may be formed by repeatedly stacking the cathode 100, the anode 130, and the separator 140, which are cut or separated at each level.

[0147] For example, electrode strips (a cathode strip and an anode strip) may protrude from each of the cathode current collector 105 and the anode current collector 125 toward one side of the housing 160. The electrode strips may be welded to one side of the housing 160 to connect to an electrode lead (a cathode lead 107 and an anode lead 127), which may be extended or exposed toward the outside of the housing 160.

[0148] For example, a bag-like housing, a prismatic housing, a cylindrical housing, a coin-like housing, etc. can be used.

[0149] The electrode assembly 150 is housed in the case 160 together with the electrolyte solution described above to form a lithium secondary battery.

[0150] Exemplary experimental examples are proposed below to more concretely describe the present disclosure. However, the following examples are only illustrative of the present invention, and those skilled in the art will naturally understand that various changes and modifications are possible within the scope and spirit of the present invention. Such changes and modifications are properly encompassed in the appended claims. <synthesebeispiel>(1) Preparation of Additive I (Cesium tetrakis(2,2,2-trifluoroacetoxy)borate)

[0151] 0.41 g (6.6 mmol) of boric acid was added to a 10 mL solution of anhydrous dimethyl carbonate in which 1.6 g (6.5 mmol) of cesium trifluoroacetate was dispersed, and the mixture was cooled to 0°C. Then, 5.0 g (24 mmol) of trifluoroacetic anhydride was slowly added to obtain a transparent solution, a reflux condenser was connected, the temperature was raised to 80°C, and the mixture was stirred for 6 hours.

[0152] A concentrate obtained by drying the stirred solution was dissolved in tetrahydrofuran, solidified by adding dichloromethane, and then filtered to obtain 3.5 g of Additive I (yield 90%) in the form of a white solid and having the structure represented by the following chemical formula 2-1.

[0153] 19 F NMR (470MHz, DMSO-d6): δ -75.8 (s, 12F) (Cesium tetrakis(2,2,2-trifluoroacetoxy)borate)(2) Preparation of Additive II (Potassium tetrakis(2,2,2-trifluoroacetoxy)borate)

[0154] 0.41 g (6.6 mmol) of boric acid was added to a 10 mL solution of anhydrous dimethyl carbonate in which 1.0 g (6.6 mmol) of potassium trifluoroacetate was dispersed, and the mixture was cooled to 0°C. Trifluoroacetic anhydride (5.0 g, 24 mmol) was then slowly added to obtain a transparent solution, a reflux condenser was connected, the temperature was raised to 80°C, and the mixture was stirred for 6 hours.

[0155] A concentrate obtained by drying the stirred solution was dissolved in tetrahydrofuran, solidified by adding dichloromethane, and then filtered to obtain 3.0 g of Additive II (yield 90%) in the form of a white solid having the structure of the following chemical formula 2-2.

[0156] 19 F NMR (470MHz, DMSO-d6): δ -75.8 (s, 12F) (Potassium tetrakis(2,2,2-trifluoroacetoxy)borate)<Beispiel und Vergleichsbeispiele> Example 1(1) Preparation of the electrolyte solution

[0157] A 1M LiPF6 solution (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) mixed solvent in a volume ratio of 25:75) was prepared.

[0158] Based on the total weight of the electrolytic solution (100 wt%), 1 wt% of fluoroethylene carbonate (FEC), 1 wt% of lithium difluorophosphate, 0.5 wt% of 1,3-propenesultone (PRS), 0.5 wt% of 1,3-propanesultone (PS), and 0.5 wt% of 1,2-ethylene sulfate (ESA) were added to the LiPF6 solution, and 1 wt% of Additive I (cesium tetrakis(2,2,2-trifluoroacetoxy)borate) according to the above Synthesis Example was added to prepare an electrolytic solution. (2) Preparation of lithium secondary battery samples

[0159] An active cathode material containing a mixture of Li[Ni ,6 Co 0,2 Mn 0,2 ]O2 and Li[Ni 0,8 Co 0,1 Mn 0,1 ]O2 in a weight ratio of 6:4, a conductive carbon black, and a polyvinylidene fluoride (PVDF) binder was mixed and dispersed in an NMP solvent in a weight ratio of 92:5:3 to form a cathode slurry.

[0160] An aluminum foil (thickness: 15 µm) with a protrusion (a cathode strip) on one side was prepared. The cathode slurry was evenly applied to an area of ​​the aluminum foil excluding the protrusion, dried, and then pressed to form a cathode.

[0161] An active anode material containing artificial graphite and natural graphite in a weight ratio of 7:3, a styrene-butadiene rubber (SBR) binder, and a carboxymethyl cellulose (CMC) thickener was mixed in distilled water in a weight ratio of 97:1:2 to prepare an anode slurry.

[0162] A copper foil (thickness: 15 µm) with a protrusion (an anode strip) on one side was prepared. The anode slurry was evenly applied to an area of ​​the copper foil excluding the protrusion, dried, and pressed into an anode.

[0163] An electrode assembly was formed by inserting a polyethylene separator (20 µm thick) between the cathode and anode. A cathode lead and an anode lead were welded and connected to the cathode strip and the anode strip, respectively.

[0164] The electrode assembly was placed in a bag (case) so that parts of the cathode lead and the anode lead were exposed to the outside, and three sides except for one electrolyte injection side were sealed.

[0165] A lithium secondary battery sample was prepared by injecting the electrolyte solution prepared as above (1), sealing the electrolyte injection side, and performing impregnation in the electrolyte solution for 12 hours. Example 2

[0166] An electrolyte solution and a lithium secondary battery sample were prepared by the same method as in Example 1, except that 1 wt% of Additive II (potassium tetrakis(2,2,2-trifluoroacetoxy)borate) according to the above Synthesis Example was used instead of Additive I. Comparison example 1

[0167] An electrolyte solution and a lithium secondary battery sample were prepared according to the same procedure as in Example 1, except that Additive I was not used. Comparison example 2

[0168] An electrolytic solution was prepared by the same method as in Example 1, except that 1 wt% of a compound having a structure represented by the following chemical formula 5 was used instead of Additive I. Comparison example 3

[0169] An electrolytic solution was prepared by the same method as in Example 1, except that 1 wt% of a compound having a structure represented by the following chemical formula 6 was used instead of Additive I. <Experimentelle Beispiele> Experimental Example 1: XPS analysis of the anode

[0170] The anode of the lithium secondary battery according to Example 1 and Comparative Example 1 was analyzed by X-ray photoelectron spectroscopy (XPS) (ESCALAB 250Xi, manufactured by Thermo Scientific) to determine the presence or absence of a cesium element and a BO bond.

[0171] Fig. 3 is a graph showing peaks appearing in a Cs-1s spectrum in an XPS measurement of anodes of a lithium secondary battery according to Example 1 and Comparative Example 1.

[0172] Fig. 4 is a graph showing peaks in a B-1s spectrum in an XPS measurement of anodes of a lithium secondary battery according to Example 1 and Comparative Example 1.

[0173] Referring to Fig. 3, in the XPS measurement for the anode of the lithium secondary battery according to Example 1 and Comparative Example 1, a peak of 726.4 eV was observed, which represents the cesium element (Cs 3d 5 / 2 ) was not detected. Therefore, it can be assumed that a cesium cation was not reduced.

[0174] Referring to Fig. 4, in the XPS measurement of the anode of the lithium secondary battery according to Example 1 and Comparative Example 1, a peak of 191.5 eV indicating the BO bond was higher in the anode of Example 1 than in the anode of Comparative Example 1. Therefore, it can be considered that an SEI film containing the BO bond was formed on the anode of the lithium secondary battery according to Example 1. Test Example 2: Initial Performance Evaluation (Room Temperature, 25°C)(1) Initial Capacity Evaluation (Room Temperature, 25°C)

[0175] The lithium secondary batteries of the examples and comparative examples were charged three times with 0.5C CC / CV (4.2V, 0.05C cut-off) and then discharged with 0.5C CC (2.7V cut-off).

[0176] The initial capacity of the lithium secondary battery was measured as a discharge capacity value at the third cycle. (2) Assessment of internal resistance (DCIR)

[0177] At a SOC point of 60%, the C-rate was changed to 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, or 3.0C. When charging and discharging at the corresponding C-rate were performed for 10 seconds, the endpoint voltage was estimated by a straight line equation, and the slope was adopted as the DCIR. Experimental Example 3: Evaluation of fast charging performance (room temperature, 25°C)

[0178] For the lithium secondary batteries of the examples and comparative examples, a voltage (V) was differentiated by a capacity (Q) from SOC 8% to SOC 80%, ranging from 1C rate to 3C rate. After monitoring the change rate (dV / dQ) for each SOC, a lithium plating point was predicted. By adjusting the optimal charging current and depth of charge, an expected QC time was derived.

[0179] Fig. 5 is a graph showing a voltage change of a lithium secondary battery according to Example 1.

[0180] Referring to Fig. 5, in the first charge / discharge cycle of the lithium secondary battery according to Example 1, a reduction / decomposition peak appeared at 0.7 V. Therefore, it can be considered that Additive I contained in the electrolyte solution of Example 1 was reduced and decomposed to form an SEI film. Experimental Example 4: Evaluation of lifetime (45°C)(1) Evaluation of capacity retention

[0181] The lithium secondary batteries of the examples and comparative examples were charged at 1C to 4.2V and discharged at 1C to 2.75V at 45°C. The charging and discharging processes were repeated 400 times, and the discharge capacity was measured at the 400th cycle.

[0182] Capacity retention was calculated as a percentage of the discharge capacity at the 400th cycle relative to the initial capacity measured in (1) of Experimental Example 2. Test Example 5: Evaluation of high-temperature storage properties (60°C)

[0183] The following evaluation was conducted on the lithium secondary batteries of the examples and comparative examples "after high-temperature storage," in which the lithium secondary batteries were stored in a constant-temperature device in air at 60°C for 12 weeks and then left at room temperature for another 30 minutes. (1) Assessment of capacity retention (Ret) after high-temperature storage

[0184] The charged lithium secondary batteries of Examples and Comparative Examples were discharged at a rate of 0.5C CC (2.7V cut-off) after high-temperature storage to measure a discharge capacity.

[0185] The capacity retention was calculated as a percentage of the discharge capacity after high-temperature storage relative to the initial capacity measured in (1) of Experimental Example 2. (2) Assessment of capacity recovery (Rec) after high-temperature storage

[0186] After measuring the capacity retention according to (1) for the lithium secondary batteries of Examples and Comparative Examples, a 0.5C rate CC / CV charge (4.2V, 0.05C cut-off) and a 0.5C rate CC discharge (2.7V cut-off) were performed to measure a discharge capacity.

[0187] The capacity recovery was calculated as a percentage of the measured discharge capacity relative to the initial capacity measured in (1) of Experimental Example 2.

[0188] The evaluation results are shown in Table 1. [Table 1] Example 1 Example 2 Comparison example 1 Initial performance Capacity (mAh) 1930 1912 1923 C_DCIR (mΩ) 31,2 32,0 32,6 D_DCIR (mΩ) 32,8 33,2 35,1 Fast charging performance 1 ) QC time (min.) 26,6 27,3 28,0 45°C lifetime 2 ) (400 cycles) Ret. (%) 88,4 85,5 85,5 60°C storage 3 ) (12 weeks) Ret. (%) 82,6 84,3 80,2 Rec. (%) 86,6 86,0 83,5 1) Step-by-step charging SOC 8-80% at 25°C 2) 1C / 1C 400 cycles at 45°C 3) 60°C Storage: 60°C SOC100% 12 weeks

[0189] As shown in Table 1, the lithium secondary batteries of the examples improved the initial performance (reduction in resistance), fast charging performance, cycle life (increased capacity retention), and high-temperature storage properties (60°C) (increased capacity retention and capacity recovery).

[0190] In the lithium secondary battery of Comparative Example 1, which did not contain the additive containing the compound with the specific structure, the initial resistance became high, the QC time was prolonged, and the capacity retention and recovery after storage at high temperatures (60°C) were reduced.< / synthesebeispiel>

Claims

[1] An electrolyte solution for a lithium secondary battery, comprising: an additive containing a compound having a structure represented by chemical formula 1; an organic solvent; and a lithium salt: where in the chemical formula 1 R 1 to R 4 are each independently a C1 to C10 alkyl group in which at least one hydrogen atom is substituted by a halogen atom, and M + is a cesium, potassium, lithium, sodium or rubidium cation. [2] The electrolytic solution for a lithium secondary battery according to claim 1, wherein R 1 to R 4 are each independently a C1 to C10 alkyl group in which all hydrogen atoms are substituted by halogen atoms. [3] An electrolytic solution for a lithium secondary battery according to claim 1 or claim 2, wherein the halogen atom is a fluorine atom and M +the cesium cation or the potassium cation. [4] An electrolyte solution for a lithium secondary battery according to any one of the preceding claims, wherein R 1 to R 4 are each independently a C1 to C5 alkyl group in which all hydrogen atoms are substituted by fluorine atoms. [5] An electrolytic solution for a lithium secondary battery according to any one of the preceding claims, wherein the compound having the structure represented by Chemical Formula 1 contains a compound having a structure represented by Chemical Formula 2-1 or Chemical Formula 2-2: [6] The electrolytic solution for a lithium secondary battery according to any one of the preceding claims, wherein the organic solvent contains at least one selected from the group consisting of a carbonate-based organic solvent, an ester-based organic solvent, an ether-based organic solvent, a ketone-based organic solvent, and an aprotic organic solvent. [7] An electrolytic solution for a lithium secondary battery according to any one of the preceding claims, wherein the organic solvent contains a cyclic carbonate-based solvent and a linear carbonate-based solvent. [8] The electrolytic solution for a lithium secondary battery according to claim 7, wherein the volume ratio of the cyclic carbonate-based solvent to the linear carbonate-based solvent in the organic solvent is in the range of 1 / 9 to 1. [9] The electrolytic solution for a lithium secondary battery according to any one of the preceding claims, wherein the content of the additive is in a range of 0.1 wt% to 10 wt% based on the total weight of the electrolytic solution. [10] An electrolytic solution for a lithium secondary battery according to any preceding claim, wherein the electrolytic solution further contains at least one auxiliary additive selected from the group consisting of a fluorine-containing carbonate-based compound, a lithium phosphate-based compound, a sultone-based compound, and a sulfate-based compound. [11] The electrolytic solution for a lithium secondary battery according to claim 10, wherein the content of the auxiliary additive is in a range of 0.01 wt% to 10 wt% based on the total weight of the electrolytic solution. [12] The electrolytic solution for a lithium secondary battery according to claim 10 or claim 11, wherein the weight ratio of the auxiliary additive relative to the additive in the electrolytic solution is in the range of 0.1 to 5. [13] Lithium secondary battery, comprising: an electrode assembly containing repeatedly stacked cathodes and anodes; and the electrolyte solution for a lithium secondary battery according to any one of the preceding claims, which impregnates the electrode assembly.

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