Electrolyte for lithium secondary battery and method for manufacturing same

Abstract

An electrolyte for a secondary battery according to exemplary embodiments comprises a lithium salt, an organic solvent, a trifluoromethanesulfonic anhydride (Tf2O), and a copolymer comprising a repeating unit represented by a predetermined chemical formula.

Description

Electrolyte for lithium secondary batteries and method for producing the same

[0001] The present invention relates to an electrolyte for a lithium secondary battery and a method for manufacturing the same.

[0002]

[0003] Secondary batteries, which can be repeatedly charged and discharged, are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptops, thanks to the advancements in the information and communication and display industries. Furthermore, battery packs containing secondary batteries are being developed and applied as power sources for eco-friendly vehicles such as hybrid vehicles.

[0004] Examples of secondary batteries include secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among these, secondary batteries are being actively developed and applied because they have high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and weight reduction.

[0005] For example, a secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator, and an electrolyte that impregnates the electrode assembly. The secondary battery may further include an outer packaging material, for example, in the form of a pouch, that accommodates the electrode assembly and the electrolyte.

[0006] Meanwhile, secondary batteries can experience structural deformation of lithium metal oxides and side reactions in the electrolyte due to repeated charging and discharging. Consequently, the life characteristics (e.g., capacity retention) of secondary batteries can deteriorate.

[0007] Accordingly, there is a need to develop electrolytes for secondary batteries that simultaneously improve stability and electrochemical properties.

[0008]

[0009] One object of the present invention is to provide an electrolyte for a lithium secondary battery having improved stability and electrical properties.

[0010] An object of the present invention is to provide a lithium secondary battery having improved stability and electrical characteristics.

[0011] One object of the present invention is to provide a method for manufacturing an electrolyte for a secondary battery having improved stability and electrical properties.

[0012]

[0013] An electrolyte for a secondary battery according to exemplary embodiments of the present invention comprises a lithium salt, an organic solvent, trifluoromethanesulfonic anhydride (Tf2O), and a copolymer comprising at least one repeating unit selected from the group consisting of a repeating unit represented by the following chemical formula 1, a repeating unit represented by the following chemical formula 2, a repeating unit represented by the following chemical formula 3, and a repeating unit represented by the following chemical formula 4.

[0014] [Chemical Formula 1]

[0015]

[0016] In chemical formula 1, n1 is a natural number, R 1 is an alkyl group having 1 to 6 carbon atoms.

[0017] [Chemical Formula 2]

[0018]

[0019] In chemical formula 2, n2 is a natural number, A 1 is a hydrogen or hydroxy group.

[0020] [Chemical Formula 3]

[0021]

[0022] In chemical formula 3, n3 is a natural number, R 2 is an organic group having 1 to 10 carbon atoms in which at least one H is replaced by F.

[0023] [Chemical Formula 4]

[0024]

[0025] In chemical formula 4, n4 is a natural number, R 3 is an organic group having 1 to 10 carbon atoms in which at least one H is replaced by F.

[0026] In some embodiments, the repeating unit represented by the above chemical formula 1 may include a repeating unit represented by the following chemical formula 1-1.

[0027] [Chemical Formula 1-1]

[0028]

[0029] In some embodiments, the repeating unit represented by the above chemical formula 2 may include a repeating unit represented by the following chemical formula 2-1.

[0030] [Chemical Formula 2-1]

[0031]

[0032] In some embodiments, the repeating unit represented by the above chemical formula 3 may include at least one of the repeating units represented by the following chemical formulas 3-1 to 3-6.

[0033] [Chemical Formula 3-1]

[0034]

[0035] [Chemical Formula 3-2]

[0036]

[0037] [Chemical Formula 3-3]

[0038]

[0039] [Chemical Formula 3-4]

[0040]

[0041] [Chemical Formula 3-5]

[0042]

[0043] [Chemical Formula 3-6]

[0044]

[0045] In some embodiments, the repeating unit represented by the above chemical formula 4 may include at least one of the repeating units represented by the following chemical formulas 4-1 to 4-3.

[0046] [Chemical Formula 4-1]

[0047]

[0048] [Chemical Formula 4-2]

[0049]

[0050] [Chemical Formula 4-3]

[0051]

[0052] In some embodiments, the lithium salt is LiPF6, LiClO4, LiBF4, LiFSI, LiTFSI, LiSO3CF3, LiBOB, LiFOB, LiDFOB, LiDFBP, LiTFOP, LiPO2F2, LiCl, LiBr, LiI, LiB 10 Cl 10 , LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN and LiC(CF3SO2)3.

[0053] In some embodiments, the organic solvent may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0054] In some embodiments, the content of the copolymer in the total weight of the electrolyte for the secondary battery may be 0.1 wt% to 10 wt%.

[0055] In some embodiments, the electrolyte for the secondary battery may include a gel form.

[0056] A secondary battery according to exemplary embodiments includes a positive electrode, a negative electrode opposite to the positive electrode, and an electrolyte for a secondary battery as described above.

[0057] According to a method for manufacturing an electrolyte for a secondary battery according to exemplary embodiments, a first mixture may be manufactured by mixing an organic solvent and the above-described copolymer. A second mixture may be manufactured by mixing a lithium salt and trifluoromethanesulfonic anhydride (Tf2O) with the first mixture. An electrolyte for a secondary battery may be manufactured by crosslinking the second mixture.

[0058] In some embodiments, the cross-linking step may be performed at 20° C. to 80° C.

[0059] In some embodiments, the cross-linking step may be performed in less than 200 hours.

[0060]

[0061] According to exemplary embodiments, an electrolyte for a secondary battery may include a copolymer including a repeating unit containing a cyano group and a repeating unit containing fluorine, and trifluoromethanesulfonic anhydride (Tf2O). Accordingly, room temperature gelation can be realized, and the range of application of the lithium salt can be improved. In addition, the stability, flame retardancy, and lifespan characteristics of a secondary battery including the electrolyte can be improved.

[0062]

[0063] Figure 1 is a schematic diagram of in-situ polymerization before and after the addition of trifluoromethanesulfonic anhydride (Tf2O) at room temperature.

[0064] Figures 2 to 5 are copolymers of Examples 1 to 4, respectively. 1 H-nuclear magnetic resonance spectroscopy ( 1 H Nuclear Magnetic Resonance, 1 These are H-NMR) graphs.

[0065] Figure 6 shows Fourier-transform infrared spectroscopy (FT-IR) graphs according to the concentration of Tf2O in the electrolyte of Example 4.

[0066] Figure 7 is a graph of discharge capacity and Coulombic efficiency (η) according to the number of cycles of Example 5 and Comparative Examples 5 and 6 at high temperature (60°C).

[0067]

[0068] Exemplary embodiments of the present invention provide an electrolyte for a secondary battery comprising an organic solvent, trifluoromethanesulfonic anhydride (Tf2O), a lithium salt, and a copolymer comprising a predetermined repeating unit.

[0069]

[0070] Electrolyte for secondary batteries

[0071] An electrolyte for a lithium secondary battery according to exemplary embodiments (secondary, which may be abbreviated as “electrolyte”) comprises an organic solvent, Tf2O, a lithium salt, and a copolymer including a cyano group.

[0072] As a comparative example, LiPF6 may be included instead of the Tf2O. In this case, gelation of the electrolyte is performed at high temperatures, and the available lithium salt may be limited.

[0073] In exemplary embodiments, gelation can be performed at room temperature (25° C.) using the Tf2O, and various types of lithium salts other than LiPF6 can be included in the electrolyte.

[0074] The gelation of the above comparative example can be represented by the following reaction mechanism 1, and the gelation using Tf2O can be represented by the following reaction mechanism 2.

[0075] [Reaction Mechanism 1]

[0076]

[0077] [Reaction Mechanism 2]

[0078]

[0079] According to exemplary embodiments, the copolymer including the cyano group may include a repeating unit represented by the following chemical formula 1.

[0080] [Chemical Formula 1]

[0081]

[0082] In chemical formula 1, n1 is a natural number, R 1 is an alkyl group having 1 to 6 carbon atoms. The repeating unit represented by the above chemical formula 1 includes a cyano group (-C≡N, cyano group), and thus the gel properties and electrochemical properties of an electrolyte including it can be improved.

[0083] According to one embodiment, the repeating unit represented by the above chemical formula 1 may include a repeating unit represented by the following chemical formula 1-1.

[0084] [Chemical Formula 1-1]

[0085]

[0086] According to some embodiments, the copolymer may include at least one repeating unit selected from the group consisting of a repeating unit represented by the following chemical formula 2, a repeating unit represented by the following chemical formula 3, and a repeating unit represented by the following chemical formula 4.

[0087] [Chemical Formula 2]

[0088]

[0089] In chemical formula 2, n2 is a natural number, A 1 is a hydrogen or hydroxy group.

[0090] [Chemical Formula 3]

[0091]

[0092] In chemical formula 3, n3 is a natural number, R 2 is an organic group having 1 to 10 carbon atoms in which at least one H is replaced by F.

[0093] [Chemical Formula 4]

[0094]

[0095] In chemical formula 4, n4 is a natural number, R 3 is an organic group having 1 to 10 carbon atoms in which at least one H is replaced by F.

[0096] For example, a copolymer containing a repeating unit represented by Chemical Formula 3 or Chemical Formula 4 may have a relatively large fluorine (F) content, thereby improving the flame retardancy and lifespan characteristics of the electrolyte.

[0097] According to one embodiment, the repeating unit represented by the above chemical formula 2 may include a repeating unit represented by the following chemical formula 2-1.

[0098] [Chemical Formula 2-1]

[0099]

[0100] Accordingly, the solubility of the electrolyte can be improved and the crosslinking speed can be increased.

[0101] According to some embodiments, the repeating unit represented by the above chemical formula 3 may include at least one of the repeating units represented by the following chemical formulas 3-1 to 3-6.

[0102] [Chemical Formula 3-1]

[0103]

[0104] [Chemical Formula 3-2]

[0105]

[0106] [Chemical Formula 3-3]

[0107]

[0108] [Chemical Formula 3-4]

[0109]

[0110] [Chemical Formula 3-5]

[0111]

[0112] [Chemical Formula 3-6]

[0113]

[0114] According to some embodiments, the repeating unit represented by the above chemical formula 4 may include at least one of the repeating units represented by the following chemical formulas 4-1 to 4-3.

[0115] [Chemical Formula 4-1]

[0116]

[0117] [Chemical Formula 4-2]

[0118]

[0119] [Chemical Formula 4-3]

[0120]

[0121] In one embodiment, the copolymer may include at least one of the repeating units represented by Chemical Formulae 3-1 to 3-6 and Chemical Formulae 4-1 to 4-3. Accordingly, the electrochemical properties of the electrolyte and the lifespan characteristics of the secondary battery may be improved.

[0122] For example, a copolymer containing a cyano group can be expressed as a PVA (polyvinyl alcohol)-CN copolymer.

[0123] For example, a copolymer containing a cyano group can be formed by reacting a base copolymer containing vinyl alcohol and a vinyloxyalkyl containing a cyano group, and a fluorine-containing compound. For example, the base copolymer can include repeating units represented by the chemical formulas 1-1 and 2-1.

[0124] For example, the fluorine-containing compound may include trifluoroacetic anhydride, pentafluoropropionic anhydride, heptafluorobutyric anhydride, 4-(trifluoromethoxy)benzoic acid, pentafluorobenzoic acid, bis(pentafluorophenyl) carbonate, trifluoromethanesulfonyl chloride, pentafluorobenzenesulfonylchloride, bis(trifluoromethyl)benzenesulfonylchloride, and the like.

[0125] In exemplary embodiments, a method for preparing a copolymer comprising a cyano group may include an esterification reaction of the base copolymer and a fluorine-containing compound.

[0126] For example, the above esterification reaction can be performed by introducing a coupling agent.

[0127] The coupling agent may include, for example, carbodiimide-based, pyridine-based, and amine-based compounds. For example, the coupling agent may include pyridine, dicyclohexylcarbodiimide (DCC), ethyldimethylaminopropyl carboxyimide, hydroxysuccinimide, diisopropylcarbodiimide (DIC), 4-dimethylaminopyridine, triethylamine, 2-chloro-1-methylpyridinium iodide, and the like.

[0128] In one embodiment, the coupling agent may include pyridine, triethylamine, or the like.

[0129] In some embodiments, the reaction for producing a copolymer containing a cyano group by reacting a base copolymer and a fluorine-containing compound can be represented by, for example, the following manufacturing formulas 1 to 9.

[0130] [Manufacturing Formula 1]

[0131]

[0132] [Manufacturing Formula 2]

[0133]

[0134] [Manufacturing Formula 3]

[0135]

[0136] [Manufacturing Formula 4]

[0137]

[0138] [Manufacturing Formula 5]

[0139]

[0140] [Manufacturing Formula 6]

[0141]

[0142] [Manufacturing Formula 7]

[0143]

[0144] [Manufacturing Formula 8]

[0145]

[0146] [Manufacturing Formula 9]

[0147]

[0148] Among the above manufacturing methods 1 to 9, R 1 is an alkyl group having 1 to 6 carbon atoms.

[0149] For example, the number average molecular weight of the copolymer including the cyano group may be 10,000 g / mol to 1,000,000 g / mol, specifically 10,000 g / mol to 300,000 g / mol, and more specifically 10,000 g / mol to 200,000 g / mol. Within the above range, the ionic conductivity, mechanical strength, electrical conductivity, heat resistance, and chemical resistance of the electrolyte may be improved.

[0150] In exemplary embodiments, the electrolyte described above may comprise a gel form.

[0151] For example, the electrolyte can be crosslinked in the presence of a lithium salt and an organic solvent.

[0152] According to some embodiments, the crosslinking reaction of the electrolyte may be performed at a temperature of 20° C. to 80° C., specifically at a temperature of 20° C. to 60° C., and more specifically at a temperature of 25° C. to 45° C. Accordingly, the electrolyte may be gelled, thereby improving the chemical resistance and mechanical strength of the electrolyte.

[0153] For example, the cross-linking reaction can be performed within a secondary battery.

[0154] According to some embodiments, the content of the copolymer including a cyano group in the total weight of the electrolyte may be 0.1 wt% to 10 wt%, specifically 0.1 wt% to 5 wt%, and more specifically 0.5 wt% to 3 wt%. Within this range, gelation of the electrolyte may be facilitated and electrical conductivity may be improved.

[0155] In some embodiments, the lithium salt is LiPF6, LiClO4, LiBF4, LiFSI, LiTFSI, LiSO3CF3, LiBOB, LiFOB, LiDFOB, LiDFBP, LiTFOP, LiPO2F2, LiCl, LiBr, LiI, LiB 10 Cl 10, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, LiC(CF3SO2)3, etc.

[0156] In one embodiment, the lithium salt may comprise LiTFSI.

[0157] In one embodiment, the lithium salt may comprise LiDFOB.

[0158] The concentration of the lithium salt dissolved in the organic solvent may be 0.5 M to 3 M, specifically 0.8 M to 1.5 M, and more specifically 0.8 M to 1.3 M. In the above range, the concentration of the electrolyte can be appropriately controlled by the lithium salt in the organic solvent, and the crosslinking reaction can be sufficiently performed.

[0159] In some embodiments, the organic solvent may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like.

[0160] In one embodiment, the organic solvent may include DMC, EC, EMC, and the like, and specifically may include EC, EMC, or a mixed organic solvent thereof.

[0161] The mixed organic solvent of the above EC and EMC may have a volume ratio of 1:1 to 1:10, specifically 1:1 to 1:5, and more specifically 1:2 to 1:3. An electrolyte including the above-described organic solvent may have improved electrochemical stability, oxidation resistance, and reduction resistance, thereby minimizing decomposition during the charge and discharge process of a secondary battery.

[0162] <Manufacturing method>

[0163] According to exemplary embodiments, an electrolyte for a secondary battery can be prepared by mixing an organic solvent and the above-described copolymer to form a first mixture. A lithium salt and trifluoromethanesulfonic anhydride (Tf2O) can be mixed with the first mixture to form a second mixture. The second mixture can be crosslinked to form an electrolyte.

[0164] In some embodiments, the cross-linking step may be performed for less than 500 hours, specifically less than 300 hours, and more specifically less than 200 hours. If the cross-linking step takes too long, there is a risk of electrolyte volatilization and cathode structural collapse.

[0165] Secondary battery

[0166] Hereinafter, the present invention will describe a secondary battery including a positive electrode, a negative electrode, and the above-described electrolyte. The present invention provides a secondary battery including a positive electrode, a negative electrode opposite to the positive electrode, and a gel polymer electrolyte disposed between the positive electrode and the negative electrode. The secondary battery can be manufactured by manufacturing an electrode assembly by interposing a separator between the positive electrode and the negative electrode, then injecting the assembled electrode assembly and the gel polymer electrolyte forming composition of the present invention into a battery case, and performing a crosslinking reaction (thermal polymerization) of the crosslinking compound.

[0167] For example, the secondary battery may be a lithium ion battery, a lithium battery, a sodium battery, a zinc battery, a potassium battery, a magnesium battery, a capacitor, a solar battery, a wind power battery, etc.

[0168] The above positive electrode may include a positive electrode active material. The lithium transition metal oxide is a compound capable of reversible intercalation and deintercalation of lithium, and may be a lithium cobalt-based oxide (e.g., LiCoO2, etc.), a lithium nickel-based oxide (e.g., LiNiO2, etc.), a lithium manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (here, 0 <Y<1), LiMn 2-z Ni z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn 2-z1 Co z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2(wherein, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni p1 Co q1 Mn r2 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2) etc.), lithium-nickel-cobalt-manganese-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2)O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of independent elements, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1) etc.), nickel-lithium transition metal composite oxide, lithium manganese-rich oxide, lithium iron phosphate (e.g., LiFePO4 etc.), and overlithiated layered oxide (OLO).

[0169] The above high nickel lithium transition metal composite oxide may contain nickel in an amount of 50 mol% or more, specifically 60 mol% or more, based on the total mole number of transition metals included in the lithium transition metal composite oxide. Specifically, the high nickel lithium transition metal composite oxide may contain nickel as the transition metal; and at least one selected from manganese, cobalt, and aluminum, and may contain nickel in an amount of 50 mol% or more, specifically 60 mol% or more, and more specifically 60 mol% to 90 mol%, based on the total mole number of transition metals.

[0170] Additionally, the lithium transition metal oxide may include a compound represented by the following chemical formula A.

[0171] [Chemical Formula A]

[0172] Li 1+x (Ni a Co b Mn c M d )O2

[0173] In the above chemical formula A, M is at least one selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and 1+x, a, b, c and d are atomic fractions of independent elements, respectively, 0≤x≤0.2, 0.50≤a<1, 0 <b≤0.30, 0<c≤0.30, 0≤d≤0.1, a+b+c+d=1이다. 바람직하게는, 상기 a, b, c 및 d는 각각 0.60≤a≤0.95, 0.025≤b≤0.25, 0.025≤c≤0.25, 0≤d≤0.05일 수 있다. 또한, 상기 a, b, c 및 d는 각각 0.80≤a≤0.95, 0.025≤b≤0.15, 0.025≤c≤0.15, 0≤d≤0.05일 수 있다. 또한, 상기 a, b, c 및 d는 각각 0.85≤a≤0.90, 0.05≤b≤0.10, 0.05≤c≤0.10, 0≤d≤0.03일 수 있다.

[0174] The lithium transition metal oxide may include a lithium manganese-rich oxide. The lithium manganese-rich oxide may include manganese in an amount of 50 mol% or more among all metals excluding lithium, and the molar ratio of lithium to the transition metal may exceed 1. Specifically, the lithium manganese-rich oxide may include a compound represented by the following chemical formula B.

[0175] [Chemical Formula B]

[0176] Li 1+s [Ni t Co u Mn v M 1 w ]O 2+z

[0177] In the above chemical formula B, 0.05≤s≤1, 0≤t≤0.5, 0≤u≤0.3, 0.5≤v<1.0, 0≤w≤0.2, 0≤z≤1. Or 0.05≤s≤1.0, 0.1≤t≤0.5, 0≤u≤0.1, 0.5≤v<1.0, 0≤w≤0.2, 0≤z≤1, or 0.10≤s≤0.50, 0.1≤t≤0.5, 0≤u≤0.1, 0.6≤v<1.0, 0≤w≤0.1, 0≤z≤0.50. M 1 It may be at least one selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo.

[0178] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. In this case, the positive electrode active material layer may include the positive electrode active material.

[0179] The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and an aluminum-cadmium alloy, or aluminum.

[0180] The above-described positive electrode current collector may typically have a thickness of 3 μm to 500 μm. The positive electrode current collector may have fine irregularities formed on its surface to enhance the bonding strength of the negative electrode active material. For example, the positive electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0181] The positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one or both surfaces of the positive electrode current collector. The positive electrode active material may be included in the positive electrode active material layer at 80 wt% to 99 wt%, or 92 wt% to 98.5 wt%, taking into account sufficient capacity of the positive electrode active material, etc.

[0182] Additionally, the thickness of the positive electrode active material layer may be 30 µm to 400 µm, or 40 µm to 110 µm.

[0183] The above-described positive electrode active material layer may further include a binder and / or a conductive material together with the above-described positive electrode active material.

[0184] The above binder is a component that assists in the binding of the active material and the conductive material and the binding to the current collector, and specifically, may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride. The binder may be included in the positive electrode active material layer in an amount of 1 wt% to 20 wt%, preferably 1.2 wt% to 10 wt%, in order to sufficiently secure binding force between components such as the positive electrode active material.

[0185] The conductive material may be used to assist and improve conductivity in a secondary battery, and is not particularly limited as long as it has conductivity without causing chemical changes. Specifically, the positive electrode conductive material may include at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, etc.; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives, or may include carbon black in terms of improving conductivity. The conductive material may be included in the positive electrode active material layer in an amount of 1 wt% to 20 wt%, or 1.2 wt% to 10 wt%, in terms of sufficiently securing electrical conductivity.

[0186] The positive electrode can be manufactured by coating a positive electrode slurry containing a positive electrode active material and optionally a binder, a conductive material, and a solvent for forming a positive electrode slurry on the positive electrode current collector, followed by drying and rolling. The solvent for forming the positive electrode slurry can include an organic solvent such as NMP (N-methyl-2-pyrrolidone). The solid content of the positive electrode slurry can be 40 wt% to 90 wt%, specifically 50 wt% to 80 wt%.

[0187] The above cathode may be opposite to the above anode.

[0188] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0189] The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. The negative electrode current collector may typically have a thickness of 3 to 500 μm.

[0190] The above-described negative electrode current collector can form fine irregularities on its surface to strengthen the bonding strength of the negative electrode active material. For example, the above-described negative electrode current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0191] The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one or both surfaces of the negative electrode current collector.

[0192] The above negative electrode active material layer may include a negative electrode active material.

[0193] The above negative electrode active material is a material capable of reversibly inserting / de-inserting lithium ions, and may include at least one selected from the group consisting of carbon-based active materials, (semi)metal-based active materials, and lithium metal, and specifically may include at least one selected from among carbon-based active materials and (semi)metal-based active materials.

[0194] The above carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, or may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0195] The average particle diameter (D) of the above carbon-based active material 50) may be 10 ㎛ to 30 ㎛, preferably 15 ㎛ to 25 ㎛, in order to ensure structural stability during charging and discharging and reduce side reactions with the electrolyte.

[0196] For example, the (semi-)metal-based active material may include at least one (semi-)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of lithium with at least one (semi-)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an oxide of at least one (semi-)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; lithium titanium oxide (LTO); lithium vanadium oxide; etc.

[0197] The above silicon-based active material is SiO x (0≤x<2) may include a compound represented by SiO2. Since SiO2 does not react with lithium ions and thus cannot store lithium, x may be within the above range, or the silicon-based active material may be SiO. The average particle diameter (D) of the silicon-based active material 50 ) may be 1 ㎛ to 30 ㎛, or 2 ㎛ to 15 ㎛, in order to reduce side reactions with the electrolyte while ensuring structural stability during charge and discharge.

[0198] The above negative active material may be included in the negative active material layer at 60 wt% to 99 wt%, or 75 wt% to 95 wt%.

[0199] Additionally, the thickness of the negative active material layer may be 10 µm to 100 µm, or 50 µm to 80 µm.

[0200] The above negative electrode active material layer may further include a binder and / or a conductive material together with the negative electrode active material.

[0201] The above binder is used to improve the performance of the battery by improving the adhesion between the negative electrode active material layer and the negative electrode current collector, and may include, for example, at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and materials in which hydrogens of these are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof. May include.

[0202] The above binder may be included in the negative electrode active material layer in an amount of 0.5 wt% to 10 wt%, or 1 wt% to 5 wt%.

[0203] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, and the like; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0204] The above conductive material may be included in the negative electrode active material layer in an amount of 0.5 wt% to 10 wt%, or 1 wt% to 5 wt%.

[0205] The above negative electrode can be manufactured by coating a negative electrode slurry including a negative electrode active material, a binder, a conductive material and / or a solvent for forming a negative electrode slurry on at least one surface of a negative electrode current collector, and then drying and rolling.

[0206] The solvent for forming the negative electrode slurry may include at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol, and isopropyl alcohol, specifically NMP, in order to facilitate dispersion of the negative electrode active material, binder, and / or conductive material, for example. The solid content of the negative electrode slurry may be 30 wt% to 80 wt%, specifically 40 wt% to 70 wt%.

[0207] For example, the electrolyte is positioned between the negative electrode and the positive electrode of a secondary battery, and can form a crosslinked polymer gel electrolyte through a crosslinking reaction in the secondary battery.

[0208] For example, in secondary batteries, the aforementioned electrolyte forms a film on the negative electrode, protecting it, thereby reducing the risk of explosion and fire. Furthermore, by suppressing side reactions between the negative electrode and electrolyte, deterioration of the negative electrode is prevented, thereby improving its lifespan.

[0209] For example, the secondary battery according to the invention can have improved life characteristics compared to a lithium secondary battery using a conventional liquid electrolyte.

[0210] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the invention. However, the present invention may be implemented in various different forms, and the embodiments described herein are merely illustrative of the present invention and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and technical idea of ​​the present invention, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0211] Manufacturing example: Manufacturing of a copolymer containing a cyano group

[0212] (1) Preparation of copolymer containing cyano group (A-1)

[0213] A mixed solution was prepared by adding 15 mL of DMF (N,N-Dimethylmethanamide) and PVA-CN (Poly[Vinylachol-co-3-(vinyloxy)propanenitrile], 1 g, 0.0055 mol) to a 50 mL round-bottom flask and stirring.

[0214] After adding TEA (triethylamine, 2.2 mL, 0.0165 mol) and DAMP (deoxyadenosine monophosphate, 0.1 g, 0.000825 mol) to the prepared mixed solution, trifluoroacetic anhydride (1.2 mL, 0.00825 mol), a fluorine-containing compound, was added, and the mixture was reacted at 30°C for 2 hours. After completion of the reaction, the precipitate was filtered, and the remaining polymer solution was precipitated in ethanol, and then dried in a vacuum oven at 60°C to prepare a copolymer A-1 including a cyano group including a repeating unit represented by Chemical Formula 2-1 and a repeating unit represented by Chemical Formula 3-1.

[0215] (2) Preparation of copolymer containing cyano group (A-2)

[0216] A copolymer A-2 including a cyano group including a repeating unit represented by Chemical Formula 2-1 and a repeating unit represented by Chemical Formula 3-2 was prepared using the same method as the copolymer A-1 including a cyano group, except that pentafluoropropionic anhydride (1.6 mL, 0.00825 mol) was added instead of trifluoroacetic anhydride as the fluorine-containing compound, and pyridine (1.329 mL, 0.0165 mol) was added instead of TEA (triethylamine, 2.2 mL, 0.0165 mol), and the reaction was performed at 30°C for 16 hours.

[0217] (3) Preparation of copolymer containing cyano group (A-3)

[0218] A copolymer A-2 including a cyano group including a repeating unit represented by Chemical Formula 2-1 and a repeating unit represented by Chemical Formula 3-4 was prepared using the same method as the copolymer A-1 including a cyano group, except that heptafluorobutyric anhydride (2 mL, 0.00825 mol) was added instead of trifluoroacetic anhydride as the fluorine-containing compound, and pyridine (1.329 mL, 0.0165 mol) was added instead of TEA (triethylamine, 2.2 mL, 0.0165 mol), and the reaction was performed at 30°C for 72 hours.

[0219]

[0220] Example 1

[0221] A preliminary solution was prepared by adding 2 wt% of PVA-CN relative to the total weight of the electrolyte to an organic solvent in which EC and EMC were mixed in a volume ratio of 3:7.

[0222] Tf2O was added to the above-mentioned preliminary solution to prepare electrolytes having Tf2O contents of 0.5 wt%, 1 wt%, 2 wt%, and 3 wt% relative to the total weight, respectively.

[0223] Example 2

[0224] An electrolyte was prepared in the same manner as in Example 1, except that A-1 was used instead of PVA-CN.

[0225] Example 3

[0226] An electrolyte was prepared in the same manner as in Example 1, except that A-2 was used instead of PVA-CN.

[0227] Example 4

[0228] An electrolyte was prepared in the same manner as in Example 1, except that A-3 was used instead of PVA-CN.

[0229] Comparative Example 1

[0230] A 1M LiPF6 solution (pre-electrolyte) was prepared using an organic solvent containing EC and EMC mixed in a volume ratio of 3:7.

[0231] PVA-CN was added to the above-mentioned preliminary electrolyte to prepare an electrolyte having a PVA-CN content of 2 wt% relative to the total weight.

[0232] Comparative Example 2

[0233] An electrolyte was prepared in the same manner as in Comparative Example 1, except that an equivalent amount of A-1 was used instead of PVA-CN.

[0234] Comparative Example 3

[0235] An electrolyte was prepared in the same manner as in Comparative Example 1, except that an equivalent amount of A-2 was used instead of PVA-CN.

[0236] Comparative Example 4

[0237] An electrolyte was prepared in the same manner as in Comparative Example 1, except that an equivalent amount of A-3 was used instead of PVA-CN.

[0238]

[0239] Experimental Example 1: Confirmation of Room Temperature Gelation

[0240] (1) 1 H-NMR analysis

[0241] For the copolymers of Examples 1 to 4, using Avance Varian III 300 (300 MHz) equipment (Bruker) 1 H-NMR analysis was performed.

[0242] Figures 2 to 5 are copolymers of Examples 1 to 4, respectively. 1 H-Nuclear Magnetic Resonance Spectroscopy 1 These are H-NMR) graphs.

[0243] Referring to FIGS. 2 to 5, a peak (4.3 to 4.5 ppm) corresponding to an OH group was observed in the PVA-CN of Example 1, but no peak corresponding to an OH group was observed in the copolymers A-1 to A-3 of Examples 2 to 4. Accordingly, high-purity synthesis of the copolymers A-1 to A-3 was confirmed.

[0244] (2) FT-IR analysis

[0245] For the electrolyte of Example 4, FT-IR analysis was performed using Nicolet 6700 (Thermo Fisher Scientific).

[0246] Fig. 6 is a Fourier-transform infrared spectroscopy (FT-IR) graph according to the Tf2O concentration of electrolytes derived from Example 4. Specifically, Fig. 6 is a FT-IR graph of electrolytes derived from Example 4 in which 0 wt% (not added), 2 wt%, 3 wt%, and 4 wt% of Tf2O were added to the electrolyte of Example 4 relative to the total weight of the electrolyte.

[0247] Referring to Fig. 6, as the amount of Tf2O added increased, the degree of gelation increased, and the electrolyte was sufficiently gelled even at room temperature.

[0248] For example, the C≡N bond may be converted to a C=N bond by the reaction of the copolymer and Tf2O. Accordingly, the peak intensity of the C=N bond relative to the peak intensity of the C≡N bond may indicate the degree of room temperature gelation of the electrolyte.

[0249]

[0250] Experimental Example 2: Gelation time at 25 ℃

[0251] A gelation reaction was performed at 25°C for the electrolyte manufactured according to the examples and comparative examples, and the time from the start of the reaction to the end of the reaction (gelation time) is shown in Table 1 below.

[0252] In Table 1, “> 2 weeks” indicates that the gelation time exceeds 2 weeks.

[0253] Example: Gelation time (25 ℃) according to Tf2O concentration Comparative example: Gelation time (25 ℃) in 1M LiPF6 0.5 wt% 1 wt% 2 wt% 3 wt% PVA-CN Example 1 Within 3 minutes (immediately) Within 3 minutes (immediately) Within 3 minutes (immediately) Comparative example 1> 2 weeks A-1 Example 2 129 h 80 h 72 h 34 h Comparative example 2> 2 weeks A-2 Example 3 180 h 140 h 100 h 60 h Comparative example 3> 2 weeks A-3 Example 4- 180 h 120 h 72 h Comparative example 4> 2 weeks

[0254] Experimental Example 3: Gelation time at 45 ℃

[0255] The gelation time at 45°C of the electrolytes manufactured according to the examples and comparative examples is shown in Table 2 below.

[0256] Example: Gelation time (45 ℃) according to Tf2O concentration Comparative example: Gelation time (45 ℃) in 1M LiPF6 0.5 wt% 1 wt% 2 wt% 3 wt% PVA-CN Example 1 Within 3 minutes (immediately) Within 3 minutes (immediately) Within 3 minutes (immediately) Comparative example 127 h A-1 Example 248 h 24 h 23 h 12 h Comparative example 280 h A-2 Example 3 110 hr 80 hr 50 hr 20 hr Comparative example 3 140 h A-3 Example 4-103 h 64 h 24 h Comparative example 4 157 h

[0257] In the examples containing Tf2O, the gelation time at room temperature and high temperature was reduced overall compared to the comparative examples containing LiPF6.

[0258]

[0259] Experimental Example 4: Evaluation of Output Characteristics and Lifetime Characteristics

[0260] Example 5

[0261] 1) Positive electrode manufacturing

[0262] Lithium Iron Phosphate (LiFePO4, hereinafter referred to as LFP), PVDF, and super-P were mixed in a mass ratio of 8:1:1, respectively, and then uniformly dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry.

[0263] The above slurry was applied onto aluminum foil, dried in a vacuum oven at 120°C for 12 hours, and loaded at a density of 7 mg / cm2. After loading, a hole having a diameter of 12.5 mm was formed to manufacture an anode.

[0264] 2) Cathode manufacturing

[0265] A negative electrode was manufactured by forming a hole with a diameter of 14 mm in a lithium metal foil with a thickness of 50 ㎛.

[0266] 3) Electrolyte manufacturing

[0267] A solution (electrolyte 1) containing 1 M LiTFSI and 0.2 M LiDFOB was prepared using an organic solvent containing EC and EMC in a volume ratio of 3:7.

[0268] Tf2O was added to the electrolyte 1 to prepare electrolyte 2 having a Tf2O content of 1 wt% relative to the total weight.

[0269] A-3 was added to the above electrolyte 2 to prepare electrolyte 3 having an A-3 content of 2 wt% relative to the total weight.

[0270] The above electrolyte 3 was used as the electrolyte of Example 5.

[0271] 4) Secondary battery manufacturing

[0272] A coin-type secondary battery was manufactured by placing electrolyte 3 between the positive electrode and the negative electrode.

[0273] For the secondary battery, initial charge / discharge was performed under the conditions of an operating voltage range of 2.8 V to 4 V, a charge / discharge rate of 0.1 C-rate (0.1 C: 170 mA / g), and an operating temperature of 25°C. After the initial charge / discharge, a cross-linking reaction was performed for a certain period of time at 25°C to 45°C to manufacture a secondary battery having a gel-type electrolyte.

[0274] Comparative Example 5

[0275] A secondary battery was manufactured in the same manner as in Example 5, except that electrolyte 1 was used instead of electrolyte 3.

[0276] Comparative Example 6

[0277] A secondary battery was manufactured in the same manner as in Example 5, except that electrolyte 2 was used instead of electrolyte 3.

[0278]

[0279] Capacity retention rate evaluation

[0280] Secondary batteries were charged to 4 V at a high temperature (60°C) with a 1 C constant current, charged at a 0.05 C constant voltage, and then discharged to 2.8 V at a 1 C constant current, which was considered one cycle. The capacity retention rates after 75 cycles for each of the secondary batteries of Example 5 and Comparative Examples 5 and 6 were calculated. The capacity retention rate was evaluated by dividing the discharge capacity of the 75th cycle by the discharge capacity of the first cycle and multiplying by 100.

[0281] The above capacity retention rate is shown in Table 3 and Fig. 7 below.

[0282] Coulomb efficiency measurement

[0283] Coulombic efficiency was measured by dividing the discharge capacity by the charge capacity for each cycle and multiplying by 100. The Coulombic efficiency was measured at high temperature (60°C) and is shown in Figure 7.

[0284] The results of evaluating the capacity retention rate and coulombic efficiency of the above-described examples and comparative examples at high temperature (60°C) are shown in Table 3 below.

[0285] Capacity retention rate (%) Coulomb efficiency (%) Example 596.2 99.3 Comparative example 594.1 99.1 Comparative example 690.3 99.5

[0286] Figure 7 is a graph of discharge capacity and Coulombic efficiency (η) according to the number of cycles of Example 5 and Comparative Examples 5 and 6 at high temperature (60°C).

[0287] Referring to Table 3 and Figure 7, in Example 5 using Tf2O and the present copolymer (A-3), the capacity retention rate was improved compared to Comparative Examples 5 and 6, and the Coulombic efficiency was improved compared to Comparative Example 5.

Claims

1. Lithium salt; organic solvent; Trifluoromethanesulfonic anhydride (Tf2O); and An electrolyte for a secondary battery, comprising a copolymer comprising at least one repeating unit selected from the group consisting of a repeating unit represented by the following chemical formula 1, a repeating unit represented by the following chemical formula 2, a repeating unit represented by the following chemical formula 3, and a repeating unit represented by the following chemical formula 4: [Chemical Formula 1] (In chemical formula 1, n1 is a natural number, R 1 is an alkyl group having 1 to 6 carbon atoms) [Chemical Formula 2] (In chemical formula 2, n2 is a natural number, A 1 is hydrogen or hydroxy group) [Chemical Formula 3] (In chemical formula 3, n3 is a natural number, R 2 is an organic group having 1 to 10 carbon atoms in which at least one H is replaced by F) [Chemical Formula 4] (In chemical formula 4, n4 is a natural number, R 3 is an organic group having 1 to 10 carbon atoms in which at least one H is replaced by F).

2. In claim 1, the repeating unit represented by the chemical formula 1 includes a repeating unit represented by the following chemical formula 1-1, an electrolyte for a secondary battery: [Chemical Formula 1-1] 3. In claim 1, the repeating unit represented by the chemical formula 2 includes a repeating unit represented by the following chemical formula 2-1, an electrolyte for a secondary battery: [Chemical Formula 2-1] 4. In claim 1, the repeating unit represented by the chemical formula 3 comprises at least one of the repeating units represented by the chemical formulas 3-1 to 3-6 below, an electrolyte for a secondary battery: [Chemical Formula 3-1] [Chemical Formula 3-2] [Chemical Formula 3-3] [Chemical Formula 3-4] [Chemical Formula 3-5] [Chemical Formula 3-6] 5. In claim 1, the repeating unit represented by the chemical formula 4 comprises at least one of the repeating units represented by the chemical formulas 4-1 to 4-3 below, an electrolyte for a secondary battery: [Chemical Formula 4-1] [Chemical Formula 4-2] [Chemical Formula 4-3] 6. In claim 1, the lithium salt is LiPF6, LiClO4, LiBF4, LiFSI, LiTFSI, LiSO3CF3, LiBOB, LiFOB, LiDFOB, LiDFBP, LiTFOP, LiPO2F2, LiCl, LiBr, LiI, LiB 10 Cl 10 An electrolyte for a secondary battery, comprising at least one selected from the group consisting of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, and LiC(CF3SO2)3.

7. An electrolyte for a secondary battery according to claim 1, wherein the organic solvent comprises at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

8. An electrolyte for a secondary battery according to claim 1, wherein the content of the copolymer in the total weight of the electrolyte for a secondary battery is 0.1 wt% to 10 wt%.

9. An electrolyte for a secondary battery, comprising a gel form, according to claim 1.

10. Bipolar; a cathode opposite to the anode; and A secondary battery comprising an electrolyte for a secondary battery according to claim 1.

11. A step of preparing a first mixture by mixing an organic solvent and a copolymer; A step of preparing a second mixture by mixing a lithium salt and trifluoromethanesulfonic anhydride (Tf2O) into the first mixture; and Comprising a step of crosslinking the second mixture to prepare an electrolyte, A method for producing an electrolyte for a secondary battery, wherein the copolymer comprises at least one repeating unit selected from the group consisting of a repeating unit represented by the following chemical formula 1, a repeating unit represented by the following chemical formula 2, a repeating unit represented by the following chemical formula 3, and a repeating unit represented by the following chemical formula 4. [Chemical Formula 1] (In chemical formula 1, n1 is a natural number, R 1 is an alkyl group having 1 to 6 carbon atoms) [Chemical Formula 2] (In chemical formula 2, n2 is a natural number, A 1 is hydrogen or hydroxy group) [Chemical Formula 3] (In chemical formula 3, n3 is a natural number, R 2 is an organic group having 1 to 10 carbon atoms in which at least one H is replaced by F) [Chemical Formula 4] (In chemical formula 4, n4 is a natural number, R 3 is an organic group having 1 to 10 carbon atoms in which at least one H is replaced by F).

12. A method for producing an electrolyte for a secondary battery according to claim 10, wherein the cross-linking step is performed at 20°C to 80°C.

13. A method for producing an electrolyte for a secondary battery according to claim 11, wherein the cross-linking step is performed for less than 200 hours.

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