Electrolyte solution and secondary battery containing same

Abstract

The present invention relates to an electrolyte solution comprising a lithium salt; a first solvent; and a second solvent, wherein, among Kamlet-Taft parameters of the first solvent and the second solvent, Lewis basicity is represented by β1 and β2, respectively, and β1 is 0.40 or more and β2 is 0.20 or less, and a secondary battery including the electrolyte solution.

Description

[Technical Field]

[0001] The present invention relates to an electrolyte solution and a secondary battery containing the same. [Background technology]

[0002] 2. Description of the Related Art With the rapid development of the electrical, electronic, communication and computer industries, the demand for high performance and high stability secondary batteries is increasing sharply.

[0003] A secondary battery has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is stacked or wound, and the electrode assembly is housed in a battery case into which an electrolyte is injected.

[0004] 2. Description of the Related Art Recently, in order to realize a secondary battery having a high capacity and a high energy density, various researches have been conducted on a lithium metal battery (LMB) using lithium metal as a negative electrode active material.

[0005] The lithium metal-containing anode used in the lithium metal battery has a large capacity relative to its volume or mass, making it an efficient material for reducing the volume and weight of the battery. It also has the advantage of being able to obtain a high battery voltage due to its lowest reduction potential among anode materials for lithium secondary batteries.

[0006] However, due to the high chemical / electrochemical reactivity of lithium metal, lithium metal can easily react with electrolytes, impurities, and lithium salts to form an electrochemically inactive solid electrolyte interphase (SEI) layer on the electrode surface. This electrochemically inactive solid electrolyte interphase can cause local current density differences, leading to the formation of lithium dendrite on the lithium metal surface. Furthermore, the lithium dendrite increases the contact area of ​​lithium metal with the electrolyte, increasing its reactivity and causing problems such as reduced stability, capacity, coulombic efficiency, and lifespan of the secondary battery.

[0007] To address this issue, efforts have been made to form a solid electrolyte interface with high electrochemical activity on the negative electrode containing lithium metal at the early stage of charge and discharge. Furthermore, in order to efficiently improve the performance of secondary batteries, attempts to form an inorganic-based solid electrolyte interface on the surface of the negative electrode containing lithium metal, rather than an organic-based interface, have become mainstream, and ongoing research is needed to further improve the performance of secondary batteries using this approach. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent Publication No. 2017-0028391 [Non-patent literature]

[0009] [Non-Patent Document 1] Ditchfield, R et al., The Journal of Chemical Physics 54, 724-728 (1971) Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been devised to solve the above-mentioned problems of the prior art, and provides a method for producing lithium ions (Li ions) in an electrolyte solution by using two or more co-solvents including a first solvent and a second solvent, the Lewis basicity of which satisfies a specific value among the Kamlet-Taft parameters of the first solvent and the second solvent. + The present invention aims to provide an electrolyte solution that can create a solvated environment in which anions are present around the negative electrode containing lithium metal, form a mechanically strong inorganic-based solid electrolyte interface on the negative electrode containing lithium metal, and further ensure the stability of the secondary battery even during long-term charging and discharging, while also improving the life characteristics. [Means for solving the problem]

[0011] According to one embodiment of the present invention, a solution containing a lithium salt, a first solvent, and a second solvent is provided. The solution contains Kamlet-Taft parameters of the first solvent and the second solvent, and Lewis basicity of the first solvent and the second solvent is represented by β1 and β2, respectively. β1 is 0.40 or more, and β2 is 0.20 or less. The volume ratio of the first solvent to the second solvent is 1:1 to 1:3. The lithium salt is selected from the group consisting of LiAsF6, LiFSI, LiTFSI, and LiCF3SO3. 、L iBF4, LiBF6, LiSbF6 , and LiN(C2F5SO2)2 mosquito and the lithium salt is present in an amount of 1 to 8 mol based on the total volume of the first solvent and the second solvent. the second solvent includes at least one selected from the group consisting of furan, anisole, and ethoxybenzene; An electrolyte is provided.

[0012] According to another embodiment of the present invention, a battery includes a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode includes lithium metal, and the electrolyte includes a lithium salt; a first solvent; and a second solvent, wherein the Lewis basicity of the Kamlet-Taft parameters of the first solvent and the second solvent is represented by β1 and β2, respectively, β1 is 0.40 or more, and β2 is 0.20 or less, a volume ratio of the first solvent to the second solvent is 1:1 to 1:3, and the lithium salt is LiAsF6, LiFSI, LiTFSI, or LiCF3SO3 、L iBF4, LiBF6, LiSbF6 , and LiN(C2F5SO2)2 mosquito and the lithium salt is present in an amount of 1 to 8 mol based on the total volume of the first solvent and the second solvent. The second solvent includes at least one selected from the group consisting of furan, anisole, and ethoxybenzene. , provides a secondary battery. [Effects of the Invention]

[0013] The electrolyte solution according to the present invention can form an inorganic-based solid electrolyte interface with high electrochemical activity on a lithium metal-containing anode, thereby minimizing detachment of the solid electrolyte interface even when a large volume change occurs during charging and discharging of the secondary battery. This can further enhance the stability of the anode, enabling stable operation of the anode over a long period of time.

[0014] In addition, the secondary battery according to the present invention can further improve its life characteristics by including an electrolyte solution having the above-described characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below through examples. The examples are not limited to the following examples, and may be modified in various ways as long as the gist of the invention is not changed.

[0016] In this specification, when a part "comprises" a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified.

[0017] Furthermore, all numerical ranges indicating the physical properties, dimensions, etc. of the components described in this specification should be understood to be modified in all cases by the term "approximately" unless otherwise specified.

[0018] [Electrolyte] An electrolyte solution according to an embodiment of the present invention includes a lithium salt; a first solvent; and a second solvent. When Lewis basicities of the first solvent and the second solvent are represented by β1 and β2, respectively, β1 is 0.40 or more, and β2 is 0.20 or less.

[0019] Typically, the electrolyte contains lithium ions (Li + The electrolyte acts as a medium for the movement of ions, enabling the reversible charging and discharging of lithium ions. In addition, since the electrolyte is in direct contact with the positive and negative electrodes, which causes a chemical reaction, the selection of the electrolyte is an important variable for stabilizing the surfaces of the positive and negative electrodes, and can have a significant impact on the performance of the secondary battery.

[0020] Such electrolytes contain lithium ions (Li + The electrolyte contains a lithium salt that acts as a path through which the lithium ions (Li) can move, and a solvent that dissolves or dissociates the lithium salt to help the ions move easily. + ) is surrounded by the solvent, resulting in solvation.

[0021] Here, the term "solvation" means that the lithium salt is dissolved in a solvent to form lithium ions (Li + ), and the lithium ions (Li + This refers to the phenomenon in which the solvent surrounds the molecule.

[0022] Conversely, the term "non-solvated" refers to a state in which the lithium salt is not dissolved by a solvent within the electrolyte, and lithium ions (Li + ) does not undergo solvation.

[0023] If the electrolyte can dissolve the lithium salt well and generate lithium ions (Li + ), the lithium ion (Li + As a result, a weak organic-based solid electrolyte interphase (SEI) layer is formed around the negative electrode, making it susceptible to cracking during repeated charge-discharge processes. This process causes localized current density differences, leading to the formation of resin-like lithium on the negative electrode surface. This not only makes it difficult to ensure stability during repeated charge-discharge cycles, but also limits the ability to improve the lifespan of secondary batteries.

[0024] In the present invention, a mixed solvent of two or more kinds including a first solvent and a second solvent is included, and among the Kamlet-Taft parameters of the first solvent and the second solvent, β1 and β2, which represent Lewis basicity, respectively satisfy specific ranges, so that lithium ions (Li + ) can be controlled to form a highly electrochemically active inorganic-based solid electrolyte interface on the negative electrode containing lithium metal, and the stability of the secondary battery can be ensured even during long-term charge and discharge, and the life characteristics can be improved. Specifically, the secondary battery has excellent life characteristics such as the ratio of the discharge capacity at a specific cycle to the discharge capacity at the first cycle, and the ability to last for more than a specific number of cycles at 0.2C charge and discharge.

[0025] Specifically, in the electrolytic solution of the present invention, by including a first solvent in which the β1 satisfies 0.4 or more, the lithium salt can be well dissolved and the lithium ions (Li +) is easily transferred, and by including a second solvent in which β2 is 0.2 or less, the second solvent acts as a cosolvent for the first solvent, and lithium ions (Li + By further stabilizing the solvation of the electrolyte, a mechanically strong, inorganic-based, stable solid electrolyte interfacial layer can be created, and by minimizing the formation of lithium resin on the anode surface, stable charging and discharging can be promoted. In this case, the stability of the anode, especially that containing lithium metal, can be further enhanced, enabling long-term operation of the anode.

[0026] According to an embodiment of the present invention, in order to achieve a desired level of solvation of lithium ions, a first solvent and a second solvent having specific levels of Kamlet-Taft parameters β1 and β2 can be selected and used.

[0027] The Kamlet-Taft parameter is a parameter determined by irradiating a solvent with light of a specific wavelength band using a UV spectrometer and determining the difference in absorbance wavelength.

[0028] Among the Kamlet-Taft parameters, Lewis basicity (β) can be determined by, for example, measuring the maximum absorption wavelength (λ) of 4-nitroaniline and N,N-diethyl-4-nitroaniline added to the first solvent and the second solvent, respectively, using a UV spectrometer. max ) is the basicity calculated using lithium ions (Li + ) can be a measure representing the degree of solvation of the first and second solvents.

[0029] Specifically, in the electrolyte, lithium ions (Li + ) acts as a Lewis acid that requires electrons, and the first solvent and the second solvent act as Lewis bases that donate electrons, so that the first solvent and the second solvent each have the lithium ions (Li +) and the maximum absorption wavelength may differ depending on the degree of binding. Therefore, the first and second solvents may be able to bind to the lithium ions (Li + ), i.e., the degree to which it bonds with lithium ions (Li + ) can be seen to determine the degree of solvation.

[0030] In one embodiment of the present invention, the Lewis basicity of the Kamlet-Taft parameters can be determined by measuring absorbance in a wavelength band of about 300 to 500 nm using, for example, a Shimadzu UV-2600 spectrometer.

[0031] Specifically, among the Kamlet-Taft parameters, the Lewis basicity is measured by adding 4-nitroaniline to the solvent (first solvent, second solvent) at a concentration of about 1×10 -4 The maximum absorption wavelength (λ max(4) ) and N,N-diethyl-4-nitroaniline (N,N-diethyl-4-nitroaniline) 1X10 -4 The maximum absorption wavelength (λ max(n) ) can be calculated respectively.

[0032] Then, the λ max(4) and λ max(n) respectively in kK (kiloK, 1 kK = 1000 cm -1 After converting to units of 1, the Lewis basicity (β) can be calculated using the following equations 1-1 and 1-2.

[0033] [Formula 1-1] λ max(N) (kK)=λ max(n) (kK)X1.035+2.64

[0034] In the formula 1-1, Said λ max(n) is a 1x10 solution of the above solvent and N,N-diethyl-4-nitroaniline. -4The maximum absorbance wavelength (λ) measured at M concentration max(n) ) and The 1.035 and 2.64 compounds were prepared by dissolving 4-nitroaniline in various non-polar solvents at approximately 1×10 -4 The maximum absorption wavelength (λ max(4) ) and N,N-diethyl-4-nitroaniline (N,N-diethyl-4-nitroaniline) 1X10 -4 The maximum absorption wavelength (λ max(n) ) are calculated, and max(4) and λ max(n) These are the gradient and y-intercept obtained by linear regression of

[0035] [Formula 1-2] TIFF0007737602000001.tif2367

[0036] In the formula 1-2, Said λ max(N) is as defined in formula 1-1 above, Said λ max(4) is a 1x10 mixed solution of the solvent and 4-nitroaniline. -4 The maximum absorbance wavelength (λ) measured at M concentration max(n) )

[0037] For example, 4-nitroaniline and N,N-diethyl-4-nitroaniline are added to the first solvent, respectively, and their maximum absorption wavelengths are determined, and the Lewis basicity (β1) of the first solvent can be calculated using the above formulas 1-1 and 1-2.

[0038] In addition, 4-nitroaniline and N,N-diethyl-4-nitroaniline are added to the second solvent, respectively, and their absorption wavelengths are measured. The Lewis basicity (β2) of the second solvent can then be calculated using Equations 1-1 and 1-2.

[0039] According to one embodiment of the present invention, the Kamlet-Taft parameter β1, which represents the Lewis basicity of the first solvent, is 0.40 or more, and the Kamlet-Taft parameter β2, which represents the Lewis basicity of the second solvent, is 0.20 or less. By including two mixed solvents having different Lewis basicities, it is possible to create a solvation environment in which anions are distributed around lithium ions, thereby further improving the performance, particularly the life characteristics, of the secondary battery.

[0040] Each component of the electrolyte solution of the present invention will be specifically described below.

[0041] lithium salts The electrolyte according to one embodiment of the present invention may include a lithium salt. The lithium salt contains lithium ions (Li + ) can act as a passageway through which they can move.

[0042] The lithium salt is not particularly limited in the present invention, and any lithium salt that can be commonly used in electrolytes for secondary batteries may be used without any limitation.

[0043] Specifically, the lithium salt may include at least one selected from the group consisting of LiPF6, LiAsF6, LiFSI, LiTFSI, LiCF3SO3, LiN(CF3SO2)2, LiBF4, LiBF6, LiSbF6, LiN(C2F5SO2)2, and LiSO3CF3. More specifically, the lithium salt may include at least one selected from the group consisting of LiPF6, LiAsF6, LiFSI, LiTFSI, and LiBF4. When the lithium salt is used, it is easily dissolved and dissociated in the first solvent, thereby further improving ion migration, solubility, and chemical stability.

[0044] Specifically, the concentration may be, for example, 1 to 8 mol, for example, 1 to 7 mol, for example, 1 to 6 mol, for example, 1 to 5 mol, for example, 2 to 5 mol, for example, 1 to 4 mol, for example, 2 to 4 mol, or for example, 1 to 3 mol, based on the total volume of the first solvent and the second solvent. If the concentration of the lithium salt is below the above range, it may be difficult to ensure ionic conductivity suitable for driving the secondary battery. If the concentration of the lithium salt exceeds the above range, the viscosity of the electrolyte solution increases, and the lithium ions (Li + ) may decrease in mobility, and the decomposition reaction of the lithium salt itself may increase, which may reduce the performance of the secondary battery.

[0045] First Solvent An electrolyte according to one embodiment of the present invention may include a first solvent.

[0046] The first solvent dissolves the lithium salt well and releases lithium ions (Li + ) can play a role in guiding the movement of the robot smoothly.

[0047] In an electrolytic solution according to one embodiment of the present invention, the first solvent may have a Lewis basicity β1 of, for example, 0.40 or more, for example, 0.45 or more, for example, 0.50 or more, for example, 0.55 or more, or for example, 0.60 or more, as measured by Kamlet Taft Peromit. Specifically, β1 may be, for example, 0.45 or more to 1.00 or less, for example, 0.50 or more to 1.00 or less, for example, 0.55 or more to less than 1.00, for example, 0.55 or more to 0.90 or less, for example, 0.55 or more to 0.80 or less, or for example, 0.55 or more to 0.75 or less, or for example, 0.55 or more to 0.70 or less. When β1 satisfies the above range, the first solvent dissolves the lithium salt well and releases lithium ions (Li + ) can be further promoted to move smoothly.

[0048] The first solvent may include, for example, one or more solvents selected from the group consisting of ether-based solvents, ester-based solvents, linear carbonate-based solvents, cyclic carbonate-based solvents, and amide-based solvents.

[0049] The ether-based solvent may include, but is not limited to, one or more selected from the group consisting of, for example, dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dimethoxyethane (e.g., 1,2-dimethoxyethane), diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol methyl ethyl ether, 1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0050] The ester solvent may include, but is not limited to, at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0051] The linear carbonate solvent may include, but is not limited to, one or more selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0052] The cyclic carbonate solvent may include, but is not limited to, one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof.

[0053] Furthermore, examples of the halide include, but are not limited to, fluoroethylene carbonate (FEC).

[0054] The amide solvent may include, but is not limited to, one or more selected from the group consisting of N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAC), and dimethylformamide (DMF).

[0055] When the electrolyte solution contains the first solvent, the lithium salt is dissolved well and the lithium ions (Li + ) can be more smoothly moved, which may be advantageous for improving the performance of the secondary battery.

[0056] Second Solvent The electrolyte according to one embodiment of the present invention may include a second solvent.

[0057] The second solvent acts as a cosolvent for the first solvent and has a Kamlet-Taft parameter smaller than that of the first solvent, and is suitable for the dissolution of lithium ions (Li + ) and limit the solvation sheath of the first solvent, so that lithium ions (Li + This allows anions to participate in the solvation of the electrolyte. This allows for the creation of a mechanically strong, inorganic-based, stable solid electrolyte interfacial layer, minimizing the formation of resinous lithium on the anode surface, thereby maintaining a relatively stable lithium anode even during sustained charging and discharging, ultimately improving the performance of secondary batteries.

[0058] In order to have such properties, it may be very important to adjust the Kamlet-Taft parameter β2, which indicates Lewis basicity, of the second solvent to have a specific value.

[0059] Specifically, in the electrolytic solution, β2 may be, for example, 0.20 or less, for example, 0.19 or less, or for example, 0.18 or less. Specifically, β2 may be, for example, −0.30 or more to 0.20 or less, for example, −0.25 or more to 0.20 or less, for example, −0.20 or more to 0.20 or less, for example, −0.10 or more to 0.20 or less, for example, 0 or more to 0.20 or less, for example, more than 0 to 0.20 or less, for example, 0.01 or more to 0.20 or less, for example, 0.02 or more to 0.20 or less, for example, 0.10 or more to 0.20 or less, for example, 0.12 or more to 0.19 or less, or for example, 0.12 or more to 0.18 or less. When β2 satisfies the above range, the solvated structure targeted in the present invention can be maintained and a mechanically strong inorganic-based solid electrolyte interface can be formed in the anode. Therefore, detachment of the solid electrolyte interface can be minimized despite large volume changes during charge and discharge of the secondary battery, thereby further enhancing the stability of the anode and enabling stable operation of the anode over a long period of time.

[0060] The difference between β1 and β2 (β1-β2) may be, for example, 0.30 or more, for example, 0.35 or more, for example, 0.40 or more, for example, 0.42 or more, for example, 0.43 or more, or for example, 0.44 or more. Specifically, the difference between β1 and β2 (β1-β2) may be, for example, 0.30 to 1.00 or less, for example, 0.35 to 1.00 or less, for example, 0.40 to 1.00 or less, for example, 0.42 to 1.00 or less, for example, 0.44 to 1.00 or less, for example, 0.44 to 0.90 or less, or for example, 0.44 to 0.87 or less. When the difference between β1 and β2 (β1-β2) satisfies the above range, it may be more advantageous to realize the effects aimed at by the present invention.

[0061] Meanwhile, according to an embodiment of the present invention, the Kamlet-Taft parameter of the second solvent, which indicates the polarizability of the solvent, may be 0.15 or more.

[0062] In order to achieve the intended effect of the present invention, the second solvent must stabilize the electrolyte environment mainly composed of dipole-shaped cations and anions, and be well mixed in the electrolyte solution without phase separation. The TIFF0007737602000002.tif98 value can be an index for determining the degree of mixing of the second solvent in the electrolyte.

[0063] The aforementioned The TIFF0007737602000003.tif98 value can be determined by irradiating a solvent with light in a specific wavelength range, for example, a wavelength range of about 400 to 700 nm, using a UV spectrometer and measuring the maximum absorbance.

[0064] For example, a zwitterionic dye (Reichardt's dye), 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate, is dissolved in a solvent (second solvent, water, tetramethylsilane (TMS)) at 1x10 -4 Add the solvent so that the concentration is M, and measure the maximum absorption wavelength (λ max ) and calculate the polarizability of the solvent using the following equations 2-1 and 2-2. TIFF0007737602000004.tif1517 can be obtained.

[0065] [Formula 2-1] TIFF0007737602000005.tif1849

[0066] In the formula 2-1, λ maxis prepared by dissolving 1x10 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate in a solvent, such as a second solvent, water, or tetramethylsilane (TMS). -4 This is the maximum absorption wavelength for the solvent when it is added to achieve a concentration of M, and the 28591 is a constant, which is the result of the product of Planck's constant (h), the speed of light (c), and Avogadro's number (NA). T (30) represents the electron transition energy per mole, and therefore has the above constant value.

[0067] [Formula 2-2] TIFF0007737602000006.tif24102

[0068] In the formula 2-2, E T (30, solvent) is E when the solvent is the second solvent T (30) E T (30, water) is E when the solvent is water. T (30) E T (30, TMS) is the E when the solvent is tetramethylsilane (TMS). T (30).

[0069] According to an embodiment of the present invention, the second solvent The TIFF0007737602000007.tif98 value may be, for example, 0.15 or more, for example, 0.16 or more, for example, 0.15 or more to less than 1.00, for example, 0.15 or more to 0.90 or less, for example, 0.15 or more to 0.80 or less, for example, 0.15 or more to 0.70 or less, for example, 0.15 or more to 0.60 or less, for example, 0.15 or more to 0.50 or less, for example, 0.15 or more to 0.40 or less, for example, 0.15 or more to 0.30 or less, for example, 0.15 or more to 0.25 or less, or for example, 0.15 or more to 0.20 or less. When the TIFF0007737602000008.tif98 value satisfies the above range, the second solvent can be well mixed in the electrolyte without phase separation, thereby achieving the desired effect of the present invention.

[0070] In particular, according to an embodiment of the present invention, the second solvent has a Kamlet-Taft parameter β2 representing Lewis basicity of 0.20 or less, and a polarizability parameter β2 representing the polarizability of the solvent. If the TIFF0007737602000009.tif98 value is 0.15 or more, it may be more advantageous to realize the effects aimed at in the present invention.

[0071] Meanwhile, according to yet another embodiment of the present invention, the LUMO (Lowest Unoccupied Molecular Orbital) energy level of the second solvent is, for example, greater than -1.0 eV and less than 0 eV, for example, -0.95 eV or more and less than 0 eV, for example, -0.95 eV or more and less than -0.01 eV, for example, -0.95 eV or more and less than -0.05 eV, for example, -0.95 eV or more and less than -0.08 eV, for example, -0.95 eV or more and less than -0.09 eV, for example, -0.95 eV or more and less than -0.10 eV, for example, -0.95 eV or more and less than -0.15 eV, For example, it may be -0.95 eV or more and -0.16 eV or less, for example, -0.95 eV or more and -0.17 eV or less, for example, -0.95 eV or more and -0.18 eV or less, for example, -0.95 eV or more and -0.20 eV or less, for example, -0.95 eV or more and -0.30 eV or less, for example, -0.95 eV or more and -0.40 eV or less, for example, -0.95 eV or more and -0.50 eV or less, or for example, -0.90 eV or more and -0.50 eV or less. When the LUMO energy level of the second solvent satisfies the above numerical range, the high LUMO energy level makes it possible to maintain a stable electrolyte environment without reducing the amount of solvent in the electrolyte even during continuous charging and discharging.

[0072] The LUMO energy level of the second solvent is calculated using the Gaussian 16, Revision A.03 program by calculation on an extended Gaussian basis, as in Ditchfield, R. et al., The Journal of Chemical Physics 54, 724-728 (1971). For example, the LUMO energy level is calculated using the program using the B3LYP / 6-31G+(d,p) level theory of density functional theory (DFT), Grimme dispersion (D3BJ), and ultrafine integration (Parr, R. G. & Yang, W. Density-functional theory of atoms and molecules (Oxford University Press [ua], 1994). Frisch, M. J. et al. Gaussian 16 Rev. C.01. (2016)).

[0073] The second solvent may include, for example, one or more selected from the group consisting of furan, anisole, ethoxybenzene, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-difluorobenzene, and fluorobenzene.

[0074] According to yet another embodiment of the present invention, the second solvent may be a non-fluorinated solvent, for example, the second solvent may include one or more selected from the group consisting of furan, anisole, and ethoxybenzene.

[0075] In this case, even in a long-term charge-discharge environment, the lithium ion (Li + ) and can maintain a stable electrolyte environment during charging and discharging. In particular, when a negative electrode containing lithium metal is used and / or when the negative electrode is combined with a positive electrode to form a complete secondary battery, stability can be maintained. This can provide excellent performance of the secondary battery and is also advantageous in terms of cost efficiency.

[0076] Meanwhile, according to an embodiment of the present invention, the contents of the first solvent and the second solvent are adjusted to maintain an optimal electrolyte environment, thereby further improving the performance of the secondary battery.

[0077] Specifically, the amount of the second solvent may be the same as or greater than the amount of the first solvent.

[0078] More specifically, the volume ratio of the first solvent to the second solvent may be, for example, 1:1 to 1:3, for example, 1:1 to 1:2, for example, 1:2 to 1:3, for example, 1:1.5 to 1:2.5, or for example, 1:2. When the volume ratio of the first solvent to the second solvent satisfies the above range, the concentration of the electrolyte solution can be reduced while the lithium ions (Li + ) can be controlled, and therefore, when a solvent having the above volume ratio is applied to a secondary battery, a stable solvated structure as intended in the present invention can be maintained.

[0079] According to one embodiment of the present invention, the first solvent may be one or more types, and the second solvent may be one or more types. Specifically, the first solvent may be one type, and the second solvent may be one type. That is, the types of solvents contained in the electrolytic solution may be two or more types, or three or more types, and specifically, may be two types, but are not limited thereto.

[0080] [Additives] The electrolyte according to one embodiment of the present invention may include an additive.

[0081] The additives may include various commonly used additives as long as they do not impair the effects of the present invention, and may be added in various amounts depending on the desired properties and applications.

[0082] Specifically, the electrolyte may further include a nitric acid compound, for example, at least one selected from the group consisting of lithium nitrate (LiNO), potassium nitrate (KNO), cesium nitrate (CsNO), magnesium nitrate (MgNO), barium nitrate (BaNO), lithium nitrite (LiNO), potassium nitrite (KNO), and cesium nitrite (CsNO).

[0083] Other examples include fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethyl carbonate (VEC), lithium fluoride (LiF), and lithium sulfide (LiS x , 2≦x≦8), and additives such as lithium phosphate difluoride (LiPO2F2).

[0084] The additive may be included in an amount of, for example, more than 0 wt % to 30 wt %, for example, 1 wt % to 30 wt %, or for example, 5 wt % to 20 wt %, based on the total weight of the electrolyte solution. If the content of the additive is too high, the performance of the secondary battery may be deteriorated.

[0085] [Secondary battery] According to one embodiment of the present invention, a secondary battery including the electrolyte solution can be provided.

[0086] The secondary battery includes a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution. The electrolyte solution includes a lithium salt; a first solvent; and a second solvent. Kamlet-Taft parameters of the first solvent and the second solvent are expressed as β1 and β2, respectively. When Lewis basicity is represented by β1 and β2, β1 may be 0.40 or more, and β2 may be 0.20 or less.

[0087] Specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material coated on one or both sides of the positive electrode current collector.

[0088] The positive electrode current collector is not particularly limited as long as it supports the positive electrode active material, does not induce chemical changes in the secondary battery, and has high conductivity.

[0089] The positive electrode current collector may be made of, for example, stainless steel, aluminum, nickel, titanium, palladium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, silver, or the like, or an aluminum-cadmium alloy.

[0090] The positive electrode current collector may have fine irregularities on its surface to strengthen the bonding force with the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a mesh, a net, a porous material, a foam, or a nonwoven fabric.

[0091] The positive electrode active material may include a positive electrode active material, and optionally a conductive material and a binder.

[0092] The positive electrode active material is, for example, LiMn2O4, V2O5, LiCoO2, LiNiO2, LiFePO4, Li4Ti5O 12 , LiNi x Co y Mn z O2(x+y+z=1) and LiNi x Co y Al z O2 (x+y+z=1).

[0093] The conductive material is used to improve electrical conductivity, and can be any electron-conductive material that does not cause chemical changes in the secondary battery.

[0094] The conductive material may be, for example, carbon black, graphite, carbon fiber, carbon nanotubes, metal powder, conductive metal oxide, organic conductive material, etc., and currently commercially available conductive materials include acetylene black series (e.g., products of Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC series (products of Armak Company), Vulcan XC-72 (products of Cabot Company), and SUPER P, etc.

[0095] The positive electrode active material may further include a binder that fixes the positive electrode active material to the positive electrode current collector and binds the active material together. Examples of the binder include various binders such as polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, styrene butadiene rubber (SBR), carboxyl methyl cellulose (CMC), poly(acrylic acid) (PAA), and poly(vinyl alcohol) (PVA).

[0096] Meanwhile, the negative electrode may include a negative electrode current collector and a negative electrode active material disposed on the negative electrode current collector, or the negative electrode may include a lithium metal thin film.

[0097] The negative electrode current collector is used to support the negative electrode active material, and is not particularly limited as long as it has excellent conductivity and is electrochemically stable in the voltage range of the secondary battery. For example, copper, stainless steel, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, or the like, aluminum-cadmium alloy, etc. may be used.

[0098] The negative electrode current collector may have fine irregularities on its surface to strengthen the bonding force with the negative electrode active material, and may be in various forms such as a film, a sheet, a foil, a mesh, a net, a porous material, a foam, or a nonwoven fabric.

[0099] The negative electrode active material is lithium (Li + The material may include a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, lithium metal, or a lithium alloy.

[0100] The lithium ion (Li + The material capable of reversibly absorbing and releasing HCl may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof.

[0101] The lithium ion (Li + The material capable of reacting with ) to reversibly form a lithium-containing compound may be, for example, tin oxide, titanium nitrate, or silicon.

[0102] The lithium alloy may be, for example, an alloy of lithium (Li) and a metal containing one or more selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

[0103] Specifically, the negative electrode active material may be lithium metal, preferably in the form of a lithium metal thin film or lithium metal powder.

[0104] The method for forming the negative electrode active material is not particularly limited, and may be a layer or film formation method commonly used in the art, such as compression bonding, coating, or vapor deposition. Furthermore, a battery may be assembled without a lithium thin film on the current collector, and then a metallic lithium thin film is formed on the metal plate by initial charging.

[0105] The electrolyte contains lithium ions and serves to cause an electrochemical oxidation or reduction reaction between the positive electrode and the negative electrode through the lithium ions, as described above.

[0106] The injection of the electrolyte may be performed at an appropriate stage in the manufacturing process of the electrochemical device depending on the manufacturing process and required properties of the final product, i.e., before assembling the electrochemical device or at the final stage of assembling the electrochemical device.

[0107] Meanwhile, a separator may be further included between the positive electrode and the negative electrode.

[0108] The separator membrane is used in the secondary battery of the present invention to physically separate the two electrodes, and any separator membrane that is typically used as a separator membrane in lithium secondary batteries can be used without any particular limitation. In particular, a separator membrane that has low resistance to ion migration of the electrolyte and excellent electrolyte wetting ability is preferred.

[0109] The separator may be made of a porous substrate. The porous substrate may be any porous substrate commonly used in electrochemical devices, such as, but not limited to, a polyolefin-based porous membrane or nonwoven fabric.

[0110] Examples of the polyolefin-based porous membrane include membranes formed from polyolefin-based polymers such as polyethylene (e.g., high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene), polypropylene, polybutylene, and polypentene, either alone or in combination.

[0111] In addition to polyolefin-based nonwoven fabrics, the nonwoven fabric may include nonwoven fabrics made of polymers such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate, either alone or in combination. The nonwoven fabric may be a spunbonded or meltblown nonwoven fabric made of long fibers.

[0112] The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm or 5 to 50 μm.

[0113] The size and porosity of the pores present in the porous substrate are not particularly limited. For example, the size of the pores present in the porous substrate may be 0.001 to 50 μm, and the porosity may be 10 to 95%.

[0114] The secondary battery according to the present invention can be manufactured by laminating (stacking) and folding the separator and electrodes in addition to the general winding process.

[0115] The shape of the secondary battery is not particularly limited, and may include various shapes such as a cylindrical type, a stacked type, and a coin type.

[0116] Furthermore, the secondary battery according to the embodiment of the present invention can last for 120 or more cycles at a charge / discharge rate of 0.2 C-rate.

[0117] The secondary battery according to an embodiment of the present invention includes the electrolyte solution, thereby improving the life characteristics of the secondary battery.

[0118] [Battery module] According to one embodiment of the present invention, a battery module including the secondary battery as a unit battery can be provided.

[0119] The battery module can be used as a power source for medium to large devices that require high temperature stability, long cycle characteristics, and high capacity characteristics.

[0120] Examples of the medium- to large-sized devices include, but are not limited to, power tools powered by battery-powered motors; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles, including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems.

[0121] The above will be described in more detail with reference to the following examples, but the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0122] <Example 1> Electrolyte and secondary battery production 1 LiFSI was prepared as the lithium salt. 1,2-dimethoxyethane (DME) with a Kamlet-Taft parameter β1 (Lewis basicity) of 0.62 was prepared as the first solvent, and anisole with a Kamlet-Taft parameter β2 (Lewis basicity) of 0.18 was prepared as the second solvent.

[0123] The first solvent and the second solvent were mixed in a volume ratio of 1:2 to prepare a mixed solvent, which was then mixed with 3.0 mol of LiFSI per total volume (L) of the mixed solvent to prepare an electrolyte solution.

[0124] In the secondary battery fabrication, a 90 μm thick LiFePO4 electrode was used as the positive electrode (LFP), and a 20 μm thick lithium metal thin film was used as the negative electrode (Li). The positive electrode (LFP) was made by mixing LiFePO4 as the positive electrode active material, Super P as the conductive material, and polyvinylidene fluoride (PVDF) as the binder in a weight ratio of 93.5:4:2.5 to prepare a slurry, which was then cast onto a 20 μm thick aluminum foil as a current collector.

[0125] The prepared positive and negative electrodes were placed facing each other, a polyethylene separator was interposed between them, and 80 μL of the electrolyte was poured into the electrode to prepare a secondary battery.

[0126] <Example 2> Electrolyte and secondary battery production 2 An electrolyte solution and a secondary battery using the same were manufactured in the same manner as in Example 1, except that a second solvent having β2 of 0.17 was used.

[0127] <Example 3> Electrolyte and secondary battery production 3 An electrolyte solution and a secondary battery using the same were manufactured in the same manner as in Example 1, except that a second solvent having a β2 of 0.12 was used and 1.0 mol of LiFSI was mixed per total volume (L) of the mixed solvent of the first solvent and the second solvent.

[0128] <Example 4> Electrolyte and secondary battery production 4 An electrolyte solution and a secondary battery using the same were manufactured in the same manner as in Example 1, except that a second solvent having β2 of −0.25 was used.

[0129] <Example 5> Preparation of electrolyte and secondary battery 5 An electrolyte solution and a secondary battery using the same were manufactured in the same manner as in Example 1, except that a second solvent with β2 of 0.02 was used.

[0130] <Example 6> Preparation of electrolyte and secondary battery 6 An electrolyte solution and a secondary battery using the same were manufactured in the same manner as in Example 1, except that a second solvent with β2 of 0.04 was used.

[0131] <Example 7> Preparation of electrolyte and secondary battery 7 An electrolyte solution and a secondary battery using the same were manufactured in the same manner as in Example 1, except that a second solvent having β2 of 0.12 was used and 2.0 mol of LiFSI was used per total volume (L) of the mixed solvent of the first solvent and the second solvent.

[0132] <Comparative Example 1> Electrolyte and Secondary Battery Production 8 An electrolyte solution and a secondary battery using the same were manufactured in the same manner as in Example 1, except that a second solvent having β2 of 0.55 was used.

[0133] <Comparative Example 2> Electrolyte and Secondary Battery Production 9 An electrolyte solution and a secondary battery using the same were manufactured in the same manner as in Example 1, except that the first and second solvents, each having β1 of 0.18 and β2 of −0.25, were used.

[0134] <Experimental Example 1> Lewis basicity (β(β1, β2)) among Kamlet-Taft parameters Among the Kamlet-Taft parameters, Lewis basicity (β(β1, β2)))) was determined by measuring absorbance in the wavelength range of approximately 300 to 500 nm using a Shimadzu UV-2600 spectrometer.

[0135] Specifically, 1x10 4-nitroaniline is added to the solvent (first solvent, second solvent) for which the (β(β1, β2)) value is to be measured. -4 The maximum absorption wavelength (λ max(4) ) and N,N-diethyl-4-nitroaniline (N,N-diethyl-4-nitroaniline) 1X10 -4 The maximum absorption wavelength (λ max(n) ) were calculated respectively.

[0136] Said λ max(4) and λ max(n) respectively in kK (kiloK, 1 kK = 1000 cm -1 ) units, and then the Lewis basicity (β(β1, β2)) was calculated using the following formulas 1-1 and 1-2.

[0137] [Formula 1-1] λ max(N) (kK)=λ max(n) (kK)X1.035+2.64

[0138] In the formula 1-1, Said λ max(n) is a 1x10 solution of the above solvent and N,N-diethyl-4-nitroaniline. -4 The maximum absorbance wavelength (λ) measured at M concentration max(n) ) and the 1.035 and 2.64 are obtained by dissolving 4-nitroaniline in various non-polar solvents at about 1×10-4 The maximum absorption wavelength (λ max(4) ) and N,N-diethyl-4-nitroaniline (N,N-diethyl-4-nitroaniline) 1X10 -4 The maximum absorption wavelength (λ max(n) ) are calculated, and max(4) and λ max(n) These are the gradient and y-intercept obtained by linear regression of

[0139] [Formula 1-2] TIFF0007737602000010.tif1747

[0140] In the formula 1-2, Said λ max(N) is as defined in the above formula 1-1, and the λ max(4) is a 1x10 mixed solution of the solvent and 4-nitroaniline. -4 The maximum absorbance wavelength (λ) measured at M concentration max(n) )

[0141] <Experimental Example 2> Solvent polarizability TIFF0007737602000011.tif1517Kamlet-Taft parameters, including the polarizability of the solvent TIFF0007737602000012.tif1517 was determined by measuring absorbance in the wavelength range of approximately 400 to 700 nm using a Shimadzu UV-2600 spectrometer.

[0142] Specifically, a zwitterionic dye (Reichardt's dye), 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate, was added to a solvent (second solvent, water, tetramethylsilane (TMS)) at a concentration of 1x10. -4Add the solvent so that the concentration is M, and measure the maximum absorption wavelength (λ max ) were calculated respectively.

[0143] The maximum absorption wavelength (λ max ) and calculate the polarizability of the solvent using the following equations 2-1 and 2-2. I wanted TIFF0007737602000013.tif1517.

[0144] [Formula 2-1] TIFF0007737602000014.tif1744In the above formula 2-1, λ max is prepared by dissolving 1x10 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate in a solvent, such as a second solvent, water, or tetramethylsilane (TMS). -4 is the maximum absorbance wavelength for the solvent when added to achieve a concentration of M, [Formula 2-2] TIFF0007737602000015.tif28118 In the formula 2-2, E T (30, solvent) is E when the solvent is the second solvent T (30) and E T (30, water) is E when the solvent is water. T (30) and E T (30, TMS) is the E when the solvent is tetramethylsilane (TMS). T (30).

[0145] <Experimental Example 3> LUMO energy level The LUMO energy level was calculated using the Gaussian 16, Revision A.03 program, based on the B3LYP / 6-31G+(d,p) level theory of density functional theory (DFT), Grimme dispersion (D3BJ), and ultrafine integration (Parr, RG & Yang, W. Density-functional theory of atoms and molecules (Oxford Univ. Press[ua], 1994). Frisch, MJ et al. Gaussian 16 Rev.C.01. (2016)).

[0146] <Experimental Example 4> Evaluation of charge / discharge and life (cycle) characteristics of secondary batteries The secondary batteries according to Examples 1 to 7 and Comparative Examples 1 and 2 were each charged for 5 cycles at 0.1C, 0.25C, 0.5C, 0.75C, 1C, 2C, and 3C up to a voltage of 3.8V, and then discharged at the same C-rate down to 2.0V to evaluate the charge / discharge rate.

[0147] After the test, the charge / discharge characteristics of the secondary battery were evaluated by comparing how much discharge capacity was maintained at 0.1C at a high C-rate for each electrolyte, and the lifespan characteristics (%) of the secondary battery were calculated using the following formula A: [Formula A] Secondary battery life characteristics (%) = Discharge capacity at 120th cycle / Discharge capacity at 1st cycle x 100 (%) The results obtained in the above Evaluation Examples 1 to 4 are summarized in Table 1 below.

[0148] [Table 1]

[0149] As can be seen from Table 1, the secondary batteries of Examples 1 to 7, which used electrolyte solutions in which the β1 of the first solvent was 0.40 or more and the β2 of the second solvent was 0.20 or less, had a ratio of discharge capacity at the 120th cycle to discharge capacity at the 1st cycle of 85% or more, and were confirmed to have excellent life characteristics by lasting for more than 120 cycles at 0.2C charge / discharge.

[0150] Conversely, in the case of the secondary battery according to Comparative Example 1, in which an electrolyte solution in which the β1 of the first solvent was 0.40 or more but the β2 of the second solvent was 0.55 was used, cycling using LFP was impossible. In the case of Comparative Example 2, in which an electrolyte in which the β1 of the first solvent was low at 0.18 but the β2 of the second solvent was 0.20 or less was used, full cell fabrication was impossible due to electrolyte layer separation, making it impossible to analyze the performance of the secondary battery.

[0151] From the above results, it was confirmed that in the case of the electrolyte solutions according to Examples 1 to 7 of the present invention, an inorganic-based solid electrolyte interface with high electrochemical activity is formed in the anode, enabling stable operation of the anode for a long period of time, thereby improving the performance of the secondary battery.

Claims

1. A lithium salt, a first solvent; and a second solvent; The Lewis basicity of the Kamlet-Taft parameters of the first solvent and the second solvent is β １ and β ２ Expressed as: Said β １ is 0.40 or more, Said β ２ is less than or equal to 0.20, the volume ratio of the first solvent to the second solvent is 1:1 to 1:3; The lithium salt is LiAsF ６ , LiFSI, LiTFSI, LiCF ３ SO ３ , LiBF ４ , LiBF ６ , LiSbF ６ , and LiN(C ２ F ５ SO ２ ) 2, The lithium salt is contained in an amount of 1 to 8 mol based on the total volume of the first solvent and the second solvent, The second solvent includes at least one selected from the group consisting of furan, anisole, and ethoxybenzene.

2. Said β １ and the β ２ The difference between １ -β ２ 2. The electrolyte solution according to claim 1, wherein the σ is 0.30 or more.

3. 2. The electrolyte solution according to claim 1, wherein the first solvent comprises at least one selected from the group consisting of ether-based solvents, ester-based solvents, linear carbonate-based solvents, cyclic carbonate-based solvents, and amide-based solvents.

4. Said β ２ The electrolyte solution according to claim 1, wherein is −0.25 to 0.

20.

5. Among the Kamlet-Taft parameters of the second solvent, 10. The electrolyte of claim 1, comprising a solvent having a value of 0.15 or greater.

6. The electrolyte solution according to claim 1, wherein the second solvent has a LUMO (Lowest Unoccupied Molecular Orbital) energy level of more than -1.0 eV and less than 0 eV.

7. A battery comprising a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution, the negative electrode comprises lithium metal; The electrolyte solution A lithium salt, a first solvent; and a second solvent; Among the Kamlet-Taft parameters of the first solvent and the second solvent, the Lewis basicity is represented by β 1 and β 2 , respectively. the β 1 is 0.40 or more; the β 2 is 0.20 or less; the volume ratio of the first solvent to the second solvent is 1:1 to 1:3; The lithium salt includes at least one selected from the group consisting of LiAsF 6 , LiFSI, LiTFSI, LiCF 3 SO 3 , LiBF 4 , LiBF 6 , LiSbF 6 , and LiN(C 2 F 5 SO 2 ) 2 ; The lithium salt is contained in an amount of 1 to 8 mol based on the total volume of the first solvent and the second solvent, The second solvent may include at least one selected from the group consisting of furan, anisole, and ethoxybenzene.

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