Composition for non-aqueous electrolyte, and electrochemical cell comprising composition

Abstract

The present application relates to a composition for a non-aqueous electrolyte, comprising a mixed solvent and optionally comprising dual lithium salts, and to an electrochemical cell comprising the composition.

Description

Composition for non-aqueous electrolyte and electrochemical cell comprising same

[0001] The present invention relates to a non-aqueous electrolyte composition comprising a mixed solvent and optionally a dual lithium salt, and an electrochemical cell comprising the same.

[0002] The demand for high-energy-density secondary batteries is increasing not only as an energy source for electronic devices such as mobile phones, camcorders, and laptop PCs, but also for transportation such as drones (taxis) and electric vehicles, and research on lithium secondary batteries that can meet these demands is actively being conducted.

[0003] Lithium secondary batteries that are being commercialized generally contain an electrolyte that is a mixture of lithium salt and organic solvent, and the organic solvent that constitutes the electrolyte is a carbonate series solvent considering electrical properties and chemical stability.

[0004] However, conventional electrochemical cells containing carbonate-based solvents exhibit unstable charging characteristics at temperatures below 0°C, which increases the likelihood of safety issues, and are therefore designed to limit charging. In particular, at low temperatures below -20°C, there are problems such as a serious decrease in discharge capacity and a rapid decline in cycle life. Therefore, there is a need to develop an electrolyte that is stable even at low temperatures, has excellent flame retardancy and heat resistance, and has excellent high-speed charge / discharge characteristics, enabling stable operation of electrochemical cells in various environments.

[0005] (Patent Document 001) Republic of Korea Registered Patent No. 10-0810634

[0006] The present invention aims to provide a non-aqueous electrolyte composition that is stable even at low temperatures, has excellent flame retardancy and heat resistance, and, in particular, has excellent high-speed charge / discharge characteristics, and an electrochemical cell including the same.

[0007] However, the problems that the present invention seeks to solve are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0008] The first aspect of the present invention provides a non-aqueous electrolyte composition comprising: a lithium salt; a first organic solvent comprising at least one selected from a cyclic carbonate compound and a cyclic ester compound; and a second organic solvent comprising a compound containing an ether group and an ester group.

[0009] The second aspect of the present invention provides an electrochemical cell comprising: a positive electrode; a negative electrode; a separator positioned between the positive electrode and the negative electrode; and a non-aqueous electrolyte composition according to the first aspect.

[0010] A non-aqueous electrolyte composition according to one embodiment of the present invention comprises a mixed solvent comprising a first organic solvent and a second organic solvent and a lithium salt. The composition utilizes a mixed solvent capable of minimizing binding energy with lithium ions, resulting in significantly improved low-temperature characteristics compared to conventional carbonate-based electrolytes. Furthermore, it also has the advantage of high-speed charge / discharge characteristics.

[0011] In addition, in general, in the case of organic electrolytes, low-temperature characteristics and high-temperature characteristics are in a trade-off relationship, but the non-aqueous electrolyte composition according to one embodiment of the present invention exhibits improved low-temperature characteristics by including the above-described mixed solvent and a mixed lithium salt optionally including an imide-based lithium salt and a lithium salt different from the above, and also exhibits excellent high-temperature characteristics, and exhibits characteristics in which safety is greatly improved due to increased flame retardancy.

[0012] Below, embodiments of the present invention are described in detail to facilitate their implementation by those skilled in the art. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0013] Throughout this specification, when it is said that an element is “on” another element, this includes not only cases where the element is in contact with the other element, but also cases where another element exists between the two elements.

[0014] Throughout this specification, when a part is said to “include” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated. The terms “about,” “substantially,” etc., used throughout this specification, are used in a sense of numerical value or approximation when manufacturing and material tolerances inherent to the meanings referred to are presented, and are used to prevent unscrupulous infringers from unfairly exploiting disclosures that contain precise or absolute values ​​to aid understanding of this specification. The terms “step of doing” or “step of” used throughout this specification do not mean “step for.”

[0015] Throughout this specification, the term “combination(s) thereof” included in the expressions in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expressions in the Makushi format, and means including one or more selected from the group consisting of said components.

[0016] Throughout this specification, references to “A and / or B” mean “A or B, or A and B.”

[0017] Hereinafter, implementation examples and embodiments of the present invention will be described in detail with reference to the attached drawings. However, the present invention may not be limited to these implementation examples and embodiments and drawings.

[0018]

[0019] The first aspect of the present invention provides a non-aqueous electrolyte composition comprising: a lithium salt; a first organic solvent comprising at least one selected from a cyclic carbonate compound and a cyclic ester compound; and a second organic solvent comprising a compound containing an ether group and an ester group.

[0020] Conventional non-aqueous electrolyte compositions contain organic solvents mixed with carbonate-based solvents such as EC (Ethylene carbonate), PC (Propylene Carbonate), DMC (Dimethyl Carbonate), EMC (Ethylmethyl Carbonate), and DEC (Diethyl Carbonate). However, conventional electrolytes containing the carbonate-based solvents have a disadvantage in that the performance of the electrochemical cell rapidly deteriorates at temperatures below -15°C, and in particular, the discharge voltage of the electrochemical cell drops significantly to the point where the use of electronic devices becomes impossible at temperatures below -20°C.

[0021] Accordingly, to solve the above problem, an electrolyte in which a nitrile-based solvent is added to the aforementioned organic solvent has been proposed, but it is still found that there is a limit to improving the characteristics at low temperatures, and the high-temperature characteristics are inferior.

[0022] On the other hand, the non-aqueous electrolyte composition of the present invention can significantly improve low-temperature characteristics compared to conventional carbonate-based electrolytes by including a mixed solvent comprising a lithium salt and the first and second organic solvents described above. In particular, the electrochemical reaction rate is significantly improved even at extremely low temperatures below -30°C, which is advantageous for high-speed charge / discharge.

[0023] In addition, in general, in the case of organic electrolytes, low-temperature characteristics and high-temperature characteristics are in a conflicting relationship, but the non-aqueous electrolyte composition according to one embodiment of the present disclosure has the advantage of being able to stably implement electrochemical characteristics over a wide temperature range by maintaining high-temperature characteristics while exhibiting improved low-temperature characteristics.

[0024] In one embodiment of the present invention, the composition for a non-aqueous electrolyte may include a mixed solvent in which a first organic solvent including at least one selected from among a cyclic carbonate compound and a cyclic ester compound as described above and a second organic solvent including a compound containing an ether group and an ester group are mixed.

[0025] For example, the cyclic carbonate compound included in the first organic solvent may include at least one selected from ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, and 1-fluoropropylene carbonate.

[0026] In addition, the cyclic ester compound included in the first organic solvent may include at least one selected from among γ-butyrolactone, γ-valerolactone, σ-valerolactone, γ-caprolactone, ε-caprolactone, and 4-vinyl-1,3-dioxolan-2-one.

[0027] An electrolyte comprising a mixed solvent containing a first organic solvent including at least one selected from the cyclic carbonate compound and the cyclic ester compound helps form a stable and functional SEI (Solid Electrolyte Interface) layer in an electrochemical cell, and has a high dielectric constant, so that lithium salts in the electrolyte can be easily dissociated.

[0028] Specifically, an SEI film is stably formed on the electrode layer by the first organic solvent, which can effectively suppress side reactions with the electrolyte and the electrode.

[0029] As an advantageous example, the first organic solvent may include at least one selected from the above-described cyclic carbonate compounds, and as a specific example, may include at least one selected from the fluorinated cyclic carbonate compounds fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, and 1-fluoropropylene carbonate.

[0030] As the first organic solvent includes a fluorinated cyclic carbonate compound containing a fluorine atom as described above, it has a more advantageous advantage in that it can stably form an SEI layer while also improving the thermal stability and electrochemical oxidation resistance of the electrolyte.

[0031] In one embodiment of the present invention, the content of the first organic solvent is 5 to 50 vol%, 10 to 50 vol%, 15 to 50 vol%, 20 to 50 vol%, 5 to 45 vol%, 10 to 45 vol%, 15 to 45 vol%, 20 to 45 vol%, 5 to 40 vol%, 10 to 40 vol%, 15 to 40 vol%, 20 to 40 vol%, 5 to 35 vol%, 10 to 35 vol%, 15 to 35 vol%, 20 to 35 vol%, 5 to 30 vol%, 10 to 30 vol%, 15 to 30 vol%, 20 to 30 vol%, 5 to 25 vol%, 10 to 25 vol%, 15 to It may be 25% by volume, or 20 to 25% by volume.

[0032] Since the first organic solvent included in the mixed solvent satisfies the above-described range, the low-temperature characteristics of the electrochemical cell including the mixed solvent can be significantly improved due to the synergistic effect with the second organic solvent described later.

[0033] In one embodiment of the present invention, the second organic solvent included in the mixed solvent together with the first organic solvent described above may be a low-melting-point organic solvent containing an ether group and an ester group. In this case, the melting point of the second organic solvent may be -20°C or lower, -30°C or lower, -40°C or lower, or -50°C or lower, and the lower limit is not limited, but may be -150°C or -100°C.

[0034] In one embodiment of the present invention, the second organic solvent may include at least one selected from the group consisting of a first compound represented by the following chemical formula 1, a second compound represented by the following chemical formula 2, and a mixture thereof:

[0035]

[0036]

[0037] The above R1 is a linear or branched alkyl group having 1 to 10 carbon atoms, the above R4 is hydrogen or a linear or branched alkyl group having 1 to 10 carbon atoms, the above R2 and R5 are each independently a linear or branched alkylene group having 1 to 10 carbon atoms, and the above R3 and R6 are each independently a linear or branched alkyl group having 1 to 10 carbon atoms.

[0038] Since the second organic solvent included in the mixed solvent includes at least one of the first compound, the second compound, and a mixture thereof, it may be advantageous in improving the low-temperature characteristics of the electrochemical cell by suppressing a decrease in the solubility of the lithium salt included in the electrolyte even in a low-temperature or ultra-low-temperature environment.

[0039] Specifically, the second organic solvent is 2-methoxyethyl acetate, 2-ethoxyethyl acetate, propylene glycol monomethyl ether acetate, methyl methoxyacetate, methyl ethoxyacetate, methyl 3-methoxypropionate, β-Ethoxy-propionsaeure-methylester, ethyl 2-methoxyacetate, ethyl 2-ethoxyethanoate, 3-Methoxy-propionsaeure-ethylester, ethyl It may include at least one selected from ethyl 3-ethoxypropionate, ethyl 3-methoxypropionate, methyl 2-methoxypropionate, 3-methoxy-2-methylpropionic acid methyl ester, methyl 3-methoxybutyrate, methyl 3-methoxyisobutyrate, methyl 4-methoxybutanoate, methyl-3-methoxy-2-methylbutyrate, and mixtures thereof.

[0040] As an advantageous example, the second organic solvent may be a compound satisfying the chemical formula 1:

[0041]

[0042] The above R1 is a linear or branched alkyl group having 1 to 10 carbon atoms, the above R2 is a linear or branched alkylene group having 1 to 10 carbon atoms, and the above R3 is a linear or branched alkyl group having 1 to 10 carbon atoms.

[0043] As a specific example, the compound satisfying the above chemical formula 1 is methyl methoxyacetate, methyl ethoxyacetate, methyl 3-methoxypropionate, ethyl 2-methoxyacetate, ethyl 2-ethoxyethanoate, ethyl 3-ethoxypropionate, ethyl 3-methoxypropionate, methyl 2-methoxypropionate, methyl 3-methoxybutyrate, methyl 3-methoxyisobutyrate, methyl It may include at least one selected from methyl 4-methoxybutanoate and methyl-3-methoxy-2-methylbutyrate.

[0044] As a more advantageous example, the second organic solvent may be a solvent that satisfies the chemical formula 1 and has a relatively lower or lowest binding energy with lithium ions, and as a specific example, may be methyl 3-methoxypropionate.

[0045] In this way, when the second organic solvent is a compound that has a relatively lower or lowest binding energy with lithium ions and satisfies the chemical formula 1, the solvation and desolvation behaviors of lithium ions in the electrolyte can occur more favorably, and in particular, since the immobility of the electrolyte is maintained even at extremely low temperatures, the decrease in the movement speed of ions can be reduced, thereby possessing an advantage that is advantageous for high-speed charging and discharging.

[0046] In one embodiment of the present invention, the content of the second organic solvent is 50 to 95 vol%, 55 to 95 vol%, 60 to 95 vol%, 65 to 95 vol%, 70 to 95 vol%, 75 to 95 vol%, 80 to 95 vol%, 85 to 95 vol%, 50 to 90 vol%, 55 to 90 vol%, 60 to 90 vol%, 65 to 90 vol%, 70 to 90 vol%, 75 to 90 vol%, 80 to 90 vol%, 85 to 90 vol%, 50 to 85 vol%, 55 to 85 vol%, 60 to 85 vol%, 65 to 85 vol%, 70 to 85 vol%, 75 to 85 % by volume, 80 to 85% by volume, 50 to 80% by volume, 55 to 80% by volume, 60 to 80% by volume, 65 to 80% by volume, 70 to 80% by volume, or 75 to 80% by volume.

[0047] In addition to the first organic solvent described above, when a second organic solvent included in the mixed solvent satisfies the above-mentioned range, there is an advantage in that the deterioration of low-temperature performance of an electrochemical cell including the mixed solvent can be minimized due to a synergistic effect with the first organic solvent.

[0048] In one embodiment of the present invention, the volume ratio of the first organic solvent to the second organic solvent included in the mixed solvent may be 1:9 to 5:5 to effectively improve the low-temperature characteristics of the electrochemical cell.

[0049] As a specific example, the volume ratio may be 1:9 to 4:6, 1:9 to 3:7, 1:9 to 2.5: 7.5, 1.5:8.5 to 5:5, 1.5:8.5 to 4:6, 1.5:8.5 to 3:7, 1.5:8.5 to 2.5: 7.5, 2:8 to 5:5, 2:8 to 4:6, 2:8 to 3:7, or 2:8 to 2.5: 7.5.

[0050] If the first organic solvent included in the mixed solvent is included in an amount less than 10% by volume or more than 50% by volume based on the total volume of the mixed solvent, the synergy effect with the second organic solvent included together with the first organic solvent may be reduced, which may limit the improvement of the low-temperature characteristics of the electrochemical cell. Therefore, it is advantageous for the volume ratio to satisfy the aforementioned range.

[0051] In one embodiment of the present invention, the lithium salt included in the non-aqueous electrolyte composition may include an imide-based lithium salt, and thus has the advantage of significantly improving charge-discharge characteristics at an extremely low temperature of -30°C. That is, the imide-based lithium salt significantly improves charge-discharge performance at an extremely low temperature due to a synergistic effect with the mixed solvent comprising the first organic solvent and the second organic solvent described above.

[0052] At this time, the imide lithium salt may include at least one selected from LiN(SO2C2F5)2, LiN(SO2CF3)2[LiTFSI], LiN(SO2CF3)(SO2C2F5), LiN(SO2CF3)(SO2C3F7), and LiN(SO2F)2[LiFSI].

[0053] In one embodiment of the present invention, the concentration of the lithium salt in the non-aqueous electrolyte composition may be 0.1 M to 3.0 M. Specifically, the concentration of the lithium salt in the non-aqueous electrolyte composition may be 0.1 to 3.0 M, 0.1 to 2.5 M, 0.1 to 2.0 M, 0.1 to 1.5 M, 0.5 to 3.0 M, 0.5 to 2.5 M, 0.5 to 2.0 M, or 0.5 to 1.5 M, but is not limited thereto.

[0054] As an advantageous example, the lithium salt may be a mixed lithium salt including a first lithium salt that is an imide-based lithium salt and a second lithium salt that is independently different from the first lithium salt.

[0055] Since the above mixed lithium salt is included in the non-aqueous electrolyte composition of the present invention, the low-temperature characteristics of the electrochemical cell described above are significantly improved, and at the same time, the high-temperature characteristics can be secured at the level of the electrolyte containing the conventional carbonate solvent, so there is an advantage in that the electrochemical cell can be used with excellent performance over a wide temperature range.

[0056] In one embodiment of the present invention, the imide-based lithium salt (first lithium salt) may include at least one selected from LiN(SO2C2F5)2, LiN(SO2CF3)2[LiTFSI], LiN(SO2CF3)(SO2C2F5), LiN(SO2CF3)(SO2C3F7), and LiN(SO2F)2[LiFSI].

[0057] In one embodiment of the present invention, the second lithium salt may include at least one selected from LiPF6, LiAsF6, LiPF4(C2O4), LiPF2(C2O4)2, LiBF4, LiB(C2O4)2, LiBF2(C2O4), LiClO4, LiBrO4, LiIO4, LiB(C6H5)4, LiCH3SO3, and LiCF3SO3.

[0058] In one embodiment of the present invention, the molar concentration ratio of the first lithium salt to the second lithium salt included in the mixed lithium salt may be 1:9 to 9:1, 1:9 to 7:3, or 1:9 to 5:5.

[0059] As an advantageous example, the molar ratio of the first lithium salt:second lithium salt may be 1:9 to 4:6, preferably 2:8 to 4:6, and more preferably 3:7.

[0060] When the molar concentration ratio of the first lithium salt:second lithium salt satisfies the above-mentioned range, an electrochemical cell including the non-aqueous electrolyte composition of the present invention can exhibit excellent low-temperature characteristics as well as high-temperature characteristics, and thus excellent electrochemical cell performance can be realized over a wide temperature range.

[0061] At this time, the molar concentration of the first lithium salt may be 0.5 M or less or 0.4 M or less, and the lower limit value is not limited, but may be 0.1 M or more.

[0062] If the molar concentration of the first lithium salt included in the mixed lithium salt is less than 0.1 M, there is a limit to improving the low-temperature characteristics, and if it exceeds 0.5 M, it may result in inferior high-temperature characteristics. Therefore, it is advantageous for the first lithium salt to have the molar concentration range described above.

[0063] The non-aqueous electrolyte composition of the present invention can obtain an optimal effect of forming a film for preventing corrosion on the electrode surface by including the mixed lithium salt and the mixed solvent described above. In addition, when the molar concentration ratio of the mixed lithium salt and the concentration of the first lithium salt satisfy the above range, the effect of improving the cycle characteristics during high-temperature storage of the electrochemical cell is sufficient, and the viscosity of the non-aqueous electrolyte is appropriate, so that the electrolyte impregnation property can be improved. Due to the organic relationship between the molar concentration ratio and the concentration of the first lithium salt, the ionic conductivity of the electrolyte increases up to a certain level as the number of charge carriers, i.e., lithium ions, increases. However, after a certain concentration, the lithium salts tend to form ion pairs by recombining at a rate faster than the rate of dissociation, which inhibits mobility and rather reduces ionic conductivity. Therefore, selecting an appropriate range is important.

[0064] In one embodiment of the present invention, the non-aqueous electrolyte composition may further include one or more additives selected from a cathode protector, a lithium salt stabilizer, a lithium deposition improver, an ion solvation promoter, a corrosion inhibitor, a wetting agent, a viscosity reducer, and a flame retardant. In this case, any additive known in the art may be used without limitation.

[0065] For example, the flame retardant included in the additive may be any one selected from among a phosphate compound, a phosphonate compound, a phosphazene compound, or a mixture thereof, but is not limited thereto.

[0066] In one specific example, the phosphate compound may be trimethyl phosphate, triethyl phosphate, tripropyl phosphate, triphenyl phosphate, tricresyl phosphate, tricylene phosphate, tris(2,2,2-trifluoroethyl phosphate), or the like.

[0067] The above phosphonate compound may be dimethyl methylphosphonate (DMMP), diethyl methylphosphonate (DEMP), or the like.

[0068] The above phosphazene compounds may include, but are not limited to, hexamethoxy cyclophosphazene (HMPN), hexatrifluoroethoxy cyclotriphosphazene (HTEPN), (ethoxy)pentafluoro cyclotriphosphazene (FPFN), etc.

[0069] Specifically, the additive may be included in an amount of 30 wt% or less, 25 wt% or less, 20 wt% or less, 15 wt% or less, 14 wt% or less, 13 wt% or less, 12 wt% or less, 11 wt% or less, 10 wt% or less, 9 wt% or less, 8 wt% or less, 7 wt% or less, 6 wt% or less, or 5 wt% or less based on the total weight of the non-aqueous electrolyte composition, and the lower limit value is not limited, but may be included in an amount of 0.01 wt% or more.

[0070] In one embodiment of the present invention, the non-aqueous electrolyte composition may be used in a battery selected from among a lithium ion battery, a lithium metal battery, a lithium air battery, and a lithium sulfur battery.

[0071] A second aspect of the present invention may include an electrochemical cell comprising: an anode; a cathode; a separator positioned between the anode and the cathode; and a non-aqueous electrolyte composition as described above.

[0072] Hereinafter, the present invention will be described in more detail through examples of the present invention. However, the following examples are provided only to help understanding of the present invention, and the contents of the present invention are not limited to the following examples.

[0073] [Example]

[0074] Example 1: Preparation of electrolyte for secondary batteries using mixed solvents

[0075] An electrolyte was prepared by adding LiPF6 to an organic solvent containing fluoroethylene carbonate (FEC) and methyl 3-methoxypropionate (MMP) in a volume ratio of 1:9 to obtain a concentration of 1 M.

[0076] Afterwards, LiNi was used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 A coin-type secondary battery was manufactured using lithium metal oxide (hereinafter referred to as NCM811) with an O2 composition, artificial graphite as an anode active material, and a polyethylene porous membrane as a separator using a conventional method.

[0077]

[0078] Examples 2 to 16: Preparation of electrolyte for secondary batteries with different volume ratios of mixed solvents

[0079] A secondary battery was manufactured using the same procedure as Example 1, but using an electrolyte prepared according to the composition shown in Table 1 below.

[0080]

[0081] Comparative Examples 1 to 3: Preparation of secondary battery electrolyte with different volume ratios of mixed solvents

[0082] A secondary battery was manufactured using the same procedure as Example 1, but using an electrolyte prepared according to the composition shown in Table 1 below.

[0083] Solvent (vol %)Lithium salt additiveExample 1MMP (90)FEC (10)1M LiPF6XExample 2MMP (90)FEC (10)1M LiFSIXExample 3MMP (80)FEC (20)XExample 4MMP (90)FEC (10)1M LiTFSIXExample 5MMP (85)FEC (15)XExample 6MMP (80)FEC (20)XExample 7MMP (75)FEC (25)XExample 8MMP (70)FEC (30)XExample 9MMP (60)FEC (40)XExample 10MEA (90)FEC (10)XExample 11MEA (80)FEC (20)XExample 12MEA (70)FEC (30)X Example 13MMA (90)FEC (10)X Example 14MMA (80)FEC (20)X Example 15MMA (70)FEC (30)X Example 16EEP (80)FEC (20)X Comparative Example 1EC (50)DEC (50)1M LiPF65wt% FEC Comparative Example 2EC (30)EMC (50)DEC (20)1M LiPF65wt% VC Comparative Example 3EP (80)FEC (20) 1M LiPF62wt% VC

[0084] In the above Table 1, MEA is 2-methoxy ethyl acetate, MMA is methyl methoxyacetate, EEP is ethyl 3-ethoxy propionate, EC is ethylene carbonate, DEC is diethyl carbonate, EMC is ethyl methyl carbonate, VC is vinylene carbonate, and EP is ethyl propionate.

[0085] Experimental Example 1: Comparative Evaluation of Room Temperature and Low Temperature Characteristics

[0086] The rate capability at room temperature and low temperature was compared and evaluated for the secondary batteries manufactured according to Examples 1 to 16 and Comparative Examples 1 to 3, and the results are summarized in Table 2 below.

[0087] The rate characteristics at room temperature were measured by charging the battery at a constant current of 0.2 C at 25°C until the voltage reached 4.3 V, charging at a constant voltage until the current reached 0.05 C while maintaining 4.3 V, and then discharging to 2.8 V, while changing the discharge rate to 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 3 C, and 4 C, respectively, and measuring the discharge capacity at each C-rate.

[0088] At this time, the rate characteristics at room temperature were calculated using Equation 1 below.

[0089] [Formula 1]

[0090] Room temperature rate characteristic (%) = Discharge capacity at 2C / Discharge capacity at 0.1C X 100

[0091] In addition, the rate characteristics at low temperatures were measured by charging at a constant current of 0.2 C at -30°C until the voltage reached 4.3 V, charging at a constant voltage until the current reached 0.05 C while maintaining 4.3 V, and then discharging to 2.8 V while changing the discharge rate to 0.05 C, 0.1 C, 0.15 C, 0.2 C, and 0.25 C, respectively, and measuring the discharge capacity at each C-rate, which was calculated using Equation 2 below.

[0092] [Formula 2]

[0093] Low temperature rate capability (%) = Discharge capacity at 0.25C / Discharge capacity at 0.05C X 100

[0094] Additionally, for each secondary battery, constant current charging was performed at 0.2C until the voltage reached 4.3V, constant voltage charging was performed while maintaining 4.3V until the current reached 0.05C, and then discharged at 0.1C until 2.8V at room temperature (25°C) and low temperature (-30°C), respectively. The low-temperature discharge characteristics were evaluated by calculating the discharge capacity at low temperature as a percentage of the discharge capacity at room temperature, and the results are summarized in Table 2 below.

[0095] Room temperature (25℃) rate characteristics (%) Low temperature (-30℃) rate characteristics (%) Low temperature (-30℃) discharge characteristics (%) Example 166.130.949.2 Example 275.851.452.1 Example 380.753.261.2 Example 482.167.351.9 Example 582.568.556.8 Example 685.670.364.7 Example 783.167.962.3 Example 875.859.659.6 Example 968.349.349.3 Example 1068.039.348.7 Example 1170.643.549.4 Example 1263.936.345.2Example 1375.542.149.6Example 1477.845.253.2Example 1569.241.347.3Example 1656.839.829.5Comparative Example 158.7N / AN / AComparative Example 269.219.815.1Comparative Example 362.122.126.2

[0096] Referring to Table 2 above, it can be seen that the examples have superior rate characteristics at both room temperature and low temperature compared to the comparative examples, and in particular, it was confirmed that the rate characteristics and discharge characteristics were significantly superior to the comparative examples at low temperatures. In the case of comparative example 1, since it was impossible to measure the low-temperature characteristics, an additional test was performed in which the electrolyte of comparative example 1 was exposed to an extremely low temperature of -30°C, and it was confirmed that the electrolyte was frozen.

[0097] Although not shown in the table above, the cycle life characteristics at room temperature were additionally confirmed, and it was confirmed that all examples had a capacity retention rate of 95% or higher after 150 cycles. At this time, the cycle life characteristics were evaluated by performing a process of charging at a constant current of 0.5C to 4.3 V at room temperature (25°C), then charging at a constant voltage while maintaining 4.3 V until the current became 0.05 C, and then discharging at 0.5 C to 2.8 V, repeating the process for a total of 150 cycles, and calculating the discharge capacity at the 150th cycle as a percentage compared to the discharge capacity at the first cycle.

[0098] Examples 17 to 28, Comparative Examples 4 and 5: Electrolyte for secondary batteries with different molar ratios of mixed lithium salts

[0099] A secondary battery was manufactured using an electrolyte prepared according to the composition shown in Table 3 below, with different lithium salts added independently.

[0100] Solvent (vol %)Lithium salt additiveExample 17MMP (90)FEC (10)0.9M LiPF60.1M LiTFSIXExample 18MMP (80)FEC (20)0.9M LiPF60.1M LiTFSIXExample 19MMP (90)FEC (10)0.7M LiPF60.3M LiTFSIXExample 20MMP (80)FEC (20)0.7M LiPF60.3M LiTFSIXExample 21MMP (70)FEC (30)0.7M LiPF60.3M LiTFSIXExample 22MMP (80)FEC (20)0.5M LiPF60.5M LiTFSIXExample 23MMP (80)FEC (20)0.3M LiPF60.7M LiTFSIX Example 24 MMP (80) FEC (20) 0.1M LiPF 6 0.9M LiTFSIX Example 25 MEA (80) FEC (20) 0.7M LiPF 6 0.3M LiTFSIX Example 26 MMA (80) FEC (20) 0.7M LiPF 6 0.3M LiTFSIX Example 27 MMP (80) FEC (20) 0.7M LiPF 6 0.3M LiTFSI 2wt% VC Example 28 MMP (80) FEC (20) 0.7M LiPF 6 0.3M LiTFSI 5wt% FPFN Comparative Example 4 EC (30) EMC (50) DEC (20) 0.7M LiPF 6 0.3M LiTFSI 5wt% VC Comparative Example 5 EP (80) FEC (20) 0.7M LiPF60.3M LiTFSI2wt% VC

[0101] In Table 3 above, FPFN is (ethoxy) pentafluorocyclotriphosphazene. Experimental Example 2: Comparative evaluation of low-temperature and high-temperature properties

[0102] The low-temperature and high-temperature characteristics of secondary batteries manufactured according to Examples 17 to 28 and Comparative Examples 4 to 5, in addition to the previously manufactured Examples 4, 6, 11, and 14, were compared and evaluated.

[0103] At this time, the low-temperature characteristics were calculated in the same manner as the low-temperature rate characteristics of the aforementioned Experimental Example 1 and compared, and the high-temperature characteristics were constant-current charged at 0.2 C at 45°C until the voltage reached 4.3 V, maintained at 4.3 V and constant-voltage charged until the current reached 0.05 C, and then discharged to 2.8 V, but changed the discharge rates to 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 3 C, and 4 C, respectively, and measured the discharge capacity for each C-rate to compare the high-temperature rate characteristics, and the results are summarized in Table 4 below.

[0104] At this time, the high temperature rate characteristics were calculated using the following equation 3.

[0105] [Formula 3]

[0106] High temperature rate capability (%) = Discharge capacity at 2C / Discharge capacity at 0.1C X 100

[0107] Low temperature (-30℃) rate characteristics (%) High temperature (45℃) rate characteristics (%) Example 467.362.1 Example 670.363.9 Example 1143.549.8 Example 1445.254.2 Example 1746.270.3 Example 1847.571.9 Example 1965.979.2 Example 2069.683.1 Example 2157.278.6 Example 2267.877.9 Example 2368.362.8 Example 2468.960.3 Example 2542.656.3 Example 2644.666.9 Example 2769.278.3 Example 2868.279.4 Comparison Example 420.978.1 Comparison Example 521.246.1

[0108] Referring to Table 4 above, it can be seen that when a mixed lithium salt is included and a specific molar ratio is satisfied in the mixed lithium salt, the high temperature rate characteristics can be significantly improved while maintaining excellent low temperature rate characteristics. Although not specifically shown in Table 4 above, the high temperature rate characteristics of Comparative Examples 2 and 3, which applied a single lithium salt instead of a mixed lithium salt, were 82.1% and 45.2%, respectively, indicating that even when a mixed lithium salt is applied as in Comparative Examples 4 and 5, it has little effect on the improvement of the high temperature rate characteristics, and it can be seen that the low temperature rate characteristics are also at an equivalent level.

[0109] On the other hand, when comparing Example 6 and Example 20, it can be seen that while the low-temperature rate characteristics are at an equivalent level, the high-temperature rate characteristics are significantly superior in Example 20, to which a specific molar ratio of mixed lithium salts is applied. In particular, it can be seen that Example 20 exhibits high-temperature characteristics at an equivalent level to those in the case where the electrolyte included in Comparative Example 1 or Comparative Example 20 is applied. In other words, it can be seen that it exhibits significantly superior low-temperature characteristics compared to Comparative Example 1 or Comparative Example 20, which has very poor low-temperature characteristics, while at the same time exhibiting high-temperature characteristics at an equivalent level.

[0110] Furthermore, it was confirmed that the room temperature rate characteristics were similar to those when an electrolyte containing a single lithium salt was applied when a mixed lithium salt was included and a specific molar ratio was satisfied in the mixed lithium salt.

[0111] As can be seen from Tables 2 and 4 mentioned above, in general, in the case of organic electrolytes, low-temperature characteristics and high-temperature characteristics are in a conflicting relationship, but the non-aqueous electrolyte composition according to one embodiment of the present invention includes the mixed solvent mentioned above and a mixed lithium salt including an imide-based lithium salt and a lithium salt different from the above-mentioned imide-based lithium salt that optionally satisfies a specific molar ratio, thereby exhibiting improved low-temperature characteristics while also having excellent high-temperature characteristics, and thus has the advantage of being able to provide excellent performance in a wide temperature range including not only an extremely low-temperature environment but also a high-temperature environment, unlike the prior art.

[0112] The above description of the present invention is for illustrative purposes only, and those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single entity may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined manner.

[0113] The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims

1. Lithium salt; A first organic solvent comprising at least one selected from among a cyclic carbonate compound and a cyclic ester compound; and A composition for a non-aqueous electrolyte, comprising a second organic solvent comprising a compound containing an ether group and an ester group.

2. In paragraph 1, A composition for a non-aqueous electrolyte, wherein the second organic solvent comprises at least one selected from the group consisting of a first compound represented by the following chemical formula 1, a second compound represented by the following chemical formula 2, and a mixture thereof. [Chemical Formula 1] ; [Chemical Formula 2] ; The above R1 is a linear or branched alkyl group having 1 to 10 carbon atoms, The above R4 is hydrogen or a linear or branched alkyl group having 1 to 10 carbon atoms, The above R2 and R5 are each independently a linear or branched alkylene group having 1 to 10 carbon atoms, The above R3 and R6 are each independently a linear or branched alkyl group having 1 to 10 carbon atoms.

3. In paragraph 1, A non-aqueous composition wherein the second organic solvent is a compound satisfying the chemical formula 1. [Chemical Formula 1] ; The above R1 is a linear or branched alkyl group having 1 to 10 carbon atoms, The above R2 is a linear or branched alkylene group having 1 to 10 carbon atoms, The above R3 is a linear or branched alkyl group having 1 to 10 carbon atoms.

4. In paragraph 1, A composition for a non-aqueous electrolyte, wherein the lithium salt is a mixed lithium salt comprising a first lithium salt that is an imide-based lithium salt and a second lithium salt that is independently different from the first lithium salt.

5. In paragraph 4, A composition for a non-aqueous electrolyte, wherein the above imide-based lithium salt comprises at least one selected from LiN(SO2C2F5)2, LiN(SO2CF3)2, LiN(SO2CF3)(SO2C2F5), LiN(SO2CF3)(SO2C3F7), and LiN(SO2F)2.

6. In paragraph 4, A composition for a non-aqueous electrolyte, wherein the second lithium salt comprises at least one selected from LiPF6, LiAsF6, LiPF4(C2O4), LiPF2(C2O4)2, LiBF4, LiB(C2O4)2, LiBF2(C2O4), LiClO4, LiBrO4, LiIO4, LiB(C6H5)4, LiCH3SO3, and LiCF3SO3.

7. In paragraph 4, A composition for a non-aqueous electrolyte, wherein the molar concentration ratio of the first lithium salt to the second lithium salt included in the above mixed lithium salt is 1:9 to 9:

1.

8. In paragraph 7, A composition for a non-aqueous electrolyte, wherein the molar concentration of the first lithium salt is 0.5 M or less.

9. In paragraph 1, A composition for a non-aqueous electrolyte, wherein the cyclic carbonate compound comprises at least one selected from ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, and 1-fluoropropylene carbonate.

10. In paragraph 1, A composition for a non-aqueous electrolyte, wherein the cyclic ester compound comprises at least one selected from γ-butyrolactone, γ-valerolactone, σ-valerolactone, γ-caprolactone, ε-caprolactone, and 4-vinyl-1,3-dioxolan-2-one.

11. In paragraph 1, A composition for a non-aqueous electrolyte, wherein the volume ratio of the first organic solvent to the second organic solvent is 1:9 to 4:

6.

12. In paragraph 1, A composition for a non-aqueous electrolyte, further comprising at least one selected from a cathode protector, a lithium salt stabilizer, a lithium deposition improver, an ion solvation promoter, a corrosion inhibitor, a wetting agent, a viscosity reducer, and a flame retardant.

13. In paragraph 12, A composition for a non-aqueous electrolyte, wherein the flame retardant comprises at least one selected from the group consisting of a phosphate compound, a phosphonate compound, a phosphazene compound, or a mixture thereof.

14. In paragraph 1, The non-aqueous electrolyte composition is used in a battery selected from among a lithium ion battery, a lithium metal battery, a lithium air battery, and a lithium sulfur battery.

15. Bipolar; cathode; A separator positioned between the anode and cathode; and Composition for non-aqueous electrolyte according to Article 1 An electrochemical cell comprising:

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