Composition for non-aqueous electrolyte and electrochemical cell comprising same

Abstract

The present invention relates to a composition for a non-aqueous electrolyte comprising a mixed solvent and optionally a dilithium salt, and an electrochemical cell comprising the composition for a non-aqueous electrolyte.

Description

Technical Field

[0001] The present invention relates to a composition for a non-aqueous electrolyte comprising a mixed solvent and an optional double lithium salt, and an electrochemical cell comprising the composition for the non-aqueous electrolyte. Background Technology

[0002] Beyond electronic devices like mobile phones, cameras, or laptops, the demand for high-energy-density secondary batteries is increasing, serving as a power source for mobile devices such as drones (taxis) and electric vehicles. Research on lithium secondary batteries that can meet this demand is actively underway.

[0003] Commercial lithium-ion batteries typically contain an electrolyte consisting of a mixture of lithium salt and organic solvent. The organic solvent that makes up the electrolyte is a carbonate solvent, taking into account electrical properties and chemical stability.

[0004] However, existing electrochemical cells containing carbonate solvents exhibit unstable charging characteristics at temperatures below 0°C, leading to a high potential for safety issues. Therefore, they are designed with charging limited, especially at temperatures below -20°C, where there are significant reductions in discharge capacity and a sharp decline in cycle life. Therefore, there is a need to develop an electrolyte for electrochemical cells that is stable even at low temperatures, possesses excellent flame retardancy and heat resistance, exhibits superior high-speed charge-discharge characteristics, and can operate stably in various environments.

[0005] Existing technical documents

[0006] (Patent Document 001) Korean Patent 10-0810634 Summary of the Invention

[0007] Technical issues

[0008] 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 especially excellent high-speed charge and discharge characteristics, as well as an electrochemical battery cell containing the non-aqueous electrolyte composition.

[0009] However, the problems to be solved by the present invention are not limited to those mentioned above, and those skilled in the art can clearly understand other problems not mentioned from the following description.

[0010] Technical means

[0011] A first aspect of the present invention provides a composition for a non-aqueous electrolyte, comprising: a lithium salt; a first organic solvent comprising one or more selected from cyclic carbonate compounds and cyclic ester compounds; and a second organic solvent comprising a compound containing an ether group and an ester group.

[0012] A second aspect of the present invention provides an electrochemical battery cell comprising: a positive electrode; a negative electrode; a separator located between the positive and negative electrodes; and a composition for a non-aqueous electrolyte according to the first aspect.

[0013] Invention Effects

[0014] A non-aqueous electrolyte composition according to an embodiment of the present invention comprises a mixed solvent containing a first organic solvent and a second organic solvent, and a lithium salt, and is characterized by significantly improved low-temperature characteristics compared to conventional carbonate-based electrolytes by using a mixed solvent that minimizes the binding energy with lithium ions. Furthermore, it also has the advantage of excellent high-speed charge-discharge characteristics.

[0015] Moreover, organic electrolytes typically exhibit a trade-off relationship between low-temperature and high-temperature properties. However, according to an embodiment of the present invention, the non-aqueous electrolyte composition, which contains the aforementioned mixed solvent and optionally a mixed lithium salt containing an imide lithium salt and a lithium salt different from it, exhibits improved low-temperature properties, as well as excellent high-temperature properties, improved flame retardancy, and significantly improved safety. Detailed Implementation

[0016] The embodiments of the present invention will now be described in detail to enable those skilled in the art to readily implement them. However, the present invention can be implemented in many different ways and is not limited to the embodiments described herein.

[0017] Throughout this invention, when it is mentioned that a component is "on" another component, it includes not only the case where the component is in contact with the other component, but also the case where there are other components between the two components.

[0018] Throughout this specification, when a part "comprises" a certain element, it means that other elements may also be included, rather than excluding, unless specifically stated otherwise. The terms "about," "substantially," etc., used throughout this specification are used in a sense equal to or close to the numerical values ​​inherent in the meaning, and are intended to prevent unethical infringers from improperly using the precise or absolute numerical disclosures provided to aid in understanding the invention. The terms "~(perform) step" or "~ step" used throughout this specification do not mean "for the purpose of ~ step."

[0019] Throughout this specification, the term “combinations of them” in the Markush form refers to a mixture or combination of one or more of the constituent elements described in the Markush form, and includes one or more of the constituent elements described above.

[0020] Throughout this specification, the reference to "A and / or B" means "A or B, or A and B".

[0021] Hereinafter, implementation examples and embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to these implementation examples, embodiments, and drawings.

[0022] A first aspect of the present invention provides a composition for a non-aqueous electrolyte, comprising: a lithium salt; a first organic solvent comprising one or more selected from cyclic carbonate compounds and cyclic ester compounds; and a second organic solvent comprising a compound containing an ether group and an ester group.

[0023] Existing non-aqueous electrolyte compositions contain organic solvents that are a mixture of carbonate solvents such as EC (ethylene carbonate), PC (propylene carbonate), DMC (dimethyl carbonate), EMC (ethylene methyl carbonate), and DEC (diethyl carbonate). However, existing electrolytes containing the above-mentioned carbonate solvents have the following drawbacks: the performance of the electrochemical cell deteriorates sharply at temperatures below -15°C, especially at temperatures below -20°C, where the discharge voltage of the electrochemical cell drops significantly to the point where the electronic device becomes unusable.

[0024] Therefore, in order to solve the above problems, an electrolyte with nitrile solvents added to the above organic solvents was proposed. However, the improvement of low-temperature properties is limited and the high-temperature properties deteriorate.

[0025] On the other hand, the non-aqueous electrolyte composition of the present invention, because it contains a lithium salt and the aforementioned mixed solvent containing a first organic solvent and a second organic solvent, significantly improves low-temperature characteristics compared to existing carbonate-based electrolytes. In particular, even at extremely low temperatures below -30°C, the electrochemical reaction rate is significantly improved, which is beneficial for high-speed charge and discharge.

[0026] Furthermore, the low-temperature and high-temperature properties of organic electrolytes are usually in a trade-off relationship, but the non-aqueous electrolyte composition according to an embodiment of the present invention exhibits improved low-temperature properties while maintaining high-temperature properties, thus enabling stable electrochemical properties over a wide temperature range.

[0027] In one embodiment of the present invention, the composition for non-aqueous electrolytes may comprise a mixed solvent as described above, which is a mixture of a first organic solvent comprising one or more selected from cyclic carbonate compounds and cyclic ester compounds and a second organic solvent comprising compounds containing ether groups and ester groups.

[0028] As an example, the cyclic carbonate compound contained in the first organic solvent may include one or more 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.

[0029] Furthermore, the cyclic ester compound contained in the first organic solvent may include one or more selected from γ-butyrolactone, γ-valerolactone, σ-valerolactone, γ-caprolactone, ε-caprolactone, and 4-vinyl-1,3-dioxolan-2-one.

[0030] An electrolyte containing a mixed solvent of one or more first organic solvents selected from the above-mentioned cyclic carbonate compounds and cyclic ester compounds helps to form a stable and functional SEI (Solid Electrolyte Interface) layer in an electrochemical cell, and has a high dielectric constant, enabling it to effectively dissociate lithium salts in the electrolyte.

[0031] Specifically, by stably forming an SEI film on the electrode layer using a first organic solvent, side reactions between the electrolyte and the electrode can be effectively suppressed.

[0032] As a preferred example, the first organic solvent may contain one or more selected from the above-mentioned cyclic carbonate compounds. As a specific example, it may contain one or more selected from fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, and 1-fluoropropylene carbonate, which are fluorinated cyclic carbonate compounds.

[0033] When the first organic solvent contains a fluorinated cyclic carbonate compound containing fluorine atoms as described above, it can stably form an SEI layer, while also improving the thermal stability and electrochemical antioxidant properties of the electrolyte, thus offering more advantageous benefits.

[0034] In one embodiment of the present invention, the content of the first organic solvent can be 5 to 50% by volume, 10 to 50% by volume, 15 to 50% by volume, 20 to 50% by volume, 5 to 45% by volume, 10 to 45% by volume, 15 to 45% by volume, 20 to 45% by volume, 5 to 40% by volume, 10 to 40% by volume, 15 to 40% by volume, 20 to 40% by volume, 5 to 35% by volume, 10 to 35% by volume, 15 to 35% by volume, 20 to 35% by volume, 5 to 30% by volume, 10 to 30% by volume, 15 to 30% by volume, 20 to 30% by volume, 5 to 25% by volume, 10 to 25% by volume, 15 to 25% by volume, or 20 to 25% by volume, based on the total volume of the mixed solvent.

[0035] When the first organic solvent contained in the mixed solvent meets the above-mentioned range, the low-temperature characteristics of the electrochemical cell containing the above-mentioned mixed solvent can be significantly improved through the synergistic effect with the second organic solvent described later.

[0036] In one embodiment of the present invention, in addition to the first organic solvent described above, the second organic solvent included in the mixed solvent is a compound containing ether and ester groups, and can be a low-melting-point organic solvent. In this case, the melting point of the second organic solvent can be below -20°C, below -30°C, below -40°C, or below -50°C, with no limitation on the lower limit, but it can be -150°C or -100°C.

[0037] In one embodiment of the present invention, the second organic solvent may comprise one or more compounds selected from the group consisting of a first compound represented by chemical formula 1, a second compound represented by chemical formula 2, and mixtures thereof.

[0038] [Chemical Formula 1]

[0039] ;

[0040] [Chemical Formula 2]

[0041] ;

[0042] R1 is a straight-chain or branched alkyl group having 1 to 10 carbon atoms, R4 is hydrogen or a straight-chain or branched alkyl group having 1 to 10 carbon atoms, R2 and R5 are each independently a straight-chain or branched alkylene group having 1 to 10 carbon atoms, and R3 and R6 are each independently a straight-chain or branched alkyl group having 1 to 10 carbon atoms.

[0043] When the second organic solvent contained in the mixed solvent contains one or more of the first compound, the second compound, and mixtures thereof, the decrease in the solubility of lithium salt contained in the electrolyte can be suppressed even at low or extremely low temperatures, which is beneficial to improving the low-temperature characteristics of the electrochemical cell.

[0044] Specifically, the aforementioned second organic solvent may comprise 2-methoxyethylacetate, 2-ethoxyethyl acetate, propylene glycol monomethyl ether acetate, methylmethoxyacetate, methyl ethoxy acetate, methyl 3-methoxypropionate, β-ethoxy-propionate, ethyl 2-methoxyacetate, ethyl 2-ethoxyethanoate, ethyl 3-methoxy-propionate, ethyl 3-ethoxypropionate, ethyl 3-methoxypropionate, and methyl 2-methoxypropionate. The following are selected from one or more of the following: 2-methoxypropionate, methyl 3-methoxy-2-methylpropionic acid methyl ester, methyl 3-methoxybutyrate, methyl 3-methoxyisobutyrate, methyl 4-methoxybutanoate, methyl-3-methoxy-2-methylbutyrate, and mixtures thereof.

[0045] As a preferred example, the second organic solvent may be a compound that satisfies the above chemical formula 1.

[0046] [Chemical Formula 1]

[0047] ;

[0048] R1 is a straight-chain or branched alkyl group having 1 to 10 carbon atoms, R2 is a straight-chain or branched alkylene group having 1 to 10 carbon atoms, and R3 is a straight-chain or branched alkyl group having 1 to 10 carbon atoms.

[0049] As a specific example, a compound satisfying the above chemical formula 1 may include one or more selected from 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 4-methoxybutanoate, and methyl -3-methoxy-2-methylbutyrate.

[0050] As a more preferred example, the second organic solvent may be a solvent that satisfies the above chemical formula 1 and has a relatively low or minimum binding energy with lithium ions. As a specific example, it may be methyl 3-methoxypropionate.

[0051] In this way, when the second organic solvent is a compound with a relatively low or minimum binding energy to lithium ions and satisfies the above chemical formula 1, the solvation and desolvation behavior of lithium ions in the electrolyte can occur more favorablely. In particular, even at extremely low temperatures, the non-fluidity of the electrolyte can be maintained, thereby reducing the decrease in ion migration rate and possessing the advantage of being conducive to high-speed charging and discharging.

[0052] In one embodiment of the present invention, the content of the second organic solvent can be 50 to 95% by volume, 55 to 95% by volume, 60 to 95% by volume, 65 to 95% by volume, 70 to 95% by volume, 75 to 95% by volume, 80 to 95% by volume, 85 to 95% by volume, 50 to 90% by volume, 55 to 90% by volume, 60 to 90% by volume, 65 to 90% by volume, 70 to 90% by volume, 75 to 90% by volume, 80 to 90% by volume, 85 to 90% by volume, 50 to 85% by volume, 55 to 85% by volume, 60 to 85% by volume, 65 to 85% by volume, 70 to 85% by volume, 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.

[0053] When the second organic solvent contained in the mixed solvent, in addition to the first organic solvent mentioned above, meets the above-mentioned range, it has the following advantages through the synergistic effect with the first organic solvent: the low-temperature performance degradation of the electrochemical cell containing the above-mentioned mixed solvent can be minimized.

[0054] In one embodiment of the present invention, in order to effectively improve the low-temperature characteristics of the electrochemical cell, the volume ratio of the first organic solvent to the second organic solvent in the mixed solvent can be from 1:9 to 5:5.

[0055] As specific examples, the above volume ratios can 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.

[0056] When the first organic solvent contained in the mixed solvent is less than 10% by volume or more than 50% by volume based on the total volume of the mixed solvent, the synergistic effect between the first organic solvent and the simultaneously contained second organic solvent decreases, which may limit the improvement of the low-temperature characteristics of the electrochemical cell. Therefore, the above volume ratio preferably meets the above range.

[0057] In one embodiment of the present invention, the lithium salt contained in the non-aqueous electrolyte composition may include an imide lithium salt, thereby having the advantage of significantly improving charge-discharge characteristics at extremely low temperatures of -30°C. That is, the aforementioned imide lithium salt significantly improves charge-discharge performance at extremely low temperatures through the synergistic effect of the mixed solvent formed by mixing the first organic solvent and the second organic solvent.

[0058] At this time, the imide lithium salt may contain one or more selected from LiN(SO2C2F5)2, LiN(SO2CF3)2[LiTFSI], LiN(SO2CF3)(SO2C2F5), LiN(SO2CF3)(SO2C3F7) and LiN(SO2F)2[LiFSI].

[0059] In one embodiment of the present invention, the concentration of the lithium salt in the above-mentioned non-aqueous electrolyte composition can be from 0.1M to 3.0M. Specifically, the concentration of the lithium salt in the above-mentioned non-aqueous electrolyte composition can be 0.1 to 3.0M, 0.1 to 2.5M, 0.1 to 2.0M, 0.1 to 1.5M, 0.5 to 3.0M, 0.5 to 2.5M, 0.5 to 2.0M, or 0.5 to 1.5M, but is not limited thereto.

[0060] In a preferred embodiment, the lithium salt may be a mixed lithium salt comprising a first lithium salt as an imide lithium salt and a second lithium salt that is independent of and different from the first lithium salt.

[0061] When the above-mentioned mixed lithium salt is included in the non-aqueous electrolyte composition of the present invention, the low-temperature characteristics of the above-mentioned electrochemical cell can be significantly improved, while ensuring that the high-temperature characteristics reach the level of existing electrolytes containing carbonate solvents. Therefore, it has the advantage of being able to use the electrochemical cell with excellent performance over a wide temperature range.

[0062] In one embodiment of the present invention, the above-mentioned imide lithium salt (first lithium salt) may contain one or more selected from LiN(SO2C2F5)2, LiN(SO2CF3)2[LiTFSI], LiN(SO2CF3)(SO2C2F5), LiN(SO2CF3)(SO2C3F7) and LiN(SO2F)2[LiFSI].

[0063] In one embodiment of the present invention, the second lithium salt may comprise one or more selected from LiPF6, LiAsF6, LiPF4(C2O4), LiPF2(C2O4)2, LiBF4, LiB(C2O4)2, LiBF2(C2O4), LiClO4, LiBrO4, LiIO4, LiB(C6H5)4, LiCH3SO3, and LiCF3SO3.

[0064] In one embodiment of the present invention, the molar ratio of the first lithium salt to the second lithium salt in the above-mentioned mixed lithium salt can be 1:9 to 9:1, 1:9 to 7:3 or 1:9 to 5:5.

[0065] As a preferred example, the molar ratio of the first lithium salt to the second lithium salt can be from 1:9 to 4:6, more preferably from 2:8 to 4:6, and even more preferably from 3:7.

[0066] When the molar concentration ratio of the first lithium salt to the second lithium salt meets the above range, the electrochemical cell containing the non-aqueous electrolyte composition of the present invention can not only exhibit excellent low-temperature characteristics, but also excellent high-temperature characteristics, thus achieving excellent electrochemical cell performance over a wide temperature range.

[0067] At this point, the molar concentration of the first lithium salt can be below 0.5M or below 0.4M, with no lower limit, but it can be above 0.1M.

[0068] When the molar concentration of the first lithium salt in the mixed lithium salt is less than 0.1M, there is a limitation to improving low-temperature characteristics. When it exceeds 0.5M, it may lead to deterioration of high-temperature characteristics. Therefore, it is preferable that the first lithium salt has the above molar concentration range.

[0069] The non-aqueous electrolyte composition of the present invention, by comprising the aforementioned mixed lithium salt and mixed solvent, achieves optimal anti-corrosion film formation on the electrode surface. Furthermore, when the molar ratio of the mixed lithium salt and the concentration of the first lithium salt satisfy the aforementioned range, the cycling characteristics of the electrochemical cell during high-temperature storage are sufficiently improved, and the viscosity of the non-aqueous electrolyte is appropriate, improving the wettability of the electrolyte. Due to the inherent correlation between the molar ratio and the concentration of the first lithium salt, within a certain range, the ionic conductivity of the electrolyte increases with the increase of the number of charge carriers (i.e., lithium ions). However, exceeding a certain concentration, compared to the dissociation rate of the lithium salt, the recombination to form ion pairs is suppressed, and the ionic conductivity tends to decrease. Therefore, selecting an appropriate range is crucial.

[0070] In one embodiment of the present invention, the above-mentioned non-aqueous electrolyte composition may further include one or more additives selected from negative electrode protectants, lithium salt stabilizers, lithium deposition improvers, ion solvation promoters, corrosion inhibitors, wetting agents, viscosity reducers, and flame retardants. In this case, additives known in the art can be used without limitation.

[0071] As an example, the flame retardant contained in the above-mentioned additives may be any of the following, but is not limited to: phosphate compounds, phosphonate compounds, phosphazene compounds, or mixtures thereof.

[0072] As specific examples, the aforementioned phosphate compounds may be trimethyl phosphate, triethyl phosphate, tripropyl phosphate, triphenyl phosphate, tricresyl phosphate, tridimethyl phosphate, tri(2,2,2-trifluoroethyl) phosphate, etc.

[0073] The aforementioned phosphonate compounds can be dimethyl methylphosphonate (DMMP), diethyl methylphosphonate (DEMP), etc.

[0074] The aforementioned phosphazene compounds may be hexamethoxycyclophosphonitrile (HMPN), hexafluoroethoxycyclotriphosphonitrile (HTEPN), (ethoxy)pentafluorocyclotriphosphonitrile (FPFN), etc., but are not limited to these.

[0075] Specifically, based on the total weight of the above-mentioned non-aqueous electrolyte composition, the content of the above-mentioned additives can be less than 30% by weight, less than 25% by weight, less than 20% by weight, less than 15% by weight, less than 14% by weight, less than 13% by weight, less than 12% by weight, less than 11% by weight, less than 10% by weight, less than 9% by weight, less than 8% by weight, less than 7% by weight, less than 6% by weight, less than 5% by weight, and there is no limit to the lower limit, but it can be more than 0.01% by weight.

[0076] In one embodiment of the present invention, the above-described non-aqueous electrolyte composition can be used in a battery selected from lithium-ion batteries, lithium metal batteries, lithium-air batteries, and lithium-sulfur batteries.

[0077] A second aspect of the present invention may include an electrochemical cell comprising: a positive electrode; a negative electrode; a membrane located between the positive and negative electrodes; and the aforementioned non-aqueous electrolyte composition.

[0078] The present invention will be described in more detail below through embodiments, but the following embodiments are only for the purpose of helping to understand the present invention, and the content of the present invention is not limited to the following embodiments.

[0079] [Example]

[0080] Example 1: Preparation of electrolyte for secondary batteries using mixed solvents

[0081] An electrolyte was prepared by adding LiPF6 to an organic solvent containing a 1:9 volume ratio of fluoroethylene carbonate (FEC) and methyl 3-methoxypropionate (MMP) to a concentration of 1M.

[0082] Then, using LiNi 0.8 Co 0.1 Mn 0.1 A coin-shaped secondary battery was prepared using a lithium metal oxide composed of O2 (hereinafter referred to as NCM811) as the positive electrode active material, artificial graphite as the negative electrode active material, and a polyethylene porous membrane as the separator, through conventional methods.

[0083] Examples 2 to 16: Preparation of electrolytes for secondary batteries with different mixed solvent volume ratios

[0084] The process was carried out in the same manner as in Example 1, but a secondary battery was prepared using an electrolyte prepared according to the composition shown in Table 1 below.

[0085] Comparative Examples 1 to 3: Preparation of electrolytes for secondary batteries with different mixed solvent volume ratios

[0086] The process was carried out in the same manner as in Example 1, but a secondary battery was prepared using an electrolyte prepared according to the composition shown in Table 1 below.

[0087] [Table 1]

[0088]

[0089] In Table 1 above, MEA is 2-methoxyethyl acetate, MMA is methylmethoxyacetic acid, EEP is ethyl 3-ethoxypropionate, EC is ethylene carbonate, DEC is diethyl carbonate, EMC is methyl ethyl carbonate, VC is vinylene carbonate, and EP is ethyl propionate.

[0090] Experimental Example 1: Comparative Evaluation of Characteristics at Room Temperature and Low Temperature

[0091] The rate capability of the secondary batteries prepared according to Examples 1 to 16 and Comparative Examples 1 to 3 at room temperature and low temperature was compared and evaluated, and the results are summarized in Table 2 below.

[0092] The rate capability at room temperature was determined by charging at 0.2C constant current to a voltage of 4.3V at 25℃, maintaining 4.3V while charging at a constant voltage to a current of 0.05C, and then discharging to 2.8V. The discharge rates were changed to 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, and 4C, and the discharge capacity at each C-rate was measured.

[0093] At this point, the rate capability at room temperature is calculated using Equation 1 below.

[0094] [Formula 1]

[0095] Rate capability at room temperature (%) = Discharge capacity at 2C / Discharge capacity at 0.1C × 100

[0096] In addition, the rate capability at low temperature was determined by charging at a constant current of 0.2C to a voltage of 4.3V at -30℃, maintaining the voltage at 4.3V while charging at a constant voltage to a current of 0.05C, and then discharging to 2.8V. The discharge rates were changed to 0.05C, 0.1C, 0.15C, 0.2C, and 0.25C, respectively. The discharge capacity at each C-rate was measured and calculated using Equation 2 below.

[0097] [Equation 2]

[0098] Low-temperature rate capability (%) = Discharge capacity at 0.25C / Discharge capacity at 0.05C × 100

[0099] In addition, each secondary battery was charged at a constant current of 0.2C until the voltage reached 4.3V. While maintaining 4.3V, it was charged at a constant voltage until the current reached 0.05C. Then it was discharged at 0.1C to 2.8V. This was carried out at room temperature (25℃) and low temperature (-30℃). The percentage of discharge capacity at room temperature to discharge capacity at low temperature was calculated to evaluate the low temperature discharge characteristics. The results are summarized in Table 2 below.

[0100] [Table 2]

[0101]

[0102] Referring to Table 2 above, it can be seen that the examples exhibit superior rate performance compared to the comparative examples at both room temperature and low temperatures, especially showing significantly superior rate performance and discharge performance at low temperatures. Low-temperature performance of Comparative Example 1 could not be measured. Furthermore, the results of a -30°C extreme low-temperature exposure test on the electrolyte of Comparative Example 1 confirmed that the electrolyte froze.

[0103] Although not shown in the table above, the results of the cycle life characteristics at room temperature were further confirmed. All embodiments maintained a capacity retention of over 95% after 150 cycles. The cycle life characteristics were determined at room temperature (25°C) by charging at a constant current of 0.5C to 4.3V, maintaining 4.3V while charging at a constant voltage to a current of 0.05C, and then discharging at 0.5C to 2.8V. This constituted one cycle, and the cycle was repeated 150 times. The percentage of discharge capacity from the first cycle to the discharge capacity from the 150th cycle was then used for evaluation.

[0104] Examples 17 to 28, Comparative Examples 4 and 5: Electrolytes for secondary batteries with different lithium salt molar ratios

[0105] Secondary batteries were prepared by independently adding different lithium salts, but using electrolytes prepared according to the compositions shown in Table 3 below.

[0106] [Table 3]

[0107]

[0108] In Table 3 above, FPFN is (ethoxy)pentafluorocyclotriphosphazene.

[0109] Experimental Example 2: Comparative Evaluation of Low Temperature and High Temperature Characteristics

[0110] The low-temperature and high-temperature characteristics of the secondary batteries prepared in Examples 4, 6, 11 and 14, as well as Examples 17 to 28 and Comparative Examples 4 to 5, were compared and evaluated.

[0111] At this point, the low-temperature characteristics were calculated and compared in the same way as the low-temperature rate characteristics in Experiment Example 1 above. The high-temperature characteristics were calculated at 45°C by charging with a constant current of 0.2C until the voltage reached 4.3V, maintaining 4.3V while charging with a constant voltage until the current reached 0.05C, and then discharging to 2.8V. The discharge rates were changed to 0.1C, 0.2C, 0.5C, 1C, 2C, 3C and 4C respectively. The discharge capacity at each C-rate was measured, and the high-temperature rate characteristics were compared. The results are summarized in Table 4 below.

[0112] At this point, the high-temperature rate characteristic is calculated using the following formula 3.

[0113] [Formula 3]

[0114] High-temperature rate capability (%) = Discharge capacity at 2C / Discharge capacity at 0.1C × 100

[0115] [Table 4]

[0116]

[0117] Referring to Table 4 above, it can be seen that when a mixed lithium salt is included and the mixed lithium salt meets a specific molar ratio, the high-temperature rate performance can be significantly improved while maintaining excellent low-temperature rate performance. Specifically, although not shown in Table 4 above, the high-temperature rate performance of Comparative Examples 2 and 3, which use a single lithium salt without using a mixed lithium salt, is 82.1% and 45.2%, respectively. It can be seen that even if a mixed lithium salt is used as in Comparative Examples 4 and 5, there is almost no impact on the improvement of high-temperature rate performance, and the low-temperature rate performance is also at the same level.

[0118] On the other hand, comparing Examples 6 and 20 reveals that the low-temperature rate performance is at a similar level, while the high-temperature rate performance in Example 20, which uses a specific molar ratio of mixed lithium salts, shows significantly superior results. In particular, Example 20 exhibits high-temperature characteristics at a similar level to the electrolytes contained in Comparative Examples 1 or 2. That is, compared to Comparative Examples 1 or 2, which have very poor low-temperature characteristics, it exhibits significantly superior low-temperature characteristics while also exhibiting a similar level of high-temperature characteristics.

[0119] Furthermore, the rate characteristics at room temperature are similar; when mixed lithium salts are included and the mixed lithium salts meet a specific molar ratio, they exhibit similar results to those using an electrolyte containing a single lithium salt.

[0120] As shown in Tables 2 and 4 above, the low-temperature and high-temperature properties of organic electrolytes are usually in a trade-off relationship. However, the non-aqueous electrolyte composition of an embodiment of the present invention has the following advantages because it contains the above-mentioned mixed solvent and optionally a mixed lithium salt containing an imide lithium salt and a different lithium salt that meets a specific molar ratio: it exhibits improved low-temperature properties while also having excellent high-temperature properties. Unlike the prior art, it can provide excellent performance not only in extreme low-temperature environments but also in a wide temperature range including high-temperature environments.

[0121] The above description of the invention is exemplary, and those skilled in the art will understand that modifications can be readily made in other specific forms without altering the technical concept or essential features of the invention. Therefore, the above embodiments should be understood in all respects as exemplary, not restrictive. For example, the various constituent elements described as a single form may be implemented separately, and similarly, the constituent elements described as separate may be implemented in combination.

[0122] The scope of the invention is shown by the further description of the claims, but is not limited to the detailed description above, and all variations or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included within the scope of this disclosure.

Claims

1. A composition for a non-aqueous electrolyte, comprising: Lithium salts; The first organic solvent comprises one or more selected from cyclic carbonates and cyclic esters; and The second organic solvent includes compounds containing ether and ester groups.

2. The composition for non-aqueous electrolytes according to claim 1, wherein, The second organic solvent comprises one or more compounds selected from the group consisting of a first compound represented by chemical formula 1, a second compound represented by chemical formula 2, and mixtures thereof. [Chemical Formula 1] ； [Chemical Formula 2] ； R1 is a straight-chain or branched alkyl group having 1 to 10 carbon atoms. R4 is hydrogen or a straight-chain or branched alkyl group having 1 to 10 carbon atoms. R2 and R5 are each independently a straight-chain or branched alkylene group having 1 to 10 carbon atoms. R3 and R6 are each independently a straight-chain or branched alkyl group having 1 to 10 carbon atoms.

3. The composition for non-aqueous electrolytes according to claim 1, wherein, The second organic solvent is a compound that satisfies the following chemical formula 1: [Chemical Formula 1] ； R1 is a straight-chain or branched alkyl group having 1 to 10 carbon atoms. R2 is a straight-chain or branched alkylene group having 1 to 10 carbon atoms. R3 is a straight-chain or branched alkyl group having 1 to 10 carbon atoms.

4. The composition for non-aqueous electrolytes according to claim 1, wherein, The lithium salt is a mixed lithium salt comprising a first lithium salt as an imide lithium salt and a second lithium salt that is independent of and different from the first lithium salt.

5. The composition for non-aqueous electrolytes according to claim 4, wherein, The imide lithium salt comprises one or more selected from LiN(SO2C2F5)2, LiN(SO2CF3)2, LiN(SO2CF3)(SO2C2F5), LiN(SO2CF3)(SO2C3F7) and LiN(SO2F)2.

6. The composition for non-aqueous electrolytes according to claim 4, wherein, The second lithium salt comprises one or more 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. The composition for non-aqueous electrolytes according to claim 4, wherein, The mixed lithium salt contains a first lithium salt: second lithium salt with a molar concentration ratio of 1:9 to 9:

1.

8. The composition for non-aqueous electrolytes according to claim 7, wherein, The molar concentration of the first lithium salt is below 0.5 M.

9. The composition for non-aqueous electrolytes according to claim 1, wherein, The cyclic carbonate compounds comprise one or more selected from ethylene carbonate, propylene carbonate, butene carbonate, vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, and 1-fluoropropylene carbonate.

10. The composition for non-aqueous electrolytes according to claim 1, wherein, The cyclic ester compounds comprise one or more selected from γ-butyrolactone, γ-valerolactone, σ-valerolactone, γ-caprolactone, ε-caprolactone, and 4-vinyl-1,3-dioxolane-2-one.

11. The composition for non-aqueous electrolytes according to claim 1, wherein, The volume ratio of the first organic solvent to the second organic solvent is 1:9 to 4:

6.

12. The composition for non-aqueous electrolytes according to claim 1, wherein, It further includes one or more selected from negative electrode protectants, lithium salt stabilizers, lithium deposition improvers, ion solvation promoters, corrosion inhibitors, wetting agents, viscosity reducers, and flame retardants.

13. The composition for non-aqueous electrolytes according to claim 12, wherein, The flame retardant comprises one or more selected from the group consisting of phosphate compounds, phosphonate compounds, phosphazene compounds, or mixtures thereof.

14. The composition for non-aqueous electrolytes according to claim 1, wherein, The non-aqueous electrolyte composition is used in batteries selected from lithium-ion batteries, lithium metal batteries, lithium-air batteries, and lithium-sulfur batteries.

15. An electrochemical battery cell, comprising: positive electrode; negative electrode; The membrane located between the positive and negative electrodes; as well as The composition for non-aqueous electrolytes according to claim 1.

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