Electrolyte additive, and electrolyte and secondary battery comprising same

Abstract

The present invention relates to an electrolyte additive, and an electrolyte and a secondary battery comprising same, and provides an electrolyte additive comprising a cyclic phosphite-based compound having a predetermined structure, and an electrolyte and a secondary battery comprising same. According to the present invention, the secondary battery comprising the electrolyte has an excellent electrode protection effect, suppressing electrode degradation and gas generation, and furthermore, the high-temperature stability of the battery is greatly improved, such that increases in resistance and battery thickness are suppressed even after long-term storage at high temperatures, thereby providing a high-capacity secondary battery that exhibits excellent battery performance such as cycle characteristics.

Description

Electrolyte additive, electrolyte containing the same, and secondary battery

[0001] The present invention relates to an electrolyte additive, an electrolyte containing the same, and a secondary battery. More specifically, the invention relates to an electrolyte additive that maximizes the electrode protection effect to suppress gas generation, increase in resistance, and decrease in capacity, and further significantly improves the high-temperature stability of the battery, thereby suppressing the increase in resistance and battery thickness even after long-term storage at high temperatures, and exhibiting excellent battery performance improvement effects such as capacity retention rate and cycle characteristics, an electrolyte containing the same, and a secondary battery.

[0002] Lithium secondary batteries enable the smooth movement of lithium ions by charging an electrolyte between the positive and negative electrodes, and facilitate the utilization of electrical energy through a method in which electricity is generated or consumed by oxidation-reduction reactions resulting from insertion and extraction at the positive and negative electrodes.

[0003] Meanwhile, as environmental concerns grow due to the recent tightening of global environmental regulations, interest in eco-friendly vehicles capable of replacing fossil fuel vehicles—one of the main causes of air pollution—is also increasing. Consequently, the domestic and international battery industries are actively developing automotive batteries.

[0004] To utilize batteries in automobiles, not only must their output and capacity be significantly increased, but issues such as improved performance at high and low temperatures and increased resistance must also be addressed to suit operating environments like weather changes. Furthermore, considering that vehicles are used outdoors regardless of the season, it is necessary to develop batteries with improved long-term charge and capacity retention rates in various conditions. In particular, with the recent active research on high-capacity rechargeable batteries, studies on increasing the nickel content in nickel oxide-based rechargeable batteries using nickel oxide compounds as cathode active materials are gaining attention. However, while increasing nickel content raises battery capacity, it also severely degrades battery stability, such as the risk of fire; consequently, attempts are being made to manufacture rechargeable batteries that exhibit excellent stability while maintaining a high nickel content.

[0005] Meanwhile, in lithium secondary batteries, a functional film called CEI (cathode electrolyte interface) and SEI (solid electrolyte interface) is formed on the electrode surface in contact with the electrolyte during the initial battery activation process to chemically protect the anode and cathode. However, since the CEI or SEI generated by the basic electrolyte composition alone is insufficient for chemical and physical stability and, in particular, has poor durability against heat, various electrolyte additives have been proposed to form a CEI or SEI with superior electrode protection effects over a wide temperature range. The main functions of these additives vary depending on the type of compound, such as preventing impurity formation, improving thermal stability, preventing electrolyte / solvent decomposition, and flame retardancy. In some cases, however, they may cause problems such as adverse reactions; therefore, the additive must be appropriately selected according to the intended function.

[0006] For example, cyclic phosphite-based additives are known to have the effect of improving the high-temperature stability of batteries by forming CEI on the surface of the anode. However, as mentioned above, in order to provide a secondary battery that can prevent the degradation of battery performance and improve stability, and especially prevent accidents such as gas generation and fire even at high temperatures, even in the case of high-capacity batteries such as secondary batteries with high nickel content, there is an urgent need to develop additives capable of forming CEI or SEI with superior stability.

[0007] [Prior Art Literature]

[0008] [Patent Literature]

[0009] Japanese Published Patent No. 2008-300126 A

[0010] Korean Registered Patent 10-1586199 B1

[0011] In order to solve the problems of the prior art as described above, the present invention aims to provide an electrolyte additive with excellent electrode protection effect and battery performance and stability improvement effect, an electrolyte containing the same, and a secondary battery.

[0012] In addition, the present invention aims to provide an electrolyte additive suitable for application in the electrolyte of a high-capacity secondary battery and an electrolyte containing the same, which exhibits excellent high-temperature stability improvement effects, such as maintaining low resistance even when stored at high temperatures for a long period and suppressing gas generation and the increase in battery thickness.

[0013] In addition, the present invention aims to provide a secondary battery having enhanced stability and excellent battery performance despite its high capacity.

[0014] The above and other objectives of the present invention can all be achieved by the present invention described below.

[0015] To achieve the above objective, I) the present invention provides an electrolyte additive characterized by comprising a compound represented by the following chemical formula 1.

[0016] [Chemical Formula 1]

[0017]

[0018] (In the above Chemical Formula 1, R1 to R4 are each independently hydrogen, a C1 to C3 alkyl group, F, Cl, Br, or I, or R1 and R2, and R3 and R4 may each independently be substituted with oxygen (=O), R5 is an C1 to C5 alkylene group, and R6 and R7 are each independently hydrogen or a C1 to C3 alkyl group.)

[0019] II) In the above I), R6 and R7 may be at least one of the two, preferably both, alkyl groups having 1 to 3 carbon atoms.

[0020] III) In I) to II) above, R1 to R4 may be hydrogen, and R5 may be an alkylene group having 1 to 3 carbon atoms.

[0021] IV) In I) to III) above, the compound represented by Chemical Formula 1 may be a compound represented by Chemical Formula 2 below.

[0022] [Chemical Formula 2]

[0023]

[0024] V) In I) to IV) above, the electrolyte additive may be an anode film (CEI) forming agent.

[0025] The present invention also provides an electrolyte characterized by comprising: VI) an organic solvent; a lithium salt; and an electrolyte additive of any one of I) to V).

[0026] VII) In I) to VI) above, the electrolyte additive may be included in an amount of 0.05 to 3 weight% based on 100 weight% of the total electrolyte.

[0027] VIII) In I) to VII) above, the electrolyte may include vinylene carbonate (VC), and the vinylene carbonate may preferably be included in an amount of 0.5 to 5 weight% based on 100 weight% of the total electrolyte.

[0028] IX) In I) to VIII) above, the electrolyte may include vinyl ethylene carbonate (VEC), pentaerythritol cyclic disulfate (DTTO), or a mixture thereof, and the vinyl ethylene carbonate (VEC), pentaerythritol cyclic disulfate (DTTO), or a mixture thereof may preferably be included in an amount of 0.2 to 3 weight% based on 100 weight% of the total electrolyte.

[0029] X) In I) to IX) above, the organic solvent may include one or more selected from the group consisting of cyclic carbonates, chain carbonates, cyclic esters, and chain esters.

[0030] XI) In I) to X) above, the lithium salt is LiPF6, LiF4, LiCl, LiBr, LiI, LiClO4, LiB 10 Cl 10 It may include one or more selected from the group consisting of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, LiN(FSO2)2, LiN(CF3SO2)2, LiBF4, LiB(C2O4)2, LiBF2(C2O4), Li[PF2(C2O4)2], LiPF4(C2O4), LiPO2F2, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, LiSCN, and LiC(CF3SO2)3.

[0031] XII) In I) to XI) above, the electrolyte may be used in an NCA-based or NCM-based secondary battery.

[0032] XIII) In the above I) to XII), the electrolyte may be used in a secondary battery comprising a nickel oxide-based cathode, and preferably may be used in a secondary battery comprising a cathode active material in which the proportion of nickel among the transition metal components excluding lithium in the cathode active material is 50 mol% or more, more preferably 60 mol% or more.

[0033] The present invention also provides an electrolyte characterized by being used in an NCM-based secondary battery, wherein XIV) LiPF6 is included in an amount of 1.1 M to 1.2 M as a lithium salt, ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate are included as organic solvents in a volume ratio of 1:1.5 to 2.5:1.5 to 2.5, vinylene carbonate is included in an amount of 1 to 2 weight%, and a compound represented by the following chemical formula 2 is included in an amount of 0.1 to 1.5 weight%.

[0034] [Chemical Formula 2]

[0035]

[0036] The present invention also provides an electrolyte characterized by being used in an NCA-based secondary battery, wherein LiPF6 is included in an amount of 1.1 M to 1.2 M as a lithium salt, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate are included as organic solvents in a volume ratio of 1:1.5 to 2.5:1.5 to 2.5, vinylene carbonate is included in an amount of 1 to 2 weight%, a compound represented by the following chemical formula 2 is included in an amount of 0.1 to 1.5 weight%, vinylethylene carbonate is included in an amount of 0.3 to 0.7 weight%, and pentaerythritol cyclic disulfate is included in an amount of 0.5 to 1.5 weight%.

[0037] [Chemical Formula 2]

[0038]

[0039] The present invention also provides a secondary battery characterized by comprising: XVI) a negative electrode; a positive electrode; a separator; and an electrolyte of any one of VI) to XV).

[0040] XVII) In I) to XVI) above, the secondary battery may be an NCM-based secondary battery or an NCA-based secondary battery.

[0041] When the electrolyte additive according to the present invention is included in an electrolyte, it forms a robust and stable film on the surface of the electrode of a battery containing the additive and effectively scavenges by-products of the electrolyte decomposition reaction. Simultaneously, by maximizing the electrode protection effect through a strong chelating action on transition metals leached from the anode, it suppresses electrode collapse, gas generation due to electrolyte decomposition, increased resistance, and reduced capacity. Furthermore, the high-temperature stability of the battery is significantly improved, thereby suppressing the increase in resistance and battery thickness even after long-term storage at high temperatures and providing an electrolyte additive, an electrolyte containing the additive, and a secondary battery.

[0042] The present invention will be described in detail below, but the invention is not limited thereto.

[0043] While researching electrolyte additives capable of improving stability without performance degradation even in high-capacity secondary batteries, such as those with high nickel content, the inventors of the present invention confirmed that all of the above objectives could be achieved by including a compound of a predetermined structure in the electrolyte, and based on this, completed the present invention.

[0044]

[0045] The electrolyte additive according to the present invention is characterized by comprising a compound represented by the following chemical formula 1. In this case, a robust and highly stable anode film (CEI) is formed on the anode surface, thereby preventing electrode degradation, collapse of the electrode crystal structure, and gas generation caused by by-products. Furthermore, the high-temperature stability of the battery is significantly improved, so that even after long-term storage of more than 60 days at a high temperature such as 60°C, the increase in resistance and the increase in battery thickness are suppressed, and the battery performance improvement effect, such as high-temperature capacity retention rate and cycle characteristics, can be provided.

[0046] [Chemical Formula 1]

[0047]

[0048] In the above chemical formula 1, R1 to R4 are each independently hydrogen, an alkyl group having 1 to 3 carbon atoms, F, Cl, Br, or I, or R1 and R2, and R3 and R4 can each be independently substituted with oxygen (=O), R5 is an alkylene group having 1 to 5 carbon atoms, and R6 and R7 are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms. When R1 and R2, or R3 and R4, are substituted with oxygen (=O), they can form a carbonyl group (>C=O) together with the carbon to which they are bonded.

[0049] In the above formula 1, preferably, R1 to R4 are each independently selected from the group consisting of hydrogen and methyl groups, R5 is an alkylene group having 1 to 3 carbon atoms, and R6 and R7 are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, wherein at least one of the two may be an alkyl group having 1 to 3 carbon atoms, and more preferably, R1 to R4 are all hydrogen, R5 is an alkylene group having 1 to 3 carbon atoms, and R6 and R7 are both alkyl groups having 1 to 3 carbon atoms.

[0050] The compound represented by Chemical Formula 1 above can act as an anode film-forming agent that forms a chemically stable polymer film on the surface of the anode through a ring-open polymerization reaction while undergoing a battery activation process, thereby providing electrode protection and improved high-temperature stability. In addition, by a structure in which an N (nitrogen)-containing organic group with high electronegativity is substituted in the PO- portion of the cyclic phosphite, the adsorption force between the electrode and the film is enhanced without hindering the flow of ions, thereby strengthening the mechanical strength of the film; effectively scavenging acidic byproducts such as hydrofluoric acid (HF) generated by the decomposition of the electrolyte; and simultaneously forming a strong coordination bond with the transition metal leached from the anode to chelate the leached transition metal, thereby preventing electrode breakdown caused by acidic byproducts and preventing the leached transition metal from migrating to and depositing on the cathode, while suppressing gas generation, it is possible to prevent an increase in resistance and a decrease in capacity, and furthermore, by eliminating the deterioration factors of CEI and SEI, it is possible to provide the effect of further improving high-temperature stability. As a result, the compound represented by the above chemical formula 1 forms an anode film with higher mechanical strength compared to conventional cyclic phosphite compounds without hindering the flow of ions, and the electrode protection effect is maximized, so it is possible to provide effects such as suppressing gas generation, improving battery life and battery performance, and also has a particularly excellent effect of improving battery performance by preventing an increase in resistance and a decrease in capacity retention rate and cycle characteristics even when exposed to a high-temperature environment for a long period of time.

[0051] In this description, battery activation refers to a process in which a positive electrode and a negative electrode are stacked on both sides of a separator during the battery manufacturing process, an electrolyte is injected and sealed to form a battery cell, and after the cell assembly, the cell is stored to allow sufficient impregnation with the electrolyte, and then charge and discharge are performed under certain conditions. During this process, CEI and SEI may be formed on the surfaces of the positive and negative electrodes, respectively. Additionally, during this process, gas removal, verification of the capacity of the manufactured battery, and sorting of defective cells are performed.

[0052] In this regard, the compound represented by Chemical Formula 1 above may preferably be a compound represented by Chemical Formula 2 below. When the structure of the cyclic phosphite portion is simplified in this way and a specific organic group is substituted in the PO- portion thereof, the strength enhancement of the anode film, the scavenging of acidic byproducts, and the chelating action on eluted transition metals are maximized without hindering ion flow, thereby providing a superior electrode protection effect and improved high-temperature stability effect compared to conventional methods. This results in excellent advantages in improving battery performance, such as suppressing the increase in resistance of the battery, cycle characteristics, and long-term high-temperature life, even after long-term storage at high temperatures.

[0053] [Chemical Formula 2]

[0054]

[0055]

[0056] The compound represented by Chemical Formula 1 above provides a significantly excellent electrode protection effect, and thus has the advantage of being suitable as an electrolyte additive for use in the electrolyte of high-capacity batteries. As a preferred example, when the compound represented by Chemical Formula 1 is applied as an additive to the electrolyte of an NCA-based secondary battery or an NCM-based secondary battery, it is possible to simultaneously improve battery stability and battery performance. In particular, as battery stability is significantly improved not only in secondary batteries with low nickel content but also in cases with high nickel content such as high-nickel secondary batteries, the loading amount of the cathode active material can be increased due to this improved battery stability effect, making it possible to design the battery output characteristics to be higher. Therefore, it has the advantage of being suitable for applications requiring high capacity and high output.

[0057] In this description, a high-nickel (High-Ni) secondary battery refers to a secondary battery in which the proportion of nickel among the transition metal components excluding lithium in the positive electrode active material is greater than 60 mol%, preferably 65 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more.

[0058] The compound represented by the above chemical formula 2 can be synthesized, for example, through the reaction pathway shown in the following reaction scheme 1.

[0059] [Reaction Equation 1]

[0060]

[0061]

[0062] The present invention also provides an electrolyte comprising an organic solvent, a lithium salt, and an electrolyte additive represented by the formula 1, wherein a robust and highly stable film is formed on the electrode surface of the battery, and the electrode protection effect can be maximized through effective scavenging action of acidic byproducts and strong chelating action on eluted transition metals, thereby suppressing gas generation and suppressing resistance increase and capacity decrease, and furthermore, the high-temperature stability of the battery is greatly improved, so that even after long-term storage of more than 60 days at a high temperature such as 60°C, the increase in resistance and battery thickness is suppressed and there is an excellent effect of improving battery performance such as cycle characteristics.

[0063] The compound represented by the above chemical formula 1 may be included, for example, in an amount of 0.05 to 3 weight% based on the total weight of the electrolyte, preferably 0.05 to 2.5 weight%, more preferably 0.07 to 2 weight%, even more preferably 0.08 to 1.5 weight%, even more preferably 0.1 to 1.2 weight%, and even more preferably 0.1 to 1 weight%, particularly preferably 0.2 to 0.6 weight%, and most preferably 0.23 to 0.55 weight%, and in this case, there is an advantage that all the aforementioned objective effects can be achieved without degrading battery performance.

[0064] The above organic solvent may include, for example, one or more selected from the group consisting of cyclic carbonates, chain carbonates, cyclic esters, and chain esters, and in this case, the flow of lithium ions is smooth and the oxidation / reduction reaction at the electrode can proceed stably.

[0065] The above organic solvent may include, as a preferred example, one or more selected from the group consisting of cyclic carbonates and chain carbonates, preferably a mixture of cyclic carbonates and chain carbonates, and in this case, there is an advantage of being able to provide high ionic conductivity while appropriately controlling the viscosity of the electrolyte.

[0066] The above-mentioned cyclic carbonate may be, for example, one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate, preferably one or more selected from the group consisting of EC and PC, and more preferably EC.

[0067] The above chain-type carbonates may be, for example, one or more selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC), and preferably one or two selected from the group consisting of DMC, DEC, and EMC.

[0068] The above chain-type ester may be, for example, one or more selected from the group consisting of methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, methyl acetate, ethyl acetate, propyl acetate, and butyl acetate.

[0069] The above cyclic ester may be one or more selected from the group consisting of, for example, γ-butyrolactone (γ-Butyrolactone; GBL), γ-valerolactone, mevalonolactone, and caprolactone.

[0070] The above organic solvent may preferably be a mixed solvent comprising: an organic solvent with a high dielectric constant having high ionic conductivity to improve the charge / discharge performance of the battery; and a low-viscosity organic solvent capable of adjusting the viscosity of the electrolyte to a viscosity suitable for application to the battery.

[0071] As the organic solvent of the high dielectric constant, EC, PC, or a mixture thereof, preferably EC, may be used as an example, and as the organic solvent of the low viscosity, one or two types selected from EMC, DMC, and DEC may be used as an example, and it is preferable to use the high dielectric constant and low viscosity organic solvents mixed in a volume ratio of 1:9 to 8:2. More specifically, the organic solvent may be a ternary mixed solvent of EC or PC; EMC; and DEC or DMC; and the ratio of EC or PC; EMC; and DEC or DMC may be, for example, 1:1 to 5:1 to 5 based on volume ratio, more preferably 1:1.2 to 4:1.2 to 4, even more preferably 1:1.3 to 3:1.3 to 3, and even more preferably 1:1.5 to 2.5:1.5 to 2.5.

[0072] The above organic solvent may also be a binary mixed solvent of EC as a high dielectric constant organic solvent and EMC as a low viscosity organic solvent, for example, in which case the ratio of EC and EMC may preferably be 1:1.5 to 7, preferably 1:2 to 5, more preferably 1:2.5 to 4 based on volume ratio.

[0073] Since the above organic solvent may hydrolyze lithium ions in the electrolyte if it contains water, it is desirable to control the water content in the organic solvent to 150 ppm or less, preferably 100 ppm or less.

[0074]

[0075] The above lithium salts are, for example, LiPF6, LiF4, LiCl, LiBr, LiI, LiClO4, and LiB 10 Cl 10 It may include one or more selected from the group consisting of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, LiN(FSO2)2, LiN(CF3SO2)2, LiBF4, LiB(C2O4)2, LiBF2(C2O4), Li[PF2(C2O4)2], LiPF4(C2O4), LiPO2F2, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, LiSCN, and LiC(CF3SO2)3, and preferably may include LiPF6, in which case the lithium ion supply of the battery is smooth, and there is an advantage of excellent battery performance.

[0076] The above lithium salt may, for example, include LiPF6 and one or more selected from the group consisting of LiB(C2O4)2, LiBF2(C2O4), Li[PF2(C2O4)2], LiPF4(C2O4), and LiPO2F2, and preferably may include one or more selected from the group consisting of LiB(C2O4)2, LiBF2(C2O4), and LiPO2F2. In this case, the proportion of the remaining lithium salt excluding LiPF6 among the total lithium salt components may be 30 mol% or less, preferably 0.5 to 30 mol%, more preferably 1 to 20 mol%, and even more preferably 2 to 10 mol%, and within this range, there is an advantage of superior long-term life characteristics of the battery without degradation of battery performance or stability.

[0077] When the above lithium salt is dissolved in the electrolyte, the lithium salt functions as a source of lithium ions within the secondary battery and can promote the movement of lithium ions between the positive and negative electrodes. Accordingly, it is preferable that the lithium salt be included in the electrolyte at a concentration of 0.6 to 2 M. If the concentration of the lithium salt is less than 0.6 M, the conductivity of the electrolyte may decrease, which may reduce the performance of the electrolyte, and if it exceeds 2 M, the viscosity of the electrolyte may increase, which may reduce the mobility of lithium ions. Considering such electrolyte conductivity and lithium ion mobility, the concentration of the lithium salt may be, as a specific example, 0.5 to 2.0 M, preferably 0.7 to 1.9 M, more preferably 0.8 to 1.8 M, even more preferably 1.0 to 1.6 M, even more preferably 1.0 to 1.5 M, and particularly preferably 1.3 to 1.2 M.

[0078] In this description, M means the number of moles of solute (mol / L) contained in 1 L of solution unless otherwise defined, and the volume of the solution means the volume at room temperature unless otherwise defined.

[0079] In this description, room temperature refers to a point within the range of 20 ± 5℃.

[0080]

[0081] The above electrolyte may include vinylene carbonate, for example, and the vinylene carbonate may be included in an amount of 0.5 to 5 weight% based on 100 weight% of the total electrolyte as a specific example, preferably 0.7 to 4 weight%, more preferably 0.8 to 3 weight%, even more preferably 0.8 to 2 weight%, even more preferably 1 to 1.8 weight%, and even more preferably 1.2 to 1.7 weight%. In this case, a more robust anode film may be formed due to a synergistic effect with the compound represented by Chemical Formula 1, thereby suppressing resistance increase and gas generation even when exposed to a high-temperature environment for a long period. In addition, due to this effect of improving battery stability, the loading amount of a high-capacity anode active material with a high nickel content can be increased, thus providing the advantage of further improving the output characteristics of the battery.

[0082] The above electrolyte may, for example, contain a compound represented by the above chemical formula 1 and vinylene carbonate in a weight ratio of 1:1 to 8:1, and the weight ratio may preferably be 1.5:1 to 7:1, more preferably 2:1 to 7:1, and even more preferably 2.5:1 to 6.5:1, and within this range, there is an advantage that the effect of improving battery stability is superior and the output characteristics of the battery can be further improved.

[0083]

[0084] The above electrolyte may include, for example, vinylethylene carbonate or pentaerythritol cyclic disulfate (2,4,8,10-Tetraoxa-3,9-dithiaspiro[5.5]undecane), and as a specific example, it may be included in an amount of 0.2 to 2.5 weight% based on 100 weight% of the total electrolyte, preferably 0.3 to 2 weight%, more preferably 0.4 to 1.8 weight%, and even more preferably 0.5 to 1.5 weight%. In this case, there is an advantage of preventing gas generation at high temperatures, thereby improving the high-temperature stability and long-term cycle characteristics of the battery.

[0085] The above electrolyte may, for example, include a mixture of vinylethylene carbonate and pentaerythritol cyclic disulfate. Specifically, it may be included in an amount of 0.5 to 3 weight% based on 100 weight% of the total electrolyte, preferably 0.7 to 2.5 weight%, more preferably 1 to 2 weight%, and even more preferably 1.2 to 1.8 weight%. It has the advantage of preventing gas generation at high temperatures, thereby providing a superior effect in improving the high-temperature stability and long-term cycle characteristics of the battery. At this time, the vinylethylene carbonate and pentaerythritol cyclic disulfate may be included in a weight ratio of, for example, 0.2:1 to 1:1. The weight ratio may preferably be 0.2:1 to 0.8:1, more preferably 0.3:1 to 0.7:1, and even more preferably 0.4:1 to 0.6:1. Within this range, it has the advantage of excellent high-temperature stability and long-term cycle characteristics of the battery.

[0086]

[0087] As a specific example, the above electrolyte may include all of the compound represented by Chemical Formula 1, vinylene carbonate, vinylethylene carbonate, and pentaerythritol cyclic disulfate. As a more specific example, the total weight thereof may be 1.5 to 5 weight%, preferably 1.7 to 4.5 weight%, more preferably 1.8 to 4 weight%, even more preferably 2 to 3.8 weight%, even more preferably 2.2 to 3.5 weight%, and particularly preferably 2.5 to 3.5 weight%. In this case, the electrode protection effect is maximized, and there is an advantage of particularly excellent effects such as suppressing the increase in battery resistance and thickness, suppressing gas generation, and improving cycle characteristics even after long-term storage at high temperatures. Furthermore, due to this battery stability improvement effect, the loading amount of a high-capacity cathode active material with a high nickel content can be increased, thereby providing an advantage of further improving the output characteristics of the battery.

[0088]

[0089] As a specific example, the electrolyte according to the present invention may be an electrolyte for use in an NCA-based or NCM-based secondary battery, wherein LiPF6 is included in an amount of 1.1 to 1.2 M, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate are included as organic solvent components in a volume ratio of 1:1.5 to 2.5:1.5 to 2.5%, vinylene carbonate is included in an amount of 1 to 2% by weight, a compound represented by the chemical formula 2 is included in an amount of 0.1 to 1.5% by weight, and optionally, vinylethylene carbonate is included in an amount of 0.3 to 0.7% by weight and pentaerythritol bicyclic sulfate is included in an amount of 0.5 to 1.5% by weight. In this case, the electrode protection effect is particularly excellent, and there is an advantage of excellent improvement in high-temperature stability, high-temperature long-term storage life, and high-temperature cycle performance of the battery. More preferably, the NCA-based or NCM-based secondary battery may be a high-nickel NCA-based secondary battery or a high-nickel NCM-based secondary battery, in which case there is an advantage of being able to provide a high-capacity battery with excellent stability and battery characteristics.

[0090]

[0091] The above electrolyte may optionally include, in addition to the electrolyte additive described above, commercial additives that can be used in the electrolyte for purposes such as improving battery life characteristics, suppressing battery capacity degradation, improving battery discharge capacity, and imparting flame retardancy.

[0092] The above commercial additive may further include one or more selected from the group consisting of, for example, fluoroethylene carbonate (FEC), lithium difluorophosphate (LiPO2F2), 1-propene-1,3-sulfone (PRS), 1,3-propanesulfone (PS), ethylene sulfate (ESA), adiponitrile (AN), and succinonitrile (SN), and in terms of electrode protection effect, it may preferably be FEC, in which case there is an advantage of preventing electrolyte decomposition and thus improving cycle performance.

[0093] The above commercial additive may also further include one or more selected from the group consisting of, for example, butanesulfone (BS), TMSPa (3-trimethoxysilanyl-propyl-N-aniline), TMSPi (Tris(trimethylsilyl) Phosphite), tetravinylsilane (TVS), 2-fluoro-1,3,2-dioxaphospholane, methylenemethanedisulfonate (MMDS), sulfolane (Sulfolane), biphenyl (BP), and fluorobenzene (FB), and preferably one or more selected from the group consisting of sulfolane, biphenyl, and fluorobenzene, in which case there is an advantage of greater stability even during overvoltage or high voltage operation.

[0094] When including the above commercial additive, preferably, 1 to 5 types or 1 to 3 types among the compounds mentioned as the above commercial additive may be included, and as a specific example, the total weight of the above commercial additive may be included in an amount of 0.05 to 10 weight%, preferably 0.1 to 5 weight%, more preferably 0.1 to 3 weight%, and even more preferably 0.2 to 2 weight% based on 100 weight% of the total electrolyte.

[0095]

[0096] The present invention also provides a secondary battery characterized by comprising a negative electrode, a positive electrode, a separator, and an electrolyte according to the present invention.

[0097]

[0098] The above anode can be manufactured, for example, by mixing an anode active material, a binder, and optionally a conductive agent to prepare a composition for forming an anode active material layer, and then applying this to an anode current collector such as aluminum foil.

[0099] As the above-mentioned positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (a re-intercalated intercalation compound) may be used, and as a specific example, it may be selected from a lithium cobalt composite oxide system having a layered structure, a lithium nickel composite oxide system having a layered structure, and a lithium manganese composite oxide system having a spinel structure.

[0100] As a specific example, the above-mentioned positive active material has the chemical formula Li[Ni x Co y Mn z ]O2(here 0 <x<95, 0<y<35, 0<z<35, 단 x+y+z=100이고, Li[Ni x Co y Mn z It may be a lithium composite metal oxide of the form satisfying the oxidation number of O2, or an NCA (lithium nickel cobalt aluminum)-based cathode active material, but is not limited thereto. For example, lithium manganese-rich (LMR, LMX, OLO, HLM) and lithium-rich (DRX) cathode active materials may also be used.

[0101] The chemical formula of the above lithium composite metal oxide is Li[Ni x Co y Mn z The variables x, y, and z of ]O2 are, for example, mole% satisfying x+y+z=100 (also, Li[Ni x Co y Mn z When expressed as ]satisfies the oxidation number of O2), 0.1 <x<99, 0.0001<y<35, 0.0001<z<35일 수 있고, 바람직하게는 10≤x≤98, 1≤y≤30, 1≤z≤30일 수 있고, 보다 바람직하게는 30≤x≤98, 3≤y≤25, 3≤z≤25, 더욱 바람직하게는 50≤x≤97, 3≤y≤20, 3≤z≤20, 보다 더욱 바람직하게는 60≤x≤95, 3≤y≤15, 3≤z≤15 일 수 있다.

[0102] The above NCA-based cathode active material is, for example, a chemical formula Li a Ni bCo c Al d It may be a compound represented by O2, where 0.7 <a≤1.2, b+c+d=1이고, b≥0.4, c≤0.4, d≤0.4, 바람직하게는 0.5≤b≤0.99, 0.1≤c≤0.3, 0.1≤d≤0.3, 보다 바람직하게는 0.6≤b≤0.97, 0.1≤c≤0.2, 0.1≤d≤0.2 일 수 있다.

[0103] Other examples of the above lithium composite metal oxides include LiCoO2, LiMnO2, LiMn2O4, LiNiO2, and LiNi x Mn (1-x) O2(where 0 <x<1), 및 LiM1 x M2 y It may be one or more selected from the group consisting of O2 (wherein 0≤x≤1, 0≤y≤1, 0≤x+y≤1, M1 and M2 are each independently selected from the group consisting of Al, Sr, Mg and La), and in this case, the capacity characteristics and stability of the battery can be improved.

[0104] As a preferred example, the above-mentioned cathode active material may be a mid-nickel (Mid-Ni) type in which the proportion of nickel among the transition metal components excluding lithium in the cathode active material is 40 to 60 mol%, or a high-nickel (High-Ni) type in which the proportion of nickel is greater than 60 mol%, preferably 65 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more, and preferably a high-nickel type. Examples of the above-mentioned mid-nickel cathode active material include NCM523, NCM622, NCM613, etc. While such mid-nickel cathodes have the advantage of relatively excellent stability and lifespan characteristics, they are insufficient for application in uses requiring high capacity and high output. Examples of the above-mentioned high-nickel cathode active material include NCM811, NCM9* (NCM9½½, etc.), LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.8 Co 0.1 Al0.1 O2, LiNi 0.9 Co 0.06 Al 0.04 O2, Li(Ni 0.9 Co 0.08 Al 0.02 Examples include O2, and while such high-nickel cathodes exhibit a high energy density suitable for applications requiring high capacity and high output, such as electric vehicles, the crystal structure of the cathode active material collapses and transition metals leach out due to acidic byproducts such as HF generated by electrolyte decomposition during the charging and discharging process, leading to easy degradation of battery performance. Furthermore, there are issues such as increased battery thickness due to gas release, fire hazards, and a high risk of thermal runaway, particularly at high temperatures. Therefore, to apply them to real-world applications, safety improvements must be prioritized. The present invention applies an electrolyte having the characteristic composition described above to form a more robust and stable film on the cathode surface. Simultaneously, it effectively scavenges acidic byproducts such as HF and provides a strong chelating action against transition metals leached from the cathode. Through this, the stability of the high-nickel battery is significantly improved, offering the advantages of excellent high-temperature stability, long-term high-temperature storage characteristics, and cycle characteristics. Consequently, since the loading amount of the high-nickel cathode active material can be increased, it has the advantage of being particularly suitable for fields requiring high capacity and high output.

[0105] The above positive active material may include a coating layer on its surface, or a mixture of a positive active material without a coating layer and a positive active material having a coating layer may be used.

[0106] The coating layer may comprise at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds forming these coating layers may be amorphous or crystalline.

[0107] The above coating elements may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or two or more of these.

[0108] As long as the process of forming the above coating layer follows the definition of the present invention, it can be coated using methods commonly used in the technical field to which the present invention belongs (e.g., spray coating, immersion method, etc.), and since this is known in the art, a detailed description is omitted.

[0109] The content of the above positive active material may be, for example, 90 weight% or more, or 90 to 98 weight% with respect to the total weight of the positive active material layer.

[0110] For example, the above anode has a loading amount of a positive active material in a positive active material layer (positive composite layer) laminated on a positive current collector of 5 mg / cm² 2 It may be higher, preferably 10 mg / cm² 2 Ideally, 15 mg / cm² 2 Ideally, 20 mg / cm² 2 Ideally, 23 mg / cm² 2 Ideally, and even more preferably 25 mg / cm² 2 It may be higher, and while the upper limit is not specifically restricted, for example, 150 mg / cm² 2 Below, preferably 100 mg / cm² 2 Below, more preferably 90 mg / cm² 2 Below, more preferably 80 mg / cm² 2 Below, more preferably 60 mg / cm² 2 Below, even more preferably 50 mg / cm² 2 It may be less than or equal to this, and in this case, there is an advantage in being able to provide a secondary battery that exhibits high capacity and high output and excellent stability.

[0111] In one embodiment of the present invention, the positive active material layer may include a binder and a conductive material. In this case, the content of the binder and the conductive material may each be 1 weight% or more, or 1 to 5 weight%, based on the total weight of the positive active material layer.

[0112] The above binder serves to attach the positive active material particles to each other and also to attach the positive active material to the current collector. Examples include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0113] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any electronically conductive material that does not cause chemical changes can be used, and may include, for example, carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber; metal-based materials such as metal powder or metal fiber such as copper, nickel, aluminum, silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0114] The above-mentioned collector may be used without particular limitation as long as it is commonly used in the technical field to which the present invention belongs, and as a specific example, Al may be used, but is not limited thereto.

[0115]

[0116] The above cathode can be manufactured, for example, by mixing a cathode active material, a binder, and optionally a conductive agent to prepare a composition for forming a cathode active material layer, and then applying this to a cathode current collector such as a copper foil.

[0117] The surface of the above cathode may further include a solid electrolyte interface (SEI) film.

[0118] The above-mentioned negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, lithium alloy, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0119] Any carbon-based negative electrode active material commonly used in lithium-ion secondary batteries can be used as a material capable of reversibly intercalating / deintercalating the above lithium ions, and for example, it may be a carbon compound.

[0120] Specific examples of the above carbon-based cathode active material may be carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon.

[0121] In addition, in addition to the carbonaceous material mentioned above, a metallic compound capable of alloying with lithium, or a composite containing a metallic compound and a carbonaceous material, can also be used as a negative electrode active material, and the carbonaceous material may be, for example, graphite.

[0122] In addition, a metallic lithium thin film may be used as the above-mentioned cathode active material, and in terms of high stability, it may be preferable to use one or more selected from the group consisting of crystalline carbon, amorphous carbon, carbon composites, lithium metal, and lithium alloy.

[0123] As for the element or metal capable of alloying with the above lithium, at least one of Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy may be used.

[0124] Materials capable of doping and dedoping the above lithium include Si, Si-C composites, and SiO₂. xExamples include (0 < x < 2), Si-Q alloy (wherein Q is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, Sn-R (wherein R is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), and at least one of these may be mixed with SiO2.

[0125] As the above elements Q and R, independently selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof may be used.

[0126] Examples of the above transition metal oxides include vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

[0127] The content of the negative electrode active material in the above negative electrode active material layer may be, for example, 95 weight% or more, or 95 to 99 weight% with respect to the total weight of the negative electrode active material layer.

[0128] The content of the binder in the above-mentioned negative electrode active material layer may be, for example, 1 weight% or more, or 1 to 5 weight% with respect to the total weight of the negative electrode active material layer.

[0129] When the above-mentioned negative electrode active material layer includes a conductive material, the negative electrode active material can be used in a range of 90 to 98 weight%, the binder in a range of 1 to 5 weight%, and the conductive material in a range of 1 to 5 weight%.

[0130] The above binder serves to attach the negative electrode active material particles to each other and also to attach the negative electrode active material to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

[0131] Examples of the above-mentioned water-insoluble binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0132] Examples of the above-mentioned water-soluble binders include rubber-based binders or polymer resin binders.

[0133] The above rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof.

[0134] The above polymer resin binder may be one or more selected from polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0135] When a water-soluble binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included.

[0136] The above cellulose-based compounds may be used by mixing one or more of, for example, carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof.

[0137] Na, K, or Li can be used as the above alkali metal.

[0138] The above cellulose-based compound may be included in an amount of, for example, 0.1 to 5 parts by weight or 0.1 to 3 parts by weight per 100 parts by weight of the negative electrode active material.

[0139] The above conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as it is a material that has electronic conductivity without causing chemical changes in the battery composed including it. Examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers; metal-based materials such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; conductive polymers such as polyphenylene derivatives; or a mixture of two or more of these.

[0140] The above current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination of two or more of these.

[0141]

[0142] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such a separator may be used without particular limitation as long as it is commonly used in the technical field to which the present invention belongs. Specific examples include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof. Additionally, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0143]

[0144] The secondary battery of the present invention has the effect of further improving battery characteristics, such as the resistance increase rate and capacity recovery characteristics after high-temperature long-term storage (60 days at 60°C) measured by the HPPC (Hybrid Pulse Power Characterization) method, and high-temperature low-cycle characteristics at 45°C, by applying an electrolyte according to the present invention in addition to conventional compounds added to the electrolyte to improve battery performance.

[0145] In this description, HPPC discharge (charge) resistance is a method that can be measured according to the method specified in the document "Battery test manual for plug-in hybrid electric vehicles" (2010, Idaho National Laboratory for the US Department of Energy), and is an important indicator representing battery characteristics such as battery output. Furthermore, charge (discharge) resistance is a resistance value measured during the charging (discharging) of a battery; the lower the charge (discharge) resistance, the less energy loss occurs, which can lead to faster charging speeds and improved battery output. The secondary battery of the present invention exhibits a low HPPC discharge resistance value as described above, resulting in excellent charging speed and output, making it suitable for use, for example, as an automotive battery.

[0146] For example, the above secondary battery may have a resistance increase rate (ratio of the resistance value measured after storage at 60°C for 60 days to the initial resistance value) calculated from resistance values ​​measured before and after storage at 60°C for 60 days, which may be 60% or less, preferably 57% or less, more preferably 50% or less, and even more preferably 45% or less, and the lower limit may not be particularly limited but may be, for example, 5% or more or 10% or more.

[0147] The battery characteristics, such as the resistance increase rate mentioned above, may vary in range depending on the cathode type, for example. Specifically, in the case of an NCA-based secondary battery using NCA as the cathode, the resistance increase rate may be 35% or less, preferably 30% or less, more preferably 28% or less, and even more preferably 27% or less. The lower limit is not specifically limited, but may be, for example, 5% or more or 10% or more. In addition, in the case of an NCM-based secondary battery using NCM as the cathode, the resistance increase rate may be 60% or less, preferably 55% or less, more preferably 50% or less, and even more preferably 45% or less. The lower limit is not specifically limited, but may be, for example, 10% or more or 15% or more.

[0148] For example, the above secondary battery may have a recovery capacity (the ratio of the discharge capacity value measured after storage at 60°C for 60 days to the initial discharge capacity value) calculated from the discharge capacity values ​​measured before and after storage at 60°C for 60 days, which is 80% or more, preferably 83% or more, more preferably 85% or more, and even more preferably 87% or more, and the upper limit is not particularly limited, but may be, for example, 99% or less or 97% or less.

[0149] As a more specific example, if the secondary battery is an NCA-based secondary battery, the recovery capacity may be 80% or more, preferably 82% or more, more preferably 83% or more, and even more preferably 85% or more, and the upper limit is not specifically limited but may be, for example, 95% or less or 93% or less. In addition, if the secondary battery is an NCM-based secondary battery in which NCM is applied as the cathode, the recovery capacity may be 85% or more, preferably 90% or more, more preferably 93% or more, and even more preferably 93.5% or more, and the upper limit is not specifically limited but may be, for example, 99% or less or 98% or less.

[0150] For example, the thickness increase rate (the ratio of the thickness value measured after storage at 60°C for 60 days to the initial battery thickness value) calculated from the thickness values ​​of the battery measured before and after storage at 60°C for 60 days may be 30% or less, preferably 29% or less, more preferably 28% or less, and even more preferably 26% or less, and the lower limit is not particularly limited but may be, for example, 1% or more or 2% or more.

[0151] As a more specific example, if the secondary battery is an NCA-based secondary battery, the thickness increase rate may be 10% or less, preferably 8% or less, more preferably 7% or less, and even more preferably 5% or less, and the lower limit is not specifically limited but may be, for example, 1% or more or 2% or more. In addition, if the secondary battery is an NCM-based secondary battery in which NCM is applied as the cathode, the thickness increase rate may be 30% or less, preferably 29% or less, more preferably 28% or less, and even more preferably 26% or less, and the lower limit is not specifically limited but may be, for example, 10% or more or 15% or more.

[0152] For example, the above secondary battery may have a high-temperature 300-cycle capacity retention rate (ratio of the discharge capacity value after 300 cycles to the initial discharge capacity value) calculated from the discharge capacity value measured before and after 300 cycles of charging and discharging at 45°C, which is 60% or more, preferably 65% ​​or more, more preferably 70% or more, and even more preferably 72% or more, and the upper limit is not particularly limited but may be, for example, 99.5% or less, or 99% or less.

[0153] As a more specific example, if the secondary battery is an NCA-based secondary battery, the high-temperature 300-cycle capacity retention rate may be 60% or more, preferably 65% ​​or more, more preferably 70% or more, and even more preferably 72% or more, and the upper limit is not specifically limited but may be, for example, 95% or less or 90% or less. In addition, if the secondary battery is an NCM-based secondary battery in which NCM is applied as the cathode, the high-temperature 300-cycle capacity retention rate may be 85% or more, preferably 90% or more, more preferably 95% or more, and even more preferably 96.5% or more, and the upper limit is not specifically limited but may be, for example, 99% or less or 98% or less.

[0154] The secondary battery according to the present invention has the advantages of suppressing the increase in resistance and thickness even after long-term storage at high temperatures as described above, having a high recovery capacity, and having an excellent cycle life under high-temperature conditions.

[0155] Therefore, when the secondary battery of the present invention is used as an automotive battery, it can exhibit excellent performance as an automotive battery by ensuring stability even when a high-content nickel cathode material is applied to achieve high capacity, along with improvements in output, which becomes important depending on the size of the vehicle, and improvements in performance at low and high temperatures, which are problematic due to the characteristics of the vehicle being exposed to sunlight for most of the time while driving or parked and due to climate change.

[0156]

[0157] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the following embodiments are merely illustrative of the invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the invention, and that such variations and modifications fall within the scope of the appended claims.

[0158]

[0159] [Example]

[0160] Synthesis Example: Synthesis of a compound represented by Chemical Formula 2

[0161] Under a nitrogen atmosphere, 42.3 g (474.4 mmol) of 2-(dimethylamino)ethanol and 300 mL of THF were added to a 1 L capacity three-necked reaction vessel. After cooling the internal temperature to between 0 and 5 °C, 57.6 g (569.3 mmol) of triethylamine was slowly added dropwise while stirring. After the dropwise addition was complete, 60 g (474.4 mmol) of 2-chloro-1,3,2-dioxaphospholane diluted in 150 mL of THF was slowly added dropwise. Once the dropwise addition was complete, the reaction temperature was maintained between 0 and 5 °C and stirred for 2 hours, after which the termination of the reaction was confirmed by NMR analysis. Subsequently, the product was filtered to remove the salt formed as a byproduct, and the filtrate was subjected to vacuum distillation to obtain 72 g of the final product (yield: 85%, purity: 98.5%, state: clear liquid).

[0162] of the above-mentioned obtained compound 1 The results of the H NMR analysis are as follows, and through the above analysis results, it was confirmed that it is a compound corresponding to Chemical Formula 2.

[0163] 1 H NMR (400 MHz, CDCl3): δ4.16-4.09 (m, 2H), 3.99-3.90 (m, 2H), 3.79 (tt,J= 9.0, 6.0 Hz, 2H), 2.42 (t,J= 6.0 Hz, 2H), 2.21 (s, 6H)

[0164]

[0165] [1. Preparation of Electrolyte for NCA Secondary Batteries]

[0166] Example 1

[0167] An electrolyte was prepared by mixing 1.15 M of LiPF6 as a lithium salt into a carbonate-based mixed solvent having a volume ratio of EC:EMC:DMC = 2:4:4, and adding electrolyte additives such as 0.25 wt% of a compound represented by Chemical Formula 2, 1.5 wt% of vinylene carbonate (VC), 0.5 wt% of vinylethylene carbonate (VEC), and 1 wt% of pentaerythritol cyclic disulfate (DTTO). Here, the concentration (M) of the lithium salt was based on the total volume of the electrolyte, and the weight% of the electrolyte additives was based on the total amount of the electrolyte.

[0168]

[0169] Comparative Example 1

[0170] In the above Example 1, the procedure was carried out in the same manner as Example 1, except that the compound represented by Chemical Formula 2 among the electrolyte additives was not added.

[0171]

[0172] [2. Preparation of Electrolyte for NCM Secondary Batteries]

[0173] Example 2

[0174] An electrolyte was prepared by mixing 1.15 M of LiPF6 as a lithium salt into a carbonate-based mixed solvent having a volume ratio of EC:EMC:DEC = 2:4:4, and adding 0.5 wt% of a compound represented by the above chemical formula 2 and 1.5 wt% of vinylene carbonate (VC) as electrolyte additives.

[0175]

[0176] Example 3

[0177] In the above Example 2, the procedure was carried out in the same manner as Example 2, except that the amount of the compound represented by Formula 2 among the electrolyte additives was changed to 1.0 wt%.

[0178]

[0179] Comparative Example 2

[0180] In the above Example 2, the procedure was carried out in the same manner as Example 2, except that 1 wt% of LiPO2F2(LDFP) was added instead of adding the compound represented by Chemical Formula 2 among the electrolyte additives.

[0181]

[0182] Comparative Example 3

[0183] In the above Example 2, the procedure was carried out in the same manner as Example 2, except that the compound represented by Chemical Formula 2 among the electrolyte additives was not added.

[0184]

[0185] [Manufacturing of NCA Batteries]

[0186] Li(Ni as a positive electrode active material 0.9 Co 0.08 Al 0.02 An anode mixture slurry was prepared by adding 292 wt% of )O, 4 wt% of carbon black as a conductive agent, and 4 wt% of polyvinylidene fluoride (PVdF) as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent. The anode mixture slurry was applied to an aluminum (Al) thin film, which is an anode current collector, with a thickness of about 20 μm, dried to produce an anode, and then subjected to a roll press to produce an anode.

[0187] A cathode mixture slurry was prepared by adding carbon powder as the cathode active material, PVdF as the binder, and carbon black as the conductive agent to NMP as the solvent in amounts of 96 wt%, 3 wt%, and 1 wt%, respectively. The cathode mixture slurry was coated onto a copper (Cu) thin film, which is a cathode current collector with a thickness of 10 μm, and dried to produce a cathode, and then a roll press was performed to produce a cathode.

[0188] After fabricating a pouch-type battery using a conventional method with the manufactured positive and negative electrodes together with a separator consisting of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP), the manufacturing of an NCA secondary battery was completed by injecting each electrolyte prepared in Example 1 and Comparative Example 1.

[0189]

[0190] [Manufacturing of NCM Batteries]

[0191] Li(Ni as a positive electrode active material 0.8 Co 0.1 Mn 0.1 An anode mixture slurry was prepared by adding 292 wt% of )O, 4 wt% of carbon black as a conductive agent, and 4 wt% of polyvinylidene fluoride (PVdF) as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent. The anode mixture slurry was applied to an aluminum (Al) thin film, which is an anode current collector, with a thickness of about 20 μm, dried to produce an anode, and then subjected to a roll press to produce an anode.

[0192] A cathode mixture slurry was prepared by adding carbon powder as the cathode active material, PVdF as the binder, and carbon black as the conductive agent to NMP as the solvent in amounts of 96 wt%, 3 wt%, and 1 wt%, respectively. The cathode mixture slurry was coated onto a copper (Cu) thin film, which is a cathode current collector with a thickness of 10 μm, and dried to produce a cathode, and then a roll press was performed to produce a cathode.

[0193] After manufacturing a pouch-type battery using a conventional method with the manufactured positive and negative electrodes together with a separator consisting of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP), the manufacturing of a lithium secondary battery was completed by injecting each electrolyte prepared in Examples 2 to 3 and Comparative Examples 2 to 3.

[0194]

[0195] Test example

[0196] To evaluate the performance of each secondary battery manufactured above, the performance was evaluated using the following method, and the results are summarized in Table 2 below.

[0197]

[0198] [Evaluation of Initial DC-IR Resistance and High-Temperature Storage DC-IR (mΩ)]

[0199] It was measured using the HPPC discharge (charge) resistance evaluation method specified in the literature "Battery test manual for plug-in hybrid electric vehicles," (2010, Idaho National Laboratory for the US Department of Energy).

[0200] Specifically, immediately after the above-mentioned secondary battery is manufactured, the measured voltage value, the charge / discharge current value corresponding to the C-rate, the change in current (△I), the change in discharge voltage (△V), the change in charge voltage (△V), the charge resistance, and the discharge resistance are periodically measured under the condition of a state of charge (SOC) of 50% at 0.5 C at room temperature (23±2℃). The resistance value is calculated using the slope value obtained from the change in current and voltage by briefly flowing the charge / discharge current for a certain period of time for each C-rate (initial resistance value).

[0201] After storing at 60℃ for 60 days, the resistance value was calculated under the same conditions (resistance value after high-temperature long-term storage), and the ratio of the resistance value after high-temperature long-term storage to the initial resistance value was calculated and expressed as the resistance increase rate after high-temperature storage.

[0202]

[0203] [High-temperature recovery capacity evaluation]

[0204] The charging conditions were performed by charging at a constant current of 0.5 C and a voltage of 4.2 V until the charging current became 1 / 10 C. The discharging conditions were performed by charging and discharging at a constant current of 0.5 C up to 3.0 V, after which the discharge capacity was measured (initial discharge capacity value).

[0205] After charging under the same charge / discharge conditions and storing at 60°C for 60 days, the discharge capacity was measured by discharging to a discharge voltage of 3 V under the same conditions (discharge capacity value after long-term high-temperature storage), and the ratio of the discharge capacity value after long-term high-temperature storage to the initial discharge capacity value was calculated and expressed as the recovery capacity after high-temperature storage.

[0206]

[0207] [Battery Thickness Measurement]

[0208] Immediately after manufacturing the battery, it was charged to 4.2 V, 1 C, CC-CV with an SOC of 100% (0.05 C cut-off), and the thickness of the battery (initial thickness) was measured using a flat plate thickness measuring device (manufactured by Mitutoyo). After storing the secondary battery at a high temperature for a long period (60℃, 60 days), the thickness was measured again, and the thickness increase rate was calculated according to the following Equation 1.

[0209] [Mathematical Formula 1]

[0210] Thickness increase rate (%) = (BA) / A × 100

[0211] (In the above mathematical formula 1, A represents the initial thickness, and B represents the thickness after long-term high-temperature storage.)

[0212]

[0213] [High Temperature Life Evaluation]

[0214] The above secondary battery was charged at a constant current rate of 1 C at 45°C until the voltage reached 4.20 V (vs. Li), and then cut off at a current rate of 0.02 C while maintaining 4.20 V in constant voltage mode. Subsequently, during discharge, it was discharged at a constant current rate of 1 C until the voltage reached 3.0 V (vs. Li) (1st cycle). After repeating the above charge-discharge cycle 300 times, the capacity was measured and expressed as the capacity retention rate after 300 cycles at 45°C.

[0215]

[0216] Classification Example 1 Comparative Example 2 Example 2 Example 3 Comparative Example 2 Comparative Example 3 Electrolyte Composition Solvent EC / EMC / DMC (2 / 4 / 4v) EC / EMC / DEC (2 / 4 / 4v) Lithium Salt LiPF6 : 1.15ML iPF6 : 1.15M Additive 1 Chemical Formula 2 (0.25 wt%) - Chemical Formula 2 (0.5 wt%) Chemical Formula 2 (1.0 wt%) - Additive 2 VC (1.5 wt%) VC 1.5 (wt%) Additive 3 VEC (0.5 wt%) - Additive 4 DTTO (1 wt%) - Additive 5 LDFP (1 wt%) - Type of Cathode Active Material NCANCM

[0217] Classification Resistance increase rate (%) before and after high-temperature storage at 45°C after 60 days of storage at 60°C Recovery capacity (%) before and after high-temperature storage Thickness increase rate (%) before and after high-temperature storage Capacity retention rate (%) after 300 cycles Example 1 25.38 8.0 3.6 73.9 Comparative Example 1 32.48 8.6 3.2 74.3 Example 2 43.29 4.22 6.09 7.2 Example 3 56.59 4.52 0.09 7.2 Comparative Example 2 45.09 2.52 7.39 6.9 Comparative Example 3 41.89 4.13 4.89 5.6

[0218] Referring to Tables 1 and 2 above, in the case of Example 1, in which an electrolyte containing the electrolyte additive according to the present invention was applied to a high-nickel NCA-based secondary battery with a nickel content of 90 mol%, when compared to Comparative Example 1, in which only a commercial additive was applied instead of the compound represented by Chemical Formula 2, the recovery capacity and thickness increase rate after long-term high-temperature storage and the improvement effect of the 300-cycle life at high temperature were found to be at an equivalent level, whereas the resistance increase rate after long-term high-temperature storage was found to be significantly reduced. This confirms that there is an effect of improving the long-term high-temperature storage life, high-temperature stability, and high-temperature cycle life, and in particular, the effect of suppressing the increase in resistance during long-term storage at high temperatures is excellent.

[0219] In addition, in the case of Examples 2 and 3, in which an electrolyte containing the electrolyte additive according to the present invention was applied to a high-nickel NCM-based secondary battery with a nickel content of 80 mol%, it was found that the recovery capacity and thickness increase rate and the improvement effect on the 300-cycle life at high temperature were superior when compared to Comparative Examples 2 and 3, in which only a commercial additive was applied instead of the compound represented by Chemical Formula 2. In particular, in the case of Example 2, the resistance increase rate, recovery capacity and thickness increase rate, and the improvement effect on the 300-cycle life at high temperature were all superior after long-term storage at high temperature, and in the case of Example 3, it was confirmed that the effect of suppressing thickness increase after long-term storage at high temperature was significantly superior.

[0220] Through the above experimental results, it was confirmed that the electrolyte additive according to the present invention exhibits particularly excellent effects in improving electrode stability along with battery performance, thereby enhancing the high-temperature stability, long-term high-temperature storage life, and high-temperature cycle life of the battery. Consequently, it was confirmed that the additive is suitable for application to high-nickel batteries, where stability was an issue in conventional technology. Furthermore, it was confirmed that by applying an electrolyte containing the above electrolyte additive, it is possible to provide a high-capacity secondary battery with excellent stability and suppressed degradation of battery performance even when exposed to high-temperature environments for a long period.

Claims

1. Characterized by comprising a compound represented by the following chemical formula 1. Electrolyte additive. [Chemical Formula 1] (In the above Chemical Formula 1, R1 to R4 are each independently hydrogen, a C1 to C3 alkyl group, F, Cl, Br, or I, or R1 and R2, and R3 and R4 may each independently be substituted with oxygen (=O), R5 is an C1 to C5 alkylene group, and R6 and R7 are each independently hydrogen or a C1 to C3 alkyl group.) 2. In Paragraph 1, The compound represented by the above chemical formula 1 is characterized as being a compound represented by the following chemical formula 2. Electrolyte additive. [Chemical Formula 2] 3. In Paragraph 1, The above electrolyte additive is characterized as being an anode film forming agent. Electrolyte additive.

4. Characterized by comprising an organic solvent; a lithium salt; and an electrolyte additive according to any one of claims 1 to 3. Electrolyte.

5. In Paragraph 4, The above electrolyte additive is characterized by being included in an amount of 0.05 to 3 weight% based on 100 weight% of the total electrolyte. Electrolyte.

6. In Paragraph 4, The above electrolyte is characterized by containing 0.5 to 5 weight percent of vinylene carbonate based on 100 weight percent of the total electrolyte. Electrolyte.

7. In Paragraph 4, The above electrolyte is characterized by containing 0.2 to 3 weight percent of vinylethylene carbonate, pentaerythritol cyclic disulfate, or a mixture thereof, based on 100 weight percent of the total electrolyte. Electrolyte.

8. In Paragraph 4, The above organic solvent is characterized by comprising one or more selected from the group consisting of cyclic carbonates, chain carbonates, cyclic esters, and chain esters. Electrolyte.

9. In Paragraph 4, The above lithium salts are LiPF6, LiF4, LiCl, LiBr, LiI, LiClO4, and LiB 10 Cl 10 Characterized by comprising one or more selected from the group consisting of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, LiN(FSO2)2, LiN(CF3SO2)2, LiBF4, LiB(C2O4)2, LiBF2(C2O4), Li[PF2(C2O4)2], LiPF4(C2O4), LiPO2F2, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, LiSCN, and LiC(CF3SO2)3. Electrolyte.

10. In Paragraph 4, The above electrolyte is characterized by being used in NCM-based or NCA-based secondary batteries. Electrolyte. 11.LiPF6 is included at 1.1M to 1.2M, ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate are included as organic solvents in a volume ratio of 1:1.5~2.5:1.5~2.5, vinylene carbonate is included at 1 to 2 weight%, a compound represented by the following chemical formula 2 is included at 0.1 to 1.5 weight%, and optionally vinylethylene carbonate 0.3 to 0.7 weight% and pentaerythritol bicyclic sulfate 0.5 to 1.5 weight% are included, and the composition is characterized by being used in an NCA-based or NCM-based secondary battery. Electrolyte. [Chemical Formula 2] 12. Characterized by comprising: a cathode; an anode; a separator; and the electrolyte of claim 4. Secondary battery.

13. In Paragraph 12, The above secondary battery is characterized by being an NCM-based or NCA-based secondary battery. Secondary battery.

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