Electrolyte additive for lithium secondary battery, electrolyte for lithium secondary battery, comprising same, and lithium secondary battery

Abstract

An electrolyte composition for a secondary battery, according to one aspect of the present invention, may comprise: a pentaerythritol diphosphate additive represented by chemical formula 1 below; an auxiliary additive; a lithium salt; and a non-aqueous organic solvent. [Chemical formula 1] In chemical formula 1, R1 and R2 are each independently an unsubstituted alkyl group or an alkyl group having a substituted halogen.

Description

Electrolyte additive for lithium secondary batteries, electrolyte for lithium secondary batteries containing the same, and lithium secondary battery

[0001] The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery containing the same, and more specifically, to an electrolyte for a lithium secondary battery having excellent high-temperature life characteristics, reduced internal resistance (IR) during high-temperature storage, suppression of battery thickness expansion, and a superior capacity retention rate, and a lithium secondary battery containing the same.

[0002]

[0003] As the application fields of rechargeable batteries expand to include not only mobile phones, digital cameras, laptop computers, and power tools, but also electric bicycles, electric vehicles, and energy storage devices, there is a growing demand for higher energy density and greater safety of the aforementioned rechargeable batteries used as power sources for electronic energy devices.

[0004] Lithium-ion batteries are rechargeable batteries that can best satisfy these requirements, and active research is being conducted on them. A lithium-ion battery consists of a negative electrode, such as a carbon material capable of inserting and extracting lithium ions; a positive electrode, such as a lithium-containing oxide; a porous separator located between the negative electrode and the positive electrode; and a non-aqueous electrolyte injected between the negative electrode and the positive electrode, which acts as a medium to enable the movement of lithium ions between the two electrodes.

[0005] As the above-mentioned non-aqueous electrolyte, a material in which a lithium salt such as LiPF6 is dissolved in a non-aqueous organic solvent such as propylene carbonate, ethyl carbonate, dimethyl carbonate, or diethyl carbonate is used.

[0006] However, generally, if these non-aqueous organic solvents are stored at high temperatures for a long time, gas is generated due to the oxidation of the electrolyte, which can cause problems such as secondary batteries igniting and exploding.

[0007] Recently, various studies have been attempted to develop electrolytes with new compositions containing additives to solve the problem of ignition and explosion in secondary batteries. However, in secondary batteries using carbonate-based organic solvents, there is a problem in that gas is generated inside the secondary battery due to the decomposition of the carbonate-based organic solvent during the reaction for forming a solid electrolyte interphase film (SEI film), which is a decomposition product of the solid electrolyte accumulated on the surface of the negative electrode. Depending on the type of non-aqueous organic solvent and the negative electrode active material, these gases include hydrogen gas (H2), carbon monoxide gas (CO), carbon dioxide gas (CO2), and methane gas (CH4).

[0008] Therefore, due to the generation of the aforementioned gases inside the secondary battery, the thickness of the battery expands during charging. Additionally, when the secondary battery is left at a high temperature in a fully charged state (e.g., left at 60°C for 4 weeks after charging to 100% V at 4.2 V), the negative electrode passivation film (SEI film) gradually collapses due to the electrochemical and thermal energy that increases over time, causing continuous side reactions in which the surrounding electrolyte reacts with the newly exposed negative electrode surface. Due to this continuous generation of gases, the internal pressure of the secondary battery rises, and performance degradation occurs, such as a reduction in the lifespan of the secondary battery at high temperatures due to volume expansion.

[0009] To prevent such performance degradation of secondary batteries and to improve battery characteristics such as lifespan and storage characteristics of lithium secondary batteries at high voltages, various studies are being conducted on non-aqueous organic solvents or additives as electrolyte components.

[0010] However, additives such as 1,3-propanesulfone and 1,3-propensulfone, which have been extensively studied as electrolyte additives in the past, improve the high-temperature storage characteristics of secondary batteries even in high-voltage environments during long-term high-temperature storage, but cause a problem in which the high-temperature life characteristics of secondary batteries decrease.

[0011]

[0012] The present invention aims to provide an electrolyte for a lithium secondary battery and a lithium secondary battery containing the same, which can simultaneously improve the high-temperature storage characteristics and high-temperature life characteristics of the secondary battery in order to solve the problems of the prior art as described above.

[0013] In addition, the purpose is to provide an electrolyte for a lithium secondary battery capable of suppressing oxidative decomposition of the electrolyte even under high voltage conditions, and a lithium secondary battery containing the same.

[0014]

[0015] An electrolyte composition for a secondary battery according to one embodiment of the present invention may comprise a pentaerythritol diphosphate additive represented by the following chemical formula 1; an auxiliary additive; a lithium salt; and a non-aqueous organic solvent.

[0016] [Chemical Formula 1]

[0017]

[0018] In the above chemical formula 1, R1 and R2 are independently an unsubstituted alkyl group or a halogen-substituted alkyl group.

[0019] In one embodiment, the above pentaerythritol diphosphate additive may be represented by the following chemical formula 2.

[0020] [Chemical Formula 2]

[0021]

[0022] In one embodiment, the pentaerythritol diphosphate additive may be included in an amount of 0.1 to 5.0 weight% based on the weight% of the electrolyte.

[0023] In one embodiment, the auxiliary additive may include one or more compounds selected from carbonate-based compounds, phosphate-based compounds, sulfonate-based compounds, sulfonyl imide-based compounds, and sulfone-based compounds.

[0024] In one embodiment, the auxiliary additive may be included in an amount of 0.1% to 4.0% by weight based on the weight percentage of the electrolyte.

[0025] In one embodiment, the auxiliary additive may include a cyclic carbonate containing unsaturated bonds, and the carbonate containing unsaturated bonds may be included in an amount of 0.1% to 2.0% by weight based on the weight percentage of the electrolyte.

[0026] In one embodiment, the auxiliary additive may include a fluoro-containing cyclic carbonate, and the fluoro-containing cyclic carbonate may be included in an amount of 0.1% to 2.0% by weight based on the weight percentage of the electrolyte.

[0027] In one embodiment, the auxiliary additive may include a sulfonate-based compound, and the sulfonate-based compound may be included in an amount of 0.1% to 2.0% by weight based on the weight percentage of the electrolyte.

[0028] In one embodiment, the sulfone-based compound may be one or more selected from 1,3-propanesulfone and 1,3-propenesulfone.

[0029] In one embodiment, the auxiliary additive may include a phosphate-based compound, and the phosphate-based compound may be included in an amount of 0.1% to 2.0% by weight based on the weight percentage of the electrolyte.

[0030] In one embodiment, the auxiliary additive may include an unsaturated bond-containing cyclic carbonate, a fluorocarbonate, and a sulfonate-based compound.

[0031] In one embodiment, the auxiliary additive may include an unsaturated bond-containing cyclic carbonate, a fluorocarbonate, a sulfonate-based compound, and a phosphate-based compound.

[0032] In one embodiment, the organic solvent may be an electrolyte composition for a secondary battery in which the volume ratio of a linear carbonate solvent and a cyclic carbonate solvent is 6:4 to 5:1.

[0033] A lithium secondary battery according to one embodiment of the present invention may include the non-aqueous electrolyte composition for the lithium secondary battery.

[0034] In one embodiment, the lithium secondary battery can be operated at a charging voltage of 4.4V or higher.

[0035]

[0036] A lithium secondary battery using the electrolyte of the present invention stabilizes the SEI layer, prevents oxidation of the electrolyte and decomposition of the electrode, exhibits excellent high-temperature life characteristics, reduces internal resistance (IR) during high-temperature storage, and suppresses battery thickness expansion, resulting in a superior capacity retention rate.

[0037] In addition, it exhibits excellent capacity retention and storage stability, especially under high voltage conditions of 4.4V or higher and / or high temperature conditions of 60℃, and can secure high output characteristics by maintaining low internal resistance.

[0038]

[0039] The present invention will be described in more detail below through examples. These examples are merely illustrative of the present invention, and therefore the scope of the present invention should not be interpreted as being limited by these examples.

[0040] Expressions such as "comprising" as used in this specification should be understood as open-ended terms implying the possibility of including other embodiments, unless specifically otherwise stated in the phrase or sentence containing such expression.

[0041] As used herein, "preferred" and "preferably" refer to embodiments of the invention that may provide certain advantages under certain conditions. However, other embodiments may also be preferred under the same or different conditions. Additionally, the mention of one or more preferred embodiments does not imply that other embodiments are not useful, nor is it intended to exclude other embodiments from the scope of the invention.

[0042]

[0043] Electrolyte composition for secondary batteries

[0044] Hereinafter, the electrolyte for a lithium secondary battery according to the present invention will be described in detail.

[0045] The electrolyte for a lithium secondary battery of the present invention may include a pentaerythritol diphosphate compound represented by Chemical Formula 1; an auxiliary additive; a lithium salt; and a non-aqueous organic solvent.

[0046]

[0047] 1. Pentaerythritol diphosphate compound represented by Chemical Formula 1

[0048] [Chemical Formula 1]

[0049]

[0050] In the above chemical formula 1, R1 and R2 are independently an unsubstituted alkyl group or a halogen-substituted alkyl group.

[0051] In the present invention, the 'alkyl group' may be in the form of a straight chain, a branched chain, a cyclic chain, or a mixture thereof. The number of carbon atoms is not particularly limited, but it is preferred to have 1 to 30 carbon atoms. Specific examples of "alkyl" may include methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, t-butyl group, n-pentyl, iso-pentyl, neo-pentyl, sec-pentyl, t-pentyl, n-hexyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, etc., but are not limited thereto.

[0052] In the present invention, the 'halogen group' may be a substituent to which, for example, fluorine (F), chlorine (Cl), bromine (Br), or iodine (I) is attached, and more preferably, fluorine (F).

[0053] Pentaerythritol diphosphate represented by the above chemical formula 1 has a double phosphate structure in which two phosphorus (P) atoms are bonded in a spiro form with pentaerythritol as the central backbone. This spiro structure imparts high structural rigidity to the molecule and, due to its stereochemical properties, can have excellent solubility in electrolyte solvents.

[0054] A small amount of moisture is inevitably present inside lithium secondary batteries, and this reacts with lithium salts (LiPF6) to produce hydrofluoric acid (HF). The generated HF attacks the positive electrode active material, causing transition metals to leach out and potentially destroying the SEI of the negative electrode. The P=O bond (Phosphoryl group) present in the compound of pentaerythritol diphosphate represented by Chemical Formula 1 acts as a strong Lewis base and can form a coordination bond with Lewis acids such as HF or PF5. Through this, it can lower the concentration of acidic impurities in the electrolyte and perform the role of a 'stabilizer' that suppresses chain decomposition reactions.

[0055] In addition, the pentaerythritol diphosphate represented by the above chemical formula 1 can be selectively adsorbed or oxidized at the active site of the anode surface at high voltage (e.g., 4.4 V or higher) to form a protective film (CEI: Cathode Electrolyte Interphase). This film acts as a barrier that prevents electrolyte solvent molecules from coming into direct contact with the anode surface and being oxidized, thereby suppressing gas generation.

[0056] In particular, when the R group is a fluoroalkyl group, the oxidation resistance of the film is further enhanced, allowing stability to be maintained even at high voltages.

[0057] For example, the pentaerythritol diphosphate represented by the above chemical formula 1 may be as follows.

[0058]

[0059] More preferably, the pentaerythritol diphosphate represented by the above chemical formula 1 may be a compound represented by the following chemical formula 2, namely 2,4,8,10-Tetraoxa-3,9-diphosphaspiro[5.5]undecane,3,9-bis(2,2-difluoroethoxy)-,3,9-dioxide.

[0060] [Chemical Formula 2]

[0061]

[0062] This is a structure in which two fluorine (F) atoms are introduced into each ethyl group, and oxidation resistance is further enhanced by the fluorine (F) atoms introduced at the ends, allowing for the formation of a more stable film (CEI).

[0063] As an example of a synthesis process, it can be obtained in high yield through a two-step process in which pentaerythritol and phosphorus oxychloride (POCl3) are reacted to form an intermediate, and then reacted with an alcohol or fluoroalcohol, but is not limited thereto.

[0064] In a more preferred embodiment, the compound represented by the above chemical formula 1 may have a purity of 98% or more, 99% or more, or 99.5% or more.

[0065] In addition, as a more preferred embodiment, the moisture content may be 50 ppm or less, 30 ppm or less, 20 ppm or less, or 10 ppm or less.

[0066] Trace amounts of impurities or moisture react with LiPF6 to produce H₂ acidic substances, which can corrode the surface of the cathode active material and become a major cause of increased resistance. The synthesis and purification processes of the compound represented by Chemical Formula 1 of the present invention are highly refined to control impurities that directly affect battery performance.

[0067] The above pentaerythritol diphosphate additive may be included in an amount of 0.1% or more, 0.5% or more, 1.0% or more, 1.5% or more, 2.0% or more, 5.0% or less, 4.0% or less, or 3.5% or less based on the weight% of the electrolyte, and more preferably, in an amount of 0.3% to 3.0%.

[0068]

[0069] 2. Auxiliary additives

[0070] An auxiliary additive according to one embodiment of the present invention may include one or more compounds selected from carbonate-based compounds, phosphate-based compounds, sulfonate-based compounds, sulfonyl imide-based compounds, and sulfone-based compounds.

[0071] More preferably, the auxiliary additive may comprise one or more selected from the group consisting of lithium difluorophosphate, lithium tetrafluoro(oxalate)phosphate, lithium bis(fluorosulfonyl)imide, 1,3-propane sultone, 1,3-propene sultone, methylenemethan disulfonate, fluoroethylene carbonate, vinylene carbonate, and vinyl ethylene carbonate.

[0072] The above auxiliary additive may be included in an amount of 0.1% or more, 0.5% or more, 1.0% or less, 4.0% or less, 3.5% or less, or 3.0% or less based on the weight% of the electrolyte.

[0073] Examples of carbonate compounds include vinylene carbonate (VC), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylmethyl carbonate (EMC).

[0074] The above carbonate compound may be included in an amount of 0.1% or more, 0.3% or more, 0.5% or more, 2.0% or less, or 1.5% or less based on the weight percentage of the electrolyte.

[0075] More preferably, the carbonate compound may include a cyclic carbonate containing unsaturated bonds, and more preferably, may include vinylene carbonate (VC). This can be reduced and decomposed on the cathode surface to form a polymeric SEI (Poly(VC)), and this film can be flexible while having an excellent effect in preventing further decomposition of the electrolyte.

[0076] More preferably, the carbonate compound may include a fluoro-containing cyclic carbonate, and more preferably, may include a fluoroethylene carbonate (FEC). This can be reduced mainly at the cathode surface to form a LiF-rich SEI. The LiF component has high mechanical strength and excellent ionic conductivity, making it effective for controlling volume expansion of not only graphite cathodes but also silicon cathodes. Additionally, it can improve oxidation resistance by forming a fluorinated film on the anode surface at high voltage.

[0077] Additionally, more preferably, the carbonate compound may include an unsaturated bond-containing cyclic carbonate and a fluorocarbon-containing cyclic carbonate, and more preferably, may include vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0078] Examples of phosphate-based compounds include lithium difluorophosphate (LiPO2F2), lithium tetrafluoro(oxalate)phosphate (LiTFOP), lithium bis(fluorosulfonyl)imide, and tris(trimethylsilyl)phosphate (TMSP). The above phosphate-based compounds, more preferably lithium difluorophosphate (LiPO2F2), dissociate in the electrolyte to form PO2F2 -It forms anions, which can form a lithium ion conductive film with very low resistance at both the anode and the cathode. In particular, it plays a role in solving the problem of increased resistance caused by sulfone-based additives and can simultaneously improve low-temperature and high-rate characteristics.

[0079] The above phosphate-based compound may be included in an amount of 0.1% or more, 0.3% or more, 0.5% or more, 2.0% or less, or 1.5% or less based on the weight% of the electrolyte.

[0080] Examples of sulfonate compounds include methylenemethanedisulfonate, butanesulfonate compounds, dimethyl sulfonate, ethyl methyl sulfonate, and pure alkyl sulfonates that are not substituted with halogens (F, Cl, etc.). Halogen-unsubstituted sulfonate compounds, more preferably methylenemethanedisulfonate, can form a flexible and dense sulfur (S)-containing film to control structural stability and resistance at high temperatures.

[0081] The above sulfonate-based compound may be included in an amount of 0.1% or more, 0.3% or more, 0.5% or more, 2.0% or less, and 1.5% or less based on the weight% of the electrolyte.

[0082] Sulfonyl imide compounds include lithium bis(fluorosulfonyl)imide, and can increase the ionic conductivity of the electrolyte and improve low-temperature output.

[0083] The above sulfonyl imide-based compound may be included in an amount of 0.1% or more, 0.3% or more, 0.5% or more, 2.0% or less, and 1.5% or less based on the weight% of the electrolyte.

[0084] Examples of sulfonate compounds include 1,3-propanesulfone (PS), 1,3-propenesulfone (PRS), and 1,4-butanesulfone. More preferably, the sulfonate compound may include one or more selected from 1,3-propanesulfone and 1,3-propenesulfone. More preferably, it may include 1,3-propanesulfone (PS) or both 1,3-propanesulfone (PS) and 1,3-propenesulfone (PRS). This has an excellent effect in suppressing gas generation during high-temperature storage and decomposes on the electrode surface to form an alkyl sulfonate film containing sulfur, which has very high thermal stability at high temperatures. However, these films have a disadvantage in that their low ionic conductivity increases the initial resistance (DCIR), and as the film resistance continuously rises during long-term cycling, it causes a decrease in capacity.

[0085] The above sulfonate-based compound may be included in an amount of 0.1% or more, 0.3% or more, 0.5% or more, 2.0% or less, or 1.5% or less based on the weight% of the electrolyte.

[0086] In a more preferred embodiment, the auxiliary additive may include a cyclic carbonate containing unsaturated bonds. A two-additive combination system including the additive of Formula 1 of the present invention can exhibit a synergistic effect in which the cyclic carbonate containing unsaturated bonds, which forms a solid SEI layer on the surface of the cathode, and the additive of Formula 1, which protects the surface of the anode and removes acidic impurities (HF) in the electrolyte, work complementarily to increase the charge / discharge efficiency of the battery and suppress the decomposition of the electrolyte.

[0087] In a more preferred embodiment, the auxiliary additive may include an unsaturated bond-containing cyclic carbonate and a fluorocarbonate. When these three types of additives, including the additive of Formula 1 of the present invention, are mixed, the fluorocarbonate forms a LiF (Lithium Fluoride)-based film with excellent lithium ion conductivity on the cathode surface, and the additive of Formula 1 scavenges Lewis acids (PF5, HF) capable of attacking the film, thereby maintaining the durability of the film and minimizing the increase in interfacial resistance even during high-voltage operation.

[0088] In a more preferred embodiment, the auxiliary additive may include an unsaturated bond-containing cyclic carbonate, a fluorocarbonate, and a sulfonate-based compound. When these four types of additives, including the additive of Formula 1 of the present invention, are mixed, the sulfonate-based compound forms a sulfur (S)-based film on the electrode surface that is stable at high temperatures to suppress gas generation, while the additive of Formula 1 can mitigate the problem of increased initial resistance that may occur as a result. Specifically, the additive of Formula 1 compensates for structural defects between the sulfonate-based films to form a dense composite film (Multi-layered SEI / CEI), thereby simultaneously achieving an excellent capacity retention rate and a swelling suppression effect even under high voltage and high temperature conditions.

[0089] In this case, as a more preferred embodiment, the sulfone-based compound may include 1,3-propane sultone and 1,3-propene sultone. Although the 1,3-propane sultone and 1,3-propene sultone have excellent high-temperature storage characteristics, there is a trade-off that degrades long-term life characteristics; however, when the additive of Formula 1 of the present invention is used in combination, the oxidative decomposition products of the electrolyte can be effectively controlled to prevent life degradation caused by the sulfone-based additive and significantly improve high-temperature life characteristics.

[0090] In another more preferred embodiment, the auxiliary additive may include an unsaturated bond-containing cyclic carbonate, a fluorocarbonate, a sulfonate-based compound, and a phosphate-based compound. When these five types of additives, including the additive of Formula 1 of the present invention, are mixed, the additive of Formula 1 can act as a stabilizer to prevent the film component formed by LiPO2F₂ from being damaged by by-products (such as HF) in the electrolyte. That is, the resistance reduction effect of LiPO2F₂ and the interfacial durability improvement effect of the additive of Formula 1 are combined, thereby maximizing the electrochemical performance of the battery, such as achieving a significantly improved capacity retention rate during high-temperature life evaluation at 45°C.

[0091] In this case, more preferably, the sulfone-based compound may include 1,3-propanesulfone (1,3-propane sultone).

[0092]

[0093] 3. Lithium salt

[0094] Lithium salts act as a source of lithium ions within the battery, enabling the basic operation of the lithium battery. It is desirable to use lithium salts that have excellent ionic conductivity due to their high degree of lattice energy dissociation, as well as superior thermal stability and oxidation resistance.

[0095] The lithium salts usable in the present invention are LiPF6, LiBF4, LiBF6, and LiB 12 F 12 , LiAsF6, LiFSO3, Li2SiF6, LiCF3CO2, LiCH3CO2, LiCF3SO3, LiC4F9SO3, LiCF3CF2SO3, LiCF3(CF2)7SO3, LiCF3CF2(CF3)2CO, Li(CF3SO2)2CH, LiNO3, LiN(CN)2, LiN(FSO2)2, LiN(F2SO2)2, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiC(CF3SO2)3, LiP(CF3)6, LiPF(CF3)5, LiPF2(CF3)4, LiPF3(CF3)3, LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF2C2O4, LiBC4O8, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2, LiSbF6, LiAlO4, LiAlF4, LiSCN, LiClO4, LiCl, LiF, LiBr, LiI, LiAlCl 4, It may include one or more selected from the group consisting of LiPF6 and LiFSI, but is not limited thereto. In particular, LiPF6 is more preferable in that it has excellent general conductivity, while LiFSI is more preferable in that it has the effect of complementing high and low temperature characteristics.

[0096] The concentration of the lithium salt can range from 0.1M to 5.0M, but considering the viscosity and ion mobility of the electrolyte, a concentration of 0.8M to 1.5M is most desirable. This range allows for securing the density of charge carriers required for high-voltage driving while maintaining the impregnation properties of the electrolyte.

[0097]

[0098] 4. Organic solvents

[0099] Organic solvents serve as a medium for dissolving additives and lithium salts, and require oxidation stability in high-voltage environments.

[0100] The organic solvent of the present invention may be selected from the group consisting of linear carbonate-based solvents, cyclic carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, and non-protic solvents, but is not limited thereto.

[0101] For example, the linear carbonate-based solvent may include at least one 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 more preferably may include ethyl methyl carbonate.

[0102] The above-mentioned cyclic carbonate-based solvent may include at least one 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, 2,3-pentylene carbonate, vinylene carbonate (VC), and fluoroethylene carbonate (FEC), and more preferably may include ethylene carbonate.

[0103] The above ester-based solvent may include methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), gamma-butyrolactone (γGBL), decanolide, valerolactone, mevalonolactone, or caprolactone.

[0104] The above ether-based organic solvent may include dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran.

[0105] The above ketone-based solvent may include cyclohexanone.

[0106] The above alcohol-based solvent may include ethyl alcohol and isopropyl alcohol.

[0107] The above non-protic solvent may include nitrile-based solvents, amide-based solvents, dioxolane-based solvents such as 1,3-dioxolane, or sulfolane-based solvents.

[0108] More preferably, the organic solvent may be a mixture of a linear carbonate solvent and a cyclic carbonate solvent. Since the cyclic carbonate solvent has high polarity and can sufficiently dissociate lithium ions, but has the disadvantage of low ionic conductivity due to its high viscosity, the characteristics of the lithium secondary battery can be optimized by mixing the cyclic carbonate solvent with a linear carbonate solvent that has low polarity but low viscosity. Accordingly, it is preferable to use a mixture of one or more solvents selected from cyclic carbonate solvents and one or more solvents selected from linear carbonate solvents as the non-aqueous solvent.

[0109] At this time, the linear carbonate solvent and the cyclic carbonate solvent may be mixed in a volume ratio of 9:1 to 1:9, and more preferably, the mixture may be composed of a ratio of 2:1 to 5:1 or 6:4 to 4:1. If the ratio of the linear carbonate is lowered to less than 2:1, the viscosity of the electrolyte of the present invention increases, thereby degrading the output characteristics; if it is higher than 5:1, a technical trade-off may occur in which the degree of dissociation of the lithium salt decreases, resulting in insufficient ion conductivity. Accordingly, by adjusting the type and composition ratio of the organic solvent of the present invention as described above, the electrolyte of the present invention minimizes oxidative decomposition of the solvent even at high pressures of 4.4V or higher, and significantly improves stable battery operation.

[0110]

[0111] lithium secondary battery

[0112] A lithium secondary battery according to one embodiment of the present invention may include the above-described non-aqueous electrolyte composition for a lithium secondary battery.

[0113] The above lithium secondary battery can be operated at a charging voltage of 4.4V or higher. This high-voltage operating condition is the critical voltage for the mid-to-high nickel cathode material to fully exhibit its designed high-energy density characteristics. Conventional electrolytes cannot withstand transition metal leaching and gas generation in this pressure range and exhibit rapid performance degradation, but the additive system of the present invention overcomes this, enabling the commercialization of next-generation high-performance batteries.

[0114] The above anode and / or cathode may be manufactured by preparing an electrode slurry composition by dispersing an electrode active material, a binder, a conductive material, and, if necessary, a thickener in a solvent, and applying the slurry composition to an electrode current collector. Aluminum or an aluminum alloy can commonly be used as the anode current collector, and copper or a copper alloy can commonly be used as the cathode current collector. Examples of the forms of the anode and cathode current collectors include foil or mesh.

[0115] The cathode active material is a compound capable of reversible interpolation and extrapolation of lithium, such as LiCoO2 (LCO) and LiNi x Co y Mn z O2(NCM), LiNi x Co y Al z It may include one or more selected from the group consisting of O2 (NCA), lithium excess layered oxide (LMR), LiFePO4 (LFP), and LiMnFePO4 (LMFP), but is not limited thereto. In particular, the transition metal leaching inhibition effect may be most pronounced in nickel systems.

[0116] The cathode active material may include carbon materials such as artificial graphite or natural graphite, or silicon (Si)-based oxides and silicon-carbon composites for realizing high capacity, but is not limited thereto. When silicon is included in the cathode, the problem of SEI breakdown due to volume expansion becomes severe; however, the electrolyte composition of the present invention helps maintain interfacial flexibility even under such harsh conditions.

[0117] The above binder is a material that serves functions such as forming the active material into a paste, mutual adhesion of the active materials, adhesion to the current collector, and a buffering effect against the expansion and contraction of the active material, and any binder that can be used by a person skilled in the art is acceptable. For example, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVdF), copolymer of polyhexafluoropropylene-polyvinylidene fluoride (PVdF / HFP)), poly(vinyl acetate), alkylated polyethylene oxide, polyvinyl ether, poly(methyl methacrylate), poly(ethyl acrylate), polyacrylonitrile, polyvinylpyridine, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, epoxy resin, nylon, etc. may be used, but are not limited thereto.

[0118] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. As the conductive material, at least one selected from the group consisting of graphite-based conductive materials, carbon black-based conductive materials, and metal or metal compound-based conductive materials may be used. Examples of the above graphite-based conductive materials include artificial graphite and natural graphite, and examples of carbon black-based conductive materials include acetylene black, Ketjen black, Denka black, thermal black, channel black, carbon nanotubes, and graphene, and examples of metal-based or metal compound-based conductive materials include perovskite materials such as tin, tin oxide, tin phosphate (SnPO4), titanium oxide, potassium titanate, LaSrCoO3, and LaSrMnO3, but are not limited thereto.

[0119] The secondary battery of the present invention may further include a separator that prevents a short circuit between the positive and negative electrodes and provides a pathway for the movement of lithium ions. As such a separator, a polyolefin-based polymer membrane such as polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, or polypropylene / polyethylene / polypropylene, or a multilayer membrane thereof, a microporous film, a woven fabric, or a nonwoven fabric may be used. Additionally, a film in which a resin with excellent stability is coated on a porous polyolefin film may be used, but is not limited thereto.

[0120] As an example, non-limiting examples of the above secondary battery may include, but are not limited to, lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, lithium-ion polymer secondary batteries, or lithium-sulfur secondary batteries.

[0121] In one embodiment, the lithium secondary battery can prevent structural degradation of the positive active material even under high voltage driving conditions of 4.4V or higher, thereby significantly improving the resistance increase rate.

[0122] In addition, the present invention can effectively suppress by-product gases generated during high-temperature storage at 60°C, thereby simultaneously ensuring the safety of the battery.

[0123]

[0124] Hereinafter, embodiments of the present invention will be described in more detail.

[0125]

[0126] Preparation of 2,4,8,10-Tetraoxa-3,9-diphosphaspiro[5.5]undecane,3,9-bis(2,2-difluoroethoxy)-,3,9-dioxide (Additive 1)

[0127] 1) Pentaerythritol was placed in a reaction flask, and after setting the vibration frequency to 50 Hz at 25°C, Phosphorus Oxychloride (POCl3) was slowly added. The exhaust gas generated during the reaction was absorbed by an alkaline solution, and the reaction temperature was maintained at 25°C. Once the addition was complete, the vibration frequency was increased to 100 Hz, and the reaction was continued for 3 hours until no more gas was generated. After the reaction, anhydrous dichloromethane was added to form a slurry, followed by filtration and washing.

[0128] 2) Pentaerythritol diphosphate diphosphoryl chloride and anhydrous dichloromethane were placed in a 1L small-necked flask, and difluoroethanol was added at a temperature between -5°C and 0°C. Anhydrous triethylamine was added at 0°C, and once the addition was complete, the mixture was heated and the reflux reaction was carried out for 5 hours. After the reaction, the solvent was removed using a rotary evaporator, and the remaining residue was washed with water and filtered. The filtered solid was dried and recrystallized with ethanol to obtain a white crystalline compound.

[0129]

[0130] Preparation of an electrolyte composition

[0131] <Examples 1 to 6, Comparative Example 1>

[0132] To verify changes in battery performance according to various additive concentrations, an electrolyte composition was prepared by adding the additives as shown in Table 1 below to a basic electrolyte (1.0M LiPF6EC:EMC = 30:70 volume ratio).

[0133]

[0134]

[0135]

[0136]

[0137] Manufacturing of lithium secondary batteries

[0138] Li[Ni 0.6 Co 0.1 Mn 0.3 A cathode active material slurry was prepared by adding 96 wt% of O2 cathode active material, 2 wt% of carbon black as a conductive agent, and 2 wt% of polyvinylidene fluoride (PVdF) as a binder to NMP (N-methyl 2-pyrrolidinone) solvent. The cathode active material slurry was coated onto an aluminum thin film serving as a current collector and dried to produce a cathode, which was then rolled using a roll press to prepare the cathode.

[0139] A cathode active material slurry was prepared by adding graphite as the cathode active material, CMC and SBR as binders, and carbon black as a conductive agent to the solvent H2O in amounts of 97.1 wt%, 1 wt%, 1 wt%, and 0.9 wt%, respectively. The cathode was prepared by coating the above cathode mixture onto a copper thin film serving as a cathode current collector and drying it.

[0140] In addition, a PE separator was placed between the anode and cathode, and the battery was manufactured with a standard capacity of 730 mAh, with a deviation of ±20 mAh in the initial capacity of each battery. The electrolytes prepared in the above examples and comparative examples were each injected to manufacture an aluminum pouch type (Al-Pouch type) lithium secondary battery.

[0141]

[0142] Experimental example

[0143] <Experimental Example 1> Evaluation of Initial Resistance (compared to Ref)

[0144] To evaluate the initial resistance after the completion of the formation process, one cycle of charging and discharging at 0.2C and two cycles at 0.5C were sequentially performed under conditions of 25℃.

[0145] After that, the SOC was adjusted to reach 50% at 25℃, and then the C-rate was gradually increased and decreased to 0.1C, 0.2C, 0.5C, 1.0C, and 1.5C, and charging and discharging were performed for 10 seconds each under each C-rate condition.

[0146] The termination point of the voltage measured at each C-rate was constructed as a straight-line equation, and the slope of the line was adopted as DCIR to calculate the initial resistance value.

[0147]

[0148] <Experimental Example 2> Evaluation of High Temperature (45℃) Lifespan and Capacity Retention Rate

[0149] After leaving at 45℃ for 2 hours, a 1C CC / CV charge (4.4V, 0.02C cut-off) was performed followed by a 10-minute rest period, and a 1C CC discharge (2.7V cut-off) was performed followed by a 10-minute rest period, and the first discharge capacity C1 was measured. This process was repeated 400 times, and the discharge capacity C2 was measured at the 300th and 400th cycles. The capacity retention rate was calculated as follows and is listed in Table 2.

[0150] Capacity retention rate (%) = C2 / C1 * 100

[0151]

[0152] <Experimental Example 3> High Temperature (60℃) Storage, Evaluation of Capacity Recovery Rate

[0153] At 25℃, 0.5C CC / CV charging (4.4V, 0.02C cut-off) and 0.5C CC discharging (2.7V cut-off) were repeated 3 times, and the 2nd discharge capacity C3 was measured.

[0154] A battery charged to SOC 100% was left at 60°C for 2 weeks using a constant temperature device, then left at 25°C for 3 hours, and then discharged at 0.5C CC (2.7V cut-off) to measure the discharge capacity C4.

[0155] The above 60℃ storage was carried out for a total of 8 weeks. The capacity retention rate was calculated as follows, and the results are listed in Table 2.

[0156] Capacity retention rate (%) = C4 / C3 * 100

[0157]

[0158] <Experimental Example 4> High-temperature (60℃) storage, evaluation of thickness increase rate

[0159] After charging to 100% SOC at 25℃ using 0.5C CC / CV (4.4V, 0.02C cut-off), the initial battery thickness T1 was measured. The charged battery was then stored at 60℃ for one week using a constant temperature device, after which the battery thickness T2 was measured. The above 60℃ storage was carried out for a total of 8 weeks.

[0160] The cell thickness was measured using a PPHG (Parallel Plate Height Gauge, Mitutoyo, 543-474B) device. The thickness increase rate was calculated as follows, and the results are listed in Table 2.

[0161] Thickness increase rate (%) = [(T2-T1) / T1 + 1] * 100

[0162]

[0163] <Experimental Example 5> High Temperature (60℃) Storage, Evaluation of Resistance Increase Rate

[0164] After leaving at 60°C for 2 weeks using a constant temperature device, the C-rate was increased and decreased to 0.1C, 0.2C, 0.5C, 1.0C, and 1.5C at the SOC 50% point at 25°C, and the terminal point of the voltage was constructed using a linear equation when charging and discharging at the corresponding C-rate was performed for 10 seconds, and the slope was adopted as DCIR.

[0165] The DCIR measured during the initial resistance evaluation was set as R1, and the DCIR measured during the resistance evaluation after leaving at 60°C for 2 weeks was set as R3. The resistance increase rate was calculated as follows, and the storage at 60°C was carried out for a total of 8 weeks. The results are listed in Table 2.

[0166] Resistance increase rate (%) = [(R3-R1) / R1 + 1] * 100

[0167]

[0168] Table 2

[0169]

[0170]

[0171] As a result of measuring the capacity retention rate after 300 charge-discharge cycles at 45℃, Example 1 containing 0.3 wt% of the additive 1 of the present invention was the lowest among the examples at 86.3%, Example 2 containing 0.5 wt% was 87.5%, Example 3 containing 1 wt% was 89.7%, Example 4 containing 2 wt% was 90.7%, Example 5 containing 3 wt% was 88.2%, and Example 6 containing 5 wt% was 86.9%, with all examples showing a value of 85% or higher, which is an improved figure compared to the capacity retention rate of 82.5% of the comparative example using a basic electrolyte without additive 1.

[0172] As a result of measuring the dose recovery rate after leaving at 60°C for 8 weeks, the dose recovery rates of the examples were as follows: Example 1 had the lowest rate at 58.8%, Example 2 had 60%, Example 3 had 61.9%, Example 4 had 63.4%, Example 5 had 66.5%, and Example 6 had 63.2%, with all examples showing a rate of 55% or higher, which is an improvement over the dose recovery rate of the comparative example, which was 42.7%.

[0173] As a result of measuring the thickness increase rate after leaving at 60°C for 8 weeks, the thickness increase rate of the examples was highest among the examples at 100% for Example 1, 83.6% for Example 2, 75.2% for Example 3, 65.9% for Example 4, 58% for Example 5, and 62.7% for Example 6, with all examples showing a thickness increase rate of 100% or less, which is an improved figure compared to the thickness increase rate of the comparative example, which was 136.8%.

[0174] As a result of measuring the resistance increase rate after leaving at 60°C for 8 weeks, the resistance increase rate of the examples was highest in Example 1 at 167.4%, followed by Example 2 at 134.8%, Example 3 at 122%, Example 4 at 101.2%, Example 5 at 97.2%, and Example 6 at 111%, with all examples showing a resistance increase rate of 170% or less, which is an improved figure compared to the resistance increase rate of 257% of the comparative example.

[0175] The lower the increase in thickness and the increase in resistance, the better, while the higher the capacity retention rate and the capacity recovery rate, the better. When the amount of Additive 1 increases, the capacity recovery rate after storage at 60°C for 8 weeks increases, and the increase in thickness and resistance decreases; however, when Additive 1 is excessively increased by more than 5%, the capacity retention rate and capacity recovery rate decrease compared to when about 3% is added, and the increase in thickness and the increase in resistance increase.

[0176] In particular, the range of Example 3 (1.0 wt%) and Example 4 (2.0 wt%) showed the most balanced results in terms of lifespan and storage characteristics. This is because Additive 1 removed HF and formed an anode protective film of appropriate thickness, thereby suppressing electrolyte decomposition. However, when the Additive 1 content exceeded 3.0 wt% (Example 6), the lifespan characteristics tended to decrease slightly due to an increase in film resistance.

[0177]

[0178] <Examples 7 to 12, Comparative Examples 2 to 3>

[0179] To verify changes in battery performance according to various additive concentrations, an electrolyte composition was prepared by adding the additives as shown in Table 3 below to a basic electrolyte (1.0M LiPF6EC:EMC = 20:80 volume ratio).

[0180] In addition, regarding the above-described electrolyte composition, a lithium secondary battery was manufactured according to the above-described lithium secondary battery manufacturing method, and the results of measuring the above-described lithium secondary battery as described above are listed in Table 4 below.

[0181]

[0182] Table 3

[0183]

[0184]

[0185] Table 4

[0186]

[0187]

[0188] In particular, Example 9 has a 45°C lifetime superior to Example 4, and in particular, the capacity retention rate and thickness increase rate were significantly lowered. Furthermore, it demonstrates a much superior gas suppression capability compared to when only Additive 1 and VC were used. These results can be interpreted as VC, FEC, and PS forming a robust and dense composite film (Multi-layered SEI) on the cathode and anode, respectively, thereby fundamentally blocking the opportunity for the solvent to react with the electrode surface at high temperatures. Additionally, it can be interpreted that the sulfonate component of PS and the LiF component of FEC filled the gaps between the phosphate film of Additive 1, thereby forming a robust protective film.

[0189] In addition, Example 9, in which Additive 1 was added excluding LiPO2F2, showed superior performance in capacity retention and capacity recovery rates compared to Comparative Example 3 (containing LiPO2F2). This suggests that Additive 1 can replace LiPO2F2 or provide an interface stabilization effect greater than that of LiPO2F2. In particular, the fact that the resistance increase rate remained very low at 98.3% even without LiPO2F2 can be interpreted as Additive 1 effectively suppressing the resistance increase caused by sulfonate-based additives (PS, PRS) or modifying the properties of the sulfonate film to impart ion conductivity. Furthermore, the HF removal capability of Additive 1 is considered to be a synergistic effect that prevents anode damage caused by hydrofluoric acid by suppressing the decomposition of FEC.

[0190] Furthermore, looking at the experimental results in Table 4, Comparative Example 3, containing FEC, PS, PRS, and LiPO2F2, exhibited superior lifespan and storage characteristics compared to Comparative Example 2. However, regarding the results of Examples 7 to 12, in which LiPO2F2 was replaced with Additive 1 of the present invention, Example 9, with a content of Additive 1 of 1.0 wt%, recorded the highest performance, with a capacity retention rate of 97.2% after 45°C cycles, surpassing Comparative Example 3. Additionally, it showed superior characteristics compared to Comparative Example 3 in terms of capacity recovery rate (91.2%) and thickness increase rate (75.2%) after high-temperature storage.

[0191] This is believed to be because when Additive 1 is used with sulfonate compounds (PS, PRS), it fills the gaps between the solid sulfur (S)-based films formed by the sulfonate, thereby compensating for structural defects, and simultaneously removes impurities (HF) in the electrolyte, thereby preventing the deterioration of the film. In particular, Example 9 achieved performance equivalent to or better than that of expensive LiPO2F2 without using it, confirming that it is a composition capable of maximizing high-voltage life characteristics while securing cost competitiveness of the electrolyte.

[0192]

[0193] <Examples 13 to 18, Comparative Example 3>

[0194] To verify changes in battery performance according to various additive concentrations, an electrolyte composition was prepared by adding the additives as shown in Table 5 below to a basic electrolyte (1.0M LiPF6EC:EMC = 20:80 volume ratio).

[0195] In addition, regarding the above-described electrolyte composition, a lithium secondary battery was manufactured according to the above-described lithium secondary battery manufacturing method, and the results of measuring the above-described lithium secondary battery as described above are listed in Table 6 below.

[0196]

[0197] Table 5

[0198]

[0199] Table 6

[0200]

[0201]

[0202] In particular, Example 14 had the lowest resistance increase rate among all examples. This was in contrast to the phenomenon where increasing the type and amount of additives typically increases film resistance and deteriorates DCIR characteristics. This suggests that LiPO2F2 formed ion-conducting channels within the film, effectively offsetting the resistance components of the PS and VC-derived films.

[0203] In addition, the synergistic effect when LiPO2F2 and the additive 1 of the present invention are used together can be confirmed through the results of Table 6.

[0204] This can be interpreted as the result of a complementary mechanism in which LiPO2F2 forms low-resistance ion-conducting channels on the electrode surface, and Additive 1 removes acidic impurities (HF) in the electrolyte to prevent damage to the film derived from LiPO2F2. When the content of Additive 1 increases to 1.0 wt% or more (Examples 15–18), an increase in resistance due to excessive film formation is observed; therefore, when used in combination with LiPO2F2, it may be desirable to control the content of Additive 1 to around 0.5 wt%.

[0205]

[0206] [Correction pursuant to Rule 91 13.01.2026] The present invention is derived as a result of research conducted under the support of the Korea Institute of Industrial Technology Planning and Evaluation as part of the Ministry of Trade, Industry and Energy’s Advanced Strategic Industry Super-Gap (Secondary Battery) Project (Project No.: 449746, Lead Organization: Enchem Co., Ltd., Research Period: 2025. 01. 01 ~ 2025.12. 31).

Claims

1. A pentaerythritol diphosphate additive represented by the following chemical formula 1; Auxiliary additives; lithium salt; and A non-aqueous organic solvent; comprising Electrolyte composition for secondary batteries: [Chemical Formula 1] In the above chemical formula 1, R1 and R2 are independently an unsubstituted alkyl group or a halogen-substituted alkyl group.

2. In Paragraph 1, The above pentaerythritol diphosphate additive is represented by the following chemical formula 2, Electrolyte composition for secondary batteries: [Chemical Formula 2] .

3. In Paragraph 1, The above pentaerythritol diphosphate additive is included in an amount of 0.1 to 5.0 weight% based on the weight% of the electrolyte, Electrolyte composition for secondary batteries.

4. In Paragraph 1, The above auxiliary additive comprises one or more compounds selected from carbonate compounds, phosphate compounds, sulfonate compounds, sulfonyl imide compounds, and sultone compounds. Electrolyte composition for secondary batteries.

5. In Paragraph 1, The above auxiliary additive is included in an amount of 0.1% to 4.0% by weight based on the weight percentage of the electrolyte, Electrolyte composition for secondary batteries.

6. In Paragraph 1, The above auxiliary additive comprises a cyclic carbonate containing unsaturated bonds, and The above unsaturated bond-containing carbonate is included in an amount of 0.1% to 2.0% by weight based on the weight% of the electrolyte, Electrolyte composition for secondary batteries.

7. In Paragraph 6, The above auxiliary additive further comprises a fluoro-containing cyclic carbonate, and The above fluoro-containing cyclic carbonate is included in an amount of 0.1% to 2.0% by weight based on the weight% of the electrolyte, Electrolyte composition for secondary batteries.

8. In Paragraph 6, The above auxiliary additive further comprises a sulfonate compound, and The above sulfonate-based compound is included in an amount of 0.1% to 2.0% by weight based on the weight percentage of the electrolyte, Electrolyte composition for secondary batteries.

9. In Paragraph 8, The above sulfone-based compound is one or more selected from 1,3-propanesulfone and 1,3-propenesulfone, Electrolyte composition for secondary batteries.

10. In Paragraph 6, The above auxiliary additive further comprises a phosphate-based compound, and The above phosphate-based compound is included in an amount of 0.1% to 2.0% by weight based on the weight percentage of the electrolyte, Electrolyte composition for secondary batteries.

11. In Paragraph 1, The above auxiliary additive comprises unsaturated bond-containing cyclic carbonates, fluorocarbonates, and sulfonate-based compounds, Electrolyte composition for secondary batteries.

12. In Paragraph 1, The above auxiliary additive comprises unsaturated bond-containing cyclic carbonates, fluorocarbonates, sulfonate-based compounds, and phosphate-based compounds. Electrolyte composition for secondary batteries.

13. In Paragraph 1, The above organic solvent is a mixture of a linear carbonate solvent and a cyclic carbonate solvent in a volume ratio of 6:4 to 5:1, for an electrolyte composition for a secondary battery.

14. A non-aqueous electrolyte composition for a lithium secondary battery according to claim 1, Lithium secondary battery.

15. In Paragraph 14, The above lithium secondary battery operates at a charging voltage of 4.4V or higher, Lithium secondary battery.

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