Lithium secondary battery with improved high-temperature safety

Abstract

The present invention relates to an electrolyte composition having improved high-temperature safety and a secondary battery including the same. The electrolyte composition includes a first additive including a compound represented by Chemical Formula 1 and a second additive including one or more cyclic carbonate compounds in a specific content. This not only effectively reduces gas generated during charging and discharging of a lithium secondary battery, but also strengthens an SEI layer on the surface of an electrode, thereby improving storage characteristics and life characteristics at high temperatures.

Description

[Technical Field]

[0001] The present invention relates to a lithium secondary battery with improved safety at high temperatures.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0155462 dated November 12, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference. [Background technology]

[0003] In recent years, secondary batteries have been widely used not only in small devices such as portable electronic devices but also in medium- to large-sized devices such as battery packs for hybrid and electric vehicles and power storage devices. Examples of such secondary batteries include non-aqueous electrolyte batteries such as lithium-ion batteries, lithium batteries, lithium-ion capacitors, and sodium-ion batteries.

[0004] For example, LiPF6, which is most commonly used as a lithium salt in electrolytes, reacts with the electrolyte solvent to accelerate solvent depletion and generate HF. The generated HF not only generates a large amount of gas under high temperature conditions, but also can leach metal ions from the positive electrode active material. If the leachate metal ions are precipitated on the surface of the negative electrode, they can increase the negative electrode potential and reduce the OCV of the cell, thereby reducing not only battery performance but also lifespan and high-temperature safety.

[0005] Lithium metal oxide is used as the positive electrode active material for lithium secondary batteries, and lithium metal, lithium alloy, crystalline or amorphous carbon, or carbon composites are used as the negative electrode active material. The active material is applied to a current collector in a suitable thickness and length, or the active material itself is applied in the form of a film and then wound or laminated together with an insulating separator to form an electrode group, which is then placed in a can or similar container and then injected with an electrolyte to manufacture a secondary battery.

[0006] These lithium secondary batteries are charged and discharged through repeated intercalation and deintercalation of lithium ions from the lithium metal oxide cathode into the graphite anode. During this process, lithium reacts with the carbon electrode to form Li2CO3, LiO, LiOH, and other compounds, forming a coating on the surface of the anode. This coating, called the solid electrolyte interface (SEI), forms early in the charging process and prevents lithium ions from reacting with the carbon anode or other materials during charging and discharging. It also acts as an ion tunnel, allowing only lithium ions to pass through. These ion tunnels solvate lithium ions and prevent the electrolyte's organic solvent, which moves with it due to its large molecular weight, from co-transporting with the carbon anode, potentially disrupting its structure.

[0007] Therefore, to improve the high-temperature cycle characteristics of lithium secondary batteries, it is essential to form a strong SEI film on the anode of the lithium secondary battery. Once formed during the first charge, the SEI film prevents reactions between lithium ions and the anode or other materials during subsequent repeated charge and discharge cycles during battery use, and acts as an ion tunnel that allows only lithium ions to pass between the electrolyte and the anode.

[0008] In the past, when an electrolyte did not contain an electrolyte additive or contained an electrolyte additive with poor properties, it was difficult to expect an improvement in output characteristics due to the formation of a non-uniform SEI film. Furthermore, even when an electrolyte additive was included, if the amount of the additive was not adjusted to the required amount, the electrolyte additive could decompose the surface of the positive electrode during high-temperature reactions or cause an oxidation reaction of the electrolyte, ultimately resulting in an increase in the irreversible capacity of the secondary battery and a decrease in output characteristics.

[0009] Therefore, there is a need to develop a compound that can be used as an electrolyte additive to form a strong SEI film on the negative electrode and improve overall battery performance, such as high-rate charge / discharge characteristics, high-temperature performance characteristics, and life characteristics. Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, an object of the present invention is to provide an electrolyte composition that can form a coating on the surface of an electrode, particularly on the surface of a negative electrode, thereby improving the high-rate charge-discharge characteristics of a lithium secondary battery, and improving high-temperature storage characteristics, high-temperature performance, and life characteristics. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, in one embodiment, the present invention provides an electrolyte composition including a non-aqueous organic solvent, a lithium salt, a first additive including a compound represented by the following Chemical Formula 1, and a second additive including one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC).

[0012] [ka]

[0013] In the above chemical formula 1, each R1 is independently a single bond, an alkylene group having 1 to 10 carbon atoms, or [ka] where R2 is independently hydrogen, an acrylate group, or a methacrylate group; R3 is an alkylene group having 1 to 4 carbon atoms; and a is an integer of 1 to 10.

[0014] Specifically, each R1 is independently a single bond, a methylene group, an ethylene group, a propylene group, or [ka] wherein R3 is an ethylene group and a can be an integer from 1 to 5.

[0015] As an example, the compound represented by Chemical Formula 1 includes one or more compounds of the following <Structural Formula 1> to <Structural Formula 8>. [Table 1]

[0016] The first additive may be contained in an amount of 0.01 to 5% by weight based on the total weight of the electrolyte composition.

[0017] The second additive may be contained in an amount of 0.01 to 5% by weight based on the total weight of the electrolyte composition.

[0018] The lithium salts include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, and (FSO2)2NLi.

[0019] The non-aqueous organic solvent may also include N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0020] Furthermore, in one embodiment, the present invention provides a lithium secondary battery including an electrolyte composition comprising an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, a non-aqueous organic solvent, a lithium salt, a first additive including a compound represented by the following Chemical Formula 1, and a second additive including at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC):

[0021] [ka]

[0022] In the above chemical formula 1, each R1 is independently a single bond, an alkylene group having 1 to 10 carbon atoms, or [ka] where R2 is independently hydrogen, an acrylate group, or a methacrylate group; R3 is an alkylene group having 1 to 4 carbon atoms; and a is an integer of 1 to 10.

[0023] In this case, the positive electrode may include a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector and including one or more lithium metal oxides represented by the following Chemical Formula 2 and Chemical Formula 3.

[0024] [Chemical formula 2] Li x [Ni y Co z Mn w M 1 v ]O2

[0025] [Chemical formula 3] LiM 2 p Mn (2-p) O4

[0026] In the above chemical formula 2 and chemical formula 3, M 1is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, z, w, and v are 1.0≦x≦1.30, 0.5≦y<1, 0 <z≦0.3、0<w≦0.3、0≦v≦0.1であり、y+z+w+v=1であり、M 2 is Ni, Co or Fe, and p is in the range of 0.05≦p≦0.6.

[0027] Specifically, the lithium metal oxide is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2, LiNi 0.7 Mn 1.3 O4, LiNi 0.5 Mn 1.5 O4 and LiNi 0.3 Mn 1.7 O4.

[0028] The negative electrode may include a negative electrode current collector and a composite layer formed on the negative electrode current collector and containing a negative electrode active material, and the negative electrode active material may include one or more carbon materials selected from the group consisting of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, and ketjen black.

[0029] The negative electrode active material of the negative electrode may be silicon (Si), silicon carbide (SiC), and silicon oxide (SiO q , where 0.8≦q≦2.5).

[0030] In this case, the silicon material may be contained in an amount of 1 to 20% by weight based on the total weight of the negative electrode active material. [Effects of the Invention]

[0031] The electrolyte composition according to the present invention contains a first additive containing a compound represented by Chemical Formula 1 and a second additive containing one or more cyclic carbonate compounds in a specific content, thereby effectively reducing gas generated during charge and discharge of a lithium secondary battery and strengthening the SEI layer on the surface of the electrode, thereby improving storage characteristics and life characteristics at high temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention is susceptible to various modifications and embodiments, and therefore, specific embodiments are described in detail in the detailed description.

[0033] However, this is not intended to limit the invention to any particular embodiment, but should be understood to include all modifications, equivalents, or alternatives falling within the spirit and scope of the present invention.

[0034] In the present invention, the terms "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the presence or possible addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0035] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion therebetween. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion therebetween. Furthermore, in this application, being "located on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0036] Additionally, in the present invention, "comprising as a main component" may mean that the defined component is contained in an amount of 50 wt % or more, 60 wt % or more, 70 wt % or more, 80 wt % or more, 90 wt % or more, or 95 wt % or more based on the total weight of the negative electrode active material. For example, "comprising graphite as a main component as a negative electrode active material" may mean that the negative electrode active material contains 50 wt % or more, 60 wt % or more, 70 wt % or more, 80 wt % or more, 90 wt % or more, or 95 wt % or more of graphite based on the total weight of the negative electrode active material. In some cases, it may mean that the entire negative electrode active material is composed of graphite, with the graphite content being 100 wt %.

[0037] The present invention will now be described in more detail.

[0038] <Electrolyte composition> In one embodiment, the present invention provides an electrolyte composition including a non-aqueous organic solvent, a lithium salt, a first additive including a compound represented by the following Chemical Formula 1, and a second additive including one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC).

[0039] [ka]

[0040] In the above chemical formula 1, each R1 is independently a single bond, an alkylene group having 1 to 10 carbon atoms, or [ka] where R2 is independently hydrogen, an acrylate group, or a methacrylate group; R3 is an alkylene group having 1 to 4 carbon atoms; and a is an integer of 1 to 10.

[0041] The electrolyte composition according to the present invention is a non-aqueous electrolyte composition containing a lithium salt, and includes a first additive containing a compound represented by Chemical Formula 1, and an additive containing one or more of cyclic carbonate compounds, namely vinylene carbonate (VC), vinylethylene carbonate (VEC), and fluoroethylene carbobate (FEC).

[0042] The compound represented by Chemical Formula 1 contains a structure in which acrylate groups are bonded to two or more oxygen atoms in a phosphate salt via saturated hydrocarbon chains and / or alkylene glycol units. This structure allows the compound represented by Chemical Formula 1 to uniformly form organic and / or inorganic coatings on the surfaces of the positive and / or negative electrodes during secondary battery activation. Specifically, the compound represented by Chemical Formula 1 decomposes from the phosphate group to one or more *-R1-R2 groups through a reaction with a lithium salt during charge and discharge of the secondary battery. The decomposed phosphate group and *-R1-R2 groups react with a non-aqueous solvent contained in the electrolyte composition to uniformly form organic and inorganic coatings (e.g., phosphate-based coatings). The organic and inorganic coatings can prevent gas generation due to electrolyte decomposition when the battery is exposed to high temperatures and can alleviate the increase in battery resistance and / or capacity decrease, thereby further improving battery performance and high-temperature safety.

[0043] For this reason, in the compound represented by the above chemical formula 1, R1's are each independently a single bond, an alkylene group having 1 to 4 carbon atoms, or [ka] where R2 is independently hydrogen, an acrylate group, or a methacrylate group; R3 is an alkylene group having 1 to 3 carbon atoms; and a is an integer of 1 to 5.

[0044] Specifically, each R1 independently represents a single bond, a methylene group, an ethylene group, a propylene group, or [ka] wherein R3 is an ethylene group and a can be an integer from 1 to 3.

[0045] For example, the compound represented by Chemical Formula 1 may include one or more compounds selected from the following <Structural Formula 1> to <Structural Formula 8>. [Table 2]

[0046] The electrolyte composition according to the present invention contains a first additive containing a compound represented by Chemical Formula 1, and a second additive containing one or more cyclic carbonate compounds, namely vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC).

[0047] By including such an additive, the electrolyte composition can reduce gas generation during charge and discharge of the secondary battery and can effectively prevent metal ions from leaching from the electrode, which increases the cell resistance and reduces the capacity, thereby further improving the performance and high-temperature safety of the battery.

[0048] Such second additives may contain vinylene carbonate (VC), vinylethylene carbonate (VEC) and fluoroethylene carbonate (FEC) either singly or in combination of two or more of them.

[0049] As an example, the second additive may include vinylene carbonate (VC) and / or vinylethylene carbonate (VEC), which are non-fluorine-based second additives, and fluoroethylene carbonate (FEC), which is a fluorine-based second additive.

[0050] The non-fluorine-based second additive, together with the first additive containing the compound represented by Chemical Formula 1, can participate in the formation of an organic coating, thereby inducing uniformity of the coating and thereby improving battery capacity. Furthermore, the fluorine-based second additive acts as a fluorine source during the formation of the organic and / or inorganic coating, thereby improving the adhesive strength between lithium atoms and organic molecules. This improved adhesive strength between lithium atoms and organic molecules can prevent organic molecules from being detached from the surface of the negative electrode during charging and discharging of a negative electrode containing a silicon material as the negative electrode active material, thereby preventing an increase in internal resistance of the battery and decomposition of the electrolyte due to the detached organic molecules. Furthermore, when used in combination with a non-fluorine-based second additive, the fluorine-based second additive can further improve ionic conductivity within the battery, thereby effectively improving the charge-discharge cycle life of the battery at room temperature.

[0051] The second additive may contain a cyclic carbonate compound used in combination at a certain ratio. Specifically, the second additive may contain 50 to 200 parts by weight of the fluorine-based second additive, specifically 50 to 150 parts by weight, 50 to 100 parts by weight, or 100 to 200 parts by weight, per 100 parts by weight of the non-fluorine-based second additive. In this case, the second additive may increase ionic conductivity during charge and discharge of the battery and simultaneously further improve the high-temperature safety of the battery.

[0052] Furthermore, the first additive including the compound represented by Formula 1 may be included in the electrolyte composition in a specific content. Specifically, the compound represented by Formula 1 may be included in an amount of 0.01 to 5 wt % based on the total weight of the electrolyte composition, and more specifically, in an amount of 0.05 to 3 wt %, 0.1 to 2.5 wt %, or 0.5 to 1.5 wt % based on the total weight of the electrolyte composition. The present invention prevents an excessive amount of the first additive outside the above range from increasing the viscosity of the electrolyte composition and reducing its wettability to the electrodes and separator, while also preventing a decrease in the ionic conductivity of the electrolyte composition and a decrease in battery performance, such as a decrease in the initial capacity of the battery. Furthermore, the present invention prevents a small amount of the first additive outside the above range from being used, which would result in the additive's effects being insignificant.

[0053] The content of the second additive may be adjusted to a specific range to achieve a synergistic effect with the first additive. Specifically, the second additive containing the cyclic carbonate compound may be included in an amount of 0.01 to 5 wt % of the total weight of the electrolyte composition, and more specifically, may be included in an amount of 0.01 to 4.5 wt %, 0.4 to 4.1 wt %, 0.1 to 2.5 wt %, 1 to 3 wt %, 1.5 to 4.5 wt %, 1.5 to 2.5 wt %, 3 to 4.5 wt %, 1.6 to 4.1 wt %, 0.5 to 2.0 wt %, or 0.5 to 1.5 wt % of the total weight of the electrolyte composition. By adjusting the content of the second additive within the above range, the present invention can prevent a significant increase in the initial resistance of the battery caused by an excessive amount of the second additive and prevent a small amount of the second additive from insignificantly improving safety at high temperatures.

[0054] Meanwhile, the lithium salt used in the electrolyte composition may be any salt used in non-aqueous electrolytes in the art without any particular limitation. Specifically, the lithium salt may be LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiFSI, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, and (FSO2)2NLi.

[0055] The concentrations of these lithium salts are not particularly limited, but a preferred lower limit of the concentration range is 0.5 mol / L or more, specifically 0.7 mol / L or more, more specifically 0.9 mol / L or more, and a preferred upper limit of the concentration range is 2.5 mol / L or less, specifically 2.0 mol / L or less, more specifically 1.5 mol / L or less. If the lithium salt concentration is below 0.5 mol / L, the ionic conductivity may decrease, which may result in a deterioration in the cycle characteristics and output characteristics of the nonaqueous electrolyte battery. If the lithium salt concentration exceeds 2.5 mol / L, the viscosity of the electrolyte for the nonaqueous electrolyte battery may increase, which may also decrease the ionic conductivity, which may result in a deterioration in the cycle characteristics and output characteristics of the nonaqueous electrolyte battery.

[0056] Furthermore, when a large amount of lithium salt is dissolved in a non-aqueous organic solvent at once, the liquid temperature may rise due to the heat of dissolution of the lithium salt. If the temperature of the non-aqueous organic solvent rises significantly due to the heat of dissolution of the lithium salt, decomposition of the fluorine-containing lithium salt may be accelerated, resulting in the production of hydrogen fluoride (HF). Hydrogen fluoride (HF) is undesirable because it can cause deterioration of battery performance. Therefore, the temperature at which the lithium salt is dissolved in the non-aqueous organic solvent is not particularly limited, but may be adjusted to −20 to 80° C., specifically, 0 to 60° C.

[0057] The non-aqueous organic solvent used in the electrolyte composition may be any organic solvent commonly used in the art for non-aqueous electrolytes, without any particular limitation. Specifically, examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate (EC), propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0058] The nonaqueous solvent used in the present invention may be one type alone or two or more types mixed in any combination and ratio depending on the application. Among these, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate are particularly preferred from the viewpoints of their electrochemical stability against oxidation-reduction and chemical stability against heat and reactions with solutes.

[0059] Meanwhile, the electrolyte composition may further contain additives in addition to the basic components described above. Additives commonly used in the nonaqueous electrolyte solution of the present invention may be added in any proportion, provided the gist of the present invention is not impaired. Specific examples include compounds that have overcharge prevention effects, anode film formation effects, and cathode protection effects, such as cyclohexylbenzene, biphenyl, t-butylbenzene, vinylene carbonate, vinylethylene carbonate, difluoroanisole, fluoroethylene carbonate, propane sultone, succinonitrile, and dimethylvinylene carbonate. Furthermore, similar to the use in nonaqueous electrolyte batteries known as lithium polymer batteries, the electrolyte solution for nonaqueous electrolyte batteries can be solidified using a gelling agent or crosslinked polymer.

[0060] <Lithium secondary battery> Furthermore, in one embodiment, the present invention provides a lithium secondary battery including an electrolyte composition comprising an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, a non-aqueous organic solvent, a lithium salt, a first additive including a compound represented by the following Chemical Formula 1, and a second additive including at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC):

[0061] [ka]

[0062] In the above chemical formula 1, each R1 is independently a single bond, an alkylene group having 1 to 10 carbon atoms, or [ka] where R2 is independently hydrogen, an acrylate group, or a methacrylate group; R3 is an alkylene group having 1 to 4 carbon atoms; and a is an integer of 1 to 10.

[0063] The lithium secondary battery according to the present invention comprises an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the electrolyte composition of the present invention described above. The inclusion of the electrolyte composition not only provides excellent lithium secondary battery performance such as initial resistance and initial capacity, but also has an excellent effect of improving battery performance and safety at high temperatures, particularly when used with a positive electrode active material containing high concentrations of nickel and / or manganese.

[0064] In this case, the positive electrode includes a positive electrode mixture layer prepared by applying a positive electrode active material onto a positive electrode current collector, drying, and pressing the positive electrode mixture layer, and may further include a conductive material, a binder, and other additives as needed.

[0065] Here, the positive electrode active material is a material that can undergo an electrochemical reaction on a positive electrode current collector, and may include at least one of lithium metal oxides represented by Chemical Formula 2 and Chemical Formula 3, which are capable of reversibly intercalating and deintercalating lithium ions.

[0066] [Chemical formula 2] Li x [Ni y Co z Mn w M 1 v ]O2

[0067] [Chemical formula 3] LiM 2 p Mn (2-p) O4

[0068] In the above Chemical Formula 2 and Chemical Formula 3, M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, z, w, and v are 1.0≦x≦1.30, 0.5≦y<1, 0 <z≦0.3、0<w≦0.3、0≦v≦0.1であり、y+z+w+v=1であり、M 2is Ni, Co or Fe, and p is in the range of 0.05≦p≦0.6.

[0069] The lithium metal oxides represented by Chemical Formula 2 and Chemical Formula 3 are materials containing high amounts of nickel (Ni) and manganese (Mn), respectively, and when used as a positive electrode active material, have the advantage of being able to stably supply high-capacity and / or high-voltage electricity.

[0070] In this case, the lithium metal oxide represented by the above chemical formula 2 is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2, etc., and the lithium metal oxide represented by the above chemical formula 3 is LiNi 0.7 Mn 1.3 O4, LiNi 0.5 Mn 1.5 O4, LiNi 0.3 Mn 1.7 O4, etc., which may be used alone or in combination.

[0071] The positive electrode may use a current collector that has high conductivity and does not induce chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used. In the case of aluminum or stainless steel, it may be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the current collector may be preferably 3 to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0072] Similarly to the positive electrode, the negative electrode includes a negative electrode mixture layer prepared by applying a negative electrode active material onto a negative electrode current collector, drying, and pressing the applied material, and may further include a conductive material, a binder, other additives, and the like, as needed.

[0073] The negative electrode active material may include a carbon material, specifically, a material containing carbon as a main component, and may include at least one carbon material selected from the group consisting of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, and ketjen black.

[0074] The negative electrode active material may further include a silicon material in addition to the carbon material. Here, the silicon material refers to a material containing silicon atoms as a main component, and such silicon material may include silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), or silicon dioxide (SiO2) alone or in combination. When silicon monoxide (SiO2) and silicon dioxide (SiO2) are uniformly mixed or combined as the silicon (Si)-containing material and contained in the negative electrode composite layer, they are referred to as silicon oxide (SiO q , where 0.8≦q≦2.5). The silicon material has excellent compatibility with the first additive contained in the electrolyte composition, and therefore when used in combination with a carbon material as the negative electrode active material, it not only provides excellent battery durability, but also has the advantage of improving the cycle characteristics of the battery compared to when the carbon material is used alone.

[0075] The silicon material may be contained in an amount of 1 to 20 wt % of the total weight of the negative electrode active material, specifically 3 to 10 wt %, 8 to 15 wt %, 13 to 18 wt %, or 2 to 8 wt %. By adjusting the content of the silicon material within the above ranges, the present invention can maximize the energy density of the battery.

[0076] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not induce chemical changes in the battery, and examples thereof include copper, stainless steel, nickel, titanium, calcined carbon, etc. In the case of copper or stainless steel, it may be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the negative electrode current collector is preferably 1 to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode to be manufactured.

[0077] The separator interposed between the positive and negative electrodes of each unit cell is an insulating thin film with high ion permeability and mechanical strength. It may be any material commonly used in the industry, including at least one polymer selected from the group consisting of polypropylene, polyethylene, and polyethylene-propylene copolymers, which are chemically resistant and hydrophobic. The separator may be in the form of a porous polymer substrate, such as a sheet or nonwoven fabric containing the polymer. In some cases, the separator may be in the form of a composite separator, in which organic or inorganic particles are coated on the porous polymer substrate with an organic binder. The separator may have an average pore diameter of 0.01 to 10 μm and an average thickness of 5 to 300 μm.

[0078] Furthermore, the secondary battery contains the non-aqueous electrolyte composition according to the present invention as an electrolyte solution.

[0079] The electrolyte composition includes a first additive containing a compound represented by the following Chemical Formula 1 as an additive, and a second additive containing one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC).

[0080] [ka]

[0081] In the above chemical formula 1, each R1 is independently a single bond, an alkylene group having 1 to 10 carbon atoms, or [ka] where R2 is independently hydrogen, an acrylate group, or a methacrylate group; R3 is an alkylene group having 1 to 4 carbon atoms; and a is an integer of 1 to 10.

[0082] The compound represented by Chemical Formula 1 contains a structure in which an acrylate group is bonded to two or more oxygen atoms in a phosphate via a saturated hydrocarbon chain and / or an alkylene glycol unit, and thus can uniformly form an organic and / or inorganic coating on the surface of the positive electrode and / or negative electrode upon activation of the secondary battery. As a result, the electrolyte additive can suppress gas generation due to decomposition of the electrolyte when the battery is exposed to high temperatures, and can improve the phenomenon of increased resistance and / or decreased capacity of the battery, thereby further improving battery performance and high-temperature safety.

[0083] For this reason, in the compound represented by the above chemical formula 1, R1's are each independently a single bond, an alkylene group having 1 to 4 carbon atoms, or [ka] where R2 is independently hydrogen, an acrylate group, or a methacrylate group; R3 is an alkylene group having 1 to 3 carbon atoms; and a is an integer of 1 to 5.

[0084] Specifically, each R1 independently represents a single bond, a methylene group, an ethylene group, a propylene group, or [ka] wherein R3 is an ethylene group and a can be an integer from 1 to 3.

[0085] For example, the compound represented by Chemical Formula 1 may include one or more compounds selected from the following <Structural Formula 1> to <Structural Formula 8>. [Table 3]

[0086] The electrolyte composition according to the present invention contains a first additive containing a compound represented by Chemical Formula 1, and a second additive containing one or more cyclic carbonate compounds, namely vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC).

[0087] By including such an additive, the electrolyte composition can reduce gas generation during charge and discharge of the secondary battery and can effectively prevent metal ions from leaching from the electrode, which increases the cell resistance and reduces the capacity, thereby further improving the performance and high-temperature safety of the battery.

[0088] Such second additives may contain vinylene carbonate (VC), vinylethylene carbonate (VEC) and fluoroethylene carbonate (FEC) either singly or in combination of two or more of them.

[0089] As an example, the second additive may include vinylene carbonate (VC) and / or vinylethylene carbonate (VEC), which are non-fluorine-based second additives, and fluoroethylene carbonate (FEC), which is a fluorine-based second additive.

[0090] The non-fluorine-based second additive, together with the first additive containing the compound represented by Chemical Formula 1, can participate in the formation of the organic coating, thereby inducing uniformity of the coating and thereby improving battery capacity. Furthermore, the fluorine-based second additive acts as a fluorine source during the formation of the organic and / or inorganic coating, thereby improving the adhesive strength between lithium atoms and organic molecules. This improved adhesive strength between lithium atoms and organic molecules can prevent organic molecules from being detached from the surface of the negative electrode during charging and discharging of a negative electrode containing a silicon material as the negative electrode active material, thereby preventing an increase in the battery's internal resistance and electrolyte decomposition due to the detached organic molecules. Furthermore, the fluorine-based second additive can further improve ionic conductivity within the battery, thereby effectively improving the battery's charge and discharge performance.

[0091] The second additive may contain a cyclic carbonate compound used in combination at a certain ratio. Specifically, the second additive may contain 50 to 200 parts by weight of the fluorine-based second additive, specifically 50 to 150 parts by weight, 50 to 100 parts by weight, or 100 to 200 parts by weight, per 100 parts by weight of the non-fluorine-based second additive. In this case, the second additive may increase ionic conductivity during charge and discharge of the battery and simultaneously further improve the high-temperature safety of the battery.

[0092] Furthermore, the first additive including the compound represented by Chemical Formula 1 may be included in the electrolyte composition in a specific content. Specifically, the compound represented by Chemical Formula 1 may be included in an amount of 0.01 to 5 wt % based on the total weight of the electrolyte composition, and more specifically, in an amount of 0.05 to 3 wt %, 0.1 to 2.5 wt %, or 0.5 to 1.5 wt % based on the total weight of the electrolyte composition. The present invention prevents an excessive amount of the first additive outside the above range from increasing the viscosity of the electrolyte composition and reducing its wettability to the electrodes and separator, while also preventing a decrease in the ionic conductivity of the electrolyte composition and a decrease in battery performance, such as a decrease in the initial capacity of the battery. The present invention also prevents a small amount of the first additive outside the above range from being used, which would result in the additive's effects being insignificant.

[0093] The content of the second additive may be adjusted to a specific range to achieve a synergistic effect with the first additive. Specifically, the second additive containing the cyclic carbonate compound may be included in an amount of 0.01 to 5 wt % of the total weight of the electrolyte composition, and more specifically, may be included in an amount of 0.01 to 4.5 wt %, 0.4 to 4.1 wt %, 0.1 to 2.5 wt %, 1 to 3 wt %, 1.5 to 4.5 wt %, 1.5 to 2.5 wt %, 3 to 4.5 wt %, 1.6 to 4.1 wt %, 0.5 to 2.0 wt %, 2.5 to 4.0 wt %, or 0.5 to 1.5 wt % of the total weight of the electrolyte composition. By adjusting the content of the second additive within the above range, the present invention can prevent a significant increase in the initial resistance of the battery caused by an excessive amount of the second additive and prevent a small amount of the second additive from insignificantly improving safety at high temperatures.

[0094] Meanwhile, the lithium salt used in the electrolyte composition may be any salt used in non-aqueous electrolytes in the art without any particular limitation. Specifically, the lithium salt may be LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiFSI, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, and (FSO2)2NLi.

[0095] The concentrations of these lithium salts are not particularly limited, but a preferred concentration range has a lower limit of 0.5 mol / L or more, specifically 0.7 mol / L or more, more specifically 0.9 mol / L or more, and an upper limit of 2.5 mol / L or less, specifically 2.0 mol / L or less, more specifically 1.5 mol / L or less. If the lithium salt concentration is below 0.5 mol / L, the ionic conductivity may decrease, which may result in a deterioration in the cycle characteristics and output characteristics of the nonaqueous electrolyte battery. If the lithium salt concentration exceeds 2.5 mol / L, the viscosity of the electrolyte for the nonaqueous electrolyte battery may increase, which may also decrease the ionic conductivity, which may result in a deterioration in the cycle characteristics and output characteristics of the nonaqueous electrolyte battery.

[0096] Furthermore, when a large amount of lithium salt is dissolved in a non-aqueous organic solvent at once, the liquid temperature may rise due to the heat of dissolution of the lithium salt. If the temperature of the non-aqueous organic solvent rises significantly due to the heat of dissolution of the lithium salt, decomposition of the fluorine-containing lithium salt may be accelerated, resulting in the production of hydrogen fluoride (HF). Hydrogen fluoride (HF) is undesirable because it can cause deterioration of battery performance. Therefore, the temperature at which the lithium salt is dissolved in the non-aqueous organic solvent is not particularly limited, but may be adjusted to −20 to 80° C., specifically, 0 to 60° C.

[0097] The non-aqueous organic solvent used in the electrolyte composition may be any organic solvent commonly used in the art for non-aqueous electrolytes, without any particular limitation. Specifically, examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate (EC), propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0098] The nonaqueous solvent used in the present invention may be one type alone or two or more types mixed in any combination and ratio depending on the application. Among these, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate are particularly preferred from the viewpoints of their electrochemical stability against oxidation-reduction and chemical stability against heat and reactions with solutes.

[0099] Meanwhile, the electrolyte composition may further contain additives in addition to the basic components described above. Additives commonly used in the nonaqueous electrolyte solution of the present invention may be added in any proportion, provided the gist of the present invention is not impaired. Specific examples include compounds that have overcharge prevention effects, anode film formation effects, and cathode protection effects, such as cyclohexylbenzene, biphenyl, t-butylbenzene, vinylene carbonate, vinylethylene carbonate, difluoroanisole, fluoroethylene carbonate, propane sultone, succinonitrile, and dimethylvinylene carbonate. Furthermore, similar to the use in nonaqueous electrolyte batteries known as lithium polymer batteries, the electrolyte solution for nonaqueous electrolyte batteries can be solidified using a gelling agent or crosslinked polymer.

[0100] The present invention will be described in more detail below with reference to examples and experimental examples.

[0101] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0102] (Examples 1 to 12 and Comparative Examples 1 to 4. Preparation of Electrolyte Compositions) LiPF6 was dissolved as a lithium salt at a concentration of 1M in a solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and a first additive containing a compound represented by structural formula 4 and a second additive containing one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC) were dissolved therein in amounts as shown in Table 1 below relative to the total weight of the electrolyte solution to prepare a non-aqueous electrolyte composition.

[0103] [Table 4]

[0104] (Examples 12 to 24 and Comparative Examples 5 to 8. Production of Lithium Secondary Batteries) The positive electrode active material is LiNi with a particle size of 5 μm.0.8 Co 0.1 Mn 0.05 Al 0.05 O4 was prepared and mixed with polyvinylidene fluoride (PVDF) as a carbon-based conductive agent and binder in N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 to form a slurry, which was then cast onto an aluminum sheet, dried in a vacuum oven at 120°C, and rolled to produce a positive electrode.

[0105] Separately, artificial graphite was prepared as a negative electrode active material, and 97 parts by weight of the negative electrode active material and 3 parts by weight of styrene butadiene rubber (SBR) were mixed with water to form a slurry. The slurry was cast on a copper sheet, dried in a vacuum oven at 130°C, and then rolled to produce a negative electrode.

[0106] The positive and negative electrodes obtained above were inserted into a case with an 18 μm polypropylene separator interposed therebetween, and then the electrolyte compositions (5 ml) prepared in Examples 1 to 12 and Comparative Examples 1 to 4 above were poured into the case as shown in Table 2 below to prepare pouch-type 2.1 Ah class small lithium secondary batteries.

[0107] [Table 5]

[0108] (Experimental example) In order to evaluate the performance of the lithium secondary battery according to the present invention, the following experiment was carried out.

[0109] a) Initial capacity and resistance of secondary batteries The initial resistance and capacity of each of the secondary batteries produced in Examples 12 to 24 and Comparative Examples 5 to 8 were observed.

[0110] Specifically, each secondary battery was activated by charging and discharging twice at 0.2C / 0.5C, and then a charge / discharge experiment was conducted once each at a charge / discharge current density of 0.5C / 0.2C, with a charge cut-off voltage of 4.8V (Li / graphite) and a discharge cut-off voltage of 3.0V (Li / graphite), while measuring the charge / discharge capacity and resistance of each secondary battery.

[0111] B) Analysis of the resistance increase rate and gas generation rate of secondary batteries after high-temperature storage The secondary batteries manufactured in Examples 12 to 24 and Comparative Examples 5 to 8 were stored at 60° C. for 8 weeks, and the changes in the resistance and capacity of the batteries were observed.

[0112] Specifically, each secondary battery was activated by charging and discharging twice at 0.2C / 0.5C, and then a charging and discharging experiment was conducted once each at a charging and discharging current density of 0.5C / 0.2C, with a charge cut-off voltage of 4.8V (Li / graphite) and a discharge cut-off voltage of 3.0V (Li / graphite).

[0113] The battery was then fully charged at 0.33C to 4.2V and stored at 60°C for 8 weeks, with the resistance measured every two weeks. After measuring the resistance and capacity of the battery, the battery was charged to a fully charged state and stored. The change in resistance and capacity was calculated from the measured battery resistance and capacity, with the initial resistance of the battery as the reference.

[0114] After completing the resistance measurement, the secondary battery was fixed in a chamber equipped with a pressure jig, and the surface of the fixed secondary battery was pressurized to degas it. The amount of gas released from the chamber was measured to determine the amount of gas generated during high-temperature storage of the secondary battery. The results are shown in Table 3 below.

[0115] [Table 6]

[0116] As shown in Table 3 above, it was confirmed that the secondary battery of the example includes an electrolyte composition containing both a first additive including a compound represented by Chemical Formula 1 and a second additive including a cyclic carbonate compound, thereby realizing high initial performance, excellent electrical performance and safety at high temperatures.

[0117] These results show that the electrolyte composition according to the present invention, which contains a first additive containing a compound represented by Chemical Formula 1 and a second additive containing one or more cyclic carbonate compounds in a specific amount, can not only effectively reduce gas generated during charge and discharge of a lithium secondary battery, but also strengthen the SEI layer on the surface of the electrode, thereby improving storage characteristics and life characteristics at high temperatures.

[0118] Although the present invention has been described above with reference to preferred embodiments, it will be understood that those skilled in the art or those with ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0119] Therefore, the technical scope of the present invention should not be limited to the content described in the Summary of the Invention of the specification, but should be defined by the claims.

Claims

1. The composition comprises a non-aqueous organic solvent, a lithium salt, a first additive containing a compound represented by the following Chemical Formula 1, a non-fluorine-based second additive containing at least one of vinylene carbonate and vinylethylene carbonate, and a fluorine-based second additive containing fluoroethylene carbonate, the total content of the non-fluorine-based second additive and the fluorine-based second additive is 2.5 to 4.5 wt % based on the total weight of the electrolyte composition; 【Chemical 1】 In the above Chemical Formula 1, R １ each independently represents a single bond, an alkylene group having 1 to 10 carbon atoms, or 【Chemistry 2】 and R ２ are each independently hydrogen, an acrylate group, or a methacrylate group; R ３ is an alkylene group having 1 to 4 carbon atoms, an electrolyte composition wherein a is an integer of 1 to 10;

2. R １ each independently represents a single bond, a methylene group, an ethylene group, a propylene group, or 【Chemistry 3】 and R ３ is an ethylene group, 2. The electrolyte composition according to claim 1, wherein a is an integer of 1 to 5.

3. The electrolyte composition according to claim 1, wherein the compound represented by Chemical Formula 1 includes at least one compound selected from the following <Structural Formula 1> to <Structural Formula 8>. 【Table 1】

4. 2. The electrolyte composition according to claim 1, wherein the first additive is contained in an amount of 0.01 to 5% by weight based on the total weight of the electrolyte composition.

5. Lithium salts include LiCl, LiBr, LiI, and LiClO. ４ , LiBF ４ , LiB １０ Cl １０ , LiPF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiSbF ６ , LiAlCl ４ , C.H. ３ SO ３ Li, (CF ３ SO ２ ) ２ NLi and (FSO ２ ) ２ 10. The electrolyte composition of claim 1, comprising one or more selected from the group consisting of NLi.

6. The electrolyte composition according to claim 1, wherein the non-aqueous organic solvent comprises N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, a phosphoric acid triester, trimethoxymethane, a dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, a propylene carbonate derivative, a tetrahydrofuran derivative, an ether, methyl propionate, or ethyl propionate.

7. an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte composition including a non-aqueous organic solvent, a lithium salt, a first additive including a compound represented by the following Chemical Formula 1, a non-fluorine-based second additive including at least one of vinylene carbonate and vinylethylene carbonate, and a fluorine-based second additive including fluoroethylene carbonate, the total content of the non-fluorine-based second additive and the fluorine-based second additive is 2.5 to 4.5 wt % based on the total weight of the electrolyte composition; 【Chemistry 4】 In the above Chemical Formula 1, R １ each independently represents a single bond, an alkylene group having 1 to 10 carbon atoms, or 【Chemistry 5】 and R ２ are each independently hydrogen, an acrylate group, or a methacrylate group; R ３ is an alkylene group having 1 to 4 carbon atoms, a is an integer of 1 to 10.

8. The positive electrode includes a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector and including one or more lithium metal oxides represented by the following Chemical Formula 2 and Chemical Formula 3: [Chemical formula 2] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ２ [Chemical formula 3] LiM ２ ｐ Mn （２－ｐ） O ４ In the above Chemical Formula 2 and Chemical Formula 3, M １ is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, and v are each in the ranges of 1.0≦x≦1.30, 0.5≦y<1, 0<z≦0.3, 0<w≦0.3, and 0≦v≦0.1, and y+z+w+v=1; M ２ is Ni, Co or Fe, 8. The lithium secondary battery according to claim 7, wherein p is in the range of 0.05≦p≦0.

6.

9. Lithium metal oxide is LiNi ０．８ Co ０．１ Mn ０．１ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２ , LiNi ０．９ Co ０．０５ Mn ０．０５ O ２ , LiNi ０．６ Co ０．２ Mn ０．１ Al ０．１ O ２ , LiNi ０．６ Co ０．２ Mn ０．１５ Al ０．０５ O ２ , LiNi ０．７ Co ０．１ Mn ０．１ Al ０．１ O ２ , LiNi ０．７ Mn １．３ O ４ , LiNi ０．５ Mn １．５ O ４ and LiNi ０．３ Mn １．７ O ４ The lithium secondary battery according to claim 8, comprising one or more selected from the group consisting of:

10. the negative electrode includes a negative electrode current collector and a composite layer formed on the negative electrode current collector and containing a negative electrode active material; 8. The lithium secondary battery according to claim 7, wherein the negative electrode active material comprises one or more carbon materials selected from the group consisting of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, and ketjen black.

11. The negative electrode active material is silicon (Si), silicon carbide (SiC), and silicon oxide (SiO ｑ 11. The lithium secondary battery according to claim 10, further comprising one or more silicon materials selected from the group consisting of , where 0.8≦q≦2.

5.

12. The lithium secondary battery according to claim 11, wherein the silicon material is contained in an amount of 1 to 20% by weight based on the total weight of the negative electrode active material.

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