Improved safety of lithium secondary batteries

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 an additive including a compound represented by Chemical Formula 1, which can strengthen an SEI layer on an electrode surface, thereby improving storage characteristics and life characteristics at high temperatures and reducing the amount of gas generation in the battery.

Description

[Technical field]

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

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0186970 dated December 24, 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] However, non-aqueous electrolytes are generally applied in the form of containing lithium salts, and in the case of LiPF6, which is the most widely used lithium salt, it reacts with the electrolyte solvent to accelerate the depletion of the solvent and generate HF. The generated HF not only generates a large amount of gas under high temperature conditions, but also dissolves metal ions from the positive electrode active material, and if the dissolved metal ions are generated in the form of being precipitated on the surface of the negative electrode, it causes an increase in the negative electrode potential and a drop in the OCV of the cell, which reduces not only the performance of the battery but also its lifespan and high-temperature safety.

[0005] Meanwhile, lithium metal oxide is used as the positive electrode active material of a lithium secondary battery, and lithium metal, lithium alloy, crystalline or amorphous carbon, or carbon composite is 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 wound or laminated together with a separator, which is an insulator, to form an electrode group, which is then placed in a can or a similar container and then an electrolyte is injected to manufacture a secondary battery.

[0006] In such lithium secondary batteries, the lithium ions are repeatedly inserted and removed from the lithium metal oxide cathode into the graphite anode during charging and discharging. At this time, lithium is highly reactive and reacts with the carbon electrode to produce Li2CO3, LiO, LiOH, etc., forming a film on the surface of the anode. This film is called a solid electrolyte interface (SEI) film, and the SEI film formed at the beginning of charging prevents the 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. This ion tunnel solvates the lithium ions and prevents the electrolyte organic solvent, which has a large molecular weight and moves with them, from being co-intercalated into the carbon anode, destroying the structure of the carbon anode.

[0007] Therefore, in order to improve the high-temperature cycle characteristics of a lithium secondary battery, it is necessary to form a strong SEI film on the negative electrode of the lithium secondary battery. Once formed during the first charge, the SEI film prevents the lithium ions from reacting with the negative electrode or other substances during repeated charging and discharging due to subsequent use of the battery, and acts as an ion tunnel that allows only lithium ions to pass between the electrolyte and the negative electrode.

[0008] However, in the case of an electrolyte that does not contain an electrolyte additive or contains an electrolyte additive with poor properties, it is difficult to expect improvement in output characteristics due to the formation of a non-uniform SEI film. Furthermore, even if an electrolyte additive is contained, if the amount of the electrolyte additive cannot be adjusted to a required amount, the electrolyte additive may decompose the positive electrode surface during high-temperature reactions or cause an oxidation reaction of the electrolyte, ultimately increasing the irreversible capacity of the secondary battery and deteriorating the output characteristics.

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

[0010] Therefore, the present invention provides an electrolyte composition that can form a film on the surface of an electrode to improve the high-rate charge / discharge characteristics of a lithium secondary battery, and can improve high-temperature storage characteristics, high-temperature performance, and life characteristics, as well as reduce the amount of gas generated, and a lithium secondary battery containing the electrolyte composition. [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, and an additive including a compound represented by the following Chemical Formula 1:

[0012] [ka]

[0013] In the above formula 1, each R1 is independently a single bond, an alkylene group having 1 to 10 carbon atoms, or [ka] wherein each R2 is independently a double bond or a triple bond containing 2 carbon atoms, each R3 is independently a hydrogen atom or an alkyl 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 each R3 is independently hydrogen or a methyl group, and a can be an integer from 1 to 5.

[0015] As an example, the compound represented by Chemical Formula 1 above may include one or more compounds selected from the following <Structural Formula 1> to <Structural Formula 8>. [Table 1]

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

[0017] The lithium salts are LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi and (FSO2)2NLi.

[0018] The non-aqueous organic solvent may also include N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0019] Furthermore, in one embodiment, the present invention provides a lithium secondary battery including an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and an electrolyte composition including a non-aqueous organic solvent, a lithium salt, and an additive including a compound represented by the following Chemical Formula 1:

[0020] [ka]

[0021] In the above formula 1, each R1 is independently a single bond, an alkylene group having 1 to 10 carbon atoms, or [ka] wherein each R2 is independently a double bond or a triple bond containing 2 carbon atoms, each R3 is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and a is an integer of 1 to 10.

[0022] 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.

[0023] [Chemical formula 2] Li x [Ni y Co z Mn w M 1 v ]O2

[0024] [Chemical formula 3] LiM 2 p Mn (2-p) O4

[0025] 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 0.05≦p≦0.6.

[0026] As an example, 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.

[0027] 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 substances selected from the group consisting of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, and ketjen black.

[0028] The negative electrode active material is silicon (Si), silicon carbide (SiC), and silicon oxide (SiO q , where 0.8≦q≦2.5).

[0029] 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. Effect of the Invention

[0030] The electrolyte composition according to the present invention contains an additive containing a compound represented by Chemical Formula 1, and thus has the advantage that the SEI layer on the electrode surface can be strengthened, thereby improving storage characteristics and life characteristics at high temperatures and reducing the amount of gas generation in the battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Since the present invention can be modified in various ways and can have various embodiments, specific embodiments are described in detail in the detailed description.

[0032] However, this is not intended to limit the invention to the particular embodiment, but should be understood to include all modifications, equivalents, or alternatives falling within the spirit and scope of the present invention.

[0033] 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, but should be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0034] In addition, 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 in between. 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 in between. In addition, in the present application, being "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.

[0035] In addition, in the present invention, "containing as a main component" may mean containing 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more of a defined component based on the total weight. For example, "containing graphite as a main component as a negative electrode active material" may mean containing 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more of graphite based on the total weight of the negative electrode active material, and in some cases, it may mean that the entire negative electrode active material is made of graphite and contains 100% by weight of graphite.

[0036] The present invention will now be described in more detail.

[0037] <Electrolyte composition> In one embodiment, the present invention provides an electrolyte composition comprising a non-aqueous organic solvent, a lithium salt, and an additive comprising a compound represented by the following Chemical Formula 1:

[0038] [ka]

[0039] In the above formula 1, each R1 is independently a single bond, an alkylene group having 1 to 10 carbon atoms, or [ka] wherein each R2 is independently a double bond or a triple bond containing 2 carbon atoms, each R3 is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and a is an integer of 1 to 10.

[0040] The electrolyte composition according to the present invention is a non-aqueous electrolyte composition containing a lithium salt, and further contains an additive containing a compound represented by Chemical Formula 1.

[0041] Here, the compound represented by the above formula 1 has a structure in which an unsaturated hydrocarbon group such as a vinyl group or a propargyl group is introduced to the end of a phosphate, and contains a carbonate group containing an oxygen atom of the phosphate as a linker between the phosphate group and the unsaturated hydrocarbon group, so that an organic and / or inorganic film can be uniformly formed on the surface of the positive electrode and / or the negative electrode when the secondary battery is activated. As a result, the electrolyte additive can suppress the decomposition of the electrolyte and the generation of gas when the battery is exposed to high temperatures, and can improve the phenomenon of an increase in resistance and / or a decrease in capacity of the battery, thereby further improving the performance and high temperature safety of the battery.

[0042] For this reason, in the compound represented by the above chemical formula 1, R1 is independently a single bond, a methylene group, an ethylene group, a propylene group or [ka] wherein each R3 is independently hydrogen or a methyl group, and a is an integer of 1 to 5.

[0043] As an example, the compound represented by Chemical Formula 1 above may include one or more compounds selected from the following <Structural Formula 1> to <Structural Formula 8>. [Table 2]

[0044] The electrolyte composition according to the present invention contains one or more compounds of the above structural formulas 1 to 8 as an additive, and thus can reduce gas generated during charging and discharging of a secondary battery, and can effectively prevent metal ions from eluting from an electrode, increasing cell resistance, and decreasing capacity, thereby further improving the performance and high temperature safety of the battery.

[0045] In addition, the 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, may be included in an amount of 0.05 to 5 wt %, 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 the use of an excessive amount of the additive out of the above range, which increases the viscosity of the electrolyte composition and reduces the wettability of the electrodes and the separator, while preventing the resistance of the battery from increasing, the charge / discharge capacity from being limited, and the recovery capacity from decreasing after storage. In addition, the present invention prevents the use of a small amount of the additive out of the above range, which prevents the effect of the additive from being insignificant.

[0046] 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.

[0047] The concentration of these lithium salts is not particularly limited, but the lower limit of the preferred 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 the upper limit of the preferred 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 concentration of the lithium salt is below 0.5 mol / L, the ionic conductivity is reduced, which may cause the cycle characteristics and output characteristics of the nonaqueous electrolyte battery to decrease. If the concentration of the lithium salt is above 2.5 mol / L, the viscosity of the electrolyte for the nonaqueous electrolyte battery increases, which may also cause the ionic conductivity to decrease, which may cause the cycle characteristics and output characteristics of the nonaqueous electrolyte battery to decrease.

[0048] In addition, 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, in the case of a lithium salt containing fluorine, decomposition may be promoted and hydrogen fluoride (HF) may be generated. Hydrogen fluoride (HF) is undesirable because it causes deterioration of battery performance. Therefore, the temperature when dissolving the lithium salt in the non-aqueous organic solvent is not particularly limited, but may be adjusted to -20 to 80°C, specifically 0 to 60°C.

[0049] In addition, the non-aqueous organic solvent used in the electrolyte composition may be applied without any particular limitation as long as it is used in the art for non-aqueous electrolytes.Specifically, the non-aqueous organic solvent may be, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate (EC), propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran (franc), 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate.

[0050] The non-aqueous solvent used in the present invention may be one type alone, or two or more types may be mixed in any combination and ratio according to the purpose. Among these, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate are particularly preferred from the viewpoints of electrochemical stability against oxidation and reduction and chemical stability against heat and reaction with solutes.

[0051] Meanwhile, the electrolyte composition may further contain additives in addition to the basic components described above. As long as the gist of the present invention is not impaired, additives generally used in the non-aqueous electrolyte of the present invention may be added at any ratio. Specifically, compounds having an overcharge prevention effect, an anode film formation effect, and a cathode protection effect, such as cyclohexylbenzene, biphenyl, t-butylbenzene, vinylene carbonate, vinylethylene carbonate, difluoroanisole, fluoroethylene carbonate, propane sultone, succinonitrile, and dimethylvinylene carbonate, may be mentioned. In addition, it is also possible to use the electrolyte for non-aqueous electrolyte batteries by solidifying it with a gelling agent or a crosslinked polymer, as in the case of using it in a non-aqueous electrolyte battery called a lithium polymer battery.

[0052] <Lithium secondary battery> Further, in one embodiment, the present invention provides a lithium secondary battery comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; and an electrolyte composition including a non-aqueous organic solvent, a lithium salt, and an additive including a compound represented by the following Chemical Formula 1:

[0053] [ka]

[0054] In the above formula 1, each R1 is independently a single bond, an alkylene group having 1 to 10 carbon atoms, or [ka] wherein each R2 is independently a double bond or a triple bond containing 2 carbon atoms, each R3 is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and a is an integer of 1 to 10.

[0055] 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 according to the present invention described above. By including the electrolyte composition, the amount of gas generated during charging and discharging of the battery is reduced, and the lithium secondary battery has excellent performance such as initial resistance and initial capacity. In particular, when used with a positive electrode active material containing a high concentration of nickel and / or manganese, the battery has excellent effects of improving battery performance and safety at high temperatures.

[0056] In this case, the positive electrode includes a positive electrode mixture layer prepared by applying a positive electrode slurry containing a positive electrode active material onto a positive electrode current collector, drying and pressing the positive electrode mixture layer, and the positive electrode mixture layer may selectively further include a conductive material, a binder, other additives, and the like, as necessary.

[0057] 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 the following Chemical Formula 2 and Chemical Formula 3 that are capable of reversibly intercalating and deintercalating lithium ions.

[0058] [Chemical formula 2] Li x [Ni y Co z Mn w M 1 v ]O2

[0059] [Chemical formula 3] LiM 2 p Mn (2-p) O4

[0060] 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 0.05≦p≦0.6.

[0061] 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 capable of stably supplying high capacity and / or high voltage electricity.

[0062] 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 formula 3 is LiNi 0.7 Mn 1.3 O4, LiNi 0.5 Mn 1.5 O4 and LiNi 0.3 Mn 1.7 O4, etc., which may be used alone or in combination.

[0063] In addition, the positive electrode may use a positive electrode current collector that has high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used, and in the case of aluminum or stainless steel, it may be surface-treated with carbon, nickel, titanium, silver, etc. In addition, the average thickness of the current collector may be preferably 3 to 500 μm, taking into consideration the conductivity and total thickness of the positive electrode to be manufactured.

[0064] Similarly to the positive electrode, the negative electrode includes a negative electrode mixture layer produced by applying a negative electrode slurry containing a negative electrode active material onto a negative electrode current collector, followed by drying and pressing. If necessary, the negative electrode mixture layer may selectively further include a conductive material, a binder, other additives, and the like.

[0065] The negative electrode active material may include a carbon material. Specifically, the carbon material means a material mainly composed of carbon atoms, and the carbon material may include at least one selected from the group consisting of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, and ketjen black.

[0066] The negative electrode active material may further include a silicon material in addition to the carbon material. Here, the silicon material means a material mainly composed of silicon atoms, 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 (SiO) and silicon dioxide (SiO2) as the silicon (Si)-containing material are uniformly mixed or composited and contained in the negative electrode composite layer, they are called silicon oxide (SiO q , where 0.8≦q≦2.5).

[0067] The silicon material may be included in an amount of 1 to 20 wt % based on 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 %. The present invention can maximize the energy density of the battery by adjusting the content of the silicon material within the above content range.

[0068] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and may be, for example, copper, stainless steel, nickel, titanium, calcined carbon, etc., and 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 may be suitably 1 to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode to be manufactured.

[0069] Meanwhile, the separator interposed between the positive and negative electrodes of each unit cell is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is one commonly used in the art, specifically, one containing 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 have the form of a porous polymer substrate, such as a sheet or nonwoven fabric containing the above-mentioned polymer, and may have 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.

[0070] Furthermore, the secondary battery contains the above-described non-aqueous electrolyte composition according to the present invention as an electrolyte solution.

[0071] The electrolyte composition includes an additive containing a compound represented by the following Chemical Formula 1:

[0072] [ka]

[0073] In the above formula 1, each R1 is independently a single bond, an alkylene group having 1 to 10 carbon atoms, or [ka] wherein each R2 is independently a double bond or a triple bond containing 2 carbon atoms, each R3 is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and a is an integer of 1 to 10.

[0074] The compound represented by the above formula 1 has a structure in which an unsaturated hydrocarbon group such as a vinyl group or a propargyl group is introduced to the end of a phosphate, and contains a carbonate group containing an oxygen atom of the phosphate as a linker between the phosphate group and the unsaturated hydrocarbon group, so that an organic and / or inorganic coating can be uniformly formed on the surface of the positive electrode and / or the negative electrode when the secondary battery is activated. As a result, the electrolyte additive can suppress the decomposition of the electrolyte and the generation of gas when the battery is exposed to high temperatures, and can improve the phenomenon of an increase in resistance and / or a decrease in capacity of the battery, thereby further improving the performance and high temperature safety of the battery.

[0075] For this reason, in the compound represented by the above chemical formula 1, R1 is independently a single bond, a methylene group, an ethylene group, a propylene group or [ka] wherein each R3 is independently hydrogen or a methyl group, and a is an integer of 1 to 5.

[0076] As an example, the compound represented by Chemical Formula 1 above may include one or more compounds selected from the following <Structural Formula 1> to <Structural Formula 8>. [Table 3]

[0077] By including such an additive, the electrolyte composition can reduce gas generated during charging and discharging of the secondary battery and can effectively prevent metal ions from eluting from the electrode, resulting in an increase in cell resistance and a decrease in capacity, thereby further improving the performance and high-temperature safety of the battery.

[0078] In addition, the additive including the compound represented by Chemical Formula 1 may be included in the electrolyte composition at a specific content. Specifically, the compound represented by Chemical Formula 1 may be included in the electrolyte composition at 0.01 to 5 wt % based on the total weight of the electrolyte composition, and more specifically, may be included at 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 can prevent the electrolyte composition from increasing in viscosity and decreasing in wettability to electrodes and separators due to the use of an excessive amount of the additive outside the above range, while preventing the electrolyte composition from decreasing in ion conductivity and decreasing battery performance, such as a decrease in initial capacity of the battery. In addition, the present invention can prevent the additive from being included in a small amount outside the above range, resulting in insignificant effects of the additive.

[0079] 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.

[0080] The concentration of these lithium salts is not particularly limited, but the lower limit of the preferred 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 the upper limit of the preferred 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 concentration of the lithium salt is below 0.5 mol / L, the ionic conductivity is reduced, which may cause the cycle characteristics and output characteristics of the nonaqueous electrolyte battery to decrease. If the concentration of the lithium salt is above 2.5 mol / L, the viscosity of the electrolyte for the nonaqueous electrolyte battery increases, which may also cause the ionic conductivity to decrease, which may cause the cycle characteristics and output characteristics of the nonaqueous electrolyte battery to decrease.

[0081] In addition, 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, in the case of a lithium salt containing fluorine, decomposition may be promoted and hydrogen fluoride (HF) may be generated. Hydrogen fluoride (HF) is undesirable because it causes deterioration of battery performance. Therefore, the temperature when dissolving the lithium salt in the non-aqueous organic solvent is not particularly limited, but may be adjusted to -20 to 80°C, specifically 0 to 60°C.

[0082] In addition, the non-aqueous organic solvent used in the electrolyte composition may be applied without any particular limitation as long as it is used in the art for non-aqueous electrolytes.Specifically, the non-aqueous organic solvent may be, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate (EC), propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran (franc), 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate.

[0083] The non-aqueous solvent used in the present invention may be one type alone, or two or more types may be mixed in any combination and ratio according to the purpose. Among these, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate are particularly preferred from the viewpoints of electrochemical stability against oxidation and reduction and chemical stability against heat and reaction with solutes.

[0084] Meanwhile, the electrolyte composition may further contain additives in addition to the basic components described above. As long as the gist of the present invention is not impaired, additives generally used in the non-aqueous electrolyte of the present invention may be added at any ratio. Specifically, compounds having an overcharge prevention effect, an anode film formation effect, and a cathode protection effect, such as cyclohexylbenzene, biphenyl, t-butylbenzene, vinylene carbonate, vinylethylene carbonate, difluoroanisole, fluoroethylene carbonate, propane sultone, succinonitrile, and dimethylvinylene carbonate, may be mentioned. In addition, it is also possible to use the electrolyte for non-aqueous electrolyte batteries by solidifying it with a gelling agent or a crosslinked polymer, as in the case of using it in a non-aqueous electrolyte battery called a lithium polymer battery.

[0085] The present invention will now be described in more detail with reference to examples and experimental examples.

[0086] However, the following examples and experimental examples are merely illustrative of the present invention, and the contents of the present invention are not limited to the following examples and experimental examples.

[0087] (Examples 1 to 5 and Comparative Examples 1 to 3. Production of Electrolyte Compositions) A non-aqueous electrolyte composition was prepared by dissolving LiPF6 as a lithium salt at a concentration of 1M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7, and dissolving additives in amounts as shown in Table 1 below relative to the total weight of the electrolyte.

[0088] [Table 4]

[0089] (Examples 6 to 10 and Comparative Examples 4 to 6. 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 0.05O4 was prepared and mixed with polyvinylidene fluoride (PVF) as a carbon-based conductive agent and binder in a weight ratio of 94:3:3 in N-methylpyrrolidone (NMP) 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.

[0090] 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, which was then cast onto a copper sheet, dried in a vacuum oven at 130°C, and rolled to produce a negative electrode.

[0091] The positive and negative electrodes obtained above were inserted into a case with a separator made of 18 μm polypropylene between them, and then the electrolyte compositions (5 ml) prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were poured in as shown in Table 2 below to prepare pouch-type 2.1 Ah class small lithium secondary batteries.

[0092] [Table 5]

[0093] (Experimental Example) In order to evaluate the performance of the lithium secondary battery according to the present invention, the following experiment was carried out.

[0094] a) Analysis of changes in resistance and capacity of secondary batteries after high-temperature storage The secondary batteries manufactured in the examples and comparative examples were stored at 60° C. for 12 weeks, and the changes in resistance and capacity of the batteries were observed.

[0095] Specifically, each secondary battery was activated by charging / discharging twice at 0.2C / 0.5C, and then a charge / discharge experiment was performed once each with a charge / discharge current density of 0.5C / 0.2C, a charge cut-off voltage of 4.8V (Li / graphite), and a discharge cut-off voltage of 3.0V (Li / graphite).

[0096] The battery was then fully charged at 0.33C and 4.2V, and stored at a high temperature of 60°C while measuring the battery resistance and capacity every two weeks. After measuring the battery resistance and capacity, the battery was charged to a fully charged state and stored. The change in the battery resistance and capacity was calculated based on the initial battery resistance and capacity, and the results are shown in Table 3 below.

[0097] B) Analysis of gas generation from secondary batteries stored at high temperatures The secondary batteries manufactured in the examples and comparative examples were stored at 60° C. for 12 weeks, and the amount of gas generated from the batteries was analyzed every two weeks. Specifically, the charge / discharge of each secondary battery during activation was performed twice at 0.2C / 0.5C, and then a charge / discharge experiment was performed once each at a charge / discharge current density of 0.5C / 0.2C, a charge cut-off voltage of 4.8V (Li / graphite), and a discharge cut-off voltage of 3.0V (Li / graphite).

[0098] Then, the secondary battery was fully charged at 0.33C and 4.2V, and stored for 12 weeks at a high temperature of 60°C. After 12 weeks, the secondary battery was degassed by applying pressure to the surface, and the amount of gas degassed was measured. The results are shown in Table 3 below.

[0099] [Table 6]

[0100] As shown in Table 3 above, it was confirmed that the secondary battery of the embodiment includes an electrolyte composition containing an additive including a compound represented by Chemical Formula 1, thereby realizing high electrical performance of the battery even under high temperature conditions and reducing the amount of gas generated.

[0101] Specifically, it was found that the secondary batteries of the Examples had significantly less gas even when exposed to high temperature conditions, had less increase in battery resistance, and had a high capacity retention rate compared to the secondary batteries of the Comparative Examples.

[0102] From these results, it can be seen that the secondary battery according to the present invention uses a positive electrode active material containing a high concentration of nickel and / or manganese, together with an additive of a specific component in a non-aqueous electrolyte, so that a film is uniformly formed on the electrode surface during activation of the battery, thereby preventing the generation of a large amount of gas under high temperature conditions, and effectively preventing metal ions from eluting from the electrode, which would increase the cell resistance and reduce the capacity, thereby effectively improving the performance and high temperature safety of the battery.

[0103] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art or those having ordinary knowledge in the art that the present invention can be modified and changed in various ways without departing from the spirit and technical scope of the present invention as described in the claims below.

[0104] Therefore, the technical scope of the present invention should not be limited to the contents described in the Summary of the Invention of the specification, but should be defined by the claims.

Claims

1. The present invention includes a non-aqueous organic solvent, a lithium salt, and an additive including a compound represented by the following chemical formula 1: 【Chemistry 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 a double or triple bond containing two carbon atoms, R ３ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, a is an integer from 1 to 10; The compound represented by the formula 1 is contained in an amount of 0.01 to 10 wt % based on the total weight of the electrolyte composition. Electrolyte composition.

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

3. The electrolyte composition described in claim 1, wherein the compound represented by chemical formula 1 includes one or more compounds selected from the following <Structural Formula 1> to <Structural Formula 8>. 【Table 1】 4. The electrolyte composition according to claim 1, wherein the compound represented by chemical formula 1 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 C 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 2. The electrolyte composition of claim 1, comprising one or more selected from the group consisting of NLi.

6. The electrolyte composition of claim 1, wherein the non-aqueous organic solvent comprises N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate and 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 comprising a non-aqueous organic solvent, a lithium salt, and an additive comprising a compound represented by the following chemical formula 1: Including, 【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 a double or triple bond containing two carbon atoms, R ３ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, a is an integer from 1 to 10; The compound represented by the formula 1 is contained in an amount of 0.01 to 10 wt % based on the total weight of the electrolyte composition. Lithium secondary battery.

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 1.0≦x≦1.30, 0.5≦y<1, 0<z≦0.3, 0<w≦0.3, 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 A ０．１ O ２ , LiNi ０．６ Co ０．２ Mn ０．１５ A ０．０５ O ２ , LiNi ０．７ Co ０．１ Mn ０．１ A 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 mixture 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 The lithium secondary battery according to claim 10, further comprising one or more silicon materials selected from the group consisting of q and q=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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