Nonaqueous electrolyte composition and lithium secondary battery containing same

Abstract

The present invention relates to an electrolyte composition and a lithium secondary battery including the same. The electrolyte composition includes one or more electrolyte additives selected from the group consisting of a compound represented by Chemical Formula 1 and a compound represented by Chemical Formula 2. This not only effectively reduces gas generated during charging and discharging of a lithium secondary battery, but also strengthens the SEI layer on the electrode surface, thereby improving storage characteristics and life characteristics at high temperatures.

Description

[Technical field]

[0001] The present invention relates to a non-aqueous electrolyte composition and a lithium secondary battery containing the same.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0026714 dated March 2, 2022, 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, power storage devices, etc. 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] Among such non-aqueous electrolyte batteries, lithium ion batteries are used by injecting an electrolyte into a battery cell including a positive electrode containing a positive electrode active material capable of intercalating and deintercalating lithium, and a negative electrode containing a negative electrode active material capable of intercalating and deintercalating lithium. In particular, the electrolyte uses an organic solvent in which a lithium salt is dissolved, and is important for determining the stability and performance of a lithium secondary battery.

[0005] For example, LiPF, which is the most commonly used lithium salt in electrolytes, 6The HF reacts with the electrolyte solvent to accelerate the depletion of the solvent and generate HF. The HF generated in this way not only generates a large amount of gas under high temperature conditions, but also can dissolve metal ions from the positive electrode active material. The metal ions thus dissolved are generated in the form of precipitates on the surface of the negative electrode, which causes an increase in the negative electrode potential and a drop in the OCV of the cell, resulting in problems such as a decrease in the battery performance, lifespan, and high-temperature safety. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Korean Patent Publication No. 10-2021-0106817 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the object of the present invention is to form a film on the surface of the electrode to prevent direct contact between the positive electrode and the electrolyte, and to prevent the positive electrode from contacting with HF, PF, etc. 5 The present invention aims to provide a technology that can prevent the oxidative decomposition of the electrolyte and suppress the generation of gas while preventing direct contact with the electrolyte, etc., and improves the capacity retention rate by improving the phenomenon of metal ion deposition from the positive electrode, while suppressing metal elution at high temperatures to prevent a decrease in the life and safety of the battery. [Means for solving the problem]

[0008] In order to solve the above problems, in one embodiment, the present invention provides an electrolyte composition for a lithium secondary battery, comprising a non-aqueous organic solvent, a lithium salt, and an electrolyte additive comprising at least one compound represented by the following Formula 1 or Formula 2:

[0009] [ka]

[0010] [ka]

[0011] In the above Chemical Formula 1 and Chemical Formula 2, R 1 is hydrogen or an alkyl group having 1 to 4 carbon atoms, and L 1 and L 2 are each a direct bond or an alkylene group having 1 to 4 carbon atoms.

[0012] Specifically, the above R 1 is hydrogen, a methyl group, an ethyl group, or a propyl group, and L 1 and L 2 may each be a direct bond, a methylene group, an ethylene group, or a propylene group.

[0013] More specifically, the compound represented by Chemical Formula 1 above may include compounds represented by the following <Structural Formula 1> to <Structural Formula 6>. [Table 1]

[0014] In addition, the compound represented by Chemical Formula 2 above may include a compound represented by the following <Structural Formula 7> or <Structural Formula 8>. [Table 2]

[0015] In addition, when the electrolyte additive contains a compound represented by Chemical Formula 1 and a compound represented by Chemical Formula 2, the compound represented by Chemical Formula 1 and the compound represented by Chemical Formula 2 may be contained in a weight ratio of 1:0.05 to 20.

[0016] The electrolyte additive may be contained in an amount of 0.01 to 30% by weight based on the total weight of the electrolyte composition.

[0017] In addition, the electrolyte composition may further include one or more auxiliary additives selected from the group consisting of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), propane sultone (PS), 1,3-propane sultone (PRS), ethylene sulfate (ESa), succinonitrile (SN), adiponitrile (AN), hexanetricarbonitrile (HTCN), gamma-butyrolactone (GBL), biphenyl (BP), cyclohexylbenzene (CHB), and tert-amylbenzene (TAB).

[0018] The lithium salts are 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 NLi may include one or more selected from the group consisting of

[0019] 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, 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.

[0020] Further, 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, the positive electrode including at least one positive electrode active material selected from the group consisting of lithium metal oxides represented by the following Chemical Formula 3 or 4, and the above-described electrolyte solution composition according to the present invention.

[0021] [Chemical formula 3] Li x [Ni y Co z Mn w M 1 v ]O 2

[0022] [Chemical formula 4] LiM 2 p Mn (2-p) O 4

[0023] In the above Chemical Formula 3 and Chemical Formula 4, 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≦y<1, 0≦z≦1, 0≦w≦1, 0≦v≦0.1, respectively, y+z+w+v=1, and M 2 is Ni, Co or Fe, and p is in the range of 0.05≦p≦0.6.

[0024] Here, the positive electrode active material 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 and LiNi 0.5 Mn 1.5 O 4 The composition may include one or more selected from the group consisting of:

[0025] The negative electrode active material may contain 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.

[0026] The negative electrode active material may also include silicon (Si), silicon carbide (SiC), and silicon oxide (SiO q(wherein 0.8≦q≦2.5) 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

[0027] The electrolyte composition according to the present invention includes one or more electrolyte additives selected from the compounds represented by Chemical Formula 1 and Chemical Formula 2, and thus has the advantages of not only effectively reducing gas generated during charging and discharging of a lithium secondary battery, but also strengthening the SEI layer on the electrode surface, thereby improving storage characteristics and life characteristics at high temperatures. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] 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.

[0029] However, this is not intended to limit the invention to the particular embodiments, but should be understood to include all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0030] 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.

[0031] 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.

[0032] In the present invention, "including as a main component" may mean that the defined component is included in an amount of 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 based on the total weight of the negative electrode active material. For example, "including graphite as a main component as a negative electrode active material" may mean that graphite is included in an amount of 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 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 that graphite is included in an amount of 100% by weight.

[0033] The present invention will now be described in more detail.

[0034] <Electrolyte composition for secondary batteries> In one embodiment, the present invention provides an electrolyte composition for a lithium secondary battery, comprising a non-aqueous organic solvent, a lithium salt, and an electrolyte additive comprising one or more compounds represented by the following Chemical Formula 1 or 2:

[0035] [ka]

[0036] [ka]

[0037] In the above Chemical Formula 1 and Chemical Formula 2, R 1is hydrogen or an alkyl group having 1 to 4 carbon atoms, and L 1 and L 2 are each a direct bond or an alkylene group having 1 to 4 carbon atoms.

[0038] Here, the above R 1 is hydrogen, a methyl group, an ethyl group, or a propyl group, and L 1 and L 2 may each be a direct bond, a methylene group, an ethylene group, or a propylene group.

[0039] The electrolyte composition for a lithium secondary battery according to the present invention contains, as an electrolyte additive, a nitrile-based compound represented by Chemical Formula 1 or Chemical Formula 2, which has a structure in which a nitrile group is introduced into a 6-atom cyclic hydrocarbon group containing three nitrogen atoms (N) symmetrically. This not only prevents metal from being eluted from an electrode active material, particularly a positive electrode active material, when exposed to high temperatures, but also allows an organic and / or inorganic film to be stably and uniformly formed on the surface of the positive electrode and / or negative electrode during activation, thereby preventing the electrolyte from being decomposed and generating gas when the battery is exposed to high temperatures.

[0040] Specifically, the nitrile-based compound represented by Formula 1 or Formula 2 has a strong complexing effect on transition metals due to the nitrogen atom contained in the cyclic hydrocarbon group of six atoms, and therefore when applied as an additive to an electrolyte composition, it directly participates in the solvation shell of lithium ions even at low potentials during initial charge and discharge, i.e., activation, of the battery, and can uniformly form a negative charge and / or inorganic film due to a reduction reaction on the negative electrode surface, and simultaneously form an inorganic film due to an oxidation reaction on the positive electrode surface. The film thus formed can suppress the electrolyte from being decomposed to generate gas when the lithium secondary battery is exposed to high temperatures, and therefore can further improve safety issues due to fire and / or explosion of the secondary battery.

[0041] In addition, the nitrile group of the nitrile compound is introduced to the carbon atom of the 6-atom hydrocarbon group containing 3 nitrogen atoms, so that it is less exposed to the influence of the nitrogen atom and easily interacts with metals. Therefore, it can be chelated with the metal of the positive electrode active material to stabilize the positive electrode active material, and can exhibit the effect of capturing the metal eluted from the positive electrode active material, thereby further improving the high temperature performance and safety of the lithium secondary battery.

[0042] For this purpose, the electrolyte composition of the present invention may contain one or more of the compounds represented by Chemical Formula 1 or Chemical Formula 2 as an electrolyte additive.

[0043] Here, the compound represented by Chemical Formula 1 above may include compounds represented by the following <Structural Formula 1> to <Structural Formula 6>. [Table 3]

[0044] The compounds represented by the above <Structural Formula 1> to <Structural Formula 6> contain a 6-atom saturated hydrocarbon group including three nitrogen atoms and a nitrile group, and are therefore excellent at capturing eluted metals. In particular, the compounds represented by <Structural Formula 1> or <Structural Formula 4>, in which a hydrogen atom is bonded to a nitrogen atom, have the advantage that the unshared electron pair of the nitrogen atom can be easily exposed, and thus a film can be formed more uniformly on the surface of the electrode, particularly the positive electrode, upon activation.

[0045] In addition, the compound represented by Chemical Formula 2 above may include a compound represented by the following <Structural Formula 7> or <Structural Formula 8>. [Table 4]

[0046] The compound represented by the above <Structural Formula 7> or <Structural Formula 8> contains a nitrogen atom inside a 6-atom aromatic hydrocarbon group, and the unshared electron pair of the nitrogen atom is easily exposed. Therefore, it can form a more uniform coating on the electrode, particularly the positive electrode surface, during activation, and can further suppress decomposition of the electrolyte composition, thereby preventing gas generation during charging and discharging of the secondary battery.

[0047] In addition, the electrolyte additive may be a combination of the compound represented by Chemical Formula 1 and the compound represented by Chemical Formula 2, and in this case, each compound may be used in combination at a certain ratio. Specifically, the electrolyte additive may contain the compound represented by Chemical Formula 1 and the compound represented by Chemical Formula 2 in a weight ratio of 1:0.05-20, more specifically, in a weight ratio of 1:0.1-0.4, 1:0.2-0.4, 1:0.05-0.2, 1:0.9-1.2, 1:1.5-3, 1:2-5, 1:5-10, 1:10-20, 1:2-20, or 1:1.1-1.5. The present invention can further improve the high temperature stability of the electrolyte composition by adjusting the mixing ratio of the compound represented by Chemical Formula 1 and the compound represented by Chemical Formula 2 to the above range.

[0048] In addition, the electrolyte additive may be included in the electrolyte composition at a specific content. Specifically, the electrolyte additive may be included in the electrolyte composition at 0.01 to 30 wt % based on the weight of the entire electrolyte composition, and more specifically, the electrolyte additive may be included at 0.01 to 20 wt %, 0.01 to 10 wt %, 0.01 to 5 wt %, 5 to 10 wt %, 10 to 30 wt %, 15 to 25 wt %, or 10 to 20 wt % based on the weight of the entire electrolyte composition. The present invention can prevent the wettability of the electrodes and the separator from decreasing due to an increase in the viscosity of the electrolyte composition by using an excessive amount of the electrolyte additive outside the above range, and can also prevent the ion conductivity of the electrolyte composition from decreasing, thereby preventing the battery performance from decreasing. In addition, the present invention can prevent the effect of the electrolyte additive from being only slightly realized by using a small amount of the electrolyte additive outside the above range.

[0049] Furthermore, the electrolyte composition according to the present invention may further include an electrolyte additive containing at least one of the compounds represented by Chemical Formula 1 or Chemical Formula 2, and at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoro ethylene carbonate (FEC), propane sultone (PS), 1,3-propane sultone (PRS), ethylene sulfate (ESa), succinonitrile (SN), adiponitrile (AN), hexane tricarbonitrile (HTCN), gamma-butyrolactone (GBL), biphenyl (BP), cyclohexyl benzene (CHB), and tert-amyl benzene (TAM). Contains auxiliary additives including one or more trifluoroacetate (TAB).

[0050] As one example, the auxiliary additives may include one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), and propane sultone (PS).

[0051] By including such an auxiliary additive, the electrolyte composition can reduce gas generation during charging and discharging of a secondary battery, and can effectively prevent metal ions from leaching out of the electrodes, increasing cell resistance, and decreasing capacity, thereby further improving the performance and high-temperature safety of the battery.

[0052] Two or more of such auxiliary additives may be used in combination. In this case, the auxiliary additives may include vinylene carbonate (VC) and fluoroethylene carbonate (FEC), vinylene carbonate (VC) and vinylethylene carbonate (VEC), or vinylene carbonate (VC), vinylethylene carbonate (VEC), and fluoroethylene carbonate (FEC).

[0053] In this case, the auxiliary additive may contain the auxiliary additive used in combination at a certain ratio. Specifically, the auxiliary additive may contain the remaining compound in 50 to 200 parts by weight, 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 vinylene carbonate (VC). In this case, the auxiliary additive may further improve safety at high temperatures.

[0054] In addition, the above-mentioned auxiliary additives may be adjusted to a specific content in order to exhibit a synergistic effect with the electrolyte additive. Specifically, the auxiliary additives may be included in an amount of 0.01 to 10 wt % based on the total weight of the electrolyte composition, and more specifically, may be included in an amount of 1 to 10 wt %, 3 to 8 wt %, 0.1 to 3.0 wt %, 1 to 4 wt %, 5 to 10 wt %, 4 to 6 wt %, or 4.5 to 6.5 wt % based on the total weight of the electrolyte composition. By adjusting the content of the auxiliary additives to the above range, the present invention can prevent the initial resistance of the battery from increasing significantly due to an excessive amount of the auxiliary additives, and can prevent the effect of improving safety at high temperatures from being only slightly realized due to a trace amount of the auxiliary additives.

[0055] Meanwhile, the lithium salt used in the electrolyte composition may be any lithium salt used in non-aqueous electrolytes in the art without any particular limitation. Specifically, the lithium salt may be LiCl, LiBr, LiI, 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 NLi may include one or more selected from the group consisting of

[0056] 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 decreases, 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.

[0057] 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. In this way, when 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 not preferable 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.

[0058] In addition, the non-aqueous organic solvent used in the electrolyte composition may be any organic solvent used in non-aqueous electrolytes in the art without any particular limitations. Specifically, examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), gamma-butyrolactone, 1,2-dimethoxyethane (DME), tetrahydroxyfuran, 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, ethers, methyl propionate (MP), ethyl propionate (EP), and propyl propionate (PP).

[0059] The non-aqueous organic solvent used in the present invention may be used alone or in any combination and ratio of two or more 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 electrochemical stability against oxidation-reduction and chemical stability against heat and reaction with solutes.

[0060] On the other hand, the electrolyte composition may further contain electrolyte additives in addition to the basic components described above. As long as the gist of the present invention is not impaired, electrolyte 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, as in the case of use in a non-aqueous electrolyte battery called a lithium polymer battery, it is also possible to use the electrolyte for a non-aqueous electrolyte battery by solidifying it with a gelling agent or a crosslinked polymer.

[0061] <Lithium secondary battery> Further, 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, the positive electrode including at least one positive electrode active material selected from the group consisting of lithium metal oxides represented by the following Chemical Formula 3 or 4, and the electrolyte solution composition according to the present invention.

[0062] [Chemical formula 3] Li x [Ni y Co z Mn w M 1 v ]O 2

[0063] [Chemical formula 4] LiM 2 p Mn (2-p) O 4

[0064] In the above Chemical Formula 3 and Chemical Formula 4, 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≦y<1, 0≦z≦1, 0≦w≦1, 0≦v≦0.1, respectively, y+z+w+v=1, and M 2 is Ni, Co or Fe, and p is in the range of 0.05≦p≦0.6.

[0065] The lithium secondary battery according to the present invention includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and the lithium salt-containing nonaqueous electrolyte composition according to the present invention described above.

[0066] Specifically, 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, other electrolyte additives, and the like as necessary.

[0067] 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 the lithium metal oxides represented by Chemical Formula 3 or Chemical Formula 4 that are capable of reversibly intercalating and deintercalating lithium ions.

[0068] The lithium metal oxides represented by the above Chemical Formula 3 and Chemical Formula 4 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.

[0069] In this case, the lithium metal oxide represented by the above formula 3 is lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), lithium manganese oxide (LiMnO 2 , LiMn 2 O 4etc.), lithium nickel cobalt manganese oxide (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 ) etc.

[0070] The lithium metal oxide represented by the above chemical formula 4 is LiNi 0.7 Mn 1.3 O 4 , LiNi 0.5 Mn 1.5 O 4 , LiNi 0.3 Mn 1.7 O 4 etc., which may be used alone or in combination.

[0071] In addition, the positive electrode may use a positive electrode current collector having 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, those surface-treated with carbon, nickel, titanium, silver, etc. may also be used. In addition, the average thickness of the current collector may be suitably applied to be 5 to 500 μm, taking into consideration 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 produced by applying a negative electrode active material onto a negative electrode current collector, followed by drying and pressing, and may further include a conductive material, a binder, other electrolyte additives, and the like as necessary.

[0073] 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.

[0074] The negative electrode active material may further include a silicon material together with the carbon material. The silicon material means a material mainly composed of silicon atoms, and examples of such silicon materials include silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), and silicon dioxide (SiO 2 The silicon (Si)-containing material may include silicon monoxide (SiO) and silicon dioxide (SiO 2 ) are mixed uniformly or composited together and included in the negative electrode mixture layer, they are treated as silicon oxide (SiO q , where 0.8≦q≦2.5).

[0075] 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.

[0076] 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. 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.

[0077] 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, but specifically, one containing at least one polymer selected from polypropylene, polyethylene, and polyethylene-propylene copolymers having chemical resistance and hydrophobicity may be used. The separator may have the form of a porous polymer substrate such as a sheet or nonwoven fabric containing the above-mentioned polymer, and in some cases, 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. In addition, 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 includes the non-aqueous electrolyte composition according to the present invention as an electrolyte, and the electrolyte composition includes one or more electrolyte additives selected from the compounds represented by the following Chemical Formula 1 or 2, together with a non-aqueous organic solvent and a lithium salt.

[0079] [ka]

[0080] [ka]

[0081] In the above Chemical Formula 1 and Chemical Formula 2, R 1 is hydrogen or an alkyl group having 1 to 4 carbon atoms, and L1 and L 2 are each a direct bond or an alkylene group having 1 to 4 carbon atoms.

[0082] The electrolyte composition for a lithium secondary battery according to the present invention contains, as an electrolyte additive, a nitrile-based compound represented by Chemical Formula 1 or Chemical Formula 2, which has a structure in which a nitrile group is introduced into a 6-atom cyclic hydrocarbon group containing three nitrogen atoms (N) symmetrically. This not only prevents metals from being eluted from electrode active materials, etc., when exposed to high temperatures, but also allows an organic and / or inorganic film to be stably and uniformly formed on the surface of the positive electrode and / or negative electrode during activation, thereby preventing the electrolyte from being decomposed and generating gas when the battery is exposed to high temperatures.

[0083] Specifically, the nitrile-based compound represented by Formula 1 or Formula 2 has a strong complexing effect on transition metals due to the nitrogen atom contained in the cyclic hydrocarbon group of six atoms, and therefore when applied as an additive to an electrolyte composition, it directly participates in the solvation shell of lithium ions even at low potentials during initial charge and discharge, i.e., activation, of the battery, and can uniformly form a negative charge and / or inorganic film due to a reduction reaction on the negative electrode surface, and simultaneously form an inorganic film due to an oxidation reaction on the positive electrode surface. The film thus formed can suppress the electrolyte from being decomposed to generate gas when the lithium secondary battery is exposed to high temperatures, and therefore can further improve safety issues due to fire and / or explosion of the secondary battery.

[0084] In addition, the nitrile group of the nitrile compound is introduced to the carbon atom of a 6-atom hydrocarbon group containing 3 nitrogen atoms, and is less susceptible to the influence of nitrogen atoms, and easily interacts with metals dissolved from the positive electrode active material or the electrode assembly, which can prevent the reduction in the life of the battery caused by metals dissolved in the electrolyte when the battery is exposed to high temperatures.

[0085] In addition, the electrolyte additive may be included in the electrolyte composition at a specific content. Specifically, the electrolyte additive may be included in the electrolyte composition at 0.01 to 30 wt % based on the total weight of the electrolyte composition, more specifically, 0.01 to 20 wt %, 0.01 to 10 wt %, 0.01 to 5 wt %, 5 to 10 wt %, 10 to 30 wt %, 15 to 25 wt %, or 10 to 20 wt % based on the total weight of the electrolyte composition. The present invention may prevent the wettability of the electrodes and the separator from decreasing due to an increase in the viscosity of the electrolyte composition by using an excessive amount of the electrolyte additive outside the above range, and at the same time, prevent the ion conductivity of the electrolyte composition from decreasing, thereby preventing the battery performance from decreasing. In addition, the present invention may prevent the effect of the electrolyte additive from being only slightly realized by using a small amount of the electrolyte additive outside the above range.

[0086] The lithium secondary battery according to the present invention has the above-mentioned configuration, and thus has the advantages of being able to strengthen the coating on each surface of the positive electrode and the negative electrode when the battery is activated, thereby improving storage characteristics and life characteristics at high temperatures, and preventing decomposition of the electrolyte during charging and discharging, thereby effectively reducing the amount of gas generated.

[0087] The present invention will now be described in more detail with reference to examples and experimental examples.

[0088] 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.

[0089] <Examples 1 to 9 and Comparative Examples 1 to 3. Preparation of electrolyte composition for lithium secondary batteries> LiPF as a lithium salt was added to a solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), ethyl propionate (EP) and propyl propionate (PP) in a volume ratio of 1:1:1:1. 6The electrolyte additives were dissolved at a concentration of 1 M. Then, one or more of the compounds represented by Structural Formula 1, Structural Formula 3, or Structural Formula 7 as electrolyte additives and vinyl ethylene carbonate (VEC) or propane sultone (PS) as auxiliary additives were weighed and dissolved as shown in Table 1 below to prepare a nonaqueous electrolyte composition. At this time, the electrolyte additives and auxiliary additives added were weighed as shown in Table 1 based on the weight of the entire electrolyte composition.

[0090] [Table 5]

[0091] <Comparative Example 4. Preparation of electrolyte composition for lithium secondary battery> A lithium secondary battery was manufactured in the same manner as in Example 2, except that a compound represented by the following Formula 5 was used as an electrolyte additive.

[0092] [ka]

[0093] <Comparative Example 5. Preparation of electrolyte composition for lithium secondary battery> A lithium secondary battery was manufactured in the same manner as in Example 2, except that a compound represented by the following Formula 6 was used as an electrolyte additive.

[0094] [ka]

[0095] <Examples 10 to 18 and Comparative Examples 6 to 10. Production of Lithium Secondary Batteries> The positive electrode active material is LiCoO with a particle size of 5 μm. 2 This LiCoO 2The carbon-based conductive material and polyvinylidene fluoride as a binder were mixed 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.

[0096] Separately, a negative electrode active material in which natural graphite and artificial graphite were mixed in a weight ratio of 1:1 was prepared, 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 on a copper sheet, dried in a vacuum oven at 130°C, and rolled to produce a negative electrode.

[0097] The positive and negative electrodes obtained above were inserted into a case with a separator made of polypropylene having a thickness of 18 μm therebetween, and then the electrolyte compositions (5 ml) prepared in Examples 1 to 9 and Comparative Examples 1 to 5 as shown in Table 2 below were injected to prepare small pouch-type lithium secondary batteries of 3 Ah class.

[0098] [Table 6]

[0099] <Experimental Example> In order to evaluate the performance of the lithium secondary battery according to the present invention, the following experiment was carried out.

[0100] a) Evaluation of high temperature life The lithium secondary batteries of the examples and comparative examples were activated by charging at a current of 200 mA (0.1 C), and the discharge capacity and resistance of each activated secondary battery were measured and set as the initial capacity and initial resistance. Then, each activated lithium secondary battery was subjected to 100 cycles at 45±2° C., and the discharge capacity of each secondary battery was measured, and the results are shown in Table 3 below. At this time, one cycle was set to 4.2 V and 660 mA (0.33 C, 0.05 C cut-off) CC / CV charging and 2.5 V and 660 mA (0.33 C) CC discharging.

[0101] b) Evaluation of high-temperature storage characteristics of secondary batteries The lithium secondary batteries of the examples and comparative examples were charged at 0.33C to 4.2V under constant current / constant voltage conditions with a 0.05C cut-off, and then discharged at 0.33C to 2.5V, after which the discharge capacity and resistance were measured as the initial capacity and initial resistance. Then, the batteries were fully charged at 0.33C to 4.2V under constant current / constant voltage conditions with a 0.05C cut-off, and then stored at 45°C for 12 weeks, after which the remaining capacity and resistance of each stored lithium secondary battery were measured. The results are shown in Table 3 below.

[0102] C) High temperature safety evaluation The lithium secondary batteries of the examples and comparative examples were charged to 4.2 V at 0.33 C with a 0.05 C cut-off under constant current / constant voltage conditions, discharged to 2.5 V at 0.33 C with a 0.05 C cut-off, and then measured as the initial capacity and initial resistance. Then, the batteries were fully charged to 4.2 V at 0.33 C with a 0.05 C cut-off under constant current / constant voltage conditions.

[0103] A fully charged secondary battery was placed in an oven and heated to 140°C at a rate of 5°C / min, and then left at 140°C for 1 hour from the time it reached 140°C, during which the secondary battery was observed for ignition and / or explosion. If no ignition and / or explosion occurred, it was rated as "○", otherwise it was rated as "×". The results are shown in Table 3 below.

[0104] [Table 7]

[0105] As shown in Table 3 above, the electrolyte composition according to the present invention contains one or more compounds represented by Formula 1 or Formula 2 as an electrolyte additive, and can improve the high temperature characteristics of a lithium secondary battery.

[0106] Specifically, the secondary battery according to the embodiment of the present invention exhibited a high capacity retention rate exceeding 90% under both high-temperature charge / discharge and storage conditions, and was shown not to ignite or explode even when exposed to high temperatures exceeding 100°C.

[0107] This means that the compound represented by Chemical Formula 1 and / or Chemical Formula 2 contained in the electrolyte composition as an electrolyte additive inhibits the elution of metal from the electrode active material into the electrolyte when the secondary battery is exposed to high temperatures, thereby maintaining high battery performance, and also inhibits the decomposition of the electrolyte at high temperatures and reduces the generation of internal gas by participating in the formation of a film on the surface of the positive and negative electrodes when the secondary battery is activated.

[0108] From these results, it can be seen that the electrolyte composition of the present invention, by including one or more electrolyte additives selected from the compounds represented by Chemical Formula 1 and Chemical Formula 2, can effectively reduce gas generated during charging and discharging of a lithium secondary battery, as well as strengthen the SEI layer on the electrode surface, thereby improving storage characteristics and life characteristics at high temperatures.

[0109] It can be seen that the secondary battery of the embodiment including the compound represented by Chemical Formula 1 as an electrolyte additive is less susceptible to decomposition of the electrolyte due to the coating formed on the surfaces of the positive and negative electrodes even when exposed to high temperature conditions, and thus the amount of gas generated is significantly reduced, and the drop in OCV generated at the positive electrode is reduced.

[0110] 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.

[0111] 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 electrolyte solution includes a non-aqueous organic solvent, a lithium salt, and an electrolyte additive including a compound represented by the following chemical formula 1: 【Chemistry 1】 In the above Chemical Formula 1, R １ is hydrogen or an alkyl group having 1 to 4 carbon atoms, The electrolyte composition for a lithium secondary battery, wherein L 1 is a direct bond or an alkylene group having 1 to 4 carbon atoms.

2. The electrolyte additive further contains a compound represented by the following chemical formula 2: 【Chemistry 2】 In the above Chemical Formula 2, 2. The electrolyte composition for a lithium secondary battery according to claim 1, wherein L 2 is a direct bond or an alkylene group having 1 to 4 carbon atoms.

3. R １ is hydrogen, a methyl group, an ethyl group, or a propyl group, 2. The electrolyte composition for a lithium secondary battery according to claim 1, wherein L 1 is a direct bond, a methylene group, an ethylene group, or a propylene group.

4. The electrolyte composition for a lithium secondary battery according to claim 2, wherein L 2 is a direct bond, a methylene group, an ethylene group or a propylene group.

5. The electrolyte composition for a lithium secondary battery according to claim 1, wherein the compound represented by Chemical Formula 1 includes compounds represented by the following <Structural Formula 1> to <Structural Formula 6>. 【Table 1】

6. The electrolyte composition for a lithium secondary battery according to claim 2, wherein the compound represented by Chemical Formula 2 includes a compound represented by the following <Structural Formula 7> or <Structural Formula 8>. 【Table 2】

7. 3. The electrolyte composition for a lithium secondary battery according to claim 2, wherein the electrolyte additive comprises the compound represented by Chemical Formula 1 and the compound represented by Chemical Formula 2 in a weight ratio of 1:0.05-20.

8. 2. The electrolyte composition for a lithium secondary battery according to claim 1, wherein the electrolyte additive is contained in an amount of 0.01 to 30% by weight based on the total weight of the electrolyte composition.

9. The electrolyte composition for a lithium secondary battery according to claim 1, further comprising one or more auxiliary additives selected from the group consisting of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), propane sultone (PS), 1,3-propane sultone (PRS), ethylene sulfate (ESa), succinonitrile (SN), adiponitrile (AN), hexanetricarbonitrile (HTCN), gamma-butyrolactone (GBL), biphenyl (BP), cyclohexylbenzene (CHB), and tert-amylbenzene (TAB).

10. 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 The electrolyte composition for a lithium secondary battery according to claim 1 , comprising at least one selected from the group consisting of NLi.

11. The non-aqueous organic solvent is selected from the group consisting of N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 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, ethers, methyl propionate, and ethyl propionate. The electrolyte composition for lithium secondary batteries according to claim 1, which includes at least one selected from the group consisting of ethyl propionate.

12. An electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, the positive electrode including at least one positive electrode active material selected from the group consisting of lithium metal oxides represented by the following Formula 3 or Formula 4: The electrolyte composition according to any one of claims 1 to 11, [Chemical formula 3] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ２ [Chemical formula 4] LiM ２ ｐ Mn （２－ｐ） O ４ In the above Chemical Formula 3 and Chemical Formula 4, 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≦y<1, 0≦z≦1, 0≦w≦1, 0≦v≦0.1, and y+z+w+v=1; M ２ is Ni, Co or Fe, A lithium secondary battery, wherein p satisfies 0.05≦p≦0.

6.

13. The positive electrode active material 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 and LiNi ０．５ Mn １．５ O ４ The lithium secondary battery according to claim 12, comprising one or more selected from the group consisting of:

14. 13. The lithium secondary battery according to claim 12, 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.

15. The negative electrode active material is silicon (Si), silicon carbide (SiC) and silicon oxide (SiO ｑ 15. The lithium secondary battery of claim 14, further comprising one or more silicon materials selected from the group consisting of q and q=0.8, q=1.5, ...

16. The lithium secondary battery according to claim 15, 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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