Nonaqueous electrolyte and lithium secondary battery including same

Abstract

The present invention provides a non-aqueous electrolyte including a lithium salt, an organic solvent, and an additive, in which the additive includes a compound represented by a specific chemical formula. The non-aqueous electrolyte according to the present invention includes an additive having excellent electrode film protection and O2 removal effects, thereby simultaneously improving cycle performance and resistance performance of a lithium secondary battery including the non-aqueous electrolyte.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2022-0125852 filed in the Korean Intellectual Property Office on September 30, 2022, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a non-aqueous electrolyte and a lithium secondary battery comprising the same. Background Art

[0004] In recent years, as the application fields of lithium secondary batteries have rapidly expanded to power supply of electronic equipment such as electrical, electronic, communication and computers, and power storage and supply of large equipment such as automobiles and power storage equipment, the demand for secondary batteries with high capacity, high output and high stability has been increasing.

[0005] In particular, in lithium secondary batteries for automobile use, high capacity, high power and long life characteristics have become important. In order to achieve high capacity of lithium secondary batteries, it is necessary to consider driving the lithium secondary batteries at high voltage.

[0006] However, when the lithium secondary battery is driven at a high voltage, due to the side reactions caused by the degradation of the electrolyte during battery charging and discharging, the film or electrode surface structure formed on the positive / negative electrode surface may deteriorate, so that transition metal ions may be dissolved from the positive electrode surface. The transition metal ions dissolved as described above are electrodeposited on the negative electrode, reducing the passivation ability of the solid electrolyte interface (SEI) film of the negative electrode, thereby causing the problem of negative electrode degradation. When the potential of the positive electrode increases, or when the battery is exposed to high temperature, the degradation phenomenon of the secondary battery tends to accelerate.

[0007] In addition, when lithium secondary batteries are driven at high voltage, there is the following problem: active oxygen is dissociated from the positive electrode active material contained in the positive electrode, and the active oxygen undergoes a side reaction with an organic solvent such as cyclic carbonate in a non-aqueous electrolyte to produce gases such as CO or CO2, which continuously reduces the durability of the battery. Summary of the invention

[0008] [Technical issues]

[0009] One aspect of the present invention provides a nonaqueous electrolyte that forms a stable film on a positive electrode / anode, thereby reducing electrolyte side reactions, inhibiting the dissolution of transition metals, having an excellent O2 scavenging effect, and effectively reducing the resistance of a secondary battery.

[0010] Another aspect of the present invention provides a lithium secondary battery having reduced resistance and excellent lifespan performance by including the above-mentioned nonaqueous electrolyte.

[0011] [Technical solution]

[0012] According to one aspect of the present invention, there is provided a non-aqueous electrolyte including a lithium salt, an organic solvent and an additive, wherein the additive includes a compound represented by Formula 1 below.

[0013] [Formula 1]

[0014]

[0015] In the above formula 1, R1 to R6 each independently include hydrogen, halogen, nitrile group, propargyl group, ester group, ether group, keto group, carboxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, substituted or unsubstituted alkoxy group, boron group, borate group, isocyanate group, isothiocyanate group, silyl group, siloxane group, sulfone group, sulfonate group, sulfate group or a combination of two or more thereof, and at least one of R1 to R6 includes a nitrile group.

[0016] According to one aspect of the present invention, there is provided a lithium secondary battery comprising: a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator disposed between the positive electrode and the negative electrode, and the above nonaqueous electrolyte.

[0017] [Beneficial Effects]

[0018] The non-aqueous electrolyte of the present invention is characterized in that it contains a chromone compound substituted with a nitrile-containing substituent as an additive. The additive can form a film having excellent durability to the positive / negative electrode and reduced resistance, thereby inhibiting electrolyte side reactions in the electrode. In addition, since the active oxygen compound produced by the positive electrode is combined with the chromone structure contained in the compound represented by the above formula 1, the non-aqueous electrolyte of the present invention has the effect of inhibiting electrolyte decomposition and gas generation (O2 scavenging effect). In addition, the nitrile group substituted on the chromone structure can prevent performance degradation at high temperatures and inhibit the dissolution of transition metals from the positive electrode active material.

[0019] Therefore, a lithium secondary battery including the above nonaqueous electrolyte may have improved resistance performance and lifespan performance at the same time. DETAILED DESCRIPTION

[0020] It will be understood that the words or terms used in the specification and claims of the present invention should not be interpreted as limited to the meanings defined in commonly used dictionaries. It will be further understood that based on the principle that the inventor can appropriately define the meaning of words or terms to best explain the present invention, the words or terms should be interpreted as having a meaning consistent with its meaning in the context of the relevant technology and the technical concept of the present invention.

[0021] In this specification, it should be understood that the terms "comprising", "including" or "having" are intended to specify the presence of stated features, numbers, steps, elements or a combination thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements or a combination thereof.

[0022] Meanwhile, before describing the present invention, unless otherwise specified in the present invention, "*" refers to a connection portion (bonding site) between the same or different atoms or terminal portions of a chemical formula.

[0023] In addition, in this specification, it will be understood that in the description of "a to b carbon atoms" herein, "a" and "b" each refer to the number of carbon atoms contained in a particular functional group. That is, the functional group may contain "a" to "b" carbon atoms. For example, "alkyl having 1 to 5 carbon atoms" refers to a C1-C5 alkyl having 1 to 5 carbon atoms, i.e., CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2CH2- and (CH3)2CHCH2CH2-, etc.

[0024] In addition, in the present specification, an alkyl group, an alkenyl group or an alkynyl group may be substituted or unsubstituted. Unless otherwise defined, the term “substituted” means that at least one hydrogen bonded to carbon is replaced by an element other than hydrogen, and for example, it means substitution with an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, a cycloalkynyl group having 3 to 12 carbon atoms, a heterocycloalkyl group having 3 to 12 carbon atoms, a heterocycloalkenyl group having 3 to 12 carbon atoms, a heterocycloalkynyl group having 2 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, a halogen atom, a fluoroalkyl group having 1 to 20 carbon atoms, a nitro group, an aryl group having 6 to 20 carbon atoms, a heteroaryl group having 2 to 20 carbon atoms, and a halogenated aryl group having 6 to 20 carbon atoms.

[0025] Hereinafter, the present invention will be described in more detail.

[0026] Non-aqueous electrolytes

[0027] The present invention relates to a non-aqueous electrolyte. More specifically, the non-aqueous electrolyte may be a non-aqueous electrolyte for a lithium secondary battery.

[0028] The nonaqueous electrolyte of the present invention includes a lithium salt, an organic solvent, and an additive, wherein the additive includes a compound represented by Formula 1 below.

[0029] [Formula 1]

[0030]

[0031] In the above formula 1, R1 to R6 each independently include hydrogen, halogen, nitrile group, propargyl group, ester group, ether group, keto group, carboxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, substituted or unsubstituted alkoxy group, boron group, borate group, isocyanate group, isothiocyanate group, silyl group, siloxane group, sulfone group, sulfonate group, sulfate group or a combination of two or more thereof, and at least one of R1 to R6 includes a nitrile group.

[0032] The non-aqueous electrolyte of the present invention is characterized in that it contains a chromone compound substituted with a substituent containing a nitrile group as an additive. The additive can form a film having excellent durability to the positive / negative electrode and having reduced resistance, thereby suppressing electrolyte side reactions in the electrode. In addition, since the active oxygen compound produced by the positive electrode is combined with the chromone structure contained in the compound represented by the above formula 1, the non-aqueous electrolyte of the present invention has the effect of suppressing electrolyte decomposition and gas generation (O2 scavenging effect). In addition, the nitrile group substituted on the chromone structure can prevent performance degradation at high temperatures and suppress the dissolution of transition metals from the positive electrode active material. Therefore, the lithium secondary battery including the above-mentioned non-aqueous electrolyte can have improved resistance performance and life performance at the same time.

[0033] (1) Lithium salt

[0034] As the lithium salt used in the present invention, various lithium salts commonly used in non-aqueous electrolytes for lithium secondary batteries can be used without limitation. For example, the lithium salt may include Li + as a cation, and may contain a cation selected from F - , Cl - Br - ,I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - 、AlO4 - 、AlCl4 - PF6 - 、SbF6 - 、AsF6 - , B 10 Cl 10 - 、BF2C2O4 - , BC4O8 - PF4C2O4 - PF2C4O8 -、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - 、C4F9SO3 - CF3CF2SO3 - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、CH3SO3 - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - At least one of the group consisting of is used as an anion.

[0035] Specifically, the lithium salt may include a salt selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , LiB(C2O4)2(LiBOB), LiCF3SO3, LiN(SO2F)2(LiFSI), LiCH3SO3, LiCF3CO2, LiCH3CO2 and LiN(SO2CF2CF3)2(LiBETI). Specifically, the lithium salt may include at least one selected from the group consisting of LiBF4, LiClO4, LiPF6, LiB(C2O4)2(LiBOB), LiCF3SO3, LiN(SO2CF3)2(LiTFSI), LiN(SO2F)2(LiFSI) and LiN(SO2CF2CF3)2(LiBETI).

[0036] In the non-aqueous electrolyte, the lithium salt may be contained in a concentration of 0.5 M to 5 M, specifically 0.8 M to 4 M, more specifically 0.8 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, Li + The transference number and the degree of dissociation of lithium ions are improved, thereby improving the output performance of the battery.

[0037] (2) Organic solvents

[0038] The organic solvent is a non-aqueous solvent commonly used in lithium secondary batteries, and is not particularly limited as long as decomposition caused by oxidation reaction or the like during charging and discharging of the secondary battery can be minimized.

[0039] Specifically, the organic solvent may include at least one selected from the group consisting of a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, a linear ester-based organic solvent, and a cyclic ester-based organic solvent.

[0040] Specifically, the organic solvent may include a cyclic carbonate-based solvent, a linear carbonate-based solvent, or a mixture thereof.

[0041] The cyclic carbonate organic solvent is a high viscosity organic solvent having a high dielectric constant and thus can easily dissociate the lithium salt in the electrolyte. Specifically, the cyclic carbonate organic solvent may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate and vinylene carbonate, and more specifically, may include ethylene carbonate.

[0042] In addition, the linear carbonate organic solvent is an organic solvent with low viscosity and low dielectric constant. Specifically, the linear carbonate organic solvent may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate, more specifically, may include ethyl methyl carbonate (EMC).

[0043] The organic solvent can be a mixture of a cyclic carbonate organic solvent and a straight-chain carbonate organic solvent. At this time, the cyclic carbonate organic solvent and the straight-chain carbonate organic solvent can be mixed with a volume ratio of 10:90 to 40:60, specifically a volume ratio of 10:90 to 30:70, more specifically a volume ratio of 15:85 to 30:70. When the mixing ratio of the cyclic carbonate solvent and the straight-chain carbonate solvent meets the above range, high dielectric constant and low viscosity characteristics can be met simultaneously, and excellent ionic conductivity characteristics can be achieved.

[0044] In addition, in order to prepare an electrolyte with high ionic conductivity, the organic solvent may include at least one carbonate organic solvent selected from the group consisting of cyclic carbonate organic solvents and linear carbonate organic solvents, and may further include at least one ester organic solvent selected from the group consisting of linear ester organic solvents and cyclic ester organic solvents.

[0045] The linear ester organic solvent may specifically include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0046] In addition, the cyclic ester organic solvent may include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0047] Meanwhile, if necessary, the organic solvent may further use any organic solvent commonly used in non-aqueous electrolytes without limitation, for example, at least one organic solvent selected from ether organic solvents, glyme organic solvents, and nitrile organic solvents may be further included.

[0048] As the ether solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL) and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL) or a mixture of two or more thereof can be used, but the present invention is not limited thereto.

[0049] Glyme solvents are solvents having a higher dielectric constant and a lower surface tension and lower reactivity with metals than linear carbonate organic solvents, and may include at least one selected from the group consisting of dimethoxyethane (glyme dimethyl ether, DME), diethoxyethane, diglyme dimethyl ether, triglyme dimethyl ether and tetraglyme dimethyl ether (TEGDME), but are not limited thereto.

[0050] The nitrile solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptanecarbonitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, benzyl cyanide, 2-fluorobenzoyl cyanide and 4-fluorobenzoyl cyanide, but is not limited thereto.

[0051] (3) Additives

[0052] The nonaqueous electrolyte of the present invention includes a compound represented by Formula 1 below.

[0053] [Formula 1]

[0054]

[0055] In the above formula 1, R1 to R6 each independently include hydrogen, halogen, nitrile group, propargyl group, ester group, ether group, keto group, carboxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, substituted or unsubstituted alkoxy group, boron group, borate group, isocyanate group, isothiocyanate group, silyl group, siloxane group, sulfone group, sulfonate group, sulfate group or a combination of two or more thereof, and at least one of R1 to R6 includes a nitrile group.

[0056] The compound represented by the above formula 1 is a chromone compound containing a nitrile-containing substituent. The chromone structure contained in the above formula 1 has a higher reaction energy with active oxygen than organic solvents such as ethylene carbonate, so it combines with active oxygen earlier than the organic solvent during the generation of active oxygen. Therefore, when the compound of the above formula 1 is contained in the non-aqueous electrolyte, the active oxygen compound generated by the positive electrode combines with the chromone structure contained in the compound represented by the above formula 1, thereby showing the effect of inhibiting electrolyte decomposition and gas generation.

[0057] In addition, the compound represented by the above formula 1 can be quickly reduced and decomposed during initial activation and form a stable solid electrolyte interphase (SEI) film on the negative electrode surface. The chromone structure contained in the compound of the above formula 1 has strong reducibility at the negative electrode, and the ring structure opens during the initial activation of the lithium secondary battery, thereby forming a polyethylene oxide polymer SEI layer. The polymer SEI layer has the advantages of excellent flexibility and resilience.

[0058] In addition, the nitrile group contained in the compound represented by the above formula 1 can not only prevent the performance of the secondary battery from being deteriorated at high temperatures, but also play a role in suppressing the dissolution of transition metals from the positive electrode active material.

[0059] Therefore, the nonaqueous electrolyte containing the compound of Formula 1 having both a chromone structure and a nitrile-containing substituent as an additive can reduce the resistance to the negative electrode and form an SEI film with excellent durability, thereby greatly improving the life performance and resistance performance of the lithium secondary battery including the nonaqueous electrolyte.

[0060] Specifically, the compound represented by the above Formula 1 may include a compound represented by the following Formula 2A.

[0061] [Formula 2A]

[0062]

[0063] In the above Formula 2A, R2 is as defined in Formula 1, and R2 includes a nitrile group.

[0064] When R2 is substituted on the chromone as in the above formula 2A, it is preferred because the durability of the film is further improved.

[0065] More specifically, the compound represented by the above Formula 1 may include a compound represented by the following Formula 3A.

[0066] [Formula 3A]

[0067]

[0068] The content of the compound represented by the above formula 1 in the non-aqueous electrolyte can be 0.01 wt % to 5 wt %, specifically 0.05 wt % to 4.5 wt %, more specifically 0.2 wt % to 1.5 wt %, and even more specifically 0.4 wt % to 0.8 wt %. When the content of the compound represented by the above formula 1 satisfies the above range, it is preferred in terms of: giving full play to the aforementioned effect of protecting the electrode interface and the effect of inhibiting the decomposition of the organic solvent and preventing the side reaction, while preventing the increase in resistance of the lithium secondary battery caused by excessive addition and the resulting decrease in life performance.

[0069] In addition to the compound of Formula 1, the additive may include additional additives. In addition, the non-aqueous electrolyte may include additional additives to prevent the non-aqueous electrolyte from decomposing under high output conditions and causing negative electrode collapse, or to achieve low-temperature high-rate discharge characteristics, high-temperature stability, prevent overcharging, and inhibit battery expansion at high temperatures.

[0070] Specifically, the additional additive can be at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, propylene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiPO2F2, lithium difluorooxalatoborate (LiODFB), lithium bis(oxalate)borate (LiBOB), 3-trimethoxysilyl-propyl-N-aniline (TMSPa) and tris(trimethylsilyl)phosphite (TMSPi), more specifically, it can be at least one selected from the group consisting of vinylene carbonate and 1,3-propane sultone.

[0071] The additional additive may be included in the non-aqueous electrolyte in an amount of 0.1 wt % to 15 wt %.

[0072] Lithium secondary battery

[0073] In addition, the present invention provides a lithium secondary battery including the above nonaqueous electrolyte.

[0074] Specifically, the lithium secondary battery includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator provided between the positive electrode and the negative electrode, and the above-mentioned nonaqueous electrolyte.

[0075] At this time, the lithium secondary battery of the present invention can be manufactured by conventional methods known in the art. For example, the lithium secondary battery of the present invention can be manufactured by the following process: forming an electrode assembly stacked with a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode in sequence, and then inserting the electrode assembly into a battery case, and then injecting the nonaqueous electrolyte of the present invention therein.

[0076] (1) Positive electrode

[0077] The positive electrode contains a positive electrode active material.

[0078] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. In this case, the positive electrode active material may be contained in the positive electrode active material layer.

[0079] The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon and aluminum-cadmium alloy, preferably aluminum.

[0080] The thickness of the positive electrode current collector may generally be 3 μm to 500 μm.

[0081] The positive electrode current collector may have fine irregularities formed on its surface to improve the binding force of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric body.

[0082] The positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one surface or both surfaces of the positive electrode current collector.

[0083] The positive electrode active material layer may include a positive electrode active material.

[0084] The positive electrode active material is a compound that can reversibly insert and release lithium, and specifically may include a lithium transition metal composite oxide containing lithium and at least one transition metal selected from the group consisting of nickel, cobalt, manganese and aluminum, preferably a lithium transition metal composite oxide containing lithium and a transition metal containing nickel, cobalt and manganese.

[0085] For example, the lithium transition metal composite oxide may be a lithium manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium cobalt oxide (e.g., LiCoO2, etc.), a lithium nickel oxide (e.g., LiNiO2, etc.), a lithium nickel manganese oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 <Y<1)、LiMn 2-z Ni zO4 (where 0 < Z < 2, etc.), lithium nickel cobalt oxides (e.g., LiNi 1- Y1 Co Y1 O2 (where 0 < Y1 < 1, etc.), lithium manganese cobalt oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2- z1 Co z1 O4 (where 0 < Z1 < 2, etc.), lithium nickel manganese cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1 and p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2 and p1 + q1 + r2 = 2, etc.) or lithium nickel cobalt transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are each atomic fractions of independent elements, where 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1 and p2 + q2 + r3 + s2 = 1), etc.), and may include any one or two or more of these complexes. Among these materials, in terms of improving the capacity and stability of the battery, the lithium transition metal composite oxide can be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.) or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.). When considering the significant improvement effects brought about by controlling the type and content ratio of the constituent elements forming the lithium transition metal composite oxide, the lithium transition metal composite oxide can be Li(Ni0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 etc., and any one of them or a mixture of two or more of them can be used.

[0086] More specifically, the positive electrode active material is a lithium transition metal composite oxide, and may contain nickel in an amount of 60 mol% or more based on the total number of moles of the transition metals contained in the lithium transition metal composite oxide. Specifically, the positive electrode active material is a lithium transition metal composite oxide, and the transition metals include nickel and at least one selected from manganese, cobalt, and aluminum, and the content of nickel may be 60 mol% or more, specifically 60 mol% to 90 mol%, based on the total number of moles of the transition metals. When a lithium transition metal composite oxide with a high nickel content is used together with the above non-aqueous electrolyte solution, it is preferable in terms of reducing gaseous by-products generated due to structural collapse.

[0087] In addition, the positive electrode active material may include a lithium transition metal composite oxide represented by the following formula 5.

[0088] [Formula 5]

[0089] Li 1+x (Ni a Co b Mn c M d )O2

[0090] In the above formula 5, M is one or more selected from 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 1+x, a, b, c, and d are each atomic fractions of independent elements, where 0 ≤ x ≤ 0.2, 0.50 ≤ a < 1, 0 < b ≤ 0.25, 0 < c ≤ 0.25, 0 ≤ d ≤ 0.1 and a + b + c + d = 1.

[0091] Preferably, a, b, c, and d can be 0.70 ≤ a ≤ 0.95, 0.025 ≤ b ≤ 0.20, 0.025 ≤ c ≤ 0.20, and 0 ≤ d ≤ 0.05, respectively.

[0092] In addition, a, b, c and d may be 0.80≤a≤0.95, 0.025≤b≤0.15, 0.025≤c≤0.15 and 0≤d≤0.05, respectively.

[0093] In addition, a, b, c and d may be 0.85≤a≤0.90, 0.05≤b≤0.10, 0.05≤c≤0.10 and 0≤d≤0.03, respectively.

[0094] Meanwhile, the positive electrode active material may include a hyper-lithium manganese-rich oxide, which includes at least 50 mol % of Mn in all metals except lithium, and whose molar ratio of lithium to transition metal is greater than 1.

[0095] When the over-lithium manganese-rich oxide is used as the positive electrode active material, during the initial activation process, the over-lithium manganese-rich oxide in the rock salt phase decomposes and generates active oxygen. The active oxygen corrodes and decomposes organic solvents such as ethylene carbonate, and produces gas and resistance byproducts, thereby reducing the physical properties of the battery. However, in the present invention, since the non-aqueous electrolyte contains a compound of formula 1 that is more reactive with active oxygen than the organic solvent, the active oxygen generated during the initial activation process can be combined with the compound of formula 1 earlier than the organic solvent, thereby minimizing the side effects caused by the decomposition of the organic solvent.

[0096] The lithium-rich manganese oxide may be a compound represented by the following formula 6:

[0097] [Formula 6]

[0098] Li 1+s [Ni t Co u Mn v M 1 w ]O 2+z

[0099] In the above formula 6, M 1 It is one or more elements selected from 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. In the above formula 6, 0.05≤s≤1, 0≤t≤0.5, 0≤u≤0.3, 0.5≤v<1.0, 0≤w≤0.2 and 0≤z≤1 may be achieved, preferably 0.05≤s≤1, 0.1≤t≤0.5, 0≤u≤0.1, 0.5≤v<1.0, 0≤w≤0.2 and 0≤z≤1, and more preferably 0.10≤s≤0.50, 0.1≤t≤0.5, 0≤u≤0.1, 0.6≤v<1.0, 0≤w≤0.1 and 0≤z≤0.50.

[0100] More specifically, the lithium-rich manganese oxide may be a compound represented by the following formula 6-1:

[0101] [Formula 6-1]

[0102] X Li2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M 1 w ]O2

[0103] In the above formula 6-1, M 1 It is one or more elements selected from 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. In the above formula 6-1, 0.1≤X≤0.5, 0.5≤y<1, 0≤z≤0.3 and 0≤w≤0.2 may be satisfied, preferably 0.2≤X≤0.5, 0.5≤y<1, 0≤z≤0.1 and 0≤w≤0.2, and more preferably 0.3≤X≤0.5, 0.6≤y<1, 0≤z≤0.1 and 0≤w≤0.2.

[0104] The positive electrode active material may be contained in the positive electrode active material layer in an amount of 80 wt % to 99 wt %, preferably 92 wt % to 98.5 wt %, in consideration of expressing sufficient capacity of the positive electrode active material.

[0105] The positive electrode active material layer may further include a binder and / or a conductive material in addition to the positive electrode active material described above.

[0106] The binder is a component used to assist the combination of active materials and conductive materials, etc. and the combination with the current collector. Specifically, the binder may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber and fluororubber, preferably polyvinylidene fluoride.

[0107] In terms of ensuring sufficient bonding force between components such as the positive electrode active material, the binder may be contained in the positive electrode active material layer in an amount of 1 to 20 wt %, preferably 1.2 to 10 wt %.

[0108] Conductive materials can be used to assist and improve the conductivity in secondary batteries, and there is no particular limitation as long as they have conductivity without causing chemical changes. Specifically, the positive electrode conductive material may include at least one of the following: graphite, such as natural graphite or artificial graphite; carbon materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives, and in terms of improving conductivity, carbon black may be preferably included.

[0109] In terms of ensuring sufficient conductivity, the conductive material may be contained in the positive electrode active material layer in an amount of 1 wt % to 20 wt %, preferably 1.2 wt % to 10 wt %.

[0110] The thickness of the positive electrode active material layer may be 30 μm to 400 μm, preferably 40 μm to 110 μm.

[0111] The positive electrode may be manufactured by coating a positive electrode collector with a positive electrode slurry including a positive electrode active material and optionally a binder, a conductive material, and a positive electrode slurry-forming solvent, and then drying and roll-pressing the resultant.

[0112] The positive electrode slurry forming solvent may include an organic solvent, such as N-methyl-2-pyrrolidone (NMP). The positive electrode slurry may have a solid content of 40 wt % to 90 wt %, specifically 50 wt % to 80 wt %.

[0113] (2) Negative electrode

[0114] The negative electrode may be opposite the positive electrode.

[0115] The negative electrode contains a negative electrode active material.

[0116] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. In this case, the negative electrode active material may be contained in the negative electrode active material layer.

[0117] The negative electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. Specifically, as the negative electrode current collector, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium and silver, and aluminum-cadmium alloys can be used.

[0118] The thickness of the negative electrode current collector may generally be 3 μm to 500 μm.

[0119] The negative electrode current collector may have fine irregularities formed on its surface to improve the binding force of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric body.

[0120] The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one surface or both surfaces of the negative electrode current collector.

[0121] The negative electrode active material layer may include a negative electrode active material.

[0122] The negative electrode active material is a material that can reversibly embed / de-embed lithium ions, and may include at least one selected from the group consisting of carbon-based active materials, (quasi-)metallic active materials and lithium metal, and specifically may include at least one selected from carbon-based active materials and (quasi-)metallic active materials.

[0123] The carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and may preferably include at least one selected from the group consisting of artificial graphite and natural graphite.

[0124] The average particle size (D 50 ) can be 10 μm to 30 μm, preferably 15 μm to 25 μm.

[0125] Specifically, the (quasi)metal active material may include at least one (quasi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti and Sn; an alloy of lithium and at least one (quasi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti and Sn; an oxide of at least one (quasi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti and Sn; lithium titanium oxide (LTO); and lithium vanadium oxide, etc.

[0126] More specifically, the (quasi)metal-based active material may include a silicon-based active material.

[0127] Silicon-based active materials may include SiO xSince SiO2 does not react with lithium ions and thus cannot store lithium, it is preferred that x is within the above range, and more preferably, the silicon-based active material may be SiO.

[0128] In terms of ensuring structural stability during charge / discharge and reducing side reactions with the electrolyte solution, the average particle size (D 50 ) can be 1 μm to 30 μm, preferably 2 μm to 15 μm.

[0129] In the negative electrode active material layer, the content of the negative electrode active material may be 60 wt % to 99 wt %, preferably 75 wt % to 95 wt %.

[0130] The negative electrode active material layer may further include a binder and / or a conductive material in addition to the negative electrode active material.

[0131] At this time, the binder is used to improve the battery performance by improving the adhesion between the negative electrode active material layer and the negative electrode current collector, and may include, for example, at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber and materials in which hydrogen is replaced by Li, Na or Ca, etc., and may also include various copolymers thereof.

[0132] In the negative electrode active material layer, the content of the binder may be 0.5 wt % to 10 wt %, preferably 1 wt % to 5 wt %.

[0133] There is no particular limitation on the conductive material as long as it has conductivity and does not cause chemical changes in the battery. For example, the following can be used: graphite, such as natural graphite or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials such as polyphenylene derivatives, etc.

[0134] In the negative electrode active material layer, the content of the conductive material may be 0.5 wt % to 10 wt %, preferably 1 wt % to 5 wt %.

[0135] The thickness of the negative electrode active material layer may be 10 μm to 100 μm, preferably 50 μm to 80 μm.

[0136] The negative electrode may be manufactured by coating at least one surface of a negative electrode collector with a negative electrode slurry including a negative electrode active material, a binder, a conductive material, and / or a negative electrode slurry-forming solvent, and then drying and roll-pressing the resultant.

[0137] In terms of promoting the dispersion of negative electrode active materials, binders and / or conductive materials, the negative electrode slurry forming solvent may include, for example, at least one selected from the group consisting of distilled water, N-methyl-2-pyrrolidone (NMP), ethanol, methanol and isopropanol, preferably distilled water. The solid content of the negative electrode slurry may be 30 wt % to 80 wt %, specifically 40 wt % to 70 wt %.

[0138] (3) Diaphragm

[0139] In addition, as a diaphragm, a common porous polymer film commonly used as a diaphragm can be used alone, for example, a porous polymer film made of a polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer), or a laminate thereof can be used. Alternatively, a common porous nonwoven fabric can be used, for example, a nonwoven fabric made of glass fiber or polyethylene terephthalate fiber with a high melting point, but the present invention is not limited thereto. Moreover, a coated diaphragm including a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and can be selectively used in a single-layer or multilayer structure.

[0140] The outer shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical using a can, square, pouch, or coin-shaped, or the like.

[0141] Hereinafter, the present invention will be described in more detail with reference to specific embodiments. However, the following embodiments are only for illustrative purposes, so as to facilitate understanding of the present invention, and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope and spirit of the present invention, and it is apparent that such changes and modifications are within the scope of the appended claims.

[0142] Examples and Comparative Examples

[0143] Example 1

[0144] (Preparation of non-aqueous electrolyte)

[0145] As the organic solvent, a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 30:70 was used.

[0146] LiPF6 as a lithium salt, a compound represented by the following formula 3A, and vinylene carbonate and 1,3-propane sultone as additional additives were added to the organic solvent to prepare a non-aqueous electrolyte.

[0147] LiPF6 is contained in the non-aqueous electrolyte at a concentration of 1.0M.

[0148] The compound represented by the following Formula 3A was contained in the non-aqueous electrolyte in an amount of 0.5 wt %.

[0149] In addition, the nonaqueous electrolyte included 0.5% by weight each of vinylene carbonate and 1,3-propane sultone.

[0150] [Formula 3A]

[0151]

[0152] (Manufacturing of lithium secondary batteries)

[0153] The positive electrode active material (Li 1.35 [Ni 0.35 Mn 0.65 ]O2, lithium-rich manganese oxide), a conductive material (carbon black) and a binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 96.0:1.5:2.5 to prepare a positive electrode slurry (solid content of 60 wt%). The positive electrode slurry was coated on one surface of a positive electrode current collector (Al film) with a thickness of 13.5 μm, and then dried and rolled to manufacture a positive electrode.

[0154] The negative electrode active material (graphite), the conductive material (carbon black) and the binder (styrene-butadiene rubber) were added to distilled water as a solvent at a weight ratio of 97:1:2 to prepare a negative electrode slurry (solid content of 60 wt%). The negative electrode slurry was coated on one surface of a negative electrode current collector (Cu film) having a thickness of 6 μm, and then dried and rolled to manufacture a negative electrode.

[0155] In a dry room, a polyethylene porous film separator was disposed between the positive electrode and the negative electrode manufactured as described above, and then the prepared nonaqueous electrolyte was injected therein to manufacture a secondary battery.

[0156] Example 2

[0157] A nonaqueous electrolyte and a secondary battery were manufactured in the same manner as in Example 1, except that in Example 1, 0.3 wt % of the compound represented by the above Formula 3A was added to the nonaqueous electrolyte.

[0158] Example 3

[0159] A nonaqueous electrolyte and a secondary battery were manufactured in the same manner as in Example 1, except that in Example 1, 1.0 wt % of the compound represented by the above Formula 3A was added to the nonaqueous electrolyte.

[0160] Comparative Example 1

[0161] A nonaqueous electrolyte and a secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by the above Formula 3A was not added.

[0162] Comparative Example 2

[0163] A nonaqueous electrolyte and a secondary battery were manufactured in the same manner as in Example 1, except that a compound represented by the following formula X was added to the nonaqueous electrolyte in an amount of 0.5 wt % instead of the compound represented by the above formula 3A.

[0164] [Formula X]

[0165]

[0166] Comparative Example 3

[0167] A nonaqueous electrolyte and a secondary battery were manufactured in the same manner as in Example 1, except that a compound represented by the following formula Y was added to the nonaqueous electrolyte in an amount of 0.5 wt % instead of the compound represented by the above formula 3A.

[0168] [Formula Y]

[0169]

[0170] Experimental example

[0171] Experimental Example 1: Evaluation of Cycle Capacity Retention Rate

[0172] The lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3 manufactured above were charged to 4.35 V and 1 / 40 C at 45° C. under CC / CV and 0.33 C using an electrochemical charge / discharge device, and then discharged to 2.0 V under CC and 0.33 C, which was set as one cycle, and 150 charge / discharge cycles were performed to measure the capacity retention rate.

[0173] The capacity retention rate was calculated by the following equation, and the results are shown in Table 1 below.

[0174] Capacity retention rate (%) = {(discharge capacity after 150 cycles / discharge capacity after 1 cycle)} × 100

[0175] Experimental Example 2: Resistance Evaluation

[0176] The lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3 manufactured as described above were charged to 4.35 V and 1 / 40 C at 45° C. under CC / CV and 0.33 C conditions, and then discharged to 2.0 V under CC and 0.33 C conditions, which was set as one cycle, and 150 charge / discharge cycles were performed.

[0177] After one charge / discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charge / discharge device. The SOC was adjusted to SOC 50%, and then a 2.5C pulse was applied for 10 seconds. The initial resistance was calculated by the difference between the voltage before and after the pulse application.

[0178] After 150 charge / discharge cycles, the resistance after 150 cycles was calculated by the same method as described above. The results are shown in Table 1 below.

[0179] [Table 1]

[0180]

[0181] Referring to Table 1, it can be confirmed that the lithium secondary batteries of Examples 1 to 3 using the nonaqueous electrolyte including the compound represented by Formula 1 simultaneously improve cycle life performance and resistance performance compared to the lithium secondary batteries of Comparative Examples 1 to 3.

[0182] In particular, for the non-aqueous electrolyte of Comparative Example 3, a compound having a phenyl group instead of a nitrile group substituted in the chromone structure is used as an additive. Since the solubility of the compound in an organic solvent is very low and the flexibility of the SEI film is reduced due to the presence of the phenyl group when the SEI film is formed, the life performance of the secondary battery is greatly reduced and the resistance is increased, which is not preferred.

[0183] Experimental Example 3: Evaluation of Metal Dissolution

[0184] The secondary batteries of Example 1, Comparative Example 1 and Comparative Example 2 were charged to 4.35 V and 1 / 40 C at 45° C. under CC / CV and 0.33 C, and then discharged to 2.0 V under CC and 0.33 C, which was considered one cycle, and 150 charge / discharge cycles were performed.

[0185] Afterwards, the concentration of all dissolved metals in the electrolyte solution was measured using an inductively coupled plasma optical emission spectrometer (ICP-OES). The amounts of metals measured using ICP analysis are shown in Table 2 below.

[0186] [Table 2]

[0187]

[0188] Referring to Table 2, it can be confirmed that the secondary battery using the non-aqueous electrolyte solution of Example 1 uses a chromone compound substituted with a nitrile group as an electrolyte additive, and therefore significantly reduces the amount of metal elution during cyclic charging and discharging compared to the secondary batteries of Comparative Examples 1 and 2.

Claims

1. A non-aqueous electrolyte comprising: Lithium salts; Organic solvents; and additive, Wherein, the additive includes a compound represented by the following formula 1: [Formula 1] Wherein, in the above formula 1, R1 to R6 each independently include hydrogen, halogen, nitrile, propargyl, ester, ether, ketone, carboxyl, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy, boron, borate, isocyanate, isothiocyanate, silyl, siloxane, sulfone, sulfonate, sulfate, or a combination of two or more thereof, and At least one of R1 to R6 includes a nitrile group.

2. The nonaqueous electrolyte according to claim 1, wherein The compound represented by the above formula 1 includes the compound represented by the following formula 2A: [Formula 2A] Wherein, in the above formula 2A, R2 is as defined in formula 1, and R2 includes a nitrile group.

3. The nonaqueous electrolyte according to claim 1, wherein The compound represented by the above formula 1 includes the compound represented by the following formula 3A: [Formula 3A] 4. The nonaqueous electrolyte according to claim 1, wherein The content of the compound represented by Formula 1 in the non-aqueous electrolyte is 0.01 wt % to 10 wt %.

5. The nonaqueous electrolyte according to claim 1, wherein The lithium salt includes a salt selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , LiB(C2O4)2(LiBOB), LiCF3SO3, LiN(SO2F)2(LiFSI), LiCH3SO3, LiCF3CO2, LiCH3CO2 and LiN(SO2CF2CF3)2(LiBETI).

6. The nonaqueous electrolyte according to claim 1, wherein The lithium salt is contained in the nonaqueous electrolyte at a molar concentration of 0.5M to 5.0M.

7. The nonaqueous electrolyte according to claim 1, wherein The organic solvent includes at least one selected from the group consisting of a cyclic carbonate organic solvent, a linear carbonate organic solvent, a linear ester organic solvent, and a cyclic ester organic solvent.

8. The nonaqueous electrolyte according to claim 1, wherein The additive further comprises at least one additional additive selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propylene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiPO2F2, lithium difluorooxalatoborate (LiODFB), lithium bis(oxalato)borate (LiBOB), 3-trimethoxysilyl-propyl-N-aniline (TMSPa) and tris(trimethylsilyl)phosphite (TMSPi).

9. A lithium secondary battery comprising: a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; A separator disposed between the positive electrode and the negative electrode; and The nonaqueous electrolyte according to claim 1.

10. The lithium secondary battery according to claim 9, wherein: The positive electrode active material comprises an over-lithium manganese-rich oxide, which comprises at least 50 mol % of Mn in all metals except lithium, and has a molar ratio of lithium to transition metal greater than 1.

11. The lithium secondary battery according to claim 10, wherein: The perlithium manganese-rich oxide is a compound represented by the following formula 6: [Formula 6] Li 1+s [Ni t Co u Mr v M 1 w ]O 2+z Among them, in the above formula 6, M 1 It is one or more selected from 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 0.05≤s≤1, 0≤t≤0.5, 0≤u≤0.3, 0.5≤v<1.0, 0≤w≤0.2 and 0≤z≤1.

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