Non-aqueous electrolytes and lithium secondary batteries containing them

Abstract

The present invention provides a lithium secondary battery including a negative electrode containing a silicon-based negative electrode active material, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte includes a lithium salt, an organic solvent, a compound represented by the following Chemical Formula 1 as a first additive, and a compound represented by the following Chemical Formula 2 as a second additive: In Chemical Formula 1, R is an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, and R1 to R3 are each independently any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group. In Chemical Formula 2, R4 to R7 are each independently any one selected from the group consisting of alkyl groups having 1 to 10 carbon atoms which may be substituted with fluorine, and alkenyl groups having 2 to 10 carbon atoms which may be substituted with fluorine. JPEG2025534118000033.jpg57170

Description

Technical Field

[0001] This application is based on Korean Patent Application No. 10-2023-0030216, filed with the Korean Intellectual Property Office on March 7, 2023, the entire contents of which are incorporated herein by reference, and claims priority therefrom.

[0002] The present invention relates to a non-aqueous electrolyte and a lithium secondary battery including the same.

Background Art

[0003] In recent years, the application fields of lithium secondary batteries have rapidly expanded not only to power supply for electronic devices such as electric, electronic, communication, and computer devices, but also to power storage and supply for large-area devices such as automobiles and power storage devices. Along with this, the demand for secondary batteries with high capacity, high output, and high stability has been increasing.

[0004] In particular, in lithium secondary batteries for automotive applications, high capacity, high output, and long-term life characteristics are important. For increasing the capacity of secondary batteries, silicon-based negative electrode active materials with high energy density but low stability can be used.

Summary of the Invention

Problems to be Solved by the Invention

[0005] As a result of conducting comprehensive research to solve the above problems, the present invention provides a lithium secondary battery that includes a negative electrode using a silicon-based negative electrode active material with low stability, and in which a non-aqueous electrolyte capable of forming a stable SEI (Solid Electrolyte Interphase) film on the negative electrode with severe volume change is included, thereby having excellent long-life characteristics, improved high-temperature storage characteristics and thermal stability, and enhanced various performances.

Means for Solving the Problems

[0006] To achieve the above objective, one embodiment of the present invention provides a lithium secondary battery comprising a negative electrode containing a silicon-based negative electrode active material, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises a lithium salt, an organic solvent, a compound of the following chemical formula 1 as a first additive, and a compound of the following chemical formula 2 as a second additive.

[0007] [ka]

[0008] In the above chemical formula 1, R is a C1-C5 alkylene group that may be substituted with fluorine, and R1-R3 are each independently selected from the group consisting of H, a C1-C5 alkyl group, and a nitrile group.

[0009] [ka]

[0010] In the above chemical formula 2, R4 to R7 are each independently selected from the group consisting of C1 to C10 alkyl groups that may be substituted with fluorine, and C2 to C10 alkenyl groups that may be substituted with fluorine.

[0011] Another embodiment of the present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent, a compound of the following chemical formula 1 as a first additive, and a compound of the following chemical formula 2 as a second additive.

[0012] [ka]

[0013] In the above chemical formula 1, R is a C1-C5 alkylene group which may be substituted with fluorine, and R1-R3 are each independently selected from the group consisting of H, a C1-C5 alkyl group, and a nitrile group. [ka] In the above chemical formula 2, R4 to R7 are each independently selected from the group consisting of C1 to C10 alkyl groups that may be substituted with fluorine, and C2 to C10 alkenyl groups that may be substituted with fluorine. [Effects of the Invention]

[0014] The compound of chemical formula 1 provided as the first additive of the present invention can form a polyethylene oxide-based polymeric SEI layer with high elasticity upon reduction, and the compound of chemical formula 2 provided as the second additive can form a polysiloxane-structured SEI layer with a high shear modulus (degree of resistance to shear stress) upon reduction.

[0015] In particular, the first additive contains a propargyl group and the second additive contains a tetravinyl group, and their presence enables the formation of a stronger polymeric coating. Furthermore, because the second additive has a cyclic siloxane structure, the reduction reaction occurs more easily compared to additives with a linear siloxane structure. In addition, the lone pairs of electrons of the imidazole present in the first additive structure promote the ring-opening reaction of the second additive, allowing for the easy formation of a polymeric coating. In other words, a synergistic effect occurs due to the combination of the first and second additives, significantly improving the durability of the coating formed on the negative electrode.

[0016] Therefore, the present invention, through the synergistic effect of the interaction between the first and second additives, makes it possible to form a stable and highly durable electrode-electrolyte interface even in lithium secondary batteries where a silicon-based negative electrode active material that undergoes drastic volume changes during charging and discharging is applied to the negative electrode, thereby suppressing unwanted electrolyte decomposition side reactions and realizing a lithium secondary battery with improved performance. [Modes for carrying out the invention]

[0017] The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0018] In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the presence of implemented features, figures, steps, components, or combinations thereof, and should be understood not to preemptively exclude the presence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0019] Furthermore, in this specification, when "a to b carbon atoms" is mentioned, "a" and "b" refer to the number of carbon atoms contained in a specific functional group. That is, the functional group may contain "a" to "b" carbon atoms. For example, "alkylene group with 1 to 5 carbon atoms" means an alkylene group containing 1 to 5 carbon atoms, i.e., -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2(CH3)CH-, -CH(CH3)CH2-, and -CH(CH3)CH2CH2-, etc.

[0020] Furthermore, in this specification, the term "alkylene group" means a branched or unbranched divalent saturated hydrocarbon group.

[0021] Furthermore, in this specification, alkyl groups may or may not be substituted. Unless otherwise defined, "substitution" means that at least one hydrogen atom bonded to a carbon atom is replaced by an element other than hydrogen.

[0022] The present invention will be described in more detail below.

[0023] Lithium-ion batteries use lithium metal oxides based on transition metals such as nickel (Ni), cobalt (Co), and manganese (Mn) as the positive electrode to achieve high energy density, and silicon-based negative electrode active materials such as silicon (Si) or silicon oxide (SiOx), which can be alloyed with lithium ions and have high theoretical capacity, can be used as the negative electrode. However, when driving a secondary battery that includes a negative electrode using a silicon-based negative electrode active material, there is a problem that the durability of the coating (e.g., SEI film) formed on the surface of the negative electrode decreases due to the drastic volume changes during repeated charging and discharging, leading to a serious decrease in capacity.

[0024] This phenomenon of capacity degradation in secondary batteries tends to accelerate when the battery is exposed to high temperatures, and this degradation leads to the problem of deterioration in the cycle characteristics of the secondary battery.

[0025] Furthermore, when lithium secondary batteries are used continuously for long periods of time or left at high temperatures, gas is generated, causing the battery to swell, a phenomenon known as swelling. It is known that the amount of gas generated at this time depends on the state of SEI (Swelling Energy Intake).

[0026] Therefore, the present invention provides a lithium secondary battery containing a non-aqueous electrolyte that can reduce the swelling phenomenon of lithium secondary batteries and improve stability at high temperatures.

[0027] [Non-aqueous electrolytes] The non-aqueous electrolyte according to the present invention may contain a lithium salt, an organic solvent, a compound of the following chemical formula 1 as a first additive, and a compound of the following chemical formula 2 as a second additive.

[0028] [ka]

[0029] In the above chemical formula 1, R is a C1-C5 alkylene group that may be substituted with fluorine, and R1-R3 are each independently selected from the group consisting of H, a C1-C5 alkyl group, and a nitrile group.

[0030] [ka]

[0031] In the above chemical formula 2, R4 to R7 are each independently selected from the group consisting of C1 to C10 alkyl groups that may be substituted with fluorine, and C2 to C10 alkenyl groups that may be substituted with fluorine.

[0032] The lithium secondary battery according to the present invention contains a compound represented by the following chemical formula 1 as a first additive in a non-aqueous electrolyte. The compound of chemical formula 1 contains a propargyl group having a triple bond and an oxygen atom, which are known to have metal ion adsorption capacity. The propargyl group, separated by bond cleavage between the nitrogen (N) atom and carbon (C) atom of the imidazole group, adsorbs metallic foreign matter such as Fe, Co, Mn, and Ni that is dissolved from the positive electrode during high-voltage charging of the lithium secondary battery, and can effectively suppress the negative electrode degradation phenomenon that occurs when these metallic foreign matter are electrodeposited onto the surface of the negative electrode. Furthermore, the lone pair of electrons of the nitrogen (N) atom of the imidazole group of the compound represented by chemical formula 1 reacts with polyvinylene carbonate, a decomposition product of fluoroethylene carbonate (FEC) used as an organic solvent, and is reduced on the surface of the negative electrode, thus forming a stable ion-conducting film on the surface of the negative electrode. Therefore, in addition to suppressing additional electrolyte decomposition reactions during the charge-discharge process, it is also possible to facilitate the intercalation and deintercalation of lithium ions from the negative electrode during overcharging or high-temperature storage, thereby improving the cycle life characteristics and high-temperature storage performance of the secondary battery.

[0033] [ka]

[0034] In the above chemical formula 1, R may be an alkylene group having 1 to 5 carbon atoms that may be substituted with fluorine, for example, an alkylene group having 1 to 3 carbon atoms.

[0035] In the above chemical formula 1, R1 to R3 may each be independently selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group, for example, one of the group consisting of H and an alkyl group having 1 to 3 carbon atoms.

[0036] As an example, the compound of chemical formula 1 may be any one selected from the group consisting of the following chemical formulas 1-1 to 1-3.

[0037] [ka]

[0038] [ka]

[0039] [ka]

[0040] The lithium secondary battery according to the present invention contains a compound represented by the following chemical formula 2 as a second additive in the non-aqueous electrolyte. The compound of chemical formula 2 readily undergoes a reduction reaction through a ring-opening reaction, allowing a polysiloxane-containing SEI layer to be formed on the negative electrode. Because the SEI layer containing the polysiloxane structure has a high shear modulus (the degree to which it can withstand shear stress), it can withstand even when the negative electrode undergoes a drastic volume change.

[0041] [ka]

[0042] In the above chemical formula 2, R4 to R7 may each be independently selected from the group consisting of C1 to C10 alkyl groups that may be substituted with fluorine, and C2 to C10 alkenyl groups that may be substituted with fluorine. For example, they may be C1 to C5 alkyl groups that may be substituted with fluorine, or C1 to C3 alkyl groups that are substituted with fluorine. When a fluorine group is substituted in the compound of chemical formula 2, an inorganic substance such as LiF can be included to form a strong and elastic polymeric coating on the electrode.

[0043] As an example, the compound of chemical formula 2 of the present invention may be any one selected from the group consisting of the following chemical formulas 2-1 to 2-3.

[0044] [ka]

[0045] [ka]

[0046] [ka]

[0047] When the non-aqueous electrolyte of the present invention, which includes the first and second additives, is used, the radicals generated by the breakdown of the ring structure of the first additive promote the film formation reaction of the second additive. The film formed by the interaction of the first and second additives has imidazole or a structure derived therefrom between the cyclic alkyl groups, forming a film morphology with excellent lithium-ion transfer characteristics, improving various performance aspects of the lithium secondary battery, such as charge-discharge characteristics and output characteristics. Because the film formed by the interaction of the first and second additives has excellent oxidation resistance, it can suppress side reactions occurring in the positive and negative electrode films even in an acidic electrolyte atmosphere. Furthermore, the film formed by the interaction of the first and second additives has excellent durability against volume changes in the negative electrode that occur during charging and discharging. Therefore, the non-aqueous electrolyte of the present invention can form an electrode-electrolyte interface that is stable and highly durable even at high temperatures, and can suppress unwanted electrolyte decomposition side reactions, thereby realizing a lithium secondary battery with improved performance.

[0048] In the non-aqueous electrolyte according to the present invention, the first additive may be present in an amount of 0.01 to 10 parts by weight per 100 parts by weight of the non-aqueous electrolyte, for example, in an amount of 0.1 to 5.0 parts by weight, or 0.5 to 3.0 parts by weight. When the content of the first additive satisfies the above range, the film-forming effect on the negative electrode is sufficient, and the long life characteristics at high temperatures and high-temperature storage characteristics are excellent.

[0049] In the non-aqueous electrolyte according to the present invention, the second additive may be present in an amount of 0.01 to 10 parts by weight per 100 parts by weight of the non-aqueous electrolyte, for example, in an amount of 0.1 to 5.0 parts by weight, or 0.5 to 3.0 parts by weight. When the content of the second additive satisfies the above range, the film-forming effect on the negative electrode is sufficient, and the long life characteristics at high temperatures and high-temperature storage characteristics are excellent.

[0050] In the non-aqueous electrolyte of the present invention, the first additive and the second additive may be contained in a weight ratio of 1:0.002 to 1:500, for example, a weight ratio of 1:0.1 to 1:10, or a weight ratio of 1:0.2 to 1:5. When the above range is satisfied, the elasticity of the SEI film becomes an appropriate range, and the SEI film can be firmly maintained during charge and discharge or at high temperatures.

[0051] The non-aqueous electrolyte according to the present invention may contain a lithium salt. The lithium salt is used as an electrolyte salt in a lithium secondary battery and is used as a mediator for transmitting ions. Usually, as the lithium salt, for example, as a cation, it contains Li + and, as an anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 -CF3CF2(CF3)2CO - (CF3SO2) 2CH - CF3(CF2)7SO3 - , and SCN - At least one of the following groups can be selected.

[0052] As an example, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10 The electrolyte may contain a single substance or a mixture of two or more substances selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiSO3CF3, LiCO2CH3, LiCO2CF3, LiAsF6, LiSbF6, LiSO3CH3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO2CF2CF3)2 (lithium bis(perfluoroethanesulfonyl)imide; LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI). In addition to these, lithium salts commonly used as electrolytes in lithium secondary batteries can be used without limitation.

[0053] The lithium salt may be appropriately changed within a range of normal use, but in order to obtain the optimal effect of forming a corrosion-preventive film on the electrode surface, it may be included in the electrolyte at a concentration of 0.5 M to 5.0 M, for example, 1.0 M to 3.0 M, or 1.2 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics during high-temperature storage of the lithium secondary battery is sufficient, and the viscosity of the non-aqueous electrolyte is appropriate, improving electrolyte impregnation.

[0054] The non-aqueous electrolyte according to the present invention may contain an organic solvent. The organic solvent may contain at least one organic solvent selected from the group consisting of cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

[0055] The additive according to the present invention is particularly effective when using a cyclic carbonate solvent. When conventional electrolyte additives are used with a cyclic carbonate solvent, the SEI film formed by the decomposition of the cyclic carbonate solvent is difficult to maintain due to the volume change of the negative electrode that occurs as the cycle progresses, and the solvent continues to decompose. This leads to a decrease in the ionic conductivity of the electrolyte and a deterioration in cycle characteristics. However, when using a combination of the additive according to the present invention with a cyclic carbonate solvent, a strong SEI film can be formed, and the cycle characteristics are maintained at a high level.

[0056] The aforementioned cyclic carbonate-based organic solvent is a highly viscous organic solvent with a high dielectric constant that readily dissociates lithium salts in the electrolyte. Specific examples include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, and among these, fluoroethylene carbonate (FEC) may be included. When fluoroethylene carbonate is used as the organic solvent, FEC exhibits excellent reducing properties, and interaction occurs with the first and second additives, allowing for the formation of a stronger film on the silicon-based negative electrode, which undergoes drastic volume changes during charging and discharging.

[0057] Furthermore, the linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and as a typical example, at least one organic solvent 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 may be used, and among these, ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) may be included.

[0058] Furthermore, in order to produce an electrolyte having high ionic conductivity, the organic solvent may further contain at least one ester organic solvent selected from the group comprising at least one linear ester organic solvent and at least one cyclic ester organic solvent, in addition to at least one carbonate organic solvent selected from the group comprising at least one cyclic carbonate organic solvent and at least one linear carbonate organic solvent.

[0059] Examples of such linear ester-based organic solvents include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0060] Furthermore, the cyclic ester organic solvents include at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0061] On the other hand, the organic solvent may be further used with any organic solvent commonly used for non-aqueous electrolytes, without limitation, as needed. For example, it may further contain at least one or more organic solvents such as ether-based organic solvents, glyme-based solvents, and nitrile-based organic solvents.

[0062] The ether-based solvent can be 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 of these, but is not limited to these.

[0063] The aforementioned glyme-based solvent is a solvent that has a higher dielectric constant and lower surface tension than linear carbonate-based organic solvents, and has low reactivity with metals. It may include, but is not limited to, at least one selected from the group consisting of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME).

[0064] The nitrile solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited to these.

[0065] Furthermore, the non-aqueous electrolyte of the present invention may, if necessary, further contain known electrolyte additives in order to prevent the non-aqueous electrolyte from decomposing in a high-power environment, which can cause the collapse of the negative electrode, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery swelling at high temperatures.

[0066] Such other electrolyte additives may include, for example, at least one SEI film-forming additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0067] Examples of the aforementioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate.

[0068] Examples of halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0069] Examples of the sultone compounds include at least one compound selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethensultone, 1,3-propensultone (PRS), 1,4-butensultone, and 1-methyl-1,3-propensultone.

[0070] Examples of the sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0071] Examples of the phosphate compound include one or more compounds selected from the group consisting of lithium difluoro(bisoxalato) phosphate, lithium difluorophosphate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(2,2,2-trifluoroethyl) phosphite.

[0072] Examples of the borate compounds include tetraphenyl borate, lithium difluoro(oxalate) borate (LiODFB), and lithium bisoxalate borate (LiB(C2O4)2, LiBOB).

[0073] Examples of the nitrile compounds include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0074] Examples of the benzene-based compound include fluorobenzene, examples of the amine-based compound include triethanolamine or ethylenediamine, and examples of the silane-based compound include tetravinylsilane.

[0075] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples include lithium difluorophosphate (LiDFP), LiPO2F2, or LiBF4.

[0076] If the other electrolyte additives further include a combination of vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (Esa), and lithium difluorophosphate (LiDFP), an even stronger SEI film can be formed on the surface of the negative electrode during the initial activation process of the secondary battery. This suppresses the generation of gases that may be produced by the decomposition of the electrolyte at high temperatures, thereby improving the high-temperature stability of the secondary battery compared to conventional secondary batteries.

[0077] On the other hand, two or more of the other electrolyte additives may be used in mixture form, and may be present in an amount of 0.050% to 20% by weight, for example, 0.10% to 15% by weight, or 0.30% to 10% by weight, based on the total weight of the non-aqueous electrolyte. When the content of the other electrolyte additives satisfies the above range, a better improvement in ionic conductivity and cycle characteristics can be obtained compared to conventional lithium-ion batteries.

[0078] [Lithium-ion secondary battery] The present invention also provides a lithium secondary battery containing the above-mentioned non-aqueous electrolyte.

[0079] For example, the lithium secondary battery according to the present invention includes a negative electrode containing a silicon-based negative electrode active material, a positive electrode, a separator, and the aforementioned non-aqueous electrolyte.

[0080] In this case, the lithium secondary battery of the present invention can be manufactured by conventional methods known in the art. For example, it can be manufactured by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator between the positive and negative electrodes are sequentially stacked, inserting the electrode assembly into a battery case, and injecting the non-aqueous electrolyte according to the present invention.

[0081] The positive electrode included in the lithium secondary battery of the present invention can be manufactured by coating a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive material, and a solvent onto a positive electrode current collector.

[0082] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. Furthermore, the bonding force of the positive electrode active material may be strengthened by forming fine irregularities on the surface, and it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0083] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may include a lithium metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum, and lithium. For example, the lithium metal oxide may be a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-manganese-cobalt-based oxide (e.g., Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), or a lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc.), and any one or two or more of these compounds may be included.

[0084] In particular, nickel-cobalt-manganese oxide may be used as the lithium metal oxide because it can improve the capacity characteristics and stability of the battery.

[0085] For example, the lithium nickel cobalt manganese oxide may have a composition represented by the following chemical formula 3.

[0086] [Chemical formula 3] Li x Ni a Co b M 1 c M 2 d O2

[0087] In the above chemical formula 3, the above M 1 This may be Mn, or a combination of Mn and Al, for example, a combination of Mn and Al from the viewpoint of enhancing structural stability.

[0088] In the above chemical formula 3, the above M 2 This may be one or more elements selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb.

[0089] The above x represents the atomic fraction of lithium in the lithium nickel cobalt manganese oxide, and may be 0.90 ≤ x ≤ 1.1, for example, 0.95 ≤ x ≤ 1.08, or 1.0 ≤ x ≤ 1.08.

[0090] The above 'a' represents the atomic fraction of nickel among the metallic elements excluding lithium in the lithium nickel cobalt manganese oxide, and may be 0.80 ≤ a < 1.0, for example, 0.80 ≤ a ≤ 0.95, or 0.80 ≤ a ≤ 0.90. When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0091] The above b represents the atomic fraction of cobalt among the metallic elements excluding lithium in the lithium nickel cobalt manganese oxide, and 0 <b<0.2、0<b≦0.15、または0.01≦b≦0.10であってよい。

[0092] The aforementioned c is M, which is the metallic element in lithium nickel cobalt manganese oxide excluding lithium. 1 It represents the atomic fraction of 0 <c<0.2、0<c≦0.15、または0.01≦c≦0.10であってよい。

[0093] The above d is M, which is the metallic element in lithium nickel cobalt manganese oxide excluding lithium. 2 This represents the atomic fraction, and may be either 0≦d≦0.1 or 0≦d≦0.05.

[0094] The positive electrode active material may be present in an amount of 60-99% by weight, for example, 70-99% by weight or 80-98% by weight, based on the total weight of the solid matter in the positive electrode mixture slurry excluding the solvent.

[0095] The aforementioned binder is a component that assists in the bonding of the active material to the conductive material and to the current collector.

[0096] Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers.

[0097] Typically, the binder may be present in an amount of 1% to 20% by weight, for example, 1% to 15% by weight, or 1% to 10% by weight, based on the total weight of the solids in the positive electrode mixture slurry excluding the solvent.

[0098] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 1% to 20% by weight based on the total weight of the solid content in the negative electrode slurry. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and may be used, for example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a well-developed crystalline structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive 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.

[0099] Typically, the conductive material may be included in an amount of 1% to 20% by weight, for example, 1% to 15% by weight, or 1% to 10% by weight, based on the total weight of the solid matter in the positive electrode mixture slurry excluding the solvent.

[0100] The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone) and may be used in an amount that results in a suitable viscosity when the positive electrode active material and selectively include a binder and conductive material. For example, the concentration of the solid content containing the positive electrode active material and selectively including the binder and conductive material may be 50% to 95% by weight, for example, 70% to 95% by weight, or 70% to 90% by weight.

[0101] The negative electrode included in the lithium secondary battery of the present invention can be manufactured by coating a negative electrode mixture slurry containing a negative electrode active material, a binder, a conductive material, and a solvent onto a negative electrode current collector.

[0102] For example, when manufacturing a negative electrode by coating a negative electrode active material slurry on the negative electrode current collector, the negative electrode current collector generally has a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. may be used. Also, similar to the positive electrode current collector, the binding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc.

[0103] Further, the negative electrode of the present invention is characterized by containing a silicon-based negative electrode active material. When using a silicon-based negative electrode active material, a lithium secondary battery having a high energy density can be provided. The silicon-based negative electrode active material may be Si or SiO x (0 < x ≤ 2), and for example, when the negative electrode active material is made of Si, the highest energy density can be provided. When using a negative electrode active material based on Si, if a strong SEI layer is not formed on the surface of the negative electrode during initial activation, the decrease in life characteristics is promoted due to the intense volume expansion and contraction during cycling. However, the lithium secondary battery of the present invention has elasticity and can form a strong SEI layer, so that excellent life characteristics and storage characteristics can be provided while using a negative electrode active material based on Si.

[0104] The negative electrode active material may be contained in an amount of 60% by weight to 99% by weight, for example, 70% by weight to 99% by weight, or 80% by weight to 98% by weight, based on the total weight of the solid content in the negative electrode active material slurry.

[0105] Examples of the aforementioned binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof. Due to its high viscosity, styrene-butadiene rubber (SBR)-carboxymethylcellulose (CMC) can be used.

[0106] Typically, the binder may be present in an amount of 1% to 20% by weight, for example, 1% to 15% by weight, or 1% to 10% by weight, based on the total weight of the solid matter in the negative electrode mixture slurry excluding the solvent.

[0107] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 1% to 20% by weight based on the total weight of the solid content in the negative electrode mixture slurry. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and may be used, for example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a well-developed crystalline structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive 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.

[0108] The conductive material may be present in an amount of 1% to 20% by weight, for example, 1% to 15% by weight, or 1% to 10% by weight, based on the total weight of the solid matter in the negative electrode mixture slurry excluding the solvent.

[0109] The solvent may include water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that results in a suitable viscosity when the negative electrode active material and selectively include binders and conductive materials. For example, the concentration of solids containing the negative electrode active material and selectively including binders and conductive materials may be 50% to 95% by weight, for example, 70% to 90% by weight.

[0110] As the separator, conventional porous polymer films used as separators, such as porous polymer films made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, may be used alone or in laminated form. Alternatively, conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used, but are not limited to these. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be used selectively as single-layer or multi-layer structures.

[0111] For example, the separator comprises a porous separator substrate and a porous coating layer that coats one or both sides of the separator substrate, wherein the coating layer may comprise a mixture of inorganic particles selected from metal oxides, metalloid oxides, metal fluorides, metal hydroxides, and combinations thereof, and a binder polymer that links and fixes the inorganic particles together.

[0112] The coating layer may contain one or more inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, and MgF. Here, the inorganic particles can improve the thermal stability of the separator. That is, the inorganic particles can prevent the separator from shrinking at high temperatures. Furthermore, the binder polymer can fix the inorganic particles and improve the mechanical stability of the separator.

[0113] The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, rectangular, pouch-shaped, or coin-shaped, for example, having a circular or square cross-section.

[0114] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative for understanding the present invention and are not intended to limit the scope of the invention. It will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the described concept and technical idea, and it goes without saying that such variations and modifications fall within the scope of the appended claims.

[0115] [Examples] Example 1 (Manufacturing of non-aqueous electrolytes) A non-aqueous solvent was prepared by dissolving LiPF6 in an organic solvent (fluoroethylene carbonate (FEC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) = 20:70:10 volume ratio) to a concentration of 1.3 M. A non-aqueous electrolyte was prepared by adding 0.1 g of the compound of chemical formula 1-1 and 0.1 g of the compound of chemical formula 2-1 to 99.8 g of the non-aqueous solvent.

[0116] [ka]

[0117] [ka]

[0118] (Manufacturing of lithium-ion batteries) Cathode active material (LiNi 0.85 Co 0.05 Mn 0.08 Al 0.02 A positive electrode slurry (solid content 75.5% by weight) was prepared by adding O2, a conductive material (carbon nanotube), and a binder (polyvinylidene fluoride) in a weight ratio of 97.74:0.7:1.56 to the solvent N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was applied to one surface of a 15 μm thick positive electrode current collector (a thin Al film), and the positive electrode was manufactured by drying and roll pressing.

[0119] A negative electrode slurry (26% solids by weight) was prepared by adding a negative electrode active material (silicon; Si), a conductive material (carbon black), and a binder (styrene-butadiene rubber (SBR)-carboxymethylcellulose (CMC)) in a weight ratio of 70:20.3:9.7 to the solvent N-methyl-2-pyrrolidone (NMP). The negative electrode slurry was applied to one surface of a 15 μm thick negative electrode current collector (Cu thin film), and the negative electrode was manufactured by drying and roll pressing.

[0120] In a dry room, a polyolefin-based porous separator coated with inorganic Al2O3 particles was interposed between the positive and negative electrodes manufactured as described above, and then the non-aqueous electrolyte manufactured as described above was injected to produce a secondary battery.

[0121] Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 0.1 g of the compound of chemical formula 1-1 and 5 g of the compound of chemical formula 2-1 to 94.9 g of the non-aqueous solvent prepared in Example 1.

[0122] Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 5 g of the compound of chemical formula 1-1 and 0.1 g of the compound of chemical formula 2-1 to 94.9 g of the non-aqueous solvent prepared in Example 1.

[0123] Example 4 A secondary battery was manufactured in the same manner as in Example 1, except that a nonaqueous electrolyte was produced by adding 2 g of the compound of chemical formula 1-1 and 2 g of the compound of chemical formula 2-1 to 96 g of the nonaqueous solvent produced in Example 1.

[0124] Example 5 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 0.1 g of the compound of chemical formula 1-2 and 0.1 g of the compound of chemical formula 2-1 to 99.8 g of the non-aqueous solvent prepared in Example 1.

[0125] [ka]

[0126] Example 6 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 0.1 g of the compound of chemical formula 1-3 and 0.1 g of the compound of chemical formula 2-1 to 99.8 g of the non-aqueous solvent prepared in Example 1.

[0127] [ka]

[0128] Example 7 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 0.1 g of the compound of chemical formula 1-1 and 0.1 g of the compound of chemical formula 2-2 to 99.8 g of the non-aqueous solvent prepared in Example 1.

[0129] [ka]

[0130] Example 8 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 0.1 g of the compound of chemical formula 1-1 and 0.1 g of the compound of chemical formula 2-3 to 99.8 g of the non-aqueous solvent prepared in Example 1.

[0131] [ka]

[0132] Comparative Example 1 A secondary battery was manufactured in the same manner as in Example 1, except that 0.1 g of the compound of chemical formula 1-1 was added to 99.9 g of the non-aqueous solvent prepared in Example 1 to produce a non-aqueous electrolyte.

[0133] Comparative Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that 5 g of the compound of chemical formula 1-1 was added to 95 g of the non-aqueous solvent prepared in Example 1 to produce a non-aqueous electrolyte.

[0134] Comparative Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that 0.1 g of the compound of chemical formula 2-1 was added to 99.9 g of the non-aqueous solvent prepared in Example 1 to produce a non-aqueous electrolyte.

[0135] Comparative Example 4 A secondary battery was manufactured in the same manner as in Example 1, except that 5 g of the compound of chemical formula 2-1 was added to 95 g of the non-aqueous solvent prepared in Example 1 to produce a non-aqueous electrolyte.

[0136] [Experimental Example 1 - Evaluation of High-Temperature Cycle Characteristics] The cycle characteristics of each secondary battery manufactured in Examples 1-8 and Comparative Examples 1-4 were evaluated.

[0137] For example, each battery manufactured in Examples 1-8 and Comparative Examples 1-4 was charged at 45°C at a rate of 0.33C to 4.2V under constant current / constant voltage conditions (0.05C cutoff), and discharged to 3.0V at a constant current of 0.33C. This constituted one cycle, and after 200 charge-discharge cycles, the capacity retention rate after 200 cycles relative to the initial capacity after one cycle was measured. In addition, the resistance increase rate after 200 cycles relative to the initial resistance after one cycle was measured. The results are shown in Table 1 below.

[0138] [Table 1]

[0139] [Experimental Example 2 - Evaluation of High-Temperature Storage Characteristics] The high-temperature storage characteristics were evaluated for each secondary battery manufactured in Examples 1-8 and Comparative Examples 1-4.

[0140] For example, after fully charging each of the secondary batteries in Examples 1-8 and Comparative Examples 1-4 to 4.2V, they were stored at 60°C for 8 weeks.

[0141] Before saving, the capacity of the fully charged rechargeable battery was measured and set as the initial capacity of the rechargeable battery.

[0142] After 8 weeks, the capacity of the stored secondary batteries was measured, and the decrease in capacity during the 8-week storage period was calculated. The capacity retention rate after 8 weeks was derived by calculating the percentage of the decreased capacity relative to the initial capacity of the secondary batteries. In addition, the resistance increase rate after 8 weeks was derived by calculating the percentage of the increased resistance relative to the initial resistance of the secondary batteries. The results are shown in Table 2 below.

[0143] [Table 2]

[0144] [Experimental Example 3 - Evaluation of Thermal Stability] The thermal stability of each secondary battery manufactured in Examples 1-8 and Comparative Examples 1-4 was evaluated.

[0145] For example, after performing a formation process on the lithium secondary batteries manufactured in the above examples and comparative examples, they were charged at 25°C at a rate of 0.33C to 4.2V under constant current / constant voltage conditions (0.05C cutoff) until they were fully charged to 100% of the State of Charge (SOC). After the fully charged batteries were heated to 140°C at a heating rate of 5°C / min, they were left for 1 hour, and a hot box evaluation experiment was conducted to check for ignition. If no ignition occurred, it was evaluated as Pass, and if ignition occurred, it was evaluated as Fail. The results are shown in Table 3 below.

[0146] [Table 3]

Claims

1. A lithium secondary battery comprising a negative electrode containing a silicon-based negative electrode active material, a positive electrode, a separator, and a non-aqueous electrolyte, The non-aqueous electrolyte comprises a lithium salt, an organic solvent, a compound of the following chemical formula 1 as a first additive, and a compound of the following chemical formula 2 as a second additive, in a lithium secondary battery. 【Chemistry 1】 (In the above chemical formula 1, R is an alkylene group having 1 to 5 carbon atoms that may be substituted with fluorine. R １ ~R ３ Each of these is independently selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group. 【Chemistry 2】 In the aforementioned chemical formula 2, R ４ ~R ７ Each of these is independently selected from the group consisting of an alkyl group having 1 to 10 carbon atoms that may be substituted with fluorine, and an alkenyl group having 2 to 10 carbon atoms that may be substituted with fluorine.

2. The lithium secondary battery according to claim 1, wherein the compound of chemical formula 1 is one selected from the group consisting of the following chemical formulas 1-1 to 1-3. 【Transformation 3】 【Chemistry 4】 【Transformation 5】

3. The lithium secondary battery according to claim 1, wherein the compound of chemical formula 2 is one selected from the group consisting of the following chemical formulas 2-1 to 2-3. 【Transformation 6】 【Transformation 7】 【Transformation 8】

4. The lithium secondary battery according to claim 1, wherein the first additive is contained in an amount of 0.01 to 10 parts by weight per 100 parts by weight of the non-aqueous electrolyte.

5. The lithium secondary battery according to claim 1, wherein the second additive is contained in an amount of 0.01 to 10 parts by weight per 100 parts by weight of the non-aqueous electrolyte.

6. The lithium secondary battery according to claim 1, wherein the first additive and the second additive are contained in a weight ratio of 1:0.002 to 1:

500.

7. The lithium salt is LiCl, LiBr, LiI, LiBF ４ , LiClO ４ , LiB １０ Cl １０ , LiAlCl ４ , LiAlO ２ , LiPF ６ , LiSO ３ CF ３ , LiCO ２ CH ３ , LiCO ２ CF ３ , LiAsF ６ , LiSbF ６ , LiSO ３ CH ３ , LiN(SO ２ F) ２ , LiN(SO ２ CF ２ CF ３ ) ２ , and LiN(SO ２ CF ３ ) ２ The lithium secondary battery according to claim 1, which is one or more selected from the group consisting of

8. The lithium secondary battery according to claim 1, wherein the lithium salt is contained in a concentration of 0.5 M to 5.0 M.

9. The lithium secondary battery according to claim 1, wherein the organic solvent comprises at least one organic solvent selected from the group consisting of cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

10. The lithium secondary battery according to claim 9, wherein the organic solvent comprises fluoroethylene carbonate.

11. The lithium secondary battery according to claim 1, wherein the silicon-based negative electrode active material is Si.

12. The lithium secondary battery according to claim 1, wherein the positive electrode contains a lithium nickel cobalt manganese oxide as the positive electrode active material.

13. The lithium secondary battery according to claim 12, wherein the lithium nickel cobalt manganese oxide has a composition represented by the following chemical formula 3. [Chemical formula 3] Li ｘ Ni ａ Co ｂ M １ ｃ M ２ ｄ O ２ (In the above chemical formula 3, M １ M is Mn, or a combination of Mn and Al, ２ (where x is one or more elements selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and the following conditions apply: 0.90 ≤ x ≤ 1.1, 0.80 ≤ a < 1.0, 0 < b < 0.2, 0 < c < 0.2, 0 ≤ d ≤ 0.1).

14. An electronic device comprising a lithium secondary battery as described in claim 11.

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