Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery containing the same

Abstract

The present invention provides a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery containing the same. The non-aqueous electrolyte for a lithium secondary battery of the present invention contains a lithium salt, an organic solvent, and a compound represented by Chemical Formula 1 as a first additive, thereby improving the high-temperature storage characteristics of the secondary battery.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0089164 filed on July 19, 2022, and all the contents disclosed in the literature of the Korean patent application are incorporated herein by reference in their entirety.

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

Background Art

[0003] In modern society, as the dependence on electric energy is increasing, the development of a large-capacity power storage device that can stably supply electric power and increase the production amount has attracted attention.

[0004] Lithium-ion batteries are devices that exhibit the highest energy density among commercially available power storage devices and are used in various applications such as small electronic devices, electric vehicles (EVs), and power storage devices. In particular, lithium-ion batteries applied to electric vehicles are required to maintain cycle characteristics and performance in various environments and have high output characteristics.

[0005] In order to improve the energy density of such lithium secondary batteries, research is actively being conducted to develop a positive electrode active material and a negative electrode active material having a high theoretical capacity.

[0006] On the other hand, research is underway to apply Si or SiO x (0 < x < 2) having a higher theoretical capacity than graphite currently used in commercially available batteries as a negative electrode active material.

[0007] However, silicon-based negative electrode active materials undergo rapid volume changes and swelling due to changes in crystal structure caused by repeated electrochemical charge and discharge or by the intercalation and deintercalation of lithium ions during high-temperature storage. This leads to severe battery degradation due to film cracking and deterioration caused by such volume changes. In particular, the SEI formed while carbonate-based non-aqueous solvents are decomposed has a high solubility in the electrolyte, causing side reactions with the electrolyte, and has low elasticity, making it difficult to maintain the film during the volume expansion of the negative electrode, thus causing battery degradation.

[0008] Therefore, when applying silicon-based negative electrode active materials, in order to solve the problem of degradation caused by the volume expansion of silicon-based negative electrode active materials, research and development are required to form a stable SEI on the surface of the negative electrode that can withstand the volume change of Si.

Summary of the Invention

Problems to be Solved by the Invention

[0009] An object of the present invention is to provide a non-aqueous electrolyte for a lithium secondary battery containing an additive capable of forming a strong film on the surface of a silicon-based negative electrode.

[0010] Another object of the present invention is to provide a lithium secondary battery having improved high-temperature storage characteristics and high-temperature cycle characteristics by including the non-aqueous electrolyte for a lithium secondary battery.

Means for Solving the Problems

[0011] In one embodiment of the present invention for achieving the above object, it includes a lithium salt, a non-aqueous organic solvent, and a first additive, and provides a non-aqueous electrolyte for a lithium secondary battery containing, as the first additive, a compound represented by the following Chemical Formula 1.

[0012]

Chem.

[0013] In the formula (1), R1 to R6 are each independently hydrogen, an alkyl group having 1 to 5 carbon atoms, or -(R’)n-C≡CH, where R’ is an alkylene group having 1 to 5 carbon atoms, n is an integer from 0 to 3, and at least one of R1 to R6 is -(R’)n-C≡CH.

[0014] Another embodiment of the present invention is to provide a lithium secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte for the lithium secondary battery.

[0015] The negative electrode may include a silicon-based negative electrode active material.

Advantages of the Invention

[0016] The non-aqueous electrolyte of the present invention contains, as an additive, a compound containing a propargyl group capable of forming a strong SEI on the surface of the electrode and a trioxane functional group excellent in elastic force and lithium ion conductivity, thereby forming a strong film based on a polyoxymethylene (POM) structure and a polymeric ether group on the surface of the silicon-based negative electrode, and improving the durability against volume change of the silicon-based negative electrode active material.

[0017] When such a non-aqueous electrolyte of the present invention is applied, a lithium secondary battery with improved cycle characteristics and high-temperature storage stability can be realized.

Modes for Carrying Out the Invention

[0018] Hereinafter, the present invention will be described in more detail.

[0019] The terms and words used in this specification and the claims are merely for explaining exemplary embodiments and are not intended to limit the present invention.

[0020] For example, in this specification, terms such as "comprising", "including", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and other parts may be added unless "only" is used.

[0021] Also, in this specification, "%" means weight % unless otherwise explicitly indicated.

[0022] In this specification, "substitution" means that at least one hydrogen bonded to carbon is substituted with an element other than hydrogen, unless otherwise defined. For example, it means being substituted with an alkyl group having 1 to 5 carbon atoms or a fluorine element.

[0023] Among conventional negative electrode materials for lithium-ion batteries, silicon-based negative electrode active materials have the advantage of excellent capacity per unit weight. However, with repeated charge and discharge, significant volume expansion (more than 300%) and contraction occur due to the intercalation and deintercalation of lithium ions, resulting in the cracking of the silicon-based negative electrode active material, the destruction of the SEI film formed on the negative electrode surface, and the continuous exposure of the surface of the silicon-based negative electrode active material to the electrolyte, leading to severe consumption of the lithium ion source. In addition, due to such side reactions, a thick and unstable film is formed at the interface between silicon and the electrolyte, which has limitations in commercialization.

[0024] In order to solve the above problems, the inventors of the present invention provide a non-aqueous electrolyte for a lithium secondary battery that can form a strong SEI on a silicon-based negative electrode by improving the composition of additives contained in the electrolyte, and aim to provide a lithium secondary battery with improved high-rate charge and discharge at high temperatures using the same.

[0025] Non-aqueous electrolyte for lithium secondary battery Specifically, one embodiment of the present invention is comprising a lithium salt, a non-aqueous organic solvent, and a first additive, Provided is a non-aqueous electrolyte for a lithium secondary battery, which contains a compound represented by the following chemical formula 1 as the first additive.

[0026]

Chem.

[0027] In the chemical formula 1, R1 to R6 are each independently hydrogen, an alkyl group having 1 to 5 carbon atoms, or -(R’)n-C≡CH, where R’ is an alkylene group having 1 to 5 carbon atoms, n is an integer of 0 to 3, and at least one of R1 to R6 is -(R’)n-C≡CH.

[0028] (1) Lithium salt First, in the non-aqueous electrolyte for a lithium secondary battery of the present invention, the lithium salt can be used without limitation as long as it is commonly used in electrolytes for lithium secondary batteries. For example, as the cation, it contains Li + and as the anion, there are F - , Cl-, Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO4 - , 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 selected from the group consisting of

[0029] Specifically, the lithium salt may include a single substance or a mixture of two or more selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2 (lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethane sulfonyl)imide, LiTFSI). Specifically, it may include at least one selected from the group consisting of LiBF4, LiPF6, LiN(SO2F)2 (Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2 (lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethane sulfonyl)imide, LiTFSI). In addition to these, lithium salts commonly used in the electrolyte of lithium secondary batteries can be used without limitation.

[0030] The lithium salt can be appropriately changed within the range that can be normally used. However, in order to obtain the effect of forming an optimal coating for preventing corrosion of the electrode surface, it may be contained in the electrolytic solution at a concentration of 0.8 M to 3.0 M, specifically at a concentration of 1.0 M to 2.0 M, preferably at a concentration of 1.0 M to 1.8 M.

[0031] When the concentration of the lithium salt is within the above range, the viscosity of the non-aqueous electrolytic solution can be controlled so as to realize optimal impregnability, the mobility of lithium ions can be improved, and the capacity characteristics and cycle characteristics of the lithium secondary battery can be improved.

[0032] (2) Non-aqueous organic solvent Moreover, the description of the non-aqueous organic solvent is as follows.

[0033] As the non-aqueous organic solvent, various organic solvents usually used in non-aqueous electrolytic solutions can be used without limitation, and decomposition due to oxidation reactions and the like during the charge and discharge process of the secondary battery can be minimized, and the type is not limited as long as it can exhibit the desired characteristics together with the additive.

[0034] Specifically, the non-aqueous organic solvent may include (i) a cyclic carbonate-based organic solvent, (ii) a linear carbonate-based organic solvent, or (iii) a mixed organic solvent thereof.

[0035] The (i) cyclic carbonate-based organic solvent is a high-viscosity organic solvent that easily dissociates the lithium salt in the non-aqueous electrolytic solution due to its high dielectric constant. Specific examples thereof 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. Among them, at least one of ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC) that can form a more stable SEI on the surface of the Si negative electrode may be included.

[0036] The (ii) linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant. Specific examples thereof 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. Specifically, it may include at least one of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0037] In addition, in order to ensure high ionic conductivity, the non-aqueous organic solvent may include a mixed organic solvent containing (i) a cyclic carbonate-based organic solvent and (ii) a linear carbonate-based organic solvent in a volume ratio of 10:90 to 50:50, specifically, 20:80 to 40:60.

[0038] On the other hand, in order to produce an electrolyte having high ionic conductivity, the non-aqueous organic solvent may further include at least one organic solvent of (iv) a linear ester-based organic solvent and (v) a cyclic ester-based organic solvent, which has a lower melting point and higher stability at high temperature compared to the cyclic carbonate-based organic solvent and / or the linear carbonate-based organic solvent.

[0039] Typical examples of the (iv) linear ester-based organic solvent may 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. Specifically, it may include at least one of ethyl propionate and propyl propionate.

[0040] The (iv) cyclic ester-based organic solvent may include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0041] On the other hand, the non-aqueous organic solvent can be used by adding, without limitation, an organic solvent commonly used in electrolytes for lithium secondary batteries as needed. For example, it may further contain at least one organic solvent selected from ether-based organic solvents, amide-based organic solvents, and nitrile-based organic solvents.

[0042] On the other hand, the remainder of the non-aqueous electrolyte of the present invention, excluding the lithium salt, the first additive, and other additives, may all contain a non-aqueous organic solvent unless otherwise specified.

[0043] (3) First additive The non-aqueous electrolyte of the present invention may contain, as the first additive, a compound represented by the following Chemical Formula 1.

[0044] [Chemical formula]

[0045] In Chemical Formula 1, R1 to R6 are each independently hydrogen, an alkyl group having 1 to 5 carbon atoms, or -(R')n-C≡CH, where R' is an alkylene group having 1 to 5 carbon atoms, n is an integer of 0 to 3, and at least one of R1 to R6 is -(R')n-C≡CH.

[0046] The compound represented by Chemical Formula 1 contained as the first additive is a compound containing both a propargyl group capable of forming a strong SEI in its structure and a trioxane functional group excellent in elastic force and lithium ion conductivity. While being reductively decomposed prior to the organic solvent during charge and discharge, it can form a stable and elastic SEI based on a polyoxymethylene (POM) polymer structure and an ether group on the surface of the silicon-based negative electrode, thus suppressing the cracking of the SEI due to the contraction and expansion of the silicon-based negative electrode active material. In particular, since the SEI based on the polyoxymethylene polymer structure and the ether group is thermally stable, it prevents side reactions caused by the direct contact between the lithium ions stored in the silicon-based negative electrode and the electrolyte at high temperatures, and can improve the high-temperature durability of the lithium secondary battery, such as cycle characteristics and capacity characteristics.

[0047] Specifically, in Chemical Formula 1, R1 to R6 are each independently hydrogen, an alkyl group having 1 to 3 carbon atoms, or -(R’)n-C≡CH, where R’ is an alkylene group having 1 to 3 carbon atoms, n is an integer from 0 to 3, and at least one of R1 to R6 may be -(R’)n-C≡CH.

[0048] Also, in Chemical Formula 1, R1, R3, and R5 are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, R2, R4, and R6 are each independently an alkyl group having 1 to 3 carbon atoms or -(R’)n-C≡CH, where R’ is an alkylene group having 1 to 3 carbon atoms, n is an integer from 0 to 3, and at least one of R2, R4, and R6 may be -(R’)n-C≡CH.

[0049] Also, in Chemical Formula 1, R1, R3, and R5 are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, and R2, R4, and R6 are -(R’)n-C≡CH, where R’ is an alkylene group having 1 to 3 carbon atoms and n may be an integer from 0 to 3.

[0050] Specifically, examples of the compound represented by Chemical Formula 1 include at least one of the compounds represented by the following Chemical Formula 1A-1 to Chemical Formula 1A-3. Preferably, the compound represented by Chemical Formula 1 may be a compound represented by the following Chemical Formula 1A-1 or Chemical Formula 1A-3 in which a relatively large number of propargyl groups having an excellent film-forming effect are substituted as compared with the compound represented by Chemical Formula 1A-2. More preferably, it may be a compound represented by Chemical Formula 1A-1 in which the largest number of propargyl groups are substituted.

[0051]

Chem.

[0052]

Chem.

[0053]

Chem.

[0054] On the other hand, the compound of Chemical Formula 1 may be contained in an amount of 0.1% by weight to 10.0% by weight based on the total weight of the non-aqueous electrolyte.

[0055] When the compound represented by Chemical Formula 1 is contained within the above range, side reactions due to excessive additives can be prevented, a strong film can be formed on the surface of the silicon-based negative electrode, and deterioration of the negative electrode during rapid charge and discharge can be effectively prevented. Therefore, a secondary battery with improved performance can be manufactured.

[0056] Specifically, when the content of the compound represented by Chemical Formula 1 is 0.1% by weight or more, the effect of film formation on the surface of the negative electrode can be more stably maintained during the driving time of the battery. Further, when the content of the compound represented by Chemical Formula 1 is 10.0% by weight or less, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnability, the increase in battery resistance due to the decomposition of the additive can be effectively suppressed, and the ionic conductivity of the electrolyte is not decreased, so that the deterioration of rate characteristics and low-temperature life characteristics can be prevented.

[0057] More specifically, the compound represented by Chemical Formula 1 may be contained in an amount of 0.1% to 7.0% by weight, more preferably 0.1% to 5.0% by weight.

[0058] (4) Second additive In addition, the non-aqueous electrolyte for a lithium secondary battery of the present invention may further contain a second additive in the non-aqueous electrolyte as needed to prevent the non-aqueous electrolyte from decomposing in a high-output environment and causing the collapse of the negative electrode, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, battery expansion suppression effect at high temperatures, and the like.

[0059] Such a second additive may include at least one second 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.

[0060] Examples of the cyclic carbonate compound include vinylene carbonate (VC) or vinyl ethylene carbonate.

[0061] Examples of the halogen-substituted carbonate compound include fluoroethylene carbonate (FEC).

[0062] Examples of the sultone compounds include at least one compound selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethenesultone, 1,3-propenesultone (PRS), 1,4-butenesultone, and 1-methyl-1,3-propenesultone.

[0063] Examples of the sulfate compounds include ethylene sulfate (Ethylene Sulfate; Esa), trimethylene sulfate (Trimethylene sulfate; TMS), or methyl trimethylene sulfate (Methyl trimethylene sulfate; MTMS).

[0064] Examples of the phosphate compounds include one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphate.

[0065] Examples of the borate compounds include tetraphenylborate and lithium oxalyldifluoroborate.

[0066] Examples of the nitrile compounds include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0067] Examples of the benzene-based compound include fluorobenzene, examples of the amine-based compound include triethanolamine or ethylenediamine, and an example of the silane-based compound is tetravinylsilane.

[0068] Examples of the lithium salt-based compound include one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2)), and LiBF4 as compounds different from the lithium salt contained in the non-aqueous electrolyte.

[0069] When vinylene carbonate, vinyl ethylene carbonate, or succinonitrile is included among such second additives, a stronger SEI film can be formed on the surface of the negative electrode during the initial activation process of the secondary battery.

[0070] On the other hand, two or more of the second additives can be mixed and used, and they may be contained in an amount of 50% by weight or less, specifically 0.01% by weight to 10% by weight, preferably 0.05% by weight to 5.0% by weight, based on the total weight of the non-aqueous electrolyte. When the content of the second additive is less than 0.01% by weight, the effects of improving the low-temperature output of the battery and the high-temperature storage characteristics and high-temperature life characteristics are slight. When the content of the second additive exceeds 50% by weight, side reactions in the electrolyte may occur excessively during charge and discharge of the battery. In particular, when the additive for forming the SEI film is added in excess, it may not be sufficiently decomposed at high temperatures and may exist as unreacted substances or remain precipitated in the electrolyte at room temperature. Therefore, there is a risk of side reactions that reduce the life or resistance characteristics of the secondary battery.

[0071] Lithium secondary battery Furthermore, still another embodiment of the present invention provides a lithium secondary battery including the non-aqueous electrolyte for a lithium secondary battery of the present invention.

[0072] On one hand, the lithium secondary battery of the present invention can be manufactured by forming an electrode assembly in which a separator is sequentially laminated between a positive electrode, a negative electrode, and then housing the electrode assembly in a battery case, and then injecting the non-aqueous electrolyte of the present invention.

[0073] The method for manufacturing such a lithium secondary battery of the present invention is manufactured by a conventional method known in the art and is applicable, and specifically, it is as described below.

[0074] (1) Positive electrode The positive electrode according to the present invention includes a positive electrode active material layer containing a positive electrode active material, and optionally, the positive electrode active material layer may further contain a conductive material and / or a binder.

[0075] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, it may include a lithium composite metal oxide represented by the following Chemical Formula 2 containing at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al), and lithium.

[0076] [Chemical Formula 2] Li 1+a Ni x Co y M 1 z M 2 w O2

[0077] In Chemical Formula 2, M 1 is Mn, Al, or a combination thereof, M 2 is at least one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca, and Sr, and 0 ≦ a ≦ 0.5, 0.55 < x < 1.0, 0 < y ≦ 0.4, 0 < z ≦ 0.4, 0 ≦ w ≦ 0.1.

[0078] The 1 + a represents the atomic fraction of lithium in the lithium transition metal oxide, and 0 ≦ a ≦ 0.5, preferably 0 ≦ a ≦ 0.2, more preferably 0 ≦ a ≦ 0.1.

[0079] The x represents the atomic fraction of nickel among all the transition metal elements in the lithium transition metal oxide, and 0.55 < x < 1.0, specifically 0.6 ≦ x ≦ 0.98, more specifically 0.6 ≦ x ≦ 0.95.

[0080] The y represents the atomic fraction of cobalt among all the transition metal elements in the lithium transition metal oxide, and 0 < y ≦ 0.4, specifically 0 < y ≦ 0.3, more specifically 0.05 ≦ y ≦ 0.3.

[0081] The z represents the atomic fraction of element M among all the transition metal elements in the lithium transition metal oxide, and 0 < z ≦ 0.4, preferably 0 < z ≦ 0.3, more preferably 0.01 ≦ z ≦ 0.3. 1

[0082] The w represents the atomic fraction of element M among all the transition metal elements in the lithium transition metal oxide, and 0 < w ≦ 0.1, preferably 0 < w ≦ 0.05, more preferably 0 < w ≦ 0.02. 2

[0083] Specifically, in order to realize a high-capacity battery, the cathode active material is Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 ​​Al 0.02 )O2, or Li(Ni 0.90 Mn 0.05 Co 0.05 )O2, etc., may contain lithium composite transition metal oxides. Specifically, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2, or Li(Ni 0.90 Mn 0.05 Co 0.05 )O2, etc., may contain High-Ni series lithium composite transition metal oxides.

[0084] The positive electrode active material containing such high nickel (High-Ni) series lithium composite transition metal oxide has a drawback of being vulnerable to side reactions with the electrolyte. However, by using it together with the electrolyte of the present invention, a stable passive film is formed on the surface of the positive electrode, and the side reactions with the electrolyte can be suppressed and reduced.

[0085] In addition, the positive electrode active material of the present invention may, if necessary, together with the lithium composite metal oxide represented by Chemical Formula 2, include lithium-manganese-based oxides (for example, LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (for example, LiCoO2, etc.), lithium-nickel-based oxides (for example, LiNiO2, etc.), lithium-nickel-manganese-based oxides (for example, LiNi 1-Y Mn Y O2(0 < Y < 1), LiMn 2-Z Ni Z O4(0 < Z < 2), lithium-nickel-cobalt-based oxides (for example, LiNi 1-Y1 Co Y1 O2(0 < Y1 < 1), lithium-manganese-cobalt-based oxides (for example, LiCo 1-Y2 Mn Y2 O2(0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4(0 < Z1 < 2), or Li(Nip1 Co q1 Mn r2 )O4 (0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2) etc. may also be used in combination.

[0086] The positive electrode active material may be contained in a content of 80 to 98% by weight, more specifically 85 to 98% by weight, based on the total weight of the positive electrode active material layer. When the positive electrode active material is contained within the above range, excellent capacity characteristics can be exhibited.

[0087] Next, the conductive material is used to impart conductivity to the electrode, and in the battery being configured, it can be used without particular limitation as long as it does not cause a chemical change and has electron conductivity. Specific examples include carbon powders such as carbon black, acetylene black (or Denka black), ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. Among these, one type may be used alone, or a mixture of two or more types may be used.

[0088] The conductive material may be contained in an amount of 0.1% to 10% by weight, preferably 0.1% to 5% by weight, based on the total weight of the positive electrode active material layer.

[0089] Next, the binder serves to improve the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the current collector. Examples of such binders include fluororesin binders containing polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders containing styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, styrene-isoprene rubber; cellulose binders containing carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose; polyalcohol binders containing polyvinyl alcohol; polyolefin binders containing polyethylene, polypropylene; polyimide binders; polyester binders; and silane binders. One of these may be used alone, or a mixture of two or more may be used.

[0090] The binder may be contained in an amount of 0.1% by weight to 15% by weight, preferably 0.1% by weight to 10% by weight, based on the total weight of the positive electrode active material layer.

[0091] Such a positive electrode of the present invention can be manufactured by a method for manufacturing a positive electrode known in the art. For example, the positive electrode is manufactured by dissolving or dispersing a positive electrode active material, a binder, and / or a conductive material in a solvent to produce a positive electrode slurry, then applying the positive electrode slurry onto a positive electrode current collector, and drying and rolling it, or by casting the positive electrode slurry onto another support and then laminating the film obtained by peeling the support onto the positive electrode current collector.

[0092] The positive current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Further, the positive current collector usually has a thickness of 3 μm to 500 μm, and the adhesion of the positive electrode material may be enhanced by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabric bodies, etc.

[0093] The solvent may be a solvent generally used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. Among these, one kind can be used alone, or a mixture of two or more kinds can be used. The usage amount of the solvent may be adjusted so that the positive electrode composite material has an appropriate viscosity in consideration of the coating thickness of the positive electrode composite material, production yield, workability, etc., and is not particularly limited.

[0094] (2) Negative electrode Next, the negative electrode will be described.

[0095] The negative electrode according to the present invention includes a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material layer may further contain a conductive material and / or a binder as necessary.

[0096] As the negative electrode active material, a silicon-based negative electrode active material may be used alone.

[0097] The silicon-based negative electrode active material is, for example, metallic silicon (Si), silicon oxide (SiO x, where 0 < x < 2), silicon carbide (SiC), and Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si) may include one or more selected from the group consisting of. The element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0098] Since the silicon-based negative electrode active material exhibits higher capacity characteristics than the carbon-based negative electrode active material, even better capacity characteristics can be obtained. However, a negative electrode containing a silicon-based negative electrode active material contains more oxygen (O)-rich components in the SEI film than a graphite negative electrode, and an SEI film containing an O-rich component tends to be more easily decomposed when a Lewis acid such as HF or PF5 is present in the electrolyte. Therefore, in order for a negative electrode containing a silicon-based negative electrode active material to maintain a stable SEI film, it is necessary to suppress the generation of Lewis acids such as HF and PF5 in the electrolyte or to remove (or scavenge) the generated Lewis acids. The non-aqueous electrolyte according to the present invention contains an electrolyte additive capable of forming a stable film on the surface of the silicon-based negative electrode, so that the decomposition of the SEI film can be effectively suppressed when using a negative electrode containing a silicon-based active material.

[0099] On the other hand, the negative electrode may further include a normal negative electrode active material capable of reversibly intercalating / deintercalating lithium ions, specifically, a carbon-based negative electrode active material, in addition to the silicon-based negative electrode active material, if necessary for the lithium battery.

[0100] As the carbon-based negative electrode active material, various carbon-based negative electrode active materials used in the art can be used. For example, graphite-based materials such as natural graphite, artificial graphite, and Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum and coal tar pitch-derived cokes, soft carbon, hard carbon, etc. can be used. The shape of the carbon-based negative electrode active material is not particularly limited, and substances with various shapes such as amorphous, plate-like, scaly, spherical, or fibrous can be used.

[0101] Specifically, at least one of natural graphite and artificial graphite can be used as the carbon-based negative electrode active material. In order to enhance the adhesion to the current collector and suppress the detachment of the active material, both natural graphite and artificial graphite may be used.

[0102] On the other hand, when both the silicon-based negative electrode active material and the carbon-based negative electrode active material are used as the negative electrode active material of the present invention, their mixing ratio may be 3:97 to 99:1, preferably 5:95 to 15:85 by weight. When the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material satisfies the above range, the capacity characteristics can be improved, the volume expansion of the silicon-based negative electrode active material can be suppressed, and excellent cycle performance can be ensured.

[0103] The negative electrode active material may be contained in an amount of 80% to 99% by weight based on the total weight of the negative electrode active material layer. When the content of the negative electrode active material satisfies the above range, excellent capacity characteristics and electrochemical characteristics can be obtained.

[0104] Next, 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 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, carbon black, acetylene black (or Denka black), ketjen black, channel black, furnace black, lamp black, or thermal black, etc. carbon powders; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, nickel powder, etc.; conductive whiskers such as zinc oxide, potassium titanate, etc.; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used.

[0105] The binder is a component that assists in binding the conductive material, active material, and current collector, and is usually added in an amount of 0.1% by weight to 10% by weight based on the total weight of the negative electrode active material layer. Examples of binders include fluororesin binders containing polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders containing styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, styrene-isoprene rubber; cellulose binders containing carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose; polyalcohol binders containing polyvinyl alcohol; polyolefin binders containing polyethylene, polypropylene; polyimide binders; polyester binders; and silane binders, etc.

[0106] The binder may be contained in an amount of 0.1% by weight to 15% by weight, preferably 0.1% by weight to 10% by weight, based on the total weight of the negative electrode active material layer.

[0107] The negative electrode can be manufactured by a method for manufacturing a negative electrode known in the art. For example, the negative electrode is manufactured by applying a negative electrode slurry prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent onto a negative electrode current collector, followed by rolling and drying, or by laminating a film obtained by peeling a support after casting the positive electrode slurry onto the support onto the negative electrode current collector.

[0108] The 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-treating the surface of copper or stainless steel with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. Further, the negative electrode current collector usually has a thickness of 3 μm to 500 μm, and 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 of the current collector. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabric bodies.

[0109] The solvent may be a solvent generally used in the art, and examples include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these can be used alone, or a mixture of two or more can be used. The amount of the solvent used may be adjusted so that the negative electrode slurry has an appropriate viscosity in consideration of the coating thickness of the negative electrode composite material, manufacturing yield, workability, etc., and is not particularly limited.

[0110] (3) Separator The lithium secondary battery according to the present invention includes a separator between a positive electrode and a negative electrode.

[0111] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. It is not particularly limited as long as it is a separator commonly used in lithium secondary batteries, and in particular, it preferably has low resistance to the migration of ions of lithium salts and has excellent electrolyte moisture retention ability.

[0112] Specifically, as the separator, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a homopolymer of ethylene, a homopolymer of propylene, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and optionally, it may be used as a single-layer or multi-layer structure.

[0113] The lithium secondary battery according to the present invention as described above can be usefully used in portable devices such as mobile phones, notebook personal computers, digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEV).

[0114] The outer shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape, a rectangular shape, a pouch shape, or a coin shape using a can.

[0115] The lithium secondary battery according to the present invention can be used not only as a battery cell for powering small devices, but also preferably as a unit cell in a medium to large-sized battery module including a number of battery cells.

[0116] Hereinafter, examples will be given to specifically describe the present invention in detail. However, the examples according to the present invention can be deformed into various other forms, and the scope of the present invention should not be construed as being limited to the examples described in detail below. The examples of the present invention are provided to more fully explain the present invention to those with average knowledge in the industry.

[0117] Example Example 1. (Manufacture of non-aqueous electrolyte for lithium secondary battery) LiPF6 was dissolved in a non-aqueous organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) were mixed at a volume ratio of 10:90 so that the concentration became 1.5 M, and then the compound represented by Chemical Formula 1A-1 was 0.1 wt%, vinylene carbonate (VC) was 0.5 wt%, and 1,3-propanesultone (PS) was added to be 0.5 wt% to manufacture a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

[0118] (Manufacture of secondary battery) Lithium nickel-manganese-cobalt-aluminum oxide (Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2) as the positive electrode active material particles, carbon black as the conductive material, and polyvinylidene fluoride as the binder were added to N-methyl-2-pyrrolidone (NMP) as the solvent at a weight ratio of 97.74:0.7:1.56 to manufacture a positive electrode slurry (solid content: 75.50 wt%). The positive electrode slurry was applied to a positive electrode current collector (Al thin film) with a thickness of 15 μm, dried, and roll-pressed to manufacture a positive electrode.

[0119] A silicon-based negative electrode active material (100% Si), a binder (SBR-CMC), and a conductive material (carbon black) were added to water as a solvent at a weight ratio of 70:20.3:9.7 to produce a negative electrode slurry (solid content: 26% by weight). After applying and drying the negative electrode slurry on a copper (Cu) thin film, which is a negative electrode current collector with a thickness of 15 μm, a roll press was performed to produce a negative electrode.

[0120] After manufacturing an electrode assembly with a porous separator, polypropylene, interposed between the manufactured positive electrode and negative electrode, it was housed in a battery case, and a non-aqueous electrolyte for the manufactured lithium secondary battery was injected to manufacture a lithium secondary battery.

[0121] Example 2. A lithium secondary battery was manufactured in the same manner as in Example 1, except that after dissolving LiPF6 in a non-aqueous organic solvent to a concentration of 1.5 M, 1.0% by weight of the compound represented by Chemical Formula 1A-1, 0.5% by weight of vinylene carbonate (VC), and 0.5% by weight of 1,3-propane sultone (PS) were added to produce a non-aqueous electrolyte (see Table 1 below).

[0122] Example 3. A lithium secondary battery was manufactured in the same manner as in Example 1, except that after dissolving LiPF6 in a non-aqueous organic solvent to a concentration of 1.5 M, 5.0% by weight of the compound represented by Chemical Formula 1A-1, 0.5% by weight of vinylene carbonate (VC), and 0.5% by weight of 1,3-propane sultone (PS) were added to produce a non-aqueous electrolyte (see Table 1 below).

[0123] Example 4. A lithium secondary battery was manufactured in the same manner as in Example 1, except that after dissolving LiPF6 in a non-aqueous organic solvent to a concentration of 1.5 M, 10.0% by weight of the compound represented by Chemical Formula 1A-1, 0.5% by weight of vinylene carbonate (VC), and 0.5% by weight of 1,3-propane sultone (PS) were added to produce a non-aqueous electrolyte (see Table 1 below).

[0124] Example 5. After dissolving LiPF6 in a non-aqueous organic solvent to a concentration of 1.5 M, a non-aqueous electrolyte solution was prepared by adding 11.0 wt% of the compound represented by Chemical Formula 1A-1, 0.5 wt% of vinylene carbonate (VC), and 0.5 wt% of 1,3-propanesultone (PS). A lithium secondary battery was manufactured in the same manner as in Example 1, except for the above (see Table 1 below).

[0125] Example 6. A lithium secondary battery was manufactured in the same manner as in Example 2, except that the compound represented by Chemical Formula 1A-2 was added instead of the compound represented by Chemical Formula 1A-1 to prepare a non-aqueous electrolyte solution (see Table 1 below).

[0126] Example 7. A lithium secondary battery was manufactured in the same manner as in Example 2, except that the compound represented by Chemical Formula 1A-3 was added instead of the compound represented by Chemical Formula 1A-1 to prepare a non-aqueous electrolyte solution (see Table 1 below).

[0127] Comparative Example 1. After dissolving LiPF6 in a non-aqueous organic solvent to a concentration of 1.5 M, a non-aqueous electrolyte solution was prepared by adding 0.5 wt% of vinylene carbonate (VC) and 0.5 wt% of 1,3-propanesultone (PS) as additives. A lithium secondary battery was manufactured in the same manner as in Example 1, except for the above (see Table 1 below).

[0128] Comparative Example 2. A lithium secondary battery was manufactured in the same manner as in Example 1, except that 0.5 wt% of the compound represented by the following Chemical Formula 3 was added as an additive instead of the compound represented by Chemical Formula 1A-1 to prepare a non-aqueous electrolyte solution (see Table 1 below).

[0129] [Chemical Formula]

[0130] Comparative Example 3 A lithium secondary battery was produced in the same manner as in Example 1 except that 0.5% by weight of the compound represented by the following Chemical Formula 4 was added as an additive instead of the compound represented by Chemical Formula 1A-1 to produce a non-aqueous electrolyte (see Table 1 below).

[0131]

Chemical formula

[0132]

Table 1

[0133] On the other hand, the abbreviations of the compounds in Table 1 above each mean the following. FEC: Fluoroethylene carbonate DEC: Diethyl carbonate

[0134] Experimental example Experimental Example 1. Evaluation of high-temperature cycle characteristics The high-temperature cycle characteristics of the secondary batteries produced in Examples 1 to 7 and the secondary batteries produced in Comparative Examples 1 to 3 were evaluated respectively.

[0135] Specifically, each of the secondary batteries produced in Examples 1 to 7 and the secondary batteries produced in Comparative Examples 1 to 3 was charged to 4.2 V at a constant current of 1C at 40 °C, and discharged to 3.0 V at a constant current of 0.5C. One cycle was defined as such, and after 200 cycles of charge and discharge, the capacity retention rate with respect to the initial capacity after one cycle was measured. The results are shown in Table 2 below.

[0136]

Table 2

[0137] Referring to Table 2, it can be seen that the secondary batteries of Examples 1 to 7 provided with the electrolyte containing the additive of the present invention had a relatively improved capacity retention rate compared to the secondary batteries of Comparative Examples 1 to 3.

[0138] From these results, when the additive of the present invention is used, it can be confirmed that due to the propargyl group, a strong SEI film is formed, and due to the trioxane functional group, a film based on a highly elastic and lithium-ion-conductive polymeric ether group is formed on the negative electrode, thereby improving the capacity retention rate at high temperatures.

[0139] Experimental Example 2. Evaluation of High-Temperature Storage Characteristics The high-temperature storage characteristics of the secondary batteries manufactured in Examples 1 to 7 and the secondary batteries manufactured in Comparative Examples 1 to 3 were evaluated.

[0140] Specifically, after the secondary batteries manufactured in Examples 1 to 7 and the secondary batteries manufactured in Comparative Examples 1 to 3 were fully charged to 4.2 V, they were stored at 60 °C for 8 weeks.

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

[0142] After 8 weeks, the capacity of the stored secondary battery was measured, and the capacity decreased during the 8-week storage period was calculated. The percentage of the decreased capacity with respect to the capacity of the initial secondary battery was calculated, and the capacity retention rate after 8 weeks was derived. The results are shown in Table 3 below.

[0143]

Table 3

[0144] Referring to Table 3, it can be seen that the secondary batteries of Examples 1 to 7 provided with the electrolyte containing the additive of the present invention had an improved capacity retention rate after high-temperature storage compared to the secondary batteries of Comparative Examples 1 to 3.

Claims

1. A non-aqueous electrolyte for a lithium secondary battery, comprising a lithium salt, an organic solvent, and a first additive, wherein the first additive is a compound represented by the following Chemical Formula 1. 【Chemical 1】 (In the above Chemical Formula 1, R １ to R ６ each independently represents hydrogen, an alkyl group having 1 to 5 carbon atoms, or -(R')n-C≡CH, where R' is an alkylene group having 1 to 5 carbon atoms, n is an integer of 0 to 3, and R １ to R ６ at least one of them is -(R')n-C≡CH.)

2. Said R １ to R ６ are each independently hydrogen, an alkyl group having 1 to 3 carbon atoms, or -(R')n-C≡CH, where R' is an alkylene group having 1 to 3 carbon atoms, n is an integer of 0 to 3, and at least one of R １ to R ６ is -(R')n-C≡CH. The non-aqueous electrolyte for a lithium secondary battery according to claim 1.

3. Said R １ , R ３ , and R ５ are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, and R ２ , R ４ , and R ６ are each independently an alkyl group having 1 to 3 carbon atoms or -(R')n-C≡CH, where R' is an alkylene group having 1 to 3 carbon atoms, n is an integer of 0 to 3, and at least one of R ２ , R ４ , and R ６ is -(R')n-C≡CH. The non-aqueous electrolyte for a lithium secondary battery according to claim 1.

4. Said R １ , R ３ , and R ５ are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, and R ２ , R ４ , and R ６ is -(R')n-C≡CH, where R' is an alkylene group having 1 to 3 carbon atoms and n is an integer from 0 to 3. The non-aqueous electrolyte for a lithium secondary battery according to claim 1.

5. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, wherein the compound represented by Chemical Formula 1 is at least one of a compound represented by Chemical Formula 1A-1 to a compound represented by Chemical Formula 1A-3. 【Chemical Formula 2】 [Chemical Formula 3] 【Chemical 4】

6. The non-aqueous electrolyte for a lithium secondary battery according to Claim 5, wherein the compound represented by Chemical Formula 1 is the compound represented by Chemical Formula 1A-1.

7. The non-aqueous electrolyte for a lithium secondary battery according to any one of Claims 1 to 6, wherein the compound represented by Chemical Formula 1 is contained in an amount of 0.1% by weight to 10.0% by weight based on the total weight of the non-aqueous electrolyte.

8. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, further comprising at least one second additive selected from the group consisting of a cyclic carbonate compound, a halogen-substituted carbonate compound, a sultone compound, a sulfate compound, a phosphate compound, a borate compound, a nitrile compound, an amine compound, a silane compound, and a lithium salt compound.

9. A lithium secondary battery, comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte for a lithium secondary battery according to Claim 1.

10. The lithium secondary battery according to Claim 9, wherein the negative electrode contains a silicon-based negative electrode active material.

11. The lithium secondary battery according to Claim 10, wherein the negative electrode further contains a carbon-based negative electrode active material.

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