Non-aqueous electrolyte for lithium secondary batteries and lithium secondary batteries 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 document of the Korean Patent Application are incorporated herein by reference as part of this specification.

[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 been attracting 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 for developing a positive electrode active material and a negative electrode active material having a high theoretical capacity has been actively conducted.

[0006] On the other hand, research for applying 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 is in progress.

[0007] However, silicon-based negative electrode active materials have a problem in that repeated electrochemical charging and discharging, or changes in crystal structure due to intercalation and deintercalation of lithium ions during high-temperature storage, cause rapid volume changes and expansion, leading to film cracking and degradation, and thus severe battery degradation. In particular, SEI formed while carbonate-based non-aqueous solvents decompose has high solubility in the electrolyte, causing side reactions with the electrolyte, and has low elasticity, making it difficult to maintain the film when the negative electrode expands in volume, thus causing battery degradation.

[0008] Therefore, when silicon-based anode active materials are applied, research and development is needed to form a stable SEI on the anode surface that can withstand the volume change of Si, in order to solve the problem of degradation due to volume expansion of the silicon-based anode active material. [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to provide a non-aqueous electrolyte for lithium secondary batteries that contains an additive capable of forming a strong film on the surface of a silicon-based negative electrode.

[0010] Furthermore, the present invention aims to provide a lithium secondary battery with improved high-temperature storage characteristics and high-temperature cycling characteristics by including the aforementioned non-aqueous electrolyte for lithium secondary batteries. [Means for solving the problem]

[0011] In one embodiment of the present invention for achieving the above objective, The solution comprises a lithium salt, a non-aqueous organic solvent, and a first additive. The present invention provides a non-aqueous electrolyte for lithium secondary batteries, comprising, as the first additive, a compound represented by the following chemical formula 1.

[0012] [ka]

[0013] In the above chemical formula 1, R1 to R6 are each independently hydrogen, an alkyl group having 1 to 5 carbon atoms, or -(R')nC≡CH, 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')nC≡CH.

[0014] Another embodiment of the present invention is, The present invention provides 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 a non-aqueous electrolyte for a lithium secondary battery.

[0015] The aforementioned negative electrode may contain a silicon-based negative electrode active material. [Effects of the Invention]

[0016] The non-aqueous electrolyte of the present invention contains a compound as an additive that includes a propargyl group capable of forming a strong SEI on the electrode surface and a trioxane functional group with excellent elasticity and lithium ion transport properties. By forming a strong film based on a polyoxymethylene (POM) structure and polymeric ether groups on the surface of the silicon-based negative electrode, the durability of the silicon-based negative electrode active material against volume changes can be improved.

[0017] By applying such a non-aqueous electrolyte of the present invention, it is possible to realize a lithium secondary battery with improved cycle characteristics and high-temperature storage stability. [Modes for carrying out the invention]

[0018] The present invention will be described in more detail below.

[0019] The terms and words used herein and in the claims are for illustrative purposes only and are not intended to limit the invention.

[0020] For example, 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 other parts may be added unless “only” is used.

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

[0022] In this specification, unless otherwise defined, “substitution” means that at least one hydrogen atom bonded to a carbon atom is replaced by an element other than hydrogen, for example, by an alkyl group having 1 to 5 carbon atoms or by a fluorine element.

[0023] While silicon-based negative electrode active materials have the advantage of superior capacity per unit weight among conventional lithium-ion battery negative electrode materials, repeated charging and discharging cause severe volume expansion (over 300%) and contraction due to lithium-ion intercalation and deintercalation. This leads to cracking of the silicon-based negative electrode active material, destroying the SEI film formed on the negative electrode surface, and continuously exposing the surface of the silicon-based negative electrode active material to the electrolyte, resulting in rapid depletion of the lithium-ion source. Furthermore, these side reactions create a thick and unstable film at the interface between silicon and the electrolyte, limiting its commercialization potential.

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

[0025] Non-aqueous electrolyte for lithium secondary batteries Specifically, one embodiment of the present invention is: The solution comprises 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 above 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 from 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 of the following groups can be selected.

[0029] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10 It may contain a single substance or a mixture of two or more substances selected from the group consisting of 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 LiBF4, LiPF6, LiN(SO2F)2(Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2(lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), and LiN(SO2CF3)2(lithium It may contain at least one selected from the group consisting of bis(trifluoromethane sulfonyl)imide (LiTFSI). In addition to these, lithium salts commonly used in the electrolytes of lithium secondary batteries can be used without limitation.

[0030] The lithium salt may be changed as appropriate within the range of normal use, but in order to obtain the optimal effect of forming a corrosion-preventive coating on the electrode surface, it may be included in the electrolyte at a concentration of 0.8 M to 3.0 M, specifically 1.0 M to 2.0 M, preferably 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 electrolyte can be controlled to achieve optimal impregnation, thereby improving the mobility of lithium ions and improving the capacity characteristics and cycle characteristics of the lithium secondary battery.

[0032] (2) Non-aqueous organic solvents Furthermore, the explanation of the non-aqueous organic solvent is as follows.

[0033] As the non-aqueous organic solvent, any organic solvent commonly used in non-aqueous electrolytes can be used without restriction. The type of organic solvent is not limited as long as it minimizes decomposition due to oxidation reactions during the charging and discharging process of the secondary battery and can exhibit the desired properties together with the additives.

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

[0035] The (i) cyclic carbonate organic solvent is a highly viscous organic solvent that has a high dielectric constant and therefore readily dissociates lithium salts in a non-aqueous 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. In particular, at least one of ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC) is more likely to form a more stable SEI on the surface of the Si negative electrode.

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

[0037] Furthermore, the non-aqueous organic solvent may also 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, in order to ensure high ionic conductivity.

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

[0039] The (iv) linear ester organic solvent mentioned above includes, as a typical example, 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, and specifically may include at least one of ethyl propionate and propyl propionate.

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

[0041] On the other hand, the non-aqueous organic solvent may be used with any additional organic solvents commonly used in electrolytes for lithium secondary batteries, as needed. For example, it may further contain at least one organic solvent from among 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 a first additive, a compound represented by the following chemical formula 1.

[0044] [ka]

[0045] In the above chemical formula 1, R1 to R6 are each independently hydrogen, an alkyl group having 1 to 5 carbon atoms, or -(R')nC≡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')nC≡CH.

[0046] The compound represented by chemical formula 1, included as the first additive, is a compound that contains both a propagyl group capable of forming a strong SEI and a trioxane functional group with excellent elasticity and lithium ion transport properties in its structure. During charging and discharging, it is reduced and decomposed before the organic solvent, and can form an elastic and stable SEI on the surface of the silicon-based anode based on the polyoxymethylene (POM) polymer structure and ether group, thereby suppressing cracking of the SEI due to the contraction and expansion of the silicon-based anode active material. In particular, since the SEI based on the polyoxymethylene polymer structure and ether group is thermally stable, it can prevent side reactions caused by direct contact between lithium ions stored in the silicon-based anode and the electrolyte at high temperatures, thereby improving the high-temperature durability of the lithium secondary battery, such as cycle characteristics and capacity characteristics.

[0047] Specifically, in the above chemical formula 1, R1 to R6 are each independently hydrogen, an alkyl group having 1 to 3 carbon atoms, or -(R')nC≡CH, 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')nC≡CH.

[0048] Furthermore, in the above 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')nC≡CH, 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')nC≡CH.

[0049] Furthermore, in the above 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 -(R')nC≡CH, R' is an alkylene group having 1 to 3 carbon atoms, and n may be an integer from 0 to 3.

[0050] Specifically, the compound represented by chemical formula 1 includes at least one of the compounds represented by chemical formulas 1A-1 to 1A-3 below. Preferably, the compound represented by chemical formula 1 may be a compound represented by chemical formula 1A-1 or 1A-3 below, which has a relatively large number of propagyl groups substituted compared to the compound represented by chemical formula 1A-2, and more preferably, it may be a compound represented by chemical formula 1A-1 in which the most propagyl groups are substituted.

[0051] [ka]

[0052] [ka]

[0053] [ka]

[0054] On the other hand, the compound of chemical formula 1 may be included in an amount of 0.1% 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 included within the above range, it is possible to prevent side reactions caused by excessive additives, form a strong film on the surface of the silicon-based negative electrode, and effectively prevent deterioration of the negative electrode during rapid charging and discharging, thereby enabling the manufacture of a secondary battery with improved performance.

[0056] Specifically, if the content of the compound represented by chemical formula 1 is 0.1% by weight or more, the film formation effect on the negative electrode surface can be maintained more stably during the battery's operating time. Furthermore, if 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 impregnation, effectively suppressing the increase in battery resistance due to the decomposition of additives, and preventing a decrease in the ionic conductivity of the electrolyte, thereby preventing a decline in rate characteristics and low-temperature life characteristics.

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

[0058] (4) Second additive Furthermore, the non-aqueous electrolyte for lithium secondary batteries of the present invention may, if necessary, further contain a second additive in the non-aqueous electrolyte 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.

[0059] Such a second additive may include, as a typical example, 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 aforementioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate.

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

[0062] Examples of the sultone compound 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.

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

[0064] 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(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphate.

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

[0066] 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.

[0067] 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.

[0068] The lithium salt compound mentioned above is one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2), and LiBF4), which are different from the lithium salt contained in the non-aqueous electrolyte.

[0069] If the second additive includes vinylene carbonate, vinylethylene carbonate, or succinonitrile, an even 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, the second additive can be used in a mixture of two or more types, and may be present in an amount of 50% by weight or less, specifically 0.01% to 10% by weight, based on the total weight of the non-aqueous electrolyte, preferably 0.05% to 5.0% by weight. If the content of the second additive is less than 0.01% by weight, the improvement in the low-temperature output of the battery, as well as the improvement in high-temperature storage characteristics and high-temperature life characteristics, will be slight. If the content of the second additive exceeds 50% by weight, excessive side reactions may occur in the electrolyte during battery charging and discharging. In particular, if an excessive amount of the SEI film-forming additive is added, it may not decompose sufficiently at high temperatures and may remain as unreacted material or precipitated in the electrolyte at room temperature. Therefore, there is a risk of side reactions occurring that reduce the life or resistance characteristics of the secondary battery.

[0071] Lithium-ion battery Furthermore, yet another embodiment of the present invention provides a lithium secondary battery comprising a non-aqueous electrolyte for lithium secondary batteries of the present invention.

[0072] On the other hand, the lithium secondary battery of the present invention 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, housing it in a battery case, and then adding the non-aqueous electrolyte of the present invention.

[0073] The method for manufacturing the lithium secondary battery of the present invention can be manufactured and applied by conventional methods known in the art, specifically as described below.

[0074] (1) Positive electrode The positive electrode according to the present invention comprises 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 may specifically include a lithium composite metal oxide represented by the following chemical formula 2, comprising lithium and at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al).

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

[0077] In the aforementioned chemical formula 2, M 1 These are 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である。

[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 positive electrode 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 [[ID=5); 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 oxides has the drawback of being vulnerable to side reactions with the electrolyte. However, by using the electrolyte of the present invention together, 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 oxides (such as LiMnO2, LiMn2O4, etc.), lithium-cobalt oxides (such as LiCoO2, etc.), lithium-nickel oxides (such as LiNiO2, etc.), lithium-nickel-manganese oxides (such as LiNi 1-Y Mn Y O2 (0 < Y < 1), LiMn 2-Z Ni Z O4 (0 < Z < 2), lithium-nickel-cobalt oxides (such as LiNi 1-Y1 Co Y1 O2 (0 < Y1 < 1), lithium-manganese-cobalt oxides (such as 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 to be configured, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. 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. One of these may be used alone, or a mixture of two or more may be used.

[0088] The conductive material may be contained in 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 plays a role in improving the adhesion between positive electrode active material particles and the adhesion 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, and styrene-isoprene rubber; cellulose binders containing carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol binders containing polyvinyl alcohol; polyolefin binders containing polyethylene and polypropylene; polyimide binders; polyester binders; and silane binders. One of these may be used alone or in mixtures of two or more.

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

[0091] Such positive electrodes of the present invention can be manufactured by methods for manufacturing positive electrodes known in the art. For example, the positive electrode may be 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, drying and rolling it, or by casting the positive electrode slurry onto another support, peeling off the support, and laminating the resulting film onto the positive electrode current collector.

[0092] 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 surface treatment using carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector usually has a thickness of 3 μm to 500 μm, and the adhesion strength to the positive electrode material may be increased by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0093] The solvent can be any solvent commonly used in the art, such as 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. The amount of solvent used is not particularly limited, as long as it can be adjusted so that the cathode composite material has an appropriate viscosity, taking into consideration the coating thickness of the cathode composite material, the manufacturing yield, and the workability of the workability.

[0094] (2) Negative electrode Next, I will explain the negative electrode.

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

[0096] As the aforementioned 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) or 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, the negative electrode containing the silicon-based negative electrode active material contains more O-rich components in the SEI film than the graphite negative electrode, and the SEI film containing the O-rich component tends to be further decomposed when a Lewis acid such as HF or PF5 is present in the electrolyte. Therefore, in order for the negative electrode containing the 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 remove (or scavenge) the generated Lewis acid. 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 anode active material, various carbon-based anode active materials used in this industry can be used, such as graphite-based materials like 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 or coal tar pitch-derived cokes, as well as soft carbon and hard carbon. The shape of the carbon-based anode active material is not particularly limited, and materials of various shapes such as amorphous, plate-like, flaky, spherical, or fibrous can be used.

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

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

[0103] The negative electrode active material may be present 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 meets the above range, excellent capacitance characteristics and electrochemical properties 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 is conductive, and may be used, for example, carbon powder such as carbon black, acetylene black (or Denka 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; conductive powders such as fluorinated carbon powder, 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.

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

[0106] The binder may be present in an amount of 0.1% to 15% by weight, preferably 0.1% 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 negative electrodes known in the art. For example, the negative electrode can be manufactured by applying a negative electrode slurry, which is prepared by dissolving or dispersing a negative electrode active material, a binder, and a conductive material selectively in a solvent, onto a negative electrode current collector, and then rolling and drying it; or by casting the positive electrode slurry onto a support, peeling off the support, and then laminating the resulting film onto the negative electrode current collector.

[0108] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector usually has a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, the bonding 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 film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0109] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone, or a mixture of two or more. The amount of solvent used is not particularly limited, and should be adjusted so that the negative electrode slurry has an appropriate viscosity, taking into consideration the coating thickness of the negative electrode mixture, the production yield, and the workability of the material.

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

[0111] The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is one that is commonly used as a separator in lithium secondary batteries. In particular, it is preferable that it has low resistance to the movement of lithium salt ions and has excellent electrolyte moisture absorption capacity.

[0112] Specifically, as separators, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as those made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used as single-layer or multi-layer structures.

[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 computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0114] 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, using a can.

[0115] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also suitably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0116] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0117] Examples Example 1. (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte for lithium secondary batteries was prepared by dissolving LiPF6 in a non-aqueous organic solvent prepared by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 10:90 to a concentration of 1.5 M. Then, a compound represented by chemical formula 1A-1 was added in an amount of 0.1% by weight, vinylene carbonate (VC) in an amount of 0.5% by weight, and 1,3-propanesultone (PS) in an amount of 0.5% by weight (see Table 1 below).

[0118] (Manufacturing of secondary batteries) Lithium nickel-manganese-cobalt-aluminum oxide (Li(Ni)) is used as the positive electrode active material particle. 0.86 Mn 0.07 Co 0.05 Al 0.02 A positive electrode slurry (solid content 75.50 wt%) was prepared by adding carbon black as a conductive material and polyvinylidene fluoride as a binder in a weight ratio of 97.74:0.7:1.56 to N-methyl-2-pyrrolidone (NMP) as a solvent. The positive electrode slurry was applied to a 15 μm thick positive electrode current collector (a thin Al film), dried, and roll-pressed to produce the 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, the solvent, in a weight ratio of 70:20.3:9.7 to produce a negative electrode slurry (solid content: 26% by weight). The negative electrode slurry was applied to a 15 μm thick copper (Cu) thin film, which served as the negative electrode current collector, and dried. The negative electrode was then manufactured by roll pressing.

[0120] After manufacturing an electrode assembly by interposing polypropylene as a porous separator between the manufactured positive electrode and negative electrode, the assembly was placed in a battery case, and a lithium secondary battery was manufactured by pouring the manufactured non-aqueous electrolyte for lithium secondary batteries into it.

[0121] Example 2. A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.5 M, and then a non-aqueous electrolyte was prepared by adding 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-propanesultone (PS) (see Table 1 below).

[0122] Example 3. A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.5 M, and then a non-aqueous electrolyte was prepared by adding 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-propanesultone (PS) (see Table 1 below).

[0123] Example 4. A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.5 M, and then a non-aqueous electrolyte was prepared by adding 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-propanesultone (PS) (see Table 1 below).

[0124] Example 5. A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.5 M, and then a non-aqueous electrolyte was prepared by adding 11.0% 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-propanesultone (PS) (see Table 1 below).

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

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

[0127] Comparative Example 1. A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.5 M, and then 0.5% by weight of vinylene carbonate (VC) and 0.5% by weight of 1,3-propanesultone (PS) were added as additives to produce a non-aqueous electrolyte (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% by weight of the compound represented by chemical formula 3 below was added as an additive to produce a non-aqueous electrolyte (see Table 1 below).

[0129] [ka]

[0130] Comparative Example 3. A lithium secondary battery was manufactured 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 to produce a non-aqueous electrolyte (see Table 1 below).

[0131] [ka]

[0132] [Table 1]

[0133] On the other hand, the abbreviations for the compounds in Table 1 above 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 manufactured in Examples 1 to 7 and the secondary batteries manufactured in Comparative Examples 1 to 3 were evaluated.

[0135] Specifically, the secondary batteries manufactured in Examples 1-7 and Comparative Examples 1-3 were each charged to 4.2V with a constant current of 1C at 40°C, and then discharged to 3.0V with a constant current of 0.5C. This constituted one cycle. After 200 charge-discharge cycles, the capacity retention rate relative 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, which are equipped with an electrolyte containing the additive of the present invention, show a relatively improved capacity retention rate compared to the secondary batteries of Comparative Examples 1 to 3.

[0138] These results confirm that when using the additive of the present invention, a strong SEI film is formed on the negative electrode by the propagyl group, and a film based on a polymeric ether group that is highly elastic and capable of lithium ion transfer is formed by the trioxane functional group, 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 1-7 and Comparative Examples 1-3 were evaluated.

[0140] Specifically, the secondary batteries manufactured in Examples 1 to 7 and the secondary batteries manufactured in Comparative Examples 1 to 3 were fully charged to 4.2V and then 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 percentage of the decreased capacity relative to the initial capacity of the secondary batteries was calculated to derive the capacity retention rate after 8 weeks. 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, which are equipped with an electrolyte containing the additive of the present invention, showed improved capacity retention after high-temperature storage compared to the secondary batteries of Comparative Examples 1 to 3.

Claims

1. The solution comprises a lithium salt, an organic solvent, and a first additive. The first additive is a compound represented by the following chemical formula 1, The compound represented by the chemical formula 1 is included in a non-aqueous electrolyte for lithium secondary batteries in an amount of 0.1% to 11.0% by weight, based on the total weight of the non-aqueous electrolyte. 【Chemistry 1】 (In the above chemical formula 1, R １ ~R ６ Each of these is independently a hydrogen atom, a C1-C5 alkyl group, or -(R')n-C≡CH, where R' is a C1-C5 alkylene group, and n is an integer from 0 to 3. １ ~R ６ At least one of these is -(R')n-C≡CH.

2. The aforementioned R １ ~R ６ Each of these is independently hydrogen, a C1-C3 alkyl group, or -(R')n-C≡CH, where R' is a C1-C3 alkylene group, and n is an integer from 0 to 3. １ ~R ６ The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein at least one of the is -(R')n-C≡CH.

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

5. The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein the compound represented by chemical formula 1 is at least one of the compounds represented by chemical formulas 1A-1 to 1A-3 below. 【Chemistry 2】 【Transformation 3】 【Chemistry 4】

6. The non-aqueous electrolyte for lithium secondary batteries 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 claim 1, further comprising 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, amine compounds, silane compounds, and lithium salt compounds.

8. A positive electrode containing a positive electrode active material, A negative electrode containing a silicon-based negative electrode active material, A separator interposed between the positive electrode and the negative electrode, A lithium secondary battery comprising the non-aqueous electrolyte for lithium secondary batteries described in claim 1.

9. The lithium secondary battery according to claim 8, further comprising a carbon-based negative electrode active material.

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