Non-aqueous electrolyte solution for lithium secondary battery, and lithium secondary battery containing same

Abstract

The invention provides a non-aqueous electrolyte solution for a lithium secondary battery and a lithium secondary battery containing the same. Specifically, the non-aqueous electrolyte solution for a lithium secondary battery according to the present disclosure may include a lithium salt, an organic solvent, and a compound represented by Formula 1 as a first additive. The present disclosure also provides a lithium secondary battery having improved high-temperature storage characteristics and high-temperature cycle characteristics by containing the non-aqueous electrolyte solution for a lithium secondary battery.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Korean Patent Application No. 10-2022-0111719 filed on September 2, 2022 and Korean Patent Application No. 10-2023-0108612 filed on August 18, 2023, the disclosures of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery containing the non-aqueous electrolyte. Background Art

[0004] As modern society becomes increasingly dependent on electrical energy, the development of large-capacity energy storage devices that can provide stable power supply and increase production has attracted much attention.

[0005] Lithium-ion batteries are the energy storage devices with the highest energy density that have been commercialized and have been used in various fields such as small electronic products, electric vehicles (EVs), and energy storage devices.

[0006] In particular, lithium-ion batteries applied to electric vehicles are required to have high output characteristics, as well as maintain cycle characteristics and performance in various environments.

[0007] A lithium-ion battery includes a positive electrode comprising a lithium-containing transition metal oxide, a negative electrode capable of storing lithium, a non-aqueous electrolyte comprising an organic solvent containing a lithium salt, and a separator.

[0008] Lithium hexafluorophosphate (LiPF6), which is mainly used as a lithium salt, easily decomposes at high temperatures to produce Lewis acid byproducts such as HF and PF5, which can react with moisture to produce more Lewis acid byproducts (HF).

[0009] These Lewis acid byproducts may corrode the passivation film formed on the electrode and its surface, resulting in the elution of transition metal ions from the positive electrode. The eluted transition metal ions promote the decomposition of the electrolyte solvent, thereby accelerating gas generation, or re-deposit on the positive electrode, thereby increasing the positive electrode resistance. They may also be transferred to the negative electrode through the electrolyte and then deposited on the negative electrode, resulting in additional lithium ion consumption and increased resistance due to negative electrode self-discharge, destruction and regeneration of the solid electrolyte interface film (SEI), etc.

[0010] Since this series of reactions reduces the number of available lithium ions in the battery, this may be the main reason for the decrease in battery capacity. In addition, when the metal ions electrodeposited on the negative electrode grow into dendrites, they cause an internal short circuit in the battery, resulting in reduced safety of the battery. Therefore, a non-aqueous electrolyte is needed that can remove byproducts (HF, PF5, etc.) generated by thermal decomposition of lithium salts and form a stable film on the electrode surface to inhibit the elution of transition metals or inhibit the deposition of eluted transition metal ions on the negative electrode, thereby improving battery performance (e.g., high rate charge / discharge characteristics) and safety. Summary of the invention

[0011] [Technical issues]

[0012] The present disclosure aims to provide a non-aqueous electrolyte for lithium secondary batteries containing an additive having an excellent effect of removing highly active Lewis acid byproducts or acidic substances formed as salt decomposition products in the electrolyte and forming a stable film on the electrode surface.

[0013] Furthermore, an object of the present disclosure is to provide a lithium secondary battery having enhanced high-temperature storage characteristics and high-temperature cycle characteristics by containing the non-aqueous electrolyte for a lithium secondary battery.

[0014] [Technical solution]

[0015] In order to achieve the above object, in one embodiment of the present disclosure, a non-aqueous electrolyte for a lithium secondary battery is provided, which contains a lithium salt, an organic solvent and a first additive, wherein the first additive contains a compound represented by the following formula 1.

[0016] [Formula 1]

[0017]

[0018] In formula 1,

[0019] Ar is a 5-membered or 6-membered nitrogen-containing ring, and

[0020] R1 and R2 are each independently an alkyl group having 1 to 8 carbon atoms.

[0021] According to another embodiment of the present disclosure, a lithium secondary battery is provided, including: a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator disposed between the negative electrode and the positive electrode, and the nonaqueous electrolyte for the lithium secondary battery.

[0022] [Beneficial Effects]

[0023] The non-aqueous electrolyte of the present invention contains a compound containing a 5-membered or 6-membered nitrogen-containing ring group and a phosphoryl group in the structure as an additive, thereby effectively removing Lewis acid byproducts as byproducts of electrolyte salts, and also suppressing metal elution by forming a solid SEI, and reducing gas by suppressing side reactions between the electrolyte and the electrode, thereby improving battery degradation caused by electrode degradation. Therefore, if the non-aqueous electrolyte for lithium secondary batteries of the present invention is applied, a lithium secondary battery with improved cycle characteristics and high-temperature storage safety can be obtained. DETAILED DESCRIPTION

[0024] Hereinafter, the present disclosure will be described in more detail.

[0025] The terms used herein are for describing exemplary embodiments only and are not intended to limit the present disclosure.

[0026] For example, it should be understood that terms such as “including,” “comprising,” or “having” used herein are intended to represent a particular feature, number, step, element, or combination thereof, and other components may be added unless these terms are used with “only.”

[0027] Furthermore, in this specification, unless otherwise specifically stated, the expression "%" means % by weight.

[0028] In addition, unless otherwise defined in the specification, the expression "substituted" means that at least one hydrogen bonded to carbon is substituted with an element other than hydrogen, for example, with an alkyl group having 1 to 5 carbon atoms or a fluorine element.

[0029] Although decomposition products such as hydrogen fluoride (HF) formed by water / thermal decomposition of conventional lithium salts form a film on the electrode surface, the transition metal constituting the positive electrode is easily eluted in the electrolyte, and the eluted transition metal ions are redeposited on the positive electrode, resulting in an increase in the positive electrode resistance. Since the transition metal that moves to the negative electrode through the electrolyte is electrodeposited on the negative electrode, the negative electrode self-discharges and destroys the solid electrolyte interface (SEI) that imparts passivation capability to the negative electrode, the interface resistance of the negative electrode is increased due to the promotion of additional electrolyte decomposition reactions.

[0030] Since this series of reactions reduces the amount of available lithium ions in the battery, it not only reduces the battery capacity, but also further decomposes the electrolyte, resulting in increased resistance.

[0031] The object of the present invention is to provide a non-aqueous electrolyte for a lithium secondary battery, which is oxidized and decomposed before the organic solvent by adding an additive that can effectively remove the decomposition products of the electrolyte salt (which cause degradation and malfunction behavior), thereby forming a solid film on the surface of the positive electrode; the present invention also provides a lithium secondary battery with improved high-rate charge and discharge at high temperature by containing the non-aqueous electrolyte.

[0032] Non-aqueous electrolyte for lithium secondary batteries

[0033] Specifically, in one embodiment of the present disclosure, the present disclosure provides a non-aqueous electrolyte for a lithium secondary battery, which includes: a lithium salt, an organic solvent and a first additive, wherein a compound represented by the following formula 1 is included as the first additive.

[0034] [Formula 1]

[0035]

[0036] In formula 1,

[0037] Ar is a 5-membered or 6-membered nitrogen-containing ring, and

[0038] R1 and R2 are each independently an alkyl group having 1 to 8 carbon atoms.

[0039] (1) Lithium salt

[0040] First, in the non-aqueous electrolyte for lithium secondary batteries of the present disclosure, any lithium salt commonly used in non-aqueous electrolytes for lithium secondary batteries may be used as the lithium salt without limitation. For example, the lithium salt may include Li + as a cation, and may include at least one selected from the following as an anion: 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 - .

[0041] Specifically, the lithium salt may include a selected from 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(trifluoromethanesulfonyl)imide LiTFSI), or a mixture of two or more thereof, preferably one or more of LiBF4, LiPF6, LiN(SO2F)2(LiFSI), LiN(SO2CF2CF3)2(LiBETI) and LiN(SO2CF3)2(LiTFSI). In addition, any lithium salt commonly used in lithium secondary battery electrolytes can be used without restriction.

[0042] The lithium salt may be appropriately changed within the normal use range, but the concentration in the electrolyte may be 0.8 M to 4.0 M, specifically 1.0 M to 3.0 M, to obtain the best effect of forming a film that prevents corrosion on the electrode surface.

[0043] When the concentration of the lithium salt is within the above range, the viscosity of the nonaqueous electrolyte can be controlled to achieve optimal impregnation, and the effect of improving the capacity and cycle characteristics of the lithium secondary battery can be obtained by increasing the mobility of lithium ions.

[0044] (2) Organic solvents

[0045] Furthermore, the organic solvent will be described.

[0046] Various organic solvents commonly used in non-aqueous electrolytes can be used as the non-aqueous organic solvent without limitation. The non-aqueous organic solvent is not limited as long as it can minimize decomposition caused by oxidation reaction during the charge and discharge process of the secondary battery and can exhibit desired properties together with the additive.

[0047] Specifically, the nonaqueous organic solvent may include a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixed organic solvent thereof.

[0048] The cyclic carbonate organic solvent is a high-viscosity organic solvent and can well dissociate the lithium salt in the non-aqueous electrolyte due to its high dielectric constant. Specific examples thereof can be at least one organic solvent selected from the following: ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, and can include at least one of ethylene carbonate (EC) and propylene carbonate (PC).

[0049] Linear carbonate organic solvents are organic solvents with low viscosity and low dielectric constant, wherein a typical example thereof may be at least one organic solvent selected from the following: dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate, and specifically may include at least one of dimethyl carbonate and ethyl methyl carbonate.

[0050] In the present disclosure, in order to ensure high ion conductivity, a mixture of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent may be used, and in this case, the mixing ratio thereof may be 10:90 to 50:50 by volume, specifically 20:80 to 40:60 by volume.

[0051] In addition, the organic solvent may also include at least one of a linear ester organic solvent and a cyclic ester organic solvent, which has a lower melting point and higher high-temperature storage stability than a cyclic carbonate organic solvent and / or a linear carbonate organic solvent, thereby being able to prepare an electrolyte with high ionic conductivity.

[0052] Specific examples of the linear ester organic solvent may be at least one organic solvent selected from methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate or butyl propionate, wherein specific examples thereof may include at least one of ethyl propionate and propyl propionate.

[0053] The cyclic ester organic solvent may include at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0054] Unless otherwise specified, the rest of the non-aqueous electrolyte of the present disclosure except the lithium salt, the first additive and the second additive may all be organic solvents.

[0055] (3) First additive

[0056] The first additive of the present disclosure may contain a compound represented by Formula 1 below.

[0057] [Formula 1]

[0058]

[0059] In formula 1,

[0060] Ar is a 5-membered or 6-membered nitrogen-containing ring, and

[0061] R1 and R2 are each independently an alkyl group having 1 to 8 carbon atoms.

[0062] The 5-membered or 6-membered nitrogen-containing ring contained in the structure of the compound represented by Formula 1 is a functional group having a Lewis base effect. When the unshared electron pair of the nitrogen atom is combined with PF5, the formation of Lewis acid substances, such as HF generated by the decomposition of PF5, can be suppressed. Therefore, this can suppress the deterioration phenomenon caused by the chemical reaction of the film on the surface of the positive or negative electrode caused by Lewis acid, and can also prevent the decomposition of additional battery electrolytes caused by the degradation or destruction of the film, and improve the high-temperature storage characteristics by reducing the self-discharge of the secondary battery.

[0063] In addition, the compound represented by Formula 1 contains a phosphoryl group in its structure and can form an inorganic film on the negative electrode surface, which inhibits the side reaction between the electrolyte and the electrode, thereby having the effect of reducing gas and preventing battery degradation.

[0064] In particular, the compound represented by Formula 1 forms a passivation film with high passivation ability on the surface of the negative electrode and the positive electrode while the functional groups such as nitrogen-containing rings or phosphoryl groups are reduced and decomposed, thereby preventing the negative electrode self-discharge reaction caused by the additional electrolyte reduction and decomposition reaction caused by the instability of SEI, preventing metal ions from eluting from the positive electrode, and inhibiting the eluted metal ions from being electro-deposited on the negative electrode. Therefore, the effect of improving the high temperature durability (such as cycle characteristics and capacity characteristics) of the lithium secondary battery can be achieved.

[0065] The compound represented by Formula 1 may be represented by Formula 1A.

[0066] [Formula 1A]

[0067]

[0068] In Formula 1A, R1 and R2 are each independently an alkyl group having 1 to 8 carbon atoms.

[0069] In Formula 1A, furthermore, R1 and R2 are each independently an alkyl group having 1 to 5 carbon atoms.

[0070] In Formula 1A, furthermore, R1 and R2 are each independently an alkyl group having 1 to 3 carbon atoms.

[0071] Preferably, the compound represented by Formula 1A may be one of the compound represented by Formula 1A-1 or the compound represented by Formula 1A-2.

[0072] [Formula 1A-1]

[0073]

[0074] [Formula 1A-2]

[0075]

[0076] The compound represented by Formula 1 may be included in an amount of 0.5 wt % to 3.0 wt % based on the total weight of the non-aqueous electrolyte.

[0077] In the case where the content of the compound represented by Formula 1 is within the above range, a secondary battery with improved overall performance can be prepared by forming a strong film on the negative electrode and the positive electrode, while preventing the side reactions caused by the additives and effectively preventing the degradation of the negative electrode during rapid charge and discharge. Specifically, if the content of the compound represented by Formula 1 is 0.5% by weight or more, the effect of removing the thermal decomposition products of the lithium salt (such as HF or PF5) during battery operation and the effect of forming a film more stably on the negative and positive electrode surfaces can be maintained. When the content of the compound represented by Formula 1 is 3.0% by weight or less, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, thereby effectively suppressing the increase in battery resistance caused by the decomposition of the additive, and preventing the degradation of the rate characteristics or low temperature life characteristics by not reducing the ionic conductivity of the electrolyte.

[0078] More specifically, the content of the compound represented by Formula 1 may be 0.5 wt % to 2.5 wt %, more preferably 0.5 wt % to 2.0 wt %.

[0079] (4) Second additive

[0080] In addition, in order to prevent the non-aqueous electrolyte from decomposing under high output conditions and causing collapse of the negative electrode, or to further improve the low-temperature high-rate discharge characteristics, high-temperature stability, overcharge protection, and the effect of inhibiting battery expansion at high temperatures, the non-aqueous electrolyte for the lithium secondary battery disclosed in the present invention may further include a second additive in the non-aqueous electrolyte if necessary.

[0081] As a typical example, the second additive may include at least one second additive selected from the following: cyclic carbonate compounds, halogenated carbonate compounds, sultone compounds, sulfate ester / salt compounds, phosphate ester / salt compounds, borate ester / salt compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds or lithium salt compounds.

[0082] The cyclic carbonate-based compound may include vinylene carbonate (VC) or vinyl ethylene carbonate.

[0083] The halogen-substituted carbonate compound may be fluoroethylene carbonate (FEC).

[0084] The sultone compound may include at least one selected from 1,3-propane sultone (PS), 1,4-butane sultone, ethylene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, or 1-methyl-1,3-propene sultone.

[0085] The sulfate compound may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyltrimethylene sulfate (MTMS).

[0086] The phosphate compound may include at least one selected from lithium difluorobis(oxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate and tris(trifluoroethyl)phosphate.

[0087] The borate compounds may include tetraphenylborate and lithium oxalyldifluoroborate.

[0088] The nitrile compound may include at least one compound selected from succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptanecarbonitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, benzyl cyanide, 2-fluorophenyl cyanide and 4-fluorophenyl cyanide.

[0089] The benzene compound may include fluorobenzene, and the amine compound may include triethanolamine or ethylenediamine.

[0090] The silane-based compound may include tetravinylsilane.

[0091] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, wherein the lithium salt compound may include at least one compound selected from LiPO2F2, LiODFB, LiBOB (lithium bis(oxalate)borate (LiB(C2O4)2) or LiBF4.

[0092] Among these second additives, in the case of containing at least one of vinylene carbonate, vinyl ethylene carbonate, or succinonitrile, a stronger SEI may be formed on the negative electrode surface during initial activation of the secondary battery.

[0093] Two or more second additives may be mixed and used, and the content of the additive may be less than 50 wt %, specifically 0.01 wt % to 10 wt %, preferably 0.05 wt % to 5.0 wt %, based on the total weight of the non-aqueous electrolyte. If the amount of the additive is less than 0.01 wt %, the effect of improving the low temperature output, high temperature storage characteristics and high temperature life characteristics of the battery is not obvious. If the amount of the second additive is greater than 50 wt %, side reactions in the electrolyte may occur excessively during the charging and discharging of the battery. In particular, if an excessive amount of an additive for forming SEI is added, the additive may not be fully decomposed at high temperatures, and may exist in the electrolyte at room temperature in the form of unreacted material or precipitation. Therefore, side reactions that reduce the life or resistance characteristics of the secondary battery may occur.

[0094] Lithium secondary battery

[0095] In addition, in another embodiment of the present disclosure, the present disclosure also provides a lithium secondary battery containing the non-aqueous electrolyte of the present disclosure.

[0096] The lithium secondary battery of the present invention can be prepared according to conventional methods known in the art. Specifically, the lithium secondary battery of the present invention can be prepared as follows: an electrode assembly having a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode is formed, the electrode assembly is contained in a battery housing, and then the non-aqueous electrolyte of the present invention is injected therein.

[0097] Next, each component of the lithium secondary battery of the present disclosure will be described in detail.

[0098] (1) Positive electrode

[0099] The positive electrode of the present disclosure may include a positive electrode active material layer including a positive electrode active material, and if necessary, the positive electrode active material layer may further include a conductive agent and / or a binder.

[0100] The positive electrode active material is a compound that can reversibly insert and release lithium, wherein the positive electrode active material can specifically contain a lithium composite metal oxide containing lithium and at least one metal selected from nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe) and aluminum (Al), for example, as shown in Formula 2 below.

[0101] [Formula 2]

[0102] Li 1+a Ni x Co yM 1 z M 2 w O2

[0103] In Formula 2,

[0104] M 1 is Mn, Al, or a combination thereof,

[0105] M 2 is at least one selected from Al, Zr, W, Ti, Mg, Ca, and Sr, where 0 ≤ a ≤ 0.5, 0.55 < x < 1.0, 0 < y ≤ 0.4, 0 < z ≤ 0.4, 0 ≤ w ≤ 0.1.

[0106] 1 + a represents the atomic fraction of lithium in the lithium transition metal oxide and can be 0 ≤ a ≤ 0.5, preferably 0 ≤ a ≤ 0.2, more preferably 0 ≤ a ≤ 0.1.

[0107] x represents the atomic fraction of nickel among all the transition metal elements in the lithium transition metal oxide and can be 0.55 < x < 1.0, more specifically 0.6 ≤ x ≤ 0.98, even more specifically 0.6 ≤ x ≤ 0.95.

[0108] y represents the atomic fraction of cobalt among all the transition metal elements in the lithium transition metal oxide and can be 0 < y ≤ 0.4, specifically 0 < y ≤ 0.3, more specifically 0.05 ≤ y ≤ 0.3.

[0109] z represents the atomic fraction of element M 1 among all the transition metal elements in the lithium transition metal oxide and can be 0 < z ≤ 0.4, preferably 0 < z ≤ 0.3, more preferably 0.01 ≤ z ≤ 0.3.

[0110] w represents the atomic fraction of element M 2 among all the transition metal elements in the lithium transition metal oxide and can be 0 < w ≤ 0.1, preferably 0 < w ≤ 0.05, more preferably 0 < w ≤ 0.02.

[0111] Specifically, the positive electrode active material may include a lithium composite transition metal oxide having a Ni content of 0.55 atm% or more to achieve a high-capacity battery, such as 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 0.1Co 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,.

[0112] As the positive electrode active material of the present disclosure, lithium manganese oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium cobalt oxides (e.g., LiCoO2, etc.), lithium nickel oxides (e.g., LiNiO2, etc.), lithium nickel manganese oxides (e.g., LiNi 1-Y Mn Y O2 (0 < Y < 1), LiMn 2-z Ni z O4 (0 < Z < 2)), lithium nickel cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (0 < Y1 < 1)), lithium manganese cobalt oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (0 < Z1 < 2) or Li(Ni p1 Co q1 Mn r2 )O4 (0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2) are used together with the lithium composite metal oxide represented by the above formula 2.

[0113] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 80% to 98% by weight, more specifically 85% to 98% by weight. When the content of the positive electrode active material is within the above range, excellent capacity characteristics can be exhibited.

[0114] Next, the conductive agent is used to provide conductivity to the electrode, wherein any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of the conductive agent can be the following conductive materials, for example: carbon black, 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 crystal structure; conductive fibers, such as carbon fibers or metal fibers; conductive powders, such as fluorocarbon powders, aluminum powders or nickel powders; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives, one or a mixture of two or more thereof can be used.

[0115] The conductive agent may be included in an amount of 0.1 wt % to 10 wt %, preferably 0.1 wt % to 5.0 wt %, based on the total weight of the positive electrode active material layer.

[0116] Next, the binder improves adhesion between positive electrode active material particles and between the positive electrode active material and a current collector.

[0117] As examples of adhesives, any one of the following or a mixture of two or more thereof can be used: fluororesin adhesives, including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber adhesives, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber or styrene-isoprene rubber; cellulose adhesives, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose or regenerated cellulose; polyol adhesives, such as polyvinyl alcohol; polyolefin adhesives, including polyethylene or polypropylene; polyimide adhesives; polyester adhesives; and silane adhesives.

[0118] The binder may be included in an amount of 0.1 wt % to 15 wt %, preferably 0.1 wt % to 10 wt %, based on the total weight of the positive electrode active material layer.

[0119] The positive electrode of the present disclosure described above can be prepared by a method for preparing a positive electrode known in the art. For example, the positive electrode can be prepared by the following method: dissolving or dispersing a positive electrode active material, a binder and / or a conductive agent in a solvent to prepare a positive electrode slurry, coating a positive electrode current collector with the positive electrode slurry, drying, and then rolling to form an active material layer, or by the following method: casting a positive electrode active material layer on a separate carrier, and then stacking a film separated from the carrier on the positive electrode current collector.

[0120] There is no particular limitation on the positive electrode current collector, as long as it has conductivity and does not cause adverse chemical changes in the battery, and for example: stainless steel, aluminum, nickel, titanium, fired carbon; or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used. In addition, the thickness of the positive electrode current collector is generally 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode material. For example, the positive electrode current collector can be used in various shapes such as a film, a sheet, a foil, a mesh, a porous body, a foam body, a non-woven fabric body, etc.

[0121] The solvent may be a commonly used solvent in the art, may include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone or water, and any one or a mixture of two or more thereof may be used. If the coating thickness, manufacturing yield and processability of the positive electrode material mixture are taken into consideration, the positive electrode material mixture may be adjusted to have an appropriate viscosity, and the amount of the solvent used may be sufficient without particular limitation.

[0122] (2) Negative electrode

[0123] Next, the negative electrode will be described.

[0124] The negative electrode of the present disclosure includes a negative electrode active material layer containing a negative electrode active material, and if necessary, the negative electrode active material layer may further include a conductive agent and / or a binder.

[0125] Various negative electrode active materials used in the art, such as a carbon-based negative electrode active material, a silicon-based negative electrode active material, or a mixture thereof, may be used as the negative electrode active material.

[0126] According to one embodiment, the negative electrode active material may include a carbon-based negative electrode active material, and as the carbon-based negative electrode active material, various carbon-based negative electrode active materials used in the art may be used, for example, graphite-based materials such as natural graphite, artificial graphite, and Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microbeads, mesophase pitch, high-temperature sintered carbon (e.g., coke derived from petroleum or coal tar pitch), soft carbon, and hard carbon. The shape of the carbon-based negative electrode active material is not particularly limited, and materials of various shapes may be used, such as irregular, planar, flaky, spherical, or fibrous.

[0127] Preferably, at least one carbon-based negative electrode active material of natural graphite and artificial graphite may be used as the negative electrode active material, and natural graphite and artificial graphite may be used together to suppress exfoliation of the active material by increasing adhesion to the current collector.

[0128] According to another embodiment, a carbon-based negative electrode active material and a silicon-based negative electrode active material may be used together as the negative electrode active material.

[0129] For example, the silicon-based negative electrode active material may include at least one selected from the following: 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 following: alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, but not Si). The element Y may be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, 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.

[0130] Since the silicon-based negative electrode active material has higher capacity characteristics than the carbon-based negative electrode active material, better capacity characteristics can be obtained when the silicon-based negative electrode active material is further included. However, for a negative electrode containing a silicon-based negative electrode active material, compared with a graphite negative electrode, its SEI contains more oxygen-rich O-components, and when the electrolyte contains a Lewis acid (such as HF or PF5), the SEI containing oxygen-rich components is more likely to be decomposed. Therefore, for a negative electrode containing a silicon-based negative electrode active material, it is necessary to suppress the formation of Lewis acids (such as HF and PF5) in the electrolyte, or remove (or scavenge) the formed Lewis acids to maintain the stability of the SEI. Since the electrolyte additive contained in the non-aqueous electrolyte of the present disclosure has excellent effects of forming a stable film on the positive and negative electrodes and scavenging Lewis acids, when a negative electrode containing a silicon-based negative electrode active material is used, the decomposition of the SEI film can be effectively suppressed.

[0131] The mixing ratio (weight ratio) of the silicon-based negative electrode active material and the carbon-based negative electrode active material may be from 3:97 to 99:1, preferably from 5:95 to 15:85. 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 volume expansion of the silicon-based negative electrode active material is suppressed, and at the same time, the capacity characteristics are improved, so excellent cycle performance can be ensured.

[0132] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material may be 80% by weight to 99% by weight. When the amount of the negative electrode active material satisfies the above range, excellent capacity characteristics and electrochemical performance can be obtained.

[0133] Next, the conductive agent is a component for further improving the conductivity of the negative electrode active material layer, and its addition amount can be 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery. For example, the following conductive materials can be used, for example: carbon black, 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 crystal 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 whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives.

[0134] The binder is a component that helps the conductive agent and the active material to adhere to each other. Based on the total weight of the negative electrode active material layer, the amount of the binder added can be 0.1 wt % to 10 wt %. Examples of the binder can be: fluororesin binders, including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber or styrene-isoprene rubber; cellulose binders, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose or regenerated cellulose; polyol binders, such as polyvinyl alcohol; polyolefin binders, including polyethylene or polypropylene; polyimide binders; polyester mixtures and silane binders.

[0135] The content of the binder may generally be 0.1 wt % to 15 wt %, preferably 0.1 wt % to 10 wt %, based on the total weight of the negative electrode active material layer.

[0136] The negative electrode can be prepared by a method for preparing a negative electrode known in the art. For example, the negative electrode can be prepared by dissolving or dispersing the negative electrode active material and optional binder and conductive agent in a solvent to prepare a negative electrode slurry, coating a negative electrode current collector with the negative electrode slurry, rolling and drying, or the negative electrode slurry can be cast on a separate support, and then a film separated from the support is laminated on the negative electrode current collector.

[0137] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. The thickness of the negative electrode current collector can generally be 3 μm to 500 μm. Similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes such as a film, a sheet, a foil, a mesh, a porous body, a foam, a non-woven fabric, etc.

[0138] The solvent may be a commonly used solvent in the art, and may include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone or water, and any one or a mixture of two or more thereof may be used. If the coating thickness, manufacturing yield and processability of the negative electrode material mixture are taken into consideration, the negative electrode slurry may be adjusted to have an appropriate viscosity, and the amount of solvent used may be sufficient without particular limitation.

[0139] (3) Diaphragm

[0140] The lithium secondary battery of the present disclosure includes a separator between a positive electrode and a negative electrode.

[0141] The separator separates the negative electrode from the positive electrode and provides a path for the movement of lithium ions. Any separator can be used without particular limitation, as long as it is commonly used as a separator in a lithium secondary battery. In particular, a separator having high moisture retention capacity for the electrolyte and low resistance to the movement of electrolyte ions is more desirable.

[0142] Specifically, as a separator, a porous polymer film can be used alone or in a laminated form, for example, a porous polymer film prepared from a polyolefin polymer (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), and a conventional porous non-woven fabric can also be used, such as a non-woven fabric formed from high melting point glass fiber or polyethylene terephthalate fiber. In addition, a coated separator comprising a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and can be optionally used in a single-layer or multi-layer structure.

[0143] As described above, the lithium secondary battery of the present disclosure can be suitably used in portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0144] The shape of the lithium secondary battery of the present disclosure is not particularly limited, but a cylindrical type using a can, a prismatic type, a pouch type, or a coin type may be used.

[0145] The lithium secondary battery of the present disclosure can be used not only in a battery cell used as a power source for small-sized devices but also can be preferably used as a unit cell of a large or medium-sized battery pack including a plurality of battery cells.

[0146] Example

[0147] Example 1.

[0148] (Preparation of non-aqueous electrolyte)

[0149] LiPF6 is dissolved in a non-aqueous organic solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 so that the concentration of LiPF6 is 1.0M, and 0.5 wt% of the compound represented by Formula 1A-1 and 0.5 wt% of vinylene carbonate (VC) are added to prepare a non-aqueous electrolyte (see Table 1 below).

[0150] (Preparation of Secondary Battery)

[0151] The positive electrode active material particles (Li(Ni 0.9 Co 0.03 Mn 0.06 Al 0.01 )O2), a conductive agent (carbon black), and a binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) at a weight ratio of 97.6:0.8:1.6 to prepare a positive electrode slurry (solid content: 60 wt%). An aluminum (Al) film with a thickness of 13.5 μm as a positive electrode current collector was coated with the positive electrode slurry, dried, and then roll-pressed to prepare a positive electrode.

[0152] The negative electrode active material (graphite: SiO = 94:6 weight ratio), the binder (SBR-CMC) and the conductive agent (carbon black) were added to water as a solvent at a weight ratio of 97.6:0.8:1.6 to prepare a negative electrode slurry (solid content: 60 weight %). A copper (Cu) film with a thickness of 6 μm as a negative electrode current collector was coated with the negative electrode slurry, dried, and then rolled to prepare a negative electrode.

[0153] A porous polypropylene separator was disposed between the prepared positive electrode and negative electrode to prepare an electrode assembly, which was then housed in a battery case, and the nonaqueous electrolyte for a lithium secondary battery of the present disclosure was then injected therein to prepare a lithium secondary battery.

[0154] Example 2.

[0155] (Preparation of non-aqueous electrolyte)

[0156] LiPF6 was dissolved in a non-aqueous organic solvent so that the concentration of LiPF6 was 1.0 M, and 1.0 wt% of the compound represented by Formula 1A-1 and 0.5 wt% of vinylene carbonate (VC) were added to prepare a non-aqueous electrolyte.

[0157] (Preparation of Secondary Battery)

[0158] A lithium secondary battery was prepared in the same manner as in Example 1, except that the nonaqueous electrolyte prepared above was injected instead of the nonaqueous electrolyte of Example 1 (see Table 1 below).

[0159] Comparative Example 1.

[0160] (Preparation of non-aqueous electrolyte)

[0161] LiPF6 was dissolved in a non-aqueous organic solvent so that the concentration of LiPF6 was 1.0 M, and 0.5 wt% of vinylene carbonate (VC) was added as an additive to prepare a non-aqueous electrolyte.

[0162] (Preparation of Secondary Battery)

[0163] A lithium secondary battery was prepared in the same manner as in Example 1, except that the nonaqueous electrolyte prepared above was injected instead of the nonaqueous electrolyte of Example 1 (see Table 1 below).

[0164] Comparative Example 2.

[0165] (Preparation of non-aqueous electrolyte)

[0166] LiPF6 is dissolved in a non-aqueous organic solvent so that the concentration of LiPF6 is 1.0M. Instead of adding the compound represented by Formula 1A-1, 0.5 wt% of the compound represented by the following Formula 3 and 0.5 wt% of vinylene carbonate (VC) are added as additives to prepare a non-aqueous electrolyte.

[0167] [Formula 3]

[0168]

[0169] (Preparation of Secondary Battery)

[0170] A lithium secondary battery was prepared in the same manner as in Example 1, except that the nonaqueous electrolyte prepared above was injected instead of the nonaqueous electrolyte of Example 1 (see Table 1 below).

[0171] Comparative Example 3.

[0172] (Preparation of non-aqueous electrolyte)

[0173] LiPF6 is dissolved in a non-aqueous organic solvent so that the concentration of LiPF6 is 1.0M, and instead of adding the compound represented by Formula 1A-1, 0.5 wt% of the compound represented by the following Formula 4 and 0.5 wt% of vinylene carbonate (VC) are added as additives to prepare a non-aqueous electrolyte.

[0174] [Formula 4]

[0175]

[0176] (Preparation of Secondary Battery)

[0177] A lithium secondary battery was prepared in the same manner as in Example 1, except that the nonaqueous electrolyte prepared above was injected instead of the nonaqueous electrolyte of Example 1 (see Table 1 below).

[0178] [Table 1]

[0179]

[0180] In Table 1, the abbreviation of each compound has the following meaning.

[0181] EC: Ethylene carbonate

[0182] EMC: Ethyl Methyl Carbonate

[0183] VC: Vinylene carbonate

[0184] Experimental example

[0185] Experimental Example 1. Evaluation of resistance increase rate after high temperature storage

[0186] After the lithium secondary battery prepared in the embodiment and the comparative example was charged at a rate of 0.1C for 3 hours for the formation process, it was charged to 4.2V (0.05C cutoff) at a rate of 0.33C under constant current / constant voltage conditions at 25°C, the battery was fully charged to SOC100%, and the battery was stored at high temperature (60°C) for 16 weeks. Subsequently, the battery was transferred to a charger and discharger at room temperature (25°C) to measure the resistance, and the resistance increase rate was calculated using the following equation 1. The results are shown in Table 2 below.

[0187] [Equation 1]

[0188] Resistance increase rate (%) = {(resistance after high temperature storage - initial resistance) / initial resistance} × 100

[0189] Experimental Example 2. Evaluation of gas generation after high-temperature storage

[0190] After the lithium secondary battery prepared in the embodiment and the comparative example was charged at a rate of 0.1C for 3 hours for the formation process, it was charged to 4.2V (0.05C cutoff) at a rate of 0.33C under constant current / constant voltage conditions at 25°C, so that the battery was fully charged to SOC100%, and the battery was stored at high temperature (60°C) for 16 weeks. The gas generation was then measured by GC analysis at room temperature (25°C). The gas generation measured in Comparative Example 1 was set to 100%, and the relative gas generation of each battery was calculated as a percentage and shown in Table 2 below.

[0191] Experimental Example 3. Evaluation of capacity retention after high temperature cycling

[0192] After the lithium secondary battery prepared in the embodiment and the comparative example was charged at a rate of 0.1C for 3 hours for the formation process, it was charged to 4.2V (0.05C cutoff) at a rate of 0.33C under constant current / constant voltage conditions at 25°C to make the battery fully charged to SOC100%. At 45°C, the fully charged battery was charged to 4.2V at a rate of 0.33C under constant current / constant voltage conditions, and discharged to 2.8V at a rate of 0.33 C under constant current conditions, which was set as one cycle. After 300 cycles, the capacity retention rate after 300 cycles was calculated using the following equation 2, and the results are shown in Table 2 below.

[0193] [Equation 2]

[0194] Capacity retention rate (%) = (capacity after 300 cycles / capacity after 1 cycle) × 100

[0195] [Table 2]

[0196] Resistance increase rate (%) Gas generation (%) Capacity retention rate (%) Example 1 14.04 72.5 89.9 Example 2 13.29 70.2 90.2 Comparative Example 1 32.84 100 88.3 Comparative Example 2 28.11 94.3 88.4 Comparative Example 3 24.54 90.1 88.8

[0197] Referring to Table 2 above, it can be seen that the resistance increase rate (%) and gas generation (%) of the secondary batteries prepared in Examples 1 and 2 of the present disclosure are reduced, and the capacity retention rate (%) is improved compared with the batteries prepared in 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 comprises a compound represented by Formula 1: [Formula 1] in, In formula 1, Ar is a 5-membered or 6-membered nitrogen-containing ring, and R1 and R2 are each independently an alkyl group having 1 to 8 carbon atoms.

2. The non-aqueous electrolyte for lithium secondary battery according to claim 1, wherein The compound represented by Formula 1 is a compound represented by Formula 1A: [Formula 1A] Wherein, in Formula 1A, R1 and R2 are each independently an alkyl group having 1 to 8 carbon atoms.

3. The non-aqueous electrolyte for lithium secondary battery according to claim 2, wherein R1 and R2 are each independently an alkyl group having 1 to 5 carbon atoms.

4. The non-aqueous electrolyte for lithium secondary battery according to claim 2, wherein R1 and R2 are each independently an alkyl group having 1 to 3 carbon atoms.

5. The non-aqueous electrolyte for lithium secondary battery according to claim 2, wherein The compound represented by Formula 1A is a compound represented by Formula 1A-1 or Formula 1A-2: [Formula 1A-1] [Formula 1A-2] 6. The non-aqueous electrolyte for lithium secondary battery according to claim 1, wherein The compound represented by Formula 1 is included in an amount of 0.5 wt % to 3.0 wt % based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.

7. The non-aqueous electrolyte for lithium secondary battery according to claim 6, wherein The compound represented by Formula 1 is included in an amount of 0.5 wt % to 2.5 wt % based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.

8. The non-aqueous electrolyte for a lithium secondary battery as claimed in claim 1, further comprising at least one second additive selected from the group consisting of: cyclic carbonate compounds, halogenated carbonate compounds, sultone compounds, sulfate ester / salt compounds, phosphate ester / salt compounds, borate ester / salt compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds or lithium salt compounds.

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 disposed between the negative electrode and the positive electrode; And the non-aqueous electrolyte for lithium secondary battery according to claim 1.

10. The lithium secondary battery according to claim 9, wherein: The positive electrode active material includes lithium and at least one metal selected from nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al).

Images