Additive and lithium secondary battery containing the same

Abstract

The present invention provides a lithium secondary battery comprising an additive represented by Chemical Formula 1, a non-aqueous organic solvent, a lithium salt, and an electrolyte solution comprising the additive; a positive electrode comprising a positive electrode active material; and a negative electrode comprising a negative electrode active material, the positive electrode active material comprising a cobalt-free lithium nickel manganese oxide. The details of Chemical Formula 1 are as described in the specification.

Description

[Technical field]

[0001] The present disclosure relates to an additive and a lithium secondary battery containing the same. [Background technology]

[0002] Lithium secondary batteries are rechargeable and have an energy density per unit weight that is more than three times higher than conventional lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and nickel-zinc batteries, and can be charged quickly. As a result, they have been commercialized for use in laptops, mobile phones, power tools, and electric bicycles, and research and development into further improving energy density is being actively conducted.

[0003] Such a lithium secondary battery is used by injecting an electrolyte into a battery cell including a positive electrode having a positive electrode active material capable of lithium intercalation and deintercalation and a negative electrode having a negative electrode active material capable of lithium intercalation and deintercalation.

[0004] The electrolyte serves as a medium for transferring lithium ions between the negative electrode and the positive electrode, and generally uses an organic solvent in which a lithium salt is dissolved. The electrolyte is important in determining the stability and performance of a lithium secondary battery.

[0005] The electrolyte is generally prepared by adding a lithium salt such as LiPF6, LiBF4, or LiFSI to a mixed solvent of a highly dielectric cyclic carbonate such as propylene carbonate or ethylene carbonate and a linear carbonate such as diethyl carbonate, ethyl methyl carbonate, or dimethyl carbonate. As battery development in various fields becomes more active, importance is attached to the development of a battery that ensures high output and high stability over a wide temperature range, and in terms of electrolyte, importance is attached to the development of an optimal combination of an organic solvent and an additive that can suppress high output, long life characteristics, storage characteristics at high temperatures, and swelling, capacity loss, and resistance increase.

[0006] On the other hand, the performance of IT devices is gradually improving, and there is a demand for higher-capacity batteries. The energy density can be increased by expanding the voltage range to achieve higher capacity, but there is a problem that the electrolyte is oxidized in the high-voltage range, degrading the performance of the positive electrode.

[0007] In particular, cobalt-free lithium nickel manganese oxide as a positive electrode active material is a positive electrode active material that does not contain cobalt in its composition and is composed mainly of nickel, manganese, etc. Positive electrodes containing this are economical and can achieve high energy density, and are therefore in the spotlight as a next-generation positive electrode active material.

[0008] However, when a positive electrode containing a cobalt-free lithium nickel manganese oxide is used in a high voltage environment, the positive electrode structure collapses, causing transition metal elution, which can lead to problems such as gas generation inside the cell and capacity reduction. This transition metal elution phenomenon tends to become more severe in high temperature environments, and the eluted transition metals are precipitated on the surface of the negative electrode, causing side reactions, which increase the battery resistance and reduce the battery life and output characteristics.

[0009] This has created a demand for an electrolyte that can be used under high voltage and high temperature conditions when using a positive electrode containing a cobalt-free lithium nickel manganese oxide. Summary of the Invention [Problem to be solved by the invention]

[0010] One embodiment is to provide an additive with good high temperature properties.

[0011] Another embodiment is to provide a lithium secondary battery having improved high voltage characteristics and high temperature characteristics by combining a positive electrode containing a cobalt-free lithium nickel manganese-based oxide with an electrolyte that can effectively protect the positive electrode containing a cobalt-free lithium nickel manganese-based oxide. [Means for solving the problem]

[0012] One embodiment of the present invention provides an additive represented by the following Chemical Formula 1:

[0013] [Chemical formula 1] [ka]

[0014] In the above Chemical Formula 1, R 1 ~R 8 are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C6 to C12 aryl group, or a combination thereof; n is an integer from 0 to 2.

[0015] The above-mentioned Chemical Formula 1 is represented by any one of the following Chemical Formulas 1-1 to 1-3.

[0016] [Chemical formula 1-1] [Chemical formula 1-2] [ka]

[0017] [Chemical formula 1-3] [ka]

[0018] In the above Chemical Formulas 1-1 to 1-3, R 1 ~R 8 is the same as above, and R 5a , R 6a , R 5b , and R 6bare each independently hydrogen, halogen, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C6 to C12 aryl group, or a combination thereof.

[0019] R 1 ~R 8 may each independently be hydrogen, halogen, or a substituted or unsubstituted C1 to C5 alkyl group.

[0020] The additive represented by Chemical Formula 1 can be selected from the compounds listed in Group 1 below.

[0021] [Group 1] [ka]

[0022] Another embodiment of the present invention provides a lithium secondary battery comprising: an electrolyte solution including a non-aqueous organic solvent, a lithium salt, and the additive described above; a positive electrode including a positive electrode active material; and a negative electrode including a negative electrode active material, the positive electrode active material including a cobalt-free lithium nickel manganese-based oxide.

[0023] The cobalt-free lithium nickel manganese oxide may include a lithium composite oxide represented by the following Chemical Formula 2.

[0024] [Chemical formula 2] Li a Ni x Mn y M1 z M2 w O 2-b X b In the above Chemical Formula 2, 0.9≦a<1.2, 0≦b<0.1, 0≦w<0.1, 0.6≦x<1.0, 0 <y<0.4、0<z<0.1、w+x+y+z=1であり、 M1 is one or more elements selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Ce, Cr, and Nb. M2 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is one or more elements selected from S, F, and P.

[0025] The chemical formula 2 is represented by the following chemical formula 2-1.

[0026] [Chemical formula 2-1] Li a Ni x1 Mn y1 Al z1 M2 w1 O 2-b X b In the chemical formula 2-1, 0.9 ≤ a < 1.2, 0 ≤ b < 0.1, 0 ≤ w1 < 0.1, 0.6 ≤ x1 < 1.0, 0 < y1 < 0.4, 0 < z1 < 0.1, and w1 + x1 + y1 + z1 = 1. M2 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is one or more elements selected from S, F, and P.

[0027] In the chemical formula 2-1, x1 may be 0.6 ≤ x1 ≤ 0.79, y1 may be 0.2 ≤ y1 ≤ 0.39, and z1 may be 0.01 ≤ z1 < 0.1.

[0028] The negative electrode active material can include at least one of graphite and a Si composite.

[0029] The Si composite can include a core containing Si particles and an amorphous carbon coating layer.

[0030] The core containing the Si particles can include one or more of a Si-C composite, SiO x (0 < x ≤ 2) and a Si alloy.

[0031] The core may include a void in the center.

[0032] The radius of the central portion may correspond to 30% to 50% of the radius of the Si-C composite, and the average particle size of the Si particles may be 10 nm to 200 nm.

[0033] The central portion does not contain amorphous carbon, and amorphous carbon may be present only in the surface portion of the negative electrode active material.

[0034] The negative electrode active material may further include crystalline carbon.

[0035] The additive may be included in an amount of 0.05 to 5.0 parts by weight based on 100 parts by weight of the total electrolyte solution.

[0036] The additive may be included in an amount of 0.05 to 3.0 parts by weight based on 100 parts by weight of the total electrolyte solution.

[0037] The additives may further include at least one other additive selected from the group consisting of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), and 2-fluorobiphenyl (2-FBP).

[0038] The lithium secondary battery can also operate at a high voltage of 4.4V or more. Effect of the Invention

[0039] By using a combination of electrolytes containing additives that can effectively protect the positive and negative electrodes, it is possible to suppress the increase in battery resistance during high-temperature storage, reduce the amount of gas generation, and realize a lithium secondary battery with improved high-temperature characteristics. [Brief description of the drawings]

[0040] [Figure 1] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] Hereinafter, a lithium secondary battery according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings, which are provided by way of example only and are not intended to limit the present invention, but are merely defined by the categories of claims set forth below.

[0042] In this specification, unless otherwise defined, "substituted" means that at least one hydrogen of a substituent or compound is replaced with deuterium, a halogen group, a hydroxyl group, an amino group, a substituted or unsubstituted C1 to C30 amine group, a nitro group, a substituted or unsubstituted C1 to C40 silyl group, a C1 to C30 alkyl group, a C1 to C10 alkylsilyl group, a C6 to C30 arylsilyl group, a C3 to C30 cycloalkyl group, a C3 to C30 heterocycloalkyl group, a C6 to C30 aryl group, a C2 to C30 heteroaryl group, a C1 to C20 alkoxy group, a C1 to C10 fluoroalkyl group, a cyano group, or a combination thereof.

[0043] In one embodiment of the present invention, "substitution" means that at least one hydrogen of a substituent or compound is substituted with deuterium, a halogen group, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C10 fluoroalkyl group, or a cyano group. In a specific example of the present invention, "substitution" means that at least one hydrogen of a substituent or compound is substituted with deuterium, a halogen group, a C1-C20 alkyl group, a C6-C30 aryl group, a C1-C10 fluoroalkyl group, or a cyano group. In a specific example of the present invention, "substitution" means that at least one hydrogen of a substituent or compound is substituted with deuterium, a halogen group, a C1-C5 alkyl group, a C6-C18 aryl group, a C1-C5 fluoroalkyl group, or a cyano group. In addition, in a specific example of the present invention, "substituted" means that at least one hydrogen of a substituent or compound is replaced with deuterium, a cyano group, a halogen group, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0044] In the present specification, the term "aryl group" refers to a general concept of a group having one or more aromatic hydrocarbon moieties, and includes a form in which all elements of the aromatic hydrocarbon moiety have p-orbitals and these p-orbitals form conjugation, such as a phenyl group, naphthyl group, etc., a form in which two or more aromatic hydrocarbon groups are linked through a sigma bond, such as a biphenyl group, a terphenyl group, a quaterphenyl group, etc., and a non-aromatic fused ring in which two or more aromatic hydrocarbon groups are directly or indirectly fused, such as a fluorenyl group, etc.

[0045] Aryl groups include monocyclic, polycyclic or fused cyclic polycyclic (ie, rings which share adjacent pairs of carbon atoms) functional groups.

[0046] More specifically, the substituted or unsubstituted C6-C20 aryl group may be, but is not limited to, a substituted or unsubstituted phenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted anthracenyl group, a substituted or unsubstituted phenanthrenyl group, a substituted or unsubstituted naphthacenyl group, a substituted or unsubstituted pyrenyl group, a substituted or unsubstituted biphenyl group, a substituted or unsubstituted p-terphenyl group, a substituted or unsubstituted m-terphenyl group, a substituted or unsubstituted o-terphenyl group, a substituted or unsubstituted chrysenyl group, a substituted or unsubstituted triphenylene group, a substituted or unsubstituted perylenyl group, a substituted or unsubstituted fluorenyl group, or a combination thereof.

[0047] Lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, into cylindrical, square, coin, pouch, and other types depending on the shape, and into bulk and thin film types depending on the size. The structure and manufacturing method of these batteries are widely known in the art, so a detailed description will be omitted.

[0048] Here, a cylindrical lithium secondary battery will be described as an example of a lithium secondary battery. FIG. 1 is a schematic diagram showing a structure of a lithium secondary battery according to an embodiment. Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment includes a battery cell including a positive electrode 114, a negative electrode 112 facing the positive electrode 114, a separator 113 disposed between the positive electrode 114 and the negative electrode 112, and an electrolyte (not shown) impregnating the positive electrode 114, the negative electrode 112, and the separator 113, a battery container 120 that houses the battery cell, and a sealing member 140 that seals the battery container 120.

[0049] The configuration of the lithium secondary battery 100 according to one embodiment of the present invention will now be described in more detail.

[0050] A lithium secondary battery according to one embodiment of the present invention includes an electrolyte, a positive electrode, and a negative electrode.

[0051] The electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive.

[0052] The additive according to one embodiment will be described below.

[0053] The additive according to one embodiment of the present invention is represented by the following Chemical Formula 1.

[0054] [Chemical formula 1] [ka]

[0055] In the above Chemical Formula 1, R 1 ~R 8 are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C6 to C12 aryl group, or a combination thereof; n is an integer from 0 to 2.

[0056] The additive represented by Chemical Formula 1 is reductively decomposed prior to the carbonate-based solvent contained in the non-aqueous organic solvent to form a solid electrolyte interface (SEI) film on the negative electrode, thereby preventing the decomposition of the electrolyte and the resulting decomposition reaction of the electrode, thereby suppressing an increase in internal resistance due to gas generation.

[0057] In addition, a film is also formed on the surface of the positive electrode, preventing decomposition of the positive electrode surface and oxidation of the electrolyte, thereby contributing to improved high-temperature life characteristics.

[0058] In other words, by including the additive, the life characteristics and high temperature characteristics of the battery can be improved.

[0059] The above-mentioned Chemical Formula 1 is represented by any one of the following Chemical Formulas 1-1 to 1-3.

[0060] [Chemical formula 1-1] [Chemical formula 1-2] [ka]

[0061] [Chemical formula 1-3] [ka]

[0062] In the above Chemical Formulas 1-1 to 1-3, R 1 ~R 8 is the same as above, R 5a , R 6a , R 5b , and R 6b are each independently hydrogen, halogen, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C6 to C12 aryl group, or a combination thereof.

[0063] R 1 ~R 8 may each independently be hydrogen, halogen, or a substituted or unsubstituted C1 to C5 alkyl group.

[0064] The additive represented by Chemical Formula 1 can be selected from the compounds listed in Group 1 below.

[0065] [Group 1] [ka]

[0066] For example, the additive may be included in an amount of 0.05 to 5.0 parts by weight, for example, 0.05 to 4.0 parts by weight, or 0.05 to 3.0 parts by weight, based on 100 parts by weight of the total electrolyte solution.

[0067] When the amount of the additive used is within the above range, a lithium secondary battery having improved resistance characteristics and gas generation during high-temperature storage can be realized.

[0068] Meanwhile, the additive may further include other additives in addition to the above-mentioned compounds.

[0069] Other additives may include at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), and 2-fluorobiphenyl (2-FBP).

[0070] By further including the other additives, the life span can be further improved and gas generated from the positive and negative electrodes during high temperature storage can be effectively controlled.

[0071] The other additives may be included in an amount of 0.2 to 20 parts by weight, specifically 0.2 to 15 parts by weight, for example, 0.2 to 10 parts by weight, based on 100 parts by weight of the total electrolyte solution for lithium secondary batteries.

[0072] In this case, the content of other additives can minimize the increase in film resistance and contribute to improving the battery performance.

[0073] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0074] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent.

[0075] Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, caprolactone, etc. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. The ketone solvent may be cyclohexanone, etc. The alcohol solvent may be ethyl alcohol, isopropyl alcohol, etc., and the aprotic solvent may be nitriles such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain an aromatic ring or an ether bond with a double bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc.

[0076] The non-aqueous organic solvent may be used alone or in combination of one or more thereof. When one or more thereof are used in combination, the mixing ratio may be appropriately adjusted according to the desired battery performance, which is widely understood by those working in the field.

[0077] In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate in a volume ratio of 5:5 to 1:9, in which case the electrolyte performance is excellent.

[0078] In particular, in one embodiment of the present invention, the non-aqueous organic solvent may contain the cyclic carbonate and the chain carbonate in a volume ratio of 5:5 to 2:8, and as a specific example, the cyclic carbonate and the chain carbonate may be contained in a volume ratio of 4:6 to 2:8.

[0079] As a more specific example, the cyclic carbonate and the chain carbonate may be contained in a volume ratio of 3:7 to 2:8.

[0080] The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent in addition to the carbonate-based solvent, and the carbonate-based solvent and the aromatic hydrocarbon-based solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0081] As the aromatic hydrocarbon solvent, an aromatic hydrocarbon compound represented by the following formula 3 can be used.

[0082] [Chemical formula 3] [ka]

[0083] In the above Chemical Formula 3, R 9 ~R 14 are the same or different and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.

[0084] Specific examples of the aromatic hydrocarbon solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorobenzene ... and combinations thereof.

[0085] The lithium salt is a material that dissolves in a non-aqueous organic solvent, acts as a source of lithium ions in a battery, enables the basic operation of a lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts include LiPF6, LiBF4, lithium difluoro(oxalate)borate (LiDFOB), LiPO2F2, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI)), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(Cy F 2y+1 The lithium salt may be one or more selected from the group consisting of LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalato)borate: LiBOB), where x and y are natural numbers, for example, integers from 1 to 20. The lithium salt is preferably used at a concentration within the range of 0.1M to 2.0M when the lithium salt concentration is within the above range, since the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance can be exhibited and lithium ions can be effectively transferred.

[0086] The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0087] The positive electrode active material provides a lithium secondary battery containing a cobalt-free lithium nickel manganese oxide.

[0088] The cobalt-free lithium nickel manganese oxide may include at least one of lithium composite oxides represented by the following Chemical Formula 2.

[0089] [Chemical formula 2] Li a Ni x Mn y M1 z M2 w O 2-b X b In the above Chemical Formula 2, 0.9≦a<1.2, 0≦b<0.1, 0≦w<0.1, 0.6≦x<1.0, 0 <y<0.4、0<z<0.1、w+x+y+z=1であり、 M1 is one or more elements selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Ce, Cr and Nb; M2 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W and Zr, and X is one or more elements selected from S, F and P.

[0090] Of course, the lithium composite oxide may have a coating layer on its surface, or the lithium composite oxide may be mixed with a compound having a coating layer. The coating layer may contain at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds constituting these coating layers may be amorphous or crystalline. The coating elements contained in the coating layer may be Mg, Al, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. In the coating layer forming step, any coating method may be used as long as the compound is coated with such elements by a method (e.g., spray coating, immersion method, etc.) that does not adversely affect the physical properties of the positive electrode active material, and this is well understood by those working in the field, so a detailed explanation will be omitted.

[0091] As an example, Formula 2 is represented by Formula 2-1 below.

[0092] [Chemical formula 2-1] Li a Ni x1 Mn y1 Al z1 M2 w1 O 2-b X b In the above Chemical Formula 2-1, 0.9 ≤ a < 1.2, 0 ≤ b < 0.1, 0 ≤ w1 < 0.1, 0.6 ≤ x1 < 1.0, 0 < y1 < 0.4, 0 < z1 < 0.1, and w1 + x1 + y1 + z1 = 1, where M2 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is one or more elements selected from S, F, and P.

[0093] In one embodiment, in the chemical formula 1-1, 0.6 ≤ x1 ≤ 0.9, 0.1 ≤ y1 ≤ 0.4, and 0 ≤ z1 ≤ 0.1 may be satisfied, or 0.6 ≤ x1 ≤ 0.8, 0.2 ≤ y1 ≤ 0.4, and 0 ≤ z1 ≤ 0.1 may be satisfied.

[0094] For example, in the chemical formula 2-1, 0.6 ≤ x1 ≤ 0.79, 0.2 ≤ y1 ≤ 0.39, and 0.01 ≤ z1 < 0.1 may be satisfied.

[0095] The content of the positive electrode active material may be 90% by weight to 98% by weight based on the total weight of the positive electrode active material layer.

[0096] In one embodiment of the present invention, the positive electrode active material layer may contain a binder. At this time, the content of the binder may be 1% by weight to 5% by weight based on the total weight of the positive electrode active material layer.

[0097] The binder serves to make the positive electrode active material particles adhere well to each other and also make the positive electrode active material adhere well to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0098] The positive electrode current collector may be made of Al, but is not limited thereto.

[0099] The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector and including a negative electrode active material.

[0100] The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0101] The material capable of reversibly inserting / extracting lithium ions is a carbon material, and any carbon-based negative electrode active material generally used in lithium ion secondary batteries may be used, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination of these. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0102] As the lithium metal alloy, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn can be used.

[0103] The material capable of doping and dedoping lithium includes Si, Si-C composite, SiO x(0 < x < 2), Si-Q alloy (wherein Q is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), Sn, SnO2, Sn-R (wherein R is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn), etc. can be mentioned, and at least one of these can also be mixed with SiO2 and used. As the elements Q and R, 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, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof can be used.

[0104] Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, or lithium titanate.

[0105] In a specific embodiment, the negative electrode active material can include at least one of graphite and a Si composite.

[0106] The Si composite includes a core containing Si particles and amorphous carbon. For example, the Si particles can include one or more of Si-C composite, SiO x (0 < x ≤ 2) and Si alloy.

[0107] For example, the Si-C composite can include a core containing Si particles and amorphous carbon.

[0108] The core can include voids in its central part, and the radius of the central part can correspond to 30% - 50% of the radius of the Si-C composite.

[0109] The average particle size of the Si particles may be 10 nm to 200 nm.

[0110] In this specification, the average particle size may be the particle size at 50% volume (D50) in a cumulative size-distribution curve.

[0111] When the average particle size of the Si particles is within the above range, volume expansion that occurs during charging and discharging can be suppressed, and the conductive path can be prevented from being broken due to particle crushing during charging and discharging.

[0112] The Si particles may be included in an amount of 1 to 60 wt %, for example, 3 to 60 wt %, based on the total weight of the Si-C composite.

[0113] The central portion does not contain amorphous carbon, and amorphous carbon may be present only in the surface portion of the negative electrode active material.

[0114] In this case, the surface portion means the region from the center to the outermost surface of the negative electrode active material.

[0115] The Si particles can be contained substantially uniformly throughout the entire volume of the negative electrode active material, that is, can be present at a substantially uniform concentration in the center and surface portions.

[0116] The amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonized, calcined coke, or a combination thereof.

[0117] The negative electrode active material may further include crystalline carbon.

[0118] When the negative electrode active material contains both a Si-C composite and crystalline carbon, the Si-C composite and crystalline carbon are in the form of a mixture, and in this case, the Si-C composite and crystalline carbon may be contained in a weight ratio of 1:99 to 50:50. More specifically, the Si-C composite and crystalline carbon may be contained in a weight ratio of 3:97 to 20:80 or a weight ratio of 5:95 to 20:80.

[0119] The crystalline carbon may be, for example, graphite, and more specifically, may include natural graphite, artificial graphite, or a mixture thereof.

[0120] The average particle size of the crystalline carbon may be 5 μm to 30 μm.

[0121] The amorphous carbon precursor may be coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or a polymer resin such as a phenol resin, a furan resin, or a polyimide resin.

[0122] The amorphous carbon precursor may be coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or a polymer resin such as a phenol resin, a furan resin, or a polyimide resin.

[0123] The content of the negative electrode active material in the negative electrode active material layer may be 95% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

[0124] In one embodiment of the present invention, the negative electrode active material layer includes a binder, and may optionally further include a conductive material. The content of the binder in the negative electrode active material layer may be 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer. When the negative electrode active material layer further includes a conductive material, the negative electrode active material may be 90 wt% to 98 wt%, the binder may be 1 wt% to 5 wt%, and the conductive material may be 1 wt% to 5 wt%.

[0125] The binder serves to adhere the negative active material particles to each other and to the current collector well. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0126] The water-insoluble binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0127] The water-soluble binder may be a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be selected from polytetrafluoroethylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0128] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. As the cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K, or Li may be used. The content of such a thickener may be 0.1 to 3 parts by weight per 100 parts by weight of the negative electrode active material.

[0129] The conductive material is used to impart conductivity to the electrodes, and any material can be used as long as it does not undergo chemical changes in the constructed battery and is electronically conductive. Examples of the conductive material that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fibers; metal-based materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures of these.

[0130] The negative electrode current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0131] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multi-layer film of two or more layers of these may be used, and of course, a mixed multi-layer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0132] The lithium secondary battery may operate at a high voltage of 4.4V or more, for example, at a voltage of 4.4V to 4.45V. EXAMPLES

[0133] Examples of the present invention and comparative examples are described below. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0134] Manufacturing of lithium secondary batteries Example 1 LiNi as the positive electrode active material0.75 Mno 0.23 Al 0.02 O2, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed in a weight ratio of 96:3:1, and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0135] The positive electrode active material slurry was coated on an aluminum foil having a thickness of 15 μm, dried at 100° C., and pressed to prepare a positive electrode.

[0136] A mixture of artificial graphite and Si-C composite in a weight ratio of 93:7 was used as the negative active material, and the negative active material was mixed with a styrene-butadiene rubber binder and carboxymethyl cellulose in a weight ratio of 98:1:1, respectively, and dispersed in distilled water to prepare a negative active material slurry.

[0137] The Si-C composite used had a core containing artificial graphite and silicon particles, and the surface of the core was coated with coal-based pitch.

[0138] The negative electrode active material slurry was coated on a copper foil having a thickness of 10 μm, dried at 100° C., and pressed to prepare a negative electrode.

[0139] The prepared positive and negative electrodes were assembled with a 10 μm thick polyethylene separator to prepare an electrode assembly, and an electrolyte was injected to prepare a lithium secondary battery.

[0140] The electrolyte composition is as follows:

[0141] (Electrolyte composition) Salt: LiPF6 1.15M Solvent: Ethylene carbonate: Ethyl methyl carbonate: Dimethyl carbonate (EC: EMC: DMC = 20: 10: 70 volume ratio) Additive represented by chemical formula 1a: 0.5 parts by weight

[0142] [Chemical formula 1a] [ka]

[0143] Other additives: Fluoroethylene carbonate (FEC) 3 parts by weight (Note that the "parts by weight" in the electrolyte composition refers to the relative weight of the additive with respect to 100 parts by weight of the entire electrolyte (lithium salt + non-aqueous organic solvent).)

[0144] Examples 2 to 4 and Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the electrolyte solution was prepared by changing the content of the additive represented by Chemical Formula 1a as shown in Table 1 below.

[0145] Example 5 A lithium secondary battery was fabricated in the same manner as in Example 1, except that an additive represented by the following Formula 1b was used instead of the additive represented by Formula 1a.

[0146] [Formula 1b] [ka]

[0147] Examples 6 to 8 A lithium secondary battery was fabricated in the same manner as in Example 5, except that the content of the additive represented by Formula 1b was changed as shown in Table 1 below.

[0148] Example 9 A lithium secondary battery was fabricated in the same manner as in Example 1, except that an additive represented by the following Formula 1c was used instead of the additive represented by Formula 1a.

[0149] [Chemical formula 1c] [ka]

[0150] Examples 10 to 12 A lithium secondary battery was fabricated in the same manner as in Example 9, except that the content of the additive represented by Formula 1c was changed as shown in Table 1 below.

[0151] Comparative Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that tetramethylsulfone represented by the following formula d was used as an additive instead of the additive represented by formula 1a.

[0152] [Chemical formula 1d] [ka]

[0153] Comparative Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that methylenemethane disulfonate represented by the following formula e was used as an additive instead of the additive represented by formula 1a.

[0154] [Chemical formula 1e] [ka]

[0155] [Table 1]

[0156] Example 1 and Comparative Example 4 Except for changing the electrode active material to LiCoO2, lithium secondary batteries according to Comparative Example 4 and Reference Example 1 were fabricated in the same manner as Comparative Example 1 and Example 2. The specific compositions are shown in Table 2 below.

[0157] [Table 2]

[0158] Evaluation 1: Gas generation measurement after high temperature storage The lithium secondary batteries according to Examples 1 to 12, Comparative Examples 1 to 4, and Reference Example 1 were fabricated as 4.4 V class 30 mAh cells, and were left at 60° C. for 7 days. The amount of gas generated (ml) on the first and seventh days was measured using a refinery gas analysis (RGA), and the results are shown in Table 3.

[0159] Evaluation 2: Evaluation of DC resistance increase rate after high temperature storage For the lithium secondary batteries manufactured in Examples 1 to 12, Comparative Examples 1 to 4, and Reference Example 1, the initial direct current resistance (DCIR) was measured in terms of △V / △I (change in voltage / change in current) value, and the maximum energy state inside the battery was set to a fully charged state (SOC 100%). After storing the batteries in this state at 60°C for 30 days, the measured direct current resistance and the increase rate [{DC-IR after 30 days) / (initial DC-IR)}*100] were calculated and shown in Table 3 below.

[0160] [Table 3]

[0161] Referring to Table 3, it can be seen that when the additive and the positive electrode composition according to the present invention are included, the amount of gas generation is significantly reduced and the high temperature storage characteristics are improved.

[0162] On the other hand, when the additive according to the present invention was not included (Comparative Examples 1 to 4) or when the positive electrode composition according to the present invention was not included (Reference Example 1), it was confirmed that the amount of gas generated was relatively large.

[0163] In addition, it was found that when the additive and positive electrode composition according to the present invention are included, the degree to which the DC resistance after high temperature storage is increased compared to the initial DC resistance is relatively reduced, thereby improving the high temperature storage characteristics.

[0164] Similarly, it was confirmed that when the additive according to the present invention was not included (Comparative Examples 1 to 4) or when the positive electrode composition according to the present invention was not included (Reference Example 1), the increase rate of DC resistance after high-temperature storage was relatively high.

[0165] Although the above describes a preferred embodiment of the present invention, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, which of course also fall within the scope of the present invention. [Explanation of symbols]

[0166] 100 Lithium secondary battery 112 Negative electrode 113 Separator 114 Positive electrode 120 Battery container 140 Enclosure material

Claims

1. An additive represented by the following chemical formula 1: [Chemical formula 1] 【Chemistry 1】 In the above Chemical Formula 1, R １ ~R ８ are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C6 to C12 aryl group, or a combination thereof; n is an integer from 0 to 2.

2. The additive according to claim 1, wherein the chemical formula 1 is represented by any one of the following chemical formulas 1-1 to 1-3: [Chemical formula 1-1] [Chemical formula 1-2] 【Chemistry 2】 [Chemical formula 1-3] 【Chemistry 3】 In the above Chemical Formula 1-1 to Chemical Formula 1-3, R １ ~R ８ is as defined in claim 1, R ５ａ , R ６ａ , R ５ｂ , and R ６ｂ are each independently hydrogen, halogen, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C6 to C12 aryl group, or a combination thereof.

3. The R １ ~R ８ and each independently is hydrogen, halogen, or a substituted or unsubstituted C1 to C5 alkyl group.

4. The additive according to claim 1, wherein the additive represented by Chemical Formula 1 is one selected from the compounds listed in Group 1 below: [Group 1] 【Chemistry 4】

5. an electrolyte solution comprising a non-aqueous organic solvent, a lithium salt, and the additive according to any one of claims 1 to 4; a positive electrode comprising a positive electrode active material; and a negative electrode including a negative electrode active material; The positive electrode active material is a lithium secondary battery containing a cobalt-free lithium nickel manganese oxide.

6. The lithium secondary battery according to claim 5, wherein the cobalt-free lithium nickel manganese oxide includes a lithium composite oxide represented by the following Chemical Formula 2: [Chemical formula 2] Li ａ ii ｘ 7N ｙ 71 ｚ 72 ｗ 9 ２－ｂ 8 ｂ In the above Chemical Formula 2, 0.9≦a<1.2, 0≦b<0.1, 0≦w<0.1, 0.6≦x<1.0, 0<y<0.4, 0<z<0.1, and w+x+y+z=1; M1 is one or more elements selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Ce, Cr and Nb; M2 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W and Zr, and X is one or more elements selected from S, F and P.

7. The lithium secondary battery according to claim 6, wherein the chemical formula 2 is represented by the following chemical formula 2-1: [Chemical formula 2-1] <h2 style=";text-align:left;direction:ltr">Li<h2 style=";text-align:left;direction:ltr"> ａ <h2 style=";text-align:left;direction:ltr"> Ni<h2 style=";text-align:left;direction:ltr"> ｘ１ <h2 style=";text-align:left;direction:ltr"> 4Mn<h2 style=";text-align:left;direction:ltr"> ｙ１ <h2 style=";text-align:left;direction:ltr"> Al<h2 style=";text-align:left;direction:ltr"> ｚ１ <h2 style=";text-align:left;direction:ltr"> 12<h2 style=";text-align:left;direction:ltr"> ｗ１ <h2 style=";text-align:left;direction:ltr"> O<h2 style=";text-align:left;direction:ltr"> ２－ｂ <h2 style=";text-align:left;direction:ltr"> 5<h2 style=";text-align:left;direction:ltr"> ｂ In the above Chemical Formula 2-1, 0.9≦a<1.2, 0≦b<0.1, 0≦w1<0.1, 0.6≦x1<1.0, 0<y1<0.4, 0<z1<0.1, w1+x1+y1+z1=1; M2 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr; and X is one or more elements selected from S, F, and P.

8. 8. The lithium secondary battery according to claim 7, wherein in the chemical formula 2-1, x1 is 0.6≦x1≦0.79, y1 is 0.2≦y1≦0.39, and z1 is 0.01≦z1<0.

1.

9. The lithium secondary battery according to claim 5 , wherein the negative electrode active material includes at least one of graphite and a Si composite.

10. The lithium secondary battery according to claim 9 , wherein the Si composite comprises a core comprising Si particles and an amorphous carbon coating layer.

11. The core containing the Si particles is a Si-C composite, SiO ｘ The lithium secondary battery according to claim 10, comprising at least one of (0<x≦2) and Si alloy.

12. The lithium secondary battery according to claim 11 , comprising a void in the center of the core.

13. the radius of the central portion corresponds to 30% to 50% of the radius of the Si-C composite; The lithium secondary battery according to claim 12, wherein the average particle size of the Si particles is 10 nm to 200 nm.

14. The lithium secondary battery according to claim 12 , wherein the central portion does not contain amorphous carbon, and amorphous carbon is present only in a surface portion of the negative electrode active material.

15. The lithium secondary battery according to claim 11 , wherein the negative electrode active material further comprises crystalline carbon.

16. The lithium secondary battery according to claim 5, wherein the additive is included in an amount of 0.05 to 5.0 parts by weight based on 100 parts by weight of the total electrolyte solution.

17. The lithium secondary battery according to claim 5, wherein the additive is included in an amount of 0.05 to 3.0 parts by weight based on 100 parts by weight of the total electrolyte solution.

18. The additives include vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF ４ ), lithium difluorophosphate (LiPO ２ F ２ 6. The lithium secondary battery according to claim 5, further comprising at least one other additive selected from the group consisting of 2-fluorobiphenyl (2-FBP) and 2-fluorobiphenyl (2-FBP).

19. 6. The lithium secondary battery according to claim 5, which operates even at a high voltage of 4.4 V or more.

Images