Additive and rechargeable lithium battery including same

Abstract

Provided are an additive represented by Chemical Formula 1 and a rechargeable lithium battery, the battery including: an electrolyte including a non-aqueous organic solvent, a lithium salt, and an additive; a positive electrode including a positive electrode active material; and a negative electrode including a negative electrode active material, wherein the positive electrode active material includes a cobalt-free lithium nickel manganese-based oxide. Details of Chemical Formula 1 are as described in the specification.

Description

Technical Field

[0001] The present disclosure relates to an additive and a rechargeable lithium battery including the same. Background Art

[0002] Rechargeable lithium batteries are rechargeable and have an energy density per unit weight that is three times or more higher than that of conventional lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, etc., and can also be charged at a high rate, and therefore are commercially manufactured for use in laptop computers, cellular phones, power tools, electric bicycles, electric vehicles, etc., and research on improving the additional energy density has been actively conducted.

[0003] Such a rechargeable lithium battery is manufactured by injecting an electrolyte into a battery cell including a positive electrode including a positive electrode active material capable of intercalating / deintercalating lithium ions and a negative electrode including a negative electrode active material capable of intercalating / deintercalating lithium ions.

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

[0005] For example, the electrolyte is prepared by adding a lithium salt (such as LiPF6, LiBF4, LiFSI, etc.) to a mixed solvent of a high dielectric cyclic carbonate (such as propylene carbonate, ethylene carbonate, etc.) and a chain carbonate (such as diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, etc.). With the active development of batteries in various fields, it is considered that the development of batteries with high output and high stability in a wide temperature range is important, and in addition, it is important to ensure the development of an electrolyte with high power, long cycle life characteristics and high temperature storage characteristics by optimally combining an organic solvent that suppresses swelling, capacity degradation and resistance increase with an additive.

[0006] On the other hand, as IT devices become more and more high-performance, high-capacity batteries are required, where high capacity can be achieved by expanding the voltage region to increase energy density, but there is a problem that the electrolyte is oxidized in the high voltage region and thus the positive electrode performance is deteriorated.

[0007] In particular, cobalt-free lithium nickel manganese oxides are positive electrode active materials that do not include cobalt in their composition but include nickel, manganese, etc. as main components, and accordingly, the positive electrode including the positive electrode active material can be economical and achieve high energy density, and therefore have attracted attention as the next generation positive electrode active material.

[0008] However, when a positive electrode including a cobalt-free lithium nickel manganese-based oxide is used in a high voltage environment, transition metals may be dissolved due to structural collapse of the positive electrode, causing problems such as gas generation inside the battery cell, reduced capacity, etc. This transition metal dissolution tends to be exacerbated in a high temperature environment, where the dissolved transition metal is precipitated on the surface of the negative electrode and may cause side reactions, thereby increasing battery resistance and deteriorating battery cycle life and output characteristics.

[0009] Accordingly, when a positive electrode including a cobalt-free lithium nickel manganese-based oxide is used, an electrolyte that can be used under high voltage and high temperature conditions is required. Summary of the invention

[0010]

Technical issues

[0011] Embodiments provide additives with improved high temperature characteristics.

[0012] Another embodiment provides a rechargeable lithium battery having improved high voltage characteristics and high temperature characteristics by combining an electrolyte capable of effectively protecting a positive electrode including cobalt-free lithium nickel manganese oxide with the use of a positive electrode including cobalt-free lithium nickel manganese oxide.

[0013]

Technical solution

[0014] An embodiment of the present invention provides an additive represented by Chemical Formula 1.

[0015] [Chemical formula 1]

[0016]

[0017] In Chemical Formula 1,

[0018] R 1 ~R 8 are each independently hydrogen, halogen, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C10 alkynyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C6-C12 aryl, or a combination thereof, and

[0019] n is an integer from 0 to 2.

[0020] Chemical Formula 1 can be represented by any one of Chemical Formula 1-1 to Chemical Formula 1-3.

[0021]

[0022] [Chemical formula 1-3]

[0023]

[0024] In Chemical Formula 1-1 to Chemical Formula 1-3,

[0025] R 1 ~R 8 As mentioned above, and R 5 a. R 6 a. R 5b and R 6b Each is independently hydrogen, halogen, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C10 alkynyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C6-C12 aryl or a combination thereof.

[0026] R 1 ~R 8 They may each independently be hydrogen, halogen or substituted or unsubstituted C1-C5 alkyl.

[0027] The additive represented by Chemical Formula 1 may be selected from the compounds of Group 1.

[0028] [Group 1]

[0029]

[0030] Another embodiment of the present invention provides a rechargeable lithium battery, comprising: an electrolyte comprising a non-aqueous organic solvent, a lithium salt and the aforementioned additives; a positive electrode comprising a positive electrode active material; and a negative electrode comprising a negative electrode active material, wherein the positive electrode active material comprises a cobalt-free lithium nickel manganese oxide.

[0031] The cobalt-free lithium nickel manganese-based oxide may include a lithium composite oxide represented by Chemical Formula 2.

[0032] [Chemical formula 2]

[0033] Li a Ni x Mn y M1 z M2 w O 2-b X b

[0034] In chemical formula 2,

[0035] 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,

[0036] M1 is at least one element selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Ce, Cr and Nb, and

[0037] M2 is at least one element selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is at least one element selected from S, F, and P.

[0038] Chemical formula 2 can be represented by chemical formula 2-1.

[0039] [Chemical formula 2-1]

[0040] Li a Ni x1 Mn y1 Al z1 M2 w1 O 2-b X b

[0041] In chemical formula 2-1,

[0042] 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 at least one element selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is at least one element selected from S, F, and P.

[0043] In chemical formula 2-1, x1 can satisfy 0.6 ≤ x1 ≤ 0.79, y1 can satisfy 0.2 ≤ y1 ≤ 0.39, and z1 can satisfy 0.01 ≤ z1 < 0.1.

[0044] The negative electrode active material may include at least one of graphite and a Si composite.

[0045] The Si composite may include: a core including Si particles and an amorphous carbon coating.

[0046] The core including Si particles may include at least one of a Si-C composite, SiO x (0 < x ≤ 2) and a Si alloy.

[0047] The central part of the core may include voids.

[0048] The radius of the central part may correspond to about 30% to about 50% of the radius of the Si-C composite, and the average particle size of the Si particles may be about 10 nm to about 200 nm.

[0049] The central part does not include amorphous carbon, and the amorphous carbon may exist only on the surface part of the negative electrode active material.

[0050] The negative electrode active material may further include crystalline carbon.

[0051] The additive may be included in an amount of 0.05 parts by weight to 5.0 parts by weight based on 100 parts by weight of the electrolyte.

[0052] The additive may be included in an amount of 0.05 parts by weight to 3.0 parts by weight based on 100 parts by weight of the electrolyte.

[0053] The additive may further include at least one other additive selected from 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-hexanetrinitrile (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2) and 2-fluorobiphenyl (2-FBP).

[0054] Rechargeable lithium batteries may operate at a high voltage of 4.4V or higher.

[0055]

Beneficial effects

[0056] A rechargeable lithium battery can achieve improved high temperature characteristics by suppressing an increase in battery resistance and reducing the amount of generated gas during high temperature storage due to combining an electrolyte including an additive capable of effectively protecting a positive electrode with a negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 is a schematic diagram showing a rechargeable lithium battery according to an embodiment of the present invention. DETAILED DESCRIPTION

[0058] Hereinafter, a rechargeable lithium battery according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, these embodiments are exemplary, the present invention is not limited thereto, and the present invention is defined by the scope of the claims.

[0059] In the present specification, when no further limitation is provided, "substituted" means that at least one hydrogen of a substituent or a compound is replaced by deuterium, halogen, hydroxyl, amino, substituted or unsubstituted C1-C30 amine, nitro, substituted or unsubstituted C1-C40 silyl, C1-C30 alkyl, C1-C10 alkylsilyl, C6-C30 arylsilyl, C3-C30 cycloalkyl, C3-C30 heterocycloalkyl, C6-C30 aryl, C2-C30 heteroaryl, C1-C20 alkoxy, C1-C10 trifluoroalkyl, cyano or a combination thereof.

[0060] In one example of the present invention, "substituted" means that at least one hydrogen of a substituent or a compound is replaced by: deuterium, halogen, C1-C30 alkyl, C1-C10 alkylsilyl, C6-C30 arylsilyl, C3-C30 cycloalkyl, C3-C30 heterocycloalkyl, C6-C30 aryl, C2-C30 heteroaryl, C1-C10 fluoroalkyl or cyano. In addition, in a specific example of the present invention, "substituted" means that at least one hydrogen of a substituent or a compound is replaced by: deuterium, halogen, C1-C20 alkyl, C6-C30 aryl, C1-C10 fluoroalkyl or cyano. In addition, in a specific example of the present invention, "substituted" means that at least one hydrogen of a substituent or a compound is replaced by: deuterium, halogen, C1-C5 alkyl, C6-C18 aryl, C1-C5 fluoroalkyl or cyano. In addition, in a specific example of the present invention, "substituted" means that at least one hydrogen of the substituent or compound is replaced by deuterium, cyano, halogen, methyl, ethyl, propyl, butyl, phenyl, biphenyl, terphenyl, trifluoromethyl or naphthyl.

[0061] In the present specification, "aryl group" refers to a group including at least one hydrocarbon aromatic part, and may include: a group in which all elements of the hydrocarbon aromatic part have p-orbitals forming a conjugation, such as phenyl, naphthyl, etc.; a group in which two or more hydrocarbon aromatic parts can be connected by a σ bond, such as biphenyl, terphenyl, quaterphenyl, etc.; and a group in which two or more hydrocarbon aromatic parts are directly or indirectly fused to provide a non-aromatic fused ring, such as fluorenyl.

[0062] Aryl groups can include monocyclic, polycyclic, or fused-ring polycyclic (ie, rings which share adjacent pairs of carbon atoms) functional groups.

[0063] More specifically, the substituted or unsubstituted C6~C20 aromatic group may be 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 naphthphenyl group, a substituted or unsubstituted pyrene 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 1,2-triphenylenyl group, a substituted or unsubstituted triphenylene group, a substituted or unsubstituted perylene group, a substituted or unsubstituted fluorenyl group, or a combination thereof, but is not limited thereto.

[0064] Depending on the types of separators and electrolytes, rechargeable lithium batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries. Depending on the shape, they can also be classified into cylindrical, prismatic, coin-shaped, pouch-shaped, etc. In addition, depending on the size, they can be block-shaped and film-shaped. The structure and manufacturing method of the lithium ion battery disclosed in the present invention are well known in the art.

[0065] Herein, a cylindrical rechargeable lithium battery will be exemplarily described as an example of a rechargeable lithium battery. Figure 1 The structure of a rechargeable lithium battery according to an embodiment is schematically shown. Figure 1 According to an embodiment, a rechargeable lithium battery 100 includes: a battery cell; a battery case 120 that accommodates the battery cell; and a sealing member 140 that seals the battery case 120, the battery cell including: a positive electrode 114, a negative electrode 112 facing the positive electrode 114, a separator 113 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.

[0066] Hereinafter, a more detailed configuration of the rechargeable lithium battery 100 according to an embodiment of the present invention will be described.

[0067] A rechargeable lithium battery according to an embodiment of the present invention includes an electrolyte, a positive electrode, and a negative electrode.

[0068] The electrolyte includes a non-aqueous organic solvent, a lithium salt and an additive.

[0069] Hereinafter, additives according to embodiments will be described.

[0070] The additive according to an embodiment of the present invention is represented by Chemical Formula 1.

[0071] [Chemical formula 1]

[0072]

[0073] In Chemical Formula 1,

[0074] R 1 ~R 8 are each independently hydrogen, halogen, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C10 alkynyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C6-C12 aryl, or a combination thereof, and

[0075] n is an integer from 0 to 2.

[0076] The additive represented by Chemical Formula 1 is reduced and decomposed before the carbonate solvent included in the non-aqueous organic solvent, and thus a SEI (solid electrolyte interface) film can be formed on the negative electrode to prevent decomposition of the electrolyte and decomposition of the electrode due to the decomposition of the electrolyte, thereby suppressing an increase in internal resistance due to gas generation.

[0077] In addition, a film is also formed on the surface of the positive electrode to prevent decomposition of the positive electrode surface and oxidation of the electrolyte, thus contributing to improvement of high temperature cycle life characteristics.

[0078] That is, the cycle-life characteristics and high-temperature characteristics of the battery may be improved by including the additive.

[0079] Chemical Formula 1 can be represented by any one of Chemical Formula 1-1 to Chemical Formula 1-3.

[0080]

[0081] [Chemical formula 1-3]

[0082]

[0083] In Chemical Formula 1-1 to Chemical Formula 1-3,

[0084] R 1 ~R 8 As mentioned above,

[0085] R 5 a. R 6 a. R 5b and R 6b Each is independently hydrogen, halogen, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C10 alkynyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C6-C12 aryl or a combination thereof.

[0086] R 1 ~R 8 They may each independently be hydrogen, halogen or substituted or unsubstituted C1-C5 alkyl.

[0087] The additive represented by Chemical Formula 1 may be selected from the compounds of Group 1.

[0088] [Group 1]

[0089]

[0090] 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 amount of the electrolyte.

[0091] When the amount of the additive is within the above range, a rechargeable lithium battery having further improved resistance characteristics and gas generation during high-temperature storage may be realized.

[0092] Meanwhile, the additive may further include other additives in addition to the aforementioned compounds.

[0093] Other additives may include at least one selected from 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-hexanetrinitrile (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2) and 2-fluorobiphenyl (2-FBP).

[0094] By further including the aforementioned other additives, the cycle life may be further improved, or the gas generated from the positive electrode and the negative electrode during high-temperature storage may be effectively controlled.

[0095] 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 electrolyte for a rechargeable lithium battery.

[0096] When the contents of the other additives are as described above, battery performance may be improved by minimizing an increase in membrane resistance.

[0097] The nonaqueous organic solvent serves as a medium for transmitting ions participating in the electrochemical reaction of the battery.

[0098] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, alcohol or an aprotic solvent.

[0099] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanoic acid lactone, mevalonate lactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. In addition, ketone solvents may be cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitriles, such as R-CN (wherein R is a hydrocarbon group having a C2 to C20 straight chain, branched or cyclic structure, and may include a double bond, an aromatic ring or an ether bond), etc.; dioxolanes such as 1,3-dioxolane, etc.; cyclopentane sulfone, etc.

[0100] The nonaqueous organic solvent may be used alone or in a mixture of one or more, and when one or more nonaqueous organic solvents are mixed and used, the mixing ratio may be appropriately adjusted according to desired battery performance, which is widely understood by those skilled in the art.

[0101] In addition, in the case of carbonate solvents, it is desirable to use a mixture of cyclic carbonate and chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 5:5 to 1:9, the electrolyte can exhibit excellent performance.

[0102] Particularly, in an embodiment of the present invention, the nonaqueous organic solvent may include cyclic carbonate and chain carbonate in a volume ratio of 5:5 to 2:8, and as a specific example, the volume ratio of the cyclic carbonate and chain carbonate may be 4:6 to 2:8.

[0103] As a more specific example, the cyclic carbonate and the linear carbonate may be included in a volume ratio of 3:7 to 2:8.

[0104] The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent in addition to the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0105] The aromatic hydrocarbon solvent may be an aromatic hydrocarbon compound represented by Chemical Formula 3.

[0106] [Chemical formula 3]

[0107]

[0108] In chemical formula 3, R 9 ~R 14 are the same or different and are selected from hydrogen, halogen, C1-C10 alkyl, haloalkyl and combinations thereof.

[0109] Specific examples of aromatic hydrocarbon organic solvents may be selected from 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, fluoroform, Benzene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0110] The lithium salt dissolved in the non-organic solvent supplies lithium ions in the battery, ensures the basic operation of the rechargeable lithium battery, and improves the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts may include those selected from 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)(C y F 2y+1 SO2) (wherein x and y are natural numbers (e.g., integers ranging from 1 to 20)), at least one of LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalato)borate: LiBOB). The lithium salt may be used in a concentration ranging from 0.1M to 2.0M. When the lithium salt is included in the above concentration range, the electrolyte may have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

[0111] The positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0112] The positive electrode active material may include a cobalt-free lithium nickel manganese-based oxide.

[0113] The cobalt-free lithium nickel manganese-based oxide may include at least one of the lithium composite oxides represented by Chemical Formula 2.

[0114] [Chemical formula 2]

[0115] Li a Ni x Mn y M1 z M2 w O 2-b X b

[0116] In chemical formula 2,

[0117] 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,

[0118] M1 is at least one element selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Ce, Cr and Nb, and

[0119] M2 is at least one element selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W and Zr, and X is at least one element selected from S, F and P.

[0120] Of course, a lithium composite oxide having a coating on the surface of the lithium composite oxide can be used, or a mixture of a lithium composite oxide and a lithium composite oxide having a coating can be used. The coating may include at least one coating element compound selected from an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a basic carbonate of a coating element. The compound used for the coating may be amorphous or crystalline. The coating element included in the coating may include Mg, Al, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. By using these elements in the compound, the coating can be provided in a method that has no adverse effect on the characteristics of the positive active material. For example, the method may include any coating method (e.g., spraying, dipping, etc.), but is not explained in more detail because it is well known to those skilled in the art.

[0121] For example, Chemical Formula 2 can be represented by Chemical Formula 2-1.

[0122] [Chemical formula 2-1]

[0123] Li a Ni x1 Mn y1 Al z1 M2 w1 O 2-b X b

[0124] In Chemical Formula 2-1,

[0125] 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 at least one element selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is at least one element selected from S, F, and P.

[0126] In an embodiment, in Chemical Formula 1-1, 0.6 ≤ x1 ≤ 0.9, 0.1 ≤ y1 ≤ 0.4, and 0 ≤ z1 ≤ 0.1, or 0.6 ≤ x1 ≤ 0.8, 0.2 ≤ y1 ≤ 0.4, and 0 ≤ z1 ≤ 0.1.

[0127] For example, in Chemical Formula 2-1, x1 may satisfy 0.6 ≤ x1 ≤ 0.79, y1 may satisfy 0.2 ≤ y1 ≤ 0.39, and z1 may satisfy 0.01 ≤ z1 < 0.1.

[0128] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material may be 90 wt% to 98 wt%.

[0129] In an embodiment of the present invention, the positive electrode active material layer may include a binder. In this case, based on the total weight of the positive electrode active material layer, the content of the binder may be 1 wt% to 5 wt%.

[0130] The binder improves the adhesion characteristics between the positive electrode active material particles and between the positive electrode active material particles and the current collector, and examples thereof may be polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon, etc., but are not limited thereto.

[0131] The positive electrode current collector may include Al, but is not limited thereto.

[0132] 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.

[0133] The negative electrode active material may include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, or a transition metal oxide.

[0134] Materials capable of reversibly inserting / extracting lithium ions may include carbon materials. The carbon materials may be any commonly used carbonaceous negative electrode active materials in rechargeable lithium ion batteries, and examples thereof may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be amorphous, or flaky, lamellar, spherical, or fibrous natural graphite or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization product, calcined coke, etc.

[0135] The lithium metal alloy includes an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0136] Materials capable of doping / dedoping lithium may be Si, Si-C composite, SiO x (0 < x < 2), Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, Sn-R (where R is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), etc., and at least one of these materials may be mixed with SiO2. The element Q and the element R 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, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0137] The transition metal oxide may be vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

[0138] In an exemplary embodiment, the negative electrode active material may include at least one of graphite and Si composite.

[0139] The Si composite includes: a core including Si-based particles and an amorphous carbon coating, and for example, the Si-based particles may include at least one of Si particles, Si-C composite, SiO x (0 < x ≤ 2) and Si alloy.

[0140] For example, the Si-C composite may include Si particles and crystalline carbon.

[0141] Void spaces may be included in the central portion of the core, and the radius of the central portion may correspond to 30% to 50% of the radius of the Si-C composite.

[0142] The average particle size of the Si particles may be 10 nm to 200 nm.

[0143] In the present specification, the average particle size may be a size (D50) of particles at 50 volume % in a cumulative size distribution curve.

[0144] When the average particle diameter of the Si particles is within the above range, volume expansion occurring during charge and discharge can be suppressed, and interruption of a conductive path due to particle crushing during charge and discharge can be prevented.

[0145] The Si particles may be included in an amount of 1 wt % to 60 wt %, for example, 3 wt % to 60 wt %, based on the total weight of the Si—C composite.

[0146] The central portion does not include amorphous carbon, and amorphous carbon may exist only on a surface portion of the negative electrode active material.

[0147] Herein, the surface portion indicates a region from the central portion of the negative electrode active material to the outermost surface of the negative electrode active material.

[0148] In addition, the Si particles are included substantially uniformly throughout the negative electrode active material, that is, are present at a substantially uniform concentration in the central portion and the surface portion of the negative electrode active material.

[0149] The amorphous carbon may be soft carbon, hard carbon, a mesophase pitch carbonization product, calcined coke, or a combination thereof.

[0150] The negative electrode active material may further include crystalline carbon.

[0151] When the negative electrode active material includes both Si-C composite and crystalline carbon, the Si-C composite and crystalline carbon may be included in the form of a mixture, and in this case, the weight ratio of the Si-C composite and the crystalline carbon may be 1:99 to 50:50. More specifically, the weight ratio of the Si-C composite and the crystalline carbon may be 3:97 to 20:80 or 5:95 to 20:80.

[0152] The crystalline carbon may be, for example, graphite, and more specifically, natural graphite, artificial graphite, or a mixture thereof.

[0153] The average particle size of the crystalline carbon may be 5 μm to 30 μm.

[0154] The amorphous carbon precursor may include coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or a polymer resin such as a phenolic resin, a furan resin, or a polyimide resin.

[0155] The amorphous carbon precursor may include coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or a polymer resin such as a phenolic resin, a furan resin, or a polyimide resin.

[0156] In the negative electrode active material layer, the negative electrode active material may be included in an amount of 95 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0157] In an embodiment of the present invention, the negative electrode active material layer includes a binder and an optional conductive material. In the negative electrode active material layer, the content of the binder may be 1wt% to 5wt% based on the total weight of the negative electrode active material layer. When the negative electrode active material layer includes a conductive material, the negative electrode active material layer includes 90wt% to 98wt% of the negative electrode active material, 1wt% to 5wt% of the binder and 1wt% to 5wt% of the conductive material.

[0158] The binder improves the binding properties between the negative electrode active material particles and between the negative electrode active material particles and the current collector. The binder may include a non-water-soluble binder, a water-soluble binder, or a combination thereof.

[0159] The water-insoluble binder may be selected from polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide or a combination thereof.

[0160] The water-soluble binder can be a rubber-based binder or a polymer resin binder. The rubber-based binder can 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 can be selected from polytetrafluoroethylene, ethylene-propylene copolymer, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol and combinations thereof.

[0161] When a water-soluble binder is used as a negative electrode binder, a cellulose compound may be further used to provide viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose or an alkali metal salt thereof. The alkali metal may be Na, K or Li. Based on 100 parts by weight of the negative electrode active material, the amount of such a thickener included may be 0.1 parts by weight to 3 parts by weight.

[0162] A conductive material is included to provide electrode conductivity, and any conductive material can be used as the conductive material unless it causes a chemical change, and examples of the conductive material may include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0163] The negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0164] Depending on the type of rechargeable lithium battery, a separator may be present between the positive electrode and the negative electrode. Such a separator may, for example, include polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer thereof, such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.

[0165] The rechargeable lithium battery may operate at a high voltage of 4.4 V or higher (eg, 4.4 V to 4.45 V).

[0166] [Best Mode of Invention]

[0167] Hereinafter, examples of the present invention and comparative examples are described. However, these examples are not to be construed as limiting the scope of the present invention in any sense.

[0168] Manufacturing of rechargeable lithium battery cells

[0169] Example

[0170] By using LiNi as the positive electrode active material at a weight ratio of 96:3:1 0.75 Mno 0.23 Al 0.02 O2, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material and disperse the mixture in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0171] The positive electrode active material slurry was coated on a 15 μm thick Al foil, dried at 100° C., and pressed to produce a positive electrode.

[0172] A negative electrode active material was prepared by mixing artificial graphite and Si—C composite in a weight ratio of 93:7, and then the negative electrode active material, styrene-butadiene rubber binder and carboxymethyl cellulose were mixed in a weight ratio of 98:1:1 and then dispersed in distilled water to prepare a negative electrode active material slurry.

[0173] The Si-C composite includes: a core including artificial graphite and silicon particles, and coal pitch coated on a surface of the core.

[0174] The negative electrode active material slurry was coated on a 10 μm thick Cu foil, dried at 100° C., and pressed to produce a negative electrode.

[0175] An electrode assembly was manufactured by assembling the manufactured positive and negative electrodes and a separator made of polyethylene having a thickness of 10 μm, and an electrolyte was injected to manufacture a rechargeable lithium battery cell.

[0176] The electrolyte solution has the following composition.

[0177] (Composition of electrolyte)

[0178] Salt: 1.15M LiPF6

[0179] Solvent: ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate (EC:EMC:DMC=volume ratio 20:10:70)

[0180] Additive represented by chemical formula 1a: 0.5 parts by weight

[0181] [Chemical formula 1a]

[0182]

[0183] Other additives: 3 parts by weight of fluoroethylene carbonate (FEC)

[0184] (In the composition of the electrolyte, "parts by weight" means the relative weight of the additive based on 100 weight of the total electrolyte (lithium salt + non-aqueous organic solvent)).

[0185] Examples 2 to 4 and Comparative Example 1

[0186] As described in Table 1, each rechargeable lithium battery cell was manufactured in the same manner as Example 1, except that the electrolyte was prepared by changing the content of the additive represented by Chemical Formula 1a.

[0187] Example 5

[0188] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that the electrolyte was prepared by using the additive represented by Chemical Formula 1b instead of the additive represented by Chemical Formula 1a.

[0189] [Chemical formula 1b]

[0190]

[0191] Embodiment 6 to Embodiment 8

[0192] Each rechargeable lithium battery cell was manufactured in the same manner as in Example 5, except that the electrolyte was prepared by changing the content of the additive represented by Chemical Formula 1b as shown in Table 1.

[0193] Example 9

[0194] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that the electrolyte was prepared by using the additive represented by Chemical Formula 1b instead of the additive represented by Chemical Formula 1a.

[0195] [Chemical formula 1c]

[0196]

[0197] Example 10 to Example 12

[0198] A rechargeable lithium battery cell was manufactured in the same manner as in Example 9, except that an electrolyte was prepared by changing the content of the additive represented by Chemical Formula 1c as shown in Table 1.

[0199] Comparative Example 2

[0200] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that the electrolyte was prepared by using tetramethylene sulfone represented by Chemical Formula d instead of the additive represented by Chemical Formula 1a.

[0201] [Chemical formula d]

[0202]

[0203] Comparative Example 3

[0204] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that the electrolyte was prepared by using methylene methanedisulfonate represented by Chemical Formula e instead of the additive represented by Chemical Formula 1a.

[0205] [Chemical formula e]

[0206]

[0207] (Table 1)

[0208]

[0209] Reference Example 1 and Comparative Example 4

[0210] Each rechargeable lithium battery cell according to Comparative Example 4 and Reference Example 1 was manufactured in the same manner as Comparative Example 1 and Example 2, except that the positive electrode active material was changed to LiCoO 2. Its specific composition is shown in Table 2.

[0211] (Table 2)

[0212]

[0213] Assessment 1: Measurement of the amount of gas generated after high temperature storage

[0214] The rechargeable lithium battery cells according to Examples 1 to 12, Comparative Examples 1 to 4 and Reference Example 1 were manufactured into 30 mAh battery cells at a 4.4 V level and placed at 60° C. for 7 days, and then the amount (ml) of each gas generated on the 1st and 7th days was measured by refinery gas analysis (RGA), and the results are shown in Table 3.

[0215] Evaluation 2: Evaluation of the DC resistance increase rate after high-temperature storage

[0216] The ΔV / ΔI (voltage change / current change) of the rechargeable lithium battery cells according to Examples 1 to 12, Comparative Examples 1 to 4 and Reference Example 1 were measured to obtain the DC initial resistance (DCIR), and then fully charged until the internal maximum energy state reached a fully charged state (SOC 100%), stored at 60°C for 30 days, and the DC resistance was measured, which was used to calculate the DC-IR increase rate (%) [{(DC-IR after 30 days) / (initial DC-IR)}×100], and the results are shown in Table 3.

[0217] (Table 3)

[0218]

[0219] Referring to Table 3, when the additive and the positive electrode composition according to the present invention are included, the amount of generated gas is significantly reduced, so that storage characteristics at high temperatures are improved.

[0220] 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), the amount of generated gas was relatively high.

[0221] In addition, when the additive and the positive electrode composition according to the present invention are included, the increase in DC resistance after storage at high temperature relative to the initial DC resistance is relatively alleviated, so that the storage characteristics at high temperature are improved.

[0222] Similarly, 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 DC resistance increase rate after storage at high temperature was relatively high.

[0223] While the invention has been described in connection with what are presently considered to be practical example embodiments, it should be understood that the invention is not limited to the disclosed embodiments, but on the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the claims.

[0224] <Description of Reference Numerals>

[0225] 100: Rechargeable lithium battery

[0226] 112: Negative electrode

[0227] 113: Diaphragm

[0228] 114: Positive electrode

[0229] 120: Battery housing

[0230] 140: Sealing member

Claims

1. An additive represented by Chemical Formula 1: [Chemical Formula 1] in, In Chemical Formula 1, R 1 ~R 8 are each independently hydrogen, halogen, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C10 alkynyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C6-C12 aryl, or a combination thereof, and n is an integer from 0 to 2.

2. The additive according to claim 1, wherein Chemical Formula 1 is represented by any one of Chemical Formulas 1-1 to 1-3: [Chemical Formula 1-3] in, In Chemical Formulas 1-1 to 1-3, R 1 ~R 8 As defined in claim 1, and R 5 a. R 6 a. R 5b and R 6b Each is independently hydrogen, halogen, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C10 alkynyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C6-C12 aryl or a combination thereof.

3. The additive according to claim 1, wherein R 1 ~R 8 Each is independently hydrogen, halogen or substituted or unsubstituted C1-C5 alkyl.

4. The additive according to claim 1, wherein The additive represented by Chemical Formula 1 is selected from the compounds of Group 1: [Group 1] 5. A rechargeable lithium battery, comprising: An electrolyte comprising a non-aqueous organic solvent, a lithium salt, and an additive according to any one of claims 1 to 4; A positive electrode comprising a positive electrode active material; And A negative electrode comprising a negative electrode active material, wherein the positive electrode active material comprises a cobalt-free lithium nickel manganese-based oxide.

6. The rechargeable lithium battery according to claim 5, wherein The cobalt-free lithium nickel manganese-based oxide comprises a lithium composite oxide represented by Chemical Formula 2: [Chemical Formula 2] The a Nor x Mn y M1 z M2 w O 2-b Xb in, In 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, M1 is at least one element selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Ce, Cr, and Nb, and M2 is at least one element selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is at least one element selected from S, F, and P.

7. The rechargeable lithium battery according to claim 6, wherein Chemical Formula 2 is represented by 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"> Mn<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"> M2<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"> X<h2 style=";text-align:left;direction:ltr"> b in, In 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 at least one element selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is at least one element selected from S, F, and P.

8. The rechargeable lithium battery according to claim 7, wherein In Chemical Formula 2-1, x1 satisfies 0.6 ≤ x1 ≤ 0.79, y1 satisfies 0.2 ≤ y1 ≤ 0.39, and z1 satisfies 0.01 ≤ z1 < 0.

1.

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

10. The rechargeable lithium battery according to claim 9, wherein The Si composite comprises: It includes a core of Si-based particles and an amorphous carbon coating.

11. The rechargeable lithium battery according to claim 10, wherein The core including the Si-based particles includes at least one of Si particles, Si-C composites, SiO x (0 < x ≤ 2) and Si alloys.

12. The rechargeable lithium battery according to claim 11, wherein The central part of the core includes voids.

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

14. The rechargeable lithium battery of claim 12, wherein The central portion does not include amorphous carbon, and the amorphous carbon exists only on a surface portion of the negative electrode active material.

15. The rechargeable lithium battery of claim 11, wherein The negative electrode active material further includes crystalline carbon.

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

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

18. The rechargeable lithium battery of claim 5, wherein The additive further includes at least one other additive selected from 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-hexanetrinitrile (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2) and 2-fluorobiphenyl (2-FBP).

19. The rechargeable lithium battery of claim 5, wherein The rechargeable lithium battery operates at a high voltage of 4.4V or higher.

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