Additive, electrolyte for lithium secondary battery including additive, positive electrode, and lithium secondary battery

Abstract

Provided are an additive represented by Chemical Formula 1, an electrolyte solution for a lithium secondary battery including the additive, a positive electrode, and a lithium secondary battery. Details about Chemical Formula 1 are as described in the specification.

Description

Technical Field

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

[0002] The rechargeable lithium battery is rechargeable, and has a high energy density per unit weight that is three or more times that of conventional lead storage batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and nickel-zinc batteries, etc. The rechargeable lithium battery can also be charged at a high speed, and therefore, it is commercially manufactured for use in laptop computers, cellular phones, power tools, electric bicycles, etc., and research to improve 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 inserting / deinserting lithium ions and a negative electrode including a negative electrode active material capable of inserting / deinserting lithium ions.

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

[0005] The electrolyte is prepared by adding a lithium salt (such as LiPF4) to a mixed solvent of a high dielectric constant cyclic carbonate (such as propylene carbonate and ethylene carbonate) and a chain carbonate (such as diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate). 6 , LiBF 4 As the development of batteries in various fields becomes active, it is considered important to develop batteries with high output and high stability in a wide temperature range, and in addition, it is important to develop electrolytes by optimizing the combination of organic solvents that suppress swelling, capacity degradation, and resistance increase with additives to ensure high power, long cycle life characteristics, and high temperature storage characteristics.

[0006] On the other hand, in a rechargeable lithium battery, the positive electrode is manufactured by mixing a positive electrode active material, a binder, and a conductive material in an organic solvent, dispersing the mixture to prepare a positive electrode slurry composition, coating the positive electrode slurry composition on a positive electrode current collector, and then drying and pressing. In order to uniformly coat the positive electrode slurry composition on the current collector, the positive electrode active material, the binder, and the conductive material should not aggregate, but should be uniformly dispersed in the organic solvent, and the positive electrode slurry composition should have a viscosity stability that varies over time. If the positive electrode slurry composition is not uniformly coated on the current collector, there may be no uniform battery chemical reaction, which may result in thickness deformation of the electrode, and therefore, problems such as electrode deformation and active material peeling during charging and discharging. Summary of the invention

[0007]

Technical issues

[0008] Embodiments provide additives with improved high temperature characteristics.

[0009] Another embodiment provides an electrolyte for a rechargeable lithium battery including the additive.

[0010] Another embodiment provides a positive electrode including the additive.

[0011] Another embodiment provides a rechargeable lithium battery having improved high temperature storage characteristics by applying an electrolyte or a positive electrode.

[0012]

Technical solution

[0013] An embodiment of the present invention provides an additive represented by Chemical Formula 1.

[0014] [Chemical formula 1]

[0015]

[0016] In Chemical Formula 1,

[0017] L 1 and L 2 Each is independently a substituted or unsubstituted C1 to C20 alkylene group.

[0018] L 1 and L 2 Each independently may be a substituted or unsubstituted C1 to C10 alkylene group.

[0019] Chemical Formula 1 can be represented by Chemical Formula 1-1.

[0020] [Chemical formula 1-1]

[0021]

[0022] Another embodiment of the present invention provides an electrolyte for a rechargeable lithium battery, the electrolyte for a rechargeable lithium battery including a nonaqueous organic solvent, a lithium salt, and an additive.

[0023] The additive may be included in an amount of 0.1 parts by weight to 10 parts by weight based on 100 parts by weight of the electrolyte for a rechargeable lithium battery.

[0024] The additive may be included in an amount of about 0.1 parts by weight to about 5 parts by weight based on 100 parts by weight of the electrolyte for a rechargeable lithium battery.

[0025] The additive may further 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-hexanetrinitrile (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF 4 ), lithium difluorophosphate (LiPO 2 F 2 ) and at least one other additive of 2-fluorobiphenyl (2-FBP).

[0026] Another embodiment of the present invention provides a rechargeable lithium battery including: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte for a rechargeable lithium battery.

[0027] Another embodiment of the present invention provides a positive electrode including a positive electrode active material, a binder, a conductive material, and an additive.

[0028] The additive may be included in an amount of 0.001 parts by weight to 0.05 parts by weight based on 100 parts by weight of the total amount of the positive electrode active material, the binder, and the conductive material.

[0029] The positive electrode active material can be represented by Chemical Formula 3.

[0030] [Chemical formula 3]

[0031] Li x M 1 y M 2 z M 3 1-y-z O 2-a X b

[0032] In chemical formula 3,

[0033] 0.5 ≤ x ≤ 1.8, 0 ≤ a ≤ 0.05, 0 ≤ b ≤ 0.05, 0 < y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ y + z ≤ 1, M 1 、M 2 and M 3 each independently includes at least one element selected from the group consisting of metals Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr, or La and combinations thereof, and X includes at least one element selected from F, S, P, or Cl.

[0034] In Chemical Formula 3, 0.8 ≤ y ≤ 1, 0 ≤ z ≤ 0.2, and M 1 may be Ni.

[0035] Another embodiment of the present invention provides a rechargeable lithium battery, which includes: the aforementioned positive electrode; a negative electrode including a negative electrode active material; and an electrolyte for the rechargeable lithium battery.

[0036] The rechargeable lithium battery further includes a positive electrode film on the surface of the positive electrode, and

[0037] the positive electrode film may be a complex compound formed by coordinating an additive represented by Chemical Formula 1 to the positive electrode active material.

[0038] The negative electrode active material may include at least one of graphite and a Si composite.

[0039] The Si composite may include a core containing Si-based particles and an amorphous carbon coating.

[0040] The Si-based particles may include at least one of silicon particles, a Si-C composite, SiO x (0 < x ≤ 2) and a Si alloy.

[0041] The core including the Si-based particles may include pores in the central part.

[0042] The radius of the central part corresponds to 30% to 50% of the radius of the Si composite, the average particle size of the Si composite may be 5 μm to 20 μm, and the average particle size of the Si-based particles may be 10 nm to 200 nm.

[0043] The core including the Si-based particles includes amorphous carbon, the central part does not include amorphous carbon, and the amorphous carbon may exist only in the surface part of the Si composite.

[0044] The negative electrode active material may further include crystalline carbon.

[0045]

Beneficial Effects

[0046] By suppressing the breakdown of the positive electrode active material, an increase in the resistance of the battery during high-temperature storage can be suppressed, and the amount of generated gas can be reduced, thereby realizing a rechargeable lithium battery with improved high-temperature characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a schematic diagram showing a rechargeable lithium battery according to an embodiment.

[0048] Figure 2 Graphs showing the results of measuring the amount of gas generated after high-temperature storage in Examples 1 to 9 and Comparative Examples 1 to 7.

[0049] Figure 3 : is a graph showing the measurement results of the DC resistance of Examples 1 to 9 and Comparative Examples 1 to 7 after high-temperature storage.

[0050] Figure 4 The XPS analysis results of the positive electrode of the rechargeable lithium battery cell manufactured according to Comparative Example 1 are shown.

[0051] Figure 5 XPS analysis results of positive electrodes of rechargeable lithium battery cells manufactured according to Examples 1 to 3 are shown.

[0052] <Description of Reference Numerals>

[0053] 100: Rechargeable lithium battery

[0054] 112: Negative electrode

[0055] 113: Diaphragm

[0056] 114: Positive electrode

[0057] 120: Battery housing

[0058] 140: Sealing member DETAILED DESCRIPTION

[0059] 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.

[0060] In the present specification, when no limitation is provided otherwise, "substituted" means that at least one hydrogen of a substituent or a compound is replaced by deuterium, halogen, hydroxyl, amino, substituted or unsubstituted C1 to C30 amine, nitro, substituted or unsubstituted C1 to C40 silyl, C1 to C30 alkyl, C1 to C10 alkylsilyl, C6 to C30 arylsilyl, C3 to C30 cycloalkyl, C3 to C30 heterocycloalkyl, C6 to C30 aryl, C2 to C30 heteroaryl, C1 to C20 alkoxy, C1 to C10 trifluoroalkyl, cyano or a combination thereof.

[0061] In one embodiment of the present invention, "substituted" refers to at least one hydrogen of a substituent or compound being replaced by deuterium, halogen, C1 to C30 alkyl, C1 to C10 alkylsilyl, C6 to C30 arylsilyl, C3 to C30 cycloalkyl, C3 to C30 heterocycloalkyl, C6 to C30 aryl, C2 to C30 heteroaryl, C1 to C10 fluoroalkyl or cyano. In addition, in a specific embodiment of the present invention, "substituted" refers to at least one hydrogen of a substituent or compound being replaced by deuterium, halogen, C1 to C20 alkyl, C6 to C30 aryl, C1 to C10 fluoroalkyl or cyano. In addition, in a specific embodiment of the present invention, "substituted" refers to at least one hydrogen of a substituent or compound being replaced by deuterium, halogen, C1 to C5 alkyl, C6 to C18 aryl, C1 to C5 fluoroalkyl or cyano. In addition, in specific embodiments 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.

[0062] 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, rechargeable lithium batteries can also be classified into cylindrical, prismatic, coin-shaped, and pouch-shaped batteries, etc. In addition, depending on the size, rechargeable lithium batteries can be block-shaped and thin-film-shaped. The structure and manufacturing method of the lithium ion battery of the present disclosure are well known in the art.

[0063] 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 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; a battery case 120 that accommodates the battery cell; and a sealing member 140 that seals the battery case 120.

[0064] Hereinafter, additives according to embodiments will be described.

[0065] The additive according to an embodiment of the present invention is represented by Chemical Formula 1.

[0066] [Chemical formula 1]

[0067]

[0068] In Chemical Formula 1,

[0069] L 1 and L 2 Each is independently a substituted or unsubstituted C1 to C20 alkylene group.

[0070] For example, L 1 and L 2 The groups may each independently be a substituted or unsubstituted C1 to C10 alkylene group, specifically a substituted or unsubstituted C2 to C10 alkylene group, and more specifically a substituted or unsubstituted C2 to C5 alkylene group.

[0071] For example, L 1 and L 2 Each may independently be a substituted or unsubstituted ethylene group, a substituted or unsubstituted propylene group, or a substituted or unsubstituted butylene group.

[0072] In an embodiment, Chemical Formula 1 may be represented by Chemical Formula 1-1.

[0073] [Chemical formula 1-1]

[0074]

[0075] The additive can inhibit the breakdown of the positive electrode active material by combining with the positive electrode active material and coordinating on the surface of the positive electrode to form a film.

[0076] The additive may be included as an additive to an electrolyte for a rechargeable lithium battery or an additive to a positive electrode.

[0077] An electrolyte for a rechargeable lithium battery according to another embodiment includes a non-aqueous organic solvent, a lithium salt, and the aforementioned additives.

[0078] The additive may be included in an amount of 0.1 parts by weight to 10 parts by weight based on 100 parts by weight of the electrolyte for a rechargeable lithium battery.

[0079] For example, the additive may be included in an amount of 0.1 parts by weight to 5.0 parts by weight based on 100 parts by weight of the electrolyte for a rechargeable lithium battery.

[0080] When the content range of the additive is as described above, a rechargeable lithium battery having improved cycle-life characteristics and output characteristics may be realized by preventing an increase in resistance at high temperatures.

[0081] The additive may further 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-hexanetrinitrile (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF 4 ), lithium difluorophosphate (LiPO 2 F 2 ) and at least one other additive of 2-fluorobiphenyl (2-FBP).

[0082] 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.

[0083] 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.

[0084] When the other additives are included in amounts as described above, battery performance may be improved by minimizing an increase in membrane resistance.

[0085] The nonaqueous organic solvent serves as a medium for transmitting ions participating in the electrochemical reaction of the battery.

[0086] The non-aqueous organic solvent may be a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent or an aprotic solvent.

[0087] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), 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 include cyclohexanone, etc. Alcohol solvents may include ethanol and isopropanol, etc., and aprotic solvents may include nitriles (such as R 1-CN (where R 1 is a hydrocarbon group having a C2 to C20 straight chain, branched chain or ring structure, and may include a double bond, an aromatic ring or an ether bond), etc.), a dioxolane (such as 1,3-dioxolane, etc.), sulfolane, etc.

[0088] The nonaqueous organic solvent may be used alone or in combination of one or more, and when one or more combinations are used, the mixing ratio may be appropriately adjusted depending on the desired battery performance, which is widely understood by workers in the relevant art.

[0089] The carbonate solvent is prepared by mixing a cyclic carbonate and a chain carbonate. When the cyclic carbonate and the chain carbonate are mixed together in a volume ratio of 1:9 to 9:1, the performance of the electrolyte can be improved.

[0090] Particularly, in an embodiment of the present invention, the nonaqueous organic solvent may include the cyclic carbonate and the chain carbonate in a volume ratio of 2:8 to 5:5, and as a specific example, may include the cyclic carbonate and the chain carbonate in a volume ratio of 2:8 to 4:6.

[0091] As a more specific example, the cyclic carbonate and the chain carbonate may be included in a volume ratio of 2:8 to 3:7.

[0092] The nonaqueous organic solvent may further include an aromatic hydrocarbon organic solvent in addition to the carbonate-based solvent. Herein, the carbonate-based solvent and the aromatic hydrocarbon organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0093] The aromatic hydrocarbon organic solvent may be an aromatic hydrocarbon compound of Chemical Formula 2.

[0094] [Chemical formula 2]

[0095]

[0096] In chemical formula 2, R 3 To R 8 are the same or different and are selected from hydrogen, halogen, C1 to C10 alkyl, haloalkyl and combinations thereof.

[0097] 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.

[0098] The lithium salt dissolved in the non-aqueous organic solvent supplies lithium ions to 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 the lithium salt include those selected from LiPF 6 , LiBF 4 、LiSbF 6 、LiAsF 6 、LiN(SO 2 C 2 F 5 ) 2 、Li(CF 3 SO 2 ) 2 N、LiN(SO 3 C 2 F 5 ) 2 、Li(FSO 2 ) 2 N(Lithium bis(fluorosulfonyl)imide: LiFSI), LiC 4 F 9 SO 3 、LiClO 4 、LiAlO 2 、LiAlCl 4 、LiPO 2 F 2 、LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 ) (wherein x and y are natural numbers, for example, integers from 1 to 20), LiCl, LiI, LiB (C 2O 4 ) 2 (lithium bis(oxalato)borate: LiBOB), LiDFBOP (lithium difluorobis(oxalato)borate) and Li[PF 2 (C 2 O 4 ) 2 ](lithium difluoro(bisoxalate)phosphate). The lithium salt may be used in a concentration range of 0.1 M to 2.0 M. 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.

[0099] Another embodiment provides a rechargeable lithium battery including: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0100] The positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0101] As the positive electrode active material, a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound) can be used.

[0102] Specifically, an oxide of a compound of lithium and at least one metal selected from the group consisting of cobalt, manganese, nickel, and a combination thereof may be used.

[0103] Of course, part of the metal of the composite oxide may be replaced by a metal other than another metal, and the composite oxide may be selected from phosphate compounds (e.g., LiFePO 4 、LiCoPO 4 and LiMnPO 4 ), and a composite oxide having a coating on its surface may also be used, or a composite oxide and a composite oxide having a coating may be used in combination. The coating may include at least one coating element compound selected from the following: 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 hydroxycarbonate of a coating element. The compound used for the coating may be amorphous or crystalline. The coating elements included in the coating may include Mg, Al, Co, 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 may be provided in a manner that has no adverse effect on the performance of the positive electrode 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.

[0104] The positive electrode active material may be, for example, at least one of the lithium composite oxides represented by Chemical Formula 3.

[0105] [Chemical formula 3]

[0106] Li x M 1 y M 2 z M 3 1-y-z O 2-a X b

[0107] In chemical formula 3,

[0108] 0.5≤x≤1.8,0≤a≤0.05,0≤b≤0.05,0 <y≤1,0≤z≤1,0≤y+z≤1,M 1 、M 2 and M 3 Each independently includes at least one element selected from metal Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr or La, and combinations thereof, and X includes at least one element selected from F, S, P or Cl.

[0109] In an embodiment, the positive electrode active material may be selected from LiCoO 2 、LiNiO 2 、LiMnO 2 、LiMn 2 O 4 、LiNi a Mn b Co c O 2 (a+b+c=1), LiNi a Mn b Co c Al d O 2 (a+b+c+d=1) and LiNi e Co f Al g O 2 At least one of (e+f+g=1).

[0110] In Chemical Formula 3, 0.8≤y≤1, 0≤z≤0.2, and M 1 Can be for you.

[0111] For example, selected from LiNi a Mn b Co c O 2 (a+b+c=1), LiNi a Mnb Co c Al d O 2 (a+b+c+d=1) and LiNi e Co f Al g O 2 The positive electrode active material of (e+f+g=1) may be a high nickel (high Ni) type positive electrode active material.

[0112] For example, in LiNi a Mn b Co c O 2 (a+b+c=1) and LiNi a Mn b Co c Al d O 2 In the case of (a+b+c+d=1), the nickel content may be 60% or more (a≥0.6), and more specifically, 80% or more (a≥0.8).

[0113] For example, in LiNi e Co f Al g O 2 In the case of (e+f+g=1), the nickel content may be 60% or more (e≥0.6), and more specifically, 80% or more (e≥0.8).

[0114] The positive electrode active material may be included in an amount of 90 wt % to 98 wt % based on the total weight of the positive electrode active material layer.

[0115] In an embodiment of the present invention, the positive electrode active material layer may optionally include a conductive material and a binder. At this time, the contents of the conductive material and the binder may be 1 wt % to 5 wt % respectively based on the total weight of the positive electrode active material layer.

[0116] The conductive material is used to provide conductivity to the positive electrode, 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.

[0117] The binder improves the bonding performance between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of the binder may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon, but are not limited thereto.

[0118] Al may be used as a positive electrode current collector, but is not limited thereto.

[0119] The positive electrode may further include the aforementioned additives.

[0120] The additive may be included in an amount of 0.001 parts by weight to 0.05 parts by weight based on 100 parts by weight of the total amount of the positive electrode active material, the binder, and the conductive material.

[0121] For example, the additive may be included in an amount of 0.002 parts by weight to 0.01 parts by weight based on 100 parts by weight of the total amount of the positive electrode active material, the binder, and the conductive material.

[0122] The additive may improve high temperature storage characteristics by binding with the positive electrode active material to form a film on the surface of the positive electrode, and particularly when added in the above content, may significantly exhibit an improved degree of gas generation without increasing resistance.

[0123] The additive may be applied to the electrolyte or the positive electrode to form the positive electrode film.

[0124] The positive electrode film may be a complex compound formed by coordinating the additive represented by Chemical Formula 1 to the positive electrode active material.

[0125] More specifically, the positive electrode film can be formed by forming a complex between the non-shared electron pair of the disulfide of the additive and the metal of the positive electrode active material, or by forming a complex between the nitrile of the additive and the metal of the positive electrode active material, or by simultaneously forming a complex between the non-shared electron pair of the disulfide of the additive and the metal of the positive electrode active material and fixing the complex to the positive electrode surface.

[0126] In particular, when applied to a positive electrode, the additive is first combined with the positive electrode active material before participating in the electrochemical reaction, so that the amount of the produced positive electrode film can be further increased.

[0127] The negative electrode includes a negative electrode current collector and a negative electrode active material layer including a negative electrode active material formed on the negative electrode current collector.

[0128] 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.

[0129] The material that reversibly intercalates / deintercalates lithium ions may include a carbon material. The carbon material may be any common carbon-based negative electrode active material in a rechargeable lithium battery. Examples of the carbon material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be amorphous, or natural graphite or artificial graphite in the form of flakes, sheets, spheres, or fibers. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization products, and calcined coke, etc.

[0130] 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.

[0131] The material capable of doping / dedoping lithium may be Si, a Si-C composite, SiO x (0 < x < 2), a 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, SnO 2 and a Sn-R 11 alloy (where R 11 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. At least one of these materials may be mixed with SiO 2

[0132] The elements Q and R 11 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.

[0133] The transition metal oxide may be vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

[0134] In a specific embodiment, the negative electrode active material may include at least one of graphite and a Si composite.

[0135] The Si composite may include a core containing Si-based particles and amorphous carbon, and for example, the Si-based particles may include silicon particles, a Si-C composite, SiO​x (0 < x ≤ 2) and at least one of Si alloys.

[0136] For example, the core including Si-based particles may include pores in the central portion, the radius of the central portion corresponding to 30% to 50% of the radius of the Si composite, the average particle size of the Si composite may be 5 μm to 20 μm, and the average particle size of the Si-based particles may be 10 nm to 200 nm.

[0137] In this specification, the average particle size may be the particle size (D 50 ) of the particles at 50% volume in the cumulative size distribution curve.

[0138] When the average particle size of the Si-based particles is within the above range, volume expansion occurring during charge and discharge can be suppressed, and interruption of the conduction path due to particle pulverization during charge and discharge can be prevented.

[0139] The core including Si-based particles may further include amorphous carbon, where the central portion does not include amorphous carbon, and amorphous carbon may be present only in the surface portion of the Si composite.

[0140] At this time, the surface portion means the region from the outermost surface of the central portion to the outermost surface of the Si composite.

[0141] In addition, Si-based particles are included substantially uniformly throughout the negative electrode active material, that is, present in the central portion and the surface portion of the negative electrode active material at a substantially uniform concentration.

[0142] The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonized product, calcined coke, or a combination thereof.

[0143] For example, the Si-C composite may include silicon particles and crystalline carbon.

[0144] Based on the total weight of the Si-C composite, the content of the silicon particles may be 1 wt% to 60 wt%, for example, 3 wt% to 60 wt%.

[0145] The crystalline carbon may be, for example, graphite, and specifically may be natural graphite, artificial graphite, or a combination thereof.

[0146] The average particle size of the crystalline carbon may be 5 μm to 30 μm.

[0147] When the negative electrode active material includes both graphite and the Si composite, graphite and the Si composite may be included in the form of a mixture, and in this case, graphite and the Si composite may be included in a weight ratio of 99:1 to 50:50.

[0148] More specifically, graphite and the Si composite may be included in a weight ratio of 97:3 to 80:20 or 95:5 to 80:20.

[0149] 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.

[0150] 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.

[0151] 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 further 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.

[0152] The binder improves the binding properties between the negative electrode active material particles and the current collector. The binder includes a non-water-soluble binder, a water-soluble binder or a combination thereof.

[0153] 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.

[0154] 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.

[0155] When a water-soluble binder is used as a negative electrode binder, a cellulose compound may be further used as a thickener 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 content of the thickener may be 0.1 parts by weight to 3 parts by weight.

[0156] A conductive material is included to provide electrode conductivity. Any electronically conductive material can be used as the conductive material unless it causes a chemical change in the battery. Examples of conductive materials 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.

[0157] The negative electrode current collector may include one 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.

[0158] Another embodiment of the present invention provides a rechargeable lithium battery including: the aforementioned positive electrode; a negative electrode including a negative electrode active material; and an electrolyte for a rechargeable lithium battery.

[0159] The negative electrode active material is as described above, and the electrolyte for the rechargeable lithium battery includes a nonaqueous organic solvent and a lithium salt, and the nonaqueous organic solvent and the lithium salt are as described above.

[0160] Depending on the type of battery, the rechargeable lithium battery may further include a separator between the negative electrode and the positive electrode. Such a separator may be a porous substrate; or a composite porous substrate.

[0161] The porous substrate is a substrate including pores through which lithium ions can move. The porous substrate may include, for example, polyethylene, polypropylene, polyvinylidene fluoride and multilayers thereof, such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator and a polypropylene / polyethylene / polypropylene three-layer separator.

[0162] The composite porous substrate may have a form including a porous substrate and a functional layer on the porous substrate. From the perspective of ensuring additional functions, the functional layer may be, for example, at least one of a heat-resistant layer and an adhesive layer. For example, the heat-resistant layer may include a heat-resistant resin and an optional filler.

[0163] Additionally, the adhesive layer may include an adhesive resin and optionally a filler.

[0164] The filler may be an organic filler or an inorganic filler.

[0165] [Invention method]

[0166] Hereinafter, Examples and Comparative Examples are described. However, these examples should not be construed as limiting the scope of the present invention in any sense.

[0167] Manufacturing of rechargeable lithium battery cells

[0168] Comparative Example 1

[0169] By using LiNi as the positive electrode active material at a weight ratio of 96:2:2 0.88 Co 0.07 Al 0.05 O 2 , polyvinylidene fluoride as a binder and Ketjen black as a conductive material, and the mixture is dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0170] The positive electrode active material slurry was coated on a 14 μm thick Al foil, dried at 100° C., and pressed to produce a positive electrode.

[0171] A negative electrode active material was prepared by mixing artificial graphite and Si-C composite in a weight ratio of 93:7, and then mixing the negative electrode active material, a styrene-butadiene rubber binder as a binder, and carboxymethyl cellulose as a thickener in a weight ratio of 97:1:2, and then dispersed in distilled water to prepare a negative electrode active material slurry.

[0172] The Si-C composite is in the form of a core including artificial graphite and silicon particles, and coal pitch coated on the surface of the core.

[0173] The negative electrode active material slurry was coated on a 10 μm-thick Cu foil, dried at 100° C., and pressed to manufacture a negative electrode.

[0174] The electrode assembly was manufactured by assembling the manufactured positive and negative electrodes, and a separator made of polyethylene having a thickness of 25 μm, and injecting an electrolyte to manufacture a rechargeable lithium battery cell.

[0175] The electrolyte solution has the following composition.

[0176] (Composition of electrolyte)

[0177] Salt: LiPF 6 1.15M

[0178] Solvent: ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate (EC:EMC:DMC=20:40:40 volume ratio)

[0179] Other additives: 1 part by weight of vinylene carbonate (VC) and 1 part by weight of LiPO 2 F 2

[0180] (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))

[0181] Example 1

[0182] A rechargeable lithium battery cell was manufactured in substantially the same manner as in Comparative Example 1, except that 0.2 parts by weight of oxalic acid and 0.01 parts by weight of the additive represented by Chemical Formula 1-1 were dispersed in N-methylpyrrolidone based on 100 parts by weight of the total amount of the positive electrode active material, the binder and the conductive material.

[0183] Examples 2 to 4 and Comparative Examples 2 and 3

[0184] Each rechargeable lithium battery cell was manufactured in substantially the same method as in Example 1, except that the content of the additive represented by Chemical Formula 1-1 was changed as shown in Table 1.

[0185] Examples 5 to 9 and Comparative Examples 4 and 5

[0186] Each rechargeable lithium battery cell was manufactured in substantially the same method as in Example 1, except that the additive represented by Chemical Formula 1-1 was added to the electrolyte at each content shown in Table 1.

[0187] Comparative Example 6

[0188] A rechargeable lithium battery cell was manufactured in substantially the same manner as in Comparative Example 1, except that the additive represented by Chemical Formula a was added in the content shown in Table 1.

[0189] [Chemical formula a]

[0190]

[0191] Comparative Example 7

[0192] A rechargeable lithium battery cell was manufactured in substantially the same manner as in Example 1, except that the additive represented by Chemical Formula a was added in the content shown in Table 1.

[0193] (Table 1)

[0194]

[0195] Assessment 1: Measurement of the amount of gas generated after high temperature storage

[0196] The rechargeable lithium battery cells according to Examples 1 to 9 and Comparative Examples 1 to 7 were left standing at 70° C. for 30 days, and then the amount of gas generated on the 30th day was measured by using a refinery gas analyzer (RGA), and the results of Examples 1 to 9 and Comparative Examples 1 to 7 were as follows: Figure 2 Shown in.

[0197] Figure 2Graphs showing the results of measuring the amount of gas generated after high-temperature storage in Examples 1 to 9 and Comparative Examples 1 to 7.

[0198] refer to Figure 2 , when the additive according to the present invention is included in a positive electrode composition or added to an electrolyte in an appropriate amount, the amount of gas generation is significantly reduced, thereby improving storage characteristics at high temperatures.

[0199] Evaluation 2: Evaluation of the DC resistance increase rate after high-temperature storage

[0200] The initial DC internal resistance (DCIR) of the rechargeable lithium battery cells of Examples 1 to 9 and Comparative Examples 1 to 7 was evaluated by measuring ΔV / ΔI (voltage change / current change). Furthermore, after the maximum energy state inside the battery was changed to a fully charged state (SOC 100%) and the battery was stored at a high temperature of 70° C. for 30 days, the DC internal resistance was measured again, and the results of Examples 1 to 9 and Comparative Examples 1 to 7 were as follows: Figure 3 Shown in.

[0201] Figure 3 : is a graph showing the measurement results of the DC resistance of Examples 1 to 9 and Comparative Examples 1 to 7 after high-temperature storage.

[0202] refer to Figure 3 , when the additive according to the present invention is included in the positive electrode composition or added to the electrolyte in an appropriate amount, it is confirmed that the increase in DC internal resistance after storage at high temperature is relatively reduced compared with the initial DC resistance, thereby improving the storage characteristics at high temperature.

[0203] Assessment 3: Analysis of positive electrode membrane components

[0204] In order to analyze the components of the positive electrode film, the rechargeable lithium battery cells of Examples 1 to 3 and Comparative Example 1 were subjected to XPS (X-ray Photoelectron Spectroscopy) analysis, and the results are shown in Figure 4 and Figure 5 Shown in.

[0205] Figure 4 The XPS analysis results of the positive electrode of the rechargeable lithium battery cell manufactured according to Comparative Example 1 are shown.

[0206] Figure 5 XPS analysis results of positive electrodes of rechargeable lithium battery cells manufactured according to Examples 1 to 3 are shown.

[0207] refer to Figure 5 , Examples 1 to 3 show S2p peaks at binding energies of about 163 eV to 165 eV, but referring to Figure 4, Comparative Example 1 does not show the S2p peak.

[0208] Accordingly, it is confirmed that in the rechargeable lithium battery cell according to the present embodiment, the additive included in the positive electrode composition is coordinated on the positive electrode surface to form a film.

[0209] While the invention has been described in connection with what are presently considered to be practical example embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements within the spirit and scope of the claims.

Claims

1. An additive represented by chemical formula 1: [Chemical formula 1] in, In Chemical Formula 1, L 1 and L 2 Each is independently a substituted or unsubstituted C1 to C20 alkylene group.

2. The additive according to claim 1, wherein L 1 and L 2 Each is independently a substituted or unsubstituted C1 to C10 alkylene group.

3. The additive according to claim 1, wherein The additive is represented by chemical formula 1-1: [Chemical formula 1-1] 4. An electrolyte for a rechargeable lithium battery, comprising An electrolyte comprising a non-aqueous organic solvent, a lithium salt and the additive according to claim 1.

5. The electrolyte for a rechargeable lithium battery according to claim 4, wherein The electrolyte for a rechargeable lithium battery may include the additive in an amount of about 0.1 parts by weight to about 10 parts by weight based on 100 parts by weight of the electrolyte for a rechargeable lithium battery.

6. The electrolyte for a rechargeable lithium battery according to claim 5, wherein The electrolyte for a rechargeable lithium battery may include the additive in an amount of about 0.1 parts by weight to about 5.0 parts by weight based on 100 parts by weight of the electrolyte for a rechargeable lithium battery.

7. The electrolyte for a rechargeable lithium battery according to 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).

8. A rechargeable lithium battery comprising: a positive electrode, including a positive electrode active material; a negative electrode, including a negative electrode active material; and An electrolyte for a rechargeable lithium battery according to any one of claims 4 to 7.

9. A positive electrode comprising: A positive electrode active material, a binder, a conductive material and the additive according to claim 1.

10. The positive electrode according to claim 9, wherein The additive may be included in an amount of 0.001 parts by weight to 0.05 parts by weight based on 100 parts by weight of the total amount of the positive electrode active material, the binder, and the conductive material.

11. The positive electrode according to claim 10, wherein The positive electrode active material is represented by Chemical Formula 3: [Chemical formula 3] Li x M 1 y M 2 z M 3 1-y-z O 2-a X b in, In chemical formula 3, 0.5≤x≤1.8,0≤a≤0.05,0≤b≤0.05,0 <y≤1、0≤z≤1、0≤y+z≤1、M 1 、M 2 and M 3 Each independently includes at least one element selected from metal Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr or La, and combinations thereof, and X includes at least one element selected from F, S, P or Cl.

12. The positive electrode according to claim 11, wherein In chemical formula 3, 0.8≤y≤1, 0≤z≤0.2, and M 1 For you.

13. A rechargeable lithium battery comprising: The positive electrode according to any one of claims 9 to 12; a negative electrode, including a negative electrode active material; and Electrolytes for rechargeable lithium batteries.

14. The rechargeable lithium battery according to claim 13, wherein The positive electrode further comprises a positive electrode film on the positive electrode, and The positive electrode film is a complex compound formed by coordinating the additive represented by Chemical Formula 1 to the positive electrode active material.

15. The rechargeable lithium battery according to claim 13, wherein The negative electrode active material includes at least one of graphite and a Si composite.

16. The rechargeable lithium battery according to claim 15, wherein The Si composite includes a core including Si-based particles and an amorphous carbon coating.

17. The rechargeable lithium battery according to claim 16, wherein The Si-based particles include at least one of silicon particles, Si-C composites, SiO x (0 < x ≤ 2), and Si alloys.

18. The rechargeable lithium battery according to claim 17, wherein The core including the Si-based particles includes a hole in a central portion.

19. The rechargeable lithium battery according to claim 18, wherein The radius of the central portion corresponds to 30% to 50% of the radius of the Si composite, The average particle size of the Si composite is 5 μm to 20 μm. The average particle size of the Si-based particles is 10 nm to 200 nm.

20. The rechargeable lithium battery according to claim 18, wherein The core including the Si-based particles includes amorphous carbon, and The central portion does not include amorphous carbon, and the amorphous carbon exists only in the surface portion of the Si composite.

21. The rechargeable lithium battery according to claim 17, wherein The negative electrode active material further includes crystalline carbon.

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