Electrolyte additive, electrolyte for lithium secondary battery including electrolyte additive, and lithium secondary battery

Abstract

Provided are an electrolyte additive represented by Chemical Formula 1 or Chemical Formula 2, an electrolyte for a lithium secondary battery including the electrolyte additive, and a lithium secondary battery including the electrolyte additive. Details about Chemical Formula 1 and Chemical Formula 2 are as described in the specification.

Description

Technical Field

[0001] The present disclosure relates to an electrolyte additive, a rechargeable lithium battery electrolyte including the electrolyte additive, and a rechargeable lithium battery. 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, for example, by adding a lithium salt (such as LiPF6, LiBF4, and LiFSI) to a mixed solvent of a high dielectric cyclic carbonate (such as propylene carbonate and ethylene carbonate, etc.) and a chain carbonate (such as diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate, etc.). As the development of batteries in various fields becomes active, it is considered important to develop batteries with high output and high stability over a wide temperature range, and in addition, it is important to develop an electrolyte by optimizing and combining an organic solvent that suppresses swelling, capacity degradation, and resistance increase with an additive to ensure high power, long cycle life characteristics, and high temperature storage characteristics. Summary of the invention

[0006]

Technical issues

[0007] Embodiments provide an electrolyte additive having improved high temperature characteristics.

[0008] Another embodiment provides an electrolyte for a rechargeable lithium battery including the additive.

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

[0010]

Technical solution

[0011] An embodiment of the present invention provides an electrolyte additive represented by Chemical Formula 1 or Chemical Formula 2.

[0012]

[0013] In Chemical Formula 1 and Chemical Formula 2,

[0014] X is O or S,

[0015] R 1 To R 6 are each independently hydrogen, cyano, halogen, substituted or unsubstituted C1 to C10 alkyl, or substituted or unsubstituted C6 to C20 aryl, and

[0016] R 1 and R 2 At least one of R 3 and R 4 At least one of R 5 and R 6 At least one of is a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C6 to C20 aryl group.

[0017] R 1 or R 2 , R 3 or R 4 and R 5 or R 6 It may be a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C6 to C20 aryl group.

[0018] R 1 or R 2 , R 3 or R 4 and R 5 or R 6 It may be a substituted or unsubstituted C1 to C6 alkyl group.

[0019] The electrolyte additive may be one selected from the compounds listed in Group 1.

[0020] [Group 1]

[0021]

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

[0023] The electrolyte additive may be included 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.

[0024] The electrolyte additive may be included in an amount of about 0.1 parts by weight to about 2.0 parts by weight based on 100 parts by weight of the electrolyte for a rechargeable lithium battery.

[0025] The electrolyte for a rechargeable lithium battery 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).

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

[0028] [Chemical formula 3]

[0029] Li x M 1 y M 2 z M 3 1-y-z O 2±a X b

[0030] In chemical formula 3,

[0031] 0.5≤x≤1.8,0≤a≤0.1,0≤b≤0.1,0 <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.

[0032] In Chemical Formula 3, 0.8≤y≤1, 0≤z≤0.2, and M 1 Can be for you.

[0033] The negative electrode active material may include at least one of graphite and Si composite.

[0034] The Si composite may include a core containing Si-based particles and an amorphous carbon coating.

[0035] The Si-based particles may include at least one of Si particles, Si-C composite, SiO x (0 < x ≤ 2), and Si alloy.

[0036]

Beneficial effects

[0037] A rechargeable lithium battery is provided, which suppresses the increase in battery resistance during high-temperature storage and achieves excellent cycle life characteristics. Description of the drawings

[0038] Figure 1 It is a schematic diagram showing a rechargeable lithium battery according to an embodiment.

[0039] Figure 2 It is a graph showing the cyclic voltammetry (CV) results of the negative electrode of the electrolytes according to Example 1 and Comparative Example 1 at room temperature.

[0040] Figure 3 It is a graph showing the cyclic voltammetry (CV) results of the negative electrode of the electrolytes according to Example 2 and Comparative Example 1 at room temperature.

[0041] Figure 4 It is a graph showing the discharge capacity of the rechargeable lithium battery monomers according to Preparation Examples 1 to 4 and Comparative Preparation Examples 1 to 3 during cycling in high-temperature charge / discharge.

[0042] Figure 5 It is a graph showing the capacity retention rate of the rechargeable lithium battery monomers according to Preparation Examples 1 to 4 and Comparative Preparation Examples 1 to 3 during high-temperature charge / discharge.

[0043] Figure 6 It is a graph showing the leakage current measured at high voltage of the rechargeable lithium battery monomers according to Preparation Examples 1 to 4 and Comparative Preparation Example 1.

[0044] <Description of reference numerals>

[0045] 100: Rechargeable lithium battery

[0046] 112: Negative electrode

[0047] 113: Separator

[0048] 114: Positive electrode

[0049] 120: Battery case

[0050] 140: Sealing member DETAILED DESCRIPTION

[0051] Hereinafter, a rechargeable lithium battery according to embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, these embodiments are exemplary, and the present disclosure is not limited thereto.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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 1According 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.

[0056] Hereinafter, an electrolyte additive according to an embodiment will be described.

[0057] The additive according to an embodiment of the present invention is represented by Chemical Formula 1 or Chemical Formula 2.

[0058]

[0059] In Chemical Formula 1 and Chemical Formula 2,

[0060] X is O or S,

[0061] R 1 To R 6 are each independently hydrogen, cyano, halogen, substituted or unsubstituted C1 to C10 alkyl, or substituted or unsubstituted C6 to C20 aryl, and

[0062] R 1 and R 2 At least one of R 3 and R 4 At least one of R 5 and R 6 At least one of is a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C6 to C20 aryl group.

[0063] For example, R 1 or R 2 , R 3 or R 4 and R 5 or R 6 It may be a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C6 to C20 aryl group.

[0064] As a specific example, R 1 or R 2 , R 3 or R 4 and R 5 or R 6 It may be a substituted or unsubstituted C1 to C10 alkyl group.

[0065] For example, R 1 or R 2 , R 3 or R4 and R 5 or R 6 It may be a substituted or unsubstituted C1 to C6 alkyl group.

[0066] In an embodiment, Chemical Formula 1 or Chemical Formula 2 may be selected from the compounds listed in Group 1.

[0067] [Group 1]

[0068]

[0069] The additive represented by Chemical Formula 1 is reductively decomposed earlier than the carbonate solvent included in the non-aqueous organic solvent to form a solid electrolyte interface (SEI) film on the negative electrode, thereby preventing electrolyte decomposition and the resulting electrode decomposition reaction and suppressing an increase in internal resistance due to gas generation.

[0070] In addition, the additive can contribute to improving high-temperature cycle life characteristics by forming a film on the positive electrode surface and preventing decomposition of the positive electrode surface and oxidation reaction of the electrolyte.

[0071] That is, by including the additive, the cycle life characteristics and high temperature characteristics of the battery can be improved.

[0072] An electrolyte for a rechargeable lithium battery according to another embodiment includes a non-aqueous organic solvent, a lithium salt, and the aforementioned electrolyte additive.

[0073] The additive may be included 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.

[0074] The additive may be included in an amount of about 0.1 parts by weight to about 2.0 parts by weight based on 100 parts by weight of the electrolyte for a rechargeable lithium battery.

[0075] 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.

[0076] The electrolyte for a rechargeable lithium battery 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).

[0077] 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.

[0078] 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.

[0079] When the other additives are included in amounts as described above, battery performance may be improved by minimizing an increase in membrane resistance.

[0080] The nonaqueous organic solvent serves as a medium for transmitting ions participating in the electrochemical reaction of the battery.

[0081] 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.

[0082] 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), a dioxolane (such as 1,3-dioxolane), sulfolane, and the like.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] The aromatic hydrocarbon organic solvent may be an aromatic hydrocarbon compound of Chemical Formula 2.

[0089] [Chemical formula 2]

[0090]

[0091] In chemical formula 2, R 7 To R 12 are the same or different and are selected from the group consisting of hydrogen, halogen, C1 to C10 alkyl, C1 to C10 haloalkyl, and combinations thereof.

[0092] 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.

[0093] 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 lithium salts include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein, x and y are integers of 1 to 20), at least one of LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalato)borate: LiBOB), LiDFBOP (lithium difluorobis(oxalato)borate) and Li[PF2(C2O4)2] (lithium difluoro(bis(oxalato)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.

[0094] 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.

[0095] 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.

[0096] As the positive electrode active material, a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound) can be used.

[0097] 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.

[0098] Of course, a part of the metal of the composite oxide can be replaced by a metal other than another metal, and the composite oxide can be at least one selected from phosphate compounds (e.g., LiFePO4, LiCoPO4, and LiMnPO4), and a composite oxide having a coating on its surface can also be used, or a composite oxide and a composite oxide having a coating can be mixed and used. 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 element 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 can be set in a method 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 since it is well known to those skilled in the art, it is not explained in more detail.

[0099] The positive electrode active material may be, for example, at least one of the lithium composite oxides represented by Chemical Formula 3.

[0100] [Chemical formula 3]

[0101] Li x M 1 y M 2 z M 3 1-y-z O 2-a X b

[0102] In chemical formula 3,

[0103] 0.5≤x≤1.8,0≤a≤0.1,0≤b≤0.1,0 <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.

[0104] In an embodiment, the positive electrode active material may be selected from LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi a Mn b Co c O2(a+b+c=1), LiNia Mn b Co c Al d O2(a+b+c+d=1) and LiNi e Co f Al g At least one of O2(e+f+g=1).

[0105] In Chemical Formula 3, 0.8≤y≤1, 0≤z≤0.2, and M 1 Can be for you.

[0106] For example, selected from LiNi b Mn c Co d O2(b+c+d=1), LiNi b Mn c Co d Al e O2(b+c+d+e=1) and LiNi b Co d Al e The positive electrode active material of O2 (b+d+e=1) may be a high nickel (high Ni) type positive electrode active material.

[0107] For example, in LiNi b Mn c Co d O2(b+c+d=1) and LiNi b Mn c Co d Al e In the case of O2 (b+c+d+e=1), the nickel content may be 60% or more (b≥0.6), and more specifically, 80% or more (b≥0.8).

[0108] For example, in LiNi b Co d Al e In the case of O2 (b+d+e=1), the nickel content may be 60% or more (b≥0.6), and more specifically, 80% or more (b≥0.8).

[0109] 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 composition.

[0110] The conductive agent and the binder may be included in an amount of about 1 wt % to about 5 wt %, respectively, based on the total weight of the positive electrode composition.

[0111] 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 chemical changes. Examples of the conductive material can include: carbon materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.); metal materials including metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0112] 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 can be polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers 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.

[0113] Al can be used as the positive electrode current collector, but is not limited thereto.

[0114] 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.

[0115] The negative electrode active material can include materials that reversibly intercalate / deintercalate lithium ions, lithium metal, lithium metal alloys, materials capable of doping / dedoping lithium, or transition metal oxides.

[0116] The materials that reversibly intercalate / deintercalate lithium ions can include carbon materials. The carbon materials can be any common carbon-based negative electrode active materials in rechargeable lithium batteries. Examples of the carbon materials can be crystalline carbon, amorphous carbon, or mixtures thereof. The crystalline carbon can be amorphous, or natural graphite or artificial graphite in the form of flakes, sheets, spheres, or fibers. The amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization products, and calcined coke, etc.

[0117] The lithium metal alloys include alloys of lithium and metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0118] The materials capable of doping / dedoping lithium can be Si, Si-C composites, SiO x (0 < x < 2), Si-Q alloys (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements excluding Si, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof), Sn, SnO2, and Sn-R 11 alloys (where R 11Elements selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements excluding Sn, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, etc. At least one of these materials may be mixed with SiO2.

[0119] 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.

[0120] The transition metal oxide may be vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

[0121] In a specific embodiment, the negative electrode active material may include at least one of graphite and Si composite.

[0122] The Si composite may include a core containing Si-based particles and an amorphous carbon layer. 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.

[0123] For example, the core including Si-based particles may include pores in the central part, the radius of the central part corresponding to 30% to 50% of the radius of the core including Si-based particles. 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.

[0124] In this specification, the average particle size may be the particle size (D50) of 50% volume in the cumulative size distribution curve.

[0125] When the average particle size of the Si-based particles is within the above range, volume expansion occurring during charging and discharging can be suppressed, and interruption of the conduction path due to particle pulverization during charging and discharging can be prevented.

[0126] The above Si composite may further include amorphous carbon, where the central part does not include amorphous carbon, and the amorphous carbon may exist only in the surface part of the Si composite.

[0127] At this time, the surface part means the region from the outermost surface of the central part to the outermost surface of the Si composite.

[0128] In addition, the Si-based particles are included substantially uniformly throughout the negative electrode active material, that is, are present in a substantially uniform concentration in the central portion and the surface portion of the negative electrode active material.

[0129] The amorphous carbon may be soft carbon, hard carbon, a mesophase pitch carbonization product, calcined coke, or a combination thereof.

[0130] For example, the Si—C composite may include Si particles and crystalline carbon.

[0131] 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.

[0132] The crystalline carbon may be, for example, graphite, and specifically may be natural graphite, artificial graphite, or a combination thereof.

[0133] The average particle size of the crystalline carbon may be 5 μm to 30 μm.

[0134] When the negative electrode active material includes both graphite and the Si composite, the graphite and the Si composite may be included in the form of a mixture, wherein in this case, the graphite and the Si composite may be included in a weight ratio of 99:1 to 50:50.

[0135] More specifically, the graphite and the Si composite may be included in a weight ratio of 97:3 to 80:20 or 95:5 to 80:20.

[0136] 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.

[0137] In the negative electrode active material layer, the negative electrode active material may be included in an amount of about 95 wt % to about 99 wt % based on the total weight of the negative electrode active material layer.

[0138] 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.

[0139] The porous substrate is a substrate including pores through which lithium ions can move. The porous substrate may include, for example, polyethylene separators, polypropylene separators, polyvinylidene fluoride and multilayer separators thereof (such as polyethylene / polypropylene double-layer separators, polyethylene / polypropylene / polyethylene three-layer separators and polypropylene / polyethylene / polypropylene three-layer separators).

[0140] 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.

[0141] Additionally, the adhesive layer may include an adhesive resin and optionally a filler.

[0142] The filler may be an organic filler or an inorganic filler.

[0143] 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.

[0144] (Synthesis Example: Synthesis of Additives)

[0145] Synthesis Example 1: Synthesis of tris(1-cyanoethyl)phosphite

[0146] The desired compound was synthesized in a yield of 76.4% by a method known from the literature (Trudy Kazan. Khim. Tekhnol. Inst. im. SM Kirova (1957), 23, 161-6).

[0147] According to NMR and GCMS spectra, the product is a mixture of two inseparable isomers, both with identical mass spectra and a molar ratio of 13.5:86.5 (by 31 P NMR).

[0148] 1H NMR (400 MHz, acetone-d6, 25°C): 5.28 (m, 3H), 1.67 (dd, 9H).

[0149] 13C NMR (100 MHz, acetone-d6, 25°C): 118.62 (m), 57.85 (m), 20.92 (m).

[0150] 31P NMR (162 MHz, acetone-d6, 25°C): 140.96 (s), 140.13 (s) (area ratio 13.5:86.5).

[0151] GC-MS (30 m RTX-200 capillary column, oven temperature program: from 40 ° C (3 minutes) to 300 ° C at 10 ° C / min, separation ratio 50: 1, injector 150 ° C): retention time 17.4 minutes (major isomer, peak area 81%), retention time 18.1 minutes (minor isomer, peak area 19%).

[0152] Synthesis Example 2: Synthesis of tris(1-cyanoethyl)phosphate

[0153] The desired compound was synthesized in a yield of 92.3% by a method known from the literature (Trudy Kazan. Khim. Tekhnol. Inst. im. SM Kirova (1957), 23, 161-6).

[0154] According to NMR and GCMS spectra, the product is a mixture of two inseparable isomers with identical mass spectra and a molar ratio of 25:75 (by 31 P NMR).

[0155] 1H NMR (400 MHz, acetone-d6, 25°C): 5.46 (m, 3H), 1.75 (m, 9H).

[0156] 13C NMR (100 MHz, acetone-d6, 25°C): 117.12 (m), 62.82 (m), 20.17 (m).

[0157] 31P NMR (162 MHz, acetone-d6, 25°C): -4.35 (s), -4.97 (s) (area ratio 25:75).

[0158] GC-MS (30 m RTX-200 capillary column, oven temperature program: from 40 ° C (3 minutes) to 300 ° C at 10 ° C / min, separation ratio 50: 1, injector 150 ° C): retention time 18.4 minutes (minor isomer, peak area 26%), retention time 18.9 minutes (major isomer, peak area 74%).

[0159] Comparative Synthesis Example: Synthesis of Tris(2-cyanoethyl) Phosphate

[0160] While stirring and cooling, phosphorus oxychloride (15.33 g, 0.10 mol) in anhydrous dioxane (dry dioxane) (133 mL) was added to a mixture of 3-hydroxypropionitrile (21.32 g, 0.30 mol) and pyridine (23.73 g, 0.30 mol) in anhydrous dioxane (200 mL) in a dropwise manner for 1 hour. The mixture obtained was stirred for one day. The precipitate formed therein was filtered with a glass filter and rinsed with a small amount of anhydrous dioxane. The filtered and rinsed liquid was passed through an activated alumina (80 mL) layer. The colorless solution obtained was distilled under reduced pressure to obtain a colorless oil. The colorless oil was heated to 80° C. to 85° C. under vacuum and stirred until the residual 3-hydroxypropionitrile (controlled by NMR) was removed. The dark oil was diluted with anhydrous dioxane (80 mL) and passed through an alumina (80 mL) layer. The colorless solution thus obtained was distilled under reduced pressure to obtain a colorless oil. The colorless oil was heated under vacuum at 35-40°C for 15 hours until the solvent was removed to obtain a colorless viscous liquid (12.14 g, 47.1%).

[0161] 1H NMR (400MHz, CDCl3, 25°C): 4.27 (m, 6H), 2.77 (td, J1=5.80Hz, J2'=0.92Hz, J2"=1.22Hz, J2"'=0.92Hz, 9H). 13C NMR (100MHz, CDCl3, 25°C): 116.83 (s), 62.82 (d, J=5.27Hz), 19.76 (d, J=7.19Hz). 31P NMR (162MHz, CDCl3, 25°C): -2.53 (s).

[0162] (Example: Preparation of electrolyte)

[0163] Example 1

[0164] An electrolytic solution having the following composition was prepared.

[0165] (Composition of electrolyte)

[0166] Lithium salt: LiPF6 1.5M

[0167] Non-aqueous organic solvent: ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate (EC: EMC: DMC = 20:10:70 volume ratio)

[0168] Additive: 0.5 parts by weight of tris(1-cyanoethyl)phosphite represented by Chemical Formula 1a

[0169] [Chemical formula 1a]

[0170]

[0171] Example 2

[0172] An electrolytic solution was prepared in the same manner as in Example 1, except that tris(1-cyanoethyl)phosphate represented by Chemical Formula 2a was used instead of tris(1-cyanoethyl)phosphite represented by Chemical Formula 1a.

[0173] [Chemical formula 2a]

[0174]

[0175] Comparative Example 1

[0176] The electrolytic solution was prepared to have a composition excluding tris(1-cyanoethyl)phosphite represented by Chemical Formula 1a.

[0177] (Manufacturing Example: Manufacture of Rechargeable Lithium Battery Cell)

[0178] Preparation Example 1

[0179] By using LiNi in a weight ratio of 96:2:2 0.88 Co 0.07 Al 0.05 O2 was used as a positive electrode active material, polyvinylidene fluoride was used as a binder, and Ketjen black was used as a conductive material, and the mixture was dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0180] 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.

[0181] 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.

[0182] The Si—C composite is in the form of a core including artificial graphite and silicon particles and a coal pitch coated on the surface of the core.

[0183] 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.

[0184] 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.

[0185] The electrolyte solution has the following composition.

[0186] (Composition of electrolyte)

[0187] Salt: LiPF6 1.3M

[0188] Solvent: Ethylene carbonate: Propylene carbonate: Propyl propionate (EC: PC: PP = 10: 15: 75 volume ratio)

[0189] Additives: 0.5 parts by weight of tris(1-cyanoethyl)phosphite represented by Chemical Formula 1a, 7 parts by weight of fluoroethylene carbonate (FEC), 0.2 parts by weight of LiBF4, 1 part by weight of vinylethylene carbonate (VEC), and 3 parts by weight of propane sultone (PS).

[0190] (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) excluding the additive.

[0191] [Chemical formula 1a]

[0192]

[0193] Preparation Example 2

[0194] A rechargeable lithium battery cell was manufactured in the same manner as in Preparation Example 1, except that tris(1-cyanoethyl)phosphite represented by Chemical Formula 1a was used in an amount of 1.0 parts by weight.

[0195] Preparation Example 3

[0196] A rechargeable lithium battery cell was manufactured in the same manner as in Preparation Example 1, except that tris(1-cyanoethyl)phosphate represented by Chemical Formula 2a was used instead of tris(1-cyanoethyl)phosphite represented by Chemical Formula 1a.

[0197] [Chemical formula 2a]

[0198]

[0199] Preparation Example 4

[0200] A rechargeable lithium battery cell was manufactured in the same manner as in Preparation Example 1, except that tris(1-cyanoethyl)phosphate represented by Chemical Formula 2a was used in an amount of 1 part by weight.

[0201] Comparative Preparation Example 1

[0202] A rechargeable lithium battery cell was manufactured in the same manner as in Preparation Example 1 to have a composition excluding tris(1-cyanoethyl)phosphite represented by Chemical Formula 1a.

[0203] Comparative Preparation Example 2

[0204] A rechargeable lithium battery cell was manufactured in the same manner as in Preparation Example 1, except that tris(2-cyanoethyl)phosphate represented by Chemical Formula C1 according to Comparative Synthesis Example was used instead of tris(1-cyanoethyl)phosphite represented by Chemical Formula 1a.

[0205] [Chemical formula C1]

[0206]

[0207] Comparative Preparation Example 3

[0208] A rechargeable lithium battery cell was manufactured in the same manner as in Preparation Example 1, except that tris(2-cyanoethyl)phosphate represented by Chemical Formula C1 was used in an amount of 1 part by weight.

[0209] Each additive composition of the electrolytes of Preparation Examples 1 to 4 and Comparative Preparation Examples 1 to 3 is shown in Table 1.

[0210] (Table 1)

[0211]

[0212] Evaluation 1: Evaluation of CV characteristics

[0213] The electrochemical stabilities of the electrolytes of Comparative Example 1 and Examples 1 and 2 were evaluated in a cyclic voltammetry (CV) method, and the results were Figure 2 and Figure 3 Shown in.

[0214] A graphite negative electrode was used as a working electrode and Li metal was used as a reference electrode and a counter electrode to fabricate a three-electrode electrochemical cell for measuring the CV of the negative electrode. Herein, scanning was performed at a scan rate of 0.1 mV / sec in 3 cycles from 3V to 0V, from 0V to 3V.

[0215] Figure 2 Graphs showing cyclic voltammetry (CV) results of negative electrodes of the electrolytes according to Example 1 and Comparative Example 1 at room temperature.

[0216] Figure 3 Graphs showing cyclic voltammetry (CV) results of negative electrodes of the electrolytes according to Example 2 and Comparative Example 1 at room temperature.

[0217] like Figure 2 and Figure 3 As shown in FIG. 1 , it was confirmed that the electrolytes of Example 1 and Example 2 including the additive according to the present invention exhibited a reduction decomposition peak at a voltage of about 1.0 V or higher.

[0218] In contrast, the electrolyte containing no additive according to Comparative Example 1 did not show a reductive decomposition peak at a lower potential.

[0219] This proves that the electrolyte including the additive according to the embodiment interacts with the solvent at a relatively high reduction potential, and accordingly, before the solvent decomposition occurs during the charging process in which lithium ions are inserted into the negative electrode, the electrolytes of Examples 1 and 2 can form an initial SEI film on the negative electrode in a wide voltage region. Accordingly, the rechargeable lithium battery cells using the electrolytes according to Examples 1 and 2 of the present invention are expected to have excellent battery performance compared to the rechargeable lithium battery cells using the electrolyte of Comparative Example 1 that does not form an initial SEI film.

[0220] Evaluation 2: Evaluation of high temperature (45°C) cycle life characteristics

[0221] The rechargeable lithium battery cells according to Preparation Examples 1 to 4 and Comparative Preparation Examples 1 to 3 were charged at a constant current to a voltage of 4.5 V at a current rate of 0.2 C, and then, cut off at a rate of 0.05 C while maintaining 4.5 V in a constant voltage mode at 25° C. Subsequently, the battery cells were discharged at a constant current to a voltage of 2.8 V at a rate of 0.2 C. Accordingly, each charge / discharge capacity was examined.

[0222] The rechargeable lithium battery cell was charged at a constant current to a voltage of 4.5V at a current rate of 1.5C, and then, cut off at a rate of 0.05C while maintaining 4.5V in a constant voltage mode at 25°C. Subsequently, during discharge (first cycle), the battery cell was discharged at a constant current to 3.0V at a rate of 0.5C. This charge and discharge cycle was repeated 100 times at 45°C. In all charge / discharge cycles, a 10-minute pause was provided after each charge / discharge cycle.

[0223] The charge / discharge test results are Figure 4 and Figure 5 Shown in.

[0224] Figure 4 is a graph showing discharge capacities of rechargeable lithium battery cells according to Preparation Examples 1 to 4 and Comparative Preparation Examples 1 to 3 according to cycles in a high temperature charge / discharge process.

[0225] Figure 5 Graphs showing capacity retention rates of rechargeable lithium battery cells according to Preparation Examples 1 to 4 and Comparative Preparation Examples 1 to 3 during high temperature charge / discharge processes.

[0226] refer to Figure 4 and Figure 5 Compared with Comparative Preparation Examples 1 to 3, Preparation Examples 1 to 4 exhibit excellent high temperature cycle characteristics.

[0227] Evaluation 3: Overcharge stability evaluation

[0228] The rechargeable lithium battery coin half cells using lithium metal as the negative electrode according to Preparation Examples 1 to 4 and Comparative Preparation Example 1 were charged to 4.5 V at a current of 0.2 C and discharged to 3.0 V at the same current of 0.2 C to continue forming. Subsequently, the leakage current of the battery cell was measured by charging the battery cell to 4.6 V at a constant current of 0.2 C and then measuring the amount of current generated without maintaining a constant current when the voltage of 4.6 V was maintained for 300 hours, and the results were Figure 6 Shown in.

[0229] Figure 6is a graph showing leakage currents of rechargeable lithium battery cells according to Preparation Examples 1 to 4 and Comparative Preparation Example 1 measured at a high voltage.

[0230] refer to Figure 6 , Comparative Preparation Example 1 shows a large amount of leakage current at high voltage, which confirms the side reaction at high voltage, but Preparation Examples 1 to 4 show a significant reduction in leakage current. Accordingly, it is confirmed that the electrolyte additive according to the present invention greatly improves the stability at high voltage.

[0231] 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 electrolyte additive represented by Chemical Formula 1 or Chemical Formula 2: in, In Chemical Formula 1 and Chemical Formula 2, X is O or S, R 1 To R 6 are each independently hydrogen, cyano, halogen, substituted or unsubstituted C1 to C10 alkyl, or substituted or unsubstituted C6 to C20 aryl, and R 1 and R 2 At least one of R 3 and R 4 At least one of R 5 and R 6 At least one of is a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C6 to C20 aryl group.

2. The electrolyte additive according to claim 1, wherein R 1 or R 2 , R 3 or R 4 and R 5 or R 6 is a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C6 to C20 aryl group.

3. The electrolyte additive according to claim 1, R 1 or R 2 , R 3 or R 4 and R 5 or R 6 is a substituted or unsubstituted C1 to C6 alkyl group.

4. An electrolyte additive selected from the compounds listed in Group 1: [Group 1] 5. An electrolyte for a rechargeable lithium battery, A non-aqueous organic solvent, a lithium salt and the electrolyte additive according to claim 1.

6. The electrolyte for a rechargeable lithium battery according to claim 5, wherein The electrolyte additive may be included 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 electrolyte additive may be included in an amount of about 0.1 parts by weight to about 2.0 parts by weight based on 100 parts by weight of the electrolyte for a rechargeable lithium battery.

8. The electrolyte for a rechargeable lithium battery according to claim 5, wherein The electrolyte 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).

9. A rechargeable lithium battery comprising: a positive electrode, including a positive electrode active material; a negative electrode, including a negative electrode active material; as well as An electrolyte for a rechargeable lithium battery according to any one of claims 5 to 8.

10. The rechargeable lithium battery according to claim 9, 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 a in, In chemical formula 3, 0.5≤x≤1.8,0≤a≤0.1,0 <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.

11. The rechargeable lithium battery according to claim 10, wherein In chemical formula 3, 0.8≤y≤1, 0≤z≤0.2, and M 1 For you.

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

13. The rechargeable lithium battery according to claim 12, wherein The Si composite includes a core including Si-based particles and an amorphous carbon coating.

14. The rechargeable lithium battery according to claim 13, wherein The Si-based particles include at least one of silicon particles, Si-C composites, SiO x (0 < x ≤ 2) and Si alloys.

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