Electrolyte additive, electrolyte for lithium secondary battery containing the same, and lithium secondary battery

Abstract

The present invention provides an electrolyte additive represented by Chemical Formula 1 or Chemical Formula 2, an electrolyte for a lithium secondary battery containing the same, and a lithium secondary battery. The details of Chemical Formula 1 and Chemical Formula 2 are as described in the specification.

Description

[Technical Field]

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

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

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

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

[0005] The electrolyte solution is generally prepared by adding a lithium salt such as LiPF6, LiBF4, or LiFSI to a mixed solvent of a highly dielectric cyclic carbonate such as propylene carbonate or ethylene carbonate and a linear carbonate such as diethyl carbonate, ethyl methyl carbonate, or dimethyl carbonate. As battery development in various fields becomes more active, importance is being placed on developing batteries that ensure high output and high stability over a wide temperature range. In terms of electrolyte solutions, importance is also being placed on developing an optimal combination of organic solvent and additive that can provide high output, long life, and high-temperature storage properties, as well as suppress swelling, capacity loss, and resistance increase. Summary of the Invention [Problem to be solved by the invention]

[0006] One embodiment of the present invention is to provide an additive with good high temperature properties.

[0007] Another embodiment of the present invention provides an electrolyte for a lithium secondary battery, comprising the additive.

[0008] Yet another embodiment of the present invention provides a lithium secondary battery including the electrolyte solution. [Means for solving the problem]

[0009] One embodiment of the present invention provides an electrolyte additive represented by the following Chemical Formula 1 or Chemical Formula 2: [ka] [ka]

[0010] In the above Chemical Formula 1 and Chemical Formula 2, X is O or S; R 1 ~R 6 are each independently a hydrogen atom, a cyano group, a halogen atom, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C6 to C20 aryl group; R 1 and R 2 At least one of R 3 and R 4 At least one of the following and R 5 and R 6 At least one of the groups is a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C6 to C20 aryl group.

[0011] R 1 or R 2 , R3 or R 4 , and R 5 or R 6 can be a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C6 to C20 aryl group.

[0012] R 1 or R 2 , R 3 or R 4 , and R 5 or R 6 can be a substituted or unsubstituted C1 to C6 alkyl group.

[0013] The electrolyte additive may be one selected from the compounds listed in Group 1 below. [ka]

[0014] Another embodiment of the present invention provides an electrolyte for a lithium secondary battery, comprising a non-aqueous organic solvent, a lithium salt, and the electrolyte additive.

[0015] The electrolyte additive may be included in an amount of 0.1 to 5.0 parts by weight based on 100 parts by weight of the total electrolyte for lithium secondary batteries.

[0016] The electrolyte additive may be included in an amount of 0.1 to 2.0 parts by weight based on 100 parts by weight of the total electrolyte for lithium secondary batteries.

[0017] The electrolyte for lithium secondary batteries may further include at least one other additive selected from the group consisting of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF), lithium difluorophosphate (LiPOF), and 2-fluorobiphenyl (2-FBP).

[0018] Yet another embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte for a lithium secondary battery.

[0019] The positive electrode active material is represented by the following chemical formula 3. [Chemical formula 3] Li x M 1 y M 2 z M 3 1-y-z O 2±a X b

[0020] In the above Chemical Formula 3, 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 comprise one or more elements selected from metals such as 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 comprises one or more elements selected from F, S, P, or Cl.

[0021] In the chemical formula 3, 0.8 ≦ y ≦ 1, 0 ≦ z ≦ 0.2, M 1 may be Ni.

[0022] The negative electrode active material may include at least one of graphite and a Si composite.

[0023] The Si composite may include a core containing Si-based particles and an amorphous carbon coating layer.

[0024] The Si-based particles may include one or more of Si particles, Si-C composites, SiO x (0 < x ≦ 2) and Si alloy.

Advantages of the Invention

[0025] The present invention provides a lithium secondary battery that suppresses an increase in the resistance of the battery during high-temperature storage and realizes excellent cycle life characteristics.

Brief Description of the Drawings

[0026] [Figure 1] It is a schematic diagram showing a lithium secondary battery according to an embodiment of the present invention. [Figure 2] It is a graph showing the results of negative electrode cyclic voltammetry (CV) at room temperature of electrolytic solutions according to Example 1 and Comparative Example 1. [Figure 3] It is a graph showing the results of negative electrode cyclic voltammetry (CV) at room temperature of electrolytic solutions according to Example 2 and Comparative Example 1. [Figure 4] It is a graph showing the discharge capacity by cycles during high-temperature charge and discharge of lithium secondary batteries according to Production Examples 1 to 4 and Comparative Production Examples 1 to 3. [Figure 5] It is a graph showing the capacity retention rate during high-temperature charge and discharge of lithium secondary batteries according to Production Examples 1 to 4 and Comparative Production Examples 1 to 3. [Figure 6] It is a graph showing the measured leak current at a high voltage for lithium secondary batteries according to Production Examples 1 to 4 and Comparative Production Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, a lithium secondary battery according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings, which are provided for illustrative purposes only and are not intended to limit the present invention, which is merely defined by the categories of the claims that follow.

[0028] In this specification, unless otherwise defined, the term "substituted" means that at least one hydrogen atom in a substituent or compound has been replaced with deuterium, a halogen group, a hydroxyl group, an amino group, a substituted or unsubstituted C1-C30 amine group, a nitro group, a substituted or unsubstituted C1-C40 silyl group, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C20 alkoxy group, a C1-C10 fluoroalkyl group, a cyano group, or a combination thereof.

[0029] In one embodiment of the present invention, the term "substituted" refers to a group in which at least one hydrogen atom in a substituent or compound is replaced with deuterium, a halogen group, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C10 fluoroalkyl group, or a cyano group. In a specific example of the present invention, the term "substituted" refers to a group in which at least one hydrogen atom in a substituent or compound is replaced with deuterium, a halogen group, a C1-C20 alkyl group, a C6-C30 aryl group, a C1-C10 fluoroalkyl group, or a cyano group. In a specific example of the present invention, the term "substituted" refers to a group in which at least one hydrogen atom in a substituent or compound is replaced with deuterium, a halogen group, a C1-C5 alkyl group, a C6-C18 aryl group, a C1-C5 fluoroalkyl group, or a cyano group. In addition, in a specific example of the present invention, the term "substituted" means that at least one hydrogen atom of a substituent or compound is substituted with deuterium, a cyano group, a halogen group, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0030] Lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, and into cylindrical, prismatic, coin, and pouch types depending on the shape, and into bulk and thin film types depending on the size. The structures and manufacturing methods of these batteries are widely known in the art, so detailed description will be omitted.

[0031] Here, a cylindrical lithium secondary battery will be described as an example of a lithium secondary battery. Fig. 1 is a diagram schematically illustrating the structure of a lithium secondary battery according to one embodiment. Referring to Fig. 1, a lithium secondary battery 100 according to one embodiment includes a battery cell including a positive electrode 114, a negative electrode 112 positioned opposite the positive electrode 114, a separator 113 disposed between the positive electrode 114 and the negative electrode 112, and an electrolyte (not shown) impregnating the positive electrode 114, the negative electrode 112, and the separator 113, a battery container 120 that houses the battery cell, and a sealing member 140 that seals the battery container 120.

[0032] An electrolyte additive according to one embodiment will be described below.

[0033] An additive according to one embodiment of the present invention is represented by the following Chemical Formula 1 or Chemical Formula 2. [ka] [ka]

[0034] In the above Chemical Formula 1 and Chemical Formula 2, X is O or S; R 1 ~R 6 are each independently a hydrogen atom, a cyano group, a halogen atom, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C6 to C20 aryl group; R 1 and R 2 At least one of R 3 and R 4 At least one of the following and R 5 and R 6 At least one of the groups is a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C6 to C20 aryl group.

[0035] As an example, the above-mentioned R 1 or R 2 , R 3or R 4 , and R 5 or R 6 can be a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C6 to C20 aryl group.

[0036] As a specific example, the R 1 or R 2 , R 3 or R 4 , and R 5 or R 6 can be a substituted or unsubstituted C1 to C6 alkyl group.

[0037] For example, the R 1 or R 2 , R 3 or R 4 , and R 5 or R 6 can be a substituted or unsubstituted C1 to C6 alkyl group.

[0038] In one embodiment, the compound represented by Chemical Formula 1 or Chemical Formula 2 is selected from the compounds listed in Group 1 below. [ka]

[0039] The additive represented by Chemical Formula 1 is reductively decomposed before the carbonate-based solvent contained in the non-aqueous organic solvent to form a solid electrolyte interface (SEI) film on the negative electrode, thereby preventing the decomposition of the electrolyte and the resulting decomposition reaction of the electrode, thereby suppressing an increase in internal resistance due to gas generation.

[0040] In addition, a coating is also formed on the surface of the positive electrode, preventing decomposition of the positive electrode surface and oxidation of the electrolyte, thereby contributing to improved high-temperature life characteristics.

[0041] In other words, by including the additive, the life characteristics and high-temperature characteristics of the battery can be improved.

[0042] An electrolyte for a lithium secondary battery according to another embodiment of the present invention includes a non-aqueous organic solvent, a lithium salt, and the electrolyte additive described above.

[0043] The additive may be included in an amount of 0.1 to 5.0 parts by weight based on 100 parts by weight of the total electrolyte solution for lithium secondary batteries.

[0044] For example, the additive may be included in an amount of 0.1 to 2.0 parts by weight based on 100 parts by weight of the total electrolyte solution for lithium secondary batteries.

[0045] When the content of the additive is within this range, an increase in resistance at high temperatures can be prevented, and a lithium secondary battery with improved life characteristics and output characteristics can be realized.

[0046] The electrolyte for lithium secondary batteries may contain at least one other additive selected from the group consisting of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF), lithium difluorophosphate (LiPOF), and 2-fluorobiphenyl (2-FBP).

[0047] By further including the other additives, the life span can be further improved or gas generated from the positive and negative electrodes during high temperature storage can be effectively controlled.

[0048] The other additives may be included in an amount of 0.2 to 20 parts by weight, specifically 0.2 to 15 parts by weight, for example, 0.2 to 10 parts by weight, based on 100 parts by weight of the total electrolyte solution for lithium secondary batteries.

[0049] In this case, the content of other additives can minimize the increase in film resistance and contribute to improving battery performance.

[0050] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0051] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent.

[0052] Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, and caprolactone. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. The ketone solvent may be cyclohexanone, etc. The alcohol solvent may be ethyl alcohol, isopropyl alcohol, etc. The aprotic solvent may be R 1 -CN(R 1(wherein R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double-bonded aromatic ring or an ether bond), nitriles such as dimethylformamide, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc. can be used.

[0053] The non-aqueous organic solvents may be used alone or in combination of two or more thereof. When two or more thereof are used in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance, as would be widely understood by those working in the art.

[0054] In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate, and in this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1:9 to 9:1, the performance of the electrolyte is excellent.

[0055] In particular, in one embodiment of the present invention, the non-aqueous organic solvent may contain the cyclic carbonate and the chain carbonate in a volume ratio of 2:8 to 5:5, and as a specific example, the cyclic carbonate and the chain carbonate may be contained in a volume ratio of 2:8 to 4:6.

[0056] As a more specific example, the cyclic carbonate and the chain carbonate may be contained in a volume ratio of 2:8 to 3:7.

[0057] The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent in addition to the carbonate-based solvent, and the carbonate-based solvent and the aromatic hydrocarbon-based solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0058] The aromatic hydrocarbon solvent may be an aromatic hydrocarbon compound represented by the following formula 2: [ka]

[0059] In the above chemical formula 2, R 7 ~R 12 are the same or different and are selected from the group consisting of hydrogen, halogen, alkyl groups having 1 to 10 carbon atoms, haloalkyl groups having 1 to 10 carbon atoms, and combinations thereof.

[0060] Specific examples of the aromatic hydrocarbon solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorobenzene, fluoroisopropyl ether ... and combinations thereof.

[0061] The lithium salt is a substance that dissolves in a non-aqueous organic solvent, acts as a lithium ion source in the battery, enables the basic operation of a lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts include LiPF6, LiBF4, 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 The lithium salt may be one or more selected from the group consisting of lithium ions, ...

[0062] Yet another embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0063] The positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0064] As the positive electrode active material, a compound capable of reversible intercalation / deintercalation of lithium (lithiated insertion compound) can be used.

[0065] Specifically, at least one of composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0066] Of course, a composite oxide in which a portion of the metal in the composite oxide is replaced with a metal other than the other metal can also be used. The composite oxide may be a phosphate compound, such as at least one selected from the group consisting of LiFePO4, LiCoPO4, and LiMnPO4. The composite oxide may have a coating layer on its surface, or the composite oxide may be mixed with a composite oxide having a coating layer. This coating layer may contain at least one coating element compound selected from the group consisting of oxides of the coating element, hydroxides of the coating element, oxyhydroxides of the coating element, oxycarbonates of the coating element, and hydroxycarbonates of the coating element. The compounds constituting these coating layers may be amorphous or crystalline. The coating element contained in the coating layer may be Mg, Al, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating layer formation process may be performed using any coating method as long as the compound contains such elements and the coating method does not adversely affect the physical properties of the positive electrode active material (e.g., spray coating, dipping, etc.). This is well understood by those skilled in the art, and therefore, detailed description thereof will be omitted.

[0067] The positive electrode active material can be, for example, one or more lithium composite oxides represented by the following chemical formula 3. [Chemical formula 3] Li x M 1 yM 2 z M 3 1-y-z O 2±a X b In the above Chemical Formula 3, 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 comprise one or more elements selected from metals such as 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 comprises one or more elements selected from F, S, P, or Cl.

[0068] In one embodiment, the positive electrode active material is LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi a Mn b Co c O2(a+b+c=1), LiNi a Mn b Co c Al d O2(a+b+c+d=1) and LiNi e Co f Al g O2 (e+f+g=1).

[0069] In the above formula 3, 0.8≦y≦1, 0≦z≦0.2, M 1 can be Ni. For example, the 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 selected from O2 (b+d+e=1) may be a high Ni-based positive electrode active material.

[0070] For example, the 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 can be 60% or more (b≧0.6), more specifically 80% or more (b≧0.8). For example, the LiNi b Co d Al e In the case of O2 (b+d+e=1), the nickel content can be 60% or more (b≧0.6), more specifically 80% or more (b≧0.8).

[0071] The content of the positive electrode active material may be 90 wt % to 98 wt % based on the total weight of the positive electrode composition.

[0072] The content of the conductive material and the binder may be 1 wt % to 5 wt % each based on the total weight of the positive electrode composition.

[0073] The conductive material is used to impart conductivity to the positive electrode, and any material can be used as long as it does not cause a chemical change in the constructed battery and is electronically conductive. Examples of such a conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based materials such as metal powder or metal fiber of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures thereof.

[0074] The binder serves to firmly adhere the positive electrode active material particles to each other and to the current collector. Representative examples of the binder include, but are not limited to, 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.

[0075] The positive electrode current collector may be made of Al, but is not limited to this.

[0076] 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.

[0077] The negative electrode active material includes a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0078] The material capable of reversibly inserting / extracting lithium ions is a carbon material, and any carbon-based negative electrode active material commonly used in lithium secondary batteries can be used, representative examples of which include crystalline carbon, amorphous carbon, or a combination of these. Examples of crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0079] As the alloy of the lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn can be used.

[0080] As the substance capable of doping and undoping lithium, Si, Si-C composite, SiOx (0 < x < 2), Si-Q alloy (where Q is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element excluding Si, a Group 15 element, a Group 16 element, a transition metal, a rare earth element and a combination thereof), Sn, SnO2, Sn-R 11 (where R 11 is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element excluding Sn, a Group 15 element, a Group 16 element, a transition metal, a rare earth element and a combination thereof), etc. can be mentioned, and at least one of these can also be used by mixing with SiO2.

[0081] As the elements Q and R 11 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 a combination thereof can be used.

[0082] Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide or lithium titanate.

[0083] In a specific embodiment, the negative electrode active material can include at least one of graphite and Si composite.

[0084] The Si composite includes a core containing Si-based particles and an amorphous carbon coating layer. For example, the Si-based particles can include one or more of Si particles, Si-C composites, SiO x (0 < x ≤ 2) and Si alloys.

[0085] As an example, the core containing the Si-based particles contains voids at the center. The radius of the center corresponds to 30% to 50% of the radius of the core containing the Si-based particles. The average particle size of the Si composite is 5 μm to 20 μm, and the average particle size of the Si-based particles can be 10 nm to 200 nm.

[0086] In this specification, the average particle size can be the particle size (D50) at a volume ratio of 50% in the cumulative size-distribution curve.

[0087] When the average particle size of the Si-based particles is within the above range, the volume expansion generated during charge and discharge can be suppressed, and the interruption of the conductive path due to particle crushing during charge and discharge can be prevented.

[0088] The Si composite further contains amorphous carbon. At this time, the center does not contain amorphous carbon, and the amorphous carbon may exist only on the surface part of the Si composite. At this time, the surface part means the region from the outermost surface of the center to the outermost surface of the Si composite.

[0089] Also, the Si-based particles are substantially uniformly contained in the negative electrode active material as a whole, that is, they may exist at a substantially uniform concentration in the center and the surface part.

[0090] The amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or a combination thereof.

[0091] For example, the Si-C composite can include Si particles and crystalline carbon.

[0092] The Si particles may be included in an amount of 1 to 60 wt % of the total weight of the Si-C composite, for example, 3 to 60 wt %.

[0093] The crystalline carbon may be, for example, graphite, and specifically may be natural graphite, artificial graphite, or a combination thereof.

[0094] The average particle size of the crystalline carbon may be 5 μm to 30 μm.

[0095] When the negative electrode active material includes graphite and a Si composite, the graphite and the Si composite may be included in the form of a mixture, and in this case, the graphite and the Si composite may be included in a weight ratio of 99:1 to 50:50.

[0096] More specifically, the graphite and Si composite may be contained in a weight ratio of 97:3 to 80:20, or 95:5 to 80:20.

[0097] The amorphous carbon precursor may be coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or a polymer resin such as a phenol resin, a furan resin, or a polyimide resin.

[0098] The content of the negative electrode active material in the negative electrode active material layer may be 95 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0099] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. The separator may be a porous substrate or a composite porous substrate.

[0100] The porous substrate is a substrate containing voids through which lithium ions can move. The porous substrate may be, for example, a polyethylene separator, a polypropylene separator, polyvinylidene fluoride, or a multilayer separator consisting of two or more of these layers. Of course, a mixed multilayer separator such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0101] The composite porous substrate may include a porous substrate and a functional layer disposed on the porous substrate. The functional layer may be at least one of a heat-resistant layer and an adhesive layer, from the viewpoint of enabling additional functions to be added. For example, the heat-resistant layer may include a heat-resistant resin and, optionally, a filler.

[0102] The adhesive layer may include an adhesive resin and optionally a filler. The filler can be an organic filler or an inorganic filler. [Example]

[0103] Examples and comparative examples of the present invention will be described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0104] (Synthesis example: synthesis of additives) Synthesis Example 1: Synthesis of Tris(1-cyanoethyl)phosphite The target compound was synthesized in 76.4% yield by the method known in the reference literature Trudy Kazan. Khim. Technol. Inst. im. SM Kirova (1957), 23, 161-6.

[0105] NMR and GCMS spectra show that the product is an inseparable mixture of two isomers with identical mass spectra and a molar ratio of 13.5:86.5 (by 31 PNMR). 1H NMR (400MHz, acetone-d6, 25℃): 5.28 (m, 3H), 1.67 (dd, 9H). 13C NMR (100MHz, acetone-d6, 25℃): 118.62(m), 57.85(m), 20.92(m). 31P NMR (162MHz, acetone-d6, 25℃): 140.96(s), 140.13(s) (area ratio 13.5:86.5). GC-MS (30m RTX-200 capillary column, temp.program of the oven:from 40℃(3 min) to 300℃ at 10℃ / min, split ratio 50:1, injector 150℃): retention time of 17.4 min(main isomer, peak area 81%), retention time of 18.1 min(minor isomer, peak area 19%).

[0106] Synthesis Example 2: Synthesis of Tris(1-cyanoethyl)phosphate The target compound was synthesized in 92.3% yield by the method known in the reference literature Trudy Kazan. Khim. Technol. Inst. im. SM Kirova (1957), 23, 161-6.

[0107] NMR and GCMS spectra show that the product is an inseparable mixture of two isomers with identical mass spectra and in a molar ratio of 25:75 (by 31P NMR). 1H NMR (400MHz, acetone-d6, 25℃) 5.46 (m, 3H), 1.75 (m, 9H). 13C NMR (100MHz, acetone-d6, 25℃): 117.12(m), 62.82(m), 20.17(m). 31P NMR (162MHz, acetone-d6, 25℃): -4.35(s), -4.97(s) (area ratio 25:75). GC-MS (30m RTX-200 capillary column,temp.program of the oven:from 40℃ (3 min)to 300℃ at 10℃ / min,split ratio 50:1,injector 150℃):retention time of 18.4 min(minor isomer, peak area26%),retention time of 18.9 min(main isomer, peak area 74%).

[0108] Comparative synthesis example: Synthesis of Tris(2-cyanoethyl)phosphate Phosphorus oxychloride (15.33 g, 0.10 mol) in dry dioxane (133 mL) was added dropwise to a mixture of 3-hydroxypropionitrile (21.32 g, 0.30 mol) and pyridine (23.73 g, 0.30 mol) in dry dioxane (200 mL) with stirring and cooling for 1 hour. The mixture was stirred for 1 day. The precipitate formed was filtered under suction through a glass filter and washed with a small amount of dry dioxane. The filtered and washed liquid was passed through a layer of activated alumina (80 mL). The resulting colorless solution was distilled under reduced pressure to obtain a colorless oil. The colorless oil was stirred under vacuum for several days while heating at 80-85 °C until the remaining 3-hydroxypropionitrile was removed (control by NMR). The dark oil was diluted with dry dioxane (80 mL) and then passed through a layer of activated alumina (80 mL). The resulting colorless solution was distilled under reduced pressure to obtain a colorless oil. The colorless oil was heated at 35-40°C under vacuum for 15 hours until the solvent was removed, yielding a colorless viscous liquid (12.14g, 47.1%). 1H NMR (400MHz, CDCl3, 25℃): 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℃): 116.83(s), 62.82(d, J=5.27Hz), 19.76(d, J=7.19Hz). 31P NMR (162MHz, CDCl3, 25℃): -2.53(s).

[0109] (Example: Production of Electrolyte Solution) Example 1 An electrolyte solution having the following composition was prepared.

[0110] (Electrolyte composition) Lithium salt: LiPF61.5M Non-aqueous organic solvent: ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate (EC:EMC:DMC = 20:10:70 volume ratio) Additive: 0.5 parts by weight of Tris(1-cyanoethyl)phosphite represented by the above chemical formula 1a [ka]

[0111] Example 2 An electrolyte solution was prepared in the same manner as in Example 1, except that Tris(1-cyanoethyl)phosphate represented by the following Formula 2a was used instead of Tris(1-cyanoethyl)phosphate represented by the following Formula 1a: [ka]

[0112] Comparative Example 1 An electrolyte solution was prepared with the composition excluding Tris(1-cyanoethyl)phosphite represented by the formula 1a.

[0113] (Manufacturing example: manufacturing of lithium secondary batteries) Manufacturing Example 1 LiNi as the positive electrode active material 0.88 Co 0.07 Al 0.05 O2, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed in a weight ratio of 96:2:2, and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0114] The positive electrode active material slurry was coated on an aluminum foil having a thickness of 14 μm, dried at 110° C., and then pressed to prepare a positive electrode.

[0115] A mixture of artificial graphite and Si-C composite in a weight ratio of 93:7 was used as the negative electrode active material. The negative electrode active material and binder, styrene-butadiene rubber binder, and carboxymethyl cellulose thickener were mixed in a weight ratio of 97:1:2 and dispersed in distilled water to prepare a negative electrode active material slurry.

[0116] The Si-C composite has a core containing artificial graphite and silicon particles, and the surface of the core is coated with coal-based pitch.

[0117] The negative electrode active material slurry was coated on a copper foil having a thickness of 10 μm, dried at 100° C., and then pressed to prepare a negative electrode.

[0118] The positive and negative electrodes prepared above were assembled with a 25 μm thick polyethylene separator to prepare an electrode assembly, and an electrolyte solution was injected to prepare a lithium secondary battery.

[0119] The electrolyte composition is as follows: (Electrolyte composition) Salt: LiPF61.3M Solvent: ethylene carbonate: propylene carbonate: propyl propionate (volume ratio of EC:PC:PP = 10:15:75) Additives: 0.5 parts by weight of Tris(1-cyanoethyl)phosphite represented by the following 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) (However, in the electrolyte composition, "parts by weight" refers to the relative weight of the additive to 100 parts by weight of the entire electrolyte (lithium salt + non-aqueous organic solvent) excluding the additive.) [ka]

[0120] Manufacturing Example 2 A lithium secondary battery was fabricated in the same manner as in Preparation Example 1, except that 1.0 part by weight of Tris(1-cyanoethyl)phosphite represented by Formula 1a was used.

[0121] Manufacturing Example 3 A lithium secondary battery was fabricated in the same manner as in Preparation Example 1, except that Tris(1-cyanoethyl)phosphate represented by the following Chemical Formula 2a was used instead of Tris(1-cyanoethyl)phosphate represented by the following Chemical Formula 1a: [ka]

[0122] Production Example 4 A lithium secondary battery was fabricated in the same manner as in Preparation Example 1, except that 1 part by weight of Tris(1-cyanoethyl)phosphate represented by Formula 2a was used.

[0123] Comparative Manufacturing Example 1 A lithium secondary battery was fabricated in the same manner as in Preparation Example 1, except that the electrolyte solution was prepared without Tris(1-cyanoethyl)phosphite represented by Chemical Formula 1a.

[0124] Comparative Manufacturing Example 2 A lithium secondary battery was fabricated in the same manner as in Preparation Example 1, except that Tris(1-cyanoethyl)phosphate represented by Chemical Formula 1a was replaced with Tris(2-cyanoethyl)phosphate represented by the following Chemical Formula C1 according to Comparative Synthesis Example. [ka]

[0125] Comparative Manufacturing Example 3 A lithium secondary battery was fabricated in the same manner as in Preparation Example 1, except that 1 part by weight of Tris(2-cyanoethyl)phosphate represented by the chemical formula C1 was used. The compositions of the electrolyte additives according to Production Examples 1 to 4 and Comparative Production Examples 1 to 3 are shown in Table 1 below.

[0126] [Table 1]

[0127] Evaluation 1: CV characteristics evaluation In order to evaluate the electrochemical stability of the electrolytes according to Comparative Example 1 and Examples 1 and 2, cyclic voltammetry (CV) measurements were carried out, and the results are shown in FIGS.

[0128] A three-electrode electrochemical cell was used, with a graphite anode as the working electrode and Li metal as the reference and counter electrodes. The anode CV measurements were performed by scanning from 3 V to 0 V and from 0 V to 3 V for three cycles at a scan rate of 0.1 mV / sec.

[0129] FIG. 2 is a graph showing the results of negative electrode cyclic voltammetry (CV) at room temperature for the electrolyte solutions according to Example 1 and Comparative Example 1.

[0130] FIG. 3 is a graph showing the results of negative electrode cyclic voltammetry (CV) at room temperature for the electrolyte solutions according to Example 2 and Comparative Example 1.

[0131] As shown in FIGS. 2 and 3, it can be seen that the electrolyte solutions according to Examples 1 and 2 containing the additive of the present invention exhibit a reduction decomposition peak at about 1.0 V or higher.

[0132] On the other hand, it can be seen that the electrolyte solution of Comparative Example 1, which does not contain any additive, exhibits a reductive decomposition peak at a lower potential.

[0133] This is evidence that the electrolyte solution containing the additive according to one embodiment of the present invention interacts with the solvent at a relatively high reduction potential, and therefore, it is expected that the electrolyte solutions according to Examples 1 and 2 will form an initial SEI film on the negative electrode over a wide voltage range before solvent decomposition occurs during the charging process in which lithium ions are inserted into the negative electrode. Therefore, it is expected that the lithium secondary batteries using the electrolyte solutions according to Examples 1 and 2 will have superior battery performance compared to the lithium secondary battery using the electrolyte solution according to Comparative Example 1, which does not form an initial SEI film.

[0134] Evaluation 2: High temperature (45°C) lifespan characteristics evaluation The lithium secondary batteries fabricated in Preparation Examples 1 to 4 and Comparative Preparation Examples 1 to 3 were charged at a constant current of 0.2 C at 25° C. until the voltage reached 4.5 V, and then cut off at a current of 0.05 C while maintaining 4.5 V in constant voltage mode. Next, they were discharged at a constant current of 0.2 C until the voltage reached 2.8 V. The charge / discharge capacity of each battery was then determined. The lithium secondary battery was charged at a constant current of 1.5 C at 25°C until the voltage reached 4.5 V, and then cut off at a current of 0.05 C while maintaining 4.5 V in constant voltage mode. It was then discharged at a constant current of 0.5 C until the voltage reached 3.0 V (first cycle). The charge-discharge cycle was repeated 100 times at 45°C. A 10-minute rest period was allowed between each charge-discharge cycle.

[0135] The results of the charge / discharge experiment are shown in FIGS.

[0136] FIG. 4 is a graph showing the discharge capacity of the lithium secondary batteries according to Production Examples 1 to 4 and Comparative Production Examples 1 to 3 over cycles of high-temperature charge and discharge.

[0137] FIG. 5 is a graph showing the capacity retention rates during high-temperature charge and discharge of the lithium secondary batteries according to Production Examples 1 to 4 and Comparative Production Examples 1 to 3.

[0138] 4 and 5, it can be seen that the high-temperature cycle characteristics of Preparation Examples 1 to 4 are superior to those of Comparative Preparation Examples 1 to 3.

[0139] Evaluation 3: Overcharge stability evaluation Coin half cells of lithium secondary batteries prepared using lithium metal as the negative electrodes of the lithium secondary batteries prepared in Preparation Examples 1 to 4 and Comparative Preparation Example 1 were charged to 4.5 V at a current of 0.2 C and then discharged to 3.0 V at the same current of 0.2 C to undergo formation. After that, they were charged to 4.6 V at a constant current of 0.2 C and then maintained at 4.6 V for 300 hours. The leakage current was measured by measuring the amount of current generated when the constant current could not be maintained, and the results are shown in FIG.

[0140] FIG. 6 is a graph showing the results of measuring the leakage current at high voltage for the lithium secondary batteries according to Preparation Examples 1 to 4 and Comparative Preparation Example 1.

[0141] 6, in Comparative Preparation Example 1, a large amount of leakage current was generated at high voltage, indicating a side reaction at high voltage, whereas in Preparation Examples 1 to 4, the leakage current was significantly reduced, indicating that the electrolyte additive according to the present invention further improved stability at high voltage.

[0142] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that these also fall within the scope of the present invention. [Explanation of symbols]

[0143] 100 Lithium secondary battery 112 Negative electrode 113 Separator 114 Positive electrode 120 Battery container 140 Enclosure material

Claims

1. An electrolyte additive represented by the following chemical formula 1 or chemical formula 2: 【Chemical 1】 【Chemistry 2】 In the above Chemical Formula 1 and Chemical Formula 2, X is O or S; R １ ~R ６ are each independently a hydrogen atom, a cyano group, a halogen atom, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C6 to C20 aryl group; R １ and R ２ At least one of R ３ and R ４ At least one of the following and 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 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 R １ or R ２ , R ３ or R ４ , and R ５ or R ６ The electrolyte additive according to claim 1, wherein is a substituted or unsubstituted C1 to C6 alkyl group.

4. The electrolyte additive of claim 1, which is one selected from the compounds listed in Group 1 below: 【Chemistry 3】

5. An electrolyte for a lithium secondary battery, comprising a non-aqueous organic solvent, a lithium salt, and the electrolyte additive according to claim 1.

6. 6. The electrolyte solution for a lithium secondary battery according to claim 5, wherein the electrolyte additive is included in an amount of 0.1 to 5.0 parts by weight based on 100 parts by weight of the total electrolyte solution for a lithium secondary battery.

7. 6. The electrolyte solution for a lithium secondary battery according to claim 5, wherein the electrolyte additive is included in an amount of 0.1 to 2.0 parts by weight based on 100 parts by weight of the total electrolyte solution for a lithium secondary battery.

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

9. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and A lithium secondary battery comprising the electrolyte solution for lithium secondary batteries according to any one of claims 5 to 8.

10. The lithium secondary battery according to claim 9, wherein the positive electrode active material is represented by the following 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 the above 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 comprise one or more elements selected from metals such as 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 comprises one or more elements selected from F, S, P, or Cl.

11. In the above formula 3, 0.8≦y≦1, 0≦z≦0.2, M １ The lithium secondary battery according to claim 10, wherein is Ni.

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

13. The lithium secondary battery of claim 12 , wherein the Si composite comprises a core comprising Si-based particles and an amorphous carbon coating layer.

14. The Si-based particles include Si particles, Si-C composites, SiO ｘ The lithium secondary battery according to claim 13, comprising at least one of (0<x≦2) and Si alloy.

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