Secondary battery electrolyte and lithium secondary battery containing the same

Abstract

The present invention relates to a secondary battery electrolyte and a lithium secondary battery employing the same. The secondary battery electrolyte of the present invention includes two or more bissulfonyl imide lithium salts as additives, thereby significantly improving the rapid charging characteristics, room temperature life characteristics, and low temperature characteristics of a lithium secondary battery employing a high nickel content as a positive electrode.

Description

Technology Field

[0001] The present invention relates to a secondary battery electrolyte and a lithium secondary battery containing the same, and more specifically, to a secondary battery electrolyte containing a mixture of two or more bissulfonyl imide lithium salts as an additive and a lithium secondary battery employing the same. Background Technology

[0002] As the industrial environment has recently shifted toward the pursuit of energy, research on new energy sources is being conducted intensively.

[0003] As such an energy source, lithium-ion batteries are already being widely used as power sources for mobile devices such as smartphones and laptops, or for electric vehicles, due to their advantages of high energy density and low self-discharge.

[0004] A lithium secondary battery consists of a lithium salt as an electrolyte and an electrolyte solution of a non-aqueous solvent, and the non-aqueous solvent requires a high dielectric constant and high ionic conductivity over a wide temperature range to dissolve the lithium salt.

[0005] To satisfy these requirements, high-boiling point solvents such as propylene carbonate and ethylene carbonate, and low-boiling point solvents such as dimethyl carbonate and diethyl carbonate are mixed and used as solvents.

[0006] In addition, various additives are added to the electrolyte to improve the initial capacity, cycle characteristics, high temperature storage characteristics, low temperature characteristics, self-discharge characteristics, and overcharge characteristics of lithium secondary batteries.

[0007] However, for lithium-ion batteries to be used as the primary or auxiliary power source for electric or hybrid vehicles, they must possess high energy density to enable stable power supply while delivering high performance.

[0008] If conventional electrolyte additives are used as is in high-voltage lithium secondary batteries while increasing the operating voltage range, a problem arises in which the battery's internal resistance and lifespan decrease rapidly.

[0009] In other words, when using a conventional general electrolyte, the battery characteristics are good at voltages below 4.2 V, but above 4.2 V, the battery performance deteriorates as the voltage increases.

[0010] Therefore, it is necessary to develop electrolyte materials with excellent voltage resistance even at high pressures.

[0011] For example, to address these issues, U.S. Patent Publication No. 2019-0386338 discloses a lithium secondary battery having improved electrical characteristics and durability.

[0012] However, there is still a need for research on secondary battery electrolytes with enhanced electrical characteristics under high voltage and high-voltage lithium secondary batteries containing them. Prior art literature

[0013] US 2019-0386338A1(2019.12.19) The problem to be solved

[0014] The present invention provides a secondary battery electrolyte with remarkably improved high-rate charge / discharge characteristics, output characteristics, rapid-charge characteristics, and low-temperature characteristics, and a lithium secondary battery including the same. means of solving the problem

[0015] The present invention provides a secondary battery electrolyte, wherein the secondary battery electrolyte of the present invention is,

[0016] lithium salt,

[0017] Non-aqueous organic solvents, and

[0018] As an additive, it includes a mixture of two or more bissulfonyl imide lithium salts represented by the following chemical formula 1.

[0019] [Chemical Formula 1]

[0020]

[0021] (In the above chemical formula 1

[0022] R 1 and R 2 are independently fluoro or fluoroC1-C10alkyl;

[0023] The above R 1 and R 2 They can be linked to each other as fluoro C2-C10 alkylenes to form a ring.

[0024] Preferably, the following chemical formula 1 according to one embodiment of the present invention may be a bissulfonylamide lithium salt represented by the following chemical formula 2 or 3.

[0025] [Chemical Formula 2]

[0026]

[0027] [Chemical Formula 3]

[0028]

[0029] (In the above chemical formulas 2 and 3,

[0030] A is -(CR 15 R 16 ) n -

[0031] R 11 to R 16 are independently fluoro or perfluoroC1-C5alkyl;

[0032] n is an integer from 0 to 3.

[0033] More preferably, the bissulfonyl imide lithium salt represented by Formula 1 according to one embodiment of the present invention may be selected from the following compounds, but is not limited thereto.

[0034]

[0035] An additive according to one embodiment of the present invention may be present at a concentration of 0.1 to 0.5 M.

[0036] More preferably, the additive according to one embodiment of the present invention may be a mixture of lithium bis(fluorosulfonyl)imide and one or more compounds selected from bissulfonylimide lithium salts represented by the following chemical formula 4.

[0037] [Chemical Formula 4]

[0038]

[0039] (In the above chemical formula 4

[0040] R 3 and R 4 are independently perfluoroC1-C10 alkyl;

[0041] The above R 3 and R 4 They can be connected to each other as perfluoroC2-C10 alkylenes to form a ring.

[0042] According to one embodiment of the present invention, the lithium bissulfonyl imide salt of Formula 4 may be included in an amount of 0.1 to 1.5 moles per 1 mole of lithium bis(fluorosulfonyl)imide.

[0043] Preferably, a secondary battery electrolyte according to one embodiment of the present invention may further include a fluorosubstituted cyclic carbonate compound, and the fluorosubstituted cyclic carbonate compound may be included in an amount of 0.1 to 5 weight percent based on the total weight of the electrolyte.

[0044] A lithium salt according to one embodiment of the present invention may be one or more selected from the group consisting of LiPF6, LiBF4, LiClO4, LiSbF6, LiAsF6, LiN(SO3C2F5)2, LiCF3SO3, LiC4F9SO3, LiC6H5SO3, LiSCN, LiAlO2, LiAlCl4, LiCl, LiI, and LiB(C2O4)2, and the secondary battery electrolyte may have a lithium salt concentration of 0.3 to 1.0 molar.

[0045] In addition, the present invention provides a lithium secondary battery comprising a secondary battery electrolyte according to one embodiment of the present invention, wherein the lithium secondary battery of the present invention is,

[0046] An anode comprising a nickel-cobalt-manganese-based anode active material comprising the following chemical formula 11, the following chemical formula 12, or a mixture thereof;

[0047] cathode;

[0048] A separator interposed between the anode and the cathode; and

[0049] It includes a secondary battery electrolyte according to one embodiment of the present invention.

[0050] [Chemical Formula 11]

[0051] Li x (Ni a Co b Mn c )O2

[0052] (0.5 from Chemical Formula 11 <x<1.3, 0.8≤a<1.2, 0<b<1, 0<c<1, a+b+c=1이다.)

[0053] [Chemical Formula 12]

[0054] Li x (Ni a Co b Mn c )O4

[0055] (0.5 in the above chemical formula 12) <x<1.3, 0.8≤a<2, 0<b<2, 0<c<2, a+b+c=2이다.)

[0056] A lithium secondary battery according to one embodiment of the present invention enables fast charging, has excellent cycle characteristics, and remarkably improved low-temperature characteristics by including a combination of a specific cathode active material and a controlled secondary battery electrolyte containing a specific additive.

[0057] In terms of having improved characteristics, preferably, the cathode active material according to one embodiment of the present invention is Li x (Ni a Co b Mnc )O2 0.95≤x≤1.10, 0.8≤a<0.9 and a+b+c=1. Effects of the invention

[0058] The secondary battery electrolyte of the present invention contains a specific additive, bissulfonyl imide lithium salt, as a mixture, so that the output does not decrease even under high voltage, rapid charging is possible, and the cycle characteristics and low-temperature capacity characteristics are excellent.

[0059] Furthermore, the lithium secondary battery of the present invention employs a secondary battery electrolyte containing a mixture of the bissulfonyl imide lithium salt of the present invention and includes a specific positive electrode active material, thereby not only having excellent lifespan characteristics without output degradation even under high voltage, but also having particularly excellent low-temperature characteristics.

[0060] In addition, the lithium secondary battery of the present invention has remarkably improved rapid charging characteristics by employing a combination of a cathode containing a high-content nickel active material and an electrolyte containing a mixture of bissulfonyl imide lithium salt, which is a specific additive.

[0061] In addition, the lithium secondary battery of the present invention has improved output characteristics by reducing the internal resistance of the battery through the use of a mixture of bissulfonyl imide lithium salt in the electrolyte.

[0062] Furthermore, the lithium secondary battery of the present invention incorporates a secondary battery electrolyte that includes a mixture of bissulfonyl imide lithium salts as an additive and a specific fluorosubstituted cyclic carbonate compound as an additional additive, thereby improving cycle characteristics and rapid charging characteristics even during low temperature, high temperature, and high voltage charging and discharging. Brief explanation of the drawing

[0063] Figure 1 is a graph showing the rapid charging characteristics of lithium secondary batteries prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention. FIG. 2 is a graph showing the cycle characteristics of lithium secondary batteries prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention. FIG. 3 is a graph showing the cycle characteristics of lithium secondary batteries prepared in Example 2, Comparative Example 1, Comparative Example 3, and Comparative Example 4 of the present invention. Specific details for implementing the invention

[0064] The present invention will be described in more detail below. Unless otherwise defined, technical and scientific terms used herein have the meanings commonly understood by those skilled in the art to which this invention pertains. Furthermore, descriptions of known functions and configurations that could unnecessarily obscure the essence of the invention are omitted in the following description.

[0065] The "alkyl" described in the present invention refers to an aliphatic hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, more preferably 1 to 5 carbon atoms, and even better 1 to 4 carbon atoms. When the alkyl is used alone or in combination, it may be a straight-chain or branched alkyl. Specifically, straight-chain or branched alkyls may include methyl, ethyl, normal propyl, isopropyl, normal butyl, isobutyl, tert-butyl, normal pentyl, neo-pentyl, normal hexyl, isohexyl, normal heptyl, normal octyl, normal nonyl, normal decyl, etc.

[0066] The term "fluoroalkyl" as described in the present invention means that some or all of the hydrogen present in the alkyl group is substituted with fluoro, and examples include -CF3, -CH2CF3, -CF2CF3, etc.

[0067] The "fluoro-substituted cyclic carbonate" described in the present invention refers to a cyclic carbonate in which hydrogen present therein is substituted with one or more fluoro groups, and examples include fluoroethylene carbonate and fluoropropylene carbonate.

[0068] The “perfluoroalkyl” described in the present invention refers to a group in which all hydrogens present in an alkyl group having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, and more preferably 1 to 4 carbon atoms are substituted with fluoro, and examples include trifluoromethane and pentafluoroethane.

[0069] As described in this specification, "discharge" refers to the process of lithium ions being detached from the negative electrode, and "charge" refers to the process of lithium ions being inserted into the negative electrode.

[0071] The present invention provides a secondary battery electrolyte having excellent rapid charging characteristics, cycle characteristics, and low-temperature characteristics, wherein the secondary battery electrolyte of the present invention is,

[0072] lithium salt,

[0073] Non-aqueous organic solvents, and

[0074] As an additive, it includes a mixture of two or more bissulfonyl imide lithium salts represented by the following chemical formula 1.

[0075] [Chemical Formula 1]

[0076]

[0077] (In the above chemical formula 1

[0078] R 1 and R 2 are independently fluoro or fluoroC1-C10alkyl;

[0079] The above R 1 and R 2 They can be linked to each other as fluoro C2-C10 alkylenes to form a ring.

[0080] The secondary battery electrolyte of the present invention enables rapid charging and improves low-temperature characteristics by including a mixture of two or more bissulfonyl imide lithium salts represented by Chemical Formula 1.

[0081] Specifically, the secondary battery electrolyte of the present invention comprises a specific compound, a fluoro-substituted bissulfonyl imide lithium salt, and by including a mixture of two or more different substituted bissulfonyl imide lithium salts, the lithium secondary battery employing the same has improved electrical characteristics.

[0082] Preferably, R in Formula 1 according to one embodiment of the present invention 1 and R 2 are independently fluoro or perfluoroC1-C10 alkyl; and R 1 and R 2 can be connected to each other as perfluoroC2-C10 alkylenes to form a ring, and more preferably R 1 and R 2 are independently fluoro or perfluoroC1-C5 alkyl; and R 1 and R 2 They can be connected to each other as perfluoro C2-C5 alkylenes to form a ring.

[0083] Preferably, Formula 1 according to one embodiment of the present invention may be represented by the following Formula 2 or 3.

[0084] [Chemical Formula 2]

[0085]

[0086] [Chemical Formula 3]

[0087]

[0088] (In the above chemical formulas 2 and 3,

[0089] A is -(CR 15 R 16 ) n -

[0090] R 11 to R 16 are independently fluoro or perfluoroC1-C5alkyl;

[0091] n is an integer from 0 to 3.

[0092] More preferably, R in Formula 2 or 3 according to one embodiment of the present invention 11 to R 16 ⅓ are independently fluoro or perfluoroC1-C4 alkyl; n can be an integer from 0 to 2.

[0093] More specifically, the bissulfonyl imide lithium salt according to one embodiment of the present invention may be selected from the following compounds, but is not limited thereto.

[0094]

[0095] An additive according to one embodiment of the present invention may be present at a concentration of 0.1 to 0.5 M, and preferably at a concentration of 0.2 to 0.5 M.

[0096] Preferably, the additive according to one embodiment of the present invention may be a mixture of acyclic lithium bis(fluorosulfonyl)imide and acyclic lithium bis(fluorosulfonyl)imide or a mixture of acyclic lithium bis(fluorosulfonyl)imide and cyclic lithium bis(fluorosulfonyl)imide.

[0097] Specifically, the additive according to one embodiment of the present invention may be a mixture of two or more selected from the bissulfonyl imide lithium salt represented by Chemical Formula 2, and may be a mixture of the bissulfonyl imide lithium salt represented by Chemical Formula 2 and the bissulfonyl imide lithium salt represented by Chemical Formula 3.

[0098] In order to have improved electrical properties, preferably, an additive according to one embodiment of the present invention may be a mixture of lithium bis(fluorosulfonyl)imide and one or more compounds selected from bissulfonylimide lithium salts represented by the following chemical formula 4.

[0099] [Chemical Formula 4]

[0100]

[0101] (In the above chemical formula 4

[0102] R 3 and R 4 are independently perfluoroC1-C10 alkyl;

[0103] The above R 3 and R 4 They can be connected to each other as perfluoroC2-C10 alkylenes to form a ring.

[0104] Preferably, R in Formula 4 according to one embodiment of the present invention 3 and R 4 are independently perfluoroC1-C5 alkyl; and R 3 and R 4 They can be connected to each other as perfluoro C2-C5 alkylenes to form a ring.

[0105] More preferably, an additive according to one embodiment of the present invention may be a mixture of lithium bis(fluorosulfonyl)imide and one or more compounds selected from the compounds of Formula 3 below.

[0106] [Chemical Formula 3]

[0107]

[0108] (In the above chemical formula 3,

[0109] A is -(CR 15 R 16 ) n -

[0110] R 13 to R 16 are independently fluoro or perfluoroC1-C5alkyl;

[0111] n is an integer from 0 to 3.

[0112] A lithium bissulfonyl imide salt represented by Formula 4 according to one embodiment of the present invention may be included in an amount of 0.1 to 1.5 moles, preferably 0.2 to 1.0 moles, per 1 mole of lithium bis(fluorosulfonyl)imide.

[0113] Preferably, the secondary battery electrolyte according to one embodiment of the present invention may further include a fluorosubstituted cyclic carbonate compound, and as a preferred example, may be one or more selected from fluoroethylene carbonate, fluorovinyl carbonate and fluoropropylene carbonate, and may be included in an amount of 0.1 to 5 weight%, preferably 0.5 to 3 weight%, based on the total weight of the electrolyte.

[0114] A secondary battery electrolyte according to one embodiment of the present invention has excellent cycle characteristics and low temperature characteristics by further including a fluorosubstituted cyclic carbonate compound.

[0115] In one embodiment of the present invention, the lithium salt may be any lithium salt used in a secondary battery electrolyte, but may be one or more selected from the group consisting of LiPF6, LiBF4, LiClO4, LiSbF6, LiAsF6, LiN(SO3C2F5)2, LiCF3SO3, LiC4F9SO3, LiC6H5SO3, LiSCN, LiAlO2, LiAlCl4, LiCl, LiI, and LiB(C2O4)2, and preferably may be one or more selected from LiPF6, LiBF4, LiClO4, LiSbF6, and LiAsF6.

[0116] In one embodiment of the present invention, the secondary battery electrolyte may have a lithium salt concentration of 0.3 to 1.0 mol, preferably 0.3 to 0.8 M.

[0117] In a lithium secondary battery according to one embodiment of the present invention, the electrolyte may further include one or more additives selected from the group consisting of an oxalate toborate-based compound, an oxalate tophosphate-based additive, a fluorine-substituted carbonate-based compound, a vinylidene carbonate-based compound, and a sulfinyl group-containing compound.

[0118] An oxaletoborate-based compound according to one embodiment of the present invention may be a compound represented by the following chemical formula A or lithium bis(oxaleto)borate (LiB(C2O4)2, lithium bis(oxaleto)borate, LiBOB).

[0119] [Chemical Formula A]

[0120]

[0121] In the above chemical formula A, R a and R b Each is independently a halogen or a halo-C1-C10 alkyl.

[0122] Specific examples of the above-mentioned oxalate-toborate-based additives include lithium difluoro(oxalate)borate (LiB(C2O4)F2, lithium difluoro(oxalate)borate, LiDFOB) or lithium bis(oxalate)borate (LiB(C2O4)2, LiBOB).

[0123] The above oxalatophosphate-based additive may be a compound represented by the following chemical formula B or lithium difluorobis(oxalato)phosphate (LiPF2(C2O4)2), lithium difluorobis(oxalato)phosphate, LiDFBOP.

[0124] [Chemical Formula B]

[0125]

[0126] In the above chemical formula B, R c to R f Each is independently a halogen or a halo-C1-C10 alkyl.

[0127] Specific examples of the above-mentioned oxalatophosphate-based additives include lithium tetrafluoro(oxalato)phosphate (LiPF4(C2O4), lithium tetrafluoro(oxalato)phosphate, LiTFOP) or lithium difluorobis(oxalato)phosphate (LiPF2(C2O4)2, LiDFBOP).

[0128] The above fluorine-substituted carbonate compound may be fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), fluorodimethyl carbonate (FDMC), fluoroethylmethyl carbonate (FEMC), or a combination thereof.

[0129] The above vinylidene carbonate-based compound may be vinylene carbonate (VC), vinyl ethylene carbonate (VEC), or a mixture thereof.

[0130] The above sulfinyl group (S=O) containing compound may be a sulfone compound, a sulfite compound, a sulfonate compound, a sultone compound, or a sulfate compound, and these may be used alone or in combination.

[0131] The above sulfone compound may specifically be a sulfone compound of the following chemical formula C.

[0132] [Chemical Formula C]

[0133]

[0134] [In the above chemical formula C,

[0135] R g and R hare independently hydrogen, halogen, C1-C10 alkyl, C2-C10 alkenyl, halo-C1-C10 alkyl, halo-C2-C10 alkenyl, or C6-C12 aryl.

[0136] Non-limiting examples of the above sulfone compounds include, but are not limited to, dimethylsulfone, diethylsulfone, ethyl methyl sulfone, methyl vinyl sulfone, and divinyl sulfone. Additionally, these compounds may be used alone or in a mixture of two or more.

[0137] The above sulfite compound may specifically be a sulfite compound of the following chemical formula D.

[0138] [Chemical Formula D]

[0139]

[0140] [In the above chemical formula D,

[0141] R i and R j are independently hydrogen, halogen, C1-C10 alkyl, C2-C10 alkenyl, halo-C1-C10 alkyl, halo-C2-C10 alkenyl, or C6-C12 aryl, or R i and R j is -CR 100 R 101 CR 102 R 103 (CR 104 R 105 ) m - can be connected to form a loop;

[0142] R 100 to R 105 Each is independently hydrogen, C1-C10 alkyl, or phenyl;

[0143] m is an integer of 0 or 1.

[0144] Non-limiting examples of the above sulfite compounds include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethyl propylene sulfite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, and 1,3-butylene glycol sulfite. Examples include, but are not limited to. In addition, these compounds may be used alone or in combination of two or more.

[0145] The above sulfonate compound may specifically be a sulfonate compound of the following chemical formula E.

[0146] [Chemical Formula E]

[0147]

[0148] [In the above chemical formula E,

[0149] R k and R l are independently hydrogen, halogen, C1-C10 alkyl, C2-C10 alkenyl, halo-C1-C10 alkyl, halo-C2-C10 alkenyl, or C6-C12 aryl.

[0150] Non-limiting examples of the above sulfonate compounds include, but are not limited to, methyl methansulfonate, ethyl methansulfonate, methyl ethansulfonate, propyl methansulfonate, methyl propansulfonate, ethyl propansulfonate, vinyl methansulfonate, allyl methanesulfonate, vinyl benzenesulfonate, and allyl prop-2-enesulfonate. Additionally, these compounds may be used alone or in a mixture of two or more.

[0151] The above-mentioned sulfonate compound may specifically be a sulfonate compound of the following chemical formula F.

[0152] [Chemical Formula F]

[0153]

[0154] [In the above chemical formula F,

[0155] represents a single bond or a double bond;

[0156] R m to R o are independently hydrogen, halogen, C1-C10 alkyl, C2-C10 alkenyl, halo-C1-C10 alkyl, halo-C2-C10 alkenyl, or C6-C12 aryl;

[0157] n is an integer from 0 to 3.

[0158] Non-limiting examples of the above sulfone compounds include, but are not limited to, ethanesulfone, 1,3-propanesulfone (PS), 1,4-butanesulfone (BS), ethensultone, 1,3-propenesulfone (PRS), 3-fluoro-1,3-propanesulfone (FPS), and 1,4-butenesulfone. Additionally, these compounds may be used individually or in a mixture of two or more.

[0159] The above sulfate compound may specifically be a cyclic sulfate compound of the following chemical formula G.

[0160] [Chemical Formula G]

[0161]

[0162] [In the above chemical formula G,

[0163] R p and R q are independently hydrogen, halogen, C1-C10 alkyl, C2-C10 alkenyl, halo-C1-C10 alkyl, halo-C2-C10 alkenyl, or C6-C12 aryl;

[0164] x is an integer from 0 to 3.

[0165] Non-limiting examples of the above sulfate compounds include, but are not limited to, ethylene sulfate (ESA), propylene sulfate, 2,3-butylene sulfate, 1,3-propylene sulfate, and 1,3-butylene sulfate. Additionally, these compounds may be used alone or in a mixture of two or more.

[0166] The electrolyte according to one embodiment of the present invention is typically stable in a temperature range of -20°C to 60°C, preferably 10°C to 60°C, and maintains electrochemically stable characteristics even at high voltages of 4.20V or higher based on positive potential, specifically 4.30V or higher, more specifically 4.35V or higher, so it can be applied to all lithium secondary batteries, such as lithium-ion batteries and lithium-polymer batteries.

[0167] Non-limiting examples of a secondary battery according to one embodiment of the present invention include a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0168] In addition, the present invention provides a lithium secondary battery comprising the secondary battery electrolyte of the present invention, wherein the lithium secondary battery of the present invention is,

[0169] An anode comprising a nickel-cobalt-manganese-based anode active material comprising the following chemical formula 11, the following chemical formula 12, or a mixture thereof;

[0170] cathode;

[0171] A separator interposed between the anode and the cathode; and

[0172] It includes a secondary battery electrolyte according to one embodiment of the present invention.

[0173] [Chemical Formula 11]

[0174] Li x (Ni a Co b Mn c )O2

[0175] 0.5 in chemical formula 11 <x<1.3, 0.8≤a<1.2, 0<b<1, 0<c<1, a+b+c=1이다.

[0176] [Chemical Formula 12]

[0177] Li x (Ni a Co b Mn c )O4

[0178] 0.5 in the above chemical formula 12 <x<1.3, 0.8≤a<2, 0<b<2, 0<c<2, a+b+c=2이다.

[0179] The lithium secondary battery of the present invention is capable of rapid charging and has excellent low-temperature characteristics and lifespan characteristics by employing a positive electrode made of an active material containing a high nickel content and an electrolyte containing a mixture of bissulfonyl imide lithium salt, which is a specific compound.

[0180] As charging and discharging progresses in lithium-ion batteries, the cathode active material structurally degrades, leading to the leaching of metal ions from the cathode surface. These leached metal ions are electrodeposited onto the anode, causing degradation. This degradation phenomenon tends to accelerate when the cathode potential increases or the battery is exposed to high temperatures. Furthermore, lithium-ion batteries face the problem that when the operating voltage increases, the coating on the cathode surface decomposes, and the surface becomes exposed to the electrolyte, resulting in adverse reactions with the electrolyte.

[0181] In particular, electric vehicles require batteries with very high energy density. To solve the problems associated with high-content Ni, which is commonly used as a cathode material when high-energy density batteries are in operation, the lithium secondary battery of the present invention has improved battery characteristics by employing an electrolyte containing a mixture of two or more bissulfonyl imide lithium salts represented by the above chemical formula 1.

[0182] Specifically, the lithium secondary battery of the present invention enables rapid charging and improves lifespan characteristics by including a combination of an electrolyte comprising a mixture of two or more bissulfonyl imide lithium salts represented by Chemical Formula 1 and a specific nickel-cobalt-manganese-based positive electrode active material represented by Chemical Formulas 11 and 12.

[0183] Furthermore, the lithium secondary battery of the present invention, which employs a combination of a specific anode and an electrolyte containing a specific additive, can improve cycle life characteristics and low-temperature output characteristics even under low temperature and high voltage.

[0184] A positive active material in a preferred combination with a secondary battery electrolyte according to one embodiment of the present invention may be Formula 11, and preferably in Formula 11, 0.8≤x<1.0, 0.8≤a<1.0, 0 <b<1, 0<c<1, a+b+c=1일 수 있다. 구체적으로 본 발명의 양극 화합물질은 LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.06 Mn 0.06 O2, LiNi 0.90 Co 0.05 Mn 0.05 It may be O2 or a mixture thereof, and more preferably LiNi 0.88 Co 0.06 Mn 0.06 O2, LiNi 0.90 Co 0.05 Mn 0.05 It may be O2, or a mixture thereof, and more preferably LiNi 0.88 Co 0.06 Mn 0.06 It could be O2.

[0185] A negative electrode of a lithium secondary battery according to one embodiment of the present invention comprises a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material capable of absorbing and releasing lithium ions, and such negative electrode active material may include carbon materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers, lithium metal, and alloys of lithium and other elements. Non-limiting examples of the amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500°C or lower, and mesophase pitch-based carbon fiber (MPCF). Non-limiting examples of the crystalline carbon include graphite-based materials, specifically natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. The above carbon material is preferably a material having an interplanar distance of 3.35 to 3.38 Å and a crystallite size (Lc) of at least 20 nm as determined by X-ray diffraction. Other elements that form an alloy with lithium may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0186] The positive or negative electrode can be manufactured by preparing an electrode slurry composition by dispersing the active material, binder, and conductive material of each electrode, and, if necessary, a thickener, in a solvent, and then applying this slurry composition to an electrode current collector. Aluminum or an aluminum alloy can commonly be used as the positive current collector, and copper or a copper alloy can commonly be used as the negative current collector. Examples of the forms of the positive and negative current collectors include foil or mesh.

[0187] A binder is a substance that plays a role in paste-forming the active material, mutual adhesion of the active material, adhesion with the current collector, and a buffering effect against the expansion and contraction of the active material. Examples include polyvinylidene fluoride (PVdF), copolymer of polyhexafluoropropylene and polyvinylidene fluoride (PVdF / HFP), poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly(methyl methacrylate), poly(ethyl acrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, acrylonitrile-butadiene rubber, etc. The content of the binder is 0.1 to 30 weight%, preferably 1 to 10 weight%, relative to the electrode active material. If the content of the above binder is too low, the adhesion between the electrode active material and the current collector is insufficient; if the content of the binder is too high, the adhesion improves, but the content of the electrode active material decreases accordingly, which is disadvantageous for increasing the battery capacity to a high level.

[0188] A conductive material is used to impart conductivity to an electrode. In the battery being constructed, any electronically conductive material that does not cause chemical changes may be used, and at least one selected from the group consisting of graphite-based conductive materials, carbon black-based conductive materials, and metal or metal compound-based conductive materials may be used. Examples of the graphite-based conductive materials include artificial graphite and natural graphite; examples of carbon black-based conductive materials include acetylene black, Ketjen black, Denka black, thermal black, and channel black; and examples of metal or metal compound-based conductive materials include perovskite materials such as tin, tin oxide, tin phosphate (SnPO4), titanium oxide, potassium titanate, LaSrCoO3, and LaSrMnO3. However, it is not limited to the conductive materials listed above.

[0189] It is preferable that the content of the conductive agent be 0.1 to 10 weight percent with respect to the electrode active material. If the content of the conductive agent is less than 0.1 weight percent, the electrochemical properties deteriorate, and if it exceeds 10 weight percent, the energy density per weight decreases.

[0190] The thickener is not particularly limited as long as it can serve to control the viscosity of the active material slurry, but for example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, etc. may be used.

[0191] Non-aqueous solvents or aqueous solvents are used as solvents in which electrode active materials, binders, conductive materials, etc. are dispersed. Examples of non-aqueous solvents include N-methyl-2-pyrrodidon (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0192] A lithium secondary battery according to one embodiment of the present invention may include a separator that prevents a short circuit between a positive electrode and a negative electrode and provides a pathway for the movement of lithium ions. As such a separator, a polyolefin-based polymer membrane such as polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, or polypropylene / polyethylene / polypropylene, or a multilayer membrane thereof, a microporous film, a woven fabric, or a nonwoven fabric may be used. Additionally, a film in which a resin with excellent stability is coated on a porous polyolefin film may be used.

[0193] The lithium secondary battery of the present invention may be formed in shapes other than the prismatic type, such as cylindrical or pouch types. In addition to existing applications such as mobile phones and portable computers, the secondary battery is suitable for applications requiring high voltage, high output, and high temperature operation, such as electric vehicles. Furthermore, the secondary battery can be used in hybrid vehicles by combining it with existing internal combustion engines, fuel cells, supercapacitors, etc., and can be used in electric bicycles, power tools, and all other applications requiring high output, high voltage, and high temperature operation.

[0195] Examples and comparative examples of the present invention are described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples. A secondary battery electrolyte was prepared by dissolving a corresponding amount of a lithium salt, such as LiPF6, and an additive, a lithium salt of bissulfonyl imide, so that the lithium ion concentration in the electrolyte becomes 1 mol (1 M) and the lithium salt becomes 1 mol (1 M) in the electrolyte.

[0197] [Examples 1 to 2]

[0198] The electrolyte was prepared by dissolving LiPF6 and bissulfonyl imide lithium salts at concentrations listed in Table 1 below in a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 25:75, and then adding 1 wt% of fluoroethylene carbonate (FEC) and 0.5 wt% of 1,3-propanesulfone (PS).

[0200] The battery to which the above-mentioned non-aqueous electrolyte is applied was manufactured as follows.

[0201] LiNi as a positive electrode active material 0.88 Co 0.06 Mn 0.06An anode slurry was prepared by mixing O2, polyvinylidene fluoride (PVdF) as a binder, and carbon as a conductive agent in a weight ratio of 98:1:1, and then dispersing the mixture in N-methyl-2-pyrrolidone. An anode was manufactured by coating this slurry onto an aluminum foil with a thickness of 12 μm, followed by drying and rolling. An anode active material slurry was prepared by mixing artificial graphite and natural graphite as the anode active material, styrene-butadiene rubber as a binder, and carboxymethylcellulose as a thickener in a weight ratio of 96:2:2, followed by dispersing the mixture in water. An anode was manufactured by coating this slurry onto a copper foil with a thickness of 8 μm, followed by drying and rolling.

[0202] A cell was formed using a pouch with dimensions of 5 mm x 50 mm x 60 mm by stacking a polyethylene (PE) film separator with a thickness of 13 μm between the electrodes manufactured above, and a 2Ah lithium secondary battery for EV was manufactured by injecting the above-mentioned non-aqueous electrolyte.

[0203] The performance of the 2Ah EV battery manufactured in this way was evaluated as follows. The evaluation items are as follows.

[0204] *Evaluation Criteria*

[0205] 1. Rapid charging characteristics: After charging to State-of-Charge (SOC) 8% at room temperature with a current of 0.33C, step-by-step charging was performed from 2.75C to 0.75C for the SOC 8~80% range, and for the SOC 80~100% range, charging was performed again with a current of 0.33C, followed by discharging to 2.7V with a current of 0.33C, and this process was repeated 150 times.

[0206] 2. Room temperature life: At room temperature, the device is charged to 4.2V and 0.05C using a CC-CV charging mode with a current of 0.5C, and then discharged to 2.7V using a current of 0.5C, repeating this process more than 100 times. At this time, the first discharge capacity was set to 1C, and the capacity retention rate during the life was calculated by dividing the 300th discharge capacity by the first discharge capacity.

[0207] 3. Low temperature capacity: At -10℃, charge to 4.2V and 0.05C using CC-CV charging mode with a current of 0.5C, then discharge to 2.7V using a current of 0.5C, 10 times. The capacity after 10 discharges was calculated.

[0209] [Comparative Examples 1 to 4]

[0210] The above Examples 1 and 2 were carried out and evaluated in the same manner as Examples 1 and 2, except that the electrolyte additives listed in Table 1 below were different, and the results are shown in Table 1.

[0212] The performance of the battery manufactured in this way was evaluated using the above evaluation criteria, and the results are listed in Table 1 below.

[0213] lithium salt additives Fast charging capacity retention rate (150cy, %) Room temperature lifespan retention rate (1200 CY, %) Room temperature lifespan retention rate (1500 cy, %) 0.5C low temperature capacity (mAh) Example 1 0.5M LiPF6 0.4M LiFSI 0.1M PEA344 93.3 84.4 - - Example 2 0.8M LiPF6 0.1M LiFSI 0.1M PEA343 - - 77.2 1396 Comparative Example 1 1M LiPF6 - - 89.8 79.5 71.0 1297 Comparative Example 2 0.5M LiPF6 0.5M LiFSI - 91.2 81.4 - - Comparative Example 3 0.8M LiPF6 0.2M LiFSI - - - 70.2 1354 Comparative Example 4 0.8M LiPF6 - 0.2M PEA343 - - 73.0 1359

[0214] Base Electrolyte: EC:EMC (25:75)vol.% FEC 1wt.% PS 0.5wt.%

[0215] LiFSI: ,

[0216] PEA343:

[0217] PEA 344:

[0219] From Table 1 and Figures 1 to 3 above, it can be seen that the lithium secondary batteries of Examples 1 and 2, which employ an electrolyte containing a mixture of two or more bissulfonyl imide lithium salts of the present invention, have significantly improved rapid charging characteristics and lifespan characteristics compared to Comparative Example 1, which does not contain bissulfonyl imide lithium salts, and Comparative Examples 2 to 4, which contain bissulfonyl imide lithium salts alone.

Claims

Claim 1 A secondary battery electrolyte comprising a lithium salt, a non-aqueous organic solvent, and as additives (i) lithium bis(fluorosulfonyl)imide; and (ii) a bissulfonylimide lithium salt represented by the following chemical formula 3 or 4. [Chemical Formula 3] In the above chemical formula 3, A is -(CR 15 R 16 ) n -is;R 13 to R 16 ≠ ≠ fluoro independently of each other; n is an integer from 0 to 3.[Chemical Formula 4] In the above chemical formula 4, R 3 and R 4 They are independently perfluoroC1-C10 alkyls. Claim 2 delete Claim 3 A secondary battery electrolyte according to claim 1, wherein the bissulfonyl imide lithium salt is selected from the following compounds. Claim 4 In claim 1, the additive is present in a secondary battery electrolyte at a concentration of 0.1 to 0.5 M. Claim 5 delete Claim 6 A secondary battery electrolyte according to claim 1, wherein the bissulfonyl imide lithium salt is included in an amount of 0.1 to 1.5 moles per 1 mole of lithium bis(fluorosulfonyl)imide. Claim 7 In claim 1, the secondary battery electrolyte further comprises a fluorosubstituted cyclic carbonate compound. Claim 8 In claim 7, the fluorosubstituted cyclic carbonate compound is included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte in a secondary battery electrolyte. Claim 9 In claim 1, the lithium salt is a secondary battery electrolyte comprising one or more selected from the group consisting of LiPF6, LiBF4, LiClO4, LiSbF6, LiAsF6, LiN(SO3C2F5)2, LiCF3SO3, LiC4F9SO3, LiC6H5SO3, LiSCN, LiAlO2, LiAlCl4, LiCl, LiI, and LiB(C2O4)2. Claim 10 In claim 9, the lithium salt is present in a secondary battery electrolyte at a concentration of 0.3 to 1.0 molar. Claim 11 A lithium secondary battery comprising: a positive electrode comprising a nickel-cobalt-manganese-based positive active material comprising the following chemical formula 11, the following chemical formula 12, or a mixture thereof; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and a secondary battery electrolyte selected from any one of claims 1, 3, 4, and 6 to 10. [Chemical Formula 11]Li x (Ni a Co b Mn c 0.5 from O2 chemical formula 11 <x<1.3, 0.8≤a<1.2, 0<b<1, 0<c<1, a+b+c=1이다. [화학식 12]Li x (Ni a Co b Mn c )O4 0.5 in the above chemical formula 12 <x<1.3, 0.8≤a<2, 0<b<2, 0<c<2, a+b+c=2이다. Claim 12 In claim 11, the above-mentioned positive active material is Li x (Ni a Co b Mn c A lithium secondary battery with )O2, 0.95≤x≤1.10, 0.8≤a<0.9, and a+b+c=1.

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