Lithium secondary battery

Abstract

Lithium secondary battery, comprehensive: a cathode (100) comprising a cathode current collector (105) and a layer of cathode-active material (110) arranged on at least one surface of the cathode current collector (105), wherein the layer of cathode-active material (110) comprises a cathode-active material containing first particles of cathode-active material, each of which has a single particle shape; an anode (130) facing the cathode (100); and a non-aqueous electrolyte comprising a non-aqueous organic solvent containing a fluorine-based organic solvent, a lithium salt and an additive.

Description

BACKGROUND1. Area

[0001] The present invention relates to a lithium secondary battery. In particular, the present invention relates to a lithium secondary battery comprising a cathode, an anode, and an electrolyte, 2. Description of the state of the art

[0002] A secondary battery that can be repeatedly charged and discharged has been widely used as a power source for mobile electronic devices such as camcorders, mobile phones, laptop computers, etc., following developments in information and display technologies. Recently, a battery pack including the secondary battery is being developed and used as a power source for environmentally friendly vehicles such as hybrid vehicles.

[0003] A lithium secondary battery is highlighted and developed among various types of secondary batteries due to high operating voltage and energy density per unit weight, high charging rate, compact size, etc.

[0004] For example, the lithium secondary battery may include an electrode assembly with a cathode, an anode, and a separator, and an electrolyte immersed in the electrode assembly. The lithium secondary battery may further include an outer casing, e.g., in a pouch shape, that accommodates the electrode assembly and the electrolyte.

[0005] A lithium metal oxide can be used as an active material for the cathode of a lithium secondary battery. Examples of the lithium metal oxide include a nickel-based lithium metal oxide.

[0006] As the application of lithium secondary battery expands, higher capacity, cycle life and operational stability are required.

[0007] However, current and capacity may be reduced due to surface damage of the nickel-based lithium metal oxide used as the active cathode material, and side reactions may occur between the nickel-based lithium metal oxide and the electrolyte.

[0008] Korean Published Patent Application No. 10-2019-0119615 discloses a method for improving battery properties by modifying a non-aqueous electrolyte for a lithium secondary battery. SUMMARY

[0009] According to one aspect of the present invention, a lithium secondary battery having improved operational stability and improved electrical characteristics is provided.

[0010] A lithium secondary battery comprises a cathode having a cathode current collector and a cathode active material layer disposed on at least one surface of the cathode current collector, wherein the cathode active material layer comprises a cathode active material comprising first cathode active material particles each having a single particle shape, an anode facing the cathode, and a non-aqueous electrolyte comprising a non-aqueous organic solvent containing a fluorine-based organic solvent, a lithium salt, and an additive.

[0011] In some embodiments, the cathode active material may further comprise second cathode active material particles, each of which has a secondary particle shape, and a content of the first cathode active material particles, based on a total weight of the cathode active material, may be in a range of 10 wt% to 40 wt%.

[0012] In some embodiments, the first cathode active material particles or the second cathode active material particles may have a structure of a lithium transition metal composite oxide particle represented by Chemical Formula 1: Li a Ni x M 1-x O 2+y [Chemical Formula 1]

[0013] In the chemical formula 1, 0.9 ≤ a ≤ 1.2, 0.5 ≤ x ≤ 0.99, -0.1 ≤ y ≤ 0.1 and M includes at least one element selected from Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba and Zr.

[0014] In some embodiments, the non-aqueous organic solvent may further comprise a non-fluorine-based organic solvent, and a volume ratio of the fluorine-based organic solvent to the non-fluorine-based organic solvent may be in a range of 1.5 to 9.

[0015] In some embodiments, the non-fluorine-based organic solvent may include at least one selected from the group consisting of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent.

[0016] In some embodiments, the fluorine-based organic solvent may include at least one of a monofluoro-based organic solvent and a difluoro-based organic solvent.

[0017] In some embodiments, the monofluoro-based organic solvent can be represented by chemical formula 2:

[0018] In chemical formula 2, R 1 a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C6-C 12 -aryl group, a substituted or unsubstituted C5-C 12 -cycloalkyl group, a substituted or unsubstituted C5-C 12 -Cycloalkenyl group, a substituted or unsubstituted 5- to 7-membered heterocycloalkyl group or a substituted or unsubstituted 5- to 7-membered heterocycloalkenyl group.

[0019] In some embodiments, the difluoro-based organic solvent can be represented by chemical formula 3:

[0020] In chemical formula 3, R 2 a hydrocarbon containing a substituted or unsubstituted C1-C6 alkyl group or a substituted or unsubstituted C6-C 12 -aryl group, and R 3 is a hydrocarbon containing a substituted or unsubstituted C1-C6 alkyl group or a substituted or unsubstituted C2-C6 alkenyl group.

[0021] In some embodiments, the additive may contain a boron-based compound.

[0022] In some embodiments, the boron-based compound may include at least one of lithium bis(oxalate)borate (LiBOB), tris(trimethylsilyl)borate (TMSB), and lithium difluoro(oxalato)borate (LiFOB).

[0023] In some embodiments, a content of the additive may be in a range of 0.1 wt% to 1.0 wt% based on a total weight of the non-aqueous electrolyte.

[0024] In some embodiments, the non-aqueous electrolyte may further contain an auxiliary additive comprising an alkyl sultone-based compound and an alkenyl sultone-based compound.

[0025] In some embodiments, a content of the auxiliary additive is in a range of 0.5 wt% to 1.5 wt% based on a total weight of the non-aqueous electrolyte.

[0026] In some embodiments, the lithium salt may include at least one of lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), and lithium difluorophosphate (LiPO2F2).

[0027] A lithium secondary battery according to embodiments of the present invention comprises a cathode active material containing first cathode active material particles having a single particle shape, and a non-aqueous electrolyte containing a fluorine-based organic solvent.

[0028] The cathode active material can contain particles in the form of single particles, so that cracks in the cathode active material can be reduced and a BET surface area that reacts with the electrolyte can be reduced. Thus, the cycle life characteristics of the lithium secondary battery and the capacity retention rate during repeated charging and discharging can be improved.

[0029] In addition, the oxidation resistance of the secondary battery can be improved by the fluorine-based organic solvent in the non-aqueous electrolyte. Accordingly, the cycle life characteristics of the lithium secondary battery can be improved and the amount of gas generated at high temperatures can be reduced.

[0030] A side reaction between the cathode active material particles and the non-aqueous electrolyte can be further suppressed by combining the cathode active material containing the first cathode active material particles in the form of individual particles and the non-aqueous electrolyte solution containing the fluorine-based organic solvent. Thus, an additional synergistic effect of improving the cycle life and high-temperature storage properties can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 and Fig. 2 are a schematic plan view and a schematic cross-sectional view, respectively, illustrating a lithium secondary battery according to exemplary embodiments. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] Embodiments of the present invention provide a lithium secondary battery having a cathode, an anode, and a non-aqueous electrolyte.

[0032] The present invention will now be described in detail with reference to exemplary embodiments and the accompanying drawings. However, those skilled in the art will appreciate that such embodiments described with reference to the accompanying drawings are provided to further understand the spirit of the present invention and do not limit the subject matter to be protected as disclosed in the detailed description and the appended claims.

[0033] Fig. 1 and Fig. 2 are a schematic plan view and a schematic cross-sectional view, respectively, illustrating a lithium secondary battery (which may be abbreviated as secondary battery) according to exemplary embodiments. For example, Fig. 2 a cross-sectional view along a line II' of Fig. 1.

[0034] With reference to Fig. 1, the lithium secondary battery may include a cathode 100 and an anode 130 facing the cathode 100.

[0035] The cathode 100 includes a cathode current collector 105 and a layer of cathode active material 110 disposed on at least one surface of the cathode current collector. The layer of cathode active material 110 includes a cathode active material containing first particles of cathode active material having a single particle shape.

[0036] The term "single particle shape" as used herein is intended to exclude secondary particles formed essentially by the aggregation of, for example, a plurality of primary particles into one particle. For example, the first particles of cathode-active material may consist essentially of particles having the single particle shape and may not include the secondary particle in which primary particles (e.g., more than 10, 20 or more, 30 or more, 40 or more, 50 or more, etc.) are aggregated.

[0037] The term "single particle form" as used herein is not intended to exclude, for example, a monolithic form in which 2 to 10 primary particles are attached or adhered to one another to form a single body.

[0038] In some embodiments, the first particle of cathode active material may include a structure in which a plurality of primary particles are integrally combined into a substantially single particle.

[0039] For example, the first particle of cathode active material may have a granular or spherical single particle shape.

[0040] In exemplary embodiments, the first cathode active material particle and a second cathode active material particle described later may include a lithium transition metal composite oxide particle.

[0041] For example, the lithium transition metal composite oxide particle may have a single-crystalline or polycrystalline structure from a crystallographic aspect.

[0042] For example, the lithium transition metal composite oxide particles may contain nickel (Ni) and may further contain at least one of cobalt (Co) and manganese (Mn).

[0043] For example, the lithium transition metal composite oxide particle can be represented by the chemical formula 1 below: Li a Ni x M 1-x O 2+y [Chemical Formula 1]

[0044] In chemical formula 1, 0.9≤a≤1.2, 0.5≤x≤0.99, -0.1≤y≤0.1. M can represent at least one element selected from Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr.

[0045] In some exemplary embodiments, the first cathode-active material particle and / or the second cathode-active material particle may further include a dopant or a coating on a surface thereof. For example, the dopant or coating may include Al, Ti, Ba, Zr, Si, B, Mg, P, W, Na, V, Cu, Zn, Ge, Ag, Ba, Nb, Ga, Cr, Sr, Y, Mo, an alloy thereof, or an oxide thereof. These may be used alone or in combination. The first cathode-active material particles and / or the second cathode-active material particles may be passivated by the dopant or coating, so that the penetration stability and lifetime can be further improved.

[0046] In some preferred embodiments, a molar ratio or concentration (x) of Ni in the chemical formula 1 may be greater than or equal to 0.8, more preferably greater than 0.8, and in one embodiment greater than or equal to 0.98.

[0047] Ni can serve as a transition metal in terms of current and capacity of a lithium secondary battery. Therefore, as described above, the high-Ni composition can be incorporated into the lithium transition metal composite oxide particle, thus providing a high-performance cathode and a lithium secondary battery.

[0048] However, with increasing Ni content, the long-term storage and lifetime stability of the cathode or secondary battery may be relatively deteriorated. However, according to exemplary embodiments, lifetime stability and capacity retention can be improved by Mn, while electrical conductivity is maintained by including Co.

[0049] For example, the lithium transition metal composite oxide particles may be in the form of a secondary particle formed by the primary particles arranged therein. However, in this case, microcracks may form on an inner surface of the secondary particle during charging and discharging of the battery, and a side reaction between the electrolyte and the cathode active material may be accelerated, and a gas may be generated within the battery. Accordingly, the cycle life characteristics of the secondary battery may deteriorate if charging and discharging are performed repeatedly.

[0050] According to exemplary embodiments of the present invention, the cathode active material may contain lithium transition metal composite oxide particles with a single particle shape (e.g., first cathode active material particles). Thus, cracks in the particles can be reduced and the BET surface area that reacts with the electrolyte can be reduced. Accordingly, the cycle life characteristics of the secondary battery and the capacity retention during repeated charging and discharging can be improved.

[0051] In some embodiments, the cathode active material may further include second cathode active material particles having the secondary particle shape, and a content of the first cathode active material particles, based on the total weight of the cathode active material, may be in a range of 10 wt% (wt%) to 40 wt%. Within the above range, the mechanical and chemical stability of the secondary battery can be improved, and excessive reduction of the particle surface area can be prevented. Therefore, the cycle life characteristics can be improved while maintaining the capacity characteristics of the battery.

[0052] The cathode active material described above can be mixed and stirred with a binder, a conductive material, and / or a dispersant in a solvent to form a slurry. The slurry can be applied to the cathode current collector 105 and dried and pressed to form the cathode 100.

[0053] The cathode current collector 105 may, for example, comprise stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and may preferably comprise aluminum or an aluminum alloy.

[0054] For example, the binder may include an organic-based binder such as polyvinylidene fluoride (PVDF), a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile, polymethyl methacrylate, etc., or an aqueous-based binder such as styrene-butadiene rubber (SBR), which may be used with a thickener such as carboxymethylcellulose (CMC).

[0055] For example, a PVDF-based binder can be used as a cathode binder. In this case, the amount of binder used to form the cathode active material layer can be reduced, and the amount of the cathode active material can be relatively increased. Thus, the capacity and current of the lithium secondary battery can be further improved.

[0056] The conductive material can be added to facilitate electron mobility between active material particles. For example, the conductive material can include a carbon-based material such as graphite, carbon black, graphene, carbon nanotubes, etc., and / or a metal-based material such as tin, tin oxide, titanium oxide, a perovskite material such as LaSrCoO3 or LaSrMnO3, etc.

[0057] The anode 130 may include an anode current collector 125 and a layer of anode active material 120 formed by applying an anode active material to the anode current collector 125.

[0058] The anode active material may comprise a material widely known in the art that may be capable of adsorbing and ejecting lithium ions. For example, the anode active material may include a carbon-based material such as crystalline carbon, amorphous carbon, a carbon complex, a carbon fiber, etc., a lithium alloy, a silicon-based material, tin, etc.

[0059] The amorphous carbon may include, for example, a hard carbon, coke, a mesocarbon microsphere (MCMB), a mesophase pitch-based carbon fiber (MPCF), etc.

[0060] The crystalline carbon may include, for example, artificial graphite, natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0061] For example, the lithium alloy may contain a metal element such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0062] The silicon-based compound may include, for example, silicon oxide, a silicon-carbon composite compound such as silicon carbide (SiC).

[0063] For example, the anode active material can be mixed and stirred with the above-described binder and conductive material, a thickener, etc., in a solvent to form a slurry. The slurry can be applied to at least one surface of the anode current collector 125, dried, and pressed to obtain the anode 130.

[0064] A separation layer 140 may be disposed between the cathode 100 and the anode 130. The separation layer 140 may include a porous polymer film made, for example, from a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or the like. The separation layer 140 may also include a nonwoven fabric formed from a high-melting-point glass fiber, a polyethylene terephthalate fiber, or the like.

[0065] In some embodiments, an area and / or volume of the anode 130 (e.g., a contact area with the separation layer 140) may be larger than that of the cathode 100. Thus, lithium ions generated by the cathode 100 can be easily transferred to the anode 130 without loss through, for example, precipitation or sedimentation.

[0066] In exemplary embodiments, an electrode cell may be defined by the cathode 100, the anode 130, and the separator layer 140, and a plurality of the electrode cells may be stacked to form an electrode assembly 150, which may, for example, have a jelly-roll shape. For example, the electrode assembly 150 may be formed by winding, laminating, or folding the separator layer 140.

[0067] The electrode assembly 150 may be housed in a casing 160 together with a non-aqueous electrolyte to define the lithium secondary battery.

[0068] The non-aqueous electrolyte comprises a non-aqueous organic solvent containing a fluorine-based organic solvent, a lithium salt, and an additive.

[0069] For example, the fluorine content in the non-aqueous electrolyte can be increased by using the fluorine-based organic solvent. Accordingly, the oxidation resistance of the secondary battery can be improved. Thus, the cycle life characteristics of the secondary battery can be improved, and the amount of gas generated at high temperatures can be reduced.

[0070] In addition, a side reaction between the cathode active material particles and the non-aqueous electrolyte can be further suppressed by using the above-described cathode active material containing the first cathode active material particles in the form of individual particles together with the non-aqueous electrolyte solution containing the fluorine-based organic solvent. Thus, an additional synergistic effect of improving the cycle life and high-temperature storage properties can be realized.

[0071] In some embodiments, the non-aqueous organic solvent may include a monofluoro-based organic solvent or a difluoro-based organic solvent.

[0072] The term “monofluorine-based organic solvent” as used herein may refer to a compound containing one fluorine (F) atom in a molecule, and “difluorine-based organic solvent” may refer to a compound containing two fluorine (F) atoms in a molecule.

[0073] In some embodiments, the monofluoro-based organic solvent can be represented by the following chemical formula 2:

[0074] In chemical formula 2, R 1 a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C6-C 12 -aryl group, a substituted or unsubstituted C5-C 12-cycloalkyl group, a substituted or unsubstituted C5-C 12 -Cycloalkenyl group, a substituted or unsubstituted 5- to 7-membered heterocycloalkyl group or a substituted or unsubstituted 5- to 7-membered heterocycloalkenyl group.

[0075] The term “C n “ (n is a natural number) as used herein refers to the number of carbon atoms.

[0076] For example, the monofluoro-based organic solvent described above may be included in the non-aqueous organic solvent to sufficiently improve the oxidation resistance of the battery while preventing a reduction in capacity retention due to excessive addition of the difluoro-based organic solvent as described later.

[0077] In one embodiment, the monofluoro-based organic solvent may contain fluoroethylene carbonate (FEC).

[0078] In exemplary embodiments, the difluoro-based organic solvent can be represented by the following chemical formula 3:

[0079] In the chemical formula 3, R 2 a hydrocarbon containing a substituted or unsubstituted C1-C6 alkyl group or a substituted or unsubstituted C6-C 12 -aryl group, and R 3 may be a hydrocarbon containing a substituted or unsubstituted C1-C6 alkyl group or a substituted or unsubstituted C2-C6 alkenyl group.

[0080] For example, a substituent present in R 1 to R 3at least one selected from the group consisting of a halogen, a C1-C6 alkyl group, a C3-C6 cycloalkyl group, a C1-C6 alkoxy group, a 3- to 7-membered heterocycloalkyl group, a C6-C 12 -aryl group, a 5- to 7-membered heteroaryl group, a hydroxyl group (-OH), -NR 4 R 5 (R 4 and R 5 are each independently hydrogen or a C1-C6 alkyl group), a nitro group (-NO2) and a cyano group (-CN).

[0081] For example, the fluorine content in the electrolyte can be increased by using the above-described difluoro-based organic solvent together with the monofluoro-based organic solvent. In this case, the oxidation resistance of the secondary battery can be improved. Accordingly, the cycle life characteristics of the secondary battery can be improved, and the amount of gas generated at high temperatures can be reduced.

[0082] For example, if only the monofluoro-based organic solvent is used, a sufficient fluorine content in the electrolyte cannot be achieved, and the oxidation resistance of the battery cannot be sufficiently improved.

[0083] In one embodiment, the difluoro-based organic solvent may contain difluoroethyl acetate (DFA).

[0084] In some embodiments, the non-aqueous organic solvent may further contain a non-fluorine-based organic solvent, and a volume ratio of the fluorine-based organic solvent relative to the non-fluorine-based organic solvent may be in a range of 1.5 to 9. Within this range, a reduction in the capacity retention of the battery due to excessive fluorine input can be prevented while sufficiently maintaining the fluorine content in the electrolyte.

[0085] In some embodiments, the non-fluorine-based organic solvent may include at least one selected from the group consisting of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent. These may be used alone or in combination.

[0086] For example, the carbonate-based solvent may contain at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, diethyl carbonate (DEC), dipropyl carbonate, propylene carbonate (PC), ethylene carbonate (EC), and butylene carbonate.

[0087] For example, the ester-based solvent may contain at least one of methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), γ-butyrolactone (GBL), decanolide, valerolactone, mevalonolactone, and caprolactone.

[0088] For example, the ether-based solvent may contain at least one of dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), and 2-methyltetrahydrofuran.

[0089] For example, the ketone-based solvent may contain cyclohexanone, etc.

[0090] For example, the alcohol-based solvent may contain at least one of ethyl alcohol and isopropyl alcohol.

[0091] For example, the aprotic solvent may include at least one selected from the group consisting of a nitrile-based solvent, an amide-based solvent (e.g., dimethylformamide), a dioxolane-based solvent (e.g., 1,3-dioxolane), and a sulfolane-based solvent.

[0092] In exemplary embodiments, a lithium salt may be provided as an electrolyte. For example, the lithium salt may be Li + X - be expressed.

[0093] For example, the anion X - F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4-, ClO4 - , PF6 - , SbF6 - , AsF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N -, CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - and PO2F2 - These can be used alone or in combination.

[0094] In some embodiments, the lithium salt may contain at least one of lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), and lithium difluorophosphate (LiPO2F2). In this case, a film with improved thermal stability can be formed on a surface of the electrode. Accordingly, improved ionic conductivity and electrode protection properties of the non-aqueous electrolyte can be implemented.

[0095] In one embodiment, the lithium salt may be present at a concentration of about 0.01 M to 5 M, preferably about 0.01 M to 2 M, relative to the non-aqueous organic solvent. Within the above range, the transfer of lithium ions and / or electrons during charging and discharging of the lithium secondary battery can be promoted, so that improved capacity can be achieved.

[0096] In exemplary embodiments, the additive may contain a boron-based compound.

[0097] For example, the boron-based compound may contain at least one of lithium bis(oxalate)borate (LiBOB), tris(trimethylsilyl)borate (TMSB), and lithium difluoro(oxalato)borate (LiFOB).

[0098] When the boron-based compound described above is included as an additive, a side reaction between the fluorine-based organic solvent and the anode can be suppressed. Accordingly, deterioration of the anode's storage and lifetime properties can be prevented while using the monofluoro-based organic solvent and the difluoro-based organic solvent as described above.

[0099] In some embodiments, the additive content, based on the total weight of the non-aqueous electrolyte, may be in a range of 0.1 wt% to 1.0 wt%. Within this range, an excessive increase in battery durability can be prevented while improving high-temperature storage and cycle life characteristics through the use of the additive. Thus, deterioration of capacity and current characteristics can be prevented while improving the high-temperature storage properties of the secondary battery.

[0100] In exemplary embodiments, the above-described non-aqueous electrolytic solution may further contain an auxiliary additive containing an alkyl sultone-based compound and an alkenyl sultone-based compound.

[0101] For example, the alkyl sultone-based compound may contain at least one of 1,3-propane sultone (PS) and 1,4-butane sultone.

[0102] For example, the alkenyl sultone-based compound may contain at least one of ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0103] The auxiliary additive described above may further contain an anhydride-based compound such as succinic anhydride and maleic anhydride, a nitrile-based compound such as glutaronitrile, succinonitrile, and adiponitrile, etc. These may be used alone or in combination thereof in addition to the above-mentioned sultone-based compound.

[0104] In one embodiment, the auxiliary additive may further contain at least one of polyethylene sulfide (PES), vinylene carbonate (VC), and vinylethylene carbonate (VEC).

[0105] In some embodiments, the content of the auxiliary additive, based on the total weight of the non-aqueous electrolyte, may be in a range of 0.5 wt% to 1.5 wt%. Within this range, the above-described side reaction of the additive can be further suppressed while suppressing an excessive increase in battery durability. Accordingly, the reduction in capacity can be suppressed while maintaining or improving the cycle life characteristics of the secondary battery by using the above-described fluorine-based organic solvent.

[0106] As in Fig.As illustrated in Figure 1, electrode tabs (a cathode tab and an anode tab) may protrude from the cathode current collector 105 and the anode current collector 125 included in each electrode cell to one side of the housing 160. The electrode tabs may be welded to one side of the housing 160 to connect to an electrode lead (a cathode lead 107 and an anode lead 127), which may be extended or exposed to an exterior of the housing 160.

[0107] The lithium secondary battery can be manufactured into a cylindrical shape using a can, a prismatic shape, a bag shape, a coin shape, etc.

[0108] Preferred embodiments are proposed below to describe the present invention more concretely. However, the following examples are given only to illustrate the present invention, and those skilled in the art will obviously understand that various changes and modifications are possible within the scope and spirit of the present invention. Such changes and modifications are properly encompassed in the appended claims. Example 1(1) Preparation of cathode active material

[0109] NiSO4, CoSO4, and MnSO4 were each mixed in a molar ratio of 0.8:0.1:0.1 using distilled water, from which internal dissolved oxygen was removed by bubbling with N2 for 24 hours. The mixed solution was added to a reactor at 50 °C, and NaOH and NH3H2O ​​were added as a precipitant and a chelating agent, respectively. Afterward, a coprecipitation reaction was carried out for 72 hours to obtain Ni. 0,8 Co 0,1 Mn 0,1 (OH)2 as a transition metal precursor. The obtained precursor was dried at 100 °C for 12 hours and then dried again at 120 °C for 10 hours.

[0110] Lithium hydroxide and the transition metal precursor were added to a dry high-speed mixer in a ratio of 1.03:1 and mixed evenly for 20 minutes. The mixture was placed in a furnace and heated to 950 °C at a heating rate of 2 °C / min. The mixture was left for 12 hours while maintaining a temperature of 950 °C.

[0111] Oxygen was continuously passed through at a flow rate of 10 ml / min during the temperature increase and maintenance. After firing, natural cooling to room temperature was carried out, followed by pulverization and classification to obtain the first particles of cathode active material in the form of single particles with a composition of LiNi. 0,8 Co 0,1 Mn 0,1 to produce O2.

[0112] A cathode active material was prepared by combining the lithium transition metal composite oxide particles in the form of the individual particles as described above with second particles of cathode active material in the form of secondary particles (composition: LiNi 0,8 Co 0,1 Mn 0,1 O2) were mixed.

[0113] A content of the first particles of cathode active material, based on the total weight of the cathode active material, was set to 30 wt.%. (2) Production of non-aqueous electrolyte

[0114] A 1M LiPF6 solution was prepared using a mixed solvent of PC / FEC / DFEA (21:4:75; weight ratio). PC was used as the non-fluorine-based organic solvent, FEC was used as the monofluorine-based organic solvent, and DFEA was used as the difluorine-based organic solvent.

[0115] Thereafter, lithium bisoxalatoborate (LiBOB) was added as an additive and mixed with the solution in an amount of 0.85 wt% based on a total weight of a non-aqueous electrolyte.

[0116] In addition, 1.0 wt% of 1,3-propanesultone (PS) and 0.5 wt% of 1,3-propenesultone (PRS) (total 1.5 wt%) were added as auxiliary additives based on the total weight of the non-aqueous electrolyte and mixed to prepare the non-aqueous electrolyte. (3) Manufacture of lithium secondary battery

[0117] The cathode active material prepared above, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 92:5:3 to form a slurry. The slurry was evenly coated on a 15 μm thick aluminum foil and vacuum dried at 130 °C to prepare a cathode for a lithium secondary battery.

[0118] An anode slurry containing 95 wt% natural graphite as an anode active material, 1 wt% Super-P as a conductive material, 2 wt% styrene-butadiene rubber (SBR) as a binder, and 2 wt% carboxymethyl cellulose (CMC) as a thickener was prepared. The anode slurry was evenly coated onto a 15 µm thick copper foil, dried, and pressed to form an anode.

[0119] The cathode and anode prepared as described above were each notched by a predetermined amount and stacked with a separator (polyethylene, thickness: 20 μm) interposed therebetween to form an electrode cell. Each tab portion of the cathode and anode was welded. The welded cathode / separator / anode assembly was inserted into a bag, and three sides of the bag, except for an electrolyte injection side, were sealed. The tab portions were also contained in sealed portions. The nonaqueous electrolyte prepared as in (2) above was injected through the electrolyte injection side, and then the electrolyte injection side was also sealed. Impregnation was carried out for more than 12 hours to obtain a lithium secondary battery. Example 2

[0120] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were prepared by the same method as in Example 1, except that the content of the first cathode active material particles was 15 wt% based on the total weight of the cathode active material in the preparation of the cathode active material. Example 3

[0121] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were prepared by the same method as in Example 1, except that the content of the first cathode active material particles was 8 wt% based on the total weight of the cathode active material in the preparation of the cathode active material. Example 4

[0122] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were prepared by the same method as in Example 1, except that the content of the first cathode active material particles was 43 wt% based on the total weight of the cathode active material. Example 5

[0123] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were prepared by the same method as in Example 1, except that a mixed solvent of PC / FEC / DFA (8:10:82; volume ratio) was used as a non-aqueous organic solvent in the preparation of the non-aqueous electrolyte. Example 6

[0124] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were prepared by the same method as in Example 1, except that a mixed solvent of PC / FEC / DFA (50:5:45; volume ratio) was used as a non-aqueous organic solvent in the preparation of the non-aqueous electrolyte. Example 7

[0125] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were prepared by the same method as in Example 1, except that LiBOB was added as an additive in an amount of 0.08 wt% based on the total weight of the non-aqueous electrolyte in the preparation of the non-aqueous electrolyte. Example 8

[0126] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were prepared by the same method as in Example 1, except that LiBOB was added as an additive in an amount of 1.1 wt% based on the total weight of the non-aqueous electrolyte in the preparation of the non-aqueous electrolyte. Example 9

[0127] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were prepared by the same method as in Example 1, except that 0.3 wt% of PS and 0.1 wt% of PRS (total 0.4 wt%) were added as the auxiliary additive based on the total weight of the non-aqueous electrolyte in the preparation of the non-aqueous electrolyte. Example 10

[0128] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were prepared by the same method as in Example 1, except that 1.3 wt% of PS and 0.3 wt% of PRS (total 1.6 wt%) were added as the auxiliary additive based on the total weight of the non-aqueous electrolyte in the preparation of the non-aqueous electrolyte. Comparison example 1

[0129] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were prepared by the same method as in Example 1, except that only the second cathode active material particles were used as the cathode active material and a mixed solvent of EC / EMC (25:75; volume ratio) was used as the non-aqueous organic solvent. Comparison example 2

[0130] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were prepared by the same method as in Example 1, except that a mixed solvent of EC / EMC (25:75; volume ratio) was used as a non-aqueous organic solvent in the preparation of the non-aqueous electrolyte. Comparison example 3

[0131] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were prepared by the same method as in Example 1, except that only the second cathode active material particles were used as the cathode active material.

[0132] The contents of the first cathode active material particles among the cathode active material, the volume ratios of the fluorine-based organic solvent to the non-fluorine-based organic solvent, the contents of additives, and the contents of auxiliary additives of the above-described Examples and Comparative Examples are shown in Table 1 below.

[00162] [Table 1] Nr. Content of the first particles of cathode active material (wt%) Volume ratio of the fluorine-based organic solvent to the non-fluorine-based organic solvent Additive content (wt%) Content of auxiliary additive (wt%) Example 1 30 3,76 0,85 1,5 Example 2 15 3,76 0,85 1,5 Example 3 8 3,76 0,85 1,5 Example 4 43 3,76 0,85 1,5 Example 5 30 11,5 0,85 1,5 Example 6 30 1,0 0,85 1,5 Example 7 30 3,76 0,08 1,5 Example 8 30 3,76 1,1 1,5 Example 9 30 3,76 0,85 0,4 Example 10 30 3,76 0,85 1,6 Comparison - - 0,85 1,5 Example 1 Comparison Example 2 30 - 0,85 1,5 Comparison Example 3 - 3,76 0,85 1,5 Experimental Example(1) Evaluation of electrochemical stability - LSV analysis (Linear Sweep Voltammetry)

[0133] A leakage current was measured at a constant rate in each lithium secondary battery according to Examples and Comparative Examples, and a voltage at a point where the electrolyte solution decomposed to generate a current was measured. Specifically, the measurement was performed at a sampling rate of 0.05 mV / s to 1.0 mV / s in a voltage range of 3 V to 7 V using Solartron's LSV measuring device. When measuring the LSV, a platinum electrode was used as the working electrode, and lithium metal was used as the reference and counter electrodes.

[0134] For example, the secondary battery can be considered electrochemically stable because the electrolyte decomposes at a high voltage. (2) Evaluation of initial performance1) Measurement of initial capacity

[0135] Charging (CC / CV 1 / 3C 4.2V 0.05C CUT-OFF) and discharging (CC 1 / 3C 2.5V CUT-OFF) were performed on each lithium secondary battery according to the examples and comparative examples described above, and an initial discharge capacity was measured. 2) Measurement of the discharge DCIR

[0136] The C-rates were sequentially increased or decreased as 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C at the point where the SOC (state of charge) of each lithium secondary battery of Examples and Comparative Examples was set to 60%. When charging and discharging at the corresponding C-rates were performed for 10 seconds, the end point voltage was estimated by a straight line equation, and the slope was taken as the DCIR (direct current internal resistance). (3) Evaluation of high-temperature lifetime properties (45 °C)

[0137] Charging (CC / CV 1C 4.3V 0.1C CUT-OFF) and discharging (CC 1C 2.5V CUT-OFF) were repeated 700 times for each lithium secondary battery according to Examples and Comparative Examples in a chamber at 45 °C. Measurement of capacity retention (45 °C)

[0138] A capacity retention of each lithium secondary battery was calculated as a percentage by dividing a discharge capacity at the 700th cycle by the initial capacity measured in Experimental Example (2)1). Capacity retention rate (%) = (700 Discharge capacity / Initial capacity) × 100 (4) Evaluation of high-temperature storage properties (60 °C)

[0139] Each lithium secondary battery according to Examples and Comparative Examples was left in a chamber at 60 °C for 8 weeks, and then the following evaluations were conducted. 1) Measurement of capacity retention (60 °C)

[0140] The lithium secondary battery was discharged (CC 1 / 3C 2.5V cut-off) to measure the discharge capacity. The discharge capacity was calculated as a percentage by dividing the discharge capacity by the initial capacity measured in Experimental Example (2)1).

[0141] The measurement of discharge capacity was carried out in the same procedure as in Experimental Example (2)1). 2) Measurement of gas production

[0142] The lithium secondary battery was left in the chamber at 60°C for 8 weeks, left under the same conditions for another 4 weeks, and then left at room temperature for 30 minutes. The gas generation was measured. After vacuuming the chamber, nitrogen gas was filled to form a normal pressure. The nitrogen volume (V0) and the internal chamber pressure (P0) were measured. After vacuuming the chamber again, a hole was formed in the battery, and the internal chamber pressure (P1) was measured. The amount of gas generation was calculated according to the following equation. Gas production quantity (ml)=(V0 / P0)*P1

[0143] The evaluation results according to the experimental examples described above are shown in Tables 2 and 3 below.

[00186] [Table 2] Nr. LSV (V) initial performance initial capacity (Ah) DCIR (mΩ) Example 1 5,96 19,1 4,40 Example 2 5,91 20,3 4,48 Example 3 5,81 21,5 4,53 Example 4 5,98 18,2 4,35 Example 5 6,03 18,7 4,40 Example 6 5,65 18,6 4,41 Example 7 5,95 19,0 4,41 Example 8 5,93 17,9 4,52 Example 9 5,91 19,2 4,42 Example 10 5,91 18,0 4,50 Comparison Example 1 5,26 19,1 4,68 Comparison Example 2 5,45 19,0 4,42 Comparison Example 3 5,53 18,8 4,70 [Table 3] Nr. High-temperature service life (45 °C, 700 cycles) High-temperature storage (60 °C) Capacity retention (%) Capacity Retention (%) Gas production (ml) Example 1 87 95 7,20 Example 2 86 94 7,41 Example 3 82 90 9,55 Example 4 90 97 5,32 Example 5 83 89 7,03 Example 6 82 90 8,11 Example 7 82 91 7,37 Example 8 86 94 7,18 Example 9 82 89 7,56 Example 10 87 95 6,98 Comparison Example 1 74 81 18,18 Comparison Example 2 77 85 13,10 Comparison Example 3 78 85 14,05

[0144] Referring to Tables 2 and 3, in Examples in which the cathode active material containing the first particles of cathode active material in the form of single particles and the fluorine-based organic solvent were used together, improved initial capacity, high-temperature life characteristics, and high-temperature storage characteristics were provided compared with those of Comparative Examples.

[0145] In Example 3, where the content of the first cathode active material particles was less than 10 wt%, the capacity retention at a high temperature was relatively reduced.

[0146] In Example 4, in which the content of the first cathode active material particles in the cathode active material exceeded 40 wt%, the initial capacity was relatively decreased.

[0147] In Example 5, where the volume of the fluorine-based organic solvent exceeded 9 times the volume of the non-fluorine-based organic solvent, the capacity retention was relatively decreased.

[0148] In Example 6, where the volume of the fluorine-based organic solvent was less than 1.5 times that of the non-fluorine-based organic solvent, the lifetime and storage characteristics at a high temperature were relatively deteriorated.

[0149] In Example 7, in which the additive content was less than 0.1 wt% based on the total weight of the non-aqueous electrolyte, a side reaction of the electrode and the fluorine-based organic solvent was not sufficiently suppressed, and the cycle life and storage characteristics at a high temperature were relatively deteriorated.

[0150] In Example 8, in which the content of the additive exceeded 1.0 wt% based on the total weight of the non-aqueous electrolyte solution, the initial capacity was relatively decreased as the battery durability was increased.

[0151] In Example 9, where the content of the auxiliary additive was less than 0.5 wt% based on the total weight of the non-aqueous electrolyte, the cycle life and storage properties were relatively deteriorated.

[0152] In Example 10, in which the content of the auxiliary additive exceeded 1.5 wt% based on the total weight of the non-aqueous electrolyte, the initial capacity was relatively decreased as the battery durability was increased.

[0153] In Comparative Example 1, in which the single particle was not included in the cathode active material and the fluorine-based organic solvent was not used, the storage and lifetime characteristics at a high temperature were remarkably deteriorated.

[0154] In Comparative Example 2, the single particle was included in the cathode active material, but the fluorine-based organic solvent was not used. In Comparative Example 3, the single particle was not included in the cathode active material, but the fluorine-based organic solvent was used.

[0155] In comparative examples 2 and 3, the storage and lifetime properties were explicitly worsened compared to those in examples. SUMMARY

[0156] A lithium secondary battery comprises a cathode having a cathode current collector and a cathode active material layer disposed on at least one surface of the cathode current collector, the cathode active material layer comprising a cathode active material comprising first cathode active material particles, each of which has a single particle shape; an anode facing the cathode; and a non-aqueous electrolyte comprising a non-aqueous organic solvent containing a fluorine-based organic solvent, a lithium salt, and an additive. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] KR 10-2019-0119615

[0008]

Claims

[1] Lithium secondary battery, comprising: a cathode (100) comprising a cathode current collector (105) and a layer of cathode active material (110) disposed on at least one surface of the cathode current collector (105), wherein the layer of cathode active material (110) comprises a cathode active material including first particles of cathode active material, each of which has a single particle shape; an anode (130) facing the cathode (100); and a non-aqueous electrolyte comprising a non-aqueous organic solvent containing a fluorine-based organic solvent, a lithium salt, and an additive. [2] The lithium secondary battery according to claim 1, wherein the cathode active material further comprises second cathode active material particles each having a secondary particle shape, and a content of the first cathode active material particles based on a total weight of the cathode active material is in a range of 10 wt% to 40 wt%. [3] The lithium secondary battery according to any one of claims 1 and 2, wherein the non-aqueous organic solvent further comprises a non-fluorine-based organic solvent, and a volume ratio of the fluorine-based organic solvent to the non-fluorine-based organic solvent is in a range of 1.5 to 9. [4] The lithium secondary battery according to any one of claims 1 to 3, wherein the fluorine-based organic solvent contains at least one of a monofluoro-based organic solvent and a difluoro-based organic solvent. [5] The lithium secondary battery according to claim 4, wherein the fluorine-based organic solvent includes the monofluoro-based organic solvent and the difluoro-based organic solvent. [6] A lithium secondary battery according to any one of claims 4 and 5, wherein the monofluoro-based organic solvent is represented by the chemical formula 2: wherein in the chemical formula 2R 1 a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C6-C 12 -aryl group, a substituted or unsubstituted C5-C 12 -cycloalkyl group, a substituted or unsubstituted C5-C 12 -cycloalkenyl group, a substituted or unsubstituted 5- to 7-membered heterocycloalkyl group or a substituted or unsubstituted 5- to 7-membered heterocycloalkenyl group. [7] A lithium secondary battery according to any one of claims 4 to 6, wherein the difluoro-based organic solvent is represented by the chemical formula 3: wherein in the chemical formula 3, R 2 a hydrocarbon containing a substituted or unsubstituted C1-C6 alkyl group or a substituted or unsubstituted C6-C 12 -aryl group, and R 3 a hydrocarbon containing a substituted or unsubstituted C1-C6 alkyl group or a substituted or unsubstituted C2-C6 alkenyl group. [8] The lithium secondary battery according to any one of claims 4 to 7, wherein the fluorine-based organic solvent contains fluoroethylene carbonate (FEC) and difluoroethyl acetate (DFA). [9] A lithium secondary battery according to any one of claims 1 to 8, wherein the first cathode active material particles or the second cathode active material particles comprise Ni, Co and Mn, and a Ni molar ratio of Ni, Co and Mn is 0.8 or more. [10] A lithium secondary battery according to any one of claims 1 to 8, wherein the first cathode active material particles or the second cathode active material particles have a structure of a lithium transition metal composite oxide particle represented by Chemical Formula 1: Li a Ni x M 1-x O 2+y [Chemical Formula 1] wherein in chemical formula 1 0.9 ≤ a ≤ 1.2, 0.5 ≤ x ≤ 0.99, -0.1 ≤ y ≤ 0.1 and M contains at least one element selected from Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba and Zr. [11] A lithium secondary battery according to any one of claims 1 to 10, wherein the additive contains a boron-based compound. [12] The lithium secondary battery according to claim 11, wherein the boron-based compound contains at least one of lithium bis(oxalate)borate (LiBOB), tris(trimethylsilyl)borate (TMSB) and lithium difluoro(oxalato)borate (LiFOB). [13] The lithium secondary battery according to any one of claims 1 to 12, wherein a content of the additive is in a range of 0.1 wt% to 1.0 wt% based on a total weight of the non-aqueous electrolyte. [14] The lithium secondary battery according to any one of claims 1 to 13, wherein the non-aqueous electrolyte further comprises an auxiliary additive containing an alkyl sultone-based compound and an alkenyl sultone-based compound. [15] The lithium secondary battery according to claim 14, wherein the alkyl sultone-based compound contains at least one of 1,3-propane sultone (PS) and 1,4-butane sultone. [16] The lithium secondary battery according to claim 14, wherein the alkenyl sultone-based compound may contain at least one of ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone. [17] A lithium secondary battery according to any one of claims 14 to 16, wherein the auxiliary additive further contains an anhydride-based compound. [18] The lithium secondary battery according to any one of claims 14 to 16, wherein a content of the auxiliary additive is in a range of 0.5 wt% to 1.5 wt% based on a total weight of the non-aqueous electrolyte.

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