Lithium secondary battery

Abstract

A lithium secondary battery according to the embodiments of the present disclosure comprises: a positive electrode comprising positive active material containing lithium metal oxide particles; a negative electrode facing the positive electrode; and a non-aqueous electrolyte solution comprising a non-aqueous organic solvent, lithium salt, and an additive containing a difluorophosphite-based compound, the molar ratio of lithium in the lithium metal oxide particles to the overall metal excluding the lithium in the lithium metal oxide particles is 1.05 or greater.

Description

lithium secondary battery

[0001] The disclosure of the present application relates to a lithium secondary battery.

[0002] Secondary batteries, which can be repeatedly charged and discharged, are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptops, thanks to the advancements in the information and communication and display industries. Furthermore, battery packs containing secondary batteries are being developed and applied as power sources for eco-friendly vehicles such as hybrid vehicles.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among these, lithium secondary batteries are actively being researched and developed due to their high operating voltage and energy density per unit weight, as well as their advantages in charging speed and weight reduction.

[0004] A lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator, and an electrolyte impregnating the electrode assembly. The lithium secondary battery may further include an outer packaging material, for example, in the form of a pouch, that accommodates the electrode assembly and the electrolyte.

[0005] The cathode active material of a lithium secondary battery may include a lithium-rich cathode active material in which lithium is present in a transition metal layer of a layered structure. The lithium-rich cathode active material has high capacity characteristics, but requires high voltage operation, which may result in reduced lifespan characteristics.

[0006] An object of the present disclosure is to provide a lithium secondary battery having improved capacity characteristics and operating stability.

[0007] A lithium secondary battery according to exemplary embodiments includes a positive electrode including a positive electrode active material including lithium metal oxide particles, a negative electrode opposite to the positive electrode, and a non-aqueous electrolyte including a non-aqueous organic solvent, a lithium salt, and an additive including a difluorophosphite compound, wherein a ratio of the number of moles of lithium included in the lithium metal oxide particles to the total number of moles of metals other than lithium included in the lithium metal oxide particles is 1.05 or more.

[0008] In some embodiments, the difluorophosphite compound may be represented by the following chemical formula 2.

[0009] [Chemical Formula 2]

[0010]

[0011] In chemical formula 2, R is hydrogen, C1-C 12 Alkyl group of C6-C 14 Aryl group of C2-C 12 alkenyl group of, or C2-C 12 It is a hydrocarbon containing an alkynyl group.

[0012] In some embodiments, the content of the difluorophosphite compound relative to the total weight of the non-aqueous electrolyte may be 0.5 wt% to 1.5 wt%.

[0013] In some embodiments, the non-aqueous electrolyte may further comprise an auxiliary additive comprising at least one selected from the group consisting of alkyl sultone compounds and alkenyl sultone compounds.

[0014] In some embodiments, the alkyl sultone compound may include at least one selected from the group consisting of 1,3-propane sultone and 1,4-butane sultone.

[0015] In some embodiments, the alkenyl sultone compound may include at least one selected from the group consisting of ethene sultone, 1,3-propene sultone, 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0016] In some embodiments, the content of the auxiliary additive relative to the total weight of the non-aqueous electrolyte may be 1.5 wt% to 3.0 wt%.

[0017] In some embodiments, the lithium salt may include at least one selected from the group consisting of lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), and lithium difluorophosphate (LiPO2F2).

[0018] In some embodiments, the non-aqueous organic solvent may include a carbonate solvent.

[0019] In some embodiments, the carbonate solvent may include at least one selected from the group consisting 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.

[0020] In some embodiments, the lithium metal oxide particles may be represented by the following chemical formula 1.

[0021] [Chemical Formula 1]

[0022] Li a [Mx Ni y Mn z ]O b

[0023] In chemical formula 1, M is at least one of Co, Na, Ca, Y, Hf, Ta, Fe, B, Si, Ba, Ra, Mg, V, Ti, Al, Ru, Zr, W, Sn, Nb, Mo, Cu, Zn, Cr, Ga, V, and Bi, and 0≤x≤0.9, 0≤y≤0.9, x+y>0, 0.1≤z≤0.9, 1.8≤a+x+y+z≤2.2, 1.05≤a / (x+y+z)≤1.95, and 1.8≤b≤2.2.

[0024] In some embodiments, in the above chemical formula 1, 1.2≤a / (x+y+z)≤1.8 may be satisfied.

[0025] According to one embodiment of the present disclosure, the capacity characteristics of the positive electrode active material can be improved.

[0026] According to one embodiment of the present disclosure, the life characteristics of a lithium secondary battery can be improved and the amount of gas generated at high temperatures can be reduced.

[0027] According to one embodiment of the present disclosure, a high voltage battery of 4.5 V or higher can be implemented while suppressing electrolyte decomposition and / or side reactions.

[0028] The lithium secondary battery of the present disclosure can be widely applied in green technology fields such as electric vehicles, battery charging stations, and other battery-powered solar and wind power generation. The lithium secondary battery of the present disclosure can be used in eco-friendly electric vehicles, hybrid vehicles, and other vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0029] FIG. 1 and FIG. 2 are schematic plan views and cross-sectional views, respectively, showing lithium secondary batteries according to exemplary embodiments.

[0030] Embodiments of the present disclosure provide a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte.

[0031] Hereinafter, embodiments of the present disclosure will be described in detail. However, these are merely exemplary and the present disclosure is not limited to the specific embodiments described as examples.

[0032] In exemplary embodiments, a lithium secondary battery includes a positive electrode, a negative electrode opposite the positive electrode, and a non-aqueous electrolyte.

[0033] The detailed structure of the lithium secondary battery is described below with reference to FIGS. 1 and 2.

[0034] In exemplary embodiments, the positive electrode comprises a positive electrode active material comprising lithium metal oxide particles containing an excess of lithium. For example, lithium may be present in a transition metal layer within a layered structure of the lithium metal oxide particles. Accordingly, the capacity characteristics of the positive electrode active material may be improved to be similar to the theoretical capacity (250 mAh / g) of the layered structure.

[0035] In exemplary embodiments, the ratio of the number of moles of lithium contained in the lithium metal oxide particles to the total number of moles of metals other than lithium contained in the lithium metal oxide particles is 1.05 or more. In this range, lithium can sufficiently exist in the transition metal layer in addition to the lithium layer in the layered structure of the lithium metal oxide particles.

[0036] In some embodiments, the lithium metal oxide particles may be represented by the following chemical formula 1.

[0037] [Chemical Formula 1]

[0038] Li a [M x Ni y Mn z ]O b

[0039] In chemical formula 1, M is at least one of Co, Na, Ca, Y, Hf, Ta, Fe, B, Si, Ba, Ra, Mg, V, Ti, Al, Ru, Zr, W, Sn, Nb, Mo, Cu, Zn, Cr, Ga, V, and Bi, and 0≤x≤0.9, 0≤y≤0.9, x+y>0, 0.1≤z≤0.9, 1.8≤a+x+y+z≤2.2, 1.05≤a / (x+y+z)≤1.95, and 1.8≤b≤2.2.

[0040] According to some embodiments, in Chemical Formula 2, 1.2≤a / (x+y+z)≤1.8 may be satisfied. For example, a / (x+y+z) may refer to the number of moles of lithium contained in the lithium metal oxide particle relative to the number of moles of transition metals contained in the lithium metal oxide particle.

[0041] In the above a / (x+y+z) range, a sufficient amount of lithium is present in the transition metal layer so that the capacity characteristics are improved while the mole number of the transition metal is suppressed from decreasing excessively.

[0042] The chemical structure represented by Chemical Formula 1 represents the bonding relationship contained within the layered structure or crystal structure of lithium metal oxide particles and does not exclude other additional elements. For example, M, Ni, and Mn of Chemical Formula 1 can serve as the main active element of the positive electrode active material. Chemical Formula 1 is provided to express the bonding relationship of the main active elements and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0043] In one embodiment, in addition to the main active element, auxiliary elements may be further included to enhance the chemical stability of the lithium metal oxide particles or the layered structure / crystal structure. The auxiliary elements may be incorporated into the layered structure / crystal structure to form bonds, and in this case, it should be understood that they are also included within the chemical structure range represented by Chemical Formula 1.

[0044] The auxiliary element may include at least one selected from the group consisting of, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra and P.

[0045] According to exemplary embodiments, a lithium secondary battery includes a non-aqueous electrolyte. For example, the non-aqueous electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0046] For example, a cathode active material including the lithium metal oxide particles described above can be operated at a high voltage of 4.5 V or higher. For example, lithium metal oxide particles having a composition of chemical formula 1 can be activated under a high voltage environment of 4.5 V or higher. However, when a lithium secondary battery is operated in the high voltage environment, the non-aqueous electrolyte may decompose, increasing the amount of gas generated. Accordingly, the life characteristics and operation stability of the lithium secondary battery may deteriorate.

[0047] According to exemplary embodiments, the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt, and an additive.

[0048] In exemplary embodiments, the non-aqueous organic solvent may further include at least one of a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, and an aprotic solvent. These may be used alone or in combination of two or more.

[0049] For example, the carbonate solvent may include at least one selected from the group consisting 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.

[0050] For example, the ester solvent may include at least one selected from the group consisting of methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), gamma-butyrolactone (GBL), decanolide, valerolactone, mevalonolactone, and caprolactone.

[0051] For example, the ether solvent may include at least one selected from the group consisting of dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), and 2-methyltetrahydrofuran.

[0052] For example, the ketone solvent may include cyclohexanone, etc.

[0053] For example, the alcohol solvent may include at least one selected from the group consisting of ethyl alcohol and isopropyl alcohol.

[0054] For example, the aprotic solvent may include at least one selected from the group consisting of nitrile solvents, amide solvents (e.g., dimethylformamide), dioxolane solvents (e.g., 1,3-dioxolane), and sulfolane solvents.

[0055] In exemplary embodiments, a lithium salt may be provided as the electrolyte. For example, the lithium salt may be Li + X - can be expressed as

[0056] For example, the anion of the lithium salt (X - ) is 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 - - It may be at least one selected from the group consisting of. These may be provided singly or in combination of two or more kinds as the anion of the lithium salt.

[0057] In some embodiments, the lithium salt may include at least one selected from the group consisting of lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), and lithium difluorophosphate (LiPO2F2). Accordingly, a film with improved thermal stability may be formed on the electrode surface. Accordingly, the electrode may be sufficiently protected while improving the ionic conductivity of the non-aqueous electrolyte.

[0058] In one embodiment, the lithium salt may be included in the non-aqueous organic solvent at a concentration of about 0.01 M to 5 M, or about 0.01 M to 2 M. In this range, the transfer of lithium ions and / or electrons may be promoted during the charge / discharge process of a lithium secondary battery, thereby improving output characteristics and capacity characteristics.

[0059] In exemplary embodiments, the additive of the non-aqueous electrolyte includes a difluorophosphite-based compound. Accordingly, the oxidation resistance of the non-aqueous electrolyte is enhanced, thereby improving the lifespan characteristics of a lithium secondary battery and reducing gas generation at high temperatures.

[0060] For example, by using a lithium metal oxide having the above-described composition and the difluorophosphite compound together, a high-voltage battery of 4.5 V or higher can be realized while suppressing electrolyte decomposition and / or side reactions. Accordingly, the capacity characteristics, output characteristics, and life characteristics of the lithium secondary battery can be improved simultaneously.

[0061] In some embodiments, the difluorophosphite compound may be represented by the following chemical formula 2.

[0062] [Chemical Formula 2]

[0063]

[0064] In chemical formula 2, R is hydrogen, C1-C 12 Alkyl group of C6-C 14 Aryl group of C2-C 12 alkenyl group of, or C2-C 12 It is a hydrocarbon containing an alkynyl group.

[0065] For example, R may not include an alicyclic structure. Accordingly, decomposition of the difluorophosphite compound may be suppressed, thereby improving the operating stability of the lithium secondary battery.

[0066] In some embodiments, R in the above formula 2 may be substituted or unsubstituted.

[0067] In some embodiments, R in the above formula 2 may include a substituent.

[0068] For example, the substituents included in R of the above chemical formula 2 include halogen, C1-C6 alkyl group, C3-C6 cycloalkyl group, C1-C6 alkoxy group, 3-7 membered heterocycloalkyl group, C6-C 12 Aryl group, 5-7 membered heteroaryl group, hydroxyl group (-OH), -NR 4 R 5 (R 4 and R 5 Each independently may include at least one selected from the group consisting of hydrogen or a C1-C6 alkyl group), a nitro group (-NO2), and a cyano group (-CN).

[0069] According to some embodiments, the content of the difluorophosphite compound relative to the total weight of the non-aqueous electrolyte may be 0.5 wt% to 1.5 wt%, and in one embodiment, 0.8 wt% to 1.2 wt%. Within this range, the oxidation resistance of the non-aqueous electrolyte may be sufficiently improved while preventing a deterioration in life characteristics due to excessive additive addition.

[0070] According to some embodiments, the non-aqueous electrolyte may further include auxiliary additives taking into account the life characteristics and / or ionic conductivity of the non-aqueous electrolyte.

[0071] For example, the auxiliary additive may include at least one selected from the group consisting of alkyl sultone compounds and alkenyl sultone compounds.

[0072] For example, the alkyl sultone compound may include at least one selected from the group consisting of 1,3-propane sultone (PS) and 1,4-butane sultone.

[0073] For example, the alkenyl sultone compound may include at least one selected from the group consisting of ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0074] The above auxiliary additives may further include, for example, anhydride compounds such as succinic anhydride, maleic anhydride, etc., nitrile compounds such as glutarnitrile, succinic nitrile, adiponitrile, etc. These may be added alone or in combination of two or more in addition to the above-described sultone compounds.

[0075] For example, the auxiliary additive may include at least one selected from the group consisting of ethylene sulfate (ESA), fluoroethylene carbonate (FEC), polyethylene sulfide (PES), vinylene carbonate (VC), and vinylethylene carbonate (VEC).

[0076] In some embodiments, the content of the auxiliary additive relative to the total weight of the non-aqueous electrolyte may be 1.5 wt% to 3.0 wt%, and in one embodiment, 1.8 wt% to 2.5 wt%. Within this range, side reactions of the non-aqueous electrolyte may be sufficiently suppressed, while preventing degradation of life characteristics due to excessive additive addition.

[0077] Hereinafter, a lithium secondary battery including the positive electrode and non-aqueous electrolyte described above is provided with reference to FIGS. 1 and 2. For example, FIG. 2 is a cross-sectional view taken along line I-I' of FIG. 1 in the thickness direction.

[0078] The structures illustrated in FIGS. 1 and 2 are examples for convenience of explanation, and the structure of the lithium secondary battery according to embodiments of the present disclosure is not limited thereto.

[0079] Referring to FIGS. 1 and 2, a lithium secondary battery may include a positive electrode (100) including a positive electrode active material including the lithium metal oxide particles described above, and a negative electrode (130) facing the positive electrode (100).

[0080] The positive electrode (100) may include a positive electrode active material layer (110) formed by applying a positive electrode active material including the lithium metal oxide particles described above to a positive electrode current collector (105).

[0081] The positive electrode current collector (105) may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector (105) may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. For example, the thickness of the positive electrode current collector (105) may be 10 μm to 50 μm.

[0082] The positive electrode active material layer (110) may include the positive electrode active material described above.

[0083] The positive electrode active material may include a plurality of the lithium metal oxide particles. For example, the total content of the lithium metal oxide particles in the total weight of the positive electrode active material may be 50 wt% or more. In some embodiments, the total content of the lithium metal oxide particles in the total weight of the positive electrode active material may be 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0084] In one embodiment, the positive electrode active material may be substantially composed of the lithium metal oxide particles.

[0085] The above-described positive electrode active material can be mixed in a solvent to prepare a positive electrode slurry. The positive electrode slurry can be coated on at least one surface of a positive electrode current collector (105), and then dried and rolled to prepare a positive electrode active material layer (110). The coating can include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting. The positive electrode active material layer (110) can further include a binder and optionally can further include a conductive agent, a thickener, etc.

[0086] As the above solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. can be used.

[0087] The above binder may include polyvinylidenefluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethylmethacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These may be used alone or in combination of two or more.

[0088] In one embodiment, a PVDF-based binder may be used as the positive electrode binder. In this case, the amount of binder used to form the positive electrode active material layer (110) may be reduced, while the amount of positive electrode active material may be relatively increased. Accordingly, the output characteristics and capacity characteristics of the secondary battery may be improved.

[0089] The conductive material may be added to enhance the conductivity and / or mobility of lithium ions or electrons of the positive electrode active material layer (110). For example, the conductive material may further include a carbon-based conductive material such as graphite, carbon black (e.g., Denka Black), acetylene black, Ketjen Black, graphene, vapor-grown carbon fiber (VGCF), carbon nanotubes (CNTs), carbon fibers, and / or a metal-based conductive material including a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3. These may be used alone or in combination of two or more.

[0090] The positive electrode slurry may further include a thickener and / or a dispersant. In one embodiment, the positive electrode slurry may include a thickener such as carboxymethyl cellulose (CMC).

[0091] The negative electrode (130) may include a negative electrode current collector (125) and a negative electrode active material layer (120) formed on at least one surface of the negative electrode current collector (125).

[0092] For example, the negative electrode current collector (125) may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, etc. These may be used alone or in combination of two or more. For example, the thickness of the negative electrode current collector (125) may be 10 μm to 50 μm.

[0093] The negative electrode active material layer (120) may include a negative electrode active material. A material capable of adsorbing and desorbing lithium ions may be used as the negative electrode active material. For example, the negative electrode active material may be a carbon-based material such as crystalline carbon, amorphous carbon, a carbon composite, or carbon fiber; lithium metal; a lithium alloy; a silicon (Si)-containing material, or a tin (Sn)-containing material. These may be used alone or in combination of two or more.

[0094] The above amorphous carbon may include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), etc.

[0095] The above crystalline carbon may include graphitic carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0096] The above lithium metal may include pure lithium metal and / or lithium metal having a protective layer formed thereon for suppressing dendrite growth, etc. In one embodiment, a lithium metal-containing layer deposited or coated on a negative electrode current collector (125) may be used as the negative electrode active material layer (120). In one embodiment, a lithium thin film layer may also be used as the negative electrode active material layer (120).

[0097] Elements included in the above lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc. These may be used alone or in combination of two or more.

[0098] The above silicon-containing material can provide increased capacity characteristics. The above silicon-containing material is Si, SiO x (0 <x<2), 금속 도핑된 SiO x(0 <x<2), 실리콘-탄소 복합체 등을 포함할 수 있다.

[0099] The above metal may include lithium and / or magnesium, and the metal-doped SiO x (0 <x<2)는 금속 실리케이트를 포함할 수 있다.

[0100] The above negative electrode active material can be mixed in a solvent to prepare a negative electrode slurry. After coating / depositing the negative electrode slurry on a negative electrode current collector (125), drying and rolling can be performed to prepare a negative electrode active material layer (120). The coating can include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting. The negative electrode active material layer (120) can further include a binder and optionally can further include a conductive agent, a thickener, etc.

[0101] The solvent included in the cathode slurry may include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc. These may be used alone or in combination of two or more.

[0102] The above-described materials that can be used in manufacturing the positive electrode (100) as the binder, conductive agent and thickener can be used.

[0103] In some embodiments, a styrene-butadiene rubber (SBR)-based binder, carboxymethyl cellulose (CMC), a polyacrylic acid-based binder, a poly(3,4-ethylenedioxythiophene, PEDOT)-based binder, or the like may be used as the negative electrode binder. These may be used alone or in combination of two or more. In exemplary embodiments, a separator (140) may be interposed between the positive electrode (100) and the negative electrode (130). The separator (140) may be configured to prevent electrical short-circuiting between the positive electrode (100) and the negative electrode (130) and to allow ion flow. For example, the thickness of the separator may be 10 μm to 20 μm.

[0104] For example, the separator (140) may include a porous polymer film or a porous nonwoven fabric.

[0105] The above porous polymer film may include a polyolefin polymer such as an ethylene polymer, a propylene polymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer. These may be used alone or in combination of two or more.

[0106] The above porous nonwoven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0107] The separator (140) may include a ceramic material. For example, inorganic particles may be coated on the polymer film or dispersed within the polymer film to improve heat resistance.

[0108] The separator (140) may have a single-layer or multi-layer structure including the above-described polymer film and / or non-woven fabric.

[0109] According to exemplary embodiments, an electrode cell is defined by an anode (100), a cathode (130), and a separator (140), and a plurality of electrode cells may be stacked to form an electrode assembly (150) in the form of, for example, a jelly roll. For example, the electrode assembly (150) may be formed through winding, stacking, z-folding, stack-folding, etc. of the separator (140).

[0110] As illustrated in FIGS. 1 and 2, electrode tabs (positive electrode tabs and negative electrode tabs) may protrude from the positive electrode collector (105) and negative electrode collector (125) belonging to each electrode cell and extend to one side of the case (160). The electrode tabs may be fused together with the one side of the case (160) to form electrode leads (positive electrode leads (107) and negative electrode leads (127)) that extend or are exposed to the outside of the case (160).

[0111] The above lithium secondary battery can be manufactured in a cylindrical, square, pouch or coin shape using, for example, a can.

[0112] Hereinafter, embodiments of the present disclosure will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present disclosure and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the examples are possible within the scope and technical idea of ​​the present disclosure, and it is also natural that such changes and modifications fall within the scope of the appended claims.

[0113] Example 1

[0114] (1) Manufacturing of positive electrode active material

[0115] Distilled water from which dissolved oxygen had been removed was introduced into a closed reactor, and NiSO4·6H2O and MnSO4·H2O were additionally introduced at a molar ratio of 38.1:61.9.

[0116] NaOH as a precipitant and NH4OH as a chelating agent were additionally added to the above reactor, and a co-precipitation reaction was performed for 60 hours to produce metal hydroxide particles.

[0117] The above metal hydroxide particles were dried at 100°C for 12 hours.

[0118] A mixture was prepared by placing dried metal hydroxide particles and lithium hydroxide into a dry mixer.

[0119] The mixing ratio of the above metal hydroxide particles and lithium hydroxide is Li according to the composition of the inductively coupled plasma (ICP) analysis of the manufactured lithium metal oxide particles. 1.11 Ni 0.34 Mn 0.55 It was adjusted to satisfy O2.

[0120] The above ICP analysis was performed using a 5800 ICP-OES instrument from Agilent.

[0121] The above mixture was placed in a kiln, and the temperature of the kiln was increased to 250°C at 2°C / min, and maintained at 250°C for 3 hours (first kiln).

[0122] After the first firing, the temperature of the firing furnace was increased to 850°C at a rate of 2°C / min, and the second firing was performed while maintaining the temperature at 850°C for 8 hours.

[0123] During the first and second firings, oxygen gas was continuously passed through the firing furnace at a rate of 10 mL / min.

[0124] After the firing was completed, the fired product was naturally cooled to room temperature, and then crushed and classified to produce lithium metal oxide particles.

[0125] As a result of performing ICP analysis on the above lithium metal oxide particles by normalizing the number of oxygen atoms to 2, Li 1.11 Ni 0.34 Mn 0.55 It was confirmed as O2.

[0126] The manufactured lithium metal oxide particles were used as a cathode active material.

[0127] (2) Preparation of non-aqueous electrolyte

[0128] A 1.0 M LiPF6 solution was prepared using a mixed solvent of EC / EMC / DEC (25:45:30; volume ratio). 1.0 wt% of phosphorodifluoridous acid, pentyl ester (represented by the following chemical formula 3) was added as an additive based on the total weight of the non-aqueous electrolyte to the prepared 1.0 M LiPF6 solution, and 1.0 wt% of FEC, 0.5 wt% of PS, 0.3 wt% of PRS, and 0.5 wt% of ESA (total content of auxiliary additives: 2.3 wt%) was added as auxiliary additives based on the total weight of the non-aqueous electrolyte to prepare a non-aqueous electrolyte.

[0129] [Chemical Formula 3]

[0130]

[0131] (3) Lithium secondary battery manufacturing

[0132] A lithium secondary battery was manufactured using the manufactured positive electrode active material and non-aqueous electrolyte.

[0133] Specifically, a cathode slurry was prepared by mixing the manufactured cathode active material, Denka Black as a conductive agent, and PVDF as a binder at a mass ratio of 93:5:2. The cathode slurry was coated on an aluminum current collector (thickness: 15 μm), vacuum-dried at 130°C, and then rolled to prepare a cathode.

[0134] Lithium metal (Li metal) with a thickness of 15 ㎛ was used as the cathode.

[0135] The positive and negative electrodes manufactured as described above were notched into circular shapes with diameters of Φ14 and Φ16, respectively, and laminated, and a separator (polyethylene, thickness 13 ㎛) notched into Φ19 was interposed between the positive and negative electrodes to form an electrode cell. ΦN (N is a positive number) can represent a circular shape with a diameter of N mm.

[0136] The above electrode cell was assembled by placing it in a coin cell outer case of a standard (CR2016) with a diameter of 20 mm and a height of 1.6 mm, injecting electrolyte, and aging for more than 12 hours so that the electrolyte could be impregnated into the inside of the electrode.

[0137] The lithium secondary battery manufactured as described above was subjected to a Mars charge-discharge test (charge condition CC-CV 1C 4.6V 0.05C CUT-OFF, discharge condition CC 1C 2.0V CUT-OFF).

[0138] Examples 2 to 7

[0139] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the content of phosphorodifluoridous acid and pentyl ester relative to the total weight of the non-aqueous electrolyte was adjusted as shown in Table 1 below.

[0140] Example 8

[0141] A positive electrode active material, a non-aqueous electrolyte, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 0.5 wt% of FEC, 0.3 wt% of PS, 0.3 wt% of PRS, and 0.3 wt% of ESA (total content of auxiliary additives: 1.4 wt%) were added as auxiliary additives relative to the total weight of the non-aqueous electrolyte.

[0142] Example 9

[0143] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 1.5 wt% of FEC, 0.7 wt% of PS, 0.4 wt% of PRS, and 0.5 wt% of ESA (total content of auxiliary additives: 3.1 wt%) were added as auxiliary additives relative to the total weight of the non-aqueous electrolyte.

[0144] Example 10

[0145] The composition of lithium metal oxide particles is Li 1.19 Ni 0.21 Co 0.02 Mn 0.58 A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the input amounts of LiOH·H2O, NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O were adjusted to become 02.

[0146] Comparative Example 1

[0147] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that phosphorodifluoridous acid and pentyl ester were not added to the non-aqueous electrolyte.

[0148] Comparative Example 2

[0149] A solution was prepared by mixing NiSO4, CoSO4, and MnSO4 in a molar ratio of 75:10:15 in distilled water, which had been bubbled with N2 for 24 hours to remove internal dissolved oxygen. The solution was placed in a reactor at 55°C, and NaOH and NH3H2O ​​were added as a precipitant and a chelating agent, respectively, and a co-precipitation reaction was performed for 36 hours to obtain metal hydroxide particles as a transition metal precursor. The transition metal precursor was dried at 80°C for 12 hours and then further dried at 110°C for 12 hours.

[0150] Lithium hydroxide and the above transition metal precursor were added to a dry high-speed mixer at a molar ratio of 1.05:1 and uniformly mixed for 5 minutes. The mixture was placed in a kiln, heated to 930°C at a heating rate of 2°C / min, and calcined at 930°C for 10 hours.

[0151] Oxygen was continuously passed at a flow rate of 10 mL / min during heating and calcination. After calcination, the product was naturally cooled to room temperature and then crushed and classified to obtain LiNi. 0.75 Co 0.10 Mn 0.15 Lithium-transition metal composite oxide particles having a composition of O2 were prepared.

[0152] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that lithium-transition metal composite oxide particles manufactured as cathode active material were used.

[0153] Comparative Example 3

[0154] A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were manufactured in the same manner as in Comparative Example 2, except that phosphorodifluoridous acid and pentyl ester were not added to the non-aqueous electrolyte.

[0155] Comparative Example 4

[0156] The composition of lithium metal oxide particles is Li 1.02 Ni 0.38 Mn 0.60 A cathode active material, a non-aqueous electrolyte, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the input amounts of LiOH·H2O, NiSO4·6H2O, and MnSO4·H2O were adjusted to become O2.

[0157] The composition (chemical formula) of the positive electrode active material, the ratio of the number of moles of lithium contained in the lithium metal oxide particles to the total number of moles of metals other than lithium contained in the lithium metal oxide particles (Li / Me), the content of the additive relative to the total weight of the non-aqueous electrolyte, and the content of the auxiliary additive relative to the total weight of the non-aqueous electrolyte are shown in Table 1 below.

[0158] Cathode active materialNon-aqueous electrolyteComposition (chemical formula)Li / MeAdditive content (weight%)Auxiliary additive content (weight%)Example 1Li 1.11 Ni 0.34 Mn 0.55 O21.251.02.3 Example 2Li 1.11 Ni 0.34 Mn 0.55 O21.250.52.3 Example 3Li 1.11 Ni 0.34 Mn 0.55 O21.250.72.3 Example 4Li 1.11 Ni 0.34 Mn 0.55 O21.251.22.3 Example 5Li 1.11 Ni 0.34 Mn 0.55 O21.251.52.3 Example 6Li 1.11 Ni 0.34 Mn 0.55 O21.250.42.3 Example 7Li 1.11 Ni 0.34 Mn 0.55 O21.251.62.3 Example 8Li 1.11 Ni 0.34 Mn 0.55 O21.251.01.4 Example 9Li 1.11 Ni 0.34 Mn 0.55 O21.251.03.1 Example 10Li 1.19 Ni 0.21 Co 0.02 Mn 0.58 021.471.02.3 Comparative Example 1Li 1.11 Ni 0.34 Mn 0.55 O21.2502.3 Comparative Example 2LiNi 0.75 Co 0.10 Mn 0.15O21.001.02.3 Comparative Example 3LiNi 0.75 Co 0.10 Mn 0.15 O21.0002.3 Comparative Example 4Li 1.02 Ni 0.38 Mn 0.60 O21.041.02.3

[0159] Experimental example

[0160] (1) Capacity retention rate evaluation - 45 ℃

[0161] The lithium secondary batteries manufactured according to the above-described examples and comparative examples were subjected to 50 cycles of charging (CC-CV 1C 4.6V 0.05C CUT-OFF) and discharging (CC 1C 2.0V CUT-OFF) in a 45°C chamber.

[0162] The capacity retention rate was calculated as a percentage by dividing the discharge capacity measured at the 50th discharge by the discharge capacity measured at the 1st discharge.

[0163] Capacity retention rate (%) = (50th discharge capacity / 1st discharge capacity) × 100

[0164] (2) Measurement of gas generation - 45 ℃

[0165] The lithium secondary batteries manufactured according to the above-described examples and comparative examples were charged (CC-CV 1C 4.6V 0.05C CUT-OFF) and then left in a 45°C chamber for 8 weeks. Thereafter, the lithium secondary batteries were left at room temperature for 30 minutes and placed in a chamber where the amount of gas generated was measured.

[0166] After forming a vacuum in the chamber, nitrogen gas was filled to form atmospheric pressure, and the nitrogen volume (V0) at atmospheric pressure and the internal pressure (P0) of the chamber were measured.

[0167] After forming a vacuum again inside the chamber, a hole was drilled in the lithium secondary battery and left for 1 hour. Afterwards, the internal pressure (P1) of the chamber was measured and the amount of gas generated was measured by substituting it into the following equation.

[0168] Gas generation (mL) = (V0 / P0)*P1

[0169] (3) Measurement of initial discharge capacity

[0170] For the lithium secondary batteries manufactured according to the above-described examples and comparative examples, charging (CC-CV 0.1C 4.6V 0.05C CUT-OFF) and discharging (CC 0.1C 2.0V CUT-OFF) were performed once, and the initial discharge capacity was measured.

[0171] The above initial discharge capacity is defined as the absolute capacity (mAh) of the lithium secondary battery divided by the total weight (g) of the positive electrode active material in the battery.

[0172] The evaluation results are shown in Table 2 below.

[0173] Classification Capacity retention rate (45 ℃) (%, 50cyc) Gas generation (45 ℃) (mL) Initial discharge capacity (mAh / g) Example 180.110.3210 Example 277.612.5211 Example 378.911.0213 Example 481.59.2210 Example 582.08.6208 Example 674.718.1211 Example 776.915.3213 Example 876.315.6210 Example 975.917.2211 Example 1080.310.8246 Comparative example 140.592.5210 Comparative example 278.516.4128 Comparative example 344.1105.3131Comparison Example 477.915.0140

[0174] Referring to Tables 1 and 2, in examples using a non-aqueous electrolyte containing a difluorophosphite compound, the amount of gas generated in a high-voltage environment was reduced and the capacity retention rate was improved compared to the comparative examples.

[0175] In the examples, a cathode active material containing excess lithium was used to increase the initial discharge capacity.

[0176] In Example 6, where the content of the difluorophosphite compound was less than 0.5 wt% relative to the total weight of the non-aqueous electrolyte, oxidation resistance was lowered compared to other examples, resulting in a decrease in capacity retention and an increase in gas generation.

[0177] In Example 7, where the content of the difluorophosphite compound exceeded 1.5 wt% relative to the total weight of the non-aqueous electrolyte, electrolyte side reactions increased and life characteristics deteriorated compared to other examples.

[0178] In Example 8, where the content of the auxiliary additive was less than 1.5 wt% relative to the total weight of the non-aqueous electrolyte, the capacity retention rate decreased and the amount of gas generation increased compared to other examples.

[0179] In Example 9, where the content of the auxiliary additive exceeded 3.0 wt% relative to the total weight of the non-aqueous electrolyte, the life characteristics were deteriorated compared to other examples.

[0180] In Comparative Example 4, where the ratio of the number of moles of lithium contained in the lithium metal oxide particles to the total number of moles of metals other than lithium contained in the lithium metal oxide particles was less than 1.05, the amount of lithium present in the transition metal layer of the layered structure decreased and the initial capacity decreased.

Claims

1. A cathode comprising a cathode active material including lithium metal oxide particles; a cathode opposite to the anode; and A non-aqueous electrolyte comprising a non-aqueous organic solvent, a lithium salt, and an additive including a difluorophosphite compound, A lithium secondary battery, wherein the ratio of the number of moles of lithium contained in the lithium metal oxide particles to the total number of moles of metals other than lithium contained in the lithium metal oxide particles is 1.05 or more.

2. In claim 1, the difluorophosphite compound is represented by the following chemical formula 2, a lithium secondary battery: [Chemical Formula 2] 3. A lithium secondary battery according to claim 1, wherein the content of the difluorophosphite compound relative to the total weight of the non-aqueous electrolyte is 0.5 wt% to 1.5 wt%.

4. A lithium secondary battery according to claim 1, wherein the non-aqueous electrolyte further comprises an auxiliary additive comprising at least one selected from the group consisting of alkyl sultone compounds and alkenyl sultone compounds.

5. A lithium secondary battery according to claim 4, wherein the alkyl sultone compound comprises at least one selected from the group consisting of 1,3-propane sultone and 1,4-butane sultone.

6. A lithium secondary battery according to claim 4, wherein the alkenyl sultone compound comprises at least one selected from the group consisting of ethene sultone, 1,3-propene sultone, 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

7. A lithium secondary battery according to claim 4, wherein the content of the auxiliary additive relative to the total weight of the non-aqueous electrolyte is 1.5 wt% to 3.0 wt%.

8. A lithium secondary battery according to claim 1, wherein the lithium salt comprises at least one selected from the group consisting of lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), and lithium difluorophosphate (LiPO2F2).

9. A lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent comprises a carbonate solvent.

10. A lithium secondary battery according to claim 9, wherein the carbonate solvent comprises at least one selected from the group consisting 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.

11. In claim 1, the lithium metal oxide particles are represented by the following chemical formula 1, a lithium secondary battery: [Chemical Formula 1] Li a [M x Ni y Mr z ]O b (In Chemical Formula 1, M is at least one of Co, Na, Ca, Y, Hf, Ta, Fe, B, Si, Ba, Ra, Mg, V, Ti, Al, Ru, Zr, W, Sn, Nb, Mo, Cu, Zn, Cr, Ga, V, and Bi, and 0≤x≤0.9, 0≤y≤0.9, x+y>0, 0.1≤z≤0.9, 1.8≤a+x+y+z≤2.2, 1.05≤a / (x+y+z)≤1.95, and 1.8≤b≤2.2) 12. A lithium secondary battery according to claim 11, wherein 1.2≤a / (x+y+z)≤1.8.

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