Lithium secondary battery and urban air traffic equipment comprising same

Abstract

The present invention relates to a lithium secondary battery and urban air traffic equipment comprising the same, in which the lithium secondary battery comprises: a positive electrode comprising a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector and having a loading amount of 2.5 mAh / cm2 to 3.8 mAh / cm2; a negative electrode including a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector; and a separator disposed between the positive electrode and the negative electrode, in which when the lithium secondary battery is discharged for 15 seconds under a 900 W constant output condition at an SOC of 35% and then discharged under a 1000 W constant output condition, the time for reaching the SOC of 0% needs 10 seconds or more.

Description

Technical Field

[0001] This application claims the benefit of Korean Patent Application Nos. 10-2022-0178732, filed on December 19, 2022, and 10-2023-0180945, filed on December 13, 2023, in the Korean Intellectual Property Office, the entire disclosures of which are incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery and an urban air mobility device including the lithium secondary battery, and more particularly, to a secondary battery capable of generating a high output for a predetermined time or more in a state of low remaining capacity, and also to an urban air mobility device including the secondary battery and having improved safety in an emergency. Background Art

[0003] With the development of technology, the demand for lithium secondary batteries as an energy source has increased rapidly. Recently, in addition to electric vehicles, portable electronic devices, etc., the demand for lithium secondary batteries as a power source for urban air mobility devices (UAMs), which are next-generation transportation modes, has also increased.

[0004] Since UAMs need to provide air services in complex urban environments, they should be designed to be able to take off and land vertically to minimize operating space, and in order to increase social acceptance for commercialization, high safety is also required.

[0005] In particular, since there are many complex variables in the operation of UAMs, such as collisions with high-rise buildings and structures, low-level turbulence, weather changes (e.g., precipitation), etc., the lithium secondary battery as a power source should also be designed to be prepared for emergency situations deviating from normal flight conditions.

[0006] However, since the research on lithium secondary batteries has mainly been focused on electric vehicle applications to date, they do not meet the performance required for UAMs (specifically, considering the output conditions for landing in an emergency), and thus, there is a need to develop lithium secondary batteries for UAMs. Summary of the Invention

[0007] [Technical Problem]

[0008] An object of the present invention is to provide a lithium secondary battery capable of generating a high output for a predetermined time or more in a state of low remaining capacity.

[0009] In addition, an object of the present invention is to provide an urban air mobility device including the lithium secondary battery and having improved safety in an emergency.

[0010] [Technical Solution]

[0011] According to one aspect of the present invention, there is provided a lithium secondary battery comprising: a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector and having a loading amount of 2.5 mAh / cm 2 to 3.8 mAh / cm 2 ; a negative electrode including a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector; and a separator disposed between the positive electrode and the negative electrode, wherein when the lithium secondary battery discharges for 15 seconds under a constant output condition of 900 W at an SOC of 35% and then discharges under a constant output condition of 1000 W, it takes more than 10 seconds to reach an SOC of 0%.

[0012] In addition, the present invention provides an urban air mobility device including the lithium secondary battery.

[0013] [Advantageous Effects]

[0014] The lithium secondary battery of the present invention includes a positive electrode with a loading amount adjusted to a predetermined range, and thus exhibits high output characteristics even at the low end of the SOC. Therefore, the urban air mobility device including the lithium secondary battery has the advantage of being able to land stably even in an emergency. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a graph showing the output evaluation results at the low end of the SOC of the lithium secondary batteries manufactured in the examples and comparative examples of the present invention. DETAILED DESCRIPTION

[0016] Hereinafter, the present invention will be described in more detail.

[0017] An urban air mobility device (UAM) operates in a vertical takeoff and landing manner, and thus requires a high level of output during takeoff and landing. In particular, due to its complex operating environment, even at a low state of charge (SOC), the urban air mobility device absolutely needs to have the function of generating a high output for a predetermined duration, so that the urban air mobility device can land safely even in some cases where the battery does not work properly. However, a conventional secondary battery for electric vehicles does not need to have the above function. Therefore, when it is applied to the UAM as it is, there is a problem that it is difficult to ensure safety.

[0018] Therefore, the present invention aims to provide a secondary battery that can generate a high output of more than 1000 W for a predetermined duration or more even in the low SOC range.

[0019] Specifically, the lithium secondary battery of the present invention includes: a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector and having a loading amount of 2.5 mAh / cm2 to 3.8 mAh / cm 2 a positive electrode; a negative electrode including a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector; and a separator disposed between the positive electrode and the negative electrode, wherein, when the lithium secondary battery discharges for 15 seconds under a constant output condition of 900 W at an SOC of 35% and then discharges under a constant output condition of 1000 W, it takes more than 10 seconds to reach an SOC of 0%.

[0020] Meanwhile, in the present invention, a "primary particle" refers to a particle unit that does not have grain boundaries in appearance when observed within a field of view of 5000 to 20000 times using a scanning electron microscope, and a "secondary particle" refers to a particle formed by the aggregation of a plurality of primary particles.

[0021] In the present invention, the "average particle diameter of primary particles" refers to the arithmetic mean calculated after measuring the particle diameters of at least 20 primary particles observed in a scanning electron microscope image. At this time, the particle diameter refers to the diameter of the longest axis of the primary particle.

[0022] In the present invention, the term "secondary particle" is a particle formed by the aggregation of a plurality of primary particles. In the present invention, a secondary particle formed by the aggregation of 30 or fewer primary particles is called a pseudo-single particle in order to distinguish it from a conventional secondary particle formed by the aggregation of dozens to hundreds of primary particles.

[0023] In the present invention, "D50" refers to the particle diameter corresponding to 50% of the cumulative volume in the volume-based cumulative particle size distribution of the corresponding particle powder. For example, D50 can be measured by the following method: dispersing the positive electrode active material powder in a dispersion medium, then introducing the mixture into a commercially available laser diffraction particle size measuring device (such as Microtrac Co. S-3500), irradiating it with ultrasonic waves at an output of 60 W at about 28 kHz to obtain a volume-based cumulative particle size distribution diagram, and then obtaining the particle diameter at the point where the cumulative volume is 50% in the obtained volume-based cumulative particle size distribution diagram.

[0024] In the present invention, the "energy density of the positive electrode" can be measured as follows: A polyethylene-based separator with a thickness of 15 μm is disposed between the corresponding positive electrode and the lithium metal negative electrode to fabricate an electrode assembly. Subsequently, the electrode assembly is placed in a battery case, and then an electrolyte solution prepared by dissolving 1 M LiPF6 in a mixed organic solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7 is injected into the battery case to fabricate a coin half-cell. Specifically, the coin half-cell is charged to 4.25 V under a constant current / constant voltage condition of 0.33 C at 25 °C, and then discharged to 3.0 V under a constant current of 0.33 C to obtain the initial discharge capacity (Ah) of the secondary battery. The value obtained by multiplying the initial discharge capacity by the average discharge voltage and dividing by the weight (kg) of the coin half-cell is described as the energy density of the positive electrode.

[0025] Hereinafter, each component constituting the present invention will be described in detail.

[0026] Positive electrode

[0027] The lithium secondary battery of the present invention includes a positive electrode, and the loading amount of the positive electrode is 2.5 mAh / cm 2 to 3.8 mAh / cm 2 Preferably, it is 3.0 mAh / cm 2 to 3.6 mAh / cm 2 More preferably, it is 3.3 mAh / cm 2 to 3.5 mAh / cm 2 .

[0028] When the loading amount satisfies the above range, after the lithium secondary battery discharges for 15 seconds under a constant output condition of 900 W at SOC 35%, an output of more than 1000 W can be generated for more than 10 seconds. To achieve the minimum energy density applicable to UAM, the loading amount of the positive electrode should be 2.5 mAh / cm 2 or more, and to achieve the minimum output property required for application to UAM, the loading amount should not exceed 3.8 mAh / cm 2 .

[0029] The positive electrode active material layer may include a positive electrode active material having a bimodal particle size distribution composed of large particles and small particles having different D50s from each other. Among them, the large particles and the small particles independently contain lithium nickel-based oxides, or the positive electrode active material layer may include a positive electrode active material having a unimodal particle size distribution. Among them, the positive electrode active material having a unimodal particle size distribution includes lithium nickel-based oxides in the form of single particles composed of one primary particle, or lithium nickel-based oxides in the form of pseudo-single particles which are secondary particles agglomerated from 30 or fewer primary particles.

[0030] In one embodiment of the present invention, the positive electrode active material layer contains a positive electrode active material having a bimodal particle size distribution composed of large particles and small particles with different D50s from each other, wherein the large particles and the small particles each independently contain a lithium nickel-based oxide.

[0031] In this case, when the electrode is roll-pressed, the small particles are filled in the pores of the large particles, so there are advantages that the energy density can be increased and a high energy density can be achieved.

[0032] The D50 of the large particles can be 8 μm to 18 μm, preferably 8 μm to 15 μm, more preferably 9 μm to 13 μm. In addition, the D50 of the small particles can be 2 μm to 7 μm, preferably 2 μm to 6 μm, more preferably 3 μm to 5 μm. When the D50 of the large particles and the D50 of the small particles satisfy the above ranges, it is beneficial to achieve a high energy density.

[0033] At the same time, the large particles and the small particles can each independently be single particles composed of one primary particle, pseudo-single particles that are secondary particles aggregated from 30 or fewer primary particles, secondary particles aggregated from more than 30 primary particles, or a combination thereof.

[0034] However, preferably, the small particles can contain a lithium nickel-based oxide in the form of a single particle composed of one primary particle, or a pseudo-single particle in the form of a secondary particle aggregated from 30 or fewer primary particles.

[0035] When mixing the large particles and the small particles to form an electrode, the small particles located between the large particles are used to reduce the direct contact between the large particles. Therefore, the small particles are subjected to relatively large physical forces (stress), which may exacerbate particle breakage. Therefore, when the small particles are introduced in the form of single particles or pseudo-single particles as described above, the breakage and deterioration of the small particles can be suppressed, and the roll-pressing properties of the electrode can be improved.

[0036] At the same time, the positive electrode active material having a bimodal particle size distribution can contain the large particles and the small particles in a weight ratio of 50:50 to 90:10, preferably 60:40 to 80:20. When the weight ratio of the large particles and the small particles is within the above range, the small particles can be arranged between the large particles while minimizing space loss. Therefore, the packing density is optimized, and the stress applied between the active materials during the roll-pressing process is more smoothly dispersed, which is beneficial to improving the roll-pressing properties of the electrode and achieving high energy.

[0037] In another embodiment of the present invention, the positive electrode active material layer contains a positive electrode active material having a unimodal particle size distribution. Among them, the positive electrode active material having a unimodal particle size distribution includes a lithium nickel-based oxide in the form of single particles composed of one primary particle, or a pseudo-single particle form of a lithium nickel-based oxide that is an agglomerate of 30 or fewer primary particles. In this case, it is beneficial for one particle to quickly participate in the reaction and achieve high output.

[0038] At the same time, in the lithium nickel-based oxide in the form of single particles or pseudo-single particles, the average particle size of the primary particles can be 1 μm to 5 μm, preferably 2 μm to 4 μm.

[0039] In addition, the lithium nickel-based oxide contains nickel, cobalt, and manganese. Specifically, the molar ratio of nickel among the transition metals can be 70 mol% or more, preferably 75 mol% or more, and more preferably 80 mol% or more. In the case of a positive electrode active material having a bimodal particle size distribution, the compositions of the lithium nickel-based oxides contained in the large particles and the small particles are the same or different from each other.

[0040] More specifically, the lithium nickel-based oxide can be represented by the following formula 1.

[0041] [Formula 1]

[0042] Li 1+x (Ni a Co b Mn c M d )O2

[0043] In the above formula 1, M is any one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0044] 1 + x, a, b, c, and d are the atomic fractions of the respective independent elements, where -0.2 ≤ x ≤ 0.2, 0.60 ≤ a < 1, 0 < b < 0.40, 0 < c < 0.40, 0 ≤ d ≤ 0.10, and a + b + c + d = 1.

[0045] 1 + x represents the molar ratio of lithium in the lithium nickel-based oxide, which can be -0.1 ≤ x ≤ 0.2 or 0 ≤ x ≤ 0.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be stably formed.

[0046] a represents the molar ratio of nickel among all the metals other than lithium in the lithium nickel-based oxide, where it can be 0.70 ≤ a < 1, 0.75 ≤ a < 1, or 0.80 ≤ a < 1. When the molar ratio of nickel satisfies the above range, a high energy density can be achieved to realize a high capacity.

[0047] b represents the molar ratio of cobalt among all metals other than lithium in the lithium nickel-based oxide, where 0 < b ≤ 0.25, 0 < b ≤ 0.20, or 0 < b ≤ 0.15. When the molar ratio of cobalt satisfies the above range, good resistance properties and output properties can be achieved.

[0048] c represents the molar ratio of manganese among all metals other than lithium in the lithium nickel-based oxide, where 0 < c ≤ 0.25, 0 < c ≤ 0.20, or 0 < c ≤ 0.15. When the molar ratio of manganese satisfies the above range, the positive electrode active material exhibits excellent structural stability.

[0049] d represents the molar ratio of element M among all metals other than lithium in the lithium nickel-based oxide, where 0 ≤ d ≤ 0.08, 0 ≤ d ≤ 0.05, or 0 ≤ d ≤ 0.03.

[0050] Meanwhile, if necessary, the lithium nickel-based oxide of the present invention may further include a coating layer on the particle surface. At this time, the coating layer may include, for example, one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mn, Sr, Sb, Bi, Si, and S. When there is a coating layer on the surface of the lithium nickel-based oxide, the contact between the electrolyte and the lithium nickel-based oxide is reduced due to the coating layer. Therefore, there is an effect of reducing the elution of transition metals or gas generation caused by side reactions with the electrolyte. Preferably, the coating layer may include B, Co, Al, or a combination thereof, and more preferably, it may include Co. If the coating layer includes Co, an effect of suppressing side reactions with the electrolyte solution, as well as effects of improving output and reducing resistance, can be obtained.

[0051] The positive electrode of the present invention includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer includes the above-mentioned positive electrode active material.

[0052] The positive electrode current collector may include a highly conductive metal and is not particularly limited as long as it is not reactive within the voltage range of the battery and the positive electrode active material layer can be easily adhered to the positive electrode current collector. As the positive electrode current collector, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used. In addition, the thickness of the positive electrode current collector can generally be 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms, such as a film, sheet, foil, net, porous body, foam, and non-woven fabric body.

[0053] When necessary, the positive electrode active material layer may optionally contain a conductive material and a binder together with the positive electrode active material.

[0054] At this time, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material may be 80% by weight to 99% by weight, more specifically 85% by weight to 98.5% by weight. When included within the above content range, excellent capacity properties can be exhibited.

[0055] The conductive material is used to impart conductivity to the electrode, and any conductive material can be used without particular limitation as long as it has electronic conductivity without causing chemical changes in the battery to be formed. Specific examples thereof may include: graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; carbonaceous materials, such as carbon fiber; metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one of them or a mixture of two or more of them can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material may be 0.1% by weight to 15% by weight.

[0056] The binder is used to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples thereof may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer (EPDM), sulfonated - EPDM, styrene - butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers in which hydrogen is replaced by Li, Na, or Ca, or various copolymers thereof, and any one of them or a mixture of two or more of them can be used. Based on the total weight of the positive electrode active material layer, the content of the binder may be 0.1% by weight to 15% by weight.

[0057] The positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the loading amount is adjusted to the above range. For example, the positive electrode can be manufactured by: preparing a positive electrode mixture by dissolving or dispersing the above-mentioned electrode active material and, when necessary, an optional binder, conductive material, and dispersant in a solvent, applying the positive electrode mixture to a positive electrode current collector, and then drying and rolling, or, the positive electrode can be manufactured by: casting the positive electrode mixture on a separate carrier, and then laminating the film peeled from the carrier on the positive electrode current collector.

[0058] The solvent can be a solvent commonly used in the art and can be dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, water, etc., and any one of them or a mixture of two or more of them can be used. Considering the coating thickness of the slurry and the manufacturing yield, and thereafter, when applying for manufacturing the positive electrode, the slurry is allowed to have a viscosity capable of exhibiting excellent thickness uniformity. If the solvent dissolves or disperses the positive electrode active material, conductive material, binder, and dispersant, the amount of the solvent to be used is sufficient.

[0059] In one embodiment of the present invention, the energy density of the positive electrode can be 250 Wh / kg or more, preferably 270 Wh / kg or more, and more preferably 280 Wh / kg or more. The higher the energy density of the positive electrode, the higher the energy can be exhibited at a smaller weight, which is advantageous. However, considering the fact that the higher the loading amount of the positive electrode for achieving a high energy density, the more difficult it is to meet the output conditions, and the fact that the proportion that the battery can occupy in the weight of the aircraft is limited, the energy density of the positive electrode can be 320 Wh / kg or less.

[0060] In one embodiment of the present invention, the porosity of the positive electrode active material layer can be 20% to 32%, preferably 21% to 28%, and more preferably 22% to 26%. When the porosity of the positive electrode active material layer is within the above range, preferably, the particle breakage of the active material is minimized while the packing density increases, which can help improve the energy density of the battery. Here, the porosity refers to the value calculated by the following [Equation 1].

[0061] [Equation 1]

[0062] Porosity (%) of the positive electrode active material layer = ((true density of the positive electrode active material - electrode density) / true density of the positive electrode active material) × 100

[0063] In the above Equation 1, the electrode density is the value calculated by the following Equation 2.

[0064] [Equation 2]

[0065] Electrode density = (weight of the positive electrode - weight of the positive electrode current collector) / (a × b × c)

[0066] In the above Equation 2, a, b, and c are the width, length, and height measured after separating the positive electrode current collector from the positive electrode, respectively.

[0067] Negative electrode

[0068] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector.

[0069] The negative electrode current collector is not particularly limited as long as it has high electrical conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., aluminum cadmium alloy, etc. can be used. In addition, the thickness of the negative electrode current collector can generally be 3 μm to 500 μm, and the same as in the case of the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabric bodies.

[0070] The negative electrode active material layer may optionally contain a binder and a conductive material together with the negative electrode active material.

[0071] As the negative electrode active material, compounds capable of reversibly inserting and extracting lithium can be used. Specific examples thereof may include: carbon materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal materials alloyable with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium such as SiO β (0 < β < 2), SnO2, vanadium oxides, and lithium vanadium oxides; or composites containing metal materials and carbon materials such as Si-C composites or Sn-C composites, and any one or a mixture of two or more thereof can be used. In addition, a thin film of metallic lithium can be used as the negative electrode active material. Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be 80 wt% to 99 wt%.

[0072] The binder is a component that helps the adhesion between the conductive material, the active material, and the current collector, and based on the total weight of the negative electrode active material layer, its addition amount is generally 0.1 wt% to 10 wt%. Examples of the binder may include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, various copolymers thereof, etc.

[0073] The conductive material is a component used to further improve the conductivity of the negative electrode active material, and based on the total weight of the negative electrode active material layer, its addition amount can be 10% by weight or less, preferably 5% by weight or less. The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, the following can be used: graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers, such as carbon fibers and metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives, etc.

[0074] The negative electrode active material layer can be prepared by the following method: preparing a negative electrode mixture by dissolving or dispersing the negative electrode active material and optionally a binder and a conductive material in a solvent, applying the negative electrode mixture onto a negative electrode current collector, and then drying and rolling it. Alternatively, the negative electrode active material layer can be prepared by the following method: casting the negative electrode mixture on a separate carrier, and then laminating the film peeled from the carrier on the negative electrode current collector.

[0075] Separator

[0076] In the lithium secondary battery of the present invention, the separator is used to separate the negative electrode from the positive electrode and provide a migration path for lithium ions, and any separator can be used as long as it is commonly used as a separator in lithium secondary batteries. In particular, a separator having excellent water retention ability for the electrolyte solution and low resistance to ion migration in the electrolyte is preferably used. Specifically, a porous polymer film can be used. For example, a porous polymer film made of a polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer), or a laminated structure having two or more layers therein. In addition, a conventional porous non-woven fabric can be used, such as a non-woven fabric made of glass fibers with a high melting point, polyethylene terephthalate fibers, etc. In addition, a coated separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and it can be optionally used in a single-layer or multi-layer structure.

[0077] Electrolyte

[0078] The lithium secondary battery of the present invention can contain an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten-type inorganic electrolyte as the electrolyte, and preferably includes an electrolyte containing an organic solvent and a lithium salt as the organic liquid electrolyte.

[0079] As the organic solvent, any organic solvent can be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can migrate. Specifically, as the organic solvent, the following can be used: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic solvents such as benzene or fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) or propylene carbonate (PC); alcohol solvents such as ethanol or isopropanol; nitriles such as R-CN (where R is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain double bonds, aromatic rings or ether bonds); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; sulfolane and the like. Among them, carbonate solvents are preferred, and a mixture of a cyclic carbonate (such as ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate compound (such as ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) is more preferred.

[0080] As the lithium salt, any compound can be used without particular limitation as long as it can provide lithium ions used in the lithium secondary battery. Specifically, the anion of the lithium salt can be selected from F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N -At least one of the components in the group, and as the lithium salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO2, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. can be used. The lithium salt is preferably used in a concentration range of 0.1 M to 4.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, and thus can exhibit excellent electrolyte performance, and lithium ions can migrate effectively.

[0081] In order to improve the life properties of the battery, suppress the reduction of the battery capacity, improve the discharge capacity of the battery, etc., the electrolyte can further contain, for example, one or more additives, such as, halogenated alkylene carbonate compounds (such as ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride. At this time, based on the total weight of the electrolyte, the content of the additive can be 0.1 wt% to 5 wt%.

[0082] Lithium secondary battery

[0083] When the lithium secondary battery of the present invention discharges for 15 seconds under a constant output condition of 900 W at SOC 35% and then discharges under a constant output condition of 1000 W, it may take more than 10 seconds, preferably more than 20 seconds, more preferably more than 30 seconds to reach SOC 0%.

[0084] Specifically, when the lithium secondary battery discharges for 18 seconds under a constant output condition of 900 W at SOC 35% and then discharges under a constant output condition of 1100 W, it may take more than 10 seconds, preferably more than 20 seconds, more preferably more than 30 seconds to reach SOC 0%.

[0085] At this time, the upper limit voltage can be 4.2 V, the lower limit voltage can be 2.5 V, and charging to the upper limit voltage can be carried out under constant current / constant voltage conditions, and discharging to SOC 35% can be carried out under constant output or constant current conditions.

[0086] In addition, the lithium secondary battery can be used in urban air mobility (UAM) devices. As described above, UAM absolutely requires a function that can generate a high output for a predetermined duration even at a low state of charge (SOC), so that UAM can land safely even when some batteries do not work properly. The fact that the lithium secondary battery of the present invention can be driven at an output of 1000 W or more for 10 seconds or more at an SOC of 35% or less indicates that even in a battery out (BO) state where one of the batteries is discharged, a landing time of 10 seconds or more can be ensured. Therefore, the lithium secondary battery is suitable for application to urban air mobility devices.

[0087] Meanwhile, discharging to an SOC of 35% means the duration during which UAM cruises and prepares to land. That is, before the subsequent transition, the battery is driven during the cruise process. The process of discharging at a constant output of 900 W for 15 seconds refers to the transition process of switching to the landing mode after the cruise. Driving at an output of 1000 W or more afterwards refers to the landing process. That is, the present invention relates to a lithium secondary battery that satisfies the minimum output conditions required for the transition and landing processes after UAM cruising.

[0088] Meanwhile, the shape of the lithium secondary battery is not particularly limited, but it can be cylindrical, square, pouch-shaped, coin-shaped, etc. using a can.

[0089] According to another embodiment of the present invention, a urban air mobility device including the lithium secondary battery is provided. Specifically, the urban air mobility device of the present invention may include a battery module or a battery pack including the lithium secondary battery as a unit cell.

[0090] Hereinafter, the present invention will be described in more detail with reference to specific examples.

[0091] Embodiment of the present invention

[0092] <Manufacturing Example: Manufacture of the Positive Electrode>

[0093] Manufacturing Example 1

[0094] Lithium composite transition metal oxides in the form of secondary particles having a composition of Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2 and D50 = 10 μm and lithium composite transition metal oxides in the form of secondary particles having a composition of Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2 and D50 = 5 μm were mixed at a weight ratio of 80:20 to prepare a bimodal positive electrode material.

[0095] The positive electrode material, carbon black as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed at a weight ratio of 97.6:1.0:1.4 in an N-methyl-2-pyrrolidone (NMP) solvent to prepare a positive electrode slurry with a solid content of 50 wt%. The positive electrode slurry was applied to one surface of an aluminum current collector with a thickness of 15 μm at a loading of 2.6 mAh / cm 2 and dried at 130 °C, then placed between two rolling rollers, and the gap between the rolling rollers was adjusted at 25 °C to fabricate a positive electrode with a porosity of 31% and an energy density of 256 Wh / kg.

[0096] Production Example 2

[0097] Lithium composite transition metal oxide in the form of secondary particles having a composition of Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2 and D50 = 10 μm and lithium composite transition metal oxide mixed with single particles and pseudo-single particles having a composition of Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2 and D50 = 3.5 μm were mixed at a weight ratio of 80:20 to prepare a bimodal positive electrode material.

[0098] The positive electrode material, carbon black as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed at a weight ratio of 97.6:1.0:1.4 in an NMP solvent to prepare a positive electrode slurry with a solid content of 50 wt%. The positive electrode slurry was applied to one surface of an aluminum current collector with a thickness of 15 μm at a loading of 3.3 mAh / cm 2 and dried at 130 °C, then placed between two rolling rollers, and the gap between the rolling rollers was adjusted at 25 °C to fabricate a positive electrode with a porosity of 26% and an energy density of 291 Wh / kg.

[0099] Production Example 3

[0100] Lithium composite transition metal oxide mixed with single particles and pseudo-single particles having a composition of Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2 and D50 = 3.5 μm as the positive electrode material, carbon black as the conductive material, and PVdF as the binder were mixed at a weight ratio of 97:1.2:1.8 in an NMP solvent to prepare a positive electrode slurry with a solid content of 50 wt%. The positive electrode slurry was applied at a loading of 3.0 mAh / cm 2The loading amount was applied to one surface of an aluminum current collector with a thickness of 15 μm, dried at 130 °C, and then placed between two rolling rollers. The gap between the rolling rollers was adjusted at 25 °C to fabricate a positive electrode with a porosity of 26% and an energy density of 270 Wh / kg.

[0101] Production Example 4

[0102] A mixture of single-particle and pseudo-single-particle lithium composite transition metal oxides as the positive electrode material, carbon black as the conductive material, and PVdF as the binder with a composition of Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2 and D50 = 3.5 μm was mixed in an NMP solvent at a weight ratio of 97:1.2:1.8 to prepare a positive electrode slurry with a solid content of 50% by weight. The positive electrode slurry was applied to one surface of an aluminum current collector with a thickness of 15 μm at a loading amount of 3.3 mAh / cm 2 , dried at 130 °C, and then placed between two rolling rollers. The gap between the rolling rollers was adjusted at 25 °C to fabricate a positive electrode with a porosity of 26% and an energy density of 280 Wh / kg.

[0103] Production Example 5

[0104] A mixture of single-particle and pseudo-single-particle lithium composite transition metal oxides as the positive electrode material, carbon black as the conductive material, and PVdF as the binder with a composition of Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2 and D50 = 3.5 μm was mixed in an NMP solvent at a weight ratio of 97:1.2:1.8 to prepare a positive electrode slurry with a solid content of 50% by weight. The positive electrode slurry was applied to one surface of an aluminum current collector with a thickness of 15 μm at a loading amount of 3.5 mAh / cm 2 , dried at 130 °C, and then placed between two rolling rollers. The gap between the rolling rollers was adjusted at 25 °C to fabricate a positive electrode with a porosity of 26% and an energy density of 280 Wh / kg.

[0105] Production Example 6

[0106] A mixture of single-particle and pseudo-single-particle lithium composite transition metal oxides as the positive electrode material, carbon black as the conductive material, and PVdF as the binder with a composition of Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02)O2 and a mixed single-particle and quasi-single-particle lithium composite transition metal oxide with D50 = 3.5 μm are mixed with carbon black as a conductive material and PVdF as a binder in a weight ratio of 97:1.2:1.8 in an NMP solvent to prepare a positive electrode paste with a solid content of 50 wt%. The positive electrode paste is applied to one surface of an aluminum current collector with a thickness of 15 μm at a loading of 3.3 mAh / cm 2 and dried at 130 °C, then placed between two rolling rollers, and the gap between the rolling rollers is adjusted at 25 °C to fabricate a positive electrode with a porosity of 21% and an energy density of 294 Wh / kg.

[0107] Comparative Production Example 1

[0108] A lithium composite transition metal oxide in the form of secondary particles having a composition of Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2 and D50 = 10 μm and a lithium composite transition metal oxide in the form of secondary particles having a composition of Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2 and D50 = 5 μm are mixed in a weight ratio of 80:20 to prepare a bimodal positive electrode material.

[0109] The positive electrode material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are mixed in a weight ratio of 97.6:1.0:1.4 in an NMP solvent to prepare a positive electrode paste with a solid content of 50 wt%. The positive electrode paste is applied to one surface of an aluminum current collector with a thickness of 15 μm at a loading of 4.0 mAh / cm 2 and dried at 130 °C, then placed between two rolling rollers, and the gap between the rolling rollers is adjusted at 25 °C to fabricate a positive electrode with a porosity of 26% and an energy density of 282 Wh / kg.

[0110] <Example: Fabrication of a Secondary Battery>

[0111] Example 1

[0112] A negative electrode active material (a mixture obtained by mixing natural graphite and artificial graphite in a weight ratio of 70:30), an SBR binder (M37, LG Chem.), and a conductive material (acetylene black) are mixed in a weight ratio of 96.0:3.0:1.0 in water as a solvent to prepare a negative electrode paste with a solid content of 60 wt%. The negative electrode paste is applied to a copper thin film with a thickness of 8 μm as a negative electrode current collector, dried, and rolled to fabricate a negative electrode.

[0113] A polyethylene separator with a thickness of 15 μm was disposed between the positive electrode fabricated in Production Example 1 and the above-described negative electrode to fabricate an electrode assembly, and then the electrode assembly was disposed in a pouch-type battery case, and thereafter an electrolyte solution was injected therein to fabricate a secondary battery. At this time, as the electrolyte solution, a solution prepared by dissolving 1 M LiPF6 in an organic solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 1:2 was used.

[0114] Examples 2 to 6

[0115] Secondary batteries of Examples 2 to 6 were fabricated by the same method as in Example 1, except that the positive electrodes fabricated in Production Examples 2 to 6 were used, respectively, instead of the positive electrode fabricated in Production Example 1.

[0116] Comparative Example 1

[0117] A secondary battery of Comparative Example 1 was fabricated by the same method as in Example 1, except that the positive electrode fabricated in Comparative Production Example 1 was used instead of the positive electrode fabricated in Production Example 1.

[0118] <Experimental Example: SOC Low-End Output Evaluation>

[0119] The secondary batteries prepared in the above Examples and Comparative Examples were charged at a constant current of 0.1 C to SOC 30% at 25°C, activated, and then degassed.

[0120] Thereafter, the secondary batteries were charged at a constant current / constant voltage condition of 0.33 C to 4.2 V, discharged at a constant output condition of 250 W to SOC 35%, and then discharged for 18 seconds at a constant output condition of about 900 W. Thereafter, while discharging the secondary batteries at a constant output condition of about 1100 W, the time required for the secondary batteries to reach 2.5 V (lower limit voltage) was measured.

[0121] The above process was equivalently repeated for SOC states of 30%, 25%, and 20% respectively to measure the time required to reach the lower limit voltage, and the time measured for each SOC was defined as the landing time, and the results are shown in Figure 1 as follows.

[0122] From Figure 1 the results, it can be confirmed that the secondary battery of Comparative Example 1 using a positive electrode with a loading of 4.0 mAh / cm 2 reached the lower limit voltage (SOC 0%) in less than 10 seconds when discharged under the conditions of Claim 1 at SOC 35%. This indicates that when this secondary battery is applied to UAM, it is difficult to ensure the time required for a safe landing in an emergency because the time for maintaining a high output in the low SOC portion is very short.

[0123] On the other hand, it can be confirmed that when the secondary batteries of Examples 1 to 6 using the positive electrode with a loading amount in the range of 2.5 mAh / cm 2 to 3.8 mAh / cm 2 discharge under the conditions of Claim 1 at SOC 35%, it takes more than 10 seconds to reach the lower limit voltage (SOC 0%), so it is suitable for application in UAM.

[0124] At the same time, it can be confirmed that compared with the positive electrodes of Production Example 1 and Comparative Example 1 that use lithium composite transition metal oxides in the form of secondary particles alone when preparing the positive electrode material, the positive electrodes of Production Examples 2 to 6 that use lithium composite transition metal oxides in the form of single particles and quasi-single particles exhibit significantly higher energy densities, specifically an energy density of 270 Wh / kg or more, and meet the output conditions of Claim 1 when applied to the battery. Among them, it can be confirmed that Examples 2 and 4 to 6 using the positive electrode with a loading amount in the range of 3.3 mAh / cm 2 to 3.5 mAh / cm 2 exhibit an energy density of 280 Wh / kg or more when applied to the battery and meet the output conditions of Claim 1.

Claims

1. A lithium secondary battery, comprising: The positive electrode, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector, and the loading amount is 2.5 mAh / cm 2 to 3.8 mAh / cm 2 ; a negative electrode including a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector; and a separator disposed between the positive electrode and the negative electrode, Among them, when the lithium secondary battery is discharged for 15 seconds under a constant output condition of 900 W at an SOC of 35% and then discharged under a constant output condition of 1000 W, it takes more than 10 seconds to reach an SOC of 0%.

2. The lithium secondary battery according to claim 1, wherein, The positive electrode active material layer includes a positive electrode active material having a bimodal particle size distribution composed of large particles and small particles having different D50s from each other, wherein the large particles and the small particles each independently include a lithium nickel-based oxide.

3. The lithium secondary battery according to claim 2, wherein The D50 of the large particles is 8 μm to 18 μm.

4. The lithium secondary battery according to claim 2, wherein, The D50 of the small particles is 2 μm to 7 μm.

5. The lithium secondary battery according to claim 2, wherein, The small particles include a lithium nickel-based oxide in the form of a single particle composed of one primary particle, or a lithium nickel-based oxide in the form of a quasi-single particle, which is a secondary particle agglomerated from 30 or fewer primary particles.

6. The lithium secondary battery according to claim 1, wherein, The positive electrode active material layer includes a positive electrode active material having a unimodal particle size distribution, wherein the positive electrode active material having a unimodal particle size distribution includes a lithium nickel-based oxide in the form of a single particle composed of one primary particle, or a lithium nickel-based oxide in the form of a quasi-single particle, which is a secondary particle agglomerated from 30 or fewer primary particles.

7. The lithium secondary battery according to claim 5 or claim 6, wherein, The average particle size of the primary particles is 1 μm to 5 μm.

8. The lithium secondary battery according to claim 2 or claim 6, wherein, The lithium nickel-based oxide is represented by the following formula 1: [Formula 1] Li 1+x (Ni a Co b Mn c M d )O2 wherein, in the above formula 1, M is at least one selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 1+x, a, b, c, and d are each atomic fractions of independent elements, wherein -0.2 ≤ x ≤ 0.2, 0.60 ≤ a < 1, 0 < b < 0.40, 0 < c < 0.40, 0 ≤ d ≤ 0.10, and a + b + c + d = 1.

9. The lithium secondary battery according to claim 1, wherein, The energy density of the positive electrode is 250 Wh / kg or more.

10. The lithium secondary battery according to claim 1, wherein, The porosity of the positive electrode active material layer is 20% to 32%.

11. The lithium secondary battery according to claim 1, wherein, When the lithium secondary battery is discharged for 18 seconds under a constant output condition of 900 W at an SOC of 35% and then discharged under a constant output condition of 1100 W, it takes more than 10 seconds to reach an SOC of 0%.

12. The lithium secondary battery according to claim 1, wherein, The lithium secondary battery is used in urban air transportation equipment.

13. An urban air transportation equipment, comprising the lithium secondary battery according to claim 1.

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