Lithium secondary battery

Abstract

A lithium secondary battery according to the present invention includes a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a negative electrode active material for which A, as represented by equation (1), is 6 or more. Equation (1): A = (TD)2 Х (0.5 Х D50) / BET, where TD, D50, and BET are respectively the tap density (unit: g / cm3), average particle diameter (μm), and specific surface area (m / g) of a negative electrode active material powder collected from the negative electrode obtained by disassembling the lithium secondary battery after activation of the lithium secondary battery.

Description

lithium secondary battery

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0195474 filed on December 24, 2024, and all contents disclosed in said Korean Patent Application are incorporated herein as part of this specification.

[0003]

[0004] Technology field

[0005] The present invention relates to a lithium secondary battery. Specifically, it relates to a lithium secondary battery with improved long-term storage performance.

[0006]

[0007] With the recent increase in demand for electric vehicles and the like, there is a growing need for automotive lithium-ion batteries with excellent long-term storage performance. This is because parking time accounts for an overwhelmingly large proportion of a vehicle's actual driving time.

[0008] While various factors can influence the lifespan characteristics of lithium-ion batteries, the physical properties of the anode active material significantly affect lifespan performance. In particular, the tap density, average particle size, and specific surface area of ​​the anode active material are interrelated, and since long-term storage performance is achieved within an appropriate range, it is important to control each property in a balanced manner.

[0009]

[0010] The present invention aims to solve the above-mentioned problems by providing a lithium secondary battery having excellent long-term storage performance, designed so that the tap density, average particle size, and specific surface area of ​​the negative electrode active material satisfy specific conditions.

[0011]

[0012] [1] The present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode comprises a negative electrode active material and the negative electrode active material has an A of 6 or more as represented by the following formula (1).

[0013] Equation (1): A = (TD) 2 Х (0.5 Х D 50 ) / BET

[0014] In the above equation (1), TD, D 50 and BET are, respectively, the tap density (unit: g / cm³) of the negative electrode active material powder collected from the negative electrode obtained by disassembling the lithium secondary battery after activating the lithium secondary battery. 3 ), average particle size (㎛) and specific surface area (m²) 2 / g) is.

[0015] [2] The present invention, in [1] above, wherein the tap density of the negative electrode active material is 0.8 g / cm³ 3 Up to 1.5 g / cm² 3 It provides a lithium secondary battery.

[0016] [3] The present invention, in [1] or [2], wherein the cathode active material D 50 A lithium secondary battery having a diameter of 10 μm to 20 μm is provided.

[0017] [4] The present invention is such that, in at least one of [1] to [3], the BET specific surface area of ​​the negative electrode active material is 1 m 2 / g to 4 m 2 Provides a lithium secondary battery with a g / g capacity.

[0018] [5] The present invention provides a lithium secondary battery comprising a graphite-based negative electrode active material in at least one of [1] to [4], wherein the negative electrode active material is a graphite-based negative electrode active material.

[0019] [6] The present invention provides a lithium secondary battery in which, in at least one of [1] to [5], the graphite-based negative electrode active material comprises artificial graphite and natural graphite.

[0020] [7] The present invention provides a lithium secondary battery in which, in at least one of [1] to [6], the graphite-based negative electrode active material comprises the artificial graphite and the natural graphite in a weight ratio of 40:60 to 60:40.

[0021]

[0022] The lithium secondary battery according to the present invention can have excellent long-term storage performance by suppressing voltage drop and resistance increase occurring inside the lithium secondary battery during long-term storage.

[0023]

[0024] FIG. 1 is a graph of discharge energy and discharge resistance of a lithium secondary battery according to one embodiment of the present invention.

[0025]

[0026] The present invention will be described in more detail below.

[0027] In the present invention, "tap density (TD)" refers to the tap density of the negative electrode active material (unit: g / cm³). 3 As a method for measuring the degree of sample packing per unit volume, it can be measured using a method generally used in the industry. For example, it may be the density (sample weight / volume) calculated through the change in volume by applying a constant force to a measuring container containing the sample in accordance with the measuring instruments and methods specified in ASTM B527. Specifically, using a Micromeritics GEOPYC 1360 tap density meter, a horizontal pressure of 1–3 N / cm² is applied to a 25.4 mm diameter chamber. 2 It can be measured by vibrating until a force is applied.

[0028] In the present invention, "average particle size (D 50"" is the average particle size (μm) of the negative electrode active material, which refers to the particle size corresponding to 50% of the volume cumulative particle size distribution of the negative electrode active material powder, and can be measured using the laser diffraction method. For example, after dispersing the negative electrode active material powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size measuring device (Malvern, Mastersizer 3000+ Ultra), irradiated with ultrasound of about 10 kHz at an output of 10 mW, and then a volume cumulative particle size distribution graph is obtained, and the particle size at the point where the volume cumulative amount is 50% is determined from the obtained volume cumulative particle size distribution graph.

[0029] In the present invention, "specific surface area (BET)" is the BET specific surface area (m²) of the negative electrode active material. 2 / g), which is the cathode active material measured by the BET method, specifically using Micromeritics’ ASAP 2020, can be calculated from the amount of gas adsorbed by the element at the liquefaction temperature (77K and 87K, respectively) for nitrogen or argon.

[0030]

[0031] The inventors have completed the present invention by discovering that, in order to devise a lithium secondary battery with excellent long-term storage performance, if the tap density, average particle size, and specific surface area of ​​the negative electrode active material are designed to satisfy specific conditions, the battery to which the negative electrode active material is applied can have excellent long-term storage performance with low levels of voltage drop and resistance increase.

[0032]

[0033] lithium secondary battery

[0034] The lithium secondary battery of the present invention comprises a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a negative electrode active material, and the negative electrode active material has an A of 6 or more as represented by the following formula (1).

[0035] Equation (1): A = (TD)2 Х (0.5 Х D 50 ) / BET

[0036] In the above equation (1), TD, D 50 and BET are, respectively, the tap density (unit: g / cm³) of the negative electrode active material powder collected from the negative electrode obtained by disassembling the lithium secondary battery after activating the lithium secondary battery. 3 ), average particle size (㎛) and specific surface area (m²) 2 / g) is.

[0037] In the above equation (1), A is an indicator representing the long-term storage performance of a lithium-ion battery, and reflects the tap density, average particle size, and specific surface area, which are representative physical properties of the negative electrode active material, with weights for high-temperature storage performance.

[0038] The above A may be 6 or higher, preferably 6.1 to 8.5, and more preferably 6.3 to 7.6. When A satisfies the above range, the negative electrode active material has appropriate tap density, average particle size, and specific surface area, thereby suppressing the voltage drop and resistance increase levels that occur during long-term storage, and thus enabling excellent energy density and resistance characteristics. If A is less than 6, the negative electrode active material has too low a tap density and average particle size or too high a specific surface area, which may increase side reactions between the negative electrode active material and the electrolyte, thereby reducing long-term storage performance.

[0039]

[0040] Meanwhile, the tap density (TD) of the negative active material powder in the above equation (1) is 0.8 g / cm³ 3 Up to 1.5 g / cm² 3 It may be, preferably 1.0 g / cm³ 3 Up to 1.4 g / cm³ 3 It may be, and more preferably 1.03 g / cm³ 3 Up to 1.35 g / cm³ 3It may be possible. Within the above tap density range, the battery may have high energy density and be advantageous for storage characteristics. On the other hand, if the above tap density is too high, internal stress due to volume change during charging and discharging increases, which may shorten the battery life. If the above tap density is too low, the battery capacity may decrease, and internal resistance may increase due to reduced contact between active materials.

[0041] Average particle size (D of the negative active material powder of the above equation (1) 50 The average particle size may be 10 μm to 20 μm, preferably 12 μm to 17 μm, and more preferably 13 μm to 16 μm. If the average particle size is too large, the ion transfer rate and electrochemical reaction rate may decrease. If the average particle size is too small, the contact area with the electrolyte increases, and an excessive SEI (Solid Electrolyte Interphase) layer may be formed.

[0042] The specific surface area (BET) of the cathode active material powder in the above equation (1) is 1 m 2 / g to 4 m 2 It can be / g, and preferably 1 m 2 / g to 3 m 2 It can be / g, and more preferably 1 m 2 / g to 2 m 2 It may be / g. If the above specific surface area is too large, the reaction at the electrode-electrolyte interface increases, which may lead to the excessive formation of the SEI layer. If the above specific surface area is too small, the contact area between the electrode and the electrolyte decreases, which may reduce electrochemical activity.

[0043]

[0044] The lithium secondary battery according to the present invention comprises a negative electrode, a positive electrode, and an electrolyte, and may further comprise a separator as needed. Each component will be described below.

[0045]

[0046] cathode

[0047] The cathode according to the present invention comprises a cathode active material. Specifically, the cathode according to the present invention comprises a cathode composite layer disposed on at least one surface of a current collector, wherein the cathode composite layer may comprise a cathode active material and, if necessary, may comprise a cathode conductive material and a cathode binder.

[0048] The above-mentioned negative electrode active material may include a graphite-based negative electrode active material, and the graphite-based negative electrode active material may include artificial graphite and natural graphite.

[0049] The above artificial graphite may be included in an amount of 40% to 60% by weight, preferably 45% to 55% by weight, and more preferably 47% to 53% by weight, based on the total weight of the graphite-based negative electrode active material. When the content of artificial graphite in the graphite-based negative electrode active material satisfies the above range, the rate characteristics and processability of the negative electrode are excellent, and if the content of artificial graphite is too low, the structural stability of the negative electrode may decrease, and if it is too high, processability during the manufacture of the negative electrode may be reduced.

[0050] When the graphite-based cathode active material is a mixture of artificial graphite and natural graphite, the weight ratio of artificial graphite to natural graphite may be 40:60 to 60:40, preferably 45:55 to 55:45, more preferably 47:53 to 53:47. When the mixing ratio of artificial graphite and natural graphite satisfies the above range, the rate characteristics and processability of the cathode can be exhibited excellently.

[0051] The total content of the graphite-based negative electrode active material may be 80 to 99 weight%, preferably 85 to 99 weight%, and more preferably 90 to 99 weight% with respect to the total weight of the negative electrode composite layer.

[0052]

[0053] Meanwhile, the above-mentioned cathode conductive material is used to impart conductivity to the cathode, and can be used without special restrictions as long as it is used as a conductive material for a lithium secondary battery. Specific examples of the above-mentioned cathode conductive material include carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. Preferably, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube, or a combination thereof may be used as the above-mentioned cathode conductive material, and it is more preferable to use point-type conductive materials and linear-type conductive materials together in terms of improving conductivity. At this time, the point-shaped conductive material is a material having a particle shape in which the contact form with the negative electrode active material is in the form of a point, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc., and the linear conductive material is a material in which the contact form with the negative electrode active material is in the form of a line, such as carbon fiber, carbon nanotube, etc.

[0054] The above cathode conductive material may typically be included in an amount of 1 to 30 weight%, preferably 1 to 20 weight%, and more preferably 1 to 10 weight% based on the total weight of the cathode composite layer.

[0055]

[0056] Next, the above-mentioned negative electrode binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector, and any material used as a negative electrode binder for a lithium secondary battery can be used without special restrictions. Specific examples of negative electrode binders include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0057] The above cathode binder may be included in an amount of 1 to 30 weight%, preferably 1 to 20 weight%, more preferably 1 to 10 weight% based on the total weight of the cathode composite layer.

[0058] Meanwhile, the above-mentioned cathode composite layer may be formed as a single-layer structure or a multi-layer structure. When the cathode composite layer is a multi-layer structure composed of two or more layers, the types and / or contents of the cathode active material, cathode binder, and / or cathode conductive material in each layer may differ from one another. By forming the cathode active material layer as a multi-layer structure and varying the composition of each layer, the performance characteristics of the battery, such as rapid charging performance and output characteristics, can be appropriately controlled.

[0059]

[0060] The above-mentioned cathode can be manufactured according to a conventional cathode manufacturing method. Specifically, the cathode according to the present invention can be manufactured by preparing a graphite-based cathode active material as a cathode active material, dissolving or dispersing the cathode active material, a cathode binder, a cathode conductive material, and / or a dispersant in a solvent to prepare a cathode slurry composition, then applying the cathode slurry onto a cathode current collector and drying and rolling, or by casting the cathode slurry composition onto a separate support and then laminating the film obtained by peeling off from the support onto a cathode current collector.

[0061] At this time, the above-mentioned negative current collector may be any negative current collectors commonly used in the relevant technical field, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy may be used. The above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0062] As the solvent for the above-mentioned cathode slurry, common solvents used in the art for manufacturing cathode slurries, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, water, or mixtures thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the cathode active material, conductive material, binder, and dispersant, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that provides excellent thickness uniformity when coated for cathode manufacturing thereafter.

[0063]

[0064] anode

[0065] The anode according to the present invention comprises an anode composite layer comprising an anode active material, an anode conductive material, and an anode binder. The anode can be manufactured by a method of forming an anode composite layer by coating an anode slurry comprising an anode active material, an anode binder, an anode conductive material, and a solvent, etc., onto an anode current collector and then rolling it.

[0066]

[0067] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used.

[0068]

[0069] The above-mentioned cathode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(where, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2Examples include )O2(wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are each atomic fractions of independent elements, such that 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc., and any one or more of these compounds may be included.

[0070] Specifically, the above positive active material may include a lithium transition metal oxide represented by the following [Chemical Formula 1].

[0071] [Chemical Formula 1]

[0072] Li x Ni a Co b M 1 c M 2 d O2

[0073] In the above chemical formula 1, the M 1 It is one or more selected from Mn and Al, and preferably, for durability, it may be Mn or a combination of Mn and Al.

[0074] M 2 It may be one or more selected from the group consisting of Zr, Y, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S.

[0075] The above x represents the atomic fraction of lithium in the lithium transition metal oxide, and may be 0.90≤x≤1.1, preferably 0.95≤x≤1.08, and more preferably 1.0≤x≤1.08.

[0076] The above a represents the atomic fraction of nickel among metal elements excluding lithium in the lithium transition metal oxide, and may be 0.50≤a<1.0, 0.60≤a≤0.95, 0.65≤a≤0.95, or 0.80≤a≤0.95. When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0077] The above b represents the atomic fraction of cobalt among the metal elements excluding lithium in the lithium transition metal oxide, where 0 <b<0.5, 0<b<0.4, 또는 0.01≤b≤0.3일 수 있다.

[0078] The above c is M among the metal elements excluding lithium in the lithium transition metal oxide. 1 Representing the atomic fraction of, 0 <c<0.5, 0<c<0.4, 또는 0.01≤c≤0.3일 수 있다.

[0079] The above d is M among the metal elements excluding lithium in the lithium transition metal oxide. 2 It represents the atomic fraction of , which can be 0≤d≤0.1 or 0≤d≤0.05.

[0080] The above positive active material may be included in an amount of 60 to 99 weight%, preferably 70 to 99 weight%, and more preferably 80 to 98 weight% based on the total weight of the positive composite layer.

[0081]

[0082] The above-mentioned anode binder is a component that assists in the bonding of the anode active material and the anode conductive material, as well as in the bonding to the current collector.

[0083] Examples of such anode binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers.

[0084] Typically, the anode binder may be included in an amount of 1 to 20 weight%, preferably 1 to 15 weight%, and more preferably 1 to 10 weight% based on the total weight of the anode composite layer.

[0085] The above-mentioned positive electrode conductive material is a component intended to further enhance the conductivity of the positive electrode active material, and is not particularly limited as long as it is conductive without causing chemical changes in the battery. For example, carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; fluorocarbon powder; conductive powders such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0086] Typically, the anode conductive material may be included in an amount of 1 to 20 weight%, preferably 1 to 15 weight%, and more preferably 1 to 10 weight% based on the total weight of the anode composite layer.

[0087]

[0088] The solvent for the anode slurry may include organic solvents such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), and acetone, and may be used in an amount that results in a desirable viscosity when including the anode active material, anode binder, and anode conductive material. For example, the concentration of the solid component, which includes the anode active material and optionally the anode binder and anode conductive material, may be 50 to 95 weight%, preferably 70 to 95 weight%, and more preferably 70 to 90 weight%.

[0089]

[0090] electrolytes

[0091] The electrolyte used in the present invention may be any of the various electrolytes usable in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., and the types thereof are not particularly limited.

[0092] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0093] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0094] The above lithium salt can be used without special limitations as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, or combinations thereof. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0 M, more preferably 0.1 to 3.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0095] Meanwhile, in addition to the above components, the electrolyte may additionally include additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. For example, the electrolyte may include at least one additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulfone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0096] Examples of the above-mentioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate.

[0097] Examples of the above-mentioned halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0098] Examples of the above sulfone-based compounds include at least one compound selected from the group consisting of 1,3-propane sulfone (PS), 1,4-butane sulfone, ethen sulfone, 1,3-propene sulfone (PRS), 1,4-butene sulfone, and 1-methyl-1,3-propene sulfone.

[0099] Examples of the above sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0100] Examples of the above-mentioned phosphate compounds include one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyl trimethylsilyl phosphate, trimethylsilyl phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0101] Examples of the above borate compounds include tetraphenylborate, lithium oxalyl difluoroborate (LiODFB), and lithium bisoxalate toborate (LiB(C2O4)2, LiBOB).

[0102] Examples of the above nitrile compounds include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0103] Examples of the above benzene-based compounds include fluorobenzene, examples of the above amine-based compounds include triethanolamine or ethylenediamine, and examples of the above silane-based compounds include tetravinylsilane.

[0104] The above lithium salt-based compound is a compound different from the lithium salt included in the above-mentioned non-aqueous electrolyte, and examples include lithium difluorophosphate (LiDFP), LiPO2F2, or LiBF4.

[0105] The above additive may be included in an amount of 0.1 to 10 weight%, preferably 0.1 to 5 weight%, based on the total weight of the electrolyte.

[0106]

[0107] Separator

[0108] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions; any separator typically used in lithium secondary batteries can be used without any special restrictions. Specifically, the separator may be a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength.

[0109]

[0110] A lithium secondary battery according to the present invention as described above can be used to manufacture a battery pack. The battery pack comprises an assembly of lithium secondary batteries electrically connected according to the present invention and a pack housing that accommodates the same, wherein the pack housing may include a busbar for electrically connecting the lithium secondary batteries, a cooling unit, an external terminal, etc. The battery pack may be mounted in a vehicle. The vehicle may be, for example, an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle. The vehicle includes a four-wheeled vehicle or a two-wheeled vehicle. In particular, the lithium secondary battery according to the present invention has high energy density, excellent rapid charging performance, and excellent storage performance, so it can be usefully used as a battery for an electric vehicle.

[0111]

[0112] The present invention will be explained in more detail below through specific embodiments. However, these embodiments are intended only to aid in understanding the invention and do not limit the scope of the invention in any way to these embodiments.

[0113]

[0114] Example 1

[0115] Cathode Manufacturing

[0116] A cathode slurry was prepared by adding cathode active material : cathode conductive material : cathode binder to distilled water in a weight ratio of 97.7 : 0.4 : 1.9.

[0117] As the cathode active material of the above cathode slurry, artificial graphite (Shinzoom, HRG-5Q) and natural graphite (Shenzhen XFH, DT-1) were mixed in a weight ratio of 50:50 and used.

[0118] Single-walled CNTs were used as the cathode conductive material. Additionally, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed in a weight ratio of 1:0.9 and used as the cathode binder. The cathode was manufactured by applying the cathode slurry to both sides of a copper current collector, followed by drying and rolling.

[0119]

[0120] Secondary Battery Manufacturing

[0121] The positive electrode is the positive electrode active material (LiNi 0.8 Co 0.1 Mn 0.1 O2): Anode conductive material (Super P): Anode binder (PVdF) was added to N-methylpyrrolidone in a weight ratio of 98:0.6:1.4 to prepare an anode slurry, and then the anode slurry was applied to both sides of an aluminum current collector, followed by drying and rolling.

[0122] An electrode assembly was manufactured by interposing a porous polyethylene separator between the above-mentioned cathode and the above-mentioned anode, and after placing the electrode assembly in a battery case, an electrolyte solution was prepared by dissolving 1.2M LiPF6 in an organic solvent mixed in a volume ratio of 20:5:75 of ethylene carbonate:ethyl methyl carbonate:diethyl carbonate. Then, the battery was charged to SOC 64% at a high temperature (55°C) rate of 0.1°C, followed by an aging process (42 hours) to perform an activation process.

[0123]

[0124] Example 2

[0125] In the above Example 1, except that the artificial graphite used was QCG-N2 from ShanShan, a negative electrode and a lithium secondary battery were manufactured in the same manner as in Example 1.

[0126]

[0127] Comparative Example 1

[0128] In the above Example 1, except that PC2-A3 from Shinzoom was used as the artificial graphite, a negative electrode and a lithium secondary battery were manufactured in the same manner as in Example 1.

[0129]

[0130] Comparative Example 2

[0131] A negative electrode and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the artificial graphite used in Example 1 was E-15 from Zichen.

[0132]

[0133] Comparative Example 3

[0134] A negative electrode and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the artificial graphite used in Example 1 was ZY-2 from Zichen.

[0135]

[0136] Experimental Example 1: Measurement of Cathode Properties

[0137] The lithium secondary batteries prepared in Examples 1 to 2 and Comparative Examples 1 to 3 were disassembled to separate the negative electrode, and the surface of the negative electrode was scraped with a razor blade to obtain a negative electrode composite layer powder. Then, the negative electrode active material powder was obtained by dispersing the mixture in a DMC solution and stirring at a speed of 150 rpm for 5 minutes.

[0138] Next, the tap density, average particle size, and specific surface area of ​​the cathode active material powder were measured according to the method described below.

[0139] (1) Tap density: Cathode active material 3.5 cm 3 After collecting the sample, it was placed in a sample container for measuring tap density marked with a volume, and the tap density was calculated by measuring the volume after tapping using a tap density meter (GEOPYC 1360 from Micromeritics).

[0140] (2) Average particle size: After dispersing 1.0 g of negative electrode active material in a dispersion medium, the sample was introduced into a laser diffraction particle size measuring device (Malvern, Mastersizer 3000+ Ultra) and irradiated with ultrasound of approximately 10 kHz at an output of 10 W to measure the D of each cathode material powder 50 Measured.

[0141] (3) Specific surface area: 6.0 g of cathode active material was measured using Micromeritics’ ASAP 2020 at a nitrogen liquefaction temperature (77 K) from the amount of nitrogen gas adsorbed.

[0142] The measurement results of the tap density, average particle size, and BET specific surface area of ​​the cathode active material and the A value are shown in [Table 1] below. The above A was calculated using the following equation (1).

[0143] Equation (1): A = (TD) 2 × (0.5 × D 50 ) / BET

[0144] In the above equation (1), TD, D 50 and BET are, respectively, the tap density (unit: g / cm³) of the negative electrode active material powder collected from the negative electrode obtained by disassembling the lithium secondary battery after activating the lithium secondary battery. 3 ), average particle size (㎛) and specific surface area (m²) 2 / g) is.

[0145]

[0146] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Tap density (g / cm³) 3 )1.05 1.25 1.10 94 1.05 Average particle size (D 50 , μm)13.4 15.6 17.0 17.5 12.0 Specific surface area (m 2 / g)1.121.672.291.463.5A6.67.34.55.31.9

[0147]

[0148] Experimental Example 2: Measurement of Long-term Storage Performance

[0149] The lithium secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 3 were accelerated to age by being stored at 55°C after charging in 4.2V CC-CV mode, and the discharge energy and resistance were measured at 0, 4, 8, and 12 weeks.

[0150] At this time, the discharge energy was measured at 24°C in a voltage range of 4.2 to 2.5V, and the resistance was measured as a 1C rate resistance in the discharge direction at 50% SOC. The measurement results are shown in Figure 1 and [Table 2] below.

[0151]

[0152] Figure 1 shows the measurement results of discharge energy and discharge resistance of lithium secondary batteries with the cathodes of Examples 1 and 2 and Comparative Examples 1 to 3. In Table 2 below, the measurement results of discharge energy and 1C rate resistance of lithium secondary batteries with the cathodes of Examples 1 and 2 and Comparative Examples 1 to 3 before accelerated aging and after 12 weeks of accelerated aging were compared.

[0153]

[0154] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Discharge Energy (Wh) 16.6 16.7 15.7 15.8 15.3 Discharge Energy Retention Rate (%) After Accelerated Aging 95.5 96.1 90.7 91.6 88.1 C Rate Resistance (mΩ) 35.9 36.7 38.0 37.7 40.0 C Rate Increase Rate (%) After Accelerated Aging 11.4 11.0 19.4 15.1 23.1

[0155] Referring to Figure 1 and Table 2, it can be seen that Examples 1 and 2, in which A is 6 or higher, have higher discharge energy and lower 1C rate resistance even after 12 weeks of accelerated aging compared to Comparative Examples 1 to 3, in which A is less than 6.

[0156] In addition, referring to Tables 1 and 2, it can be seen that as tap density and average particle size values ​​increase, capacity retention rate and resistance increase rate improve, and as specific surface area values ​​increase, capacity retention rate and resistance increase rate improve. Based on this trend, the above equation (1) can be derived by applying weights to the variables.

Claims

1. Includes an anode, a cathode, and an electrolyte, The above-mentioned negative electrode comprises a negative electrode active material, and the above-mentioned negative electrode active material is a lithium secondary battery in which A is 6 or more as represented by the following formula (1). 식 (1): A = (TD) 2 X (0.5 X D 50 ) / FORMER In the above equation (1), TD, D 50 and BET are, respectively, the tap density (unit: g / cm³) of the negative electrode active material powder collected from the negative electrode obtained by disassembling the lithium secondary battery after activating the lithium secondary battery. 3 ), average particle size (㎛) and specific surface area (m²) 2 / g) is.

2. In Paragraph 1, The tap density of the above negative electrode active material is 0.8 g / cm³ 3 Up to 1.5 g / cm² 3 lithium secondary battery.

3. In Paragraph 1, D of the above negative electrode active material 50 A lithium secondary battery with a thickness of 10 μm to 20 μm.

4. In Paragraph 1, The BET specific surface area of ​​the above cathode active material is 1 m² 2 / g to 4 m 2 lithium secondary battery in g.

5. In Paragraph 1, The above negative electrode active material is a lithium secondary battery comprising a graphite-based negative electrode active material.

6. In Paragraph 5, The above graphite-based negative electrode active material is a lithium secondary battery comprising artificial graphite and natural graphite.

7. In Paragraph 6, The above graphite-based negative electrode active material is a lithium secondary battery comprising the above artificial graphite and natural graphite in a weight ratio of 40:60 to 60:40.

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