Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising: an anode comprising an anode mixture layer containing an anode active material; a cathode comprising a cathode mixture layer containing a cathode active material; and an electrolyte, wherein the anode mixture layer comprises an Si-C composite, and X defined by relation (1) satisfies 0.5 to 0.6. Relation (1): In relation (1), A is the value of the ionic conductivity of the electrolyte extracted from the lithium secondary battery, which is measured in mS / cm, B is the viscosity of the electrolyte extracted from the lithium secondary battery, which is measured in cP, and T is the tortuosity of the anode.

Description

lithium secondary battery

[0001] The present application claims the benefit of priority based on Korean Patent Application No. 10-2024-0194806 filed on December 23, 2024 and Korean Patent Application No. 10-2025-0205562 filed on December 19, 2025, and all contents disclosed in said Korean patent application documents are incorporated herein as part of the specification.

[0002] The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery with excellent rapid charging performance.

[0003] A lithium secondary battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive and negative electrodes include an active material capable of lithium ion intercalation and deintercalation.

[0004] The electrode of a lithium secondary battery is manufactured by applying an electrode slurry containing an electrode active material, a conductive material, and a binder onto an electrode current collector, drying it, rolling the electrode until it reaches a desired thickness, and vacuum drying it.

[0005] With the recent increase in demand for electric vehicles and the like, there is a growing need for batteries with high energy density and excellent fast-charging performance. However, the fast-charging performance of lithium-ion batteries is difficult to predict because it is determined by the complex interplay of cathode, anode, and electrolyte designs. Furthermore, as various fast-charging protocols are being developed, it is difficult to determine whether a specific design offers superior or inferior fast-charging performance. Consequently, developing lithium-ion batteries with excellent fast-charging capabilities requires significant cost and time.

[0006] The present invention aims to solve the above-mentioned problems by providing a lithium secondary battery with excellent rapid charging performance, wherein the electrolyte and negative electrode of the lithium secondary battery are designed to satisfy specific conditions.

[0007] [1] The present invention provides a lithium secondary battery comprising a cathode comprising a cathode composite layer comprising a cathode active material, a positive electrode comprising a positive electrode composite layer comprising a positive electrode active material, and an electrolyte, wherein the cathode composite layer comprises a Si-C composite and X, defined by the following formula (1), satisfies 0.4 to 0.7.

[0008] Equation (1):

[0009]

[0010] In the above equation (1), A is the ionic conductivity of the electrolyte extracted from the lithium secondary battery measured in units of mS / cm, B is the viscosity of the electrolyte extracted from the lithium secondary battery measured in units of cP, and T is the curvature of the negative electrode.

[0011] [2] The present invention provides a lithium secondary battery according to [1], wherein the negative electrode composite layer further comprises a graphite-based negative electrode active material.

[0012] [3] The present invention provides a lithium secondary battery in which, in [1] or [2], the Si-C composite has a structure in which Si is deposited or embedded within a carbon matrix.

[0013] [4] The present invention provides a lithium secondary battery in which, in [2] or [3], the graphite-based negative electrode active material comprises artificial graphite and natural graphite.

[0014] [5] The present invention provides a lithium secondary battery in which, in at least one of [2] to [4], the Si-C composite and the graphite-based negative electrode active material are included in a weight ratio of 5:95 to 20:80.

[0015] [6] The present invention provides a lithium secondary battery in which the negative electrode curvature (T) is 2 to 5 in at least one of [1] to [5].

[0016] [7] The present invention provides a lithium secondary battery in which, in at least one of [1] to [6], the resistance of the negative electrode composite layer is 0.02 to 0.05 Ω·cm.

[0017] [8] The present invention, in at least one of [1] to [7], wherein the cathode loading amount is 10 to 14 mg / cm² 2 It provides a lithium secondary battery.

[0018] [9] The present invention provides a lithium secondary battery in which the resistance of the positive electrode composite layer is 4 to 6 Ω·cm, in at least one of [1] to [8].

[0019]

[0010] The present invention, in at least one of [1] to [9], wherein the anode loading amount is 24 to 26 mg / cm² 2 It provides a lithium secondary battery.

[0020]

[0011] The present invention provides a lithium secondary battery in which, in at least one of [1] to

[0010] , the ionic conductivity (A) of the electrolyte extracted from the lithium secondary battery is 10 mS / cm to 14 mS / cm.

[0021]

[0012] The present invention provides a lithium secondary battery in which, in any one of [1] to

[0011] , the viscosity (B) of the electrolyte extracted from the lithium secondary battery is 2.5 to 3.5 cP.

[0022]

[0013] The present invention provides a lithium secondary battery having an energy retention rate of 90% or more when the lithium secondary battery is charged and discharged 130 cycles under 1C charging and 1C discharging conditions, in any one of [1] to

[0012] .

[0023] A lithium secondary battery according to the present invention, in which the negative electrode comprises a Si-C composite and the negative electrode and electrolyte are designed to satisfy specific conditions, can achieve excellent rapid charging performance by balancing the movement of lithium ions in the positive and negative electrodes during high-rate charging and discharging.

[0024] Figure 1 is a graph showing the high-rate charge / discharge cycle characteristics of lithium secondary batteries manufactured by the examples and comparative examples.

[0025] The present invention will be described in more detail below.

[0026] In the present invention, "cathode curvature (T)" is a value defined by the following formula (1) as an indicator representing the degree to which the internal flow path of the cathode composite layer is bent.

[0027] Equation (A): Cathode curvature (T) = L e / L0

[0028] In the above equation (A), L0 is the theoretical resistance to lithium migration within the cathode composite layer, which can be calculated through the loading amount of the cathode composite layer, the thickness of the cathode composite layer, and the conductivity of the electrolyte. e is the actual distance that lithium ions move within the cathode composite layer, and is a value calculated by measuring the electrode pore resistance through AC impedance measurement after manufacturing a cell with a cathode / separator / cathode structure (symmetric cell).

[0029] In the present invention, "electrolyte ion conductivity" is a value measured by an ion conductivity meter (mettle toledo S230) after taking 10 μL of electrolyte and placing it in a vial.

[0030] In the present invention, “electrolyte viscosity” is a value measured at room temperature using a rotational viscometer (DV35LV, Brookfield) and a low-viscosity spindle.

[0031] In the present invention, “anode resistance” and “cathode resistance” can be measured by the following method. First, an electrode assembly is disassembled to separate the anode and cathode, and then each of the anode and cathode is stamped out to a size of 5 cm × 5 cm, washed with dimethyl carbonate for about 10 seconds, and dried in the atmosphere for 30 minutes to remove foreign substances, thereby preparing an anode sample and a cathode sample. Then, probes of a multi-probe resistor are inserted into the surface of each of the anode sample and cathode sample, and a current of 1 μA to 10 mA is applied to measure the voltage. By using this to calculate the sheet resistance, the anode resistance and cathode resistance are measured. In the present invention, a multi-probe resistor with 46 probes was used, and the anode resistance and cathode resistance were measured by applying a current of 10 μA.

[0032] In the present invention, the “loading amount” can be measured by the following method. First, the electrode assembly is disassembled to separate the anode and the cathode, and then the anode and cathode are each stamped out to a size of 5 cm × 5 cm to produce an anode sample and a cathode sample. Then, the weight of each sample is measured using an electron low rate with an effective range of 0.001 g, and after subtracting the weight of the current collector from the weight of the sample, the area of ​​the sample (25 cm²) 2 The loading amount can be measured by dividing it into ). In the present invention, for accuracy, five samples were prepared by stamping five times per electrode, and the average value of the loading amount measured in each sample was evaluated as the loading amount.

[0033]

[0034] As a result of repeated research to develop a lithium secondary battery with excellent rapid charging performance, the inventors discovered that when a Si-C composite is used as the negative electrode active material and the curvature of the negative electrode, electrolyte viscosity, and ion conductivity satisfy specific conditions, the balance of lithium ion and electron movement in the positive and negative electrodes is appropriately maintained during high-rate charging and discharging, thereby achieving the effect of improved rapid charging performance, and thus completed the present invention.

[0035]

[0036] Specifically, the lithium secondary battery according to the present invention comprises a negative electrode including a negative electrode composite layer including a negative electrode active material, a positive electrode including a positive electrode composite layer including a positive electrode active material, and an electrolyte, wherein the negative electrode composite layer includes a Si-C composite, and X defined by the following formula (1) satisfies 0.4 to 0.7, preferably 0.5 to 0.6.

[0037] Equation (1):

[0038]

[0039] In the above equation (1), A is the ionic conductivity of the electrolyte extracted from the lithium secondary battery measured in units of mS / cm, B is the viscosity of the electrolyte extracted from the lithium secondary battery measured in units of cP, and T is the curvature of the negative electrode.

[0040]

[0041] When X satisfies the above range, the balance of lithium ion and electron movement at the anode and cathode is properly maintained, resulting in excellent rapid charging performance.

[0042] Specifically, during rapid charging, each resistance element increases rapidly due to the fast reaction speed. In this case, the reaction speed of the negative electrode must be appropriately controlled to match the reaction speed of the positive electrode so that the resistance balance between the positive and negative electrodes is properly maintained, thereby improving rapid charging performance. In the present invention, rapid charging performance is improved by designing a battery such that the type of negative electrode active material, the negative electrode curvature, the electrolyte viscosity, and the ion conductivity, which are major factors affecting the reaction speed of the negative electrode, satisfy specific relationships.

[0043] When X is less than 0.4, the reaction rate at the cathode is slower than the reaction rate at the anode, resulting in reduced rapid charging performance, and when X exceeds 0.7, the reaction rate at the cathode is faster than the reaction rate at the anode, resulting in reduced rapid charging performance. Specifically, when X is less than 0.4, the cathode flexibility and / or electrolyte viscosity is high or the electrolyte ion conductivity is low. In this case, the liquid diffusion resistance or charge transfer resistance increases, reducing lithium ion mobility, and consequently, the reaction rate at the cathode becomes slower than the reaction rate at the anode. On the other hand, when X exceeds 0.7, the cathode flexibility and / or electrolyte viscosity is low or the electrolyte ion conductivity is high. In this case, the liquid diffusion resistance or charge transfer resistance decreases, increasing lithium ion mobility, and consequently, the reaction rate at the cathode becomes faster than the reaction rate at the anode.

[0044]

[0045] Hereinafter, each component of the lithium secondary battery of the present invention will be described in more detail.

[0046]

[0047] cathode

[0048] The cathode according to the present invention comprises a cathode composite layer comprising a cathode active material. Specifically, the cathode comprises a cathode current collector; and a cathode composite layer disposed on at least one surface of the cathode current collector and comprising a cathode active material. The cathode composite layer may further comprise a cathode conductive material and a cathode binder in addition to the cathode active material.

[0049] The above-mentioned cathode active material comprises a Si-C composite and, optionally, may further comprise a graphite-based cathode active material. Preferably, the above-mentioned cathode active material may comprise a Si-C composite and a graphite-based cathode active material.

[0050] The above Si-C composite is a material having a structure in which silicon and carbon are composited by depositing or embedding Si within a carbon matrix. Compared to silicon oxide (SiO), which was conventionally used as a Si-based negative electrode active material, it has lower irreversible capacity and superior conductivity. Therefore, when using a Si-C composite, higher energy density can be achieved compared to when using silicon oxide, and rapid charging performance can be improved due to a faster reaction rate with lithium ions.

[0051] Preferably, the Si-C composite may have a Si grain size of 20 nm or less, preferably 1 nm to 20 nm, and more preferably 1 nm to 18 nm. When the grain size of the Si-C composite satisfies the above range, excellent improvement effects on cell resistance characteristics and lifespan characteristics are observed.

[0052] In addition, the above Si-C composite is D 50 This can be 1㎛ to 15㎛, preferably 2㎛ to 10㎛, more preferably 3㎛ to 10㎛. In addition, the Si-C composite is D 10 This can be 5㎛ or less, preferably 1 to 5㎛, and D 90This can be 6㎛ to 20㎛, preferably 6㎛ to 15㎛. When the particle size distribution of the Si-C composite satisfies the above range, the cathode electrode density is increased, and high energy density can be achieved.

[0053] Meanwhile, while using a Si-C composite as the negative electrode active material can improve capacity and rapid charging performance, there is a problem where lifespan characteristics deteriorate due to volume changes in the Si-C composite during charging and discharging. When a Si-C composite is used together with a graphite-based negative electrode active material, the graphite-based material suppresses the volume change of the Si-C composite during charging and discharging, thereby improving lifespan characteristics.

[0054] The graphite-based negative electrode active material comprises artificial graphite. Preferably, the graphite-based negative electrode active material may be a mixture of artificial graphite and natural graphite.

[0055] 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 the volume expansion of the Si-C composite during charging and discharging is suppressed, thereby improving the lifespan characteristics.

[0056] 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, and 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 are excellent, and the volume change of the Si-C composite during charging and discharging can be effectively suppressed.

[0057] Meanwhile, in the present invention, the Si-C composite and the graphite-based negative electrode active material may be included in a weight ratio of 5:95 to 20:80, preferably 5:95 to 15:85, and more preferably 5:95 to 10:90. When the mixing ratio of the Si-C composite and the graphite-based negative electrode active material satisfies the above range, both rapid charging performance and lifespan characteristics are excellent.

[0058] The total content of the total negative electrode active material, which is the sum of the graphite-based negative electrode active material and the Si-C composite, 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.

[0059] 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.

[0060] The above cathode conductive material may typically be included in an amount of 0.01 to 30 weight%, preferably 0.01 to 20 weight%, and more preferably 0.01 to 10 weight% based on the total weight of the cathode composite layer.

[0061] 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.

[0062] The above cathode binder may be included in an amount of 0.1 to 30 weight%, preferably 0.1 to 20 weight%, more preferably 0.1 to 10 weight% based on the total weight of the cathode composite layer.

[0063] 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.

[0064] The above-mentioned cathode can be manufactured according to a conventional cathode manufacturing method. Specifically, the cathode according to the present invention may be manufactured by preparing a Si-C composite and a graphite-based cathode active material as cathode active materials, 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, applying the cathode slurry onto a cathode current collector, and then 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.

[0065] As the above-mentioned negative current collector, negative current collectors generally used in the relevant technical field may be used, for example, copper, stainless steel, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm. If necessary, fine irregularities may be formed on the surface of the above-mentioned negative current collector to strengthen the bonding strength 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.

[0066] 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 if it 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 can exhibit excellent thickness uniformity when coated for cathode manufacturing thereafter.

[0067] The cathode according to the present invention may have a curvature (T) of 2 to 5, preferably 2.2 to 4, and more preferably 2.5 to 3. When the cathode curvature satisfies the above range, an effect of improving rapid charging performance can be obtained.

[0068] The above cathode may have a cathode composite layer resistance of 0.02 to 0.05 Ω·cm, preferably 0.023 to 0.04 Ω·cm, and more preferably 0.025 to 0.035 Ω·cm. When the cathode resistance satisfies the above range, it is possible to suppress the occurrence of a bottleneck in the movement of lithium ions and electrons during rapid charging caused by the cathode resistance.

[0069] The above cathode has a loading amount of 10 to 14 mg / cm² 2 , preferably 11 to 13 mg / cm² 2 , more preferably 12.2 ~ 12.7 mg / cm² 2 It may be possible. When the cathode loading amount satisfies the above range, the cathode curvature is appropriately formed, and an effect of improving rapid charging performance can be obtained.

[0070]

[0071] anode

[0072] The anode according to the present invention comprises an anode composite layer comprising an anode active material. Specifically, the anode comprises an anode current collector; and an anode composite layer disposed on at least one surface of the anode current collector and comprising an anode active material. The anode composite layer may further comprise an anode conductive material and an anode binder in addition to the anode active material.

[0073] 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(Nip2 Co q2 Mn r2 M s2 Examples 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.

[0074] Specifically, the above positive active material may include a lithium transition metal oxide represented by the following [Chemical Formula 1].

[0075] [Chemical Formula 1]

[0076] Li x Ni a Co b M 1 c M 2 d O2

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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≤0.98, 0.65≤a≤0.98, 0.80≤a≤0.98, or 0.83≤a≤0.98. When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0081] 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, 0.01≤b≤0.3 또는 0.01≤b≤0.17일 수 있다.

[0082] 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, 0.01≤c≤0.3 또는 0.01≤c≤0.17일 수 있다.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] Typically, the anode binder may be included in an amount of 0.1 to 20 weight%, preferably 0.1 to 15 weight%, and more preferably 0.1 to 10 weight% based on the total weight of the anode composite layer.

[0088] 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.

[0089] Typically, the anode conductive material may be included in an amount of 0.01 to 20 weight%, preferably 0.01 to 15 weight%, and more preferably 0.01 to 10 weight% based on the total weight of the anode composite layer.

[0090]

[0091] The above anode may be manufactured according to a conventional anode manufacturing method. Specifically, the above anode may be manufactured by coating an anode slurry containing an anode active material, an anode binder, an anode conductive material, and a solvent onto an anode current collector and then rolling to form an anode composite layer, or by casting the anode slurry onto a separate support and then laminating a film obtained by peeling from the support onto an anode current collector.

[0092] The anode current collector mentioned above may be any anode current collector commonly used in the relevant technical field, for example, aluminum, stainless steel, nickel, titanium, calcined carbon, aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy. The anode current collector may typically have a thickness of 3 μm to 500 μm. If necessary, fine irregularities may be formed on the surface of the anode current collector to strengthen the bonding strength of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0093] 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%.

[0094] The anode may have an anode composite layer resistance of 4 to 6 Ω·cm, preferably 4.2 to 5.8 Ω·cm, and more preferably 4.5 to 5.5 Ω·cm. When the anode composite layer resistance satisfies the above range, the reaction rate of the anode during rapid charging can be appropriately controlled.

[0095] The above anode has a loading amount of 24 to 26 mg / cm² 2 , preferably 23.3 ~ 24.7 mg / cm² 2 , more preferably 23.5 ~ 24.5 mg / cm² 2 It may be possible. When the anode loading amount satisfies the above range, the reaction rate of the anode during rapid charging can be appropriately controlled.

[0096]

[0097] electrolytes

[0098] In the present invention, the electrolyte may include an organic solvent and a lithium salt.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] Examples of the above-mentioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate.

[0103] Examples of the above-mentioned halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0104] 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.

[0105] Examples of the above sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0106] 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.

[0107] Examples of the above borate compounds include tetraphenylborate, lithium oxalyl difluoroborate (LiODFB), and lithium bisoxalate toborate (LiB(C2O4)2, LiBOB).

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] For example, the electrolyte of the present invention may use a mixed solvent of ethylene carbonate and dimethyl carbonate as the organic solvent, use LiPF6 as the lithium salt, and use vinylene carbonate as an additive, but is not limited thereto.

[0113] The electrolyte according to the present invention may have an ionic conductivity (A) of 10 mS / cm to 14 mS / cm, preferably 10.5 mS / cm to 14 mS / cm, and more preferably 11 mS / cm to 12 mS / cm. When the ionic conductivity of the electrolyte satisfies the above range, the reaction rate of the anode and cathode can be appropriately controlled to improve rapid charging performance.

[0114] The electrolyte according to the present invention may have a viscosity (B) of 2.5 cP to 3.5 cP, preferably 2.6 cP to 3.4 cP, and more preferably 2.7 cP to 3.3 cP. When the electrolyte viscosity satisfies the above range, the cathodic reaction rate can be appropriately controlled. If the electrolyte viscosity is too low, the cathodic reaction rate may increase excessively, and if the electrolyte viscosity is too high, the cathodic reaction rate may decrease excessively.

[0115] The ionic conductivity and viscosity of the electrolyte mentioned above are values ​​measured after the activation of the lithium secondary battery by extracting the electrolyte from the lithium secondary battery. In this case, the electrolyte extraction can be performed by drilling a hole in the case of the lithium secondary battery and extracting the electrolyte through centrifugation. As organic solvents, lithium salts, and additives are consumed during the activation process, the physical properties (ionic conductivity, viscosity) of the electrolyte change before and after activation. Since lithium secondary batteries in actual use are activated batteries, designing a cell using the ionic conductivity and viscosity of the electrolyte before activation results in a difference from the performance during actual operation. Therefore, in this invention, the ionic conductivity and viscosity of the electrolyte after activation were used as variables.

[0116]

[0117] Separator

[0118] 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.

[0119] The lithium secondary battery according to the present invention as described above has excellent lifespan characteristics even during high-rate charging and discharging, with an energy retention rate of 90% or more, preferably 92% or more, when charged and discharged 130 times under 1C charging and 1C discharging conditions.

[0120]

[0121] 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 and excellent rapid charging performance, so it can be usefully used as a battery for an electric vehicle.

[0122]

[0123] The present invention will be explained in more detail below through specific embodiments. However, the following embodiments are intended only to aid in understanding the present invention, and the scope of the present invention is not limited to these embodiments.

[0124]

[0125] Example 1

[0126] Cathode Manufacturing

[0127] A first cathode slurry was prepared by adding cathode active material, cathode conductive material, and cathode binder to distilled water in a weight ratio of 97:0.5:2.5.

[0128] As the cathode active material of the first cathode slurry, a Si-C composite and a graphite-based cathode active material were mixed in a weight ratio of 5:95 and, as the graphite-based cathode active material, artificial graphite and natural graphite were mixed in a weight ratio of 50:50. Single-walled CNTs were used as the cathode conductive material. In addition, as the cathode binder, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed in a weight ratio of 1.5:1.0.

[0129] A second cathode slurry was prepared by adding cathode active material, cathode conductive material, and cathode binder to distilled water in a weight ratio of 98:0.5:1.5.

[0130] As the cathode active material of the second cathode slurry, a Si-C composite and a graphite-based cathode active material were mixed in a weight ratio of 5:95 and, as the graphite-based cathode active material, artificial graphite and natural graphite were mixed in a weight ratio of 50:50. Single-walled CNTs were used as the cathode conductive material. In addition, as the cathode binder, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed in a weight ratio of 0.5:1.0.

[0131] After sequentially applying the first cathode slurry and the second cathode slurry onto a copper current collector, drying and rolling are performed, and vacuum drying is carried out to obtain a cathode loading amount of 13 mg / cm² 2 A phosphorus cathode was manufactured.

[0132]

[0133] <Anode Manufacturing>

[0134] A cathode active material, cathode conductive material, and cathode binder were added to N-methylpyrrolidone in a weight ratio of 97:1.5:1.5 to prepare a cathode slurry. LiNi was used as the cathode active material. 0.9 Co 0.05 Mn 0.05O2 was used, and Super P was used as the anode conductive material. In addition, PVdF was used as the anode binder.

[0135] After applying the above anode slurry onto an aluminum current collector, it is dried and rolled to achieve an anode loading of 25 mg / cm² 2 A phosphorus anode was manufactured.

[0136]

[0137] Electrolytes

[0138] An electrolyte was prepared by dissolving LiPF6 to a concentration of 1.5 M in a non-aqueous organic solvent mixed with ethylene carbonate and dimethyl carbonate in a volume ratio of 30:70, and then adding 4% by weight of vinylene carbonate.

[0139]

[0140] Lithium secondary battery manufacturing

[0141] An electrode assembly was manufactured by interposing a separator between the anode and cathode manufactured as described above, laminating them, and then winding them. The electrode assembly was then placed in a cylindrical battery case, the electrolyte was injected, the battery was charged at a constant current of 0.2C to 4.2V, stored at 60℃ for 24 hours, and then discharged to 2.5V to activate it, thereby manufacturing a lithium secondary battery.

[0142]

[0143] Example 2

[0144] A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that when manufacturing the first negative electrode slurry and the second negative electrode slurry, a mixture of artificial graphite and natural graphite was used as the graphite-based negative electrode active material in a weight ratio of 45:55.

[0145] Example 3

[0146] A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that when preparing the first negative electrode slurry and the second negative electrode slurry, a mixture of artificial graphite and natural graphite in a weight ratio of 45:55 was used as the graphite-based negative electrode active material, and when preparing the electrolyte, a non-aqueous organic solvent mixed in a volume ratio of ethylene carbonate and dimethyl carbonate in a volume ratio of 30:70 was used instead of a non-aqueous organic solvent mixed in a volume ratio of ethylene carbonate and dimethyl carbonate in a volume ratio of 30:40:30.

[0147]

[0148] Comparative Example 1

[0149] A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that when manufacturing the first negative electrode slurry and the second negative electrode slurry, a mixture of artificial graphite and natural graphite was used as the graphite-based negative electrode active material in a weight ratio of 30 to 70.

[0150]

[0151] Comparative Example 2

[0152] A positive electrode, a negative electrode, and a lithium secondary battery were prepared in the same manner as in Example 1, except that a non-aqueous organic solvent mixed with methyl acetate and dimethyl carbonate in a volume ratio of 30:70 was used instead of a non-aqueous organic solvent mixed with ethylene carbonate and dimethyl carbonate in a volume ratio of 30:70 when preparing the electrolyte.

[0153]

[0154] Experimental Example 1: Measurement of Physical Properties

[0155] The cathode bending (T), anode resistance, cathode resistance, electrolyte ion conductivity (A), and electrolyte viscosity (B) were measured in the following manner. The measurement results are shown in Table 1 below.

[0156] (1) Curvature (T): An electrode assembly was manufactured by interposing a separator between two negative electrodes, the electrode assembly was placed in a battery case, an electrolyte that does not contain lithium salt (ethylene carbonate : ethylmethyl carbonate = 3 : 7 v / v%) was injected, and the symmetric coin cell was manufactured by aging for 12 to 24 hours. Then, a current of 0.1 to 1000000 Hz and 10 Mv was applied to the manufactured symmetric coin cell, and the electrode pore resistance was measured using a graph measured by EIS (Electrochemical Impedance Spectroscopy) to calculate the average movement distance Ls of lithium ions inside the negative electrode composite layer, and the curvature was calculated by dividing this by the thickness L0 of the negative electrode composite layer.

[0157] (2) Anode resistance and cathode resistance (unit: Ω·cm): The electrode assembly was disassembled to separate the anode and cathode, and each anode and cathode was stamped out to a size of 5 cm × 5 cm. After washing with dimethyl carbonate for about 10 seconds, the anode and cathode samples were prepared by drying in the atmosphere for 30 minutes to remove foreign substances. Then, probes of a multi-probe resistor with 46 probes were inserted into the surface of each anode and cathode sample, and a current of 10 μA was applied to measure the voltage, and the sheet resistance was calculated using this.

[0158] (3) Electrolyte ion conductivity (unit: mS / cm): After making a hole in the case of the lithium secondary battery of the example and comparative example, the electrolyte was extracted by centrifugation, and 10 μl of the extracted electrolyte was placed in a vial and the ion conductivity of the electrolyte was measured using an ion conductivity meter (mettle toledo S230).

[0159] (5) Electrolyte viscosity (unit: cP): After drilling holes in the cases of the lithium secondary batteries of the examples and comparative examples and extracting the electrolyte by centrifugation, the electrolyte viscosity at room temperature was measured using a rotational viscometer (DV35LV, Brookfield) and a low-viscosity spindle.

[0160]

[0161] Cathode Flexibility (T) Anode Resistance Cathode Resistance Electrolyte Ion Conductivity (A) Electrolyte Viscosity (B) X Example 1 2.8 5.10.0 28 11.28 3.0 0.5 69 Example 2 3.3 5.30.0 27 11.1 13.1 0.4 22 Example 3 3.3 5.10.0 27 13.9 2.9 0.6 36 Comparative Example 14.8 5.30.0 30 11.36 3.0 0.2 68 Comparative Example 22.8 5.00.0 28 14.2 2.2 1.2 22

[0162]

[0163] Experimental Example 2:

[0164] The lithium secondary batteries prepared according to Examples 1 to 3 and Comparative Examples 1 to 2 were charged at 24°C in 1C, CCCV mode with a maximum charging voltage of 4.25V and a 0.05C cut-off condition, and then discharged to 2.5V in 1C, CC mode, with each cycle comprising 130 cycles, to measure the energy retention rate (%). The measurement results are shown in Figure 1.

[0165] Through FIG. 1, it can be confirmed that the lithium secondary batteries of Examples 1 to 3, in which X defined by Equation (1) satisfies 0.4 to 0.7, maintain a high capacity retention rate during high-rate charging and discharging compared to the lithium secondary batteries of Comparative Examples 1 to 2, which demonstrates that the rapid charging performance of Examples 1 to 3 is excellent.

Claims

1. A cathode comprising a cathode composite layer comprising a cathode active material, an anode comprising an anode composite layer comprising an anode active material, and an electrolyte, and The above cathode composite layer includes a Si-C composite, and A lithium secondary battery in which X, defined by the following formula (1), satisfies 0.4 to 0.

7. Equation (1): In the above equation (1), A is the value of the ionic conductivity of the electrolyte extracted from the lithium secondary battery measured in units of mS / cm, B is the viscosity of the electrolyte extracted from the lithium secondary battery measured in units of cP, and T is the curvature of the negative electrode.

2. In Paragraph 1, A lithium secondary battery in which the above-mentioned negative electrode composite layer further comprises a graphite-based negative electrode active material.

3. In Paragraph 1, The above Si-C composite is a lithium secondary battery having a structure in which Si is deposited or embedded within a carbon matrix.

4. In Paragraph 2, A lithium secondary battery in which the above graphite-based negative electrode active material includes artificial graphite and natural graphite.

5. In Paragraph 2, A lithium secondary battery comprising the above Si-C composite and the above graphite-based negative electrode active material in a weight ratio of 5:95 to 20:

80.

6. In Paragraph 1, A lithium secondary battery having a negative electrode curvature (T) of 2 to 5.

7. In Paragraph 1, The above-described negative electrode composite layer is a lithium secondary battery having a resistance of 0.02 to 0.05 Ω·cm.

8. In Paragraph 1, The above cathode has a loading amount of 10 to 14 mg / cm² 2 lithium secondary battery.

9. In Paragraph 1, The above positive composite layer is a lithium secondary battery having a resistance of 4 to 6 Ω·cm.

10. In Paragraph 1, The above anode has a loading amount of 24 to 26 mg / cm² 2 lithium secondary battery.

11. In Paragraph 1, A lithium secondary battery having an ionic conductivity (A) of an electrolyte extracted from the above lithium secondary battery of 10 mS / cm to 14 mS / cm.

12. In Paragraph 1, A lithium secondary battery in which the viscosity (B) of the electrolyte extracted from the above lithium secondary battery is 2.5 to 3.5 cP.

13. In Paragraph 1, The above lithium secondary battery is a lithium secondary battery having an energy retention rate of 90% or more when charged and discharged 130 times under 1C charging and 1C discharging conditions.

Images