Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery designed to have high electrode density and suppress the occurrence of a short circuit. The lithium secondary battery according to the present invention comprises: a cathode including a cathode active material; an anode including an anode active material; a separator interposed between the cathode and the anode; and an electrolyte, wherein the R.D value defined by equation (1) is 180 or less. Equation (1): R.D = (Rac × Dc) / Ts In equation (1), Rac is the average roughness of the surface of the cathode measured in nm units, Dc is the electrode density of the cathode measured in g / cc units, and Ts is the thickness of the separator measured in μm units.

Description

lithium secondary battery

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0196376 filed on December 24, 2024, and all contents disclosed in said Korean Patent Application are incorporated herein as part of this specification.

[0002] The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery designed to suppress the occurrence of short circuit defects.

[0003] In a lithium secondary battery, the separator physically separates the positive and negative electrodes to prevent contact. If the adhesion between the separator and the electrode is poor, a void space may form at the interface between the electrode and the separator, resulting in an uneven current distribution and the formation of lithium dendrites. Additionally, during the charging and discharging process, the volume expansion of the electrode may cause movement of the electrode or the separator, which may lead to a short circuit.

[0004] In particular, as the demand for high-energy density batteries has recently increased, electrodes are often manufactured by mixing large and small particles to increase electrode density. However, when two or more types of active materials with different particle sizes are used in this way, the surface roughness of the electrode surface increases, which reduces adhesion to the separator and leads to an increasing trend of short circuits.

[0005] Therefore, there is a need to develop electrodes that have sufficient electrode density while minimizing short circuits.

[0006] The present invention aims to solve the above-mentioned problems by providing a lithium secondary battery capable of suppressing short circuits by designing the surface roughness of the positive electrode active material, the thickness of the separator, and the electrode density of the positive electrode to satisfy specific conditions.

[0007] [1] The present invention provides a lithium secondary battery comprising: a positive electrode including a positive active material; a negative electrode including a negative active material; a separator interposed between the positive electrode and the negative electrode; and an electrolyte, wherein the RD value defined by the formula (1) is 180 or less.

[0008] Equation (1): RD = (Ra c × D c ) / T s

[0009] In the above equation (1), the Ra c is the average surface roughness of the anode measured in nm units, and the D c is the electrode density of the anode measured in units of g / cc, and Ts is the thickness of the separator measured in units of μm.

[0010] [2] The present invention, in [1] above, Ra c / T S A lithium secondary battery with a diameter of 20 to 52 is provided.

[0011] [3] The present invention provides a lithium secondary battery according to [1] or [2], wherein the average surface roughness of the anode is 300 nm to 610 nm.

[0012] [4] The present invention provides a lithium secondary battery in which, in at least one of [1] to [3], the electrode density of the positive electrode is 3.0 g / cc to 3.8 g / cc.

[0013] [5] The present invention provides a lithium secondary battery in which the porosity of the positive electrode is 20% to 25% in at least one of [1] to [4].

[0014] [6] The present invention provides a lithium secondary battery in which, in at least one of [1] to [5], the positive electrode comprises a single-particle positive electrode active material comprising 30 or fewer nodules as a first positive electrode active material.

[0015] [7] The present invention provides a lithium secondary battery according to [6], wherein the positive electrode comprises at least 20% by weight of the first positive electrode active material based on the total weight of the positive electrode active material.

[0016] [8] The present invention provides a lithium secondary battery in which, in [6] or [7], the first positive active material comprises a lithium nickel-based oxide represented by the following [Chemical Formula 1].

[0017] [Chemical Formula 1]

[0018] Li 1+x Ni a Co b M 1 c M 2 d O2

[0019] In the above chemical formula 1, M 1 is Mn, Al, or a combination thereof, and M 2 ... comprises one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta, Sr, and Nb, and -0.2≤x≤0.5, 0.5≤a<1, 0 <b<0.5, 0<c<0.5, 및 0≤d≤0.2이다.

[0020] [9] The present invention provides a lithium secondary battery according to [8], wherein in the formula 1, 0.5≤a≤0.8, 0.01≤b<0.5, 0.01≤c<0.5, and 0≤d≤0.1.

[0021]

[0010] The present invention provides a lithium secondary battery in which, in at least one of [6] to [9], the average particle size of the first positive active material is 3 μm to 10 μm.

[0022]

[0011] The present invention provides a lithium secondary battery, wherein, in at least one of [6] to

[0010] , the positive electrode is a second positive electrode active material, and further comprises a positive electrode active material in the form of a secondary particle in which 31 or more primary particles are aggregated.

[0023]

[0012] The present invention provides a lithium secondary battery in which, in

[0011] the second positive active material comprises a lithium nickel-based oxide represented by the following [Chemical Formula 2].

[0024] [Chemical Formula 2]

[0025] Li 1+x' Ni a' Co b' M 3 c' M 4 d' O2

[0026] In the above chemical formula 2, M 3 is Mn, Al, or a combination thereof, and M 4 ... comprises one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and -0.2≤x'≤0.5, 0.5≤a'<1, 0 <b'<0.5, 0<c'<0.5, 및 0≤d'≤0.2이다.

[0027]

[0013] The present invention provides a lithium secondary battery in which, in

[0012] or

[0013] , the average particle size of the second positive active material is 7 μm to 20 μm.

[0028]

[0014] The present invention provides a lithium secondary battery in which, in at least one of [1] to

[0013] , the thickness of the separator is 5 μm to 15 μm.

[0029]

[0015] The present invention provides a lithium secondary battery, wherein, in at least one of [1] to

[0014] , the separator comprises a porous substrate; and a coating layer disposed on at least one surface of the porous substrate and comprising ceramic particles.

[0030] The lithium secondary battery according to the present invention is designed such that the positive electrode surface roughness, positive electrode density, and separator thickness satisfy a specific relationship, thereby increasing the adhesion between the separator and the positive electrode, and enabling the suppression of short circuits while maintaining a relatively high level of electrode density.

[0031] Figure 1 is a diagram showing the results of observing the surface of anode A prepared according to Preparation Example 1 using an optical profiler.

[0032] Figure 2 is a diagram showing the results of observing the surface of anode B prepared according to Preparation Example 2 using an optical profiler.

[0033] Figure 3 is a diagram showing the results of observing the surface of anode C prepared according to Manufacturing Example 3 using an optical profiler.

[0034] The terms or words used in this invention should not be interpreted as being limited to their ordinary or dictionary meanings, and should be interpreted in a meaning and concept consistent with the technical spirit of this invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0035] In the present invention, the “surface average roughness” can be measured by measuring the 3D shape of the anode surface using an optical profiler and then obtaining the absolute value of the average height from the measured roughness profile.

[0036] In the present invention, “electrode density (unit: g / cc)” is the ratio of the electrode weight to the electrode volume, and can be measured by manufacturing a sample by stamping the electrode into a specific area (e.g., 5cm x 5cm), measuring the thickness and mass of the manufactured sample, and then using the value obtained by subtracting the thickness and mass of the current collector from the measured thickness and mass.

[0037] In the present invention, the “porosity (%)” can be calculated as (1 - electrode density / electrode true density) × 100. Electrode density can be measured by dividing the electrode weight by the electrode volume after measuring the electrode weight and volume, and electrode true density can be measured using a Gas Pycnometer. A Gas Pycnometer is a device capable of measuring density by placing a sample of known weight into a sample chamber and injecting helium or nitrogen gas to determine the volume occupied by the sample excluding pores. Specifically, the volume of the sample can be measured from the pressure change between the sample chamber containing the sample and a reference chamber with a known volume, and then the density value of the sample can be calculated by applying the ideal gas state equation (PV=nRT).

[0038] In the present invention, "single particle type" refers to a particle composed of 30 or fewer nodules, and is a concept that includes a single particle composed of one nodule and a pseudo-single particle which is a complex of 2 to 30 nodules.

[0039] The above “nodule” is a sub-grain unit constituting a single particle and a pseudo-single particle, and may be a single crystal that does not have crystalline grain boundaries, or a polycrystalline one in which no grain boundaries appear to exist when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope.

[0040] In the present invention, "secondary particle type" refers to a particle formed by aggregating a plurality of primary particles, for example, tens to hundreds of primary particles. Specifically, the secondary particle may be an aggregate of 31 or more primary particles.

[0041] In the present invention, the term “particle” is a concept that includes any one or all of a single particle, a pseudo-single particle, a primary particle, a nodule, and a secondary particle.

[0042] In the present invention, the average particle size (Dmean) of nodules or primary particles refers to the arithmetic mean value calculated after measuring the particle sizes of nodules or primary particles observed in scanning electron microscope or backscatter electron diffraction (EBSD) images. For example, the particle size of the nodules or primary particles can be measured by manufacturing an electrode using the positive electrode active material powder to be measured, then cutting the electrode before rolling using ion milling (HITACHI IM-500, acceleration voltage 6kV) to obtain a cross-section, and then measuring the number of primary particles on a scale of approximately 400±10 using an FE-SEM (JEOL JSM7900F) device under conditions of acceleration voltage 15kV and WD 15 mm.

[0043] In the present invention, "average particle size D50" refers to a particle size corresponding to 50% of the volume cumulative amount of the volume cumulative particle size distribution of the powder to be measured, and can be measured using a laser diffraction method. For example, the powder to be measured can be measured by dispersing it in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasound of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then determining the particle size corresponding to 50% of the volume cumulative amount.

[0044]

[0045] The present invention will be described in more detail below.

[0046] As a result of repeated research to develop a lithium secondary battery capable of achieving high energy density while suppressing short circuits, the inventors discovered that it is possible to achieve high energy density and suppress short circuits when the ratio of the anode surface roughness to the separator thickness and the anode density satisfy a specific range, thereby completing the present invention.

[0047] Specifically, the lithium secondary battery according to the present invention has an RD value defined by the following formula (1) that is 180 or less, 175 or less, or 172 or less. The RD value defined by the above formula (1) may be 50 or more, 70 or more, 80 or more, or 90 or more.

[0048] Equation (1): RD = (Ra c × D c ) / T s

[0049] In the above equation (1), the Ra c is the average roughness of the anode surface measured in nm units, and D c is the electrode density of the anode measured in units of g / cc, and Ts is the thickness of the separator measured in units of μm.

[0050] When the RD value defined by Equation (1) satisfies the above numerical range, the surface roughness of the anode is low, so damage to the separator is prevented, effectively suppressing the occurrence of a short circuit, and the electrode density is maintained at a relatively high level, allowing for the realization of high energy density. If the RD value exceeds 180, the surface roughness of the anode is high, so the separator is damaged and the risk of a short circuit increases. On the other hand, if the RD value is too small, safety increases but energy density may decrease, so it is desirable that the RD value be 50 or higher.

[0051] The lithium secondary battery according to the present invention is Ra c / T sGa may be 20 to 52, 25 to 52, 27 to 52, or 20 to 35. Ra c / T s When the above range is satisfied, the short-circuit suppression effect is excellent. Ra c / T s If the value is less than 20, the separator thickness becomes too thin, the separator strength decreases, and the short-circuit suppression effect decreases; if the value exceeds 52, the adhesion between the separator and the anode decreases as the anode surface roughness increases, and the short-circuit suppression effect decreases.

[0052] The average surface roughness (Ra) of the above anode c ) may be, for example, 610 nm or less, 600 nm or less, 590 nm or less, or 580 nm or less. The lower the surface roughness of the anode, the better the short-circuit suppression effect. Considering energy density and anode processability, the average surface roughness (Ra) of the anode c ) may be 300nm or larger, 310nm or larger, or 320nm or larger.

[0053] The average surface roughness of the anode described above can be controlled by appropriately adjusting the particle size, particle shape, and rolling conditions of the anode active material constituting the anode composite layer. For example, when small particles are used as the anode active material, the surface roughness of the anode appears lower compared to when large particles are used. Additionally, when the rolling line pressure is high during anode manufacturing, the surface roughness of the anode appears lower than when the rolling line pressure is low.

[0054] Considering the anode manufacturing processability and energy density, the anode has an electrode density (D c ) may be 3.0g / cc to 3.8g / cc, preferably 3.0g / cc to 3.7g / cc, more preferably 3.3g / cc to 3.7g / cc.

[0055] The above anode may have a porosity of 15% to 30%, 15% to 25%, 20% to 30%, or 20% to 27%. When the anode porosity satisfies the above range, lithium movement within the anode proceeds smoothly, and excellent capacity characteristics are exhibited.

[0056] The thickness of the separator (Ts) may be 5㎛ to 15㎛, 7㎛ to 15㎛, or 7㎛ to 12㎛. If the separator thickness is too thin, the separator strength decreases, reducing the short-circuit suppression effect, and if it is too thick, the energy density of the battery may decrease.

[0057]

[0058] A lithium secondary battery according to the present invention comprises a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and an electrolyte. Hereinafter, each component of the lithium secondary battery according to the present invention will be described in more detail.

[0059]

[0060] anode

[0061] The above-mentioned anode may be structured such that an anode composite layer is formed on one or both sides of an anode current collector, and the anode composite layer comprises an anode active material and may optionally further comprise an anode conductive material and an anode binder.

[0062] For example, the anode can be manufactured by preparing an anode slurry by dispersing an anode active material, an anode conductive material, and an anode binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, applying the anode slurry to one or both sides of an anode current collector, removing the solvent from the anode slurry through a drying process, and then rolling.

[0063] Various positive current collectors used in the relevant technical field may be used as the positive current collector. For example, the positive current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. The positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the positive current collector to increase the adhesion of the positive active material. The positive current collector may be used in various forms, such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0064] In the present invention, the positive electrode active material may include a single-particle type positive electrode active material as the first positive electrode active material. The single-particle type positive electrode active material is a particle-shaped positive electrode active material comprising 30 or fewer nodules, and specifically, includes a lithium nickel-based oxide having a quasi-single-particle form consisting of a single particle made of one nodule and / or an aggregate of 30 or fewer nodules.

[0065] Conventional lithium nickel-based oxides were generally in the form of spherical secondary particles formed by the aggregation of tens to hundreds of primary particles. However, lithium nickel-based oxides in the form of secondary particles with many aggregated primary particles have high particle surface roughness, and consequently, the surface roughness of the cathode manufactured using them is also high. In particular, when a mixture of large and small secondary particles is used, the difference in particle size between the particles is added to the high surface roughness of the particles themselves, resulting in an even higher surface roughness of the cathode.

[0066] In contrast, single-particle cathode active materials have less curvature on the particle surface compared to secondary-particle cathode active materials, resulting in lower surface roughness. Therefore, manufacturing a cathode using a single-particle cathode active material can reduce the surface roughness of the cathode.

[0067] In addition, single-particle cathode active materials have higher particle strength compared to secondary-particle cathode active materials, resulting in less particle breakage during rolling and fewer side reactions with the electrolyte. Furthermore, because single-particle cathode active materials have a smaller number of nodules, which are the lower particle units constituting the particles, there is less change due to volume expansion and contraction during charging and discharging, and consequently, the occurrence of internal cracks is significantly reduced. Therefore, when single-particle cathode active materials are included as cathode active materials, the surface roughness of the cathode can be reduced, and the amount of gas generated and metal leaching caused by particle breakage and internal cracking can be significantly reduced.

[0068] The above single-particle type cathode active material may be included in an amount of 20% or more by weight, preferably 20% to 100% by weight, more preferably 30% to 100% by weight, more preferably 50% to 100% by weight, and even more preferably 50% to 95% by weight of the total cathode active material included in the cathode. When the content of the single-particle type cathode active material among the total cathode active material satisfies the above range, the surface roughness of the cathode is lowered, the adhesion with the separator increases, and the occurrence of short circuits is effectively suppressed.

[0069] The above single-particle type cathode active material may have an average particle size of nodules of 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less, for example, 0.5 μm to 5 μm, preferably 1 μm to 5 μm, more preferably 2 μm to 5 μm. When the average particle size of nodules satisfies the above range, a single-particle type cathode active material with excellent electrochemical properties can be formed. If the average particle size of nodules is too small, the effect of suppressing particle breakage during rolling decreases, and if the average particle size of nodules is too large, the lithium diffusion path inside the particle becomes longer, increasing resistance and potentially degrading output characteristics.

[0070] The above single-particle type positive electrode active material is D 50This can be 3㎛ to 10㎛, preferably 3㎛ to 8㎛. D of the single-particle type cathode active material 50 If it is too large, the lithium mobility inside the positive electrode active material particles decreases, which can have an adverse effect on capacity and output characteristics, and if it is too small, the phase stability of the positive electrode slurry decreases, which can reduce the coating processability.

[0071] The above single-particle type positive electrode active material is D 90 This can be 10㎛ or less, preferably 5㎛ to 10㎛. D of the first lithium nickel-based oxide 90 If this is too large, capacity and output characteristics may be degraded.

[0072] The above single-particle type positive electrode active material is D 10 The µm can be 4 µm or less, preferably 1 µm to 4 µm. D of the first lithium nickel-based oxide 10 When the above range is satisfied, thermal stability and electrochemical properties are exhibited to be even better.

[0073] Meanwhile, the above-mentioned positive active material may, if necessary, further include a second positive active material having a secondary particle form in which 31 or more primary particles are aggregated, in addition to the above-mentioned single-particle positive active material. If the positive active material in the form of a secondary particle is additionally included, an effect of improving electrolyte impregnation and rollability can be obtained.

[0074] When a secondary particle-shaped cathode active material is additionally included as a second cathode active material, the secondary particle-shaped cathode active material may be included in an amount of 80% by weight or less, preferably 5% to 80% by weight, more preferably 5% to 70% by weight, and even more preferably 5% to 50% by weight, based on the total weight of the cathode active material included in the cathode composite layer. If the content of the secondary particle-shaped cathode active material is too high, the surface roughness of the cathode increases, and the short-circuit suppression effect may decrease.

[0075] Meanwhile, in the present invention, the second positive active material is D50 This can be 7㎛ to 20㎛, preferably 8㎛ to 20㎛, more preferably 10㎛ to 20㎛. D of the second positive active material 50 When the above range is satisfied, the packing density of the anode increases, which can further improve energy density.

[0076] In addition, the second positive active material is D 90 This can be 25㎛ or less, preferably 10㎛ to 20㎛. D of the second positive active material 90 If this is too large, a problem may arise regarding reduced rollability during electrode manufacturing.

[0077] In addition, the second positive active material is D 10 The µm may be 7㎛ or less, preferably 2㎛ to 6㎛. D of the second positive active material 10 When the above range is satisfied, thermal stability and electrochemical properties are exhibited to be even better.

[0078]

[0079] Meanwhile, the first positive active material and the second positive active material may have the same or different composition.

[0080] The first positive active material and the second positive active material may each independently include a lithium nickel-based oxide containing 50 mol% or more of Ni among the total metals excluding lithium.

[0081] For example, the first positive active material may include a lithium nickel-based oxide represented by the following [Chemical Formula 1].

[0082] [Chemical Formula 1]

[0083] Li 1+x Ni a Co b M 1 c M 2 d O2

[0084] In the above chemical formula 1, M 1It may be Mn, Al, or a combination thereof, and preferably may be Mn or Mn and Al.

[0085] The above M 2 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. 2 Although the element is not necessarily included, if included in an appropriate amount, it can play a role in promoting grain growth during sintering or improving crystal structure stability.

[0086] The above 1+x represents the lithium molar ratio in the lithium nickel-based oxide, and may be -0.2≤x≤0.5, -0.2≤x≤0.2, or -0.1≤x≤0.1.

[0087] The above a represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel-based oxide, and may be 0.5≤a<1, 0.5≤a≤0.8, or 0.5≤a≤0.75.

[0088] The above b represents the molar ratio of cobalt among the total metals excluding lithium in the lithium nickel-based oxide, where 0 <b<0.5, 0.01≤b<0.5 또는 0.01≤b≤0.4일 수 있다.

[0089] The above c is M among the total metals excluding lithium in the lithium nickel-based oxide. 1 Representing the molar ratio of elements, 0 <c<0.5, 0.01≤c<0.5 또는 0.01≤c≤0.4일 수 있다.

[0090] The above d is M among the total metals excluding lithium in the lithium nickel-based oxide. 2 It represents the molar ratio of the elements, which can be 0≤d≤0.2, 0≤d≤0.1, or 0≤d≤0.05.

[0091]

[0092] The above second positive active material may include a lithium nickel-based oxide represented by the following [Chemical Formula 2].

[0093] [Chemical Formula 2]

[0094] Li 1+x' Ni a' Co b' M 3 c' M 4 d' O2

[0095] In the above chemical formula 2, M 3 It may be Mn, Al, or a combination thereof, and preferably may be Mn or Mn and Al.

[0096] The above M 4 It may be one or more selected from the group consisting of Zr, W, Y, Ba, Sr, Ca, Ti, Mg, Ta, and Nb, and preferably one or more selected from the group consisting of Zr, W, Y, and Sr.

[0097] The above 1+x' represents the lithium molar ratio in the lithium nickel-based oxide, and may be -0.2≤x'≤0.5, -0.2≤x'≤0.2, or -0.1≤x'≤0.1.

[0098] The above a' represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel-based oxide, and may be 0.5≤a'<1, 0.5≤a'≤0.9, or 0.5≤a'≤0.85.

[0099] The above b' represents the molar ratio of cobalt among the total metals excluding lithium in the lithium nickel-based oxide, where 0 <b'<0.5, 0.01≤b'<0.5 또는 0.01≤b'≤0.4일 수 있다.

[0100] The above c' is M among the total metals excluding lithium in the lithium nickel-based oxide. 3 Representing the molar ratio of elements, 0 <c'<0.5, 0.01≤c'<0.5 또는 0.01≤c'≤0.4일 수 있다.

[0101] The above d is M among the total metals excluding lithium in the lithium nickel-based oxide. 4 It represents the molar ratio of the elements, which can be 0≤d'≤0.2, 0≤d'≤0.1, or 0≤d'≤0.05.

[0102]

[0103] Meanwhile, the first positive active material and / or the second positive active material may further include a coating layer on the lithium nickel-based oxide particle surface, as needed, comprising one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S. Preferably, the coating element may be Al, B, Co, or a combination thereof. When a coating layer is present on the surface of the lithium nickel-based oxide particle, contact between the electrolyte and the lithium complex transition metal oxide is suppressed by the coating layer, thereby reducing the leaching of transition metals or gas generation caused by side reactions with the electrolyte.

[0104]

[0105] The above positive active material may be included in an amount of 80 to 99 weight%, preferably 85 to 99 weight%, and more preferably 90 to 99 weight% based on the total weight of the positive composite layer.

[0106] The above-mentioned positive electrode conductive material is used to improve conductivity of the electrode, and in the battery being constructed, it may be used without special restrictions as long as it possesses electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; 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 as the conductive material. The above-mentioned positive electrode conductive material may be included in an amount of 5% by weight or less, 0.01% by weight to 5% by weight, or 0.01% by weight to 3% by weight based on the total weight of the positive electrode composite layer.

[0107] Next, the anode binder serves to improve adhesion between anode active material particles and adhesion between the anode active material and the anode current collector. Specific examples 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. The above anode 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 anode composite layer.

[0108]

[0109] cathode

[0110] A lithium secondary battery according to the present invention comprises a negative electrode comprising a negative electrode active material. Specifically, the negative electrode comprises a negative electrode current collector and a negative electrode composite layer formed on at least one surface of the negative electrode current collector, and the negative electrode composite layer may comprise a negative electrode active material, a negative electrode conductive material, and a negative electrode binder.

[0111] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 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 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.

[0112] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. For example, as the above-mentioned negative electrode active material, carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal or metalloid compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; SiO₂ βExamples include metal oxides or metalloid oxides capable of doping and dedoping lithium, such as (0<β< 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal or metalloid compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used.

[0113] The above-mentioned cathode conductive material is used to impart conductivity to the cathode, and in the battery being constructed, any material that possesses electronic conductivity without causing chemical changes can be used without any particular limitations. Specific examples include graphite such as natural graphite or artificial graphite; 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.

[0114] The above cathode conductive material may typically be included in an amount of 0.1 to 10 weight%, preferably 0.5 to 8 weight%, and more preferably 1 to 5 weight% based on the total weight of the cathode composite layer.

[0115] The above-mentioned cathode binder serves to improve adhesion between cathode active material particles and adhesion between the cathode active material and the cathode current collector. Specific examples 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.

[0116] The above cathode binder may be included in an amount of 1 to 10 weight%, preferably 1 to 8 weight%, more preferably 1 to 5 weight% based on the total weight of the cathode composite layer.

[0117] The above cathode may be manufactured according to a conventional cathode manufacturing method. For example, the above cathode may be manufactured by mixing a cathode active material, a cathode binder, and / or a cathode conductive material in a solvent to prepare a cathode slurry, applying the cathode slurry onto a cathode current collector, and then drying and rolling, or by casting the cathode slurry onto a separate support and then laminating a film obtained by peeling off from the support onto a cathode current collector.

[0118] Meanwhile, solvents commonly used in the relevant technical field may be used as solvents for the cathode slurry, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, etc., may be used alone or as a mixture of two or more.

[0119]

[0120] Separator

[0121] The above separator separates the negative and positive electrodes and provides a pathway for the movement of lithium ions; it can be used without any special restrictions as long as it is commonly used as a separator in a lithium secondary battery.

[0122] For example, the separator may include a porous polymer film made of a polyolefin-based polymer such as polyethylene, polypropylene, ethylene-butene copolymer, ethylene-hexene copolymer, and ethylene-methacrylate copolymer, or a film laminate in which two or more layers thereof are laminated. If necessary, the separator may further include a coating layer on one or both sides of the porous polymer film or film laminate to reinforce heat resistance, mechanical strength, etc.

[0123] Specifically, the separator may comprise a substrate layer comprising a porous polymer film; and a porous coating layer disposed on at least one surface of the substrate layer. In this case, the porous coating layer may comprise a mixture of inorganic particles selected from metal oxides, metalloid oxides, metal fluorides, metal hydroxides, and combinations thereof, and a binder polymer that connects and fixes the inorganic particles to each other.

[0124] The above inorganic particles may be, for example, one or more selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, and MgF, but are not limited thereto. The above inorganic particles suppress shrinkage of the membrane at high temperatures, thereby improving the thermal stability of the membrane. The above binder polymer fixes the inorganic particles and improves the mechanical stability of the membrane.

[0125] The thickness of the separator may be 5㎛ to 15㎛, 7㎛ to 15㎛, or 7㎛ to 12㎛. In this case, the thickness of the separator refers to the combined thickness of the substrate layer and the porous coating layer. If the separator thickness is too thin, the separator strength decreases, reducing the short-circuit suppression effect, and if it is too thick, the energy density of the battery may decrease.

[0126]

[0127] electrolytes

[0128] 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.

[0129] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0130] 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.

[0131] 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, or LiB(C2O4)2. 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.

[0132] 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.

[0133] Examples of the above-mentioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate.

[0134] Examples of the above-mentioned halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0135] 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.

[0136] Examples of the above sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0137] 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.

[0138] Examples of the above borate compounds include tetraphenylborate, lithium oxalyl difluoroborate (LiODFB), and lithium bisoxalate toborate (LiB(C2O4)2, LiBOB).

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143]

[0144] The lithium secondary battery according to the present invention can be usefully applied to portable devices such as mobile phones, laptop computers, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0145] The lithium secondary battery according to the present invention can be applied as a unit cell of a battery module and / or battery pack.

[0146] According to one embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising a plurality of battery modules are provided.

[0147] According to another embodiment of the present invention, a battery pack comprising a plurality of lithium secondary batteries according to the present invention as unit cells is provided. The battery pack may not include a battery module.

[0148] In addition, the present invention provides a pack cell assembly.

[0149] According to one embodiment, the battery module may include 10 to 50, preferably 16 to 36 unit cells. The battery pack may include 10 to 1,000, preferably 10 to 500 unit cells.

[0150] The above battery module and / or battery pack may be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0151]

[0152] The present invention will be explained in more detail below through specific embodiments.

[0153]

[0154] Preparation Example 1

[0155] A positive electrode slurry was prepared by mixing a positive electrode active material, a conductive material (CNT), and a PVdF binder in a weight ratio of 97:1:2 in N-methylpyrrolidone. The positive electrode active material is a single-particle lithium nickel-based oxide (LiNi 0.6 Co 0.1 Mn 0.3 100% of O2 was used.

[0156] After applying the above anode slurry to one side of an aluminum current collector, anode A was manufactured by drying and rolling. At this time, the rolling was performed at a linear pressure of 3 ton / cm.

[0157]

[0158] Preparation Example 2

[0159] Single-particle lithium nickel-based oxide (LiNi) as a positive electrode active material 0.6 Co 0.1 Mn 0.3 O2): Secondary particulate lithium nickel-based oxide (LiNi 0.87 Co0.04 Mn 0.07 Al 0.02 Anode B was prepared in the same manner as in Preparation Example 1, except that O2) was mixed and used in a weight ratio of 80:20.

[0160]

[0161] Preparation Example 3

[0162] Single-particle lithium nickel-based oxide (LiNi) as a positive electrode active material 0.6 Co 0.1 Mn 0.3 )O2: Secondary particulate lithium nickel-based oxide (LiNi 0.87 Co 0.04 Mn 0.07 Al 0.02 Anode C was prepared in the same manner as in Preparation Example 1, except that O2) was mixed and used in a weight ratio of 20:80.

[0163]

[0164] Experimental Example 1

[0165] Average roughness (Ra) of the surfaces of anodes A to C prepared according to the above Preparation Examples 1 to 3 c ), porosity (P) and electrode density (D c ) was measured using the following method. The measurement results are shown in Table 1 below.

[0166] (1) Average surface roughness (nm): The anode surface was measured by observing it at 20x magnification using an optical profiler. Figures 1 to 3 show the results of observing the surfaces of anodes A to C using an optical profiler.

[0167] (2) Porosity (%): Porosity was calculated as (1 - electrode density / true electrode density) × 100, electrode density was measured using the method below, and true electrode density was measured using a Gas Pycnometer.

[0168] (3) Electrode density (g / cc): A sample was prepared by stamping an electrode to an area A, and the thickness (T1) and mass (W1) of the prepared sample were measured. Then, after removing the electrode composite layer from the sample, the thickness (T2) and mass (W2) of the current collector were measured and calculated by substituting them into the following formula.

[0169] Electrode density = (W1- W2) / (A ×(T1-T2))

[0170]

[0171] Ra c [nm]P[%]D c [g / cc] Anode A330.221.943.504 Anode B371.621.693.559 Anode C606.726.43.389

[0172] Example 1

[0173] Cathode Manufacturing

[0174] A cathode slurry was prepared by mixing a cathode active material, a conductive material (carbon black), and a PVdF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. At this time, natural graphite and artificial graphite were mixed in a weight ratio of 5:5 and used as the cathode active material. After applying the cathode slurry onto a cathode current collector, a cathode was manufactured by drying and rolling.

[0175]

[0176] Lithium secondary battery manufacturing

[0177] An electrode assembly was manufactured by interposing a separator between the positive electrode A manufactured in Preparation Example 1 and the negative electrode manufactured above, and stacking them in the order of separator / positive electrode / separator / negative electrode. At this time, a polyethylene film with a thickness of 12 μm was used as the separator. After inserting the electrode assembly manufactured as above into a battery case, an electrolyte was injected and sealed to manufacture a lithium secondary battery.

[0178]

[0179] Example 2

[0180] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a 9㎛ thick polyethylene film was used as the separator.

[0181]

[0182] Example 3

[0183] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a 7㎛ thick polyethylene film was used as the separator.

[0184]

[0185] Example 4

[0186] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode B manufactured in Example 2 was used instead of the cathode A manufactured in Example 1.

[0187]

[0188] Example 5

[0189] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode B manufactured in Example 2 was used instead of the cathode A manufactured in Example 1, and a polyethylene film with a thickness of 9 μm was used as the separator.

[0190]

[0191] Example 6

[0192] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode C manufactured in Example 3 was used instead of the cathode A manufactured in Example 1.

[0193]

[0194] Comparative Example 1

[0195] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode B manufactured in Example 2 was used instead of the cathode A manufactured in Example 1, and a polyethylene film with a thickness of 7 μm was used as the separator.

[0196]

[0197] Comparative Example 2

[0198] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode C manufactured in Example 3 was used instead of the cathode A manufactured in Example 1, and a polyethylene film with a thickness of 9 μm was used as the separator.

[0199]

[0200] Comparative Example 3

[0201] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode C manufactured in Example 3 was used instead of the cathode A manufactured in Example 1, and a polyethylene film with a thickness of 7 μm was used as the separator.

[0202]

[0203] Experimental Example 2: Verification of Short Circuit Occurrence

[0204] For each of the lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3 above, 50V was applied for 0.5 seconds, and a Hi-Pot test was performed in which the current was measured and determined that no short circuit occurred if the measured current was 0.5mA or less, and determined that a short circuit occurred if the measured current exceeded 0.5mA. The number of times a short circuit occurred was measured. The measurement results are shown in [Table 2] below.

[0205] In addition, the RD of the lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3 was calculated according to Equation (1) and is shown in [Table 2].

[0206] Equation (1): RD = (Ra c Х D c ) / T s

[0207] The above Ra c is the average surface roughness of the anode measured in nm units, and the D cis the electrode density of the anode measured in units of g / cc, and Ts is the thickness of the separator measured in units of μm.

[0208]

[0209] Number of RD Short Occurrences Example 1: 96.40 Example 2: 128.60 Example 3: 165.30 Example 4: 110.20 Example 5: 146.90 Example 6: 171.30 Comparative Example 1: 188.93 Comparative Example 2: 228.55 Comparative Example 3: 293.78

[0210] Through Table 2 above, it can be confirmed that while a short circuit occurred in the lithium secondary batteries of Comparative Examples 1 to 3, which have an RD value exceeding 170, a short circuit did not occur in the lithium secondary batteries of Examples 1 to 6, which have an RD value of 180 or less.

Claims

1. A positive electrode comprising a positive electrode active material; A cathode comprising a cathode active material; A separator interposed between the anode and the cathode; and Contains electrolytes, A lithium secondary battery having an RD value of 180 or less as defined by the above equation (1). Equation (1): RD = (Ra c × D c ) / T s In the above equation (1), The above Ra c is the average roughness of the anode surface measured in nm units, and The above D c is the electrode density of the above anode measured in units of g / cc, and The above Ts is the thickness of the separation membrane measured in μm units.

2. In Paragraph 1, Ra c / T S A lithium secondary battery with 20 to 52 members.

3. In Paragraph 1, A lithium secondary battery having an average surface roughness of 300 nm to 610 nm on the anode.

4. In Paragraph 1, The above positive electrode is a lithium secondary battery having an electrode density of 3.0 g / cc to 3.8 g / cc.

5. In Paragraph 1, The above positive electrode is a lithium secondary battery having a porosity of 20% to 25%.

6. In Paragraph 1, A lithium secondary battery in which the above-mentioned positive electrode comprises a single-particle type positive electrode active material comprising 30 or fewer nodules as a first positive electrode active material.

7. In Paragraph 6, A lithium secondary battery in which the above-mentioned positive electrode comprises at least 20% by weight of the above-mentioned first positive electrode active material based on the total weight of the positive electrode active material.

8. In Paragraph 6, A lithium secondary battery wherein the first positive active material comprises a lithium nickel-based oxide represented by the following [Chemical Formula 1]. [Chemical Formula 1] Li 1+x Ni a Co b M 1 c M 2 d O2 In the above chemical formula 1, M 1 is Mn, Al, or a combination thereof, and M 2 ... comprises one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and -0.2≤x≤0.5, 0.5≤a<1, 0 <b<0.5, 0<c<0.5, 및 0≤d≤0.2임.

9. In Paragraph 8, A lithium secondary battery in the above chemical formula 1, wherein 0.5≤a≤0.8, 0.01≤b<0.5, 0.01≤c<0.5, and 0≤d≤0.

1.

10. In Paragraph 6, The above-mentioned first positive active material is a lithium secondary battery having an average particle size of 3㎛ to 10㎛.

11. In Paragraph 6, A lithium secondary battery wherein the above-mentioned positive electrode further comprises, as a second positive electrode active material, a positive electrode active material in the form of secondary particles in which 31 or more primary particles are aggregated.

12. In Paragraph 11, A lithium secondary battery wherein the second positive active material comprises a lithium nickel-based oxide represented by the following [Chemical Formula 2]. [Chemical Formula 2] Li 1+x' Ni a' Co b' M 3 c' M 4 d' O2 In the above chemical formula 2, M 3 is Mn, Al, or a combination thereof, and M 4 ... comprises one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta, Sr, and Nb, and -0.2≤x'≤0.5, 0.5≤a'<1, 0 <b'<0.5, 0<c'<0.5, 및 0≤d'≤0.2임.

13. In Paragraph 11, The above second positive active material is a lithium secondary battery having an average particle size of 7㎛ to 20㎛.

14. In Paragraph 1, The above separator is a lithium secondary battery having a thickness of 5㎛ to 15㎛.

15. In Paragraph 1, A lithium secondary battery wherein the separator comprises: a substrate layer including a porous polymer film; and a porous coating layer disposed on at least one surface of the substrate layer.

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