Positive electrode for lithium secondary battery and lithium secondary battery

Abstract

The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the same. The positive electrode for the lithium secondary battery sequentially includes a first coating layer and a second coating layer on a current collector. Among them, a pattern layer in which a conductive material is dispersed in an adhesive is introduced between the first coating layer and the second coating layer at a specific area ratio, thereby improving the safety of the battery. Therefore, when a metal body penetrates the electrode from the outside, not only will it not generate heat, catch fire, etc. due to overcurrent, but also the adhesion between the multiple layers constituting the positive electrode can be improved, and the life characteristics of the battery can be improved.

Description

Technical Field

[0001] The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery, and more particularly, to a positive electrode for a lithium secondary battery and a lithium secondary battery having improved safety without deteriorating battery life characteristics. This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0043090 filed on April 2, 2021, and all content disclosed in the Korean patent application document is incorporated as part of this specification. Background Art

[0002] With the development of technology and the increasing demand for mobile devices, the demand for secondary batteries as an energy source has also increased rapidly. Among these secondary batteries, lithium secondary batteries having a high energy density, a working potential, a long cycle life, and a low self-discharge rate have been commercialized and widely used.

[0003] In recent years, as lithium secondary batteries are used as power sources for medium and large-sized devices such as electric vehicles, there has been a further demand for high capacity, high energy density, and low cost of lithium secondary batteries. Therefore, research has been actively conducted to use inexpensive Ni, Mn, Fe, etc. instead of expensive Co.

[0004] One of the main research tasks of lithium secondary batteries is to improve the safety of batteries using high-capacity and high-output electrode active materials while implementing them. Lithium transition metal composite oxides are used as the positive electrode active material of lithium secondary batteries. Among these oxides, lithium cobalt composite metal oxide LiCoO2 having a high working voltage and excellent capacity characteristics is mainly used. However, since LiCoO2 has an unstable crystal structure due to delithiation, its thermal performance is very poor. When an internal short circuit occurs due to external pressure in the charged state, the positive electrode active material itself decomposes, which may cause the battery to rupture and catch fire. In addition, in the case of an overcurrent flowing instantaneously, there is a problem that safety problems such as fire or explosion may be caused thereby.

[0005] Therefore, Korean Patent Publication No. 2019-0047203 discloses a technique for ensuring battery safety by inserting an overcharge prevention layer between a positive electrode current collector and a positive electrode active material layer to increase the resistance during overcharging to block the charging current. However, although the electrode having the overcharge prevention layer described above improves safety, due to the different compositions between the overcharge protection layer and the positive electrode active material layer, the adhesion is low, and thus there is a possibility of generating interlayer cracks, thereby deteriorating the battery life characteristics. In addition, the through resistance of the electrode is low, and when it is penetrated by a nail, there may be a safety problem.

[0006] Therefore, when a metal body such as a nail penetrates the electrode from the outside, it is necessary to develop a technique that not only has high safety so as not to cause heat generation, fire, etc. due to overcurrent, but also can improve the deterioration of battery life characteristics caused by cracks appearing between the positive electrode layers. Summary of the Invention

[0007] Technical Problem

[0008] Therefore, an object of the present invention is to provide a positive electrode for a secondary battery and a lithium secondary battery, which are highly safe when a metal body such as a nail penetrates the electrode from the outside, do not cause heat generation, fire, etc. due to overcurrent, and can also improve the deterioration of battery life characteristics caused by cracks occurring between the positive electrode layers.

[0009] Technical Solution

[0010] In order to solve the above problems, in one embodiment, the present invention provides a positive electrode for a lithium secondary battery, which includes:

[0011] A current collector;

[0012] A first coating provided on one or both surfaces of the current collector and containing a first positive electrode active material;

[0013] A pattern layer provided on the first coating and containing a binder and a conductive material dispersed in the binder; and

[0014] A second coating provided on the first coating on which the pattern layer is provided, and containing a second positive electrode active material, and

[0015] wherein the area of the first coating on which the pattern layer is provided is 30% to 80% of the total area of the first coating.

[0016] At this time, the pattern layer may have a surface structure such as a dot shape, a mesh shape, a stripe shape, or a dendritic shape.

[0017] In addition, each of the first coating and the second coating contains 1 to 10 parts by weight of a binder based on 100 parts by weight of the first coating and the second coating, respectively, and the binder in each coating may include at least one resin selected from the group consisting of polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, and copolymers thereof.

[0018] In addition, the binder of the pattern layer may include at least one resin selected from the group consisting of polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene - propylene - diene monomer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, and copolymers thereof.

[0019] In addition, the conductive material of the pattern layer may include at least one selected from the group consisting of: graphite, including natural graphite or artificial graphite; carbon black, including acetylene black, Ketjen black, channel black, furnace black, lamp black or thermal cracking carbon black; conductive fibers, including carbon fibers or metal fibers; carbon nanotubes; metal powders, including fluorocarbons, aluminum or nickel; zinc oxide; potassium titanate; titanium dioxide; and polyphenyl derivatives.

[0020] In addition, based on 100 parts by weight of the binder, the content of the conductive material of the pattern layer may be 1 part by weight to 50 parts by weight.

[0021] In addition, the average height of the pattern layer may be 0.5 μm to 50 μm based on the cross-section, and the average thickness of the first coating layer may be 0.1 μm to 10 μm.

[0022] In addition, the second coating layer may satisfy Formula 1:

[0023] [Formula 1]

[0024] 6 ≤ SD / PD ≤ 100

[0025] Wherein,

[0026] SD represents the average thickness of the second coating layer,

[0027] PD represents the average thickness of the pattern layer.

[0028] In addition, the first positive electrode active material may include a lithium iron phosphate compound represented by the following Chemical Formula 1:

[0029] [Chemical Formula 1]

[0030] Li 1+a Fe 1-b M 1 b (PO 4-c )X c

[0031] Wherein,

[0032] M 1 is at least one selected from the group consisting of Al, Mg, and Ti,

[0033] X is at least one selected from the group consisting of F, S, and N, and

[0034] a, b, and c are -0.5 ≤ a ≤ +0.5, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.1, respectively.

[0035] In addition, the second positive electrode active material may include a lithium metal composite oxide represented by the following Chemical Formula (2):

[0036] [Chemical Formula 2]

[0037] LiCo 1-q M 2 q O2

[0038] Among them,

[0039] M 2 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0040] q is 0 ≤ q ≤ 0.4.

[0041] In addition, in one embodiment, the present invention provides a lithium secondary battery having the positive electrode of the present invention.

[0042] Beneficial effects

[0043] The positive electrode for a lithium secondary battery of the present invention sequentially includes a first coating and a second coating on a current collector, and a pattern layer with a specific area ratio is introduced in the form of a conductive material dispersed in an adhesive between the first coating and the second coating, improving the safety of the battery. Therefore, when a metal body penetrates the electrode from the outside, not only will it not generate heat, catch fire, etc. due to overcurrent, but also the adhesion between the multiple layers constituting the positive electrode can be improved, and the life characteristics of the battery can be improved. Description of the drawings

[0044] Figure 1 is a cross-sectional view showing the structure of the positive electrode for a lithium secondary battery of the present invention. Detailed description of the embodiments

[0045] Since the present invention can have various variations and various embodiments, the specific embodiments will be described in detail in the specification.

[0046] However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents, or substitutions included in the spirit and scope of the present invention.

[0047] In the present invention, it should be understood that terms such as "including" or "having" are intended to specify the presence of the described features, quantities, steps, operations, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, operations, components, and their combinations.

[0048] In addition, in the present invention, when a part of a layer, film, region, plate, etc. is described as being "on" another part, it includes not only the case of being "directly" on another part, but also the case where there are other parts between them. Conversely, when a part of a layer, film, region, plate, etc. is described as being "under" another part, this includes the case of being "directly" under another part, and also the case where there are other parts between them. In addition, the setting on "..." as described herein may include not only being set on the top, but also being set on the bottom.

[0049] Hereinafter, the present invention will be described in more detail.

[0050] Positive electrode for lithium secondary battery

[0051] In one embodiment, the present invention provides a positive electrode for a lithium secondary battery, which includes:

[0052] A current collector;

[0053] A first coating provided on one or both surfaces of the current collector and containing a first positive electrode active material;

[0054] A pattern layer provided on the first coating and containing a conductive material dispersed in a binder; and

[0055] A second coating provided on the first coating on which the pattern layer is formed, and containing a second positive electrode active material, and

[0056] The area of the region where the pattern layer is provided is 30% to 80% of the total area of the first coating.

[0057] Figure 1 is a cross-sectional view showing the structure of the positive electrode 100 for a lithium secondary battery of the present invention. As Figure 1 shown, the positive electrode 100 for a lithium secondary battery of the present invention has a structure in which a current collector 110, a first coating 120, and a second coating 140 are sequentially stacked, and a pattern layer 130 is introduced between the first coating 120 and the second coating 140.

[0058] At this time, the pattern layer 130 is provided between the first coating 120 and the second coating 140 to enhance the adhesion between the first coating 120 and the second coating 140, and at the same time can play a role in improving the conductivity of the positive electrode 100.

[0059] For this purpose, the pattern layer 130 has a form in which a conductive material is dispersed in a binder, and the binder may contain additives such as a dispersant and a surfactant in addition to the conductive material, but does not contain a positive electrode active material showing electroactivity.

[0060] The binder contained in the pattern layer 130 may be the same as or different from the binders contained in the first coating layer 120 and the second coating layer 140. For example, the binder that may be contained in the pattern layer 130 may include at least one resin selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and their copolymers. As an example, the binder may include polyvinylidene fluoride-hexafluoropropylene copolymer.

[0061] In addition, the conductive material that may be contained in the pattern layer 130 may include at least one selected from the group consisting of: graphite, including natural graphite or artificial graphite; carbon black, including acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal cracking carbon black; conductive fibers, including carbon fibers or metal fibers; carbon nanotubes; metal powders, including fluorocarbon, aluminum, or nickel; zinc oxide; potassium titanate; titanium dioxide; and polyphenylene derivatives. As an example, the conductive material may include at least one of carbon black, including acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black.

[0062] Furthermore, based on 100 parts by weight of the binder, the content of the conductive material may be 1 part by weight to 50 parts by weight, specifically 5 parts by weight to 40 parts by weight, 10 parts by weight to 20 parts by weight, 20 parts by weight to 40 parts by weight, 30 parts by weight to 50 parts by weight, 15 parts by weight to 35 parts by weight, or 15 parts by weight to 25 parts by weight.

[0063] In the present invention, by controlling the content of the conductive material contained in the pattern layer 130 within the above range, it is possible to prevent the adhesion between the first coating layer 120 and the second coating layer 140 from not being effectively improved due to a low binder content, or prevent the conductivity of the positive electrode 100 from not being effectively increased due to a decrease in the content of the conductive material.

[0064] In addition, the application of the pattern layer 130 is not particularly limited as long as it maximizes the surface area without covering the entire surface of the first coating layer 120. Specifically, the pattern layer 130 may have a surface structure such as dot-like, net-like, stripe-like, or dendritic. As an example, the pattern layer 130 may have a dendritic surface structure.

[0065] In addition, the adhesive of the pattern layer 130 may be in a form that partially or completely penetrates into the gaps between the first positive electrode active materials constituting the first coating layer 120, and at the same time, may be in a form that partially or completely penetrates into the gaps between the second positive electrode active materials constituting the second coating layer 140.

[0066] In addition, the pattern layer 130 may account for 30% to 80% of the total area of the first coating layer 120, specifically 30% to 70%, 30% to 60%, 30% to 50%, 40% to 70%, or 30% to 45%. In the present invention, by controlling the area of the pattern layer 130 formed on the first coating layer 120 within the same range as described above, it is possible to prevent a decrease in the mobility of lithium ions and a decrease in battery performance, while increasing the adhesion between the first coating layer 120 and the second coating layer 140.

[0067] In addition, the average height of the pattern layer 130 may be 0.5 μm to 50 μm based on the cross-section, specifically 0.5 μm to 40 μm, 0.5 μm to 20 μm, 0.5 μm to 10 μm, 1 μm to 40 μm, 5 μm to 30 μm, 5 μm to 20 μm, 15 μm to 25 μm, 5 μm to 15 μm, 10 μm to 20 μm, 3 μm to 17 μm, or 1 μm to 10 μm. The pattern layer 130 of the present invention may have a semi-circular cross-sectional structure when it is in a dot shape, and may have a shape close to a triangular pyramid when it is in a dendritic shape. Therefore, the "average height" used in the present invention may refer to one-half of the highest height based on the cross-sectional structure of the pattern layer 130. In the present invention, by adjusting the average height of the pattern layer 130 as described above, the specific surface area of the pattern layer 130 can be maximized, thereby improving the adhesion between the first coating layer 120 and the second coating layer 140.

[0068] At the same time, the first coating layer 120 is formed on one or both surfaces of the current collector 110, and includes a first positive electrode active material, a first conductive material, and a first adhesive. At this time, the first positive electrode active material may include a lithium iron phosphate compound represented by the following Chemical Formula 1:

[0069] [Chemical Formula 1]

[0070] Li 1+a Fe 1-b M 1 b (PO 4-c )X c

[0071] Wherein,

[0072] M 1 is at least one selected from Al, Mg, and Ti,

[0073] X is at least one selected from F, S, and N, and

[0074] a, b, and c are -0.5 ≤ a ≤ +0.5, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.1, respectively.

[0075] Specifically, the first positive electrode active material is a lithium iron phosphate compound represented by Chemical Formula 1 and may use at least one compound selected from the group consisting of LiFePO4, Li(Fe,Al)PO4, Li(Fe,Mg)PO4, and Li(Fe,Ti)PO4. More specifically, LiFePO4 may be used.

[0076] The lithium iron phosphate compound represented by Chemical Formula 1 may have an olivine structure. At an overcharge voltage equal to or higher than about 4.5 V, as lithium escapes, the volume of the lithium iron phosphate with an olivine structure shrinks. As a result, the conduction path of the first coating is rapidly blocked, causing the first coating to act as an insulating layer, thereby increasing the resistance of the second coating and blocking the charging current up to the overcharge termination voltage.

[0077] In addition, the first coating 120 may include at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber as the first conductive material. For example, the first conductive material may include acetylene black.

[0078] In addition, the first binder may include at least one resin selected from the group consisting of polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, and their copolymers. As an example, the first binder may include polyvinylidene fluoride.

[0079] In addition, based on a total of 100 parts by weight, the first coating 120 may include 80 to 98 parts by weight of the first positive electrode active material, 1 to 10 parts by weight of the first conductive material, and 1 to 10 parts by weight of the first binder. As an example, based on a total of 100 parts by weight, the first coating 120 may include 84 to 96 parts by weight of the first positive electrode active material, 2 to 8 parts by weight of the first conductive material, and 2 to 8 parts by weight of the first binder; as another example, based on a total of 100 parts by weight, it may include 88 to 96 parts by weight of the first positive electrode active material, 2 to 6 parts by weight of the first conductive material, and 2 to 6 parts by weight of the first binder.

[0080] In addition, the average thickness of the first coating 120 may be 0.1 μm to 10 μm, specifically 2 μm to 10 μm, 4 μm to 10 μm, or 5 μm to 9 μm.

[0081] In addition, a second coating layer 140 is formed on the first coating layer 120 on which the pattern layer 130 is formed, and includes a second positive electrode active material, a second conductive material, and a second binder. At this time, the second positive electrode active material may include a lithium metal composite oxide represented by the following Chemical Formula (2):

[0082] [Chemical Formula 2]

[0083] LiCo 1-q M 2 q O2

[0084] Wherein,

[0085] M 2 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0086] q is 0 ≤ q ≤ 0.4.

[0087] The second positive electrode active material may be applied without particular limitation as long as it is a lithium metal composite oxide represented by Chemical Formula 2. Specifically, the second positive electrode active material may include one or more compounds selected from the group consisting of LiCoO2, LiCo 0.5 Zn 0.5 O2, LiCo 0.7 Zn 0.3 O2, LiNi 0.5 Co 0.5 O2, LiCo 0.6 Fe 0.4 O2, LiCo 0.9 Fe 0.1 O2, LiCo 0.8 Al 0.2 O2, LiCo 0.8 Mn 0.2 O2, LiCo 0.9 Mn 0.1 O2, and LiCo 0.8 Mn 0.1 Al 0.1 O2.

[0088] As an example, the positive electrode active material may include LiCoO2 or LiCo 0.7 Zn 0.3 O2 as the lithium nickel cobalt oxide represented by Chemical Formula 2, and they may be used alone or in combination.

[0089] In addition, the second coating 140 may include at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber as the second conductive material. For example, the first conductive material may include acetylene black.

[0090] In addition, the binder may include at least one resin selected from the group consisting of polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, and their copolymers. As an example, the second binder may include polyvinylidene fluoride.

[0091] In addition, based on a total of 100 parts by weight, the second coating 140 may contain 80 to 98 parts by weight of the second positive electrode active material, 1 to 10 parts by weight of the second conductive material, and 1 to 10 parts by weight of the second binder. As an example, based on a total of 100 parts by weight, the second coating 140 may contain 84 to 96 parts by weight of the second positive electrode active material, 2 to 8 parts by weight of the second conductive material, and 2 to 8 parts by weight of the second binder; as another example, based on a total of 100 parts by weight, it may contain 88 to 96 parts by weight of the second positive electrode active material, 2 to 6 parts by weight of the second conductive material, and 2 to 6 parts by weight of the second binder.

[0092] In addition, the average thickness of the second coating 140 is not particularly limited and may specifically be 50 μm to 300 μm, more specifically 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm, or 150 μm to 190 μm.

[0093] In addition, the second coating 140 may satisfy Equation 1:

[0094] [Equation 1]

[0095] 6 ≤ SD / PD ≤ 100

[0096] In Equation 1, SD represents the average thickness of the second coating 140, and PD represents the average thickness of the pattern layer 130.

[0097] Equation 1 represents the ratio (SD / PD) of the average thickness (SD) of the second coating 140 to the average thickness (PD) of the pattern layer 130. In Equation 1 of the present invention, the ratio satisfies 6 to 100, specifically 6 to 80, 10 to 60, 10 to 40, 10 to 30, 10 to 20, 20 to 70, 30 to 60, 15 to 35, 11 to 13, or 10 to 15. By adjusting the average thickness ratio of the second coating 140 to the pattern layer 130 to the above range, the present invention improves the adhesion between the first coating 120 and the second coating 140, thereby improving the generation of interlayer cracks.

[0098] Meanwhile, in the positive electrode 100 for a lithium secondary battery of the present invention, a current collector 110 having high conductivity and not causing chemical changes in the battery can be used. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, etc. can be used. In the case of using aluminum or stainless steel, surface treatment can be performed with carbon, nickel, titanium, silver, etc. In addition, the current collector 110 can have fine concavo-convex objects on the surface to increase the adhesion of the positive electrode active material, and can have various forms, such as a film, sheet, foil, net, porous body, foam, and non-woven fabric body. Additionally, considering the conductivity and total thickness of the positive electrode 100 to be manufactured, the average thickness of the current collector 110 can be in the range of 3 μm to 500 μm.

[0099] The positive electrode 100 for a lithium secondary battery of the present invention includes a first coating 120 and a second coating 140 in sequence on the current collector 110 as described above, and a pattern layer 130 with a specific area ratio is introduced in the form of a conductive material dispersed in the binder between the first coating 120 and the second coating 140, improving the safety of the battery. Therefore, when a metal body penetrates the electrode from the outside, not only will it not heat up, catch fire, etc. due to overcurrent, but also the adhesion between the multiple layers constituting the positive electrode 100 can be improved, thereby improving the life characteristics of the battery.

[0100] Lithium secondary battery

[0101] In addition, in one embodiment, the present invention provides a lithium secondary battery including the positive electrode, negative electrode, and separator located between the positive electrode and the negative electrode of the present invention as described above.

[0102] The lithium secondary battery of the present invention can include the positive electrode and negative electrode of the present invention as described above, and has a structure in which the positive electrode and the negative electrode are impregnated with an electrolyte containing a lithium salt.

[0103] Here, the negative electrode is manufactured by coating, drying, and pressing a negative electrode active material on a negative electrode current collector, and optionally, the conductive material, organic binder polymer, filler, etc. described above can also be included as needed.

[0104] In addition, as the negative electrode active material, for example, the following can be used: graphite having a completely layered crystal structure such as natural graphite; soft carbon having a layered crystal structure with low crystallinity (graphene structure; a structure in which hexagonal honeycomb planes of carbon are arranged in layers) and graphite materials such as hard carbon, artificial graphite, expanded graphite, carbon fiber, non-graphitized carbon, carbon black, carbon nanotubes, fullerenes, activated carbon, etc., in which carbon and these structures are mixed with an amorphous portion; metal composite oxides such as Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Group 1, Group 2 and Group 3 of the periodic table, and halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 and Bi2O5; conductive polymers such as polyacetylene; lithium cobalt nickel-based materials; titanium dioxide; lithium titanium oxide, etc.

[0105] As an example, the negative electrode active material may include both graphite and silicon (Si)-containing particles, and the graphite includes at least one of natural graphite having a layered crystal structure and artificial graphite having an isotropic structure, and the silicon (Si)-containing particles may include particles mainly containing silicon (Si) as a metal component, such as silicon (Si) particles, silicon dioxide (SiO2) particles, or a mixture of silicon (Si) particles and silicon dioxide (SiO2) particles.

[0106] In this case, based on a total of 100 parts by weight, the negative electrode active material may include 80 to 95 parts by weight of graphite and 1 to 20 parts by weight of silicon (Si)-containing particles. By adjusting the contents of graphite and silicon (Si)-containing particles in the negative electrode active material to the above ranges, the present invention can reduce the consumption of lithium and the irreversible capacity loss during the initial charge and discharge process of the battery, while increasing the charge capacity per unit mass.

[0107] In addition, the average thickness of the negative electrode composite layer may be 100 μm to 200 μm, specifically 100 μm to 180 μm, 100 μm to 150 μm, 120 μm to 200 μm, 140 μm to 200 μm, or 140 μm to 160 μm.

[0108] In addition, the negative electrode current collector is not particularly limited as long as it has high electrical conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, sintered carbon, etc. can be used. In the case of copper or stainless steel, surface treatment can be carried out with carbon, nickel, titanium, silver, etc. In addition, in order to strengthen the bonding force with the negative electrode active material, the negative electrode current collector can have fine irregularities on the surface like the positive electrode current collector, and can be in various forms such as films, sheets, foils, meshes, porous materials, foams, non-woven materials, etc. In addition, considering the electrical conductivity and total thickness of the negative electrode to be manufactured, the average thickness of the negative electrode current collector can be in the range of 3 μm to 500 μm.

[0109] In addition, the separator is disposed between the negative electrode and the positive electrode and an insulating film with high ion permeability and mechanical strength is used. The separator is not particularly limited as long as it is commonly used in the art. Specifically, polypropylene with chemical resistance and hydrophobicity; glass fiber; sheets or non-woven fabrics made of polyethylene, etc. can be used. In some cases, a composite separator can be used, in which inorganic particles / organic particles are coated with an organic binder polymer on a porous polymer substrate such as a sheet or non-woven fabric. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte can also act as the separator. In addition, the separator can have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0110] Meanwhile, the positive electrode and the negative electrode can be wound in the form of a gel roll and stored in a cylindrical battery, a prismatic battery or a pouch-type battery, or can be stored in a pouch-type battery in a folded or stacked-folded form, but not limited thereto.

[0111] In addition, the lithium salt-containing electrolyte of the present invention can be composed of an electrolyte and a lithium salt. As the electrolyte, non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, etc. can be used.

[0112] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetra-hydroxyl franc, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate or ethyl propionate can be used.

[0113] As the organic solid electrolyte, for example, polyethylene derivatives, poly(ethylene oxide) derivatives, poly(propylene oxide) derivatives, phosphate esters polymers, poly agitation lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, polymeric materials containing ionic dissociative groups, etc. can be used.

[0114] As the inorganic solid electrolyte, for example, nitrides, halides and sulfates of Li such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc. can be used.

[0115] The lithium salt is a material soluble in non-aqueous electrolytes. For example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylates, lithium 4-phenylborate, imides, etc. can be used.

[0116] In addition, in order to improve the charge-discharge characteristics, flame retardancy, etc. of the electrolyte, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. can be added. In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and trifluoroethylene can be further included, and carbon dioxide gas can be further included to improve the high-temperature storage characteristics, and fluoroethylene carbonate (FEC), propylene sultone (PRS), etc. can be further included.

[0117] Battery module

[0118] Furthermore, in one embodiment, the present invention provides a battery module including the secondary battery described above as a unit cell, and provides a battery pack including the battery module.

[0119] The battery pack can be used as a power source for medium and large-sized devices that require high-temperature stability, long cycle characteristics, and high-rate characteristics. Specific examples of medium and large-sized devices include: power tools driven by all-knowing motors and moving; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.; electric two-wheel vehicles, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and systems for storing electricity; more specifically, hybrid electric vehicles (HEVs), but not limited thereto.

[0120] Hereinafter, the present invention will be described in detail according to embodiments.

[0121] However, the following embodiments and experimental examples are only for illustrating the present invention, and the content of the present invention is not limited to the following embodiments and experimental examples.

[0122] Examples 1 to 3 and Comparative Examples 1 to 4: Fabrication of the positive electrode for lithium secondary batteries

[0123] Weigh 88 parts by weight of LiFePO4 as the first positive electrode active material, 10 parts by weight of PVdF as the binder, and 2 parts by weight of carbon black as the conductive material, and mix them in an N-methylpyrrolidone (NMP) solvent to prepare a slurry for the first coating.

[0124] In addition, weigh 95 parts by weight of LiCoO2 as the second positive electrode active material, 2 parts by weight of PVdF as the binder, and 3 parts by weight of carbon black as the conductive material, and mix them in an N-methylpyrrolidone (NMP) solvent to prepare a slurry for the second coating.

[0125] Apply the slurry for the first coating onto the aluminum foil, dry and roll-press it to form the first coating (average thickness: 8 μm), and then pattern PVdF containing 20 wt% of carbon black on the first coating to form a pattern layer with a reticulated surface structure. Then, apply the slurry for the second coating, dry and roll-press it to fabricate the positive electrode for lithium secondary batteries. At this time, the area ratio and average thickness of the pattern layer relative to the first coating, and the average thicknesses of the pattern layer (PD) and the second coating (SD) are shown in Table 1 below.

[0126] [Table 1]

[0127] Experimental examples

[0128] In order to evaluate the performance of the positive electrode for lithium secondary batteries of the present invention, the following experiments were conducted.

[0129] A) Interlayer adhesion evaluation

[0130] The positive electrodes fabricated in the examples and comparative examples were cut into pieces with a horizontal length and a vertical length of 25 mm and 70 mm, respectively, and laminated at 70 °C and 4 MPa using a press to prepare samples. The prepared specimens were attached to a glass plate using double-sided tape and fixed. At this time, the current collector was placed facing the glass plate. Using a tensile testing machine, the second coating of the specimen was peeled off at an angle of 90° at 25 °C at a speed of 100 mm / min, and the peeling force at this time was measured in real time, and the average value was defined as the interfacial adhesion force between the first and second coatings. The results are shown in Table 2 below.

[0131] [Table 2]

[0132] Interlayer adhesion (N / m) Example 1 360 Example 2 390 Example 3 320 Comparative Example 1 281 Comparative Example 2 507 Comparative Example 3 423 Comparative Example 4 224

[0133] As shown in Table 2, in the positive electrode for a lithium secondary battery of the present invention, it was confirmed that each layer constituting the positive electrode had an interfacial adhesion force of 300 N / m or more. This means that the interfacial adhesion force of each layer constituting the positive electrode of this example is excellent, and the occurrence of cracks is alleviated.

[0134] B) Nail penetration test

[0135] Lithium secondary batteries were fabricated using each of the positive electrodes fabricated in the examples and comparative examples. Specifically, natural graphite, a carbon black conductive material, and a PVDF binder as negative electrode active materials were mixed at a weight ratio of 85:10:5 in an N-methylpyrrolidone solvent to prepare a slurry for forming a negative electrode, and then this slurry was applied to a copper foil to prepare a negative electrode. An electrode assembly was fabricated by laminating a separator (thickness: about 16 μm) made of porous polyethylene (PE) film between each of the positive electrodes fabricated in the examples and comparative examples and the negative electrode fabricated above. After the fabricated electrode assembly was placed in a battery case, an electrolyte was injected into the case to fabricate a lithium secondary battery. At this time, an electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF6) at a concentration of 1.0 M in an organic solvent composed of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (the mixing volume ratio of EC / DMC / EMC is 3 / 4 / 3).

[0136] For the fabricated lithium secondary batteries, in the same manner as the PV8450 certification conditions, it was evaluated whether ignition occurred when a metal body with a diameter of 3 mm was dropped and penetrated the battery cell at a speed of 80 mm / second. The results are shown in Table 3 below.

[0137] [Table 3]

[0138] Referring to Table 3, it was confirmed that in the positive electrode for a lithium secondary battery of the present invention, when a metal object such as a nail penetrates the electrode from the outside, no heat is generated and no fire occurs. From these results, it can be seen that the positive electrode for a lithium secondary battery of the present invention improves the safety of the battery by achieving a high penetration resistance when penetrated by a nail.

[0139] C) Cycle life performance evaluation

[0140] In the same manner as the nail penetration test, lithium secondary batteries were manufactured using each positive electrode produced in the examples and comparative examples. For each manufactured lithium secondary battery, 100 charge-discharge cycles (n = 100) and 200 charge-discharge cycles (n = 200) were carried out under the conditions of 25 °C, a charge cut-off voltage of 4.25 V, a discharge cut-off voltage of 2.5 V, and 0.5C / 0.5C to measure the capacity retention rate (%). At this time, the capacity retention rate was calculated using the following formula 2, and the results are shown in Table 4 below:

[0141] [Formula 2]

[0142] Capacity retention rate (%) = (discharge capacity at the nth charge-discharge cycle / discharge capacity at the initial charge-discharge cycle) × 100

[0143] [Table 4]

[0144]

[0145] As shown in Table 4, it can be seen that the positive electrodes of the examples manufactured according to the present invention have the effect of improving the electrical performance of the battery.

[0146] Specifically, it is known that the lithium secondary battery having the positive electrode manufactured in the example has a capacity retention rate of up to 95% or more even when 100 charge-discharge cycles and 200 charge-discharge cycles are carried out.

[0147] From these results, it can be seen that the positive electrode for a lithium secondary battery of the present invention includes a first coating and a second coating in sequence on the current collector, and a pattern layer with a specific area ratio is introduced in the form of a conductive material dispersed in the binder between the first coating and the second coating, thereby improving the safety of the battery. And thus, when a metal body penetrates the electrode from the outside, not only will it not heat up or catch fire due to overcurrent, etc., but also the adhesion between the multiple layers constituting the positive electrode can be improved, thereby improving the life characteristics of the battery.

[0148] Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art or ordinary technicians in the relevant field should understand that various changes and modifications can be made without departing from the spirit and scope of the present invention described in the appended claims.

[0149] Therefore, the technical scope of the present invention should not be limited to the content described in the detailed description part of the specification, but should be defined by the claims.

[0150] Description of Reference Numerals

[0151] 100: Positive electrode for lithium secondary battery

[0152] 110: Current collector

[0153] 120: First coating

[0154] 130: Pattern layer

[0155] 140: Second coating

Claims

1. A positive electrode for a lithium secondary battery, comprising: A current collector; A first coating provided on one or both surfaces of the current collector and containing a first positive electrode active material; A pattern layer provided on the first coating and containing a binder and a conductive material dispersed in the binder; And A second coating provided on the first coating on which the pattern layer is provided and containing a second positive electrode active material, wherein The area of the first coating provided with the pattern layer is 30% to 80% of the total area of the first coating, Wherein, the second coating satisfies the following formula 1: [Formula 1] 6 ≤ SD / PD ≤ 100 In formula 1, SD represents the average thickness of the second coating, PD represents the average thickness of the pattern layer.

2. The positive electrode for a lithium secondary battery according to claim 1, wherein, The pattern layer has a surface structure of dots, meshes, stripes or dendrites.

3. The positive electrode for a lithium secondary battery according to claim 1, wherein, The first coating and the second coating each contain 1 to 10 parts by weight of a binder based on 100 parts by weight of the first coating and the second coating respectively, and The binder in each coating includes one or more resins selected from the group consisting of polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, and copolymers thereof.

4. The positive electrode for a lithium secondary battery according to claim 1, wherein, The binder in the pattern layer includes one or more resins selected from the group consisting of polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene - propylene - diene monomer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, and copolymers thereof.

5. The positive electrode for a lithium secondary battery according to claim 1, wherein, The conductive material in the pattern layer includes one or more selected from the group consisting of the following materials: graphite, including natural graphite or artificial graphite; carbon black, including acetylene black, Ketjen black, channel black, furnace black, lamp black or thermal cracking carbon black; conductive fibers, including carbon fibers or metal fibers; carbon nanotubes; metal powders, including fluorocarbons, aluminum or nickel; zinc oxide; potassium titanate; titanium dioxide; and polyphenylene derivatives.

6. The positive electrode for a lithium secondary battery according to claim 1, wherein, In the pattern layer, based on 100 parts by weight of the binder, the content of the conductive material is 1 to 50 parts by weight.

7. The positive electrode for a lithium secondary battery according to claim 1, wherein, The average height of the pattern layer is 0.5 μm to 50 μm based on the cross - section.

8. The positive electrode for a lithium secondary battery according to claim 1, wherein, The average thickness of the first coating is 0.1 μm to 10 μm.

9. The positive electrode for a lithium secondary battery according to claim 1, wherein, The second coating further satisfies: 10 ≤ SD / PD ≤ 60.

10. The positive electrode for a lithium secondary battery according to claim 1, wherein, The first positive electrode active material includes a lithium iron phosphate compound represented by the following Chemical Formula 1: [Chemical Formula 1] Li 1+a Fe 1-b M 1 b (PO 4-c )X c Wherein, in Chemical Formula 1, M 1 is one or more selected from the group consisting of Al, Mg, and Ti, X is one or more selected from the group consisting of F, S, and N, and a, b, c are respectively - 0.5 ≤ a ≤ + 0.5, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.

1.

11. The positive electrode for a lithium secondary battery according to claim 1, wherein, The second positive electrode active material includes a lithium metal composite oxide represented by the following Chemical Formula 2: [Chemical Formula 2] LiCo 1-q M 2 q O2 Wherein, in Chemical Formula 2, M 2 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and q is 0 ≤ q ≤ 0.

4.

12. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 1.

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