Lithium secondary battery cathode and lithium secondary battery comprising same

Abstract

Provided is a lithium secondary battery cathode comprising: a cathode current collector; a functional layer, which is positioned on the cathode current collector and contains a lithium transition metal phosphorus oxide; a cathode active material layer, which is positioned on the functional layer and contains a cathode active material; and a ceramic insulating layer positioned on a functional-layer-uncoated area of the cathode current collector, wherein the ceramic insulating layer includes inorganic particles and a flame retardant. The lithium secondary battery cathode and the lithium secondary battery comprising same can ensure safety and reliability while minimizing a decrease in energy density during operation.

Description

Anode for a lithium secondary battery and a lithium secondary battery comprising the same

[0001] The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the same.

[0002] Lithium secondary batteries, which boast high energy density and portability, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research is underway to utilize high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles, or as power storage devices.

[0003] To implement lithium secondary batteries suitable for these applications, various cathodes are being investigated. However, conventional cathodes have the problem of generating heat when a short circuit occurs in a lithium secondary battery, leading to thermal runaway. Therefore, research is still needed to address this issue.

[0004] Provided are a cathode for a lithium secondary battery and a lithium secondary battery including the same, which can ensure safety and reliability while minimizing a decrease in energy density during operation of a high-energy-density lithium secondary battery.

[0005] In one embodiment, a positive electrode for a lithium secondary battery is provided, comprising: a positive electrode current collector; a functional layer positioned on the positive electrode current collector and containing a lithium transition metal phosphate; a positive electrode active material layer positioned on the functional layer and containing a positive electrode active material; and a ceramic insulating layer positioned on a portion of the positive electrode current collector on which the functional layer is not applied; wherein the ceramic insulating layer includes inorganic particles and a flame retardant.

[0006] In another embodiment, a lithium secondary battery is provided comprising the positive electrode, the negative electrode, and the electrolyte.

[0007] A positive electrode for a lithium secondary battery according to an embodiment of the present invention and a lithium secondary battery including the same can secure safety and reliability while minimizing a decrease in energy density during operation.

[0008] Figures 1 to 4 are schematic drawings showing a lithium secondary battery according to one embodiment.

[0009] Below, specific implementation examples are described in detail to facilitate their implementation by those skilled in the art. However, the present invention may be implemented in various different forms and is not limited to the implementation examples described herein.

[0010] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0011] Here, “combination of these” means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of the components.

[0012] It should be understood that the terms "include," "comprising," or "having" herein are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0013] To clearly illustrate various layers and regions in the drawings, their thicknesses are enlarged, and similar parts are designated by the same drawing reference numerals throughout the specification. When an element such as a layer, film, region, or plate is said to be "over" or "on" another element, this includes not only the case where it is "directly over" the other element, but also the case where there are other elements in between. Conversely, when an element is said to be "directly over" another element, it means that there are no other elements in between.

[0014] Here, “layer” includes not only shapes formed on the entire surface when observed in a plan view, but also shapes formed on some surfaces.

[0015] The average particle size can be measured by methods well known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with transmission electron microscope images or scanning electron microscope images. Alternatively, the average particle size can be obtained by measuring using dynamic light scattering, performing data analysis, counting the number of particles for each particle size range, and calculating from the counted number. Unless otherwise defined, the average particle size is the diameter (D) of the particles in the particle size distribution that have a cumulative volume of 50% by volume. 50 ) can mean. In addition, unless otherwise defined, the average particle size is obtained by measuring the size (diameter or length of major axis) of about 20 particles randomly in a scanning electron microscope image to obtain a particle size distribution, and the diameter (D) of the particle having a cumulative volume of 50% by volume in the particle size distribution 50 ) may be taken as the average particle diameter.

[0016] Here, “or” is not interpreted in an exclusive sense, for example, “A or B” is interpreted to include A, B, A+B, etc.

[0017] Here, “metal” is interpreted as a concept that includes ordinary metals, transition metals, and metalloids (semi-metals).

[0018] anode

[0019] In one embodiment, a positive electrode for a lithium secondary battery is provided, comprising: a positive electrode current collector; a functional layer positioned on the positive electrode current collector and containing a lithium transition metal phosphate; a positive electrode active material layer positioned on the functional layer and containing a positive electrode active material; and a ceramic insulating layer positioned on a portion of the positive electrode current collector on which the functional layer is not applied; wherein the ceramic insulating layer includes inorganic particles and a flame retardant.

[0020] The above positive electrode can ensure safety and reliability while minimizing the decrease in energy density during operation of a lithium secondary battery including the positive electrode. Specifically, when a short circuit occurs in a lithium secondary battery including the positive electrode, current does not flow directly to the positive electrode current collector, but flows in the form of positive electrode active material ↔ functional layer ↔ positive electrode current collector, thereby inducing a decrease in Joule heat. Accordingly, a lithium secondary battery including the positive electrode can ensure safety and reliability while reducing the overall amount of heat generated when a short circuit occurs.

[0021] Hereinafter, the configuration of the above anode will be described in detail.

[0022] functional layer

[0023] According to one embodiment, the functional layer is positioned on the positive electrode current collector and below the positive electrode active material layer. Accordingly, when a short circuit occurs in a lithium secondary battery including the positive electrode, current flows in the form of positive electrode active material ↔ functional layer ↔ positive electrode current collector, thereby inducing a reduction in Joule heat. In addition, the functional layer may perform the same role as the positive electrode active material layer, that is, the role of increasing capacity or increasing output.

[0024] To perform the above role, the functional layer may contain a lithium transition metal phosphate. The lithium transition metal phosphate may play a role in increasing capacity or output while improving heat resistance, thermal safety, and fire safety by inducing a reduction in joule heat when a short circuit occurs. Specifically, the lithium transition metal phosphate may include a compound represented by the following chemical formula 1, chemical formula 2, chemical formula 3, chemical formula 4, or chemical formula 5, or a combination thereof.

[0025] [Chemical Formula 1]

[0026] Li a1 Fe (1-x1) M 1 x1 PO4

[0027] In chemical formula 1, 0.90≤a1≤1.5, 0≤x1≤0.4, and M 1 can be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof. Here, 0.90≤a1≤1.5, for example, 0.90≤a1≤1.2, or 0.95≤a1≤1.1. In addition, 0≤x1≤0.4, 0≤x1≤0.3, 0≤x1≤0.2, 0≤x1≤0.1, or 0≤x1≤0.05.

[0028] [Chemical Formula 2]

[0029] Li a2 Mn x2 Fe (1-x2-y2) M 2 y2 PO4

[0030] In chemical formula 2, 0.90≤a2≤1.5, 0.1≤x2≤0.9, M 2 can be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof. Here, 0.90≤a2≤1.5 can be satisfied, for example, 0.90≤a2≤1.2, or 0.95≤a2≤1.1. In addition, 0.1≤x2≤0.9, 0.3≤x2≤0.9, or 0.4≤x2≤0.8 can be satisfied, and 0≤y2≤0.4, 0≤y2≤0.3, 0≤y2≤0.2, 0≤y2≤0.1, or 0≤y2≤0.05 can be satisfied.

[0031] [Chemical Formula 3]

[0032] Li a3 Mn (1-x3) M 3 x3 PO4

[0033] In chemical formula 3, 0.90≤a3≤1.5, 0≤x3≤0.4, and M 3may be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof. Here, 0.90≤a3≤1.5 may be satisfied, for example, 0.90≤a3≤1.2, or 0.95≤a3≤1.1. In addition, 0≤x3≤0.4, 0≤x3≤0.3, 0≤x3≤0.2, 0≤x3≤0.1, or 0≤x3≤0.05 may be satisfied.

[0034] [Chemical Formula 4]

[0035] Li a4 Ti (2-x4) M 4 x4 (PO4)3

[0036] In chemical formula 4, 0.90≤a4≤1.5, 0≤x4≤0.4, and M 4 may be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof. Here, 0.90≤a4≤1.5 may be satisfied, for example, 0.90≤a4≤1.2, or 0.95≤a4≤1.1. In addition, 0≤x4≤0.4, 0≤x4≤0.3, 0≤x4≤0.2, 0≤x4≤0.1, or 0≤x4≤0.05 may be satisfied.

[0037] [Chemical Formula 5]

[0038] Li a5 Ti (1-x5) M 5 x5 PO5

[0039] In chemical formula 5, 0.90≤a5≤1.5, 0≤x5≤0.4, and M 5may be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof. Here, 0.90≤a5≤1.5 may be satisfied, for example, 0.90≤a5≤1.2, or 0.95≤a5≤1.1. In addition, 0≤x5≤0.4, 0≤x5≤0.3, 0≤x5≤0.2, 0≤x5≤0.1, or 0≤x5≤0.05 may be satisfied.

[0040] More specifically, the lithium transition metal phosphate is LiFePO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 It may include PO4, LiMnPO4, LiTiPO5, LiTi2(PO4)3, or a combination thereof.

[0041] The above lithium transition metal phosphate is in particle form, and the average particle diameter (D) of the particles 50 ) may be 0.01 ㎛ to 2 ㎛, for example 0.1 ㎛ to 1 ㎛, or 0.2 ㎛ to 0.9 ㎛.

[0042] Furthermore, the functional layer may further include a first binder and a first conductive material.

[0043] The first binder may serve to ensure that the materials within the functional layer adhere to each other and to ensure that the functional layer adheres to the active material layer. The first binder may be an insoluble binder, a water-soluble binder, or a combination thereof.

[0044] The above-mentioned non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, an ethylene propylene copolymer, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0045] The water-soluble binder may be a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber (ABR), acrylic rubber, butyl rubber, fluoroelastomer, and combinations thereof. The polymer resin binder may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0046] When using a water-soluble binder as the first binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0047] The first binder may be included in an amount of 0.1 to 15 wt% based on 100 wt% of the functional layer, for example, 0.5 to 11 wt%, 0.5 to 5 wt%, or 0.5 to 3 wt%.

[0048] The first conductive material may be a conductive material including, for example, a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or carbon nanotube; a metal-based material containing copper, nickel, aluminum, or silver in the form of metal powder or metal fiber; a conductive polymer such as a polyphenylene derivative; or a mixture thereof.

[0049] The first conductive agent may be included in an amount of 0.1 to 5 wt% based on 100 wt% of the functional layer, for example, 0.1 to 3 wt%, 0.1 to 2 wt%, 0.1 to 1 wt%, or 0.1 to 0.9 wt%.

[0050] For example, the first conductive material may be carbon nanofibers, carbon nanotubes, or a combination thereof, in which case excellent conductivity can be achieved even if the content of the first conductive material in the functional layer is reduced, and by reducing the content of the conductive material, the capacity can be increased and heat resistance can be further improved. For example, when the first conductive material is carbon nanofibers, carbon nanotubes, or a combination thereof, it may be included in an amount of 1 wt% or less with respect to 100 wt% of the functional layer, and for example, it may be included in an amount of 0.1 to 0.9 wt%.

[0051] When the functional layer includes a first conductive material and a first binder, the functional layer may contain 80 to 99.8 wt% of the lithium transition metal phosphate, 0.1 to 15 wt% of the first binder, and 0.1 to 5 wt% of the conductive material, based on 100 wt% of the functional layer. When each component of the functional layer satisfies the above content range, the capacity of the battery can be maximized while improving heat resistance.

[0052] The thickness of the functional layer may be 1 to 30 μm, for example, 1 to 20 μm, 1 to 10 μm, or 2 to 8 μm. When this range is satisfied, the functional layer can sufficiently contribute to ensuring heat resistance, safety, and reliability while minimizing a decrease in energy density while the lithium secondary battery is being operated.

[0053] The area of ​​the functional layer may be equal to or smaller than the area of ​​one side of the positive electrode current collector, and more specifically, the ratio of the area of ​​the functional layer to the area of ​​the positive electrode current collector may be 0.7 to 0.99, or 0.8 to 0.9. Accordingly, a portion of the surface of the positive electrode current collector may be exposed without being covered by the functional layer, and a ceramic insulating layer may be applied to a portion of the surface of the positive electrode current collector that is exposed without the functional layer applied, thereby maximizing the stability of the lithium secondary battery.

[0054] positive electrode active material layer

[0055] According to one embodiment, the positive electrode active material layer is positioned on the functional layer, contains a positive electrode active material, and may further include a second binder and / or a second conductive material.

[0056] A compound capable of reversible intercalation and deintercalation of lithium (a lithiated intercalation compound) can be used as a cathode active material. Specifically, one or more of a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0057] The above composite oxide may be a lithium transition metal composite oxide, and specific examples thereof include lithium nickel-based oxide, lithium cobalt-based oxide, lithium manganese-based oxide, lithium iron phosphate-based compound, cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0058] As an example, a compound represented by any one of the following chemical formulas may be used: Li a A1-b X b About 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b About 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c About 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mn b X c About 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni b Co c L 1 d G e O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li a NiG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2); Li a FePO4(0.90≤a≤1.8).

[0059] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al or a combination thereof.

[0060] More specifically, the positive electrode active material may include a lithium nickel-based composite oxide represented by the following chemical formula 6, a lithium cobalt-based composite oxide represented by the following chemical formula 7, or a combination thereof.

[0061] [Chemical Formula 6]

[0062] Li a6 Ni x6 M 6 y6 M 7 z6 O 2-b6 X b6

[0063] In chemical formula 6, 0.9≤a6≤1.8, 0.3≤x6≤1, 0≤y6≤0.7, 0≤z6≤0.7, 0.9≤x6+y6+z6≤1.1, and 0≤b6≤0.1, and M 6 and M 7 are each independently one or more elements of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements of F, P, and S.

[0064] In chemical formula 6, 0.6≤x6≤1, 0≤y6≤0.4, and 0≤z6≤0.4, or 0.8≤x6≤1, 0≤y6≤0.2, and 0≤z6≤0.2.

[0065] [Chemical Formula 7]

[0066] Li a7 Co x7 M 8y7 O 2-b7 X b7

[0067] In chemical formula 7, 0.9≤a7≤1.8, 0.7≤x7≤1, 0≤y7≤0.3, 0.9≤x7+y7≤1.1, and 0≤b7≤0.1, and M 8 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0068] In chemical formula 7, 0.8≤x7≤1, and 0≤y7≤0.2, or 0.7≤x7≤0.9, and 0≤y7≤0.2.

[0069] For example, the cathode active material may be a high-nickel cathode active material in which the nickel content is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less, based on 100 mol% of metals excluding lithium in the lithium transition metal composite oxide. The high-nickel cathode active material can realize high capacity and thus can be applied to high-capacity, high-density lithium secondary batteries.

[0070] As another example, the positive electrode active material may include a lithium cobalt-based composite oxide, in which case excellent capacity and life characteristics can be realized in a high voltage range.

[0071] The content of the positive electrode active material may be 90 wt% to 99.8 wt%, for example, 95 wt% to 98 wt%, based on the total weight of the positive electrode active material layer. The content of the second binder and the second conductive material may be 0.1 wt% to 5 wt%, or 0.1 wt% to 3 wt%, respectively, based on the total weight of the positive electrode active material layer.

[0072] The second binder serves to adhere the positive electrode active material particles well to each other and also to adhere the positive electrode active material well to the current collector, and representative examples thereof include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0073] The second conductive material is used to provide conductivity to the electrode, and any material that does not cause a chemical change and is electronically conductive in the battery to be constructed can be used. Examples of such conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or conductive materials including mixtures thereof.

[0074] For example, the second conductive material may be carbon nanofibers, carbon nanotubes, or a combination thereof, in which case excellent conductivity can be achieved even if the content of the second conductive material in the positive electrode active material layer is reduced, and capacity can be maximized by reducing the content of the conductive material. For example, when the second conductive material is carbon nanofibers, carbon nanotubes, or a combination thereof, it may be included in an amount of 1 wt% or less with respect to 100 wt% of the positive electrode active material layer, and may be included in an amount of, for example, 0.1 to 0.9 wt%.

[0075] The thickness of the positive electrode active material layer may be 10 μm to 300 μm, for example, 12 μm to 280 μm, 15 μm to 250 μm, 18 μm to 220 μm, or 20 μm to 200 μm. In this case, the positive electrode active material layer may sufficiently contribute to the capacity and / or output of the lithium secondary battery.

[0076] The area of ​​the functional layer may be equal to or greater than the area of ​​the positive electrode active material layer, and more specifically, the ratio of the area of ​​the functional layer to the area of ​​the positive electrode active material layer may be 1 to 1.5, or 1.1 to 1.4. Accordingly, a portion of the surface of the functional layer may be exposed without being covered by the positive electrode active material layer, and a reduction in Joule heat is induced as current flows in the form of positive electrode active material ↔ functional layer ↔ positive electrode current collector. Accordingly, a lithium secondary battery including the positive electrode can secure safety and reliability while reducing the overall heat generation when a short circuit occurs.

[0077] Ceramic insulating layer

[0078] The above ceramic insulating layer is a layer that performs an insulating function by including inorganic particles and is located on a non-functional layer portion, i.e., a non-coated portion, on the positive electrode current collector. The ceramic insulating layer according to one embodiment is characterized by including not only inorganic particles but also a flame retardant. By including a flame retardant in the ceramic insulating layer, the thermal safety and fire safety of a lithium secondary battery can be further improved.

[0079] The inorganic particles may include, for example, aluminum oxide, silicon dioxide, magnesium oxide, titanium dioxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite (AlO(OH)) or combinations thereof.

[0080] The average particle diameter of the above inorganic particles (D 50) may be 0.1 ㎛ to 20 ㎛, for example, 0.1 ㎛ to 10 ㎛, 0.1 ㎛ to 5 ㎛, and for example, may be more than 2 ㎛, for example, 2.1 ㎛ to 5 ㎛. By appropriately adjusting the size of the inorganic particles, the adhesion and heat resistance of the ceramic insulating layer can be improved.

[0081] The inorganic particles may be included in an amount of 50 wt% to 99.9 wt% based on 100 wt% of the ceramic insulating layer, for example, 65 wt% to 99 wt%, 70 wt% to 98 wt%, 80 wt% to 97 wt%, or 90 wt% to 96 wt%. When the inorganic particles are included in the above content range, the ceramic insulating layer can realize excellent insulating performance, heat resistance, and fire safety.

[0082] The above flame retardant may include a phosphorus-based flame retardant, a silicone-based flame retardant, a nitrogen-based flame retardant, a sulfur-based flame retardant, a boron-based flame retardant, a halogenated flame retardant, an inorganic oxide flame retardant, or a combination thereof.

[0083] The above-mentioned flame retardant is not particularly limited as long as it is of a type generally used in industry, and may include, for example, phosphate, phosphite, phosphonate, phosphinate, phosphine oxide, phosphazene, or a combination thereof, and more specifically, phosphazene may be used.

[0084] The above-mentioned phosphorus flame retardant has an organic functional group such as an alkyl group, an aryl group, an alkenyl group, etc., and the organic functional group may be substituted with a halogen group, an amine group, a hydroxyl group, a thiol group, etc. Here, the alkyl group may be an alkyl group having 1 to 20 carbon atoms, the aryl group may be an aryl group having 6 to 20 carbon atoms, and the alkenyl group may be an alkenyl group having 2 to 20 carbon atoms. The phosphate may be, for example, trialkyl phosphate, alkyldiaryl phosphate, triaryl phosphate, ammonium polyphosphate, etc., and the phosphinate may be a metal dialkyl phosphinate.

[0085] As a specific example, the phosphorus flame retardant is ammonium phosphate, ammonium polyphosphate, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tripentyl phosphate, tris(2-ethylhexyl) phosphate, trioctyl phosphate, tris(2-butoxyethyl) phosphate, tris(2-chloroethyl) phosphate, tris(1-chloro-2-propyl) phosphate, tris(2-chloropropyl) phosphate, tris(3-chloropropyl) phosphate, tris(1,3-dichloro-2-propyl) phosphate, tris(2,3-dibromopropyl) phosphate, tris(tribromoneopentyl) phosphate, trimethylpropane methylphosphonic oligomer, pentaerythritol phosphate, cyclic neopentyl thiophosphoric acid Anhydride, 2-ethylhexyl diphenyl phosphate, isodecyl diphenyl phosphate, cresyl diphenyl phosphate, triphenyl phosphate, tricresyl phosphate, tert-butylphenyl diphenyl phosphate, tris(2,4-dibromophenyl) phosphate, N,N'-bis(2-hydroxyethyl)aminomethyl phosphate, resorcinol bis(diphenyl phosphate), bisphenol A bis(diphenyl phosphate), tetraphenyl mp-phenylene diphosphate, tetrakis(2-chloroethyl)dichloroisopentyl diphosphate, dimethyl propane phosphonate, dimethyl methane phosphonate, diethyl ethane phosphonate, diethyl hydroxymethane phosphonate, aluminum diethyl phosphinate, zinc diethyl phosphinate, aluminum dipropyl phosphinate, aluminum 2-carboxyethyl It may include phenyl phosphinate, phosphazene, or a combination thereof. When using a phosphorus flame retardant, it has the advantage of excellent flame retardancy and thermal stability, a high melting point, and low volatility, so that even when applied to a resin, it does not deteriorate the inherent physical properties of the resin.

[0086] The above nitrogen-based flame retardant is not particularly limited as long as it is a type generally used in industry, and may include, for example, melamine cyanurate, melamine phosphate, melamine polyphosphate, melamine pyrophosphate, melamine ammonium polyphosphate, melamine ammonium pyrophosphate, melamine borate, melamine sulfate, or a combination thereof.

[0087] The above sulfur-based flame retardant is not particularly limited as long as it is a type generally used in industry, and may include, for example, alkylbenzenesulfonic acid, alkylsulfonic acid, naphthelanesulfonic acid, or a combination thereof.

[0088] The above boron-based flame retardant is not particularly limited as long as it is of a type generally used in industry, and may include, for example, zinc borate, zinc metaborate, barium metaborate, or a combination thereof.

[0089] The above halogenated flame retardant is not particularly limited as long as it is a type generally used in industry, and may include, for example, hexabromobenzene, hexabromobiphenyl ether, tribromophenol, decabromodiphenyl ether, decabromodiphenyl oxide, halogenated polycarbonate, halogenated polystyrene, halogenated polyolefin, or a combination thereof.

[0090] The above inorganic oxide flame retardant is not particularly limited as long as it is a type generally used in industry, and may include, for example, aluminum oxide, magnesium oxide, magnesium hydroxide, zinc oxide, titanium oxide, silicon oxide, ammonium hydroxide, or a combination thereof.

[0091] The flame retardant may be included in an amount of 0.1 wt% to 50 wt% based on 100 wt% of the ceramic insulating layer, for example, 1 wt% to 45 wt%, 2 wt% to 40 wt%, 5 wt% to 35 wt%, 10 wt% to 30 wt%, or 20 wt% to 30 wt%. When the flame retardant is included in an amount within the above range, the overall heat generation when a short circuit occurs can be reduced, thereby ensuring safety and reliability.

[0092] Furthermore, the ceramic insulating layer may further include a third binder.

[0093] The third binder can serve to adhere the materials within the ceramic insulating layer well to each other and to adhere the ceramic insulating layer well to the positive electrode current collector.

[0094] The third binder may be an insoluble binder, a water-soluble binder, or a combination thereof. The description of these materials is the same as that of the first binder.

[0095] The third binder may be included in an amount of 0.1 to 15 wt%, for example, 4 to 11 wt%, based on 100 wt% of the ceramic insulating layer.

[0096] The thickness of the ceramic insulating layer may be 1 μm to 20 μm, for example, 3 μm to 18 μm, 5 μm to 16 μm, 10 μm to 15 μm, or 12 μm to 15 μm. In this case, the ceramic insulating layer can sufficiently contribute to the insulating effect during operation of the lithium secondary battery.

[0097] The area of ​​the ceramic insulating layer may be small compared to the area of ​​the positive electrode current collector, and more specifically, the ratio of the area of ​​the ceramic insulating layer to the area of ​​the positive electrode current collector may be 0.01 to 0.3, or 0.1 to 0.2.

[0098] For example, the ceramic insulating layer and the functional layer may be spaced apart from each other or may be in contact with each other. Similarly, the ceramic insulating layer and the positive electrode active material layer may be spaced apart from each other or may be in contact with each other. When each layer is in contact with each other, a mixed region in which the components of each layer are mixed may exist at the interface. When the ceramic insulating layer and each layer are spaced apart from each other, the separation distance between the ceramic insulating layer and the functional layer may be shorter than the separation distance between the ceramic insulating layer and the positive electrode active material layer.

[0099] positive current collector

[0100] Aluminum foil may be used as the positive electrode current collector, but is not limited thereto.

[0101] lithium secondary battery

[0102] In one embodiment, a lithium secondary battery is provided comprising the aforementioned positive electrode, negative electrode, and electrolyte. As an example, the lithium secondary battery may comprise a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrolyte.

[0103] Lithium secondary batteries can be classified into cylindrical, square, pouch, coin, etc. shapes according to their form. FIGS. 1 to 4 are schematic diagrams illustrating lithium secondary batteries according to one embodiment, wherein FIG. 1 can be said to be a circular battery shape, FIG. 2 a square battery shape, and FIGS. 3 and 4 a pouch battery shape. Referring to FIGS. 1 to 4, a lithium secondary battery (100) may include an electrode assembly (40) having a separator (30) interposed between a positive electrode (10) and a negative electrode (20), and a case (50) in which the electrode assembly (40) is built. The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown). The lithium secondary battery (100) may include a sealing member (60) that seals the case (50) as shown in FIG. 1. In addition, in FIG. 2, the lithium secondary battery (100) may include a positive lead tab (11), a positive terminal (12), a negative lead tab (21), and a negative terminal (22). As in FIGS. 3 and 4, the lithium secondary battery (100) may include electrode tabs (70), i.e., a positive tab (71) and a negative tab (72), which serve as electrical paths for inducing current formed in the electrode assembly (40) to the outside.

[0104] A lithium secondary battery according to one embodiment may be capable of being charged at a high voltage or may be suitable for being driven at a high voltage. For example, the charging voltage of the lithium secondary battery may be 4.45 V or higher, or may be 4.45 V to 4.7 V, 4.45 V to 4.6 V, or 4.45 V to 4.55 V, etc. By applying a cathode active material according to one embodiment, the lithium secondary battery can significantly reduce the amount of gas generated even when charged at a high voltage and can implement high capacity and long life characteristics.

[0105] cathode

[0106] The negative electrode may include a current collector and a negative electrode active material layer positioned on the current collector, and the negative electrode active material layer includes a negative electrode active material and may further include a binder, a conductive material, or a combination thereof.

[0107] Negative active material

[0108] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0109] The material capable of reversibly intercalating / deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0110] As the above lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0111] As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, silicon-carbon composite, SiOx(0 <x≤2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소(Si를 제외함), 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합에서 선택되는 원소이며, 예컨대 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, 및 이들의 조합에서 선택됨), 또는 이들의 조합일 수 있다. 상기 Sn계 음극 활물질로는 Sn, SnO2, Sn 합금 또는 이들의 조합일 수 있다.

[0112] The above silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle diameter (D) of the silicon-carbon composite particles 50 ) may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it may include secondary particles (cores) in which silicon primary particles are assembled and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the silicon primary particles, so that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0113] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles, and an amorphous carbon coating layer positioned on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon may include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0114] When the above silicon-carbon composite includes silicon and amorphous carbon, the content of silicon may be 10 wt% to 50 wt%, and the content of amorphous carbon may be 50 wt% to 90 wt%, based on 100 wt% of the silicon-carbon composite. In addition, when the composite includes silicon, amorphous carbon, and crystalline carbon, the content of silicon may be 10 wt% to 50 wt%, the content of crystalline carbon may be 10 wt% to 70 wt%, and the content of amorphous carbon may be 20 wt% to 40 wt%, based on 100 wt% of the silicon-carbon composite.

[0115] In addition, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle diameter (D) of the silicon particles (primary particles) 50 ) may be 10 nm to 1 ㎛, or 10 nm to 200 nm. The silicon particles may exist as silicon alone, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is SiO x (0 <x≤2)로 표시될 수 있다. 이때, 산화 정도를 나타내는 Si:O의 원자 함량 비율은 99:1 내지 33:67일 수 있다. 본 명세서에서, 별도의 정의가 없는 한, 평균 입경(D 50 ) means the diameter of the particle whose cumulative volume is 50% by volume in the particle size distribution.

[0116] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material. When the Si-based negative electrode active material or Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio can be 1:99 to 90:10 by weight.

[0117] bookbinder

[0118] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0119] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0120] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0121] When using an aqueous binder as the cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0122] The dry binder is a polymeric material capable of being fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0123] Challenge

[0124] Conductive materials are used to impart conductivity to electrodes, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, and silver in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0125] The content of the negative active material may be 95 wt% to 99.5 wt% with respect to 100 wt% of the negative active material layer, and the content of the binder may be 0.5 wt% to 5 wt% with respect to 100 wt% of the negative active material layer. For example, the negative active material layer may include 90 wt% to 99 wt% of the negative active material, 0.5 wt% to 5 wt% of the binder, and 0.5 wt% to 5 wt% of the conductive material.

[0126] Whole house

[0127] The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, and may be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0128] electrolyte

[0129] An electrolyte for a lithium secondary battery may be, for example, an electrolyte solution, which may include a non-aqueous organic solvent and a lithium salt.

[0130] Non-aqueous organic solvents serve as a medium through which ions involved in the electrochemical reactions of a battery can move. Non-aqueous organic solvents can be carbonate, ester, ether, ketone, or alcohol solvents, aprotic solvents, or combinations thereof.

[0131] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, and caprolactone. Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. In addition, examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol, and examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0132] Non-aqueous organic solvents can be used alone or in combination of two or more, and when two or more are used in combination, the mixing ratio can be appropriately adjusted depending on the desired battery performance, which is widely understood by those working in the relevant field.

[0133] When using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0134] The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent. For example, a carbonate-based solvent and an aromatic hydrocarbon-based organic solvent may be mixed and used in a volume ratio of 1:1 to 30:1.

[0135] The electrolyte may further contain vinylethyl carbonate, vinylene carbonate or ethylene carbonate compounds to improve battery life.

[0136] Representative examples of the above ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0137] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions in the battery, enabling the basic operation of lithium secondary batteries and promoting the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, LiN(C x F2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), lithium bis(oxalato)borate (LiBOB).

[0138] It is recommended that the concentration of lithium salt be within the range of 0.1 M to 2.0 M. When the concentration of lithium salt is within the above range, the electrolyte can exhibit excellent performance due to its appropriate ionic conductivity and viscosity, and lithium ions can move effectively.

[0139] separator

[0140] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films comprising two or more layers thereof. Furthermore, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0141] The above separator may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof, positioned on one or both sides of the porous substrate.

[0142] The above porous substrate may be a polymer film formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyarylether ketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more thereof.

[0143] The porous substrate may have a thickness of about 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0144] The organic material may include a (meth)acrylic copolymer comprising a first structural unit derived from (meth)acrylamide, and a second structural unit comprising at least one of a structural unit derived from (meth)acrylic acid or a (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0145] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include inorganic particles selected from SrTiO3, BaTiO3, Mg(OH)2, boehmite and combinations thereof, but is not limited thereto. The average particle diameter (D) of the inorganic particles 50 ) can be from 1 nm to 2000 nm, for example, from 100 nm to 1000 nm, from 100 nm to 700 nm.

[0146] The organic and inorganic substances may be mixed and present in one coating layer, or a coating layer including an organic substance and a coating layer including an inorganic substance may be present in a laminated form.

[0147] The thickness of the above coating layer may be 0.5 ㎛ to 20 ㎛, for example, 1 ㎛ to 10 ㎛, or 1 ㎛ to 5 ㎛.

[0148]

[0149] Hereinafter, examples and comparative examples of the present invention are described. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0150] Example 1

[0151] 1. Manufacturing of the anode

[0152] LiFePO4 (95 wt% lithium transition metal phosphate), polyvinylidene fluoride (3 wt% polyvinylidene fluoride) as a binder, and Ketjen Black (2 wt% conductive material) are mixed in an N-methylpyrrolidone solvent. These are applied vertically (lengthwise) from one end of one side of an aluminum current collector and dried to produce a functional layer having a thickness of 4 μm. Here, a microgravure device was used as the application method.

[0153] A slurry of positive electrode active material is prepared by mixing 95 wt% LiCoO2 as a positive electrode active material, 3 wt% polyvinylidene fluoride as a binder, and 2 wt% Ketjen Black as a conductive material in an N-methylpyrrolidone solvent. The slurry is applied in the vertical (length) direction from the end of the functional layer and dried to prepare a positive electrode active material layer having a thickness of 50 μm.

[0154] A ceramic insulating layer slurry is prepared by mixing 80 wt% of boehmite as a ceramic, 10 wt% of polyvinylidene fluoride as a binder, and 10 wt% of phosphazene as a flame retardant in a water solvent. The slurry is applied in the vertical (length) direction from one side of the aluminum current collector where the functional layer is not present, and dried to prepare a ceramic insulating layer having a thickness of 10 μm. Here, a micro gravure coater was used as the application method.

[0155] 2. Manufacturing of the cathode

[0156] A slurry of negative active material is prepared by mixing 97.3 wt% of graphite, 0.5 wt% of Denka black, 0.9 wt% of carboxymethyl cellulose, and 1.3 wt% of styrene-butadiene rubber in an aqueous solvent. This is applied to copper foil and dried to prepare a negative active material layer.

[0157] 3. Manufacturing of lithium secondary batteries

[0158] A polyethylene separator was placed between the positive electrode and the negative electrode to manufacture a laminate, and the laminate was pressed in a vertical direction while being rolled up to manufacture a rolled electrode assembly.

[0159] After placing the above-mentioned coil-type electrode assembly in a pouch, a lithium secondary battery is manufactured by injecting an electrolyte solution in which 1.0 M LiPF6 lithium salt is added to a solvent in which ethylene carbonate and diethyl carbonate are mixed in a volume ratio of 50:50.

[0160] Examples 2 to 12

[0161] In the manufacture of the positive electrode, the positive electrode and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the type and content of the flame retardant in the ceramic insulating layer were mixed as shown in Table 1 below.

[0162] Comparative Example 1

[0163] In the manufacture of the positive electrode, the positive electrode and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that no flame retardant was used in the ceramic insulating layer.

[0164] The above examples and comparative examples are summarized and shown in Table 1 below.

[0165] Flame retardant Flame retardant content (% by weight) Ceramic insulation layer thickness (㎛) Example 1 Phosphazene 10 10 Example 2 Phosphazene 20 10 Example 3 Phosphazene 30 10 Example 4 Phosphazene 10 13 Example 5 Phosphonate 20 10 Example 6 Phosphonate 30 10 Example 7 Phosphonate 10 13 Example 8 Phosphonate 20 13 Example 9 Phosphate 20 10 Example 10 Phosphate 30 10 Example 11 Phosphate 10 13 Example 12 Phosphate 20 13 Comparative Example 1 ---

[0166]

[0167] Evaluation Example 1: Measurement of self-extinguishing time (SET)

[0168] In order to evaluate the flame retardancy of the positive electrodes manufactured in Examples 1 to 12 and Comparative Example 1, the self-combustion time (SET) was measured. The self-combustion time (SET) was measured by pouring 0.3 g of electrolyte into the coin cell lid and measuring whether it caught fire when a torch flame was applied to it for about 1 second (refer to international standards ASTM D93-11, JIS K 2265:1996). In Table 2 below, “non-combustible” means that it does not catch fire even when repeatedly applied to a flame three or more times, and the numerical value is the time from when it catches fire until it goes out.

[0169] Self-combustion time (sec / g) Example 110 Example 2 Non-combustible Example 3 Non-combustible Example 410 Example 577 Example 654 Example 783 Example 877 Example 968 Example 1048 Example 1181 Example 1268 Comparative Example 197

[0170] Referring to Table 2, when a flame retardant is included in the ceramic insulating layer according to Examples 1 to 12, it can be confirmed that the self-combustion time is shorter compared to Comparative Example 1, and thus the flame retardancy is excellent. In particular, in the case of Examples 1 to 4 using phosphazene as the flame retardant in the ceramic insulating layer, it can be confirmed that the flame retardancy is even better, and in the case of Examples 2 and 3 containing 20 wt% or more of phosphazene, it can be confirmed that the flame retardancy is the best because it does not catch fire even when repeatedly exposed to a flame three or more times.

[0171] Evaluation Example 2: Penetration Stability Evaluation

[0172] The penetration stability of the lithium secondary batteries manufactured in Examples 1 to 12 and Comparative Example 1 was evaluated at a penetration speed of (150 m / sec) using a 2.5-pie nail, and the results are shown in Table 3. The evaluation criteria are as follows.

[0173] <Evaluation Criteria>

[0174] 0F / 3: No response

[0175] 1F / 3: Battery performance is impaired.

[0176] 2F / 3: The weight of the battery electrolyte has decreased by less than 50%.

[0177] 3F / 3: The weight of the battery's electrolyte has decreased by more than 50%.

[0178] Penetration Stability Example 11F / 3 Example 20F / 3 Example 30F / 3 Example 40F / 3 Example 51F / 3 Example 60F / 3 Example 71F / 3 Example 80F / 3 Example 91F / 3 Example 100F / 3 Example 112F / 3 Example 120F / 3 Comparative Example 13F / 3

[0179] Referring to Table 3, it can be confirmed that when a flame retardant is included in the ceramic insulating layer according to Examples 1 to 12, the penetration stability is superior compared to Comparative Example 1. In particular, it can be confirmed that the flame retardancy is even superior in Examples 1 to 4, in which phosphazene is used as the flame retardant in the ceramic insulating layer. In addition, even when phosphonate or phosphate is used as the flame retardant, it can be confirmed that the flame retardancy is even superior in Examples 6 and 10, in which 30 wt% or more of the flame retardant is included, or in Examples 8 and 12, in which 20 wt% or more of the flame retardant is included and the thickness of the ceramic insulating layer is 13 ㎛ or more.

[0180] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention.

[0181] [Explanation of symbols]

[0182] 100: Lithium secondary battery 10: Cathode

[0183] 11: Positive lead tab 12: Positive terminal

[0184] 20: Negative lead tab 21: Negative lead tab

[0185] 22: Negative terminal 30: Separator

[0186] 40: Electrode assembly 50: Case

[0187] 60: Sealing member 70: Electrode tab

[0188] 71: Positive tab 72: Negative tab

Claims

1. Bipolar collector; A functional layer located on the positive electrode collector and containing a lithium transition metal phosphate; A positive electrode active material layer located on the functional layer and containing a positive electrode active material; and A ceramic insulating layer located on the non-functional layer portion on the above-mentioned positive electrode collector; The above ceramic insulating layer is a positive electrode for a lithium secondary battery containing inorganic particles and a flame retardant.

2. In paragraph 1, The above lithium transition metal phosphate is a cathode for a lithium secondary battery comprising a compound represented by Chemical Formula 1, Chemical Formula 2, Chemical Formula 3, Chemical Formula 4, Chemical Formula 5, or a combination thereof: [Chemical Formula 1] Li a1 Fe (1-x1) M 1 x1 PO4 In chemical formula 1, 0.90≤a1≤1.5, 0≤x1≤0.4, and M 1 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof, [Chemical Formula 2] Li a2 Mn x2 Fe (1-x2-y2) M 2 y2 PO4 In chemical formula 2, 0.90≤a2≤1.5, 0.1≤x2≤0.9, M 2 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof, [Chemical Formula 3] Li a3 Mn (1-x3) M 3 x3 PO4 In chemical formula 3, 0.90≤a3≤1.5, 0≤x3≤0.4, and M 3 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof, [Chemical Formula 4] Li a4 You (2-x4) M 4 x4 (PO4)3 In chemical formula 4, 0.90≤a4≤1.5, 0≤x4≤0.4, and M 4 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof, [Chemical Formula 5] Li a5 You (1-x5) M 5 x5 PO5 In chemical formula 5, 0.90≤a5≤1.5, 0≤x5≤0.4, and M 5 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof.

3. In paragraph 2, The above lithium transition metal phosphates are LiFePO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 A cathode for a lithium secondary battery comprising PO4, LiMnPO4, LiTiPO5, LiTi2(PO4)3, or a combination thereof.

4. In paragraph 1, The above positive electrode active material includes a lithium transition metal composite oxide, The above lithium transition metal composite oxide is a positive electrode for a lithium secondary battery comprising a lithium nickel-based composite oxide, a lithium cobalt-based composite oxide, a lithium manganese-based composite oxide, or a combination thereof.

5. In paragraph 1, The positive electrode active material is a positive electrode for a lithium secondary battery including a lithium nickel-based composite oxide represented by chemical formula 6, a lithium cobalt-based composite oxide represented by chemical formula 7, or a combination thereof: [Chemical Formula 6] Li a6 Ni x6 M 6 y6 M 7 z6 O 2-b6 X b6 In chemical formula 6, 0.9≤a6≤1.8, 0.3≤x6≤1, 0≤y6≤0.7, 0≤z6≤0.7, 0.9≤x6+y6+z6≤1.1, and 0≤b6≤0.1, and M 6 and M 7 are each independently one or more elements of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn and Zr, and X is one or more elements of F, P and S, [Chemical Formula 7] Li a7 Co x7 M 8 y7 O 2-b7 X b7 In chemical formula 7, 0.9≤a7≤1.8, 0.7≤x7≤1, 0≤y7≤0.3, 0.9≤x7+y7≤1.1, and 0≤b7≤0.1, and M 8 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

6. In paragraph 1, The thickness of the above functional layer is 1 ㎛ to 30 ㎛, A positive electrode for a lithium secondary battery, wherein the thickness of the positive electrode active material layer is 10 ㎛ to 300 ㎛.

7. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the ratio of the area of ​​the functional layer to the area of ​​the positive electrode current collector is 0.7 to 0.

99.

8. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the ratio of the area of ​​the functional layer to the area of ​​the positive electrode active material layer is 1 to 1.

5.

9. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the inorganic particles include aluminum oxide, silicon dioxide, magnesium oxide, titanium dioxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite (AlO(OH)), or a combination thereof.

10. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the flame retardant comprises a phosphorus-based flame retardant, a silicone-based flame retardant, a nitrogen-based flame retardant, a sulfur-based flame retardant, a boron-based flame retardant, a halogenated flame retardant, an inorganic oxide flame retardant, or a combination thereof.

11. In paragraph 10, A positive electrode for a lithium secondary battery, wherein the above-mentioned flame retardant comprises a phosphate, a phosphite, a phosphonate, a phosphinate, a phosphine oxide, a phosphazene, or a combination thereof.

12. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the flame retardant is contained in an amount of 0.1 wt% to 50 wt% based on 100 wt% of the ceramic insulating layer.

13. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the thickness of the ceramic insulating layer is 1 ㎛ to 20 ㎛.

14. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the area of ​​the ceramic insulating layer relative to the area of ​​the positive electrode current collector is 0.01 to 0.

3.

15. A positive electrode for a lithium secondary battery according to any one of claims 1 to 14; cathode; and A lithium secondary battery comprising an electrolyte.

Images