Electrode laminate for lithium secondary battery and lithium secondary battery including the same

Abstract

The present invention relates to an electrode laminate for a lithium secondary battery in which one or more positive electrodes and one or more negative electrodes are alternately laminated with a separator sandwiched therebetween, in which an insulating layer having an average thickness of 1 μm to 8 μm is formed on a positive electrode at the outermost edge of the electrode laminate, and the positive electrode includes a positive electrode current collector, a positive electrode active material layer, and a protective layer containing an inorganic compound interposed between the positive electrode current collector and the positive electrode active material layer; and an electrode assembly and a lithium secondary battery including the electrode laminate.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0103164, filed on August 5, 2021, and all contents disclosed in the document of the Korean patent application are incorporated herein by reference in their entirety.

[0002] The present invention relates to an electrode laminate for a lithium secondary battery and a lithium secondary battery including the same.

Background Art

[0003] Recently, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries that are small, light, and relatively high-capacity has been rapidly increasing. In particular, lithium secondary batteries are lightweight and have a high energy density, and have been in the spotlight as a driving power source for portable devices. Along with this, research and development efforts for improving the performance of lithium secondary batteries have been actively carried out.

[0004] A lithium secondary battery generally includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator, and an electrolyte, and is charged and discharged by insertion and extraction of lithium ions. At this time, after manufacturing an electrode assembly with a separator interposed between the positive electrode and the negative electrode, it is inserted into a battery case and finally an electrolyte is injected for manufacturing.

[0005] When an external impact is applied to such a secondary battery, for example, when a sharp object penetrates the secondary battery, a short circuit may occur due to contact between the positive electrode and the negative electrode. Such a short circuit can cause generation of a large amount of gas, an increase in temperature, etc. at a high speed in a short time, and furthermore, a large explosion may occur, leading to a major accident.

[0006] Therefore, development of new technologies that can solve such safety problems is required.

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide an electrode laminate for a lithium secondary battery with improved safety by reducing heat generation and preventing short - circuit between electrodes during an external impact, and a lithium secondary battery including the same.

Means for Solving the Problems

[0008] The present invention provides an electrode laminate in which one or more positive electrodes and one or more negative electrodes are alternately laminated with a separator therebetween, an insulating layer with an average thickness of 1 μm to 8 μm is formed on the outermost - edge positive electrode of the electrode laminate, and the positive electrode includes a positive - electrode current collector, a positive - electrode active - material layer, and a protective layer including an inorganic compound interposed between the positive - electrode current collector and the positive - electrode active - material layer, to provide an electrode laminate for a lithium secondary battery.

[0009] The present invention also provides an electrode assembly for a lithium secondary battery including the electrode laminate for a lithium secondary battery.

[0010] The present invention further provides a lithium secondary battery including the electrode assembly for a lithium secondary battery.

Advantages of the Invention

[0011] The electrode laminate for a lithium secondary battery according to the present invention is characterized by improved safety. Specifically, by forming a protective layer on the electrode current collector and including an insulating layer with a thickness in a specific numerical range at the outermost edge of the electrode laminate, heat generated at the positive electrode during an external impact can be effectively released, and it is possible to prevent large - scale accidents such as explosions caused by short - circuit between electrodes.

Brief Description of the Drawings

[0012]

Figure 1

Best Mode for Carrying Out the Invention

[0013] Hereinafter, in order to facilitate the understanding of the present invention, the present invention will be described in more detail.

[0014] In this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0015] In this specification, when a certain member is located "on" another member, this includes not only the case where a certain member is in contact with another member, but also the case where there is still another member between the two members.

[0016] In this specification, "single-sided positive electrode" means a positive electrode in which a positive electrode active material layer is formed only on one of the two surfaces of the positive electrode current collector, and "double-sided positive electrode" means a positive electrode in which a positive electrode active material layer is formed on both surfaces of the positive electrode current collector.

[0017] In this specification, "single-sided negative electrode" means a negative electrode in which a negative electrode active material layer is formed only on one of the two surfaces of the negative electrode current collector, and "double-sided negative electrode" means a negative electrode in which a negative electrode active material layer is formed on both surfaces of the negative electrode current collector.

[0018] As the utilization rate of lithium secondary batteries increases and they are exposed to various driving environments, ensuring safety has become a very important problem to be solved. For example, when a short circuit occurs between the positive electrode and the negative electrode due to an external impact, the temperature rises at a high speed, so an explosion accident may occur due to rapid gas generation and heat generation. Therefore, in order to prevent this in advance, a nail piercing test is performed in the manufacturing process. The electrode laminate according to the present invention is characterized in that its safety against such a nail piercing test is enhanced.

[0019] Specifically, the electrode laminate for a lithium secondary battery of the present invention provided to solve the above problems is an electrode laminate in which one or more positive electrodes and one or more negative electrodes are alternately laminated with a separator interposed therebetween, and an insulating layer having an average thickness of 1 μm to 8 μm is formed on the outermost edge positive electrode of the electrode laminate, and the positive electrode includes a positive electrode current collector, a positive electrode active material layer, and a protective layer interposed between the positive electrode current collector and the positive electrode active material layer.

[0020] Hereinafter, each configuration of the present invention will be described more specifically.

[0021] <Structure of the electrode assembly> In one embodiment of the present invention, the electrode laminate can include two or more of the positive electrodes. Specifically, on both sides of the outermost edge of the electrode laminate, single-sided positive electrodes in which a positive electrode active material layer is formed on one side of a positive electrode current collector are located, and the insulating layer can be formed on the opposite surface of the surface of the positive electrode current collector on which the positive electrode active material layer is formed.

[0022] In one embodiment of the present invention, the electrode laminate has a structure in which a double-sided negative electrode in which a negative electrode active material layer is formed on both sides of a negative electrode current collector, a double-sided positive electrode in which a positive electrode active material layer is formed on both sides of a positive electrode current collector, and a double-sided negative electrode in which a negative electrode active material layer is formed on both sides of a negative electrode current collector are alternately laminated with a separator interposed therebetween, between the single-sided positive electrodes located on both sides of the outermost edge.

[0023] Referring to the left diagram of FIG. 1 showing an example of the electrode laminate according to the present invention, the electrode laminate 8 of the present invention has a structure in which a positive electrode including a positive electrode current collector 1, a protective layer 2, and a positive electrode active material layer 3, and a negative electrode including a negative electrode current collector 5 and a negative electrode active material layer 6 are alternately laminated with a separator 4 interposed therebetween. Specifically, the single-sided positive electrodes located on both sides of the outermost edge of the electrode laminate 8 have a structure in which a positive electrode active material layer 3, a protective layer 2, a positive electrode current collector 1, and an insulating layer 7 are laminated in this order from the inside to the outside. Between the two single-sided positive electrodes located on both sides of the outermost edge, a double-sided negative electrode in which a negative electrode active material layer 6 is formed on both sides of a negative electrode current collector 5, a double-sided positive electrode in which a positive electrode active material layer 3 is formed on both sides of a positive electrode current collector 1, and the double-sided negative electrodes are alternately laminated with a separator interposed therebetween. However, this is a typical example, and the electrode and separator configuration laminated between the single-sided positive electrodes located on both sides of the outermost edge can be changed as necessary.

[0024] For such an electrode laminate 8, as shown in the right diagram of FIG. 1, a nail piercing test is performed.

[0025] According to the prior art, when a nail piercing test is performed on a general electrode laminate without the protective layer, the pierced part is cut and the positive electrode current collector comes into contact with the negative electrode active material layer, and the temperature rapidly rises due to the short-circuit current, which may lead to a fire accident such as an explosion.

[0026] Therefore, in the present invention, by introducing the protective layer 2 between the positive electrode current collector 1 and the positive electrode active material layer 3, even if the structure of the electrode laminate is broken by nail piercing, the possibility of direct contact between the positive electrode current collector 1 and the negative electrode active material layer 6 is greatly reduced, and by reducing the short-circuit resistance, the risk of an accident is reduced.

[0027] Furthermore, when the positive electrode current collector 1 at the outermost edge comes into direct contact with the nail, a strong short-circuit current may flow through the nail and the ignition rate may rapidly increase. However, as in the electrode laminate 8 of the present invention, when an insulating layer 7 is included on the positive electrode current collector at the outermost edge, it was confirmed that the resistance at the cross-section where the nail contacts the outermost edge portion becomes significantly higher, and the ignition rate can be reduced.

[0028] <Positive electrode> In one embodiment of the present invention, the positive electrode can be manufactured by forming a protective layer by coating a composition for forming a protective layer containing an inorganic compound on a positive electrode current collector, and then coating a positive electrode slurry containing a positive electrode active material on the protective layer to form a positive electrode active material layer.

[0029] In one embodiment of the present invention, the positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, aluminum; stainless steel; nickel; titanium; fired carbon; or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used.

[0030] In one embodiment of the present invention, in the case of the single-sided positive electrode, the protective layer is formed on one side of the positive electrode current collector, and in the case of the double-sided positive electrode, the protective layer is formed on both sides of the positive electrode current collector.

[0031] In one embodiment of the present invention, the inorganic compound contained in the protective layer can be one or more selected from metal oxides, non-metal oxides, metal carbides, and non-metal carbides.

[0032] In one embodiment of the present invention, the inorganic compound can be a lithium iron phosphate-based oxide which is a metal oxide. In this case, it has higher thermal stability compared to other inorganic compounds, contains a lithium source, and is preferable in terms of capacity expression and safety.

[0033] In one embodiment of the present invention, the lithium iron phosphate-based oxide can be represented by the following Chemical Formula 1, and preferably, it is LiFePO4.

[0034] [Chemical Formula 1] LiFe 1-a M a PO4

[0035] In Chemical Formula 1, M is one or more selected from Ni, Co, Mn, Al, Mg, Y, Zn, In, Ru, Sn, Sb, Ti, Te, Nb, Mo, Cr, Zr, W, Ir, and V, 0 ≦ a < 1.

[0036] In one embodiment of the present invention, the protective layer may further include a binder, a conductive material, and a dispersant.

[0037] In one embodiment of the present invention, the binder can be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer, styrene - butadiene rubber, fluororubber, or various copolymers thereof.

[0038] In one embodiment of the present invention, as the conductive material, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, carbon nanotube, or graphite with a highly developed crystal structure; conductive fibers such as carbon fiber or metal fiber; conductive powder such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whisker such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive material such as polyphenylene derivative can be used.

[0039] In one embodiment of the present invention, the dispersant can be hydrogenated nitrile butadiene rubber (HNBR).

[0040] In one embodiment of the present invention, the protective layer can be formed by coating a protective layer-forming composition, in which the inorganic compound, binder, conductive material, and dispersant are mixed in an organic solvent such as N-methyl-2-pyrrolidone (NMP), onto the positive electrode current collector.

[0041] In one embodiment of the present invention, the content of the inorganic compound relative to the total weight of the protective layer can be 85% by weight to 96% by weight, preferably 90% by weight to 96% by weight.

[0042] In one embodiment of the present invention, the positive electrode active material layer contains a positive electrode active material and is formed on the protective layer. It can be manufactured by applying a positive electrode slurry containing a positive electrode active material, binder, conductive material, and solvent described later onto the positive electrode current collector with the protective layer formed thereon, and then drying and rolling. In the case of the single-sided positive electrode, the positive electrode active material layer is formed on one side of the positive electrode current collector with the protective layer formed thereon. In the case of the double-sided positive electrode, the positive electrode active material layer is formed on each of the protective layers formed on both sides of the positive electrode current collector.

[0043] In one embodiment of the present invention, a lithium transition metal oxide can be used as the positive electrode active material. The lithium transition metal oxide can be used without limitation as long as lithium ions can be easily inserted or desorbed during charge and discharge. For example, LCO (LiCoO2), LNO (LiNiO2), LMO (LiMnO2), LiMn2O4, LiCoPO4, LFP (LiFePO4), LiNiMnCoO2, and NMC (LiNiCoMnO2), etc., including LiNi 1-x-y-z Co x M 1 y M 2 z O2 (M 1 and M 2is any one selected independently from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg, and Mo, and x, y, and z are independently, as atomic fractions of the oxide composition elements, 0 ≦ x < 0.5, 0 ≦ y < 0.5, 0 ≦ z < 0.5, and x + y + z = 1. It can be one or more selected from ().

[0044] Specifically, it can include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum.

[0045] More specifically, the lithium metal oxide is a lithium-manganese-based oxide such as LiMnO2, LiMn2O4; a lithium-cobalt-based oxide such as LiCoO2; a lithium-nickel-based oxide such as LiNiO2; LiNi 1-Y Mn Y O2(0 < Y < 1), LiMn 2-z Ni z O4(0 < Z < 2) and other lithium-nickel-manganese-based oxides; LiNi 1-Y1 Co Y1 O2(0 < Y1 < 1) and other lithium-nickel-cobalt-based oxides; LiCo 1-Y2 Mn Y2 O2(0 < Y2 < 1), LiMn 2-z1 Co z1 O4(0 < Z1 < 2) and other lithium-manganese-cobalt-based oxides; Li(Ni p Co q Mn r1 )O2(0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1), Li(Ni p1 Co q1 Mn r2 )O4(0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2) and other lithium-nickel-manganese-cobalt-based oxides; and Li(Ni p2 Co q2 Mn r3 M S2)O2(M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are, respectively, as atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), and can be one or more selected from lithium-nickel-cobalt-transition metal (M) oxides such as this.

[0046] The solvent of the positive electrode slurry can be an organic solvent such as N-methyl-2-pyrrolidone (NMP), and when containing the positive electrode active material and optionally a binder, a conductive material, etc., it can be used in an amount that results in a preferable viscosity. For example, it can be included such that the solid content concentration in the positive electrode slurry is 10 wt% to 90 wt%, preferably 40 wt% to 85 wt%.

[0047] The binder in the positive electrode slurry is a component that facilitates the binding of the positive electrode material and the conductive material and the binding to the current collector, and is usually added in an amount of 1 wt% to 30 wt% based on the total weight of the solid content in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber, fluorine rubber, or various copolymers thereof.

[0048] The conductive material in the positive electrode slurry can be added in an amount of 0.5 wt% to 20 wt% based on the total weight of the solid content in the positive electrode slurry as a substance that does not cause a chemical change to the battery and imparts conductivity.

[0049] As the conductive material, carbon powder such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives can be used.

[0050] The positive electrode active material can be contained in an amount of 80% to 99% by weight, specifically 90% to 99% by weight, based on the total weight of the solid content in the positive electrode slurry. Here, when the content of the positive electrode active material is 80% by weight or less, the energy density may be low and the capacity may decrease.

[0051] In one embodiment of the present invention, a protective layer and a positive electrode active material layer are sequentially formed on the inner surface of the positive electrode current collector of the single-sided positive electrode located on both sides of the outermost edge, and an insulating layer with an average thickness of 1 μm to 8 μm is formed on the outer surface. That is, the insulating layer can be formed by coating a composition for forming an insulating layer on the opposite surface of the surface on which the protective layer of the positive electrode current collector is formed. The thickness of the insulating layer is 1 μm to 8 μm, preferably 3 μm to 7 μm. When the thickness of the insulating layer is 1 μm or more, exposure of the positive electrode current collector metal can be prevented, and when it is 8 μm or less, cracking of the insulating layer during the nail penetration test can be prevented. Specifically, the insulating layer coating can be performed by a gravure process. Here, the coating thickness can be adjusted according to the coating amount of the composition, the viscosity of the composition, the mesh design of the roll, the rotation speed of the roll, etc. When forming with a thickness less than 1 μm, the viscosity of the composition becomes low and non-uniform coating may occur due to dripping, resulting in exposure of the positive electrode current collector metal. Conversely, when forming an insulating layer that is excessively thick over 8 μm, cracking may occur during the drying process and the insulating layer cannot be properly maintained, and similarly, exposure of the positive electrode current collector metal may occur.

[0052] In one embodiment of the present invention, the insulating layer can contain a cellulose-based compound, and the cellulose-based compound can be carboxymethyl cellulose (CMC), carboxyethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, or a mixture thereof, and preferably can be carboxymethyl cellulose. The cellulose-based compound can serve as a dispersant for the insulating layer-forming composition.

[0053] In one embodiment of the present invention, the insulating layer can contain the cellulose-based compound in a content of 0.1% by weight to 1% by weight based on the total weight of the insulating layer.

[0054] In one embodiment of the present invention, the insulating layer can further contain a ceramic.

[0055] In one embodiment of the present invention, the ceramic is Al2O3, BaTiO3, CaO, CeO2, NiO, MgO, SiO2, SnO2, SrTiO3, TiO2, Y2O3, ZnO, ZrO2, Pb(Zr x , Ti 1-x )O3 (PZT, 0 < x < 1), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, 0 < x < 1, 0 < y < 1), (1 - x)Pb(Mg 1 / 3 Nb 2 / 3 )O 3-x PbTiO3 (PMN - PT, 0 < x < 1) and hafnia (HfO2), and can be one or more selected therefrom, and preferably can be Al2O3.

[0056] In one embodiment of the present invention, the content of the ceramic based on the total weight of the insulating layer can be 10% by weight to 49.9% by weight, preferably 15% by weight to 40% by weight, and more preferably 20% by weight to 30% by weight.

[0057] In one embodiment of the present invention, the insulating layer is formed to prevent the nail from directly contacting the outermost single-sided positive electrode during the nail penetration test, and to prevent the positive electrode current collector from being exposed even during penetration. As an adhesive, it can further contain one or more polymers selected from polybutadiene, polyurethane, polyimide, polyvinyl acetate, polyester, polyphenylene sulfide, polypropylene, styrene-butadiene copolymer, (meth)acrylate copolymer, polyacrylonitrile, polyvinyl chloride, polyfluoro, polyvinyl alcohol, and polycyanoacrylate, and preferably can contain a styrene-butadiene copolymer. Since the styrene-butadiene copolymer has excellent thermal stability, it has the advantage of maintaining performance even when the temperature rises during nail penetration.

[0058] In one embodiment of the present invention, the content of the polymer relative to the total weight of the insulating layer can be 50% to 90% by weight, preferably 50% to 85% by weight, and more preferably 70% to 80% by weight. When the content of the polymer is 50% by weight or more, sufficient adhesive strength can be ensured. When it is 90% by weight or less, the content of the ceramic can be sufficiently ensured, and the problem of the polymer shrinking due to heat and the positive electrode current collector being exposed can be prevented.

[0059] In one embodiment of the present invention, the insulating layer can be formed by coating a composition for forming an insulating layer, which is a mixture of the cellulose-based compound, ceramic, and polymer in one or more solvents selected from water, glycerol, ethylene glycol, propylene glycol, dimethyl sulfoxide, dimethylformamide, acetonitrile, ethylene carbonate, furfuryl alcohol, and methanol, on the positive electrode current collector.

[0060] <Negative electrode and separator> The electrode laminate according to one embodiment of the present invention is one of the unit cells forming the electrode assembly, and includes a separator between the above-described positive electrode and negative electrode. In the case of the negative electrode and the separator, those usually used in a lithium secondary battery can be applied to the present invention without particular limitation.

[0061] In one embodiment of the present invention, the negative electrode can be manufactured by coating a negative electrode current collector with a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, a solvent, etc., and then drying and rolling to form a negative electrode active material layer.

[0062] The negative electrode active material layer contains a negative electrode active material, and the negative electrode active material can include one or more selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0063] As the carbon material capable of reversibly intercalating / deintercalating lithium ions, any carbon-based negative electrode active material generally used in a lithium ion secondary battery can be used without particular limitation, and typical examples thereof include crystalline carbon, amorphous carbon, or both of these can be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite and artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature fired carbon) or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0064] As the metal or the alloy of these metals and lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn or an alloy of these metals and lithium can be used.

[0065] Examples of the metal composite oxide include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1) and Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), and one or more selected from the group consisting thereof can be used.

[0066] Examples of the substance capable of doping and undoping lithium include Si, SiO x (0 < x < 2), Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, Sn-Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), etc. Also, at least one of these can be mixed with SiO2 and used. Specifically, the element Y can be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), 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, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0067] Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0068] The negative electrode current collector generally has a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper; stainless steel; aluminum; nickel; titanium; fired carbon; those obtained by surface treatment of copper or stainless steel with carbon, nickel, titanium, silver, etc.; or aluminum-cadmium alloy, etc. can be used. Also, similar to the positive electrode current collector, fine irregularities can be formed on the surface to strengthen the binding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven bodies, etc.

[0069] The solvent of the negative electrode slurry can include water; or organic solvents such as NMP (N-methyl-2-pyrrolidone), alcohol, etc., and can be used in an amount that results in a preferable viscosity when including the negative electrode active material, and optionally a binder, a conductive material, etc. For example, the concentration of the solid content including the negative electrode active material, and optionally the binder and the conductive material, can be included so as to be 50% by weight to 95% by weight, preferably 70% by weight to 90% by weight.

[0070] The negative electrode active material can be included in an amount of 60% by weight to 99% by weight, preferably 70% by weight to 99% by weight, more preferably 80% by weight to 98% by weight, based on the total weight of the solids other than the solvent in the negative electrode slurry.

[0071] The binder in the negative electrode slurry is a component that facilitates the binding between the conductive material, the active material, and the current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluorine rubber, and various copolymers thereof.

[0072] The binder can be contained in an amount of 1% by weight to 20% by weight, preferably 1% by weight to 15% by weight, more preferably 1% by weight to 10% by weight, based on the total weight of the solids other than the solvent in the negative electrode slurry.

[0073] The conductive material in the negative electrode slurry is a component for further improving the conductivity of the negative electrode active material. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0074] The conductive material can be contained in an amount of 1% by weight to 20% by weight, preferably 1% by weight to 15% by weight, more preferably 1% by weight to 10% by weight, based on the total weight of the solids other than the solvent in the negative electrode mixture slurry.

[0075] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. A porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, a copolymer of ethylene and butene, a copolymer of ethylene and hexene, or a copolymer of ethylene and methacrylate; or a laminate structure of two or more layers thereof can be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. can be used. Further, in order to ensure heat resistance or mechanical strength, a separator containing or coated with a ceramic component or a film, fiber or powdery polymer substance can also be used, and it can be used as a single-layer or multi-layer structure.

[0076] <Lithium Secondary Battery> The electrode assembly for a lithium secondary battery according to the present invention includes the above-described electrode laminate. The electrode assembly can include a plurality of the electrode laminates as unit cells, and can be in the form of a winding type manufactured by winding one or more unit cells, a stacking type manufactured by stacking them in order, or a stack-and-folding type manufactured by placing unit cells in parallel on a folding separator and then folding them.

[0077] The lithium secondary battery according to the present invention includes the above-described electrode assembly. Specifically, it includes an electrode assembly, a battery case for housing the electrode assembly, an electrolyte injected after housing in the battery case, and a sealing member for sealing the battery case.

[0078] The battery case can be classified into a pouch type and a can type according to the material. The pouch type means a pouch made of a soft polymer material, and the can type means a case made of a material such as metal or plastic. After inserting the electrode assembly into the battery case, injecting an electrolyte and sealing it, a lithium secondary battery can be manufactured.

[0079] As the electrolyte used in the present invention, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that can be used in the manufacture of lithium secondary batteries can be used without limitation. In this specification, typically, organic liquid electrolytes will be described.

[0080] Specifically, the electrolyte can include an organic solvent and a lithium salt.

[0081] As the organic solvent, any medium can be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, aromatic ring, or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among them, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can enhance the charge and discharge performance of the battery, and a linear carbonate compound having low viscosity (e.g., ethylmethylcarbonate, dimethylcarbonate, or diethylcarbonate) is more preferred. In this case, the cyclic carbonate and the linear carbonate are preferably mixed and used at a volume ratio of about 1:1 to about 1:9.

[0082] The lithium salt can be used without limitation, such as those commonly used in electrolytes for lithium secondary batteries. For example, as a cation, Li + is included, and as an anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , BF2C2O4CHF - , PF4C2O4 - , PF2C4O8 - , PO2F2 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - can include at least any one selected from the group consisting of.

[0083] Specifically, the lithium salt may include one or more mixtures selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiN(FSO2)2: Lithium bis(fluorosulfonyl)imide, LiFSI), LiPF6, LiClO4, LiBF4, LiTFSI, lithium bis(pentafluoroethanesulfonyl)imide (Lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), LiSO3CF3, LiPO2F2, lithium bis(oxalate)borate (Lithium bis(oxalate)borate, LiBOB), lithium difluoro(oxalate)borate (Lithium difluoro(oxalate)borate, LiFOB), lithium difluoro(bisoxalate)phosphate (Lithium difluoro(bisoxalate)phosphate, LiDFBP), lithium tetrafluoro(oxalate)phosphate (Lithium tetrafluoro(oxalate)phosphate, LiTFOP), and lithium fluoromalonato(difluoro)borate (Lithium fluoromalonato(difluoro)borate, LiFMDFB).

[0084] In addition to the electrolyte components, the electrolyte may selectively contain additives as needed to prevent the electrolyte from decomposing in a high-voltage environment and causing electrode collapse, or to further improve characteristics such as low-temperature high-rate discharge performance, high-temperature stability, overcharge prevention, and suppression of battery swelling at high temperatures.

[0085] The additive can be one or more selected from cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, amine compounds, silane compounds, benzene compounds, and lithium salt compounds. The content of the additive can be 0.01 wt% to 5 wt% based on the total weight of the electrolyte.

[0086] The lithium secondary battery according to the present invention can be applied to fields such as portable devices such as mobile phones, notebook computers, digital cameras, and the field of electric vehicles.

[0087] According to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0088] The battery module or battery pack can be used as a power source for one or more medium and large-sized devices such as power tools; electric vehicles including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); or power storage systems.

[0089] Hereinafter, the present invention will be specifically described with specific examples.

[0090] [Examples and Comparative Examples: Production of Electrode Laminate] [Example 1] 90.5% by weight of LiFePO4, 4% by weight of acetylene black, 4% by weight of polyvinylidene fluoride (PVDF), and 1.5% by weight of hydrogenated nitrile butadiene rubber (HNBR) were mixed in an N-methylpyrrolidone (NMP) solvent so that the solid content became 60% by weight to produce a composition for forming a protective layer.

[0091] Separately, 96.8% by weight of LiCoO2, 1.5% by weight of carbon black as a conductive material, 1.5% by weight of PVDF as a binder, and 0.2% by weight of hydrogenated nitrile butadiene rubber (HNBR) were mixed in an N-methylpyrrolidone (NMP) solvent to produce a positive electrode active material slurry having a solid content of 75% by weight.

[0092] After applying the composition for forming the protective layer manufactured above on the Al foil current collector, it was dried to form a protective layer with a thickness of 10 μm. Next, the positive electrode active material slurry was applied on the protective layer and dried, and then roll pressing was performed to manufacture a single-sided positive electrode on which a protective layer and a positive electrode active material layer were sequentially formed on the positive electrode current collector. In the case of a double-sided positive electrode, it was manufactured in the same manner as the single-sided positive electrode, except that the protective layer and the positive electrode active material layer were formed on both sides of the positive electrode current collector, respectively.

[0093] On the other hand, graphite as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, carbon black as the conductive material, CMC as the dispersant, and distilled water as the solvent were mixed at a weight ratio of 76.4:1.95:0.5:1.15:20, respectively, to produce a negative electrode slurry. The negative electrode slurry was applied to both sides of a Cu current collector with a thickness of 20 μm and dried, and then roll pressing was performed to manufacture a double-sided negative electrode.

[0094] By laminating the single-sided positive electrode, double-sided negative electrode, double-sided positive electrode, double-sided negative electrode, and single-sided positive electrode manufactured above in an alternating manner with a polyethylene separator, an electrode laminate with a bicell structure was manufactured. Then, on the protective layer formed on the outermost positive electrode, the composition for forming the insulating layer was applied by the gravure coating method at 1 mg per 1 cm 2 After application and drying, an insulating layer with an average thickness of 5 μm was formed to manufacture a lithium secondary battery with the structure shown in FIG. 1.

[0095] The composition for forming the insulating layer used was a mixture obtained by dissolving 20% by weight of alumina (Al2O3), 79.9% by weight of styrene-butadiene rubber (SBR), and 0.1% by weight of carboxymethyl cellulose (CMC) in water so that the solid content was 40% by weight.

[0096] <Comparative Example 1> A lithium secondary battery was manufactured in the same process as in Example 1, except that the insulating layer was not formed in Example 1.

[0097] <Comparative Example 2> A lithium secondary battery was manufactured in the same process as in Example 1, except that the positive electrode without the protective layer formed in Example 1 was used.

[0098] <Comparative Example 3> A lithium secondary battery was manufactured in the same process as in Example 1, except that a composition for forming an insulating layer was applied at 0.5 mg per 1 cm² on the protective layer formed on the outermost edge positive electrode in Example 1, and then dried to form an insulating layer with an average thickness of 0.5 μm. 2 A lithium secondary battery was manufactured in the same process as in Example 1, except that a composition for forming an insulating layer was applied at 0.5 mg per 1 cm² on the protective layer formed on the outermost edge positive electrode in Example 1, and then dried to form an insulating layer with an average thickness of 0.5 μm.

[0099] <Comparative Example 4> A lithium secondary battery was manufactured in the same process as in Example 1, except that a composition for forming an insulating layer was applied at 1.8 mg per 1 cm² on the protective layer formed on the outermost edge positive electrode in Example 1, and then dried to form an insulating layer with an average thickness of 9 μm. 2 A lithium secondary battery was manufactured in the same process as in Example 1, except that a composition for forming an insulating layer was applied at 1.8 mg per 1 cm² on the protective layer formed on the outermost edge positive electrode in Example 1, and then dried to form an insulating layer with an average thickness of 9 μm.

[0100] [Experimental Example: Nail Prick Test] After placing the electrode laminates manufactured in Example 1 and Comparative Examples 1 to 4 inside a pouch-type battery case, an electrolytic solution was injected into the case to manufacture a lithium secondary battery. Here, the electrolytic solution was prepared by dissolving LiPF6 with a concentration of 1.0 M in an organic solvent in which ethylene carbonate (EC): ethyl methyl carbonate (EMC) were mixed at a volume ratio of 30:70.

[0101] The lithium secondary battery manufactured as described above was fully charged to SOC 100% at 4.47 V (0.05C cut-off) under CC / CV conditions at 0.5C at 25°C, aged by storing at room temperature for 24 hours, and then a nail prick test was performed using a nail prick tester.

[0102] Specifically, each lithium secondary battery manufactured in Example 1 and Comparative Examples 1 to 4 was placed on a flat plate, and a nail made of stainless steel with a diameter of 3 ± 0.2 mm was penetrated through the center of the cell at an angle of 32° and a penetration speed of 50 mm / sec to measure whether ignition occurred. For each of the batteries manufactured in Example 1 and Comparative Examples 1 to 4, the same experiment was conducted 10 times each to measure the ignition rate, and the results are shown in Table 1 below.

[0103]

Table 1

[0104] From the results in the above table, it can be confirmed that the lithium secondary battery of Example 1 containing both the insulating layer and the protective layer did not ignite at all in the nail penetration test. However, it can be confirmed that ignition occurs when the insulating layer is not included (Comparative Example 1) or when the protective layer is not included (Comparative Example 2). Moreover, in the case of Comparative Example 3 containing an insulating layer with a thickness of less than 1 μm, a phenomenon of dripping occurred due to low viscosity during the coating process of the insulating layer, and the insulating layer was not formed uniformly, resulting in the exposure of the Al foil and showing the same ignition rate as Comparative Example 1 without the insulating layer. In the case of Comparative Example 4 where the insulating layer was formed excessively thick at more than 8 μm, cracks occurred in the insulating layer during the drying process, exposing the Al foil, and it can be confirmed that ignition occurred.

Explanation of Reference Numerals

[0105] 1 Positive current collector 2 Protective layer 3 Positive electrode active material layer 4 Separator 5 Negative current collector 6 Negative electrode active material layer 7 Insulating layer 8 Electrode laminate

Claims

1. An electrode laminate in which one or more positive electrodes and one or more negative electrodes are alternately laminated with a separator interposed therebetween, an insulating layer having an average thickness of 1 μm to 8 μm is formed on the outermost edge positive electrode of the electrode laminate, the positive electrode includes a positive electrode current collector, a positive electrode active material layer, and a protective layer including an inorganic compound interposed between the positive electrode current collector and the positive electrode active material layer, the inorganic compound contained in the protective layer is one or more selected from metal oxides, non-metal oxides, metal carbides, and non-metal carbides, the positive electrode active material is a lithium metal oxide containing one or more metals selected from cobalt, manganese, nickel, and aluminum and lithium, the insulating layer contains a cellulose-based compound, the insulating layer further includes one or more polymers selected from polybutadiene, polyurethane, polyimide, polyvinyl acetate, polyester, polyphenylene sulfide, polypropylene, styrene-butadiene copolymer, (meth)acrylate copolymer, polyacrylonitrile, polyvinyl chloride, polyfluoro, polyvinyl alcohol, and polycyanoacrylate, an electrode laminate for a lithium secondary battery.

2. The electrode laminate for a lithium secondary battery according to claim 1, wherein two or more positive electrodes are included.

3. On both sides of the outermost edge of the electrode laminate, a single-sided positive electrode having a positive electrode active material layer formed on one side of a positive electrode current collector is located, The electrode laminate for a lithium secondary battery according to claim 2, wherein the insulating layer is formed on the opposite surface of the surface of the positive electrode current collector on which the positive electrode active material layer is formed.

4. Between the single-sided positive electrodes located on both sides of the outermost edge, a double-sided negative electrode having a negative electrode active material layer formed on both sides of a negative electrode current collector, a double-sided positive electrode having a positive electrode active material layer formed on both sides of a positive electrode current collector, The electrode laminate for a lithium secondary battery according to claim 3, wherein double-sided negative electrodes having negative electrode active material layers formed on both sides of a negative electrode current collector are alternately laminated with a separator interposed therebetween.

5. The electrode laminate for a lithium secondary battery according to claim 1, wherein the insulating layer contains carboxymethyl cellulose.

6. The electrode laminate for a lithium secondary battery according to claim 1, wherein the insulating layer further contains a ceramic.

7. The ceramic for the electrode laminate for a lithium secondary battery according to claim 6 is one or more selected from Al2O3, BaTiO3, CaO, CeO2, NiO, MgO, SiO2, SnO2, SrTiO3, TiO2, Y2O3, ZnO, ZrO2, Pb(Zrx,Ti1-x)O3 (PZT, 0 < x < 1), Pb1-xLaxZr1-yTiyO3 (PLZT, 0 < x < 1, 0 < y < 1), (1 - x)Pb(Mg1 / 3Nb2 / 3)O3 - xPbTiO3 (PMN-PT, 0 < x < 1), and hafnia (HfO2).

8. The electrode laminate for a lithium secondary battery according to claim 1, wherein the insulating layer contains styrene-butadiene rubber.

9. The electrode laminate for a lithium secondary battery according to claim 8, wherein the content of the polymer is 50% by weight to 90% by weight based on the total weight of the insulating layer.

10. The electrode laminate for a lithium secondary battery according to claim 1, wherein the average thickness of the insulating layer is 3 μm to 7 μm.

11. The electrode laminate for a lithium secondary battery according to claim 1, wherein the inorganic compound is a lithium iron phosphate-based oxide.

12. An electrode assembly for a lithium secondary battery, comprising the electrode laminate for a lithium secondary battery according to claim 1.

13. A lithium secondary battery, comprising the electrode assembly for a lithium secondary battery according to claim 12.

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