Lithium secondary battery and method for manufacturing the same

Abstract

The present invention provides an electrode assembly including an electrode and a porous coating layer formed on the electrode, in order to enhance safety while maintaining various performances of a lithium secondary battery; and a lithium secondary battery including a flame-retardant electrolyte including a flame-retardant solvent defined by a predetermined flash point and a lithium salt, wherein the porous coating layer includes polymer particles or ceramic particles having an absolute value of zeta potential of 25 mV or more.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit of priority based on Korean Patent Application No. 10 - 2022 - 0069165 filed on June 7, 2022, Korean Patent Application No. 10 - 2022 - 0073089 filed on June 15, 2022, and Korean Patent Application No. 10 - 2023 - 0061581 filed on May 12, 2023, and all the contents disclosed in the documents of the Korean patent applications are incorporated herein by reference in their entirety.

[0002] The present invention relates to a lithium secondary battery and a method for manufacturing the same.

Background Art

[0003] Recently, as the application fields of lithium secondary batteries have rapidly expanded not only to power supply for electronic devices such as electric, electronic, communication, and computer devices but also to power storage supply for large - area devices such as automobiles and power storage devices, the demand for lithium secondary batteries with high capacity, high output, long life, and high stability has been increasing.

[0004] A lithium secondary battery generally includes a positive electrode, a negative electrode, a separator, and an electrolyte, and it is known in the art that the positive electrode, which has an unstable structure in the charged state and may generate oxygen, is included. Since the generation of oxygen in this way poses a high risk of ignition, research and development on methods to improve the safety of lithium secondary batteries have been attempted.

[0005] In a lithium secondary battery, a separator is used to ensure electrical insulation between the positive electrode and the negative electrode. Generally, such a separator is a thin film made of polyolefin. However, such a separator may easily shrink at high temperatures, making it impossible to insulate between the positive electrode and the negative electrode. Also, when folding or mis-matching of the separator occurs during the process of assembling a lithium secondary battery, it may operate normally initially, but there is a problem that a short circuit may occur due to the generation of lithium dendrites or the like over time. When electrical insulation between the positive electrode and the negative electrode becomes impossible, a short circuit occurs, and ignition may occur due to the action of oxygen generated by the unstable positive electrode. That is, when a short circuit occurs in a charged lithium secondary battery due to high temperature or impact applied during the process, there may be a problem that ignition of the lithium secondary battery occurs.

[0006] In addition, it is known that a solvent with good volatility and flammability is used for the electrolyte of a lithium secondary battery, but this has the problem that ignition is likely to occur. To solve this, a flame-retardant electrolyte containing a flame-retardant solvent can be used, but such a flame-retardant electrolyte has the problem that it is not well impregnated by a conventional separator. When the electrolyte is not well impregnated in a lithium secondary battery, since lithium ions are not well transmitted, there is a problem that the capacity, output, and life characteristics of the lithium secondary battery all decrease. Also, when the electrolyte is not well impregnated in a lithium secondary battery, a non-uniform reaction occurs between the electrode and the electrolyte, dendrites are generated, and a short circuit occurs.

[0007] Therefore, in order to solve such problems, research and development have been attempted on methods that can improve safety while maintaining various performances of lithium secondary batteries. Summary of the Invention Problems to be Solved by the Invention

[0008] Accordingly, an object of the present invention is to provide a lithium secondary battery with improved stability, suppressed ignition, improved electrolyte impregnation properties, and improved various characteristics, and a method for manufacturing the same.

Means for Solving the Problems

[0009] The present invention provides a lithium secondary battery including an electrode assembly including an electrode and a porous coating layer formed on the electrode; and a nonflammable electrolyte including a nonflammable solvent having a flash point of 100°C or higher or no flash point and a lithium salt, wherein the porous coating layer includes polymer particles or ceramic particles having an absolute value of zeta potential of 25 mV or more.

[0010] The present invention also provides a method for manufacturing the lithium secondary battery. In one embodiment, such a manufacturing method includes forming a porous coating layer including polymer particles or ceramic particles having an absolute value of zeta potential of 25 mV or more on an electrode; forming an electrode assembly including the electrode coated with the porous coating layer; and impregnating the electrode assembly with a nonflammable electrolyte including a nonflammable solvent having a flash point of 100°C or higher or no flash point and a lithium salt.

Effects of the Invention

[0011] In the lithium secondary battery of the present invention, an existing separator is not used to ensure electrical insulation between the positive electrode and the negative electrode, and a porous coating layer formed on the electrode is used. In such an electrode assembly including a porous coating layer, the occurrence of a short circuit due to shrinkage of an existing separator or the like is suppressed, so that ignition due to high temperature, external impact, or the like can be reduced.

[0012] In addition, while the lithium secondary battery contains a flame-retardant electrolyte to suppress ignition, the flame-retardant electrolyte is well impregnated into the electrode assembly including the porous coating layer, and a uniform reaction can occur throughout the electrode. Therefore, various performances such as the capacity, output, and life characteristics of the lithium secondary battery can be improved. Further, in the lithium secondary battery, since the electrolyte is well impregnated into the electrode assembly and a uniform reaction occurs between the electrode and the electrolyte, the generation of dendrites is suppressed, and the effect of suppressing the occurrence of short circuits is achieved.

Brief Description of the Drawings

[0013]

Figure 1

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Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0014] The terms and words used in this specification and the claims should not be construed as being limited to the ordinary or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way, they should be construed in a meaning and concept consistent with the technical idea of the present invention.

[0015] As used herein, terms such as "comprising," "including," or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and should be understood not to preclude in advance the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0016] According to one embodiment of the invention, a lithium secondary battery includes an electrode assembly including an electrode and a porous coating layer formed on the electrode; and a nonflammable electrolyte including a nonflammable solvent having a flash point of 100°C or higher or no flash point and a lithium salt, wherein the porous coating layer includes polymer particles or ceramic particles having an absolute value of zeta potential of 25 mV or more.

[0017] As described above, in such a lithium secondary battery of one embodiment, a porous coating layer that substantially replaces an existing separator in the electrode assembly is formed on the positive or negative electrode, and such a porous coating layer includes polymer particles or ceramic particles having an absolute value of zeta potential above a certain level. The absolute value of the zeta potential can define the surface polarity of the polymer particles or ceramic particles, and having an absolute value above a certain level can mean that the surface polarity increases.

[0018] Also, in the case of the nonflammable solvent included in the battery of the above embodiment, it has a higher polarity than the organic solvents included in the electrolytes for general lithium-ion batteries. Therefore, by combining the porous coating layer containing the particles with high surface polarity and the nonflammable solvent, excellent affinity between the nonflammable electrolyte and the electrode with the porous coating layer formed can be achieved, and excellent impregnation of the nonflammable electrolyte into the porous coating layer can be shown, and problems such as short circuits due to thermal shrinkage of the existing separator can be solved.

[0019] Further, the lithium secondary battery of the above-described embodiment includes a flame-retardant electrolyte containing a flame-retardant solvent and a lithium salt having a flash point that is not measured (substantially non-flammable) or a flash point of 100°C or higher. As a result, while the ignition of the battery is suppressed, such a flame-retardant electrolyte can be uniformly impregnated into the aforementioned porous coating layer.

[0020] Thus, the lithium secondary battery of one embodiment includes a porous coating layer that substitutes for the separator and a predetermined flame-retardant electrolyte, thereby suppressing short circuits and ignition and exhibiting excellent stability. At the same time, the flame-retardant electrolyte can be uniformly impregnated into the porous coating layer, improving various electrochemical properties such as capacity, output, or life characteristics.

[0021] Hereinafter, the lithium secondary battery and its manufacturing method according to the embodiments of the invention will be described more specifically.

[0022] Electrode assembly The lithium secondary battery of one embodiment basically includes an electrode assembly. Such an electrode assembly includes an electrode including a positive electrode and a negative electrode, and a porous coating layer formed on the electrode, for example, on the positive electrode and / or the negative electrode. The porous coating layer includes polymer particles or ceramic particles having an absolute value of zeta potential of 25 mV or more.

[0023] At this time, the zeta potential of the polymer particles or ceramic particles is a physical property that reflects the surface polarity of these particles and defines the electrostatic repulsive force or dispersibility between these particles. Polymer particles or ceramic particles with a large absolute value of the zeta potential can be uniformly dispersed on the electrode and exhibit good and uniform coating properties, and a large number of fine and uniform pores through which lithium ions can pass can be defined between these particles. Further, due to the particles satisfying such a zeta potential, the porous coating layer can exhibit excellent impregnation properties with respect to a flame-retardant electrolyte containing a flame-retardant solvent. With such a combination of the porous coating layer and the flame-retardant electrolyte, a lithium secondary battery of one embodiment can exhibit the above-described excellent characteristics.

[0024] The zeta potential of the polymer particles or ceramic particles can be measured, for example, by an electrophoretic light scattering method using dynamic light scattering equipment. At this time, the zeta potential can be measured in a state where the polymer particles or ceramic particles are dispersed in water or an alcohol-based solvent without a separate dispersant. In a specific example, the zeta potential can be measured in a state where the polymer particles or ceramic particles are dispersed in a water solvent at a concentration of 0.1% by weight or less.

[0025] The absolute value of the zeta potential of the polymer particles or ceramic particles can be 25 mV or more, or 35 mV or more, or 45 mV or more, and can be 100 mV or less, or 90 mV or less, or 80 mV or less. Within such a range, good coating properties and porosity of the porous coating layer are achieved, and high impregnation properties of the flame-retardant electrolyte are ensured, whereby a battery of one embodiment can exhibit excellent stability and various electrochemical characteristics.

[0026] Specific examples of the polymer particles include one or more selected from the group consisting of polymethyl (meth) acrylate, polystyrene, polyvinyl chloride, polycarbonate, polysulfone, polyethersulfone, polyetherimide, polyphenylsulfone, polyamideimide, polyimide, polybenzimidazole, polyether ketone, polyphthalamide, polybutylene terephthalate, polyethylene terephthalate, and polyphenylene sulfide.

[0027] In addition, specific examples of the ceramic particles include boehmite (γ-AlO(OH)), Al 2 O 3 , TiO 2 , Fe 2 O 3 , SiO 2 , ZrO 2 , Co 3 O 4 , SnO 2 , NiO, ZnO, V 2 O 5 , and one or more selected from the group consisting of MnO.

[0028] The zeta potential of the polymer particles or ceramic particles can be adjusted not only by the type of each particle but also by the particle size or surface characteristics of these particles. Therefore, in order to achieve the appropriate zeta potential, dispersibility, or porosity of the porous coating layer of the polymer particles or ceramic particles, the polymer particles or ceramic particles can have a particle size of 50 nm to 3 μm, or 50 nm to 1.5 μm, or 100 nm to 1 μm.

[0029] In addition, as will be described in more detail below, for controlling the surface characteristics of the polymer particles or ceramic particles and adjusting the zeta potential and the like thereby, the polymer particles or ceramic particles can be included in the porous coating layer in a state of being surface-treated with plasma or an ion beam.

[0030] On the one hand, the porous coating layer can have a form including a polymer binder and the polymer particles or ceramic particles dispersed on such a polymer binder. At this time, as the polymer binder, the same kind of polymer as the binder contained in the electrode active material layer can be used. Specific examples thereof include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, or fluororubber, etc. A mixture or copolymer of two or more selected from these can also be used. However, the specific composition of the polymer binder can be self-evidently determined by those skilled in the art considering the types, properties of the polymer particles or ceramic particles, and the formation method of the porous coating layer, etc.

[0031] Also, considering the good coating property and porosity of the aforementioned porous coating layer, and the good dispersibility of the particles, etc., the porous coating layer can contain the polymer binder: the polymer particles or ceramic particles at a weight ratio of 5:95 to 40:60, or 10:90 to 35:65.

[0032] From the aspects of excellent impregnation property for the flame-retardant electrolyte and effectively substituting the role of the separator, the aforementioned porous coating layer can have a thickness of 5 to 50 μm, or 10 to 45 μm, or 15 to 40 μm, and can contain a plurality of pores having a diameter of 10 nm or more, or 20 nm to 3 μm, or 50 nm to 1 μm. At this time, the thickness of the porous coating layer can mean the total thickness of the porous coating layer formed on the positive electrode and / or negative electrode.

[0033] On the one hand, the electrode assembly including the porous coating layer described above, for example, as shown in FIG. 1, includes a positive electrode having a positive electrode tab protruding from a positive electrode current collector; a negative electrode having a negative electrode tab protruding from a negative electrode current collector; and the porous coating layer formed on the positive electrode or the negative electrode so as to be disposed between the positive electrode and the negative electrode.

[0034] Further, the positive electrode and the negative electrode may each include a positive electrode active material layer and a negative electrode active material layer formed on the positive electrode current collector and the negative electrode current collector, respectively. The porous coating layer described above may be formed on such a positive electrode active material layer and / or negative electrode active material layer, and may be disposed in contact with these between the positive electrode and negative electrode active material layers. In a more specific example, as shown in FIG. 1, the porous coating layer may be formed on the positive electrode and negative electrode active material layers, respectively, and the porous coating layer formed on the negative electrode active material layer and the porous coating layer formed on the positive electrode active material layer may be in contact with each other.

[0035] On the other hand, in the electrode assembly, the positive electrode current collector included in the positive electrode is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used.

[0036] Also, the positive electrode active material layer on the positive electrode current collector may include a positive electrode active material, a binder, and a conductive material.

[0037] At this time, the positive electrode active material is a compound capable of reversible insertion and desorption of lithium, and specifically, may include a lithium metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium metal oxide is a lithium-manganese-based oxide (for example, LiMnO 2 , LiMn 2 O 4etc.), lithium-cobalt-based oxides (e.g., LiCoO 2 etc.), lithium-nickel-based oxides (e.g., LiNiO 2 etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-Y Mn Y O 2 (where 0 < Y < 1), LiMn 2-Z Ni Z O 4 (where 0 < Z < 2) etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O 2 (where 0 < Y1 < 1) etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O 2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O 4 (where 0 < Z1 < 2) etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r )O 2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O 4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2) etc.), lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O 2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1) etc.), or lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )Xb (Here, M is one or more selected from Al, Mg, and Ti, X is one or more selected from F, S, and N, -0.5 ≦ a ≦ +0.5, 0 ≦ x ≦ 0.5, 0 ≦ b ≦ 0.1), etc. may be mentioned, and any one or two or more of these compounds may be included.

[0038] Among these, in terms of being able to enhance the capacity characteristics and safety of the battery, the lithium metal oxide is LiCoO 2 , LiMnO 2 , LiNiO 2 , lithium nickel manganese cobalt oxide (for example, Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O 2 , Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2 , Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 , Li(Ni 0.7 Mn 0.15 Co 0.15 )O 2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2 etc.), lithium nickel cobalt aluminum oxide (for example, Li(Ni 0.8 Co 0.15 Al 0.05 )O 2 etc.), lithium nickel manganese cobalt aluminum oxide (for example, Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O 2 ), or lithium iron phosphate (for example, LiFePO 4 ) etc. may be used, and any one or two or more of these mixtures can be used.

[0039] Among these, from the viewpoint of being able to maximize the capacity characteristics of the battery, a cathode active material having a nickel content of 80 atm% or more can be used. For example, the lithium transition metal oxide can include those represented by the following Chemical Formula 1.

[0040] [Chemical Formula 1] Li x Ni a Co b M 1 c M 2 d O 2 In Chemical Formula 1, the M 1 can be one or more selected from Mn and Al or a combination thereof.

[0041] M 2 can be one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S.

[0042] The x represents the atomic fraction of lithium in the lithium transition metal oxide, and can be 0.90 ≦ x ≦ 1.1, or 0.95 ≦ x ≦ 1.08, or 1.0 ≦ x ≦ 1.08.

[0043] The a represents the atomic fraction of nickel among the metal elements excluding lithium in the lithium transition metal oxide, and can be 0.80 ≦ a < 1.0, or 0.80 ≦ a ≦ 0.95, or 0.80 ≦ a ≦ 0.90. When the nickel content satisfies the above range, high capacity characteristics can be realized.

[0044] The b represents the atomic fraction of cobalt among the metal elements excluding lithium in the lithium transition metal oxide, and can be 0 < b < 0.2, 0 < b ≦ 0.15, or 0.01 ≦ b ≦ 0.10.

[0045] The c represents M among the metal elements excluding lithium in the lithium transition metal oxide 1It represents the atomic fraction of c, and can be 0 < c < 0.2, 0 < c ≤ 0.15, or 0.01 ≤ c ≤ 0.10.

[0046] Said d represents the atomic fraction of M among the metal elements excluding lithium in the lithium transition metal oxide. 2 It represents the atomic fraction of d, and can be 0 ≤ d ≤ 0.1, or 0 ≤ d ≤ 0.05.

[0047] Said positive electrode active material can be contained at 60 to 99% by weight, or 70 to 99% by weight, or 80 to 98% by weight based on the total weight of the positive electrode active material layer.

[0048] Said binder is a component that assists in binding the active material and the conductive material, etc., and binding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, or fluorine rubber, etc. It is also possible to use a mixture or copolymer of two or more selected from these.

[0049] Usually, said binder can be contained at 1 to 20% by weight, or 1 to 15% by weight, or 1 to 10% by weight based on the total weight of the positive electrode active material layer.

[0050] The conductive material is a component for further improving the conductivity of the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, 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; carbon fluoride powder; conductive powder such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives can be used.

[0051] Generally, the conductive material can be contained in an amount of 1 to 20% by weight, or 1 to 15% by weight, or 1 to 10% by weight based on the total weight of the positive electrode active material layer.

[0052] On the other hand, the negative electrode in the electrode assembly can include a negative electrode current collector, a negative electrode active material layer containing a negative electrode active material, a binder, a conductive material, etc., and optionally the aforementioned porous coating layer.

[0053] The negative electrode current collector generally has a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has high conductivity without inducing a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, 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 bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc.

[0054] Further, the negative electrode active material can include at least one or more selected from the group consisting of lithium metal, a carbon material capable of reversibly inserting / desorbing lithium ions, a metal, an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0055] As the carbon material capable of reversibly inserting / desorbing the lithium ions, any carbon-based negative electrode active material generally used in a lithium ion secondary battery can be used without particular limitation. Representative examples thereof include crystalline carbon, amorphous carbon, or a combination of these. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0056] 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.

[0057] Examples of the metal composite oxide include PbO, PbO 2 、Pb 2 O 3 、Pb 3 O 4 、Sb 2 O 3 、Sb 2 O 4 、Sb 2 O 5 、GeO, GeO 2 、Bi 2 O 3 、Bi 2 O 4 、Bi 2 O 5 、Li x Fe2 O 3 (0 ≦ x ≦ 1), Li x WO 2 (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) can be selected from the group consisting of.

[0058] As the substance capable of doping and undoping the lithium, Si, SiO x (0 < x ≦ 2), Si-Y alloy (wherein 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, SnO 2 , Sn-Y (wherein 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. can be mentioned, and at least one of these and SiO 2 can also be used by mixing. As the element Y, 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, Ge, P, As, Sb, Bi, S, Se, Te, Po and combinations thereof can be selected.

[0059] Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0060] The negative electrode active material can be contained at 60 to 99% by weight, or 70 to 99% by weight, or 80 to 98% by weight based on the total weight of the negative electrode active material layer.

[0061] On the one hand, the types of binders and conductive materials that can be included in the negative electrode active material layer and their contents are substantially the same as the description of the positive electrode active material layer mentioned above, so additional explanations regarding this are omitted.

[0062] An example of an electrode assembly including the aforementioned positive electrode, negative electrode, and the porous coating layer formed on these electrodes is shown in FIG. 1. Referring to FIG. 1, in the electrode assembly, at a position corresponding to the positive electrode tab of the positive electrode, an insulating layer covering it may further be included on the conductive surface of the negative electrode (see "A" in FIG. 1).

[0063] In a general lithium secondary battery, considering the irreversible capacity at the initial stage of charge and discharge, etc., the negative electrode is often formed with a larger area than the positive electrode. However, due to such an area difference, during the manufacturing process of the lithium secondary battery, when the electrode assembly is crimped and the positive electrode tab is bent, the positive electrode tab may come into contact with the conductive surface of the negative electrode (see "A" in FIG. 1), resulting in a short circuit.

[0064] The conductive surface of the negative electrode (see "A" in FIG. 1) where a short circuit with the positive electrode tab can occur can typically be the side surface of the negative electrode at a position corresponding to the positive electrode tab. Also, due to the area difference between the positive electrode and the negative electrode, etc., an exposed plane may occur on the plane of the negative electrode where the negative electrode current collector is exposed without the formation of the negative electrode active material layer and the porous coating layer. Such an exposed plane can also become the conductive surface of the negative electrode (see "A" in FIG. 1) where a short circuit with the positive electrode tab can occur.

[0065] By additionally forming the insulating layer so as to surround such a conductive surface of the negative electrode (see "A" in FIG. 1), it is possible to prevent a short circuit caused by the bending of the positive electrode tab, etc.

[0066] On the other hand, the thickness of the insulating layer can be 100 μm or less, or 10 - 100 μm, or 30 - 70 μm. When the thickness of the insulating layer satisfies the above range, it can exhibit a sufficient insulating effect while not interfering with other components of the electrode assembly.

[0067] Also, such an insulating layer can be formed by coating an insulating liquid or attaching an insulating tape, and the insulating liquid can include a solvent and an insulating polymer. Further, the insulating tape can include polyimide.

[0068] And the insulating liquid can include a polymer resin and ceramic particles. The polymer resin can include one or more selected from the group consisting of polyethylene, polypropylene, polybutylene, polystyrene, polyethylene terephthalate, natural rubber, and synthetic rubber. Among these, polyethylene, polypropylene, etc. with excellent insulation properties and electrolyte resistance can be used.

[0069] Flame-retardant electrolyte On the other hand, a lithium secondary battery according to one embodiment includes the aforementioned electrode assembly and a flame-retardant electrolyte including a flame-retardant solvent having a flash point of 100 °C or higher or no flash point and a lithium salt. Such a flame-retardant solvent can include a substantially non-flammable organic solvent having no flash point and an organic solvent having a high flash point of 100 °C or higher, or 100 to 250 °C, or 110 to 200 °C and low volatility. Including such a flame-retardant solvent and a flame-retardant electrolyte containing a lithium salt, a lithium secondary battery according to one embodiment can exhibit excellent safety and stability. Also, since the flame-retardant electrolyte can be uniformly impregnated into the aforementioned porous coating layer, various electrochemical properties of the lithium secondary battery can be excellently achieved. The flash point defining the flame-retardant solvent can be measured by a closed or open method according to the standard methods of ASTM D93 or ASTM D1310.

[0070] In a specific example, the flame-retardant solvent can be an organic solvent having low volatility of the organic solvent and a functional group that can contribute to flame retardancy or nonflammability, for example, a functional group selected from the group consisting of a sulfone-based functional group, a fluorine-containing functional group such as a fluorine-substituted hydrocarbon group, a phosphorus-containing functional group such as a phosphate group or a phosphonate group, and a nitrile-based functional group, and one or more of such organic solvents can be mixed and used. More specifically, the flame-retardant solvent can contain one or more organic solvents selected from the group consisting of a sulfone-based compound, a nitrile-based compound, a phosphoric acid-based compound, and a carbonate-based compound substituted with fluorine.

[0071] Among these, the sulfone-based compound can be a cyclic sulfone-based compound or a linear sulfone-based compound, and specifically, it can contain one or more selected from the group consisting of sulfolane, ethyl methyl sulfone, dibutyl sulfone, ethyl vinyl sulfone, methyl propyl sulfone, ethyl-i-propyl sulfone, ethyl-i-butyl sulfone, i-propyl-i-butyl sulfone, i-propyl-s-butyl sulfone, and butyl-i-butyl sulfone.

[0072] Also, the nitrile-based compound can contain one or more selected from the group consisting of malononitrile, succinonitrile, glutaronitrile, adiponitrile, suberonitrile, and sebaconitrile.

[0073] Also, the phosphoric acid-based compound can contain one or more selected from the group consisting of dimethyl methyl phosphate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, diethyl ethyl phosphate, dimethyl methyl phosphate, dimethyl(2-methoxyethoxy)methyl phosphonate, diethyl(2-methoxyethoxy)methyl phosphonate, and triphenyl phosphate.

[0074] In addition, the fluorine-substituted carbonate compound can include one or more selected from the group consisting of bis(2,2,3,3-tetrafluoro-propyl) carbonate, methyl-2,2,2-trifluoroethyl carbonate, ethyl-2,2,2-trifluoroethyl carbonate, propyl-2,2,2-trifluoroethyl carbonate, methyl-2,2,2,2’,2’,2’-hexafluoro-i-propyl carbonate, ethyl-2,2,2,2’,2’,2’-hexafluoro-i-propyl carbonate, di-2,2,2-trifluoroethyl carbonate, 2,2,2-trifluoroethyl-N,N-dimethyl carbonate, hexafluoro-i-propyl-N,N-dimethyl carbonate, 4-(2,2,3,3-tetrafluoropropoxymethyl)-[1,3]-dioxolan-2-one, and bis(2,2,3,3-pentafluoro-propyl) carbonate.

[0075] On the other hand, the lithium salt contained in the flame-retardant electrolyte is used as a mediator for transmitting ions in the lithium secondary battery. The lithium salt contains, for example, Li as a cation + and contains F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , B 10 Cl 10 - , AlCl 4 - , AlO 2 - , PF 6 - , CF 3 SO 3 - , CH 3 CO 2 - , CF 3 CO 2 - , AsF6 - , SbF 6 - , CH 3 SO 3 - , (CF 3 CF 2 SO 2 ) 2 N - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2 N - , BF 2 C 2 O 4 - , BC 4 O 8 - , PF 4 C 2 O 4 - , PF 2 C 4 O 8 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , C 4 F 9 SO 3 - , CF 3 CF 2 SO 3 - , CF 3 CF 2 (CF 3 ) 2 CO - , (CF 3 SO 2 ) 2 , CH- , CF 3 (CF 2 ) 7 SO 3 - and SCN - can contain an anion selected from the group consisting of them together.

[0076] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF 4 , LiClO 4 , LiB 10 Cl 10 , LiAlCl 4 , LiAlO 2 , LiPF 6 , LiCF 3 SO 3 , LiCH 3 CO 2 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiCH 3 SO 3 , LiFSI (Lithium bis(fluorosulfonyl) imide, LiN(SO 2 F) 2 ), LiBETI (Lithium bis(perfluoroethanesulfonyl) imide, LiN(SO 2 CF 2 CF 3 ) 2 and LiTFSI (Lithium bis(trifluoromethanesulfonyl) imide, LiN(SO 2 CF 3 ) 2 ) and can contain one or more selected from the group consisting of them, but considering excellent stability, it is preferable to contain LiN(SO 2 CF 3 ) 2 . In addition to these, lithium salts usually used in the electrolyte of lithium secondary batteries can be used without special restrictions.

[0077] The concentration of the lithium salt can be appropriately changed within the range that can be normally used. However, in order to obtain the optimal effect of forming a film for preventing corrosion of the electrode surface, it can be contained in the flame-retardant electrolyte at a concentration of 0.5 M to 6 M, or 1 M to 3 M, or 1 M to 2.5 M in the electrolyte. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics is sufficient during the high-temperature storage of the lithium secondary battery, and the viscosity of the flame-retardant electrolyte is appropriate and the impregnation property of the flame-retardant electrolyte can be improved.

[0078] In addition, the above-mentioned flame-retardant electrolyte can prevent the electrolyte from being decomposed in a high-power environment and inducing negative electrode collapse, and can be additionally contained with an electrolyte additive as needed in consideration of low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, or the effect of suppressing battery swelling at high temperature.

[0079] Typical examples of such electrolyte additives include one or more selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0080] Among these, examples of the cyclic carbonate compound include vinylene carbonate (VC) or vinyl ethylene carbonate. Examples of the halogen-substituted carbonate compound include fluoroethylene carbonate (FEC). Examples of the sultone compound include compounds selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone. Examples of the sulfate compound include ethylene sulfate (Ethylene Sulfate; Esa), trimethylene sulfate (Trimethylene sulfate; TMS), or methyl trimethylene sulfate (Methyl trimethylene sulfate; MTMS). Examples of the phosphate compound include one or more selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, and tris(2,2,2-trifluoroethyl) phosphate.

[0081] Examples of the borate compound include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), or lithium bisoxalatoborate (LiB(C 2 O 4 ) 2, such as LiBOB. As the nitrile compound, one or more selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile are included. Additionally, the benzene compound includes fluorobenzene, the amine compound includes triethanolamine or ethylenediamine, etc., and the silane compound includes tetravinylsilane. Further, the lithium salt compound is a compound different from the lithium salt contained in the flame-retardant electrolyte, and includes lithium nitrate, lithium difluorophosphate (LiDFP), LiPO 2 F 2 or LiBF 4 etc. are included.

[0082] The aforementioned electrolyte additive is contained at 0.1 to 10% by weight, or 0.2 to 8% by weight, or 0.5 to 8% by weight based on the total weight of the flame-retardant electrolyte, and can contribute to the improvement of ionic conductivity or cycle characteristics.

[0083] The aforementioned lithium secondary battery may be in a form in which the electrode assembly is housed in a case and the flame-retardant electrolyte is injected and impregnated, and may be a cylindrical, square, pouch type or coin type battery, etc., depending on the form of the case, etc.

[0084] Method for manufacturing a lithium secondary battery On the other hand, according to another embodiment of the invention, there is provided a method for manufacturing the aforementioned lithium secondary battery. Such a manufacturing method may include: forming a porous coating layer containing polymer particles or ceramic particles with an absolute value of zeta potential of 25 mV or more on the electrode; forming an electrode assembly including the electrode coated with the porous coating layer; and impregnating the electrode assembly with a non-flammable electrolyte containing a non-flammable solvent having a flash point of 100 °C or more or no flash point and a lithium salt.

[0085] In the manufacturing method of the other embodiment, since the forming method of each electrode can follow general methods such as coating a slurry composition for forming each active material layer on a current collector with an electrode tab defined thereon and drying and rolling, additional description thereof is omitted.

[0086] On the other hand, the step of forming a porous coating layer on the electrode can be performed through a dry or wet process. For example, in the case of the dry process, it can be performed by a method of transferring a porous coating layer containing free-standing or separately coated polymer particles or ceramic particles and optionally a polymer binder onto the electrode (e.g., on the electrode active material layer).

[0087] Also, in the case of the wet process, it can be performed by a method of coating a slurry containing the polymer particles or ceramic particles, a polymer binder, and a liquid medium on the electrode (e.g., on the electrode active material layer) and drying.

[0088] An additional rolling process can be performed on the porous coating layer formed through the above method as needed.

[0089] On the other hand, the manufacturing method of the foregoing other embodiment can further include a step of surface-treating the polymer particles or ceramic particles by a method such as plasma, ion beam, or surface coating to adjust the absolute value of the zeta potential to 25 mV or more. As already described above, through such surface treatment, the surface characteristics of the polymer particles or ceramic particles can be controlled to satisfy the absolute value within the foregoing zeta range.

[0090] At this time, the surface treatment step such as the plasma can be performed before the polymer particles or ceramic particles are put into the slurry for forming the porous coating layer, or can also be performed after the slurry is coated on the electrode.

[0091] As a typical example of the surface treatment step, a method of forming oxygen plasma in a reactor and using this to surface-treat the polymer particles or ceramic particles can be mentioned, whereby the absolute value of the zeta potential on the particle surface can be increased.

[0092] After forming the porous coating layer, the two electrodes can be joined and assembled so that the porous coating layer is disposed between the two electrodes to form an electrode assembly. At this time, when the porous coating layers are all formed on both electrodes, they can be joined and assembled so as to contact each other, and when the porous coating layer is formed only on one of the electrodes, the porous coating layer can be joined and assembled so as to face the remaining electrode.

[0093] Thereafter, the step of impregnating the electrode assembly with a nonflammable electrolyte containing a nonflammable solvent and a lithium salt can be performed by a general method of injecting the foregoing nonflammable electrolyte into a case containing the electrode assembly.

[0094] Hereinafter, the invention will be described more specifically through specific examples. However, the following examples are merely illustrative for helping the understanding of the invention and do not limit the scope of the invention.

[0095] Examples First, in the following examples, the zeta potential of the polymer particles or ceramic particles was measured by the electrophoretic light scattering method using dynamic light scattering equipment (product name: ELS-Z) with the polymer particles or ceramic particles dispersed at 0.1% by weight or less in an aqueous solvent at a temperature of 25°C.

[0096] Also, the flash point of the (flame-retardant) organic solvent contained in the (flame-retardant) electrolyte was measured by the closed method according to the standard method of ASTM D93. Specifically, the sample container was filled with the organic solvent sample, covered with the lid of the container and sealed, and then the sample container was heated at a constant rate by the aforementioned standard method. During heating, the sample container was periodically opened to check whether a flame was generated, and the temperature at the time of flame generation was measured as the flash point.

[0097] Example 1 As the positive electrode active material, a positive electrode with a thickness of 60 μm containing Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2 and a negative electrode with a thickness of 75 μm containing artificial graphite as the negative electrode active material were prepared.

[0098] Polymethyl methacrylate (PMMA) polymer particles having a zeta potential of -50 mV and a particle size of 1 μm were put into an N-methyl-2-pyrrolidone (NMP) solvent so that the mass ratio of PMMA:hydrogenated nitrile rubber (H-NBR):polyvinylidene fluoride (PVDF) was 7:1:2 and dispersed to prepare a porous coating layer slurry (solid content: 21% by weight). After the negative electrode active material layer was formed, this was coated on the rolled negative electrode, dried, and a porous coating layer was formed on the negative electrode (the thickness of the porous coating layer was 30 μm). The porous coating layer of the negative electrode and the positive electrode were arranged in contact with each other to manufacture an electrode assembly.

[0099] In the flame-retardant solvent sulfolane (flash point: about 165°C), LiN(SO 2 CF3 ) 2 (LiFSI) was dissolved to a concentration of 1.5 M to produce a flame-retardant electrolyte. The electrode assembly was impregnated with the flame-retardant electrolyte to produce a lithium secondary battery.

[0100] Example 2 As the positive electrode active material, Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2 A positive electrode with a thickness of 60 μm containing the above and a negative electrode with a thickness of 75 μm containing artificial graphite as the negative electrode active material were prepared.

[0101] Polymethyl methacrylate (PMMA) polymer particles having a zeta potential of -50 mV and a particle size of 1 μm were placed in an N-methyl-2-pyrrolidone (NMP) solvent so that the mass ratio of PMMA:hydrogenated nitrile rubber (H-NBR):polyvinylidene fluoride (PVDF) was 7:1:2 and dispersed to prepare a porous coating layer slurry (solid content: 21% by weight). After the positive electrode active material layer was formed, this was coated on the rolled positive electrode and dried to form a porous coating layer on the positive electrode (the thickness of the porous coating layer was 30 μm). The porous coating layer of the positive electrode and the negative electrode were arranged in contact with each other to manufacture an electrode assembly.

[0102] LiN(SO 2 CF 3 ) 2 (LiFSI) was dissolved to a concentration of 1.5 M to produce a flame-retardant electrolyte. The electrode assembly was impregnated with the flame-retardant electrolyte to produce a lithium secondary battery.

[0103] Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode formed with the porous coating layer manufactured in Example 1 and the negative electrode formed with the porous coating layer manufactured in Example 2 were arranged such that their respective porous coating layers were in contact with each other to manufacture an electrode assembly.

[0104] Example 4 Nine negative electrodes with a porous coating layer formed in the same manner as in Example 1 and eight positive electrodes without a porous coating layer were each manufactured.

[0105] Eight positive electrodes were placed and stacked between each of the nine negative electrodes with a porous coating layer. A polyimide insulating tape was attached to a region (「A」 in Fig. 1) corresponding to the position where the positive electrode tab protruded in each of the stacked negative electrodes to form an insulating layer, thereby manufacturing an electrode assembly (the thickness of the insulating layer was 60 μm).

[0106] Lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in sulfolane (flash point: about 165 °C), which is a flame-retardant solvent, to a concentration of 1.5 M and triethyl phosphate (TEP) was added to a concentration of 1 wt% to produce a flame-retardant electrolyte. The electrode assembly was impregnated with the flame-retardant electrolyte to manufacture a lithium secondary battery. 2 CF 3 ) 2 (LiFSI) to produce a flame-retardant electrolyte. The electrode assembly was impregnated with the flame-retardant electrolyte to manufacture a lithium secondary battery.

[0107] Example 5 Eight positive electrodes with a porous coating layer formed in the same manner as in Example 2 and nine negative electrodes without a porous coating layer were each manufactured.

[0108] Eight positive electrodes with a porous coating layer were placed and stacked between each of the nine negative electrodes. A polyimide insulating tape was attached to a region (「A」 in Fig. 1) corresponding to the position where the positive electrode tab protruded in each of the stacked negative electrodes to form an insulating layer, thereby manufacturing an electrode assembly (the thickness of the insulating layer was 60 μm). At this time, the insulating tape was attached so as to surround not only the side surface of the negative electrode but also a part of the plane of the negative electrode where the negative electrode current collector was exposed without forming a negative electrode active material layer or the like.

[0109] Lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in sulfolane (flash point: about 165 °C), which is a flame-retardant solvent, to a concentration of 1.5 M and triethyl phosphate (TEP) was added to a concentration of 1 wt% to produce a flame-retardant electrolyte. 2 CF 3 ) 2A non-flammable electrolyte was produced by dissolving (LiFSI) at a concentration of 1.5 M and triethyl phosphate (TEP) at 1 wt%. A lithium secondary battery was produced by impregnating the electrode assembly with the non-flammable electrolyte.

[0110] Comparative Example 1 As the positive electrode active material, Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2 A positive electrode with a thickness of 60 μm containing the above and a negative electrode with a thickness of 75 μm containing artificial graphite as the negative electrode active material were prepared.

[0111] An electrode assembly was produced with a polyolefin-based separator interposed between a positive electrode and a negative electrode without a porous coating layer.

[0112] LiPF was dissolved in an organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 30:70 volume ratio) to a concentration of 1 M to produce a non-aqueous electrolyte. 6

[0113] A lithium secondary battery was produced by impregnating the electrode assembly with the non-aqueous electrolyte.

[0114] Comparative Example 2 Instead of polymethyl methacrylate (PMMA) polymer particles having a zeta potential of -50 mV and a particle size of 1 μm, Al having a zeta potential of +20 mV and a particle size of 1 μm 2 O 3 A lithium secondary battery was produced in the same manner as in Example 1 except that ceramic particles were used to form a porous coating layer on the negative electrode.

[0115] Reference Example 1 A lithium secondary battery was produced in the same manner as in Example 1 except that an insulating layer was not formed on the electrode assembly.

[0116] Experimental Example 1 - Evaluation of Thermal Stability ​The results of the hot box tests conducted on each of the lithium secondary batteries manufactured in Examples 1 to 3 and the lithium secondary battery manufactured in Comparative Example 1 are shown in FIGS. 2 to 5. Specifically, in the hot box test, the temperature was increased from 25°C at a rate of 5°C / min, held at 100°C, 120°C, 140°C, 150°C, 160°C, 170°C, and 180°C for 30 minutes each, and then the temperature was increased to 200°C at a rate of 2°C / min. FIGS. 2 to 5 show the voltage-temperature changes over time. Also, the ignition start temperature is shown in Table 1 below.

[0117] On the other hand, in the case of the lithium secondary battery of Comparative Example 2, since it is not impregnated with a flame-retardant electrolyte and cannot be fully charged, there is a side where it is difficult to compare the thermal safety under equivalent conditions, and it was omitted from the evaluation of thermal safety.

[0118] [Table 1]

[0119] As shown in FIGS. 2 to 5 and Table 1, it was confirmed that the lithium secondary batteries of Examples 1 to 3 have a higher ignition start temperature and exhibit improved thermal stability compared to Comparative Example 1.

[0120] Experimental Example 2 - Evaluation of Various Electrochemical Performances The initial capacity and capacity retention rate were measured for each of the lithium secondary batteries manufactured in Examples 1 to 3 and the lithium secondary battery manufactured in Comparative Example 2, and the results are shown in Table 2 below.

[0121] The capacity retention rate was calculated as the ratio of the capacity after 200 charge-discharge cycles to the initial capacity after performing 200 charge-discharge cycles, where each of the batteries manufactured in Examples 1 to 3 and Comparative Example 2 was charged to 4.2V at a constant current of 0.33C at 45°C and discharged to 3.0V at a constant current of 0.33C in one cycle.

[0122] [Table 2]

[0123] Referring to Table 2 above, it was confirmed that the lithium secondary batteries of Examples 1 to 3 exhibited excellent capacity characteristics and capacity retention rates as compared with the lithium secondary battery manufactured in Comparative Example 2. This is presumably because the impregnation properties of the flame-retardant electrolyte were excellent in Examples 1 to 3 due to the zeta potential and dispersibility of the polymer particles contained in the porous coating layer.

[0124] Experimental Example 3 - Short-circuit prevention effect The insulation resistance was measured for each of the lithium secondary batteries manufactured in Examples 4 and 5 and Reference Example 1 to evaluate the short-circuit prevention effect.

[0125] Specifically, the insulation resistance at 50 V was measured for each of the lithium secondary batteries manufactured in Examples 4 and 5 and Comparative Example 1 using a Hioki insulation resistance measuring instrument. The results are shown in Table 3.

[0126]

Table 3

[0127] Referring to Table 3, it was confirmed that the lithium secondary batteries of Examples 4 and 5 had an excellent short-circuit prevention effect due to the additional formation of the insulating layer.

Claims

1. An electrode assembly including an electrode and a porous coating layer formed on the electrode; and A lithium secondary battery including a nonflammable electrolyte containing a nonflammable solvent having a flash point of 100 °C or higher or having no flash point and a lithium salt, The porous coating layer contains polymer particles or ceramic particles having an absolute value of zeta potential of 25 mV or more. A lithium secondary battery.

2. The lithium secondary battery according to claim 1, wherein the polymer particles include one or more selected from the group consisting of polymethyl (meth) acrylate, polystyrene, polyvinyl chloride, polycarbonate, polysulfone, polyethersulfone, polyetherimide, polyphenylsulfone, polyamideimide, polyimide, polybenzimidazole, polyetherketone, polyphthalamide, polybutylene terephthalate, polyethylene terephthalate, and polyphenylene sulfide.

3. The ceramic particles are boehmite, Al ２ O ３ , TiO ２ , Fe ２ O ３ , SiO ２ , ZrO ２ , Co ３ O ４ , SnO ２ , NiO, ZnO, V ２ O ５ and one or more selected from the group consisting of MnO, the lithium secondary battery according to claim 1.

4. The lithium secondary battery according to claim 1, wherein the polymer particles or ceramic particles have a particle size of 50 nm to 3 μm.

5. The lithium secondary battery according to claim 1, wherein the porous coating layer includes a polymer binder and the polymer particles or ceramic particles dispersed on the polymer binder.

6. The lithium secondary battery according to claim 5, wherein the porous coating layer contains the polymer binder: the polymer particles or ceramic particles in a weight ratio of 5:95 to 40:

60.

7. The lithium secondary battery according to claim 1, wherein the porous coating layer has a thickness of 5 to 50 μm and includes a plurality of pores having a diameter of 10 nm or more.

8. The lithium secondary battery according to claim 1, wherein the nonflammable solvent includes one or more organic solvents having a functional group selected from the group consisting of a sulfone-based functional group, a fluorine-containing functional group, a phosphorus-containing functional group, and a nitrile-based functional group.

9. The lithium secondary battery according to claim 1, wherein the nonflammable solvent includes one or more organic solvents selected from the group consisting of a sulfone-based compound, a nitrile-based compound, a phosphoric acid-based compound, and a fluorine-substituted carbonate-based compound.

10. The sulfone compound-containing lithium secondary battery according to claim 9, wherein the sulfone compound contains one or more selected from the group consisting of sulfolane, ethyl methyl sulfone, dibutyl sulfone, ethyl vinyl sulfone, methyl propyl sulfone, ethyl-i-propyl sulfone, ethyl-i-butyl sulfone, i-propyl-i-butyl sulfone, i-propyl-s-butyl sulfone, and butyl-i-butyl sulfone.

11. The nitrile compound-containing lithium secondary battery according to claim 9, wherein the nitrile compound contains one or more selected from the group consisting of malononitrile, succinonitrile, glutaronitrile, adiponitrile, suberonitrile, and sebaconitrile.

12. The lithium secondary battery according to claim 9, wherein the phosphate compound contains one or more selected from the group consisting of dimethyl methyl phosphate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, diethyl ethyl phosphate, dimethyl methyl phosphate, dimethyl (2-methoxyethoxy) methyl phosphonate, diethyl (2-methoxyethoxy) methyl phosphonate, and triphenyl phosphate.

13. The lithium secondary battery according to claim 9, wherein the fluorine-substituted carbonate compound contains one or more selected from the group consisting of bis(2,2,3,3-tetrafluoro-propyl) carbonate, methyl-2,2,2-trifluoroethyl carbonate, ethyl-2,2,2-trifluoroethyl carbonate, propyl-2,2,2-trifluoroethyl carbonate, methyl-2,2,2,2',2',2'-hexafluoro-i-propyl carbonate, ethyl-2,2,2,2',2',2'-hexafluoro-i-propyl carbonate, di-2,2,2-trifluoroethyl carbonate, 2,2,2-trifluoroethyl-N,N-dimethyl carbonate, hexafluoro-i-propyl-N,N-dimethyl carbonate, 4-(2,2,3,3-tetrafluoropropoxymethyl)-[1,3]-dioxolan-2-one, and bis(2,2,3,3-pentafluoro-propyl) carbonate.

14. The lithium salt is LiN(SO ２ CF ３ ). ２ The lithium secondary battery according to claim 1, which contains the same.

15. The lithium secondary battery according to claim 1, wherein the flame-retardant electrolyte contains the lithium salt at a concentration of 0.5 M to 6 M.

16. The electrode assembly includes a positive electrode having a positive tab, a negative electrode having a negative tab, and the porous coating layer formed on the positive electrode or the negative electrode so as to be disposed between the positive electrode and the negative electrode. The lithium secondary battery according to claim 1, further comprising an insulating layer covering the conductive surface of the negative electrode at a position corresponding to the positive tab.

17. The lithium secondary battery according to claim 16, wherein the insulating layer covers an exposed plane where the porous coating layer is not formed, among a side surface of the negative electrode at a position corresponding to the positive tab and a flat surface of the negative electrode facing the positive electrode.

18. The lithium secondary battery according to claim 16, wherein the porous coating layer is formed on each of the positive electrode and the negative electrode, and the porous coating layer formed on the negative electrode and the porous coating layer formed on the positive electrode are in contact with each other.

19. Forming a porous coating layer containing polymer particles or ceramic particles having an absolute value of zeta potential of 25 mV or more on the electrode; Forming an electrode assembly including the electrode coated with the porous coating layer; Impregnating the electrode assembly into a nonflammable electrolyte containing a nonflammable solvent having a flash point of 100 °C or higher or no flash point and a lithium salt. A method for manufacturing a lithium secondary battery, comprising:

20. The method for manufacturing a lithium secondary battery according to claim 19, further comprising a step of plasma-treating the polymer particles or ceramic particles to adjust the absolute value of the zeta potential to 25 mV or more.

21. The forming step of the porous coating layer includes a step of coating and drying a slurry containing the polymer particles or ceramic particles, a polymer binder, and a liquid medium on the electrode. The method for manufacturing a lithium secondary battery according to claim 19.

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