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 of related applications This application claims priority rights based on Korean Patent Application No. 10-2022-0069165 dated June 7, 2022, Korean Patent Application No. 10-2022-0073089 dated June 15, 2022, and Korean Patent Application No. 10-2023-0061581 dated May 12, 2023, and all content disclosed in the documents of said Korean patent applications is incorporated herein by reference.

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

[0003] Recently, as the application areas of lithium-ion batteries have rapidly expanded from power supply for electronic devices such as electrical, electronic, telecommunications, and computers to power storage and supply for large-area devices such as automobiles and energy storage devices, the demand for lithium-ion batteries that are high-capacity, high-output, long-life, and highly stable is increasing.

[0004] Lithium-ion batteries generally consist of a positive electrode, a negative electrode, a separator membrane, and an electrolyte. It is known in the art that the positive electrode, due to its unstable structure in the charged state, can generate oxygen. Because the generation of oxygen poses a significant fire risk, research and development efforts are being made to improve the safety of lithium-ion batteries.

[0005] In lithium-ion batteries, a separator membrane is used to ensure electrical insulation between the positive and negative electrodes. Typically, this separator membrane is a thin film made of polyolefin. However, such membranes can easily shrink at high temperatures, making it impossible to insulate between the positive and negative electrodes. Furthermore, if folding or mismatching of the separator membrane occurs during the assembly process of lithium-ion batteries, while the battery may function normally initially, over time, the formation of lithium dendrites can lead to short circuits. When electrical insulation between the positive and negative electrodes becomes impossible, a short circuit occurs, and this can react with oxygen generated by the unstable positive electrode, potentially causing a fire. In short, if a short circuit occurs in a charged lithium-ion battery due to high temperatures or shocks during the manufacturing process, there is a risk of the lithium-ion battery catching fire.

[0006] Furthermore, it is known that lithium secondary batteries use highly volatile and flammable solvents as electrolytes, which presents the problem of being prone to ignition. To solve this, flame-retardant electrolytes containing flame-retardant solvents can be used, but such flame-retardant electrolytes have the problem of not being well impregnated into conventional separation membranes. If the electrolyte is not well impregnated in a lithium secondary battery, lithium ions are not transferred well, resulting in a decrease in the capacity, output, and life characteristics of the lithium secondary battery. In addition, if the electrolyte is not well impregnated in a lithium secondary battery, non-uniform reactions occur between the electrode and electrolyte, leading to dendrite formation and short circuits.

[0007] Therefore, in order to solve these problems, research and development are being conducted on methods that can improve safety while maintaining the overall performance of lithium-ion batteries. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Therefore, the object of the present invention is to provide a lithium secondary battery and a method for manufacturing the same, which have improved stability, suppressed ignition, and improved electrolyte impregnation properties, thereby improving various other characteristics. [Means for solving the problem]

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

[0010] Furthermore, the present invention provides a method for manufacturing the lithium secondary battery. In one embodiment, such a manufacturing method may include the steps of: forming a porous coating layer on an electrode containing polymer particles or ceramic particles having an absolute zeta potential of 25 mV or more; forming an electrode assembly including the electrode coated with the porous coating layer; and impregnating the electrode assembly with a flame-retardant electrolyte containing a flame-retardant solvent having a flash point of 100°C or higher or having no flash point, and a lithium salt. [Effects of the Invention]

[0011] In the lithium secondary battery of the present invention, instead of using an existing separation membrane to ensure electrical insulation between the positive and negative electrodes, a porous coating layer formed on the electrodes is used. In an electrode assembly including such a porous coating layer, the occurrence of short circuits due to shrinkage of the existing separation membrane is suppressed, thereby reducing the risk of ignition due to high temperatures or external impacts.

[0012] Furthermore, the lithium secondary battery contains a flame-retardant electrolyte to suppress ignition, while the flame-retardant electrolyte is well impregnated into the electrode assembly including the porous coating layer, allowing for a uniform reaction throughout the electrode. As a result, various performance characteristics such as capacity, output, and lifespan of the lithium secondary battery can be improved. In addition, in the lithium secondary battery, because the electrolyte is well impregnated into the electrode assembly and a uniform reaction occurs between the electrode and the electrolyte, the formation of dendrites is suppressed, and the occurrence of short circuits is suppressed. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram showing an electrode assembly of a lithium secondary battery according to one embodiment of the invention. [Figure 2] This shows the results of a hot box test performed on the lithium secondary battery of Example 1. [Figure 3] This shows the results of a hot box test performed on the lithium secondary battery of Example 2. [Figure 4] This shows the results of a hot box test performed on the lithium secondary battery of Example 3. [Figure 5] This is the result of a hot box test performed on the lithium secondary battery of Comparative Example 1. [Modes for carrying out the invention]

[0014] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner and concept consistent with the technical idea of ​​the present invention, based on the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0015] In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the presence of implemented features, figures, stages, components, or combinations thereof, and should be understood not to preemptively exclude the presence or possibility of adding one or more other features, figures, stages, components, or combinations thereof.

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

[0017] As described above, in one embodiment of the lithium secondary battery, a porous coating layer is formed on the positive or negative electrode within the electrode assembly, substantially replacing an existing separation membrane, and such porous coating layer includes polymer particles or ceramic particles whose absolute value of zeta potential is 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 is high.

[0018] Furthermore, the flame-retardant solvent contained in the battery of the above embodiment has a higher polarity than the organic solvent contained in general lithium-ion battery electrolytes. Therefore, by combining a porous coating layer containing particles with high surface polarity with a flame-retardant solvent, an excellent affinity can be achieved between the flame-retardant electrolyte and the electrode on which the porous coating layer is formed, demonstrating excellent impregnation of the flame-retardant electrolyte into the porous coating layer, and solving problems such as short circuits due to thermal shrinkage of existing separation membranes.

[0019] Furthermore, the lithium secondary battery of the above embodiment includes a flame-retardant electrolyte containing a flame-retardant solvent and lithium salt having a flash point that is not detectable (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 porous coating layer.

[0020] Thus, in one embodiment, the lithium secondary battery, by including a porous coating layer that replaces the separation membrane and a predetermined flame-retardant electrolyte, exhibits excellent stability by suppressing short circuits and ignition, while the flame-retardant electrolyte is uniformly impregnated into the porous coating layer, thereby improving various electrochemical characteristics such as capacity, output, and lifespan.

[0021] The lithium secondary battery and its manufacturing method according to embodiments of the invention will be described in more detail below.

[0022] electrode assembly One embodiment of a lithium secondary battery basically includes an electrode assembly. As shown in Figure 1, such an electrode assembly includes electrodes including a positive electrode and a negative electrode, and a porous coating layer formed on the electrodes, for example, the positive electrode and / or the negative electrode, wherein the porous coating layer includes polymer particles or ceramic particles having an absolute value of zeta potential of 25 mV or more.

[0023] In this case, 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 repulsion or dispersibility between them. 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 that allow lithium ions to pass through can be defined between these particles. Furthermore, particles that satisfy such a zeta potential allow the porous coating layer to exhibit excellent impregnation properties with flame-retardant electrolytes containing flame-retardant solvents. By combining such a porous coating layer with a flame-retardant electrolyte, a lithium secondary battery of one embodiment can exhibit the aforementioned excellent properties.

[0024] The zeta potential of the polymer particles or ceramic particles can be measured, for example, by electrophoretic light scattering using dynamic light scattering equipment. In this case, the zeta potential can be measured when 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 when the polymer particles or ceramic particles are dispersed in water 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 may be 25mV or more, 35mV or more, or 45mV or more, and may be 100mV or less, 90mV or less, or 80mV or less. Within this range, good coating properties and porosity of the porous coating layer are achieved, and high impregnation of the flame-retardant electrolyte is ensured, so that the battery of one embodiment can exhibit excellent stability and electrochemical properties.

[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, polyetherketone, polyphthalamide, polybutylene terephthalate and polyethylene terephthalate, and polyphenylene sulfide.

[0027] Furthermore, specific examples of the ceramic particles include one or more selected from the group consisting of boehmite (γ-AlO(OH)), Al2O3, TiO2, Fe2O3, SiO2, ZrO2, Co3O4, SnO2, NiO, ZnO, V2O5, and MnO.

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

[0029] Furthermore, as will be explained in more detail below, in order to control the surface properties of the polymer particles or ceramic particles and thereby adjust the zeta potential, the polymer particles or ceramic particles may be included in the porous coating layer in a state in which they have been surface-treated with plasma or an ion beam.

[0030] On the other hand, the porous coating layer may have a form comprising a polymer binder and polymer particles or ceramic particles dispersed on such polymer binder. In this case, the polymer binder may be the same type of polymer as the binder contained in the electrode active material layer. Specific examples include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, or fluororubber. 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 obviously determined by a person skilled in the art, taking into account the type and properties of the polymer particles or ceramic particles, and the method of forming the porous coating layer.

[0031] Furthermore, taking into consideration the good coating properties and porosity of the porous coating layer mentioned above, as well as the good dispersibility of the particles, the porous coating layer may contain the polymer binder and the polymer particles or ceramic particles in a weight ratio of 5:95 to 40:60, or 10:90 to 35:65.

[0032] The aforementioned porous coating layer can have a thickness of 5-50 μm, 10-45 μm, or 15-40 μm, due to its excellent impregnation properties for flame-retardant electrolytes and its effective replacement of a separation membrane. It can also contain multiple pores with diameters of 10 nm or more, 20 nm to 3 μm, or 50 nm to 1 μm. In this case, the thickness of the porous coating layer can refer to the total thickness of the porous coating layer formed on the positive and / or negative electrode.

[0033] On the other hand, the electrode assembly including the porous coating layer described above may include, for example, 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 positioned between the positive electrode and the negative electrode, as shown in Figure 1.

[0034] Furthermore, the positive electrode and the negative electrode may each include a positive electrode current collector and a positive electrode active material layer and a negative electrode active material layer formed on the negative electrode current collector, respectively. The aforementioned porous coating layer may be formed on such a positive electrode active material layer and / or negative electrode active material layer and may be arranged between these positive and negative electrode active material layers in a manner that is in contact with them. In a more specific example, as shown in Figure 1, the porous coating layer may be formed on the positive electrode and the negative electrode active material layer, 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, the positive electrode current collector included in the positive electrode of the electrode assembly is not particularly limited as long as it is conductive without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., can be used.

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

[0037] At this time, the positive electrode active material is a compound capable of reversible insertion and extraction of lithium, and specifically, it can 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 (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-manganese-cobalt-based oxide (e.g., Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), a lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (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 independent elements, respectively, 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 Fe1-x M x (PO 4-b )X b (Here, M is one or more selected from Al, Mg, and Ti, and X is one or more selected from F, S, and N, with -0.5 ≤ a ≤ +0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1), and one or more of these compounds may be included.

[0038] Among these, lithium metal oxides such as LiCoO2, LiMnO2, LiNiO2, and lithium nickel manganese cobalt oxide (e.g., Li(Ni)) are particularly noteworthy for their ability to improve the capacity characteristics and safety of batteries. 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 etc.), lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2 etc.), lithium nickel manganese cobalt aluminum oxide (e.g., Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 This could be O2, or lithium iron phosphorus oxide (e.g., LiFePO4), and one or more of these in mixtures can be used.

[0039] Among these, a positive electrode active material with a nickel content of 80 atm% or more can be used because it can best enhance the battery's capacity characteristics. For example, the lithium transition metal oxide may include one represented by the following chemical formula 1.

[0040] [Chemical Formula 1] Li x Ni a Co b M 1 c M 2 d O2 In the above Chemical Formula 1, the M 1 may be one or more selected from Mn and Al or a combination thereof.

[0041] M 2 may 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 may 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 in the metal elements excluding lithium in the lithium transition metal oxide, and may 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 in the metal elements excluding lithium in the lithium transition metal oxide, and may be 0 < b < 0.2, 0 < b ≤ 0.15, or 0.01 ≤ b ≤ 0.10.

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

[0046] The d represents the atomic fraction of M 2This represents the atomic fraction and can be 0 ≤ d ≤ 0.1 or 0 ≤ d ≤ 0.05.

[0047] The positive electrode active material may be present in an amount of 60-99% by weight, 70-99% by weight, or 80-98% by weight, based on the total weight of the positive electrode active material layer.

[0048] The aforementioned binder is a component that assists in the bonding of the active material to the conductive material and to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, or fluororubber. A mixture or copolymer of two or more of these can also be used.

[0049] Typically, the binder may be present in an amount of 1 to 20% by weight, 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, and 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 crystalline structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0051] Typically, the conductive material may be included in an amount of 1 to 20% by weight, 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 may include a negative electrode current collector, a negative electrode active material layer containing a negative electrode active material, a binder, a conductive material, and selectively 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 chemical changes in the battery, and can be made of materials such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy. 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 a variety of forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0054] Furthermore, the negative electrode active material may include at least one selected from the group consisting of lithium metal, carbon materials capable of reversibly inserting / de-inserting lithium ions, metals or alloys of these metals with lithium, metal composite oxides, materials capable of doping and de-doping lithium, and transition metal oxides.

[0055] As the carbon material capable of reversibly inserting / desorbing the lithium ions, any carbonaceous negative electrode active material generally used in lithium ion secondary batteries can be used without particular limitation. Representative examples thereof include crystalline carbon, amorphous carbon, or both of them can be used. 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 an 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, 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, elements of Group 1, Group 2, Group 3 of the periodic table, halogen; 0 <x≦1; 1≦y≦3; 1≦z≦8) can be selected and used from the group consisting of them.

[0058] As the substance capable of doping and de-doping lithium, 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. may be mentioned, and at least one of these and SiO2 can also be mixed and used. As the element Y, it may be selected from the group consisting of 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.

[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 may 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 other hand, since the types of the binder and the conductive material that may be contained in the negative electrode active material layer and their contents are substantially the same as the description regarding the positive electrode active material layer described above, additional description regarding this is 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 be further included on the conductive surface of the negative electrode (see "A" in FIG. 1).

[0063] In typical lithium-ion secondary batteries, the negative electrode is often formed with a larger surface area than the positive electrode, taking into consideration irreversible capacity during the initial stages of charging and discharging. However, due to this difference in surface area, when the electrode assembly is compressed during the manufacturing process of lithium-ion secondary batteries, the positive electrode tab may be bent, causing it to come into contact with the conductive surface of the negative electrode ("A" in Figure 1), resulting in a short circuit.

[0064] Thus, the conductive surface of the negative electrode where a short circuit with the positive electrode tab can occur (labeled "A" in Figure 1) can typically be the side surface of the negative electrode at the position corresponding to the positive electrode tab. Furthermore, due to differences in the area of ​​the positive and negative electrodes, an exposed surface may occur on the plane of the negative electrode where the negative electrode active material layer and porous coating layer are not formed, exposing the negative electrode current collector. Such an exposed surface can also become a conductive surface of the negative electrode where a short circuit with the positive electrode tab can occur (labeled "A" in Figure 1).

[0065] By forming the aforementioned insulating layer so as to surround the conductive surface of the negative electrode (labeled "A" in Figure 1), it is possible to prevent short circuits caused by bending of the positive electrode tab.

[0066] On the other hand, the thickness of the insulating layer may be 100 μm or less, or 10 to 100 μm, or 30 to 70 μm. When the thickness of the insulating layer is within the above range, sufficient insulating effect can be achieved without interfering with other components of the electrode assembly.

[0067] Furthermore, such an insulating layer may be formed by coating with an insulating liquid or by attaching an insulating tape, and the insulating liquid may contain a solvent and an insulating polymer. The insulating tape may also contain polyimide.

[0068] The insulating liquid may contain a polymer resin and ceramic particles. The polymer resin may contain one or more selected from the group consisting of polyethylene, polypropylene, polybutylene, polystyrene, polyethylene terephthalate, natural rubber, and synthetic rubber, among which polyethylene, polypropylene, etc., which have excellent insulating properties and electrolyte resistance can be used.

[0069] Flame-retardant electrolyte On the other hand, a lithium secondary battery of one embodiment includes the aforementioned electrode assembly and a flame-retardant electrolyte containing a flame-retardant solvent having a flash point of 100°C or higher or having no flash point and a lithium salt. Such a flame-retardant solvent can include substantially non-flammable organic solvents with no flash point and organic solvents having a high flash point of 100°C or higher, or 100-250°C, or 110-200°C and low volatility. Including such a flame-retardant solvent and flame-retardant electrolyte containing a lithium salt, a lithium secondary battery of one embodiment can exhibit excellent safety and stability. Furthermore, since the flame-retardant electrolyte can be uniformly impregnated into the aforementioned porous coating layer, the 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 may be an organic solvent having low volatility and a functional group that can contribute to flame retardancy or non-flammability, such as a sulfone 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 phosphonate group, and a nitrile functional group, and one or more such organic solvents may be used in mixture form. More specifically, the flame-retardant solvent may include one or more organic solvents selected from the group consisting of sulfone compounds, nitrile compounds, phosphoric acid compounds, and fluorine-substituted carbonate compounds.

[0071] Among these, the sulfone compound may be a cyclic sulfone compound or a linear sulfone compound, and specifically may include one or more selected from the group consisting of sulfolane, ethylmethylsulfone, dibutylsulfone, ethylvinylsulfone, methylpropylsulfone, ethyl-i-propylsulfone, ethyl-i-butylsulfone, i-propyl-i-butylsulfone, i-propyl-s-butylsulfone, and butyl-i-butylsulfone.

[0072] Furthermore, the nitrile compound may include one or more selected from the group consisting of malononitrile, succinonitrile, glutalonitrile, adiponitrile, suberonitrile, and sebaconitrile.

[0073] Furthermore, the phosphate compound may include one or more selected from the group consisting of dimethylmethyl phosphate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, diethylethyl phosphate, dimethylmethyl 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 - , 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 -, PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - It can contain anions selected from the group consisting of together.

[0076] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (Lithium bis(fluorosulfonyl) imide, LiN(SO2F)2), LiBETI (Lithium bis(perfluoroethanesulfonyl) imide, LiN(SO2CF2CF3)2) and LiTFSI (Lithium bis(trifluoromethanesulfonyl) imide, LiN(SO2CF3)2), and can contain one or more selected from the group consisting of. In consideration of excellent stability, it is preferable to contain LiN(SO2CF3)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 a range that is normally usable, but in order to obtain the optimal effect of forming a protective film to prevent corrosion on the electrode surface, it may be included 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. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics during high-temperature storage of the lithium secondary battery is sufficient, the viscosity of the flame retardant electrolyte is appropriate, and the impregnation of the flame retardant electrolyte can be improved.

[0078] Furthermore, the aforementioned flame-retardant electrolyte may contain additional electrolyte additives as needed, taking into consideration factors such as preventing the electrolyte from decomposing and inducing negative electrode collapse in high-power environments, low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, or suppression of battery swelling at high temperatures.

[0079] Typical examples of such electrolyte additives include one or more compounds 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, vinylene carbonate (VC) or vinylethylene carbonate can be cited as the cyclic carbonate compound. Fluoroethylene carbonate (FEC) can be cited as the halogen-substituted carbonate compound. Furthermore, compounds selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethensultone, 1,3-propensultone (PRS), 1,4-butensultone, and 1-methyl-1,3-propensultone can be cited as the sultone compound. Examples of the sulfate compound include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and 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 oxalyl difluoroborate (LiODFB), or lithium bisoxalatoborate (LiB(C2O4)2, LiBOB). Examples of the nitrile compound include one or more selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile. Additionally, examples of the benzene compound include fluorobenzene, examples of the amine compound include triethanolamine or ethylenediamine, and examples of the silane compound include tetravinylsilane. Furthermore, the lithium salt compound is a compound different from the lithium salt contained in the flame-retardant electrolyte, and examples include lithium nitrate, lithium difluorophosphate (LiDFP), LiPO2F2, or LiBF4.

[0082] The aforementioned electrolyte additives can be included in amounts of 0.1 to 10% by weight, 0.2 to 8% by weight, or 0.5 to 8% by weight, relative to the total weight of the flame-retardant electrolyte, and can contribute to improving the ionic conductivity or cycling properties.

[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 within it, and depending on the form of the case and other components, it may be cylindrical, rectangular, pouch-type, or coin-type battery.

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

[0085] In the manufacturing method of the other embodiments described above, the method for forming each electrode can follow a general method such as coating an electrode current collector, in which electrode tabs are defined, with a slurry composition for forming each active material layer, followed by drying and rolling; therefore, no further explanation is given thereto.

[0086] On the other hand, the process of forming a porous coating layer on the electrode can be carried out through a dry or wet process. For example, in the dry process, a porous coating layer containing polymer particles or ceramic particles that are free-standing or coated on a separate substrate, and a polymer binder, can be transferred onto the electrode (for example, onto the electrode active material layer).

[0087] Furthermore, in the case of the wet process, the process can be carried out by coating the electrode (for example, on the electrode active material layer) with a slurry containing the polymer particles or ceramic particles, a polymer binder, and a liquid medium, and then drying it.

[0088] The porous coating layer formed by the above method can be subjected to an additional rolling process as needed.

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

[0090] At this time, the surface treatment step such as plasma treatment may be performed before the polymer particles or ceramic particles are introduced into the slurry for forming the porous coating layer, or it may be performed after the slurry has been coated onto the electrode.

[0091] A typical example of the aforementioned surface treatment step is a method in which an oxygen plasma is formed in a reactor and used to surface-treat polymer particles or ceramic particles, thereby increasing the absolute value of the zeta potential on the particle surface.

[0092] After forming the porous coating layer, the electrodes can be joined and assembled to form an electrode assembly so that the porous coating layer is positioned between the two electrodes. In this case, if the porous coating layer is formed on both electrodes, they can be joined and assembled so that they are in contact with each other; if the porous coating layer is formed on only one of the electrodes, they can be joined and assembled so that the porous coating layer faces the remaining electrode.

[0093] Subsequently, the step of impregnating the electrode assembly with a flame-retardant electrolyte containing a flame-retardant solvent and a lithium salt can be carried out by a general method of pouring the aforementioned flame-retardant electrolyte into a case containing the electrode assembly.

[0094] The invention will be described in more detail below through specific examples. However, the following examples are merely illustrative to aid in understanding the invention and do not limit its scope.

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

[0096] Furthermore, the flash point of the (flame-retardant) organic solvent contained in the (flame-retardant) electrolyte was measured using the sealed method according to the ASTM D93 standard method. Specifically, the organic solvent sample was filled into a sample container, the lid of the container was covered and sealed, and then the sample container was heated at a constant rate according to the aforementioned standard method. The sample container was opened periodically during heating 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 Li(Ni) is used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 A positive electrode with a thickness of 60 μm containing O2 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 with a zeta potential of -50mV and a particle size of 1μm were dispersed in N-methyl-2-pyrrolidone (NMP) solvent in a mass ratio of PMMA:hydrogenated nitrile rubber (H-NBR):polyvinylidene fluoride (PVDF) of 7:1:2 to create a porous coating layer slurry (solid content: 21 wt%). This slurry was coated onto the negative electrode, which had been rolled after the negative electrode active material layer was formed, and then dried to form a porous coating layer on the negative electrode (thickness of the porous coating layer: 30μm). The porous coating layer of the negative electrode and the positive electrode were placed in contact to manufacture an electrode assembly.

[0099] A flame-retardant electrolyte was prepared by dissolving LiN(SO2CF3)2(LiFSI) in a flame-retardant solvent sulfolane (flash point: approximately 165°C) to a concentration of 1.5 M. A lithium secondary battery was manufactured by impregnating the electrode assembly with the flame-retardant electrolyte.

[0100] Example 2 Li(Ni) is used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 A positive electrode with a thickness of 60 μm containing O2 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 with a zeta potential of -50mV and a particle size of 1μm were dispersed in N-methyl-2-pyrrolidone (NMP) solvent in a mass ratio of PMMA:hydrogenated nitrile rubber (H-NBR):polyvinylidene fluoride (PVDF) of 7:1:2 to create a porous coating layer slurry (solid content: 21 wt%). This slurry was coated onto the positive electrode, which had been rolled after the positive electrode active material layer was formed, and then dried to form a porous coating layer on the positive electrode (thickness of the porous coating layer: 30μm). The porous coating layer of the positive electrode and the negative electrode were placed in contact to manufacture an electrode assembly.

[0102] A flame-retardant electrolyte was prepared by dissolving LiN(SO2CF3)2(LiFSI) in a flame-retardant solvent sulfolane (flash point: approximately 165°C) to a concentration of 1.5 M. A lithium secondary battery was manufactured by impregnating the electrode assembly with the flame-retardant electrolyte.

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

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

[0105] Nine negative electrodes, each with a porous coating layer, were stacked with eight positive electrodes placed between them. Polyimide insulating tape was applied to the area corresponding to the position where the positive electrode tab protruded on each stacked negative electrode (labeled "A" in Figure 1) to form an insulating layer and manufacture the electrode assembly (insulating layer thickness: 60 μm).

[0106] A flame-retardant electrolyte was prepared by dissolving LiN(SO2CF3)2(LiFSI) at a concentration of 1.5 M and triethyl phosphate (TEP) at 1% by weight in sulfolane (flash point: approximately 165°C), which is a flame-retardant solvent. A lithium secondary battery was manufactured by impregnating the electrode assembly with the flame-retardant electrolyte.

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

[0108] Eight positive electrodes, each with a porous coating layer, were arranged and stacked between nine negative electrodes. Polyimide insulating tape was applied to the area corresponding to the position where the positive electrode tab protruded on each stacked negative electrode (labeled "A" in Figure 1) to form an insulating layer and manufacture the electrode assembly (insulating layer thickness: 60 μm). At this time, the insulating tape was attached not only to the sides of the negative electrodes but also to a portion of the negative electrode's surface where the negative electrode current collector was exposed without the formation of a negative electrode active material layer.

[0109] A flame-retardant electrolyte was prepared by dissolving LiN(SO2CF3)2(LiFSI) at a concentration of 1.5 M and triethyl phosphate (TEP) at 1% by weight in sulfolane (flash point: approximately 165°C), which is a flame-retardant solvent. A lithium secondary battery was manufactured by impregnating the electrode assembly with the flame-retardant electrolyte.

[0110] Comparative Example 1 Li(Ni) is used as the positive electrode active material.0.8 Mn 0.1 Co 0.1 A positive electrode with a thickness of 60 μm containing O2 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 manufactured by placing a polyolefin separation membrane between the positive and negative electrodes, which did not have a porous coating layer.

[0112] A non-aqueous electrolyte was prepared by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 30:70 volume ratio) to a concentration of 1 M.

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

[0114] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that a porous coating layer was formed on the negative electrode using Al2O3 ceramic particles having a zeta potential of +20mV and a particle size of 1μm, instead of polymethyl methacrylate (PMMA) polymer particles having a zeta potential of -50mV and a particle size of 1μm.

[0115] Reference example 1 A lithium secondary battery was manufactured 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 Qualitative Properties Figures 2 to 5 show the results of hot box tests performed on the lithium secondary batteries manufactured in Examples 1 to 3 and the lithium secondary battery manufactured in Comparative Example 1. Specifically, the hot box test was performed by increasing the temperature from 25°C at a rate of 5°C / min, holding the temperature at 100°C, 120°C, 140°C, 150°C, 160°C, 170°C, and 180°C for 30 minutes each, and then increasing the temperature to 200°C at a rate of 2°C / min. Figures 2 to 5 show the voltage-temperature changes over time. The ignition start temperature is shown in Table 1 below.

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

[0118] [Table 1]

[0119] As shown in Figures 2 to 5 and Table 1, the lithium secondary batteries of Examples 1 to 3 were found to have a higher ignition temperature and improved thermal stability compared to Comparative Example 1.

[0120] Experimental Example 2 - Evaluation of various electrochemical properties The initial capacity and capacity retention rate were measured for the lithium secondary batteries manufactured in Examples 1-3 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 by charging each of the batteries manufactured in Examples 1 to 3 and Comparative Example 2 to 4.2V at 45°C with a constant current of 0.33C, and then discharging them to 3.0V at a constant current of 0.33C, with each cycle being defined as one charge-discharge cycle. After performing 200 charge-discharge cycles, the ratio of the capacity after 200 cycles to the initial capacity was calculated.

[0122] [Table 2]

[0123] Referring to Table 2 above, it was confirmed that the lithium secondary batteries of Examples 1 to 3 exhibited superior capacity characteristics and capacity retention rates compared to the lithium secondary battery manufactured in Comparative Example 2. This is presumed to be due to the superior impregnation of the flame-retardant electrolyte in Examples 1 to 3, resulting from 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 of each lithium secondary battery manufactured in Examples 4 and 5 and Reference Example 1 was measured to evaluate the short-circuit prevention effect.

[0125] Specifically, the insulation resistance at 50V was measured for each of the lithium secondary batteries manufactured in Examples 4 and 5 and Comparative Example 1 using a Hioki insulation resistance meter. 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 have excellent short-circuit prevention effects due to the additional formation of an insulating layer.

Claims

1. An electrode assembly comprising an electrode and a porous coating layer formed on the electrode; and A lithium secondary battery comprising a flame-retardant electrolyte containing a flame-retardant solvent having a flash point of 100°C or higher or having no flash point, and a lithium salt, The electrode assembly includes a positive electrode comprising a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and a positive electrode tab in a form protruding from the positive electrode current collector; a negative electrode comprising a negative electrode current collector, a negative electrode active material layer formed on the negative electrode current collector, and a negative electrode tab in a form protruding from the negative electrode current collector; and a porous coating layer formed on the positive electrode or the negative electrode so as to be positioned between the positive electrode and the negative electrode, wherein the porous coating layer is formed on the positive electrode active material layer and / or the negative electrode active material layer and is positioned between these positive and negative electrode active material layers in a form in contact with them. The porous coating layer is a lithium secondary battery containing polymer particles or ceramic particles having an absolute value of 25 mV or more for its zeta potential.

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 comprises a polymer binder and 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 and 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 flame-retardant solvent comprises one or more organic solvents having a functional group selected from the group consisting of sulfone-based functional groups, fluorine-containing functional groups, phosphorus-containing functional groups, and nitrile-based functional groups.

9. The lithium secondary battery according to claim 1, wherein the flame-retardant solvent comprises one or more organic solvents selected from the group consisting of sulfone compounds, nitrile compounds, phosphoric acid compounds, and fluorine-substituted carbonate compounds.

10. The lithium secondary battery according to claim 9, wherein the sulfone compound comprises one or more selected from the group consisting of sulfolane, ethylmethylsulfone, dibutylsulfone, ethylvinylsulfone, methylpropylsulfone, ethyl-i-propylsulfone, ethyl-i-butylsulfone, i-propyl-i-butylsulfone, i-propyl-s-butylsulfone, and butyl-i-butylsulfone.

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

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

13. The aforementioned fluorine-substituted carbonate compounds include bis(2,2,3,3-tetrafluoropropyl) 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, and ethyl-2,2,2,2',2',2'-hexafluoro-i-propyl carbonate. A lithium secondary battery according to claim 9, comprising one or more selected from the group consisting of nate, 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-pentafluoropropyl) carbonate.

14. The lithium salt mentioned above is LiN(SO ２ CF ３ ) ２ A lithium secondary battery according to claim 1, comprising:

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 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 electrode tab.

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

18. The lithium secondary battery according to claim 16, wherein the porous coating layer is formed on 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. A method for manufacturing a lithium secondary battery according to Claim 1, The steps include: forming a porous coating layer on an electrode containing polymer particles or ceramic particles having an absolute value of 25 mV or more of zeta potential; The steps include forming an electrode assembly that includes an electrode coated with a porous coating layer; A method for manufacturing a lithium secondary battery, comprising the steps of: impregnating the electrode assembly with a flame-retardant electrolyte containing a flame-retardant solvent having a flash point of 100°C or higher or having no flash point, and a lithium salt;

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

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

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