Detailed description of the invention Technical challenges [18] An object of the present invention is to solve the above problems, and an object of the present invention is to solve the problem that the flame retardant properties are uneven despite the flame retardant of the same chemical formula. An object of the present invention is to provide a separator for a secondary battery including a flame retardant capable of expressing flame retardant properties by solving the above problems, and a secondary battery including the same. Task resolution [19] A first aspect of the present invention for solving the above problems is a separator for a secondary battery comprising a flame-retardant inorganic material that may exist in a stable and metastable form, [20] It provides a separator for a secondary battery that necessarily contains the metastable type flame retardant inorganic material. [21] The second aspect of the present invention for solving the above problems provides a secondary battery comprising the separator for the secondary battery. [22] The flame-retardant inorganic material is a metal hydroxide or metal hydrate, specifically aluminum hydroxide (Al(OH) 3 ), magnesium hydroxide (Mg(OH) 2 ), aluminum oxyhydroxide (AlO(OH)) and CaO·Al 2 O It is at least one of 3 ·6H 2 O. [23] The safety-type flame retardant inorganic material is a Gibbsite type, and the semi-safe type flame-retardant inorganic material is one or more of Bayerite, Doyleite and Nordstrandite types. . [24] The separator for the secondary battery, as the inorganic particles in addition to the flame-retardant inorganic substance, is a high-permittivity inorganic particle having a dielectric constant of 1 or higher, an inorganic particle having piezoelectricity, an inorganic particle having lithium ion transfer ability, or a mixture of two or more thereof. As Al 2 O 3 , SiO 2 , MgO, TiO 2 and BaTiO 2 It may include one or more selected from the group consisting of. [25] The binder material used for the separator for the secondary battery is polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene, polyvinylpyrrolidone, polyacrylonitrile, polyvinylidene fluoride-trichloroethylene , Polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polymethyl methacrylate, polyvinyl acetate, ethylene-co-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butylate, cellulose acetate Propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose, acrylonitrile styrene butadiene copolymer, polyimide, polyacrylonitrile -Styrene copolymer, gelatin, polyethylene glycol, polyethylene glycol dimethyl ether, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber (SBR), tetrafluoroethylene (TFE), fluorine rubber and polyether It is 1 or more types selected from the group which consists of a mid, Specifically, it is 1 or more types selected from the group which consists of PVdF, TFE, and polyimide. [26] The separator for a secondary battery is an organic/inorganic composite porous separator that uses a mixture of inorganic particles and a binder polymer and does not have a polyolefin substrate, or a mixture of inorganic particles and a binder polymer is coated on the surface of a porous polyolefin substrate and/or on the pores of the substrate. A separator for forming an organic/inorganic composite porous coating layer, and is a separator for a secondary battery in which the flame-retardant inorganic material is distributed over the entire separator or can be coated on a part of the surface. Brief description of drawings [27] 1 is a crystal structure of aluminum hydroxide in a gibsite form and a bierite form. [28] 2 is a process chart of the Buyer method. [29] 3 is a graph and a photograph showing the results of safety measurement in Example 1 and Comparative Example 1. [30] 4 is an XRD measurement result of metal hydroxides according to Example 1 and Comparative Example 1. Mode for carrying out the invention [31] Hereinafter, the present invention will be described in detail. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to ordinary or lexical meanings, and the inventor appropriately explains the concept of terms in order to explain his or her invention in the best way. Based on the principle that it can be defined, it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention. Therefore, the configurations presented in the embodiments described in the present specification are only the most preferred embodiments of the present invention, and do not represent all the technical spirit of the present invention, and various equivalents that can replace them at the time of application It should be understood that there may be variations. [32] The present invention provides a separator for a secondary battery comprising a flame-retardant inorganic material that may exist in a stable and metastable form, and the separator for a secondary battery necessarily includes the metastable flame-retardant inorganic material. [33] 1) Flame retardant mineral [34] The flame-retardant inorganic material according to the present invention is at least one selected from the group consisting of antimony-containing compounds, metal hydroxides or metal hydrates, guanidine-based compounds, boron-containing compounds, and zinc stannate. [35] The antimony-containing compound is selected from antimony trioxide (Sb 2 O 3 ), antimony tetraoxide (Sb 2 O 4 ), and antimony pentoxide (Sb 2 O 5 ); The metal hydroxide or metal hydrate is in aluminum hydroxide (Al(OH) 3 ), magnesium hydroxide (Mg(OH) 2 ), aluminum oxyhydroxide (AlO(OH)), CaO·Al 2 O 3 ·6H 2 O Selected; The guanidine-based compound is selected from the group consisting of guanidine nitrified, guanidine sulfamate, guanidine phosphate, and guanylurea phosphate; The boron-containing compound is H 3 BO 3 or HBO 2 ; The zinc stannate compound is Zn 2 SnO 4, ZnSnO 3 , ZnSn (OH) 6 It is selected from. [36] The preferred flame-retardant inorganic material is at least one of aluminum hydroxide (Al(OH) 3 ), magnesium hydroxide (Mg(OH) 2 ), aluminum oxyhydroxide (AlO(OH)), CaO·Al 2 O 3 ·6H 2 O Or, more preferably, the flame-retardant inorganic material is aluminum hydroxide (Al(OH) 3 ). [37] The Al(OH) 3 , Mg(OH) 2 , AlOOH, CaO·Al 2 O 3 ·6H 2 O are flame-retardant according to the following formula. [38] 2Al(OH) 3 → Al 2 O 3 + 3H 2 O (mainly 180~300℃, -280cal/g (-1172kJ/kg)) [39] Mg(OH) 2 → MgO + H 2 O (Mainly 300~400℃, -328ca/g (-1372kJ/kg)) [40] 3CaO·Al 2 O 3 ·6H 2 O → Al 2 O 3 + 3CaO + 6H 2 O (mainly 250℃, -340cal/mol) [41] When the flame-retardant inorganic material is aluminum hydroxide (Al(OH) 3 , the stable form is a Gibbsite type, and the semi-safe type flame-retardant inorganic material is Bayerite, Doyleite, nor It is one or more of the forms of Nordstrandite. [42] The specific gibsite and bierite crystal structures are shown in FIG. 1, and values ​​for comparing their hydrogen bond lengths are shown in the following table. [43] [44] [45] [46] When a metal hydroxide or metal hydrate causes a phase transition from a liquid state to a metallic state, various polymorphs may be formed depending on the rate of phase transition and the type of solvent. Each polymorph has a difference in Gibbs Free Energy, and the polymorph with the lowest Gibbs free energy is defined as a stable form. Since Gibbs free energy is the same as defined in thermodynamics, a detailed description thereof will be omitted. [47] The unstable form with high Gibbs free energy exhibits flame retardant properties by reacting at a low temperature compared to the stable form. In addition, when a stable form and an unstable form exist at the same time, it is inferred that the reaction initiated by the unstable form induces the reaction of the entire form. That is, when unstable forms exist together, it is inferred that the starting temperature of the dehydration reaction in the stable form is accelerated. [48] Among the flame-retardant inorganic substances according to the present invention, the metal hydroxide undergoes dehydration, which is an endothermic reaction, as the temperature increases. At this time, the flame retardant effect is exhibited by the endothermic reaction and the generated water. When applying Al(OH) 3 which is one of the embodiments of the present invention, when only the gibbsite form is present, when the nail penetration test is performed, a flame retardant effect is not exhibited, and when there is a metastable form, such as vialite, etc. When the nail penetration test was conducted, the flame retardant effect appeared. [49] When only the gibsite form is present, the reaction is interpreted as proceeding at 180°C or higher, and if some metastable form is present, the reaction is interpreted as proceeding at 150°C. [50] The flame retardant properties of the metal hydroxide according to the shape of such a polymorph have not been recognized as a problem so far. The inventors of the present application have recognized that the non-uniform flame-retardant properties appear due to the above-mentioned problems as a result of each effort to solve the non-uniform flame-retardant properties that appear intermittently, and the present invention has been solved. [51] XRD Bruker AXS D4 Endeavor XRD, 40kV, 40mA, Cu Kα radiation (wavelength 1.54Å)) was used to investigate the shape and distribution of the polymorphism. The relative quantitative ratio of each type was calculated using the sum of the peaks on the XRD as 100. [52] The metastable form of the flame retardant inorganic material is 2% by weight, preferably 5% by weight or more of the total flame retardant inorganic material. In addition, the flame-retardant inorganic material may exist asymmetrically in only one of the positive or negative electrode faces of the separator. This is because water, which is a product of the decomposition reaction of metal hydroxides among flame-retardant inorganic materials, may cause an additional reaction with lithium of the electrode. [53] Bauxite ore is a mixture of hydrated aluminum oxide and a compound of other elements such as iron. FIG. 2 shows a Bayer process, which is a method of smelting metallic aluminum using bauxite as a raw material. [54] 2, bauxite ore is heated with sodium hydroxide solution at 150°C to 200°C in a pressure vessel. At this temperature, aluminum is dissolved as sodium aluminate (2NaAlO 2 ) in the extraction process . The aluminum compound of bauxite may exist as gibsite (Al (OH) 3 ), boehmite (AlOOH) or dispore (AlOOH), and different forms of aluminum components are determined according to different extraction conditions. After separating the residue by filtration, when the liquid is cooled, gibbsite (aluminum hydroxide) precipitates and is seeded with fine aluminum hydroxide. [55] The extraction process converts the aluminum oxide of the ore into soluble sodium aluminate 2NaAlO 2 according to the following chemical reaction formula . [56] [57] Al 2 O 3 + 2NaOH → 2NaAlO 2 + H 2 O [58] [59] This treatment dissolves the silica, but does not dissolve the other components of bauxite. Sometimes lime is added at this stage to precipitate the silica as calcium silicate. The solution is generally filtered to remove particulates, using a rotary sand trap and a flocculant such as starch to purify solid impurities. The undissolved waste after the aluminum compound has been extracted contains iron oxide, silica, calcia, titania and some unreacted alumina. The original process is to cool the alkaline solution and bubble carbon dioxide through it, and aluminum hydroxide is precipitated in this way. [60] [61] 2NaAlO 2 + CO 2 → 2Al(OH) 3 + Na 2 CO 3 + H 2 O [62] [63] 2) Separator [64] The separator for a secondary battery according to the present invention is an organic/inorganic composite porous separator that uses a mixture of inorganic particles and a binder polymer and does not have a polyolefin substrate, or contains inorganic particles and a binder polymer on the surface of the porous polyolefin substrate and/or in the pores of the substrate. As a separator for forming an organic/inorganic composite porous coating layer coated with a mixture, the flame-retardant inorganic material may be distributed over the entire separator or coated on a part of the surface. [65] In the lithium secondary battery, the precipitation of lithium ions occurs mainly at the negative electrode, so coating the hydroxide-based inorganic flame retardant that can generate moisture to the separator on the opposite side of the positive electrode brings the effect of flame retardance, but the reaction occurs when the precipitated lithium meets moisture. Can be prevented. [66] At this time, a binder for forming an adhesive layer or an existing alumina-based SRS can be coated on the opposite side of the cathode facing side, but it is effective to make the anode facing side thicker than the cathode facing side to increase the flame retardant effect. [67] The overall thickness of the separator according to the present invention is generally similar to that of the separator coated with inorganic materials on the anode and cathode facing surfaces. The thickness may be in the range of 5㎛ to 30㎛. When the thickness of the separator is less than 5 μm, the strength of the separator is weak and can be easily damaged. When the thickness of the separator is larger than 30 μm, the thickness of the entire electrode assembly may increase and the capacity may decrease, which is not preferable. [68] The charge/discharge cycle characteristics at 35° C. or more and 50° C. or less of the battery including the separator according to the present invention are the same as the battery composed of the separator coated with the inorganic material on both sides. This is because the effect according to the temperature is not distinguishable below 35°C, and above 50°C, the conventional separator coated with the inorganic material on both sides has poor thermal stability compared to the separator according to the present invention. [69] 3) inorganic particles [70] The inorganic particles used in the separation membrane according to the present invention are added separately from the flame-retardant inorganic material. By enabling the formation of empty spaces between inorganic particles, it plays a role of forming micropores and a kind of spacer that can maintain a physical shape. In general, it has a characteristic that the physical properties do not change even when the temperature is higher than 200℃. . [71] These inorganic particles are not particularly limited as long as they are electrochemically stable, that is, the inorganic particles that can be used in the present invention are oxidized and/or in the operating voltage range of the applied battery (eg, 0-5V based on Li/Li+) Or it is not particularly limited as long as the reduction reaction does not occur. Particularly, in the case of using inorganic particles having a high electrolyte ion transfer ability, it is possible to improve the performance in the electrochemical device, so it is preferable that the electrolyte ion transfer ability is as high as possible. In addition, when the inorganic particles have a high density, it is difficult to disperse when forming a separator, as well as a problem of increasing weight during battery manufacturing, so it is preferable that the density is as small as possible. In addition, in the case of an inorganic material having a high dielectric constant, the ionic conductivity of the electrolyte may be improved by contributing to an increase in the degree of dissociation of an electrolyte salt, such as a lithium salt, in a liquid electrolyte. [72] For the reasons described above, the inorganic particles are high-k inorganic particles having a dielectric constant of 1 or more, preferably 10 or more, inorganic particles having piezoelectricity, inorganic particles having lithium ion transfer ability, or two or more thereof. It can be a mixture. [73] Examples of inorganic particles having a dielectric constant of 1 or more include SrTiO 3 , SnO 2 , CeO 2 , MgO, NiO, CaO, ZnO, ZrO 2 , Y 2 O 3 , Al 2 O 3 , TiO 2 , SiC or a mixture thereof. However, it is not limited thereto. [74] The piezoelectricity inorganic particles are non-conductors at normal pressure, but when a certain pressure is applied, they refer to a material having physical properties that allow electricity to flow through changes in the internal structure, and not only exhibit high dielectric constant properties of 100 or more, but also a constant pressure. When tensioned or compressed by applying, electric charges are generated and one side is positively charged and the other side is negatively charged, thereby generating a potential difference between both sides. [75] In the case of using inorganic particles having the above characteristics, when an internal short circuit occurs between both electrodes due to external impacts such as local crush, nail, etc. In addition, a potential difference in the particles occurs due to the piezoelectricity of the inorganic particles, and thus electron transfer between the two electrodes, that is, a flow of a fine current, can be achieved, thereby reducing the voltage of the battery gently and thereby improving safety. [76] Examples of the piezoelectric inorganic particles include BaTiO 3 , Pb(Zr,Ti)O 3 (PZT), Pb 1-x La x Zr 1-y Ti y O 3 (PLZT), Pb(Mg 1/3 Nb 2 /3 )O 3 -PbTiO 3 (PMN-PT) hafnia (HfO 2 ) or a mixture thereof, and the like, but is not limited thereto. [77] The inorganic particle having the lithium ion transfer ability refers to an inorganic particle having a function of transferring lithium ions without storing lithium but containing lithium elements, and the inorganic particle having a lithium ion transfer ability exists inside the particle structure Since lithium ions can be transferred and moved due to a kind of defect, the lithium ion conductivity in the battery is improved, and thus, battery performance can be improved. [78] Examples of the inorganic particles having the lithium ion transfer ability include lithium phosphate (Li 3 PO 4 ), lithium titanium phosphate (Li x Ti y (PO 4 ) 3 , 0 [107] As a flame-retardant inorganic material constituting the coating layer of the separator, Al(OH) 3 containing 95% by weight of gibsite and 5% by weight of bierite was applied, and as a binder polymer, polyvinylidene fluoride-hexafluoropropylene and inorganic particles The slurry was prepared by mixing and dispersing alumina. [108] The slurry was coated on a separator substrate and dried to complete a separator. [109] [110] [111] In Example 1, a separator was prepared in the same manner as in Example 1, except that only gibsite was used as a flame-retardant inorganic material except for vialite. [112] [113] [114] After fabricating a battery using the separators of Comparative Example 1 and Example 1, a nail penetration test was performed on the battery, and a graph showing a change in voltage and temperature over time and a photograph of the result are shown in FIG. 3. [115] The nail has a diameter of 3 mm and a slope of 30 degrees, and the speed through the nail is 80 ㎜/sec. [116] Referring to FIG. 3, in the case of Comparative Example 1, it was found that the surface temperature of the battery rapidly increased, and thus the safety was very poor. On the other hand, in Example 1 according to the present invention, the surface temperature of the battery was maintained at about 20°C, respectively, to confirm that the flame retardant performance was very good. As a result of disassembling each battery, it was observed that all of the inner fabric melted and the pores of the fabric itself disappeared. [117] Therefore, it can be assumed that the internal temperature of Example 1 also increased above 135°C, which is the melting point of the separator substrate. Nevertheless, it was confirmed that the battery with the flame retardant according to the present invention was maintained at a very stable external temperature and was very stable even with very serious damage such as nail penetration. [118] [119] [120] XRD measurement was performed for structural analysis of the metal hydroxide used in Example 1 and Comparative Example 1, and the results are shown in FIG. 4. [121] Referring to FIG. 4, it was analyzed that the aluminum hydroxide applied to Example 1 is a mixture of a gibsite phase and a bierite phase, and it can be seen that the aluminum hydroxide applied to Comparative Example 1 is composed of only gibsite. [122] That is, it can be seen that the safety is improved when both the gibbsite and the viarite are included as in the safety test result of Example 1. Industrial availability [123] The separator for a secondary battery according to the present invention has the advantage that 1) flame retardant properties are necessarily expressed, and 2) similar electrochemical properties can be maintained as compared to the conventional inorganic material coated separator. Claim [Claim 1] A separator for a secondary battery comprising a flame-retardant inorganic material that may exist in a stable and metastable form, wherein the separator for a secondary battery necessarily includes a flame-retardant inorganic material in the metastable form. [Claim 2] The separator according to claim 1, wherein the flame-retardant inorganic material is at least one selected from the group consisting of an antimony-containing compound, a metal hydroxide or metal hydrate, a guanidine-based compound, a boron-containing compound, and zinc stannate. [Claim 3] According to claim 2, The antimony-containing compound is selected from antimony trioxide (Sb 2 O 3 ), antimony tetraoxide (Sb 2 O 4 ) and antimony pentoxide (Sb 2 O 5 ); The metal hydroxide or metal hydrate is in aluminum hydroxide (Al(OH) 3 ), magnesium hydroxide (Mg(OH) 2 ), aluminum oxyhydroxide (AlO(OH)) and CaO·Al 2 O 3 ·6H 2 O Is selected; The guanidine-based compound is selected from the group consisting of guanidine nitrified, guanidine sulfamate, guanidine phosphate, and guanylurea phosphate; The boron-containing compound is H 3 BO 3 or HBO 2 ; The zinc stannate compound is Zn 2 SnO 4, ZnSnO 3 and ZnSn (OH) 6 A separator for a secondary battery that is selected from. [Claim 4] The method of claim 3, wherein the flame-retardant inorganic material is aluminum hydroxide (Al(OH) 3 ), magnesium hydroxide (Mg(OH) 2 ), aluminum oxyhydroxide (AlO(OH)) and CaO·Al 2 O 3 ·6H A separator for a secondary battery of at least one of 2 O. [Claim 5] The separator of claim 4, wherein the flame-retardant inorganic material is aluminum hydroxide (Al(OH) 3 ). [Claim 6] 6. ) A separator for secondary batteries in one or more types. [Claim 7] The separator for a secondary battery according to claim 1, wherein the metastable-type flame-retardant inorganic material is 2% by weight or more of the total flame-retardant inorganic material. [Claim 8] The separator for a secondary battery according to claim 7, wherein the metastable form of the flame retardant inorganic material is 5% by weight or more of the total flame retardant inorganic material. [Claim 9] The separator according to claim 1, wherein the flame-retardant inorganic material is asymmetrically present only in one of the positive and negative electrodes. [Claim 10] The method of claim 1, wherein the separator for the secondary battery is an organic/inorganic composite porous separator that uses a mixture of inorganic particles and a binder polymer and does not have a polyolefin substrate, or an inorganic particle and a binder on the surface of the porous polyolefin substrate and/or in the pores of the substrate. A separator for forming an organic/inorganic composite porous coating layer coated with a mixture of polymers, wherein the flame-retardant inorganic material is distributed throughout the separator or may be coated on a part of a surface of the separator. [Claim 11] 11. The method of claim 10, The inorganic particles are added separately from the flame-retardant inorganic, high-permittivity inorganic particles having a dielectric constant of 1 or higher, inorganic particles having piezoelectricity, inorganic particles having lithium ion transfer ability, or their A separator for secondary batteries that is a mixture of two or more. [Claim 12] The separator of claim 10, wherein the inorganic particles are at least one selected from the group consisting of Al 2 O 3 , SiO 2 , MgO, TiO 2 and BaTiO 2 . [Claim 13] The method of claim 10, wherein the binder polymer is polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene, polyvinylpyrrolidone, polyacrylonitrile, polyvinylidene fluoride-trichloroethylene , Polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polymethyl methacrylate, polyvinyl acetate, ethylene-co-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate Propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxy methyl cellulose, acrylonitrile styrene-butadiene copolymer, polyimide, polyacrylonitrile -Styrene copolymer, gelatin, polyethylene glycol, polyethylene glycol dimethyl ether, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber (SBR), tetrafluoroethylene (TFE), fluorine rubber and polyether A separator for secondary batteries of at least one selected from the group consisting of mids. [Claim 14] The separator of claim 13, wherein the binder polymer is at least one selected from the group consisting of PVdF, TFE, and polyimide. [Claim 15] The method of claim 13, wherein the binder polymer is phenol containing baicalin, luteolin, taxipoline, myricetin, quercetin, lutein, catechin, epigallocatechin gallate, butein, piceatechinol, and tannic acid. Separation membrane for a secondary battery further comprising at least one or more of a water-based or non-aqueous polymer consisting of a system-based compound, pyrogallic acid, amylose, amylopectin, xanthan gum, fatty acid.