Title of the invention: Porous separator and lithium secondary battery including the same Technical field [One] This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0122101 filed on October 12, 2018, and all contents disclosed in the documents of the Korean patent application are incorporated as part of this specification. [2] The present invention relates to a porous separator and a lithium secondary battery including the same, and to a porous separator capable of blocking lithium ion dentride and improving high temperature safety due to excellent thermal properties, and a lithium secondary battery including the same. Background [3] Recently, interest in energy storage technology is increasing. As the fields of application to mobile phones, camcorders, notebook PCs, and even electric vehicles are expanded, efforts for research and development of electrochemical devices are increasingly being materialized. Electrochemical devices are the field that is receiving the most attention in this respect, and among them, the development of a rechargeable battery capable of charging and discharging has become the focus of interest, and in recent years, in developing such a battery, a new electrode is used to improve capacity density and specific energy. It is proceeding with research and development on the design of and battery. [4] Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has the advantage of having a higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries using aqueous electrolyte solutions. Is in the limelight. However, such a lithium ion battery has safety problems such as ignition and explosion due to the use of an organic electrolyte, and it is difficult to manufacture. [5] The recent lithium-ion polymer battery is considered as one of the next-generation batteries by improving the weaknesses of these lithium-ion batteries. However, the capacity of the battery is still relatively low compared to that of the lithium-ion battery, and the discharge capacity at low temperatures is insufficient. This is urgently required. [6] The electrochemical devices as described above are produced by many companies, but their safety characteristics are different from each other. It is very important to evaluate the safety of these electrochemical devices and ensure safety. The most important consideration is that if an electrochemical device malfunctions, it should not injure the user, and for this purpose, the safety standards strictly regulate ignition and smoke in the electrochemical device. In terms of the safety characteristics of an electrochemical device, there is a high concern that an explosion may occur when the electrochemical device is overheated to cause thermal runaway or the separator is penetrated. In particular, polyolefin-based porous substrates, which are commonly used as separators for electrochemical devices, exhibit extreme thermal shrinkage behavior at a temperature of 100°C or higher due to material properties and manufacturing process characteristics including stretching. Caused. [7] In order to solve the safety problem of such an electrochemical device, a separator in which a porous organic-inorganic coating layer is formed by coating a mixture of an excessive amount of inorganic particles and a binder polymer on at least one surface of a polyolefin-based porous substrate having a large number of pores is proposed. Became. [8] However, in this case, a coating defect may occur on the surface of the porous layer due to cracks generated during a manufacturing process, for example, during a drying process. For this reason, the organic/inorganic composite porous layer may be easily detached from the polyolefin-based porous substrate when assembling the secondary battery or when using the battery, which leads to a decrease in the safety of the battery. In addition, the slurry for forming a porous layer applied to a polyolefin-based porous substrate to form the porous layer has a problem in that the density of the particles increases during drying, resulting in a portion that is packed with high density, thereby deteriorating the air permeability characteristics. . [9] In addition, heavy metal components inevitably mixed during the electrode plate manufacturing process and the raw material manufacturing process of the battery are redoxed during the activation process of the battery and are deposited on the surface of the negative electrode, resulting in metal lithium needle crystals (dendrite). There is a problem in that a voltage drop of the battery occurs by causing a micro-short to the positive electrode or the negative electrode. [10] Therefore, there is still a need for an improved separator that can contribute to the stability of a battery due to the characteristics of the battery industry that requires a higher level of stability. [11] (Patent Document 1) Korean Patent Laid-Open Publication No. 10-2015-0099648 "Separator, a method for manufacturing a separator, a lithium polymer secondary battery including the same, and a method for manufacturing a lithium polymer secondary battery using the same" Detailed description of the invention Technical challenge [12] Accordingly, the problem to be solved by the present invention is to provide a porous separator with improved high temperature safety due to excellent thermal properties and improved high temperature stability and an electrochemical device including the same, which can prevent a short circuit between the anode and the cathode due to the growth of dentride . Means of solving the task [13] In order to solve the above problems, the present invention provides a porous layer comprising a plurality of plate-shaped inorganic particles, and a first binder polymer positioned on a part or all of the surface of the plate-shaped inorganic particles to connect and fix the plate-shaped inorganic particles; And a metal layer formed on one side of the porous layer. [14] In addition, the present invention provides a lithium secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes, wherein the separator is the porous separator. Effects of the Invention [15] According to the present invention, by providing a base layer containing plate-shaped inorganic particles, the path between the positive electrode and the negative electrode, that is, the so-called torsion, can be increased. Since it becomes difficult to reach the anode, the reliability against a dendrite short can be further increased. [16] In addition, since the porous separator according to the present invention does not include a porous polymer substrate, there is an effect of cost reduction, and a uniform porous separator can be implemented by controlling the pore size and porosity of the entire separator, and the thickness of the separator is reduced. Can reduce weight. In addition, even when exposed to a high temperature of 120°C or higher, there is no phenomenon such as heat shrinkage, so there is an advantage of improving safety. [17] In addition, the porous separator according to the present invention has an advantage of suppressing Li dendrite growth by forming a metal having a low Li diffusion barrier through an evaporation or sputter process in a portion where the cathode contacts. [18] In addition, the porous separator according to the present invention has an advantage of improving output characteristics by coating a ceramic having a large dielectric constant on a portion where the anode contacts. Brief description of the drawing [19] 1 is a schematic diagram illustrating the degree of torsion in a porous layer composed of inorganic particles. [20] 2 is a schematic diagram illustrating a degree of torsion in a porous layer composed of spherical inorganic particles. [21] 3 is a schematic diagram illustrating a degree of torsion in a porous layer composed of plate-shaped inorganic particles. [22] 4 is a schematic diagram of a porous separator according to an embodiment of the present invention. [23] 5 is a schematic diagram of a porous separator according to an embodiment of the present invention. [24] 6 is a schematic diagram of a porous separator according to an embodiment of the present invention. Best mode for carrying out the invention [25] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily implement it. The terms or words used in the specification and claims should not be construed as limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of ​​the present invention based on the principle that there is. [26] In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and similar reference numerals are used for similar parts throughout the specification. In addition, the size and relative size of the components indicated in the drawings are not related to the actual scale, and may be reduced or exaggerated for clarity of description. [27] [28] Porous separator [29] The porous separator according to an aspect of the present invention is a porous layer comprising a plurality of plate-shaped inorganic particles, and a first binder polymer positioned on a part or all of the surface of the plate-shaped inorganic particles to connect and fix the plate-shaped inorganic particles. ; And a metal layer formed on any one surface of the porous layer. [30] The porous separator of the present invention may be interposed between the anode and the cathode to serve as a separator, as described later, so the porous separator may correspond to a porous separator (separating film, separator), and organic Since a substance and an inorganic substance are mixed, it may correspond to an organic-inorganic complex. [31] Since this organic-inorganic composite is composed of only inorganic materials and binder polymers without a porous polymer substrate such as polyolefin, the separator does not heat shrink even when exposed to a high temperature of 120°C or higher compared to a separator made of a conventional porous polymer substrate, and the melting point of the polymer substrate Even if the temperature rises to the vicinity, it is not decomposed or damaged, so the possibility of a short circuit between the anode and the cathode can be fundamentally blocked, and the thickness of the separator can be reduced, thereby reducing the weight. [32] On the other hand, in order to safely use an electrochemical device such as a secondary battery for a long period of time, foreign metal ions in the battery generated during charging and discharging form dendrites by reduction on the surface of the negative electrode. It is necessary to suppress the internal short phenomenon. In addition, from the viewpoint of the manufacturing quality of the cell, the defect rate during the manufacturing of the cell increases due to the dendrite generated by reduction of such metal ions during charging and discharging during the cell manufacturing process. In addition, if the dendrite generated during the manufacturing process electrically connects the positive electrode and the negative electrode to each other due to external pressure or vibration, it may cause problems in the safety and stability of the battery even during use, and additional metals generated during use of the battery. Reduction of ions also causes dendrite formation, which can greatly impair the safety and stability of the cell. Therefore, in the lithium secondary battery as described above, it is necessary to suppress the formation and growth of dendrites in which the positive electrode and the negative electrode may be electrically connected within the battery. [33] When a porous organic-inorganic layer with inorganic particles is used as a separator, the pores of the porous organic-inorganic layer, that is, the spacing and path between inorganic particles, can have a great influence on the growth of dendrites and the electrical short-circuit between the anode and cathode . In the case of dendrites, in which metal ions are reduced and deposited on the cathode surface, the time for the metal ions to pass through the separation membrane to be transferred to the cathode becomes longer, or even if dendrites are deposited on the cathode surface through the separation membrane, the deposition and growth of the dendrites are opposite If the path leading to it is complicated or the time required is increased, dendrite growth may also be inhibited or delayed. [34] The movement path in the porous organic-inorganic layer including inorganic particles that affect the precipitation and growth of such foreign metal ions may be described as tortuosity. [35] The degree of torsion is a numerical value of how curved or twisted a curve is, and this degree of torsion is often used to describe the diffusion that occurs in porous materials. Referring to FIG. 1, the torsion degree τ may be defined as follows. [36] , At this time, △ι: actual moving length, △χ: unit length. [37] [38] That is, even if the thickness of the porous layer composed of a plurality of particles (1) corresponds to △χ, the time required to pass through the pores (2) of the porous layer from one side to the other side is proportional to the actual travel distance △ι Is to do it. [39] Referring to FIGS. 2 and 3, it can be seen that in a porous separator including a binder polymer and inorganic particles, the actual moving distance may vary greatly depending on the shape of the inorganic particles. In the case of the spherical shape of the inorganic particles 3 as shown in FIG. 2, compared to the case in which the shape of the inorganic particles 5 is plate-shaped as shown in FIG. It is possible to pass through the length from one side to the other side. From this, when the inorganic particles in the porous separator have a plate-like shape, as the movement length increases, the dendrite formed on the surface of the cathode grows and passes through the pores of the separator and is connected to the anode, which takes much more time. It can be seen that the growth of dendrites and the resulting short-circuit phenomenon are suppressed because it is difficult to achieve. [40] Accordingly, in the present invention, it is intended to provide a porous separator including a porous layer having plate-shaped inorganic particles. [41] Referring to Figure 4, the porous separator 100 according to an embodiment of the present invention, a plurality of plate-shaped inorganic particles 11, and located on a part or all of the surface of the plate-shaped inorganic particles 11 It includes a porous layer 10 including a first binder polymer (not shown) connecting and fixing particles. [42] [43] Further, according to an embodiment of the present invention, a metal layer formed on any one surface of the porous layer may be included. [44] As the metal layer, a metal (M) having a low Li diffusion barrier, capable of forming an alloy of Li x M (x=1 to 2.25) by reacting with lithium may be used. Here, "x is 1 to 2.25" means that x of lithium meet with the metal (M ) to form an alloy of Li x M. [45] Since the copper current collector does not undergo an alloy reaction with lithium, lithium plating takes place. In this case, more energy is required than the metal in which the alloy reaction occurs. Therefore, when lithium metal is used as the negative electrode, lithium growth occurs intensively in the area where lithium was initially grown during charging to form dendrite. There may be a high probability that it will be concentrated in the local area where it has started. [46] However, if there is a metal layer having a low lithium diffusion barrier, lithium growth does not occur in a local area during charging, but is grown evenly over a wide range, thereby suppressing the formation of dendrite. [47] Specific examples of the metal (M) having a low Li diffusion barrier include Al, In, Au, Ni, or Mg. [48] [49] The metal layer may have a thickness of 0.01 to 1 μm. As the metal layer is formed on one side of the porous layer, it is possible to suppress the growth of dendrite due to the growth of lithium metal. [50] Referring to FIG. 5, the porous separator 200 according to an embodiment of the present invention includes a plurality of plate-shaped inorganic particles 11, and a plurality of plate-shaped inorganic particles 11 located on a part or all of the surface of the plate-shaped inorganic material. A porous layer 10 including a first binder polymer (not shown) connecting and fixing particles; And a metal layer 20 positioned on one surface of the base porous layer. [51] According to an embodiment of the present invention, the inorganic particles in the porous layer may be made of only plate-shaped inorganic particles, or 50% by weight or more, specifically 50 to 90% by weight of a plate-shaped inorganic material based on the total inorganic particle weight of the porous layer. It may also contain particles. In the latter case, spherical inorganic particles may be further included as inorganic particles of the porous layer. [52] Non-limiting examples of the plate-shaped inorganic particles include alumina, silica, zirconia, titanium dioxide, magnesia, ceria, yttrium oxide, zinc oxide, iron oxide, barium titanium oxide, alumina-silica composite oxide, or a mixture of two or more thereof. I can. [53] Non-limiting examples of the spherical inorganic particles may include high dielectric constant inorganic particles having a dielectric constant of 5 or more, specifically 10 or more, inorganic particles having a lithium ion transfer ability, or a mixture thereof. [54] Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO 3 , Pb(Zr,Ti)O 3 (PZT), Pb 1 - x La x Zr 1 - y Ti y O 3 (PLZT), PB(Mg 3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT), Hafnia (HfO 2 ), SrTiO 3 , SnO 2 , CeO 2 , MgO, NiO, CaO, ZnO, ZrO 2 , Y 2 O 3 , Al 2O 3 , TiO 2 , SiC ,AlO(OH), Al 2 O 3 ·H 2 O or mixtures thereof. [55] In addition, the inorganic particles having a lithium ion transfer ability refer to inorganic particles containing a lithium element but not storing lithium and having a function of moving lithium ions, and are non-limiting examples of inorganic particles having a lithium ion transfer ability Is lithium phosphate (Li 3 PO 4 ), lithium titanium phosphate (Li x Ti y (PO 4 ) 3 , 0 [108] After mixing PVdF-HFP polymer binder (LBG Grade from Arkama) and inorganic particles (alumina, NW-710 Grade from Ticera, aspect ratio=67) in a ratio of 2:8, N-methyl-2-pyrrolidone (NMP ) A coating solution was prepared by mixing in a solvent at a solid content of 40%. [109] After coating the prepared coating solution on a polyethylene terephthalate (PET) film (SKC's RX12G 50㎛) whose surface was treated with corona with a strength of 0.7Kw, the prepared coating solution was coated with an applicator and dried in a Mathis oven at 130℃ for 5 minutes. A PET film coated with a 100 μm-thick porous separator was prepared. [110] The PET film coated with the porous separator was rolled in a roll press equipment (Calendering machine, CIS CLP-2025H) to make the porous separator to a thickness of 20 μm, and then the PET film was peeled off. [111] Thereafter, an aluminum metal layer of 0.5 μm was formed on one side of the porous separator under conditions of a vacuum degree of 10 mTorr and 1 kV in an Ar gas atmosphere using Novellus' Sputtering Systems. [112] [113] [114] A positive electrode mixture was prepared by mixing 96.7 parts by weight of LiCoO 2 functioning as a positive electrode active material, 1.3 parts by weight of graphite functioning as a conductive agent, and 2.0 parts by weight of polyvinylidene fluoride (PVdF) functioning as a binder. A positive electrode mixture slurry was prepared by dispersing the obtained positive electrode mixture in 1-methyl-2-pyrrolidone serving as a solvent. This slurry was coated, dried, and pressed on both sides of an aluminum foil having a thickness of 20 μm, respectively, to prepare a positive electrode. [115] As a negative electrode, a Li metal electrode (Honzo, Japan) formed with a 100% Li metal layer having a thickness of 20 μm on a copper foil current collector was used. [116] LiPF6 was dissolved to a concentration of 1.0M in an organic solvent mixed with ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a composition of 1:2:1 (volume ratio), and organic solvent 100 A non-aqueous electrolyte was prepared by dissolving 2 parts by weight of vinylene carbonate based on parts by weight. [117] A porous separator was interposed between the positive electrode and the negative electrode prepared above, and the electrolyte was injected to prepare a coin-cell type lithium secondary battery. At this time, the metal layer of the porous separator was interposed in contact with the negative electrode. [118] [119] [Example 2] [120] A coating solution was prepared by mixing PVdF-HFP polymer binder (LBG Grade from Arema Co., Ltd.) and BaSrTiO 3 in a 1:9 ratio, followed by mixing in a N-methyl-2-pyrrolidone (NMP) solvent at a solid content concentration of 20 wt%. . In the same manner as in Example 1, except that the coating solution was coated on the other surface of the porous separator prepared in Example 1 on which the metal layer was not formed in the same manner as in Example 1 to prepare a porous separator. A lithium secondary battery was prepared [121] [122] [Comparative Example 1] [123] PVdF-HFP polymer binder (Arkema LBG Grade) and inorganic particles (alumina, Ticera NW-710 Grade) were mixed in a 1:9 ratio, and in the same manner as in Example 1, except that a metal layer was not formed. A lithium secondary battery was prepared. [124] [125] [Comparative Example 2] [126] A lithium secondary battery was manufactured in the same manner as in Example 1, except that Optodot's CSP20 product was used as a porous separator. [127] [128] [Comparative Example 3] [129] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the metal layer was not formed. [130] [131] Experimental Example 1: Analysis of battery life characteristics [132] Using PNE SOLUTION's Small Cell cycler device, charge CC until it reaches 4.25V with a constant current of 0.2C (CC), and then charge 5% of 1C with a constant voltage of 4.25V (CV). Charged once with a current cut-off, and then, discharged at a constant current of 0.5C until 3V becomes 1 cycle, and this cycle was repeated. [133] The cycle performance according to the cycle characteristics and the 2C discharge capacity compared to 0.2C were measured, and are shown in Table 1 below. [134] [Table 1] 2C discharge capacity compared to 0.2C (%) Cycle performance (capacity retention under 90%) Example 1 91% 38 cycle Example 2 96% 46 cycle Comparative Example 1 91% 30 cycle Comparative Example 2 91% 20 cycle Comparative Example 3 91% 27 cycle [135] Referring to Table 1, the results of applying the porous inorganic separators of Comparative Examples 1 to 3 show that fading begins 30 cycles before, whereas the porous separators of Examples 1 to 2 have stable discharge even at longer cycles. It represents the capacity, and it was found that the 2C discharge capacity was also better than the 0.2C. This is analyzed as a result that the porous separators of Examples 1 to 2 have excellent properties of inhibiting the growth of lithium dendrite. [136] [137] Experimental Example 2: High-temperature stability analysis of the separator [138] The high-temperature stability of the separator was examined by using a convection oven to expose the separator at a temperature of 150°C for 30 minutes to measure the area of ​​the separator before and after exposure to calculate the shrinkage rate. [139] As a result, in the case of Example 1, shrinkage of 8% relative to the area occurred, and in the case of Example 2, shrinkage of 5% occurred. In contrast, the shrinkage of 6% in Comparative Example 1, 80% in Comparative Example 2, and 10% in Comparative Example 3 occurred. It is determined that high temperature stability is improved due to the inorganic particles and the metal layer coated on the surface of the porous separator of Examples 1 to 2. [140] [141] All simple modifications to changes of the present invention belong to the scope of the present invention, and the specific scope of protection of the present invention will be made clear by the appended claims. Claims [Claim 1] A porous layer including a plurality of plate-shaped inorganic particles and a first binder polymer positioned on a part or all of the surface of the plate-shaped inorganic particles to connect and fix the plate-shaped inorganic particles; And a metal layer formed on any one surface of the porous layer. [Claim 2] The porous separator according to claim 1, further comprising a ceramic coating layer formed on the other side of the porous layer. [Claim 3] The method of claim 1, wherein the plate-shaped inorganic particles are alumina, silica, zirconia, titanium dioxide, magnesia, ceria, yttrium oxide, zinc oxide, iron oxide, barium titanium oxide, alumina-silica composite oxide, or a mixture of two or more thereof, Porous separator. [Claim 4] The porous separator according to claim 1, wherein the aspect ratio of the plate-shaped inorganic material particles is 5 to 100. [Claim 5] The porous separator according to claim 1, wherein an aspect ratio of the plate-shaped inorganic material particles is 50 to 100. [Claim 6] The porous separator according to claim 1, wherein the metal layer comprises a metal (M) capable of forming an alloy of Li x M (x=1 to 2.25) by reacting with lithium . [Claim 7] The porous separator according to claim 1, wherein the metal layer comprises at least one metal selected from the group consisting of Al, In, Au, Ni, and Mg. [Claim 8] The porous separator according to claim 1, wherein the metal layer has a thickness of 0.01 to 1 μm. [Claim 9] The porous separator according to claim 2, wherein the ceramic coating layer has a dielectric constant of 20 to 1000. [Claim 10] The porous separator according to claim 2, wherein the ceramic coating layer comprises at least one inorganic particle selected from the group consisting of HfO 2 , ZrO 2 , BaSrTiO 3 and PbLaZrTiO 3 . [Claim 11] The porous separator according to claim 1, wherein the porous layer further comprises spherical inorganic particles. [Claim 12] A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is the porous separator of claim 1. [Claim 13] The lithium secondary battery according to claim 12, wherein the negative electrode and the metal layer of the porous separator come into contact with each other. [Claim 14] The lithium secondary battery according to claim 12, wherein the lithium secondary battery includes a lithium metal or a lithium alloy in the negative electrode.