KR20160051069A - A separator for a secondary battery - Google Patents

Abstract

The present invention relates to a separation membrane of a secondary battery. More particularly, the present invention relates to a separation membrane of a secondary battery having improved shrinkage ratio of a separation membrane under high temperature conditions and excellent safety. The separator according to the present invention has a low shrinkage ratio of the separator even at a high temperature, and is excellent in heat resistance and dimensional stability. Therefore, there is an effect of improving the high-temperature safety of the battery manufactured through the separator according to the present invention.

Description

Technical Field The present invention relates to a separator for a secondary battery,

The present invention relates to a separation membrane of a secondary battery. More particularly, the present invention relates to a separation membrane of a secondary battery having improved shrinkage ratio of a separation membrane under high temperature conditions and excellent safety.

Polyolefin microporous films are widely used for various battery separators, separating filters, and microfiltration membranes due to their chemical stability and excellent physical properties.

The lithium ion secondary battery is an excellent battery having a very high energy density. However, there is a risk of explosion when a short circuit occurs. Therefore, a separation membrane to be used requires a high quality level as well as quality stability. In recent years, in accordance with the high capacity and high output trend of lithium ion secondary batteries such as batteries for hybrid vehicles, the thermal stability of the separator has been demanded in addition to the quality stability of existing wet products. If the thermal stability of the separator is lowered, the risk of explosion due to melt breakage of the separator due to overheating of the battery is increased.

The thermal stability of the separator in the cell is determined by the shut-down temperature and the melt fracture temperature. For the stability of the battery, the shut-down temperature is low and the melt fracture temperature is high. In particular, the melt fracture temperature is a temperature at which the current can be continuously cut off in a situation where the explosion of the battery may be caused, which is most closely related to the stability of the battery.

Efforts to improve the thermal stability of the separator have been developed in three directions. A method of increasing the heat resistance of a separator by adding an inorganic or heat resistant resin to a conventional polyethylene, a method of coating a heat resistant material on the surface, and a method of making a multilayer separator having a heat resistant layer.

U.S. Patent No. 6,949,315 discloses a film in which an ultrahigh molecular weight polyethylene is kneaded with an inorganic substance such as titanium oxide in an amount of 5-15% by weight to improve the thermal stability of the separation membrane. However, this method has the effect of improving the thermal stability according to the addition of the inorganic substance, but the problems such as the lowering of the kneading property due to the addition of the inorganic substance and the lowering of the kneading property are liable to occur, Compatibility is insufficient, resulting in deterioration of film properties such as impact strength. These disadvantages are inevitable for separators using inorganic materials.

A separation membrane prepared by kneading a resin having excellent heat resistance instead of an inorganic material is disclosed in U.S. Patent No. 5,641,565. The technique involves mixing 30-75% by weight of an organic liquid compound and 10-50% by weight of an inorganic material in a resin mixture obtained by mixing 5-45% by weight of polypropylene with polyethylene, separating the organic liquid compound and the inorganic material, Technology. Although this technique extracts minerals, it has a problem in the above-mentioned inorganic material kneading, and as mentioned in the above-mentioned patent, the physical properties are lowered by the addition of polypropylene which is not kneaded with polyethylene. In addition, this method has a disadvantage in that the process is complicated by adding a process for extracting and removing the used minerals, and a relatively large amount of polypropylene is required in order to obtain a sufficient heat-resistant effect.

A method of coating a heat-resistant material on the surface of a microporous membrane is disclosed in US 2006-0055075A1. However, the coating method has a limitation in increasing the transmittance of the coating layer, so that the transmittance of the entire film is lowered and the wettability between the coating layer and the microporous membrane film is likely to cause quality irregularities.

Lamination is used to make a multilayer separator to increase the thermal stability of the separator. U.S. Patent No. 5,691,077 discloses a method for making a three-layered separator by laminating a polypropylene resin having a high melt breaking temperature (high melting temperature) to polyethylene having excellent closure characteristics (low melting temperature). This separator is excellent in thermal properties, but it has disadvantages such as non-uniformity in drawing, pinhole occurrence and thickness variation in the manufacturing process of a fabric film by a low temperature drying method, as well as a problem of productivity deterioration due to addition of a lamination process, There is also a problem of delamination and it is not widely used. This method has a problem that the rigidity, permeability, quality uniformity and productivity required for the secondary battery separator are inferior despite the excellent heat resistance.

Japanese Patent Application Laid-Open No. 2002-321323 and International Patent Publication No. WO2004 / 089627 disclose a multilayer separator wherein a polyethylene microporous membrane layer produced by a wet method is used as a main layer and a layer in which polyethylene and polypropylene, Is introduced. These separation membranes can be manufactured by a wet process and have excellent quality stability, but they have limitations in that they have heat resistance more than heat resistance of polypropylene resin. In addition, since the multi-layer separator is manufactured by the wet process, the manufacturing process becomes complicated. International Patent Publication No. WO2006 / 038532 discloses a multi-layered wet separator comprising inorganic particles. As mentioned above, this separator also has to be extracted in the process of producing the film to the surface layer and the hard kneading process required for producing all the multi- (50% or more) of the diluent, and the low physical property improvement effect of the production of the product (the stretching effect is reduced due to the stretching in the softened state including the diluent).

Essential characteristics of the secondary battery separator are rigidity, permeability, and uniformity of quality, and recently, thermal stability is further required. However, the above-mentioned conventional techniques fail to simultaneously achieve quality stability, rigidity / transparency and high thermal stability.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a separation membrane for a secondary battery with improved heat shrinkage and strength. Other objects and advantages of the present invention will become apparent from the following description. It is also to be easily understood that the objects and advantages of the present invention can be realized by the means or method described in the claims, and the combination thereof.

The present invention provides a multi-layered separator for solving the above-mentioned technical problems. The separation membrane has a layered structure in which a plurality of porous film layers are sequentially laminated. The stretching ratio of each film layer gradually decreases sequentially from the center to the surface along a direction perpendicular to the lamination interface of the film layers.

Here, the porous film layer may include a polyolefin-based polymer resin.

Here, the separation membrane includes a center layer portion, first and second inner layer portions located on both side surfaces of the center layer portion, a first surface layer portion positioned on the first inner layer portion, and a second surface layer positioned on the second inner layer portion. Wherein the stretching ratio of the film layers included in the center layer portion is 4 to 8 times, the stretching ratio of the film layers included in the first and second inner layer portions is 2 to 5 times, and the first and second surface layers The stretching ratio of the film layers included in the portion may be 1 to 4 times.

Here, the center layer portion may be 5 to 50% of the entire thickness of the separator.

Here, the total thickness of the first and second surface layer portions may be 5% to 50% of the total thickness of the separator.

Here, the total thickness of the first and second inner layers may be 100% to 5% to 50% of the total thickness of the separator.

According to an embodiment of the present invention, the stretching ratio of the film layer having the lowest stretch ratio among the film layers included in the center stratum part is higher than that of the film layer having the highest stretch ratio among the film layers included in the first and second inner layer parts Wherein the stretching ratio of the film layer having the lowest stretching ratio among the film layers included in the first and second inner layer portions is higher than the stretching ratio of the film layer having the highest stretching ratio among the film layers included in the first and second surface layer portions, Of the stretching ratio.

Wherein the stretching ratio of one of the film layers included in the middle layer portion is higher than the stretching ratio of the film layer having the highest stretching ratio among the film layers included in the first and second inner layer portions, The stretching ratio of any one of the film layers included in the layer portion may be higher than the stretching ratio of the film layer having the highest stretching ratio among the film layers included in the first and second surface layer portions.

Here, the separation membrane may have an air permeability of 50 sec / 100 cc to 800 sec / 100 cc.

The separation membrane may have a penetration strength of 100 gf to 1,000 gf.

Here, the separation membrane may further include a ceramic porous coating layer including inorganic particles and a binder polymer resin on the outermost surface.

The ceramic porous coating layer is formed of inorganic particles having a plurality of fine pores formed by the interstitial volume of inorganic particles, which are fixed to each other by point bonding and / or face binding between particles via a binder polymer resin Porous structure.

Here, the thickness of the porous coating layer is from 1 m to 30 m.

In addition, the present invention includes a cathode, an anode, and a separator interposed between the cathode and the anode, and the separator provides an electrochemical irradiation, which is a separator according to the present invention.

Here, the electrochemical device may be a secondary battery, a lithium ion secondary battery, a lithium metal secondary battery, a fuel cell, a solar cell, or a supercapacitor.

The separator according to the present invention has a low shrinkage ratio of the separator even at a high temperature, and is excellent in heat resistance and dimensional stability. Therefore, there is an effect of improving the high-temperature safety of the battery manufactured through the separator according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. On the other hand, the shape, size, scale or ratio of the elements in the drawings incorporated herein can be exaggerated to emphasize a clearer description.
1 and 2 are schematic cross-sectional views of a separation membrane according to the present invention.

The present invention will now be described in detail with reference to the accompanying drawings. The terms or words used in the present specification and claims should not be construed to be limited to ordinary or dictionary terms and the inventor shall properly define the concept of the term in order to best explain its invention The present invention should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

The present invention relates to a separation membrane having a layered structure in which a plurality of porous film layers having different stretching ratios are stacked. The separation membrane can be used as a separation membrane of an electrochemical device such as a secondary battery, and is excellent in heat resistance, thereby contributing to safety improvement of the battery.

1 schematically shows an embodiment of a separation membrane according to the present invention. Hereinafter, the present invention will be described in detail with reference to FIG.

The separation membrane of the present invention is a multilayer separation membrane having a layered structure in which a plurality of porous film layers having different stretching ratios are sequentially laminated. According to a specific embodiment of the present invention, the stretching ratio of each layer in the separator decreases progressively or sequentially from the center to the surface along a direction perpendicular to the lamination interface of the films.

FIG. 2 schematically shows a pattern of increase and decrease in the stretching ratio of each film layer included in the separation membrane of the present invention. FIG. In FIG. 2, a indicates the center portion of the separation membrane, and b indicates the surface portion of the separation membrane. The stretching ratios of the respective film layers tend to decrease gradually or sequentially or stepwise along the direction a → b.

In one specific embodiment of the present invention, the film layer comprises a polyolefin-based polymer resin. The polyolefin-based polymer resin is selected from the group consisting of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMWPE), polypropylene, polybutene, polymethylpentene, Or mixtures thereof. According to a specific embodiment of the present invention, the polyolefin-based polymer resin may include at least one polypropylene-based resin. Examples of the polypropylene resin include homopolymers of propylene homopolymers and copolymers of propylene with at least one of ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, , 1-undecene, 1-dodecene and the like, or a propylene copolymer such as a graft copolymer or a block copolymer, but the present invention is not limited thereto.

However, if the stretching ratio of the film is high, the strength and porosity of the film are increased and the separator thickness is thin, which can contribute to the production of a thin film battery. However, when the stretching ratio is too high, the shrinkage due to the residual stress is high when exposed to a high temperature. Therefore, a porous film having a high elongation ratio has a disadvantage that heat resistance is poor.

The present invention relates to a multi-layer separator formed by laminating films having various stretch ratios. The multi-layer separator has the advantages of being excellent in mechanical strength and heat resistance by complementing the disadvantages of the single-layer film separator.

3 schematically shows a multilayer separator according to one specific embodiment of the present invention. The separation membrane of FIG. 3 includes a first surface layer portion C / a first inner layer portion B / a center layer portion A / a second inner layer portion B '/ a second surface layer portion C'. Each C / B / A / B '/ C' may include one or more than two film layers of the same or different types.

In one embodiment of the present invention, the stretching ratio of the film layer having the lowest stretch ratio among the film layers included in the center stratum part (A) is the stretch ratio of the film layers included in the inner layer parts (B, B ' And the stretching ratio of the film layer having the lowest stretching ratio among the film layers included in the inner layer portions B and B 'is higher than that of the film layers included in the surface layer portions C and C' Is higher than the stretching ratio of the film layer having the stretching ratio. The film layers included in the same layer portion may have the same or different stretching ratios.

In another embodiment of the present invention, the stretching ratio of any one of the film layers included in the center stratum part A is set such that the stretching ratio of the film layer having the highest stretching ratio among the film layers included in the inner layer parts B and B ' And the stretching ratio of any of the film layers included in the inner layer portions B and B 'is higher than the stretching ratio of the film layer having the highest stretching ratio among the film layers included in the surface layer portions C and C'. Further, the film layers included in the same layer portion may have the same or different stretching ratios.

The film layers included in the center layer portion (A) have a stretching ratio of 4 to 8 times or 5 to 7 times. The center layer portion is contained in the separator and has a higher elongation ratio than the other layers. Accordingly, the strength and porosity of the core layer contribute to the improvement of the strength and porosity of the entire separator. The thickness of the center stratum part A is 5% to 50% of the entire thickness of the separator. If the thickness of the center layer portion is less than 5%, the strength of the separator may be decreased. If the thickness of the core layer portion is more than 50%, the proportion of the portion having a high shrinkage percentage may be increased.

The film layers included in the surface layer portions C and C 'have a stretching ratio of 1 to 4 times or 1 to 3 times. The surface layer portion forms a surface layer portion of the separation membrane and has a lower elongation ratio than other layers and thus has a small residual stress and thus does not shrink the separation membrane even when exposed to a high temperature temperature so that it contributes to improvement in heat resistance and / .

The thickness of the surface layer portion (C, C ') is 5% to 50% of the entire thickness of the separation membrane. If the thickness of the center layer portion is less than 5%, the heat resistance of the separator may be deteriorated and the surface layer portion may shrink as the central layer portion shrinks, which may cause shorting of the electrode. On the other hand, if it exceeds 50%, the porosity of the separation membrane is lowered and the movement of the lithium ion is inhibited, so that the resistance can be increased and the wettability of the separation membrane can be lowered.

The film layers included in the inner layer portions (B, B ') have stretching ratios of 2 to 6 times, or 3 to 5 times. The inner layer portion is located between the center layer portion and the surface layer portion and functions to block or reduce stress transmitted to the surface layer by shrinkage when the center layer portion is shrunk. In the case where the center layer portion having a large difference in stretching ratio is laminated by direct contact with the surface layer portion, when the center layer portion is shrunk and deformed at a high shrinkage ratio under a high temperature environment, the stress generated by the deformation is transmitted to the surface layer portion, have. In order to prevent such a problem from occurring, the inner layer portion is further provided between the surface layer portion and the center layer portion, and the deformation stress of the center layer portion is absorbed and blocked by the inner layer portion, thereby preventing damage to the surface layer portion. The thickness of the inner layer portion (B, B ') is 5% to 50% of the entire thickness of the separator. If the thickness of the inner layer portion is less than 5%, the mechanical strength of the inner layer portion may be lowered, so that the deformation stress of the center layer portion can not be suppressed and the film layer of the inner layer portion may be deformed and / or damaged. For example, the heat resistance of the multilayered separator may be deteriorated, and the surface layer may shrink together as the center layer shrinks, causing short-circuiting of the electrodes. On the other hand, when the film layer of the inner layer portion exceeds 50%, the porosity of the separation membrane is lowered and the movement of the lithium ion is inhibited, so that the resistance can be increased and the wettability of the separation membrane can be lowered.

Next, a method of manufacturing the multilayered separator will be described. However, the manufacturing method described below is an example of one of various methods of manufacturing the multilayer separator of the present invention, and the production of the multilayer separator of the present invention is not limited to the following method.

The multilayer separation membrane may be prepared by preparing each film layer by a wet method and / or a dry method and laminating them. According to a specific embodiment of the present invention, the film layer can be produced according to a dry manufacturing method. As the dry manufacturing method, a method which is generally performed in the technical field of the present invention can be used. The dry-type method is a method in which micro-cracks are generated in the polymer thin film by stretching. Further, the film layer can be produced by a wet process. The wet process is a method of kneading a polyethylene resin with a pore-forming agent at a high temperature to form a single phase, separating the polyolefin and the pore-forming agent during the cooling process, and then extracting the pore-forming agent portion to form pores in the polyolefin.

After the unstretched film is obtained by a dry or wet method, the unmodified polymer is stretched in the uniaxial or biaxial direction at a temperature not lower than the melting point, generally at the second transition point or higher, and the molecules are oriented in that direction. This increases the impact strength and transparency of the film, increases the barrier property, and increases the crystallinity of the film. In addition, micropores are formed in the film by stretching to increase the porosity.

Next, the films subjected to the stretching treatment are subjected to a heat fixing step to remove residual stress and reduce the shrinkage ratio of the final film. In the heat-setting process, the film to be shrunk is forced by holding the heat to remove the residual stress, and the shrinkage rate and the high-temperature puncture strength are affected by the fixing temperature and the fixing ratio. If the heat fixing temperature is high, the stress of the resin lowers, the shrinkage rate becomes small, and the high temperature puncture strength becomes high. The puncture strength decreases as the measured temperature rises as the stress relaxation of the resin occurs. However, when the heat fixation temperature is high, sufficient stress relaxation is performed in the heat fixation process, It will be higher. However, when the heat fixing temperature is too high, the film is partially melted and the formed micropores are clogged to degrade the permeability. The preferred heat-setting temperature is selected within a temperature range where 10 to 40% by weight of the crystalline portion of the polyethylene layer is melted. If the heat fixing temperature is selected in a temperature range lower than the melting point of 10 wt% of the crystalline portion of the polyethylene layer, reorientation of the polyethylene molecules in the film is insufficient and there is no effect of removing the residual stress of the film. If the temperature is higher than the melting temperature of 40 wt% of the crystalline portion, the micropores are blocked by partial melting and the permeability is lowered. In addition, it is possible to improve the mechanical properties such as tensile strength and piercing strength and to reduce the shrinkage rate by performing heat fixing stepwise by using an open and regular tenter type machine. In the first step in the heat setting process, the transverse direction is elongated by 20 to 50% to increase the transmittance and improve the tensile strength and the puncture strength. The stretching of more than 50% has the advantage of improving the transmittance and tensile strength, but it has a disadvantage in that the shrinkage ratio increases and the transverse directional orientation increases, so that the transverse TMA shrinkage increases and the pore size excessively increases. In the second step, the width of the first stretched film is reduced by 15 to 40%. In the state of applying heat, it relaxes the stress through transverse shrinkage and alleviates the orientation of the resin, thereby reducing the shrinkage ratio and the transverse TMA shrinkage. At this time, when the width of the film is shrunk to 40% or more, the transparency and the puncture strength are excessively lowered. When the shrinkage is less than 15%, the stress and the resin orientation are not alleviated and the shrinkage ratio and the transverse TMA shrinkage ratio are increased. The stability of the battery can not be ensured. The heat setting time can be relatively short when the heat setting temperature is high, and relatively long when the heat setting temperature is low. Preferably 15 seconds to 1 minute.

Next, each of the film layers having different stretching ratios is produced by the above-mentioned method, and then laminated to produce a multilayered separator. An adhesive layer (not shown) may be interposed between the laminated film layers for interlayer adhesion. Or each film may be sequentially laminated to form a laminated structure, and the laminated structure may be pressed to achieve interlayer adhesion. As a method of laminating the film layers, for example, each film layer can be bonded under heating and pressurizing conditions. However, the present invention is not limited to the above method, and various methods can be applied within the scope of the present invention.

As described above, the multilayer separation membrane of the present invention is characterized in that the stretching ratio is gradually decreased and / or stepwise from the center portion of the separation membrane to the surface portion, and the low stretched film layer having the high- The mechanical strength is improved while the air permeability is excellent. The separation membrane according to the present invention has a penetration strength of 100 gf to 1,000 gf and an air permeability of 50 sec / 100cc to 800sec / 100cc. The penetration strength and air permeability may be appropriately selected depending on the intended use of the final product by controlling physical properties such as the thickness of each film layer within the scope of the present invention.

According to a specific embodiment of the present invention, the multilayer separation membrane may further include a ceramic porous coating layer including inorganic particles on one or both surfaces thereof.

The inorganic particles form an interstitial volume between inorganic particles to provide micropores. It also serves as a kind of spacer capable of maintaining the physical form. In addition, since the inorganic particles generally have a characteristic that their physical properties do not change even at a high temperature of 200 DEG C or more, the formed ceramic porous coating layer has excellent heat resistance. The porous coating layer has a thickness of 1 탆 to 30 탆, or 2 탆 to 20 탆, or 2 탆 to 14 탆.

Although the size of the inorganic particles is not limited, it is preferably in the range of 0.001 to 10 μm for the formation of a film having a uniform thickness and an appropriate porosity, and the porosity of the substrate (porous film or nonwoven web) on which the ceramic porous coating layer is formed And can be appropriately adjusted. When the particle size is less than 0.001 탆, the dispersibility is lowered and it is difficult to control the physical properties of the ceramic porous coating layer. When the particle size exceeds 10 탆, the thickness of the ceramic porous coating layer is increased to decrease the mechanical properties, The probability of an internal short circuit occurring during charging and discharging of the battery increases.

The content of the inorganic particles is preferably in the range of 50% by weight to 99% by weight, more preferably 60% by weight to 95% by weight, based on 100% by weight of the mixture of the inorganic particles constituting the ceramic porous coating layer and the binder polymer resin.

The binder polymer resin may be a polymer resin conventionally used in the art. Particularly, it is possible to use a glass transition temperature (Tg) as low as possible, preferably in the range of -200 to 200 ° C. This is because the mechanical properties such as flexibility and elasticity of the final film can be improved. The polymer resin faithfully performs a binder function to connect and stably fix inorganic particles and particles, thereby contributing to prevention of deterioration of mechanical properties of the finally formed ceramic porous coating layer.

According to one embodiment of the present invention, the ceramic porous coating layer is prepared by mixing an inorganic particle and a binder polymer resin with an appropriate solvent to prepare a slurry for a ceramic porous coating layer, The slurry may be applied and dried to form the slurry.

In the present invention, the inorganic particles contained in the slurry are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles are not particularly limited as long as the oxidation and / or reduction reaction does not occur in the operating voltage range of the applied electrochemical device (for example, 0 to 5 V based on Li / Li +). Particularly, when inorganic particles having ion transfer ability are used, the ion conductivity in the electrochemical device can be increased to improve the performance. When inorganic particles having a high dielectric constant are used as the inorganic particles, dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte is also increased, so that the ion conductivity of the electrolyte can be improved.

For the reasons stated above, the inorganic particles may include high-permittivity inorganic particles having a dielectric constant of 5 or more, or 10 or more, inorganic particles having lithium ion transferring ability, or a mixture thereof. Non-limiting examples of the 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 _1/3 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 ₂ O ₃ , SiC, and TiO ₂ may be used alone or in combination of two or more. Particularly, the above-mentioned BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1 -x} La _x Zr _{1 -y} Ti _y O ₃ (PLZT, where 0 <x <1, 0 < Inorganic particles such as Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT) and hafnia (HfO ₂ ) exhibit a high dielectric constant of 100 or more, And a piezoelectricity is generated so that a potential difference is generated between both sides by generating a charge when being stretched or compressed so as to prevent the occurrence of an internal short circuit between the two electrodes due to an external impact so as to improve the safety of the electrochemical device can do. Further, when the above-mentioned high-permittivity inorganic particles and inorganic particles having lithium ion-transferring ability are mixed, their synergistic effect can be doubled.

In the present invention, the inorganic particles having a lithium ion-transferring ability refer to inorganic particles containing a lithium element but not lithium and having a function of moving lithium ions. The inorganic particles having a lithium ion- Since lithium ions can be transferred and transferred due to a kind of defect present, the lithium ion conductivity in the battery is improved, thereby improving battery performance. Examples of the inorganic particles having lithium ion transferring ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y < (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ as such (LiAlTiP) _x O _y series glass (0 <x <4, 0 <y <13), lithium lanthanum titanate _{(Li x La y TiO 3,} 0 <x <2, 0 <y <3 _{), Li 3.25 Ge 0.25 P 0.75} S 4 lithium germanate Mani help thiophosphate _{(Li x Ge y P z S} w, 0 <x <4, 0 <y <1, 0 <z <1, 0 <w , such as < 5), Li ₃ N lithium nitride _{(Li x N y, 0 <} x <4, 0 <y <2), Li 3 PO 4 SiS 2 family, such as _{-Li 2 S-SiS 2 glass (} Li x such as _{Si y S z, 0 <x} <3, 0 <y <2, 0 <z <4), LiI-Li 2 SP 2 S 5 P 2 S 5 based glass (Li _x P _y S _z, such as 0 < x <3, 0 <y <3, 0 <z <7), or mixtures thereof.

On the other hand, the pore size and porosity of the organic / inorganic composite porous layer depends mainly on the size of the inorganic particles. For example, when inorganic particles having a particle size of 1 탆 or less are used, pores to be formed also become 1 탆 or less. Such a pore structure is filled with an electrolyte solution to be injected at a later stage, and the filled electrolyte serves as an ion transfer function. Therefore, the pore size and porosity are important factors for controlling the ionic conductivity of the organic / inorganic composite porous film. The pore size and the porosity of the organic / inorganic composite porous layer of the present invention are preferably 0.001 to 10 μm, and preferably 5 to 95%.

In addition, the thickness of the organic / inorganic composite porous layer of the present invention is not particularly limited, but may be adjusted in consideration of cell performance. More preferably in the range of 1 to 100 mu m, and particularly preferably in the range of 2 to 30 mu m. By adjusting the thickness range, battery performance can be improved.

The separation membrane according to the present invention can be used as a separation membrane in an electrochemical device such as an energy storage device. The electrochemical device includes all devices that perform an electrochemical reaction. Specific examples of the electrochemical device include a capacitor such as a primary cell, a secondary cell, a fuel cell, a solar cell, or a supercapacitor. Particularly, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery among the above secondary batteries is preferable.

Claims (15)

Wherein the stretching ratio of each of the film layers is gradually or sequentially decreased from the center to the surface along a direction perpendicular to the lamination interface of the film layers, Battery separator.
The method according to claim 1,
Wherein the porous film layer comprises a polyolefin-based polymer resin.
The method according to claim 1,
The separation membrane includes a center layer portion, first and second inner layer portions located on both sides of the center layer portion, a first surface layer portion located on the first inner layer portion, and a second surface layer portion located on the second inner layer portion, , The stretching ratio of the film layers included in the center layer portion is 4 to 8 times, the stretching ratio of the film layers included in the first and second inner layer portions is 2 to 5 times, and the stretching ratio of the film layers included in the first and second surface layer portions Wherein the stretching ratio of the film layers is 1 to 4 times.
The method of claim 3,
Wherein the center layer portion corresponds to 5 to 50% of the total thickness of the separator.
The method of claim 3,
Wherein the total thickness of the first and second surface layer portions is 5% to 50% of the total thickness of the separator.
The method of claim 3,
Wherein the total thickness of the first and second inner layers corresponds to 100% to 5% to 50% of the total thickness of the separator.
The method of claim 3,
The stretching ratio of the film layer having the lowest stretching ratio among the film layers included in the center stratum is higher than the stretching ratio of the film stratum having the highest stretching ratio among the film layers included in the first and second inner layer portions, Wherein the stretching ratio of the film layer having the lowest stretching ratio among the film layers included in the inner layer portion is higher than the stretching ratio of the film layer having the highest stretching ratio among the film layers included in the first and second surface layer portions, Membrane.
The method of claim 3,
The stretching ratio of any one of the film layers included in the center layer portion is higher than the stretching ratio of the film layer having the highest stretch ratio among the film layers included in the first and second inner layer portions and is included in the first and second inner layer portions Wherein the stretching ratio of one of the film layers is higher than the stretching ratio of the film layer having the highest stretching ratio among the film layers included in the first and second surface layer portions.
The method according to claim 1,
Wherein the separation membrane has an air permeability of 50 sec / 100cc to 800sec / 100cc.
The method according to claim 1,
Wherein the separation membrane has a penetration strength of 100 gf to 1,000 gf.
The method according to claim 1,
Wherein the separation membrane further comprises a ceramic porous coating layer including inorganic particles and a binder polymer resin on the outermost surface.
12. The method of claim 11,
The ceramic porous coating layer is formed of inorganic particles having a plurality of fine pores formed by the interstitial volume of inorganic particles, which are fixed to each other by point bonding and / or face binding between particles via a binder polymer resin Wherein the separator has a porous structure.
10. The method of claim 9,
Wherein the thickness of the porous coating layer is 1 to 30 占 퐉.
A cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is the separator according to any one of claims 1 to 13.
15. The method of claim 14,
Wherein the electrochemical device is a secondary battery, a lithium ion secondary battery, a lithium metal secondary battery, a fuel cell, a solar cell, or a supercapacitor.

Images