KR20140112668A - Porous Separator for Secondary cell and its manufacturing method with Polyvinylidene fluoride electrospinning on polyolefin substrate and inorganic compound coating - Google Patents

Abstract

The present invention relates to a porous separation membrane for a secondary battery and a manufacturing method thereof. The porous separation membrane has improved heat-resistant stability by coating a polyvinylidene fluoride nanoweb, provided by electrospinning polyvinylidene fluoride (PVDF) on a polyolefin base material, with inorganic slurry composed of inorganic particles and binder with a casting method in order to solve the problem of low heat-resistant stability of the separation membrane for a lithium secondary battery, the separation membrane being made of an existing polyolefin film.

Description

TECHNICAL FIELD [0001] The present invention relates to a porous separator for a secondary cell and a method for manufacturing the same, and a porous separator for a secondary battery, which comprises polyvinylidene fluoride (PVDF)

The present invention relates to a porous separator for a secondary battery and a method for manufacturing the same, and more particularly, to a porous separator for a secondary battery, which comprises casting inorganic particles onto a polyvinylidene fluoride nanoweb on which a polyvinylidene fluoride (PVDF) The present invention relates to a porous separator for a secondary battery and a method of manufacturing the same.

In recent years, miniaturization, thinning, light weight, and the like of electronic devices have been made rapidly and rapidly, and batteries that supply electric power in accordance with this tendency are also required to have high performance.

A lithium secondary battery is the battery best suited to such a demand, and the lithium secondary battery comprises an anode, a cathode, an electrolyte, and a separator.

Here, the positive electrode active material used in the positive electrode is a material capable of absorbing and desorbing lithium, and is a complex of lithium cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium nickel cobalt oxide, lithium iron phosphate oxide Metal oxides are mainly used.

In the negative electrode, the negative electrode active material is a lithium alloy, carbon, cokes, activated carbon, graphite, silicon, tin (Sn), or the like capable of intercalating and deintercalating lithium Metals and / or alloys are mainly used.

Further, as the non-aqueous electrolyte comprises a lithium salt and an organic solvent as an electrolytic solution, the lithium salt is _{LiClO 4, LiCF 3 SO 3,} LiAsF 6, LiBF 4, LiPF 6, LiSCN, LiC (CF 3 SO 2) 3, LiBOB Propylene carbonate (PC), dimethyl carbonate (DMC), dimethoxyethane (DME), diethoxyethane (DEE), 2-methyltetrahydrofuran (2-MeTHF ), Dimethylsulfoxide (DMSO), and the like are used respectively or in combination.

On the other hand, the separator is one of the four core materials composing the battery. It is located between the anode and the cathode of the battery and separates the lithium oxide, which is a highly active cathode material, directly from the cathode to prevent the explosion. And because it is located between two electrodes, it has pore structure so that lithium ions move smoothly between electrodes.

The thinner the separator, the smaller the volume in the cell, and the greater the amount of electricity produced per unit volume. However, if the thickness is unconditionally thinned, the strength of the separator may be weakened. Therefore, the mechanical and thermal strength and durability of the separator should also be focused. High-temperature storage and overcharging of the battery are related to the thermal stability of the separator, and safety problems due to nail penetration and foreign matter are related to mechanical properties.

Polyolefin-based films such as polyethylene (PE) and polypropylene (PP) are mainly used as separation membranes used in lithium ion batteries. Polyolefins are disadvantageous in that they have high thermal shrinkage at high temperatures and are physically weak .

In order to improve the poor thermal stability of the polyolefin-based separator, attempts have been made to co-extrude a heat-resistant polymer having a high melting temperature with a polyolefin resin, or to use a heat-resistant polymer as a nonwoven fabric.

Polyvinylidene fluoride (PVDF) is one of the polymers of the fluoro series, and the fluororesin contains fluorine, which is excellent in thermal and chemical properties.

반응식 1. 폴리비닐리덴플루오라이드의 제조

Reaction 1. Preparation of polyvinylidene fluoride

Polyvinylidene fluoride is produced by the same process as in the above Reaction Scheme 1, and has a melting point (177 ° C) and a density (1.78) lower than those of other fluororesin, low cost, It is often used as a premium paint for exterior walls of a building.

In addition, polyvinylidene fluoride is a representative organic material exhibiting piezoelectricity, and many studies have been conducted since the 1960s. In the polyvinylidene fluoride polymer, four kinds of crystals are mixed, and it can be classified into at least four types of α, β, γ and δ type depending on crystal form. Among them, the? -Form crystal of polyvinylidene fluoride has a trans-type molecular chain filled in parallel, and all the permanent dipoles of the monomers are aligned in one direction, and exhibit large spontaneous polarization. This means that the polyvinylidene fluoride molecules can be regularly arranged through stretching to impart piezoelectricity to the aggregated state by imparting anisotropy thereto. In order to improve such piezoelectric characteristics, various methods for increasing the? -Form crystal in the polyvinylidene fluoride fiber have been studied. In general, melt spinning systems have been applied to produce polyvinylidene fluoride fibers. However, it is expensive to construct melt spinning equipment, and the size of fibers produced by melt spinning is limited.

Due to the coagulation mechanism of wet spinning, fibers prepared by wet spinning have a significantly higher β-form crystal ratio in the fiber at the initial stage of spinning than the α-form crystal ratio, and the spinning speed is slower than the melt spinning. However, It also has the advantage of reducing fiber size. In addition, wet spinning has the advantage of improving physical properties through continuous post-treatment processes (stretching, crimping, etc.).

For wet spinning, the polymer is dissolved in a solvent to make a spinning solution, and the spinning solution is discharged through a gear pump and spinning nozzle into a coagulation bath containing an aqueous solution containing a solvent. As the discharged spinning liquid phase and the co-diffusion with the solvent and the precipitating agent in the coagulating bath occur, the precipitating agent penetrates into the spinning liquid phase and phase separation and precipitation occur in the three-component system of the polymer-solvent-precipitating agent, Is obtained. Such a wet spinning system has the advantage of enhancing the mechanical properties of fibers by orienting the polymer in a fiber direction by stretching and tensioning in a spinning bath.

On the other hand, when the non-woven fabric is used as a membrane material as another method for improving the thermal stability of the membrane, it is in the form of a fibrous mat made by chemical, physical or mechanical connection of natural or synthetic fibers. Porosity and a large melting point. Such nonwoven fabrics have been used for nickel-cadmium batteries, but they have not only been applied to lithium secondary batteries because they have a relatively high mechanical strength and are relatively difficult to prevent short-circuiting of the battery due to a relatively large open structure and rough surfaces .

However, in recent years, in order to improve safety and lifetime, a polyester nonwoven fabric separator has been studied, and high temperature stability using a high melting point of polyester and lifetime improvement effect due to uniform pore structure have been reported.

Electrospinning is a technique to fabricate microfibers and porous webs, ie, nonwoven fabrics, up to several to several tens of nanometers in diameter using electrostatic spraying of high viscosity fluids such as polymers. Electrospinning attracts the solution by electrostatic force of the electrodes Which is a device that emits ultra-fine fibers.

The polymer solution at the tip of the vertically positioned capillary tube forms an equilibrium between gravity and surface tension to form a hemispherical droplet which causes the charge or dipole orientation on the hemispherical droplet surface to be induced at the air layer and interface when an electric field is applied , So that a force opposing the surface tension is generated due to charge or dipole repulsion. Thus, the hemispherical surface of the solution suspended at the tip of the capillary is stretched into a conical shape known as a Taylor cone. At some critical electric field strength (Vc), the repulsive electrostatic force overcomes the surface tension, ) Is emitted from the end of the Taylor cone. In the case of a solution with low viscosity, the jet collapses into fine droplets and exhibits a spray phenomenon. However, in the case of a solution having a high viscosity such as a polymer, the jet is not collapsed, the solvent is evaporated as it flows toward the collecting plate toward the air, and the charged continuous polymer fibers are accumulated on the collecting plate. This phenomenon is called electrospinning . The reason why very thin fibers are produced by electrospinning is because the jet is thinned by the elongation of the jet and the spraying phenomenon in the course of flying towards the collector plate. Because of this small diameter, the electrospun fiber will have a larger surface area and volume, and more moisture can be absorbed than other fibers of larger diameter. The ultrafine fiber web thus produced is ultra thin and light in weight and has a very high volume to surface area ratio and high porosity as compared with conventional fibers. Therefore, it is possible to manufacture the structure so that liquid does not come in from the outside of the membrane. Therefore, studies are being conducted to apply the electrospinning phenomenon of polymers to various fields such as the manufacture of ultrafine high performance filters, porous supports for tissue engineering, and chemical sensors.

Further, as the battery has become larger, the problem of wettability with electrolyte has become more serious. If the affinity of the electrolyte solution and the separator membrane is low, the lithium ion transfer capacity in the membrane is deteriorated, leading to a phenomenon in which the output characteristics of the battery are deteriorated. In particular, when the electrolytic solution component has a polarity such as ethylene carbonate (EC) or propylene carbonate (PC), it exhibits poor wettability to the non-polar polyolefin-based separator. Therefore, The problem of aspect appears more clearly.

Therefore, techniques for modifying the surface of the separator to improve the affinity with the electrolyte have been developed. In particular, the inorganic composite separator or the ceramic separator is manufactured by connecting inorganic particles of a very small size with a small amount of a binder. Show high wettability to electrolytes due to their high hydrophilicity and large specific surface area, and excellent wettability in electrolytes such as EC and PC improves battery life and performance. These ceramic separators have very good thermal stability and hardly shrink even at high temperatures.

However, such a ceramic separator exhibits excellent electrolyte wettability and thermal stability, but has disadvantages in that it does not show adequate mechanical properties, particularly flexibility, for a battery assembly process including a winding.

In the present invention, in order to improve the low thermal stability of the polyolefin substrate and the low affinity to the electrolyte, a polyvinylidene fluoride nanoweb, which is a heat resistant polymer, is prepared, and inorganic particles are coated thereon to solidly bind the inorganic substance, To provide a porous separator capable of improving battery stability and output characteristics, and a method for manufacturing the same.

The present invention relates to a method for preparing a polyvinylidene fluoride nanoweb, which comprises: preparing a polyvinylidene fluoride nanoweb by electrospinning a spinning solution prepared by dissolving polyvinylidene fluoride in an organic solvent on a polyolefin substrate; And coating an inorganic slurry on the polyvinylidene fluoride nanoweb to form an inorganic coating layer. The present invention also provides a method of manufacturing a porous separator for a secondary battery.

According to a preferred embodiment of the present invention, the polyvinylidene fluoride has a weight average molecular weight (Mw) of 10,000 to 500,000, and the organic solvent is selected from the group consisting of N, N-Dimethylformamide (DMF) and dimethylacetamide N-dimethylacetamide, DMAc) solvent.

According to another preferred embodiment of the present invention, the electrospinning is characterized by using a bottom-up electrospinning method.

According to another preferred embodiment of the present invention, the weight ratio of the inorganic material and the binder in the inorganic slurry is 95: 5 to 50:50, and the binder is selected from the group consisting of polyvinylidene fluoride (PVDF), polymethyl (PMMA), polyacrylonitrile (PAN), and carboxymethylcellulose (CMC).

The present invention also relates to a polyolefin substrate; A polyvinylidene fluoride nano-web layer formed by electrospinning on one surface of the polyolefin substrate; And an inorganic coating layer formed on one surface of the polyvinylidene fluoride nanoweb by coating an inorganic material on the surface of the porous separator.

According to a preferred embodiment of the present invention, the inorganic substance is _{SiO 2, Al 2 O 3,} TiO 2, Li 3 PO 4, zeolites, MgO, CaO, BaTiO _3, Li ₂ O, LiF, LiOH, Li ₃ N, BaO , Na ₂ O, Li ₂ CO ₃ , CaCO ₃ , LiAlO ₂ , SiO, SnO, SnO ₂ , PbO ₂ , ZnO, P ₂ O ₅ , CuO, MoO, V ₂ O ₅ , B ₂ O ₃ , Si ₃ N ₄ , CeO ₂ , Mn ₃ O ₄ , Sn ₂ P ₂ O ₇ , Sn ₂ B ₂ O ₅ , Sn ₂ BPO _6, and mixtures thereof.

Since the porous separator for a secondary battery of the present invention is strongly bonded to the inorganic coating layer by the electrospun polyvinylidene fluoride nanoweb, the separator using the conventional polyolefin film and the polyolefin substrate having the inorganic Stability.

1 is a schematic view of a porous separation membrane provided by the present invention.
2 is a schematic view of a method for producing a porous separation membrane provided by the present invention.
3 is a schematic view of a method of manufacturing a downwardly porous separator of the present invention.

The present invention relates to a method for producing a polyvinylidene fluoride nanowire, comprising: electrospinning a polyvinylidene fluoride solution on a polyolefin substrate to form a polyvinylidene fluoride nanoweb; And coating an inorganic slurry containing an inorganic material and a polyvinylidene fluoride-affinity polymer on the polyvinylidene fluoride nanoweb to form an inorganic coating layer.

The thickness of the polyolefin substrate is preferably 5 to 50 μm and the porosity (porosity (%)) = 1- (apparent density of the membrane / resin density) x 100] is preferably 30 to 80%. The tensile strength was 700 kg / cm 2 or more in the mechanical direction (MD), 150 kg / cm 2 or more in the transverse direction (CD), the piercing strength was 200 g or more per mil (1 mil = 25.4 탆) It is particularly suitable for use in an electrochemical device having a physical property of less than 10% for 1 hour, an average pore size of 0.005 to 3 占 퐉 and an electrical characteristic of electric resistance of 10,000? / Cm2 or more at 130 to 185 占 폚.

The electrospinning device used in the present invention includes a spinning liquid main tank for storing a spinning solution, a metering pump for supplying a spinning solution in a fixed amount, and a plurality of tubular nozzles composed of a plurality of pins in a block form. A collector for collecting short fibers emitted at a position corresponding to the nozzle block, a voltage generating device for generating a high voltage, and a spinning solution discharging device connected to the top of the nozzle block.

The step of preparing the nanoweb (nanofiber nonwoven fabric) by electrospinning the polyvinylidene fluoride of the present invention proceeds as follows.

First, a spinning solution is prepared by dissolving polyvinylidene fluoride (PVDF) in an appropriate organic solvent, and the polyvinylidene fluoride spinning solution is stored in the spinning solution main tank and metered by a separate metering pump It is supplied to the spinning liquid drop device.

The polyvinylidene fluoride is a homopolymer of vinylidene fluoride or a copolymer polymer containing vinylidene fluoride in a molar ratio of 50% or more. The polyvinylidene fluoride is a homopolymer from the viewpoint of excellent strength of the polyvinylidene fluoride resin When the polyvinylidene fluoride resin is a copolymer polymer, known copolymerizable monomers copolymerizable with the vinylidene fluoride monomers can be appropriately selected and used. Examples thereof include, but are not limited to, fluorine-based monomers and chlorine-based Monomers and the like can be suitably used. The weight average molecular weight (Mw) of the polyvinylidene fluoride resin is not particularly limited, but is preferably 10,000 to 500,000, more preferably 50,000 to 500,000.

When the weight average molecular weight of the polyvinylidene fluoride resin is less than 10,000, sufficient physical properties for forming a nonwoven fabric can not be obtained. When the weight average molecular weight exceeds 500,000, the solution handling is not easy and the uniformity of the porous film is obtained It becomes difficult.

Examples of the organic solvent include propylene carbonate, butylene carbonate, 1,4-butyrolactone, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,3-dimethyl- 2- imidazolidinone, dimethylsulfoxide N, N-dimethylacetamide, N-methyl-2-pyrrolidone, polyethylene sulfolane, tetraethylene glycol dimethyl ether, acetone, alcohol or a mixture thereof. And N, N-dimethylacetamide (hereinafter referred to as 'DMAc') as a solvent, and more preferably at least one selected from the group consisting of N, N-dimethylformamide (hereinafter referred to as 'DMF') or dimethylacetamide Is more preferable.

In this way, the spinning solution supplied into the spinning solution dropping device is supplied to the spinning solution supply plate of the nozzle block in which a high voltage is applied discretely while passing through the spinning solution dropping device and the stirrer is installed. The spinning liquid drop device also blocks the flow of spinning liquid and prevents electricity from flowing into the spinning liquid main tank.

Subsequently, in the nozzle block, a spinning liquid is discharged through a multi-tubular nozzle to a collector at an upper portion where a high voltage is applied to manufacture a nano-web.

The spinning solution transferred to the spinning solution supply pipe is discharged to the collector through the multi-tubular nozzle to form the fibers. At this time, the nanofibers electrospun from the tubular nozzle are widely spread by the air injected from the nozzle for supplying air, and are collected on the collector, thereby widening the collecting area and making the density uniform. The excess flushing liquid which is not fibrous in the multistage nozzle is collected in the overflow removing nozzle and moved to the flushing liquid supply plate through the temporary storage plate of the overflow liquid.

In the case of manufacturing a nano-web, the speed of the air in the air supply nozzle is preferably 0.05 m to 50 m / sec, more preferably 1 to 30 m / sec. When the velocity of the air is less than 0.05 m / sec, the spreadability of the nanoweb collected on the collector is low and the collecting area is not greatly improved. If the velocity of the air exceeds 50 m / sec, The area to be focused on the collector is rather reduced, and the more serious problem is attached to the collector in the form of coarse tufts rather than the shape of the fibers, so that the capability of forming nanofibers is remarkably deteriorated.

In addition, the spinning solution which is excessively supplied to the top of the nozzle block is forcibly transferred to the spinning liquid main tank by the spinning solution discharging device.

In order to promote the formation of the nanoweb by the electric force, a voltage of 1 kV or more, preferably 20 kV or more, generated in the voltage generator is applied to the conductive plate and the collector provided at the lower end of the nozzle block. It is more advantageous in terms of productivity to use an endless belt as the collector. It is preferable that the collector reciprocates by a predetermined distance in order to make the density of the web uniform.

When the nanoweb formed on the collector is wound on the winding roller through the web supporting roller, the nano-web manufacturing process is completed.

The manufacturing apparatus can increase the collecting area to uniform the density of the nano-web, effectively prevent the droplet phenomenon, improve the quality of the web, and increase the fiber-forming effect by the electric force, Mass production is possible. In addition, the width and thickness of the web can be freely changed and adjusted by arranging the nozzles constituted by a plurality of pins in block form.

In addition, the electrospinning apparatus may be installed in a bottom-up, top-down, horizontal, and combined type, and more preferably, a bottom-up type electrospinning apparatus as shown in FIG.

After the polyvinylidene fluoride nanoweb was adhered to the polyolefin substrate through the electrospinning method as described above, the slurry prepared by adding the inorganic particles and the binder resin to the acetone was coated on the polyvinylidene fluoride nanoweb A porous separator is prepared by preparing an inorganic coating layer.

The inorganic particles are _{SiO 2, Al 2 O 3,} TiO 2, Li 3 PO 4, _{zeolites, MgO, CaO, BaTiO 3,} Li 2 O, LiF, LiOH, Li 3 N, BaO, Na 2 O, Li 2 CO _{3, CaCO 3, LiAlO 2,} SiO, SnO, SnO 2, PbO 2, ZnO, P 2 O 5, CuO, MoO, V 2 O 5, B 2 O 3, Si 3 N 4, CeO 2, Mn 3 O ₄ , Sn ₂ P ₂ O ₇ , Sn ₂ B ₂ O ₅ , Sn ₂ BPO _6, and mixtures thereof, and is preferably SiO ₂ or Al ₂ O ₃ Do.

Wherein the binder is at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), and carboxymethyl cellulose (CMC) Particles are used to coat and adhere to the nanocomposite.

The coating method may be various coating methods such as chemical vapor deposition (CVD), physical vapor deposition (PVD), spray coating, dip coating, spin coating, casting, , In particular a coating by a casting method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The porous separator coated with inorganic particles by electrospinning a polyvinylidene fluoride nanoweb on a polyolefin substrate of the present invention and a method for producing the same will be described in detail with reference to the following examples and drawings. It will be apparent, however, to those skilled in the art that the scope of the invention is not limited to the disclosed embodiments and modifications or improvements made therefrom.

(1) Heat shrinkage measurement

A porous membrane sample of 5 cm x 2.5 cm was placed between two slide glasses and clamped with a clip. The sample was allowed to stand at 150 ° C for 30 minutes and the shrinkage ratio was calculated.

Example 1

Polyvinylidene fluoride having a weight average molecular weight (Mw) of 50,000 was dissolved in a DMAc solvent to prepare a spinning liquid. The spinning solution was sprayed on a polyolefin substrate (Celgard 2400) having a thickness of 10 탆 by a distance of 40 cm, Under a condition of an applied voltage of 15 kV, a spinning liquid flow rate of 0.1 mL / h, a temperature of 22 캜 and a humidity of 20%, a polyvinylidene fluoride nanoweb having a thickness of 3 탆 is formed.

A slurry prepared by adding Al ₂ O ₃ inorganic particles having a size of 0.5 μm and poly (methyl methacrylate) (PMMA) (LG IG 840) as a binder to acetone at a weight ratio of 9: 1 was dispersed in polyvinylidene fluoride Coated on a nano-web by a casting method to a thickness of 5 탆.

The heat shrinkage was evaluated using the porous separator for a secondary battery manufactured by the above method, and the results are shown in Table 1 below.

Example 2

Except for adding Al ₂ O ₃ inorganic particles having a size of 0.5 μm and polymethyl methacrylate (using PMMA, LG IG 840) as a binder to acetone at an 8: 2 weight ratio, the porous material for a secondary battery After the membrane was prepared, the performance of the membrane was evaluated.

Comparative Example 1

The performance of the separator was evaluated by using a polyolefin film (Celgard 2400) having a thickness of 18 탆 which was not subjected to any further treatment.

Comparative Example 2

A porous separator for a secondary battery was prepared by coating the inorganic slurry of Example 1 with a thickness of 5 탆 on a polyolefin substrate (Celgard 2400) having a thickness of 13 탆, and performance of the separator was evaluated by the same method as in Example.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Heat shrinkage (%) One 3 42 12 Thickness (㎛) 18 18 18 18

As described above, the porous separation membrane provided by the present invention is improved in heat stability of the separation membrane by firmly adhering the inorganic coating layer by the nonwoven fabric composed of nanofloids by electrospinning as compared with the separation membrane coated with inorganic material on the general polyolefin film and polyolefin Able to know.

The present invention is not limited to the above embodiments and is protected by the claims.

1: Fluid Main tank 2: Metering pump
3: Fluid drop device 4: Nozzle block
5: nozzle 6: nanofiber
7: Collector 8: Collector support roller
9: voltage generating device 10: nozzle block left-right reciprocating device
11: Stirrer 12: Fluid discharging device
13: Transfer tube 14: Nano web support roller
15: Nano web 16: Nano web winding roller

Claims (7)

A step of electrospinning a spinning solution prepared by dissolving polyvinylidene fluoride in an organic solvent on a polyolefin substrate to form a polyvinylidene fluoride nanoweb; And
And coating an inorganic slurry on the polyvinylidene fluoride nanoweb to form an inorganic coating layer.
The method according to claim 1,
The polyvinylidene fluoride has a weight average molecular weight (Mw) of 10,000 to 500,000 and the organic solvent is N, N-Dimethylformamide (DMF) or N, N-Dimethylacetamide (DMAc) Wherein the porous separator is a porous separator.
The method according to claim 1,
Wherein the electrospinning uses a bottom-up electrospinning method.
The method according to claim 1,
Wherein the weight ratio of the inorganic material and the binder in the inorganic slurry is 95: 5 to 50:50.
5. The method of claim 4,
Wherein the binder is any one selected from the group consisting of polyvinylidene fluoride (PVDF), polymethylmethacrylate (PMMA), polyacrylonitrile (PAN), and carboxymethylcellulose (CMC) A method for producing a porous separator.
Polyolefin substrates;
A polyvinylidene fluoride nano-web layer formed by electrospinning on one surface of the polyolefin substrate; And
And an inorganic coating layer formed by coating an inorganic material on one surface of the polyvinylidene fluoride nanoweb.
The method according to claim 1,
The inorganic substance is _{SiO 2, Al 2 O 3,} TiO 2, Li 3 PO 4, _{zeolites, MgO, CaO, BaTiO 3,} Li 2 O, LiF, LiOH, Li 3 N, BaO, Na 2 O, Li 2 CO 3 , CaCO ₃ , LiAlO ₂ , SiO, SnO, SnO ₂ , PbO ₂ , ZnO, P ₂ O ₅ , CuO, MoO, V ₂ O ₅ , B ₂ O ₃ , Si ₃ N ₄ , CeO ₂ , Mn ₃ O _{4 , Sn 2 P 2 O 7,} Sn 2 B 2 O 5, Sn 2 BPO 6 and the secondary battery porous separator, characterized in that a selected one from the group consisting of a mixture thereof.

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