KR20150037333A - Separator based non-woven fabric for secondary battery, a method of making the same and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a separator for a secondary battery to improve the flat leveling of a non-woven fabric base material by filling a large pore among pores formed on the non-woven fabric with inorganic particles, a method for producing the same, and a secondary battery including the same. According to the present invention, the separator for a secondary battery is formed with pores having the longest diameter of 0.1 to 100μm; and uses a non-woven fabric as a base material, which has pores having the longest diameter between 10 and 100μm filled with inorganic particles.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator for a secondary battery based on a nonwoven fabric, a method for manufacturing the separator, and a secondary battery including the separator,

The present invention relates to a separator for a secondary battery based on a nonwoven fabric, a method for producing the same, and a secondary battery comprising the same. More particularly, the present invention relates to a separator for a secondary battery, An improved secondary battery separator, a manufacturing method thereof, and a secondary battery including the same.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified.

Electrochemical devices have attracted the greatest attention in this respect. Among them, the development of rechargeable secondary batteries has become a focus of attention. In recent years, in order to improve capacity density and specific energy, And research and development on the design of the battery.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has advantages such as higher operating voltage and higher energy density than conventional batteries such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution . However, such a lithium ion battery has safety problems such as ignition and explosion in using an organic electrolytic solution, and has a disadvantage that it is difficult to manufacture. Recently, the lithium ion polymer battery is considered to be one of the next generation batteries by improving the weak point of the lithium ion battery. However, since the capacity of the battery is still relatively low as compared with the lithium ion battery, Is urgently required.

One of the important components that determines the characteristics of the secondary battery is a separator that functions as a passage of electrolytic ions by impregnating the electrolyte. The separator should have a uniform pore structure to satisfy the function of the ion channel to exhibit the desired ion conductivity, and besides the basic ion conductivity, the separator should have thermal stability and excellent electrolyte wettability. Therefore, the separator must have a uniform pore structure to have excellent ionic conductivity and to exhibit excellent cell performance.

On the other hand, the nonwoven fabric used as the separator base has the advantages of low cost and relatively simple manufacturing process, but has a drawback that the pore size is formed nonuniformly. Referring to Fig. 1, a separator including a nonwoven base material is described. The nonwoven fabric is made of nonwoven fabric 1, and pores are formed between the nonwoven fabric 1. The pores formed in the nonwoven fabric are not uniform in size, and the large pores 2 and the small pores 3 are mixed. Therefore, when the battery is charged or discharged, the flux of lithium ions is formed toward a large pore, and insulation may be deteriorated due to leakage current. In addition, the leveling of the porous base material is not constant, so that the lithium movement is not uniform and the battery reliability may be deteriorated.

The present invention seeks to provide a separator for a secondary battery comprising a nonwoven fabric as a porous base material, the separator including a nonwoven base material having improved level leveling.

The present invention also provides a method of manufacturing a separator for a secondary battery including a nonwoven substrate improved in plane leveling and a secondary battery including the separator for the secondary battery.

According to one aspect of the present invention, there is provided a nonwoven fabric comprising pores having a pore diameter ranging from 0.1 to 100 mu m based on the longest diameter and having pores having a maximum diameter of 10 to 100 mu m filled with inorganic particles A separator for a secondary battery is provided.

The inorganic particles may have a diameter of 5 to 100 mu m.

The inorganic particles may be inorganic particles having a dielectric constant of 5 or more, lithium ion transferring ability, or a mixture thereof.

Inorganic particles is greater than or equal to the dielectric constant of 5, _{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 ) 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 , TiO ₂ , SiC, or mixtures thereof.

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 <3), lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), (LiAlTiP) _x O _y series glass <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), lithium germanium thiophosphate (Li _x Ge _y P _z S _w , (Li _x N _y , 0 <x <4, 0 <y <2), SiS ₂ series glass (Li _x Si, 0 <y <1, 0 <z < _{y S z, 0 <x <} 3, 0 <y <2, 0 <z <4), P 2 S 5 based _{glass (Li x P y S z} , 0 <x <3, 0 <y <3, 0 < z < 7) and mixtures thereof.

According to another aspect of the present invention, there is provided a secondary battery including the aforementioned separator for a secondary battery.

The secondary battery may be a lithium secondary battery.

In the present invention, inorganic particles are filled only in the large pores of the nonwoven fabric, so that the leveling of the surface of the nonwoven fabric substrate is improved, and as a result, a nonwoven fabric-based separator having uniform lithium mobility is provided.

1 is a schematic view of a conventional nonwoven fabric substrate formed by nonwoven fabrics.
2 is a schematic view of an embodiment of the present invention in which inorganic pores are filled with large pores among nonwoven fabrics formed by nonwoven fabrics.

Hereinafter, the present invention will be described in detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

2 is a schematic view of an embodiment of the present invention in which inorganic pores are filled with large pores among nonwoven fabrics formed by nonwoven fabrics. The separator according to the present invention includes the nonwoven fabric 1 and the relatively large pores 2 of the pores formed between the nonwoven fabrics 1 are filled with the inorganic particles 20, (void) state.

The nonwoven fabric used in the present invention is not particularly limited as long as it is a polymer capable of producing a nonwoven fabric. Non-limiting examples of the nonwoven fabric include polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, Polyamide, polyacetal, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene. The nonwoven fabric may be made of a heat-resistant polymer in order to improve the thermal stability of the nonwoven fabric substrate. Non-limiting examples of the nonwoven fabric fiber include polyethylene terephthalate, polyimide, polyamide, polysulfone, Polyvinylidene fluoride, derivatives thereof, and mixtures thereof. The thickness of the nonwoven base material is preferably 9 to 30 탆.

The diameter of the nonwoven fabric fibers is not particularly limited, and may be, for example, microfine fibers having an average thickness of 0.5 to 10 mu m, preferably 1 to 7 mu m.

Such a nonwoven fabric may be formed into a nonwoven fabric by a method commonly known in the art. The nonwoven fabric has a large number of pores, and usually has a porosity of 50 vol% or more, but is not limited thereto.

In the nonwoven fabric, pores having a diameter ranging from 0.1 to 100 mu m are formed based on the longest diameter. Among these, pores having a maximum diameter of 10 to 100 mu m are filled with inorganic particles. For convenience, the pores having the longest diameter in the numerical range are referred to as 'large pores' for convenience, and the pores having a size smaller than the lower limit are referred to as 'small pores'.

Since the size of the inorganic particles should fill the large pores of the nonwoven fabric and should not flow into the small pores, it is preferable that the inorganic particles have a maximum diameter of 5 to 100 mu m. The shape of the inorganic particles is also not particularly limited, and may be, for example, a shape such as a sphere. As the large pores of the nonwoven fabric are filled with inorganic particles, the leveling of the surface of the nonwoven fabric is improved.

In the present specification, the term 'plane leveling' is understood as a term indicating the degree to which lithium ions are uniformly moved through pores formed in a nonwoven fabric substrate. That is, 'improvement of plane leveling' means improvement of flux phenomenon of lithium ion, which means that the movement of lithium ions through the nonwoven fabric substrate moves more uniformly.

The kind of the inorganic particles filled in the large pores of the nonwoven fabric is electrochemically stable so that 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 ⁺ ) Is not particularly limited. Particularly, when inorganic particles having a high dielectric constant are used as the inorganic particles, the dissociation of the electrolyte salt, for example, the lithium salt in the liquid electrolyte, can be increased, and the ion conductivity of the electrolyte can be improved.

For the reasons stated above, it is preferable that the inorganic particles include high-permittivity inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of the inorganic particles is less than a dielectric constant of 5 is _{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 2 O ₃ , TiO ₂ , SiC, or a mixture thereof.

As the inorganic particles, inorganic particles having a lithium ion transferring ability, that is, inorganic particles containing a lithium element but having a function of transferring lithium ions without storing lithium can be used. Non-limiting examples of 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, including (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 _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1) such as Li _{3 .25} Ge _{0 .25} P _{0 .75} S ₄ , , 0 <w <5), Li 3 N lithium nitride _{(Li x N y, 0 <} x <4, 0 <y <2) such _{as, Li 3 PO 4 -Li 2 S} -SiS 2 SiS 2 , including series _{glass (Li x Si y S z} , 0 <x <3, 0 <y <2, 0 <z <4), such as _{LiI-Li 2 SP 2 S 5} P 2 S 5 based glass (Li _x P _y S _z , 0 <x <3, 0 <y <3, 0 <z <7), or a mixture thereof.

The separator of the present invention may be used only as the nonwoven fabric substrate described above, or the porous coating layer may be provided on at least one surface of the nonwoven fabric substrate. The porous coating layer is formed of a mixture of a plurality of inorganic particles and a binder polymer. The type of inorganic particles used in the porous coating layer refers to inorganic particles that fill the large pores of the nonwoven fabric. Many inorganic particles are interconnected by a binder polymer, and voids may form between the inorganic particles.

In the separator of the present invention, the inorganic particle size of the porous coating layer is not limited. However, in order to form a coating layer having a uniform thickness and a proper porosity, it is preferable that the range is 0.001 to 10 탆. If it is less than 0.001 탆, the dispersibility may be lowered. If it is more than 10 탆, the thickness of the porous coating layer may increase, and because of the large pore size, the probability of occurrence of internal short circuit during charging and discharging of the battery is increased.

As the binder polymer contained in the porous coating layer, a polymer conventionally used for forming the porous coating layer on the nonwoven fabric substrate can be used in the art. Particularly, it is preferable to use a polymer having a glass transition temperature (T _g ) of -200 to 200 ° C because it can improve the mechanical properties such as flexibility and elasticity of the finally formed porous coating layer . Such a binder polymer acts as a binder to connect and stably fix the inorganic particles and the non-woven substrate between the inorganic particles.

In addition, the binder polymer does not necessarily have ion conductivity, but the performance of the electrochemical device can be further improved by using a polymer having ion conductivity. Therefore, it is preferable that the binder polymer has a high permittivity constant. In fact, since the dissociation degree of the salt in the electrolyte depends on the permittivity constant of the electrolyte solvent, the higher the permittivity constant of the binder polymer, the better the salt dissociation in the electrolyte. The dielectric constant of such a binder polymer may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), preferably 10 or more.

In addition to the functions described above, the binder polymer may be characterized by being capable of exhibiting a high degree of swelling of the electrolyte by being gelled upon impregnation with a liquid electrolyte. Accordingly, it is preferable to use a solubility parameter of 15 to 45 MPa ^1/2 of a polymer, and the more preferred solubility parameter of 15 to 25 MPa ^1/2, and 30 to 45 MPa ^1/2 range. Therefore, it is preferable to use hydrophilic polymers having many polar groups, rather than hydrophobic polymers such as polyolefins. If the solubility is more than 15 MPa ^1/2 and less than 45 MPa ^1/2, it is difficult to be impregnated with (swelling) by conventional liquid electrolyte batteries.

Non-limiting examples of such polymers include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-trichlorethylene, polymethylmethacrylate, But are not limited to, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, Cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylpolyvinylalcohol, Ethylcellulose (cyanoethylcellulose), shea Cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and the like.

The composition ratio of the inorganic particles and the binder polymer in the porous coating layer coated on the nonwoven fabric substrate according to the present invention is preferably in the range of, for example, 50:50 to 99: 1, more preferably 70:30 to 95: 5. When the content ratio of the inorganic particles to the binder polymer is less than 50:50, the content of the polymer is increased and the pore size and porosity of the porous coating layer may be reduced. If the content of the inorganic particles exceeds 99 parts by weight, the fillerability of the porous coating layer may be weakened because the content of the binder polymer is small. The pore size and porosity of the porous coating layer are not particularly limited, but the pore size is preferably in the range of 0.001 to 10 mu m, and the porosity is preferably in the range of 10 to 90%. The pore size and porosity mainly depend on the size of the inorganic particles. For example, when inorganic particles having a particle size of 1 탆 or less are used, pores formed are also about 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. When the pore size and the porosity are 0.001 탆 or less and 10% or less, respectively, it can act as a resistive layer. If the pore size and porosity exceed 10 탆 and 90% respectively, the mechanical properties may be deteriorated.

The binder polymer solution in which the inorganic particles are dispersed can be applied to the nonwoven substrate in a dispersed form by adding the inorganic particles to the binder polymer solution by dissolving the binder polymer in the solvent. It is preferable that the solvent has a solubility index similar to that of the binder polymer to be used and a low boiling point. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of usable solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone ( N-methyl-2-pyrrolidone, NMP), cyclohexane, water or a mixture thereof. It is preferable to add inorganic particles to the binder polymer solution and then crush the inorganic particles. In this case, the disintegration time is preferably 1 to 20 hours, and the particle size of the disintegrated inorganic particles is preferably 0.001 to 10 .mu.m as mentioned above. As the crushing method, a conventional method can be used, and a ball mill method is particularly preferable.

The binder polymer solution in which the inorganic particles are dispersed is coated on the nonwoven fabric substrate under a humidity condition of, for example, 10 to 80% and dried, and a conventional coating method known in the art can be used. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a combination thereof can be used. In addition, the porous coating layer can be selectively formed on both or only one side of the nonwoven base material. The porous coating layer formed according to such a coating method is present not only on the surface of the nonwoven fabric base material, but also because of the nature of the nonwoven fabric base material.

The separator of the present invention is interposed between the positive electrode and the negative electrode to be made of an electrochemical device. In this case, in the case of using a polymer capable of gelation upon impregnation with a liquid electrolyte as a binder polymer component, after the cell is assembled using the separator, the injected electrolyte may react with the polymer to gel.

The electrochemical device of the present invention includes all devices that perform an electrochemical reaction, and specific examples thereof include capacitors such as all kinds of primary, secondary cells, fuel cells, solar cells, and super capacitors . 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 is preferable.

The electrode to be used together with the separator of the present invention is not particularly limited, and the electrode active material may be bound to an electrode current collector according to a conventional method known in the art. Examples of the cathode active material include, but are not limited to, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a combination thereof It is preferable to use a lithium composite oxide. As a non-limiting example of the negative electrode active material, a conventional negative electrode active material that can be used for a negative electrode of an electrochemical device can be used. In particular, lithium metal or a lithium alloy, carbon, petroleum coke, activated carbon, Lithium-adsorbing materials such as graphite or other carbon-based materials and the like are preferable. Non-limiting examples of the positive current collector include aluminum, nickel, or a combination thereof. Examples of the negative current collector include copper, gold, nickel, or a copper alloy or a combination thereof Foil to be manufactured, and the like.

Electrolyte that may be used in the present invention is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, K ⁺ comprises an alkaline metal cation or an ion composed of a combination thereof, such as, and B ^- is PF _{6 ^{-, BF 4 -, Cl -}} , Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO _{2) 3} ^- anion, or a salt containing an ion composed of a combination of propylene carbonate (PC like), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC) , Dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma-butyrolactone, But are not limited to, those dissolved or dissociated in an organic solvent.

The electrolyte injection may be performed at an appropriate stage of the battery manufacturing process, depending on the manufacturing process and required properties of the final product. That is, it can be applied before assembling the cell or at the final stage of assembling the cell.

As a process for applying the separator of the present invention to a battery, lamination, stacking and folding processes of a separator and an electrode are possible in addition to a general winding process.

Claims (7)

A separator for a secondary battery, comprising a nonwoven fabric in which pores having a diameter in the range of 0.1 to 100 mu m are formed based on the longest diameter and pores having a maximum diameter of 10 to 100 mu m are filled with inorganic particles.
The method according to claim 1,
Wherein the inorganic particles have a maximum diameter of 5 to 100 占 퐉.
The method according to claim 1,
Wherein the inorganic particles are inorganic particles having a dielectric constant of 5 or more and lithium ion transferring ability or a mixture thereof.
The method of claim 3,
The inorganic particles is greater than or equal to the dielectric constant of _{5 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 ) 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 , TiO ₂ , SiC, or a mixture thereof.
The method of claim 3,
Wherein the inorganic particles having lithium ion transferring ability are lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3), lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), (LiAlTiP) _x O _y series glass <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), lithium germanium thiophosphate (Li _x Ge _y P _z S _w , (Li _x N _y , 0 <x <4, 0 <y <2), SiS ₂ series glass (Li _x Si, 0 <y <1, 0 <z < _{y S z, 0 <x <} 3, 0 <y <2, 0 <z <4), P 2 S 5 based _{glass (Li x P y S z} , 0 <x <3, 0 <y <3, 0 <z <7), and mixtures thereof.
A secondary battery comprising a separator for a secondary battery according to any one of claims 1 to 5.
The method according to claim 6,
Wherein the secondary battery is a lithium secondary battery.

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