KR100889207B1 - Organic/inorganic composite porous film and electrochemical device using the same - Google Patents

Abstract

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), an organic / inorganic composite porous film containing one or more inorganic particles composed of hafnia (HfO ₂ ) and used as a battery separator, and an electrochemical device including the organic / inorganic composite porous film.

The electrochemical device having the organic / inorganic composite porous film of the present invention can simultaneously improve safety and performance.

Inorganic materials, polymers, pores, films, separators, electrolytes, lithium secondary batteries, electrochemical devices

Description

Organic / inorganic composite porous film and electrochemical device using the same {ORGANIC / INORGANIC COMPOSITE POROUS FILM AND ELECTROCHEMICAL DEVICE USING THE SAME}

1 is a schematic diagram of an organic / inorganic composite porous film prepared according to the present invention.

FIG. 2 is a scanning electron microscope (SEM) photograph of the organic / inorganic composite porous film (PVdF-HFP / BaTiO ₃ ) prepared in Example 1. FIG.

3 is a SEM photograph of the polyolefin-based separator (PP / PE / PP) used in Comparative Example 1.

4 is an SEM photograph of a porous film prepared using a plasticizer according to Comparative Example 4.

5 is a photograph of the organic / inorganic composite porous film (PVdF-HFP / BaTiO ₃ ), commercially available PP / PE / PP separator and PE separator prepared in Example 1 after being left at 150 ° C. for 1 hour.

6 is an overcharge experiment of lithium secondary batteries of Comparative Examples 1 and 1 each equipped with a commercialized PP / PE / PP separator and an organic / inorganic composite porous film (PVdF-HFP / BaTiO ₃ ) prepared in Example 1, respectively. Comparison picture.

7 is a graph showing the change in the ionic conductivity according to the content change of the inorganic particles in the organic / inorganic composite porous film of the present invention.

The present invention is an organic / inorganic composite porous film of a new concept that can exhibit excellent thermal stability, excellent lithium ion conductivity, and electrolyte impregnation rate compared to the conventional polyolefin-based separator, and an electrochemical device which simultaneously improves safety and improves performance. It is about.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders, notebooks and PCs, and even electric vehicles, efforts for research and development of batteries are becoming more concrete. The electrochemical device is the most attracting field in this respect, and among them, the development of a secondary battery capable of charging and discharging has been the focus of attention.

Secondary batteries are chemical cells capable of repeating charging and discharging using reversible interconversion of chemical and electrical energy, and are classified into Ni-MH secondary batteries and lithium secondary batteries. Lithium secondary batteries include lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries or lithium ion polymer secondary batteries.

Lithium secondary batteries are currently produced by many companies because of their high operating voltage and high energy density, compared to conventional Ni-MH batteries using aqueous electrolyte solutions, but their safety characteristics are different. The safety evaluation and safety of the battery are the most important considerations, and accordingly, the safety standard of the lithium secondary battery strictly regulates ignition and smoke in the battery.

Lithium ion batteries and lithium ion polymer batteries currently in production use polyolefin-based separators to prevent short circuits between the positive and negative electrodes. Since the polyolefin-based separator has a property of melting at 200 ° C. or lower, when the battery rises to a high temperature due to internal and / or external magnetic poles, a volume change such as shrinkage or melting of the separator occurs. An explosion may occur due to a short circuit, the release of electrical energy, or the like. Therefore, there is a demand for development of a separator in which heat shrinkage does not occur at high temperatures.

In order to improve the above problems of the polyolefin-based separator, there have been many attempts to develop an electrolyte to which an inorganic material can be substituted for the conventional separator. The first is to prepare a composite solid electrolyte by using inorganic particles having lithium ion transfer capability alone or by mixing inorganic particles and polymer matrix having lithium ion transfer capability (Japanese Laid-Open Publication No. 2003-022707; Solid State Ionics , vol. 158, n.3, p275, 2003; Journal of Power Sources , vol. 112, n.1, p209, 2002; Electrochimica Acta , vol. 48, n. 14, p2003, 2003). However, it is known that no further progress has been made due to the lower ionic conductivity of inorganic materials and the increase of interfacial resistance between inorganic materials and polymers when mixed with polymers.

Second, an electrolyte is prepared by mixing an inorganic particle having no or no lithium ion transfer capacity with a gel polymer electrolyte composed of a polymer and a liquid electrolyte. In this case, the inorganic material is added in a small amount compared to the polymer and the liquid electrolyte, and has an auxiliary function to assist the lithium ion transfer made by the liquid electrolyte.

However, the electrolyte prepared as described above did not faithfully serve as a separator even if no pores existed in the electrolyte or even if there were pores, due to the pore size and low porosity of the angstrom unit formed by artificial plasticizer injection. This necessitated a decrease in battery performance.

The present inventors have found that organic / inorganic composite porous films formed using (1) inorganic particles and (2) binder polymers as components may not only improve the weak thermal stability of conventional polyolefin-based separators, but are also formed by inorganic particles in the film. The pore structure of the micro unit increases the space for the liquid electrolyte to increase the lithium ion conductivity and the electrolyte impregnation rate, thereby simultaneously improving the performance and safety of the electrochemical device using the organic / inorganic composite porous film as a separator. It turns out that you can.

Accordingly, an object of the present invention is to provide an organic / inorganic composite porous film and a manufacturing method thereof, and an electrochemical device including the same, which can improve both performance and safety of an electrochemical device.

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), an organic / inorganic composite porous film containing at least one inorganic particle composed of hafnia (HfO ₂ ) and used as a battery separator, and an electrochemical device comprising the organic / inorganic composite porous film, preferably lithium secondary Provide a battery.

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EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention not only faithfully performs the function of the conventional separator for passing ions while preventing electronic contact between the positive electrode and the negative electrode of the battery, and a new concept of organic / inorganic composite showing thermal safety, excellent lithium ion conductivity, and electrolyte impregnation rate. It is the biggest feature to provide a porous film.

The organic / inorganic composite porous film is manufactured by using inorganic particles and a binder polymer as a constituent component, and at this time, the separator is formed due to the uniform and heat resistant micro-unit pore structure formed by the interstitial volume between the inorganic particles. Can be used as In addition, in the case of using a gelable polymer when impregnating a liquid electrolyte as a binder polymer component, it may be used simultaneously as an electrolyte.

If more specific description of the characteristics of the organic / inorganic composite porous film, as follows.

1) The present invention may exhibit thermal safety due to the inorganic particles which are components of the organic / inorganic composite porous film.

That is, in the conventional polyolefin-based separator, since the melting point is 120 to 140 ° C., heat shrinkage occurs at high temperature. However, the organic / inorganic composite porous film made of the inorganic particles and the binder polymer does not generate high temperature heat shrinkage due to the heat resistance of the inorganic particles. Therefore, in the electrochemical device using the organic / inorganic composite porous film as a separator, the safety deterioration due to the internal short circuit of the anode / cathode does not occur at all even under excessive conditions such as high temperature and overcharging, and thus it is very safe compared to conventional batteries. Will be displayed.

2) The solid electrolyte prepared using the inorganic particles and the binder polymer in the related art is non-uniform even though there is no pore structure or no pore in the electrolyte, and is non-uniform and allows lithium ions to pass through due to the pore size and pore structure of the angstrom unit. Failed to perform the role of a spacer faithfully, this caused a deterioration of the performance of the battery. In contrast, the organic / inorganic composite porous film of the present invention has a plurality of pore structures of uniform micro units due to the void space between the inorganic particles, as shown in FIGS. Smooth movement is achieved, and a large amount of electrolyte can be filled to exhibit a high impregnation rate, so that the performance of the battery can be improved together.

3) The organic / inorganic composite porous film can adjust pore size and porosity by varying the particle diameter of the inorganic particles as a component or the composition ratio of the inorganic particles and the polymer. This pore structure is filled with the liquid electrolyte injected later, which results in a significant reduction in the interfacial resistance generated between the inorganic particles or between the inorganic particles and the binder polymer.

4) When the inorganic particles, which are components of the organic / inorganic composite porous film, have a high dielectric constant, lithium ion conductivity can be improved as well as heat resistance of the inorganic particles, thereby improving performance of the battery.

5) In addition, when the binder polymer which is a component of the organic / inorganic composite porous film is a polymer having an excellent electrolyte solution impregnation rate, the electrolyte injected after battery assembly is permeated into the polymer, and the polymer having the absorbed electrolyte is electrolyte ions. You will have the ability to evangelize. Therefore, it is possible to improve the performance of the electrochemical device as compared to the conventional organic / inorganic composite electrolyte. In addition, compared with the conventional hydrophobic polyolefin-based separator, the wettability of the battery electrolyte is improved and the polar electrolyte solution for the battery, which has been difficult to be used in the related art, is also possible.

6) In addition, in the case where the polymer is a gelable polymer when the electrolyte is impregnated, then the injected electrolyte and the polymer may react to gel to form a gel-type organic / inorganic composite electrolyte. The electrolyte thus formed is easier to manufacture than conventional gel electrolytes, and exhibits high ion conductivity and electrolyte impregnation rate, thereby improving battery performance.

One of the main components of the organic / inorganic composite porous film according to the present invention is Pb (Zr, Ti) O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT), PB (Mg ₃ At least one inorganic particle consisting of Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT) and hafnia (HfO ₂ ). The inorganic particles serve as a main component for producing the final organic / inorganic composite porous film, and form micro pores by enabling an interstitial volume between the inorganic particles. It also serves as a kind of spacer to maintain physical shape. In addition, since the inorganic particles generally have a property that physical properties do not change even at a high temperature of 200 ° C. or more, the formed organic / inorganic composite porous film has excellent heat resistance.

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as the oxidation and / or reduction reactions do not occur in the operating voltage range of the battery to be applied (for example, 0 to 5 V on the basis of Li / Li ⁺ ). In particular, in the case of using the inorganic particles having the ion transfer ability, since the ion conductivity in the electrochemical device can be improved to improve the performance, it is preferable that the ion conductivity is as high as possible. In addition, when the inorganic particles have a high density, it is not only difficult to disperse during coating, but also has a problem of weight increase during battery manufacturing, and therefore, the smallest density is desirable. In addition, in the case of the inorganic material having a high dielectric constant, it is possible to improve the dissociation degree of the electrolyte salt, such as lithium salt, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte solution.

For the above reasons, the inorganic particles are preferably high dielectric constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more.

Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1 - x} La _x Zr _{1 - y} Ti _y O ₃ (PLZT), PB (Mg _{3 Nb 2/3) O 3 -PbTiO} 3 (PMN-PT), hafnia (HfO 2), SrTiO 3, SnO 2, CeO 2, MgO, NiO, CaO, ZnO, ZrO 2, Y 2 O 3, Al 2 O ₃ , TiO _{2 ,} SiC Or mixtures thereof.

In the present invention, the non-reactive used as a conventional coating material; In addition, the inorganic particles having higher dielectric constant characteristics than the low dielectric constant inorganic particles are used, as well as the use of inorganic particles that have not been used conventionally is characterized in using a new membrane application.

Mineral particles that have not been conventionally used, i.e., _{Pb (Zr, Ti) O 3} (PZT), Pb 1 - x La x Zr 1 - yTi y O 3 (PLZT), PB (Mg 3 Nb 2/3) O 3 - PbTiO ₃ (PMN-PT) and hafnia (HfO ₂ ) not only exhibit high dielectric constants with dielectric constants of more than 100, but also piezoelectricity, in which electric charges occur when tension or compression is applied under constant pressure, resulting in a potential difference between both sides. By having this, the internal short circuit of the positive electrode due to external impact can be prevented and the safety of the battery can be fundamentally improved. In addition, the synergistic effect of the above-described high dielectric constant inorganic particles may be doubled.

The organic / inorganic composite porous film of the present invention can form pores in micro units by adjusting the size of inorganic particles, the content of inorganic particles, and the composition of inorganic particles and polymers, and also control pore size and porosity. Can be.

The size of the inorganic particles is not limited, but is preferably in the range of 0.001 to 10 μm as much as possible for film formation and proper porosity of uniform thickness. If the thickness is less than 0.001㎛, it is difficult to control the physical properties of the organic / inorganic composite porous film because the dispersibility is lowered. If the thickness is more than 10㎛, the thickness of the organic / inorganic composite porous film manufactured with the same solids content is increased, thereby decreasing the mechanical properties. In addition, due to the excessively large pore size, there is a high probability that an internal short circuit occurs during battery charging and discharging.

The content of the inorganic particles is preferably in the range of 50 to 99% by weight, more preferably 60 to 95% by weight, per 100% by weight of the mixture of the inorganic particles and the binder polymer constituting the organic / inorganic composite porous film. If the content is less than 50% by weight, the content of the polymer may be excessively large, resulting in a decrease in pore size and porosity due to a decrease in the void space formed between the inorganic particles, resulting in deterioration of final battery performance. If the content exceeds 99% by weight, the polymer content is too small, and the mechanical properties of the final organic / inorganic composite porous film are reduced due to the weakening of the adhesion between the inorganic materials.

The other one of the main components of the organic / inorganic composite porous film according to the present invention is a polymer commonly used in the art. In particular, it is possible to use a glass transition temperature (T _g ) as low as possible, preferably in the range of -200 to 200 ℃. This is because the mechanical properties such as flexibility and elasticity of the final film can be improved. The polymer faithfully plays a role of a binder for stably connecting and stably connecting the inorganic particles and the particles, thereby contributing to the prevention of mechanical property deterioration of the organic / inorganic composite porous film to be manufactured.

In addition, the binder polymer does not necessarily have an ion conducting ability, but when the polymer having an ion conducting ability is used, the performance of the electrochemical device may be further improved. Therefore, the binder polymer is preferably as high as possible dielectric constant. In fact, since the dissociation degree of the salt in the electrolyte depends on the dielectric constant of the electrolyte solvent, the higher the dielectric constant of the polymer, the higher the salt dissociation in the electrolyte of the present invention. The dielectric constant of the polymer may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), particularly preferably 10 or more.

In addition to the functions described above, the binder polymer of the present invention may have a feature that can exhibit a high degree of swelling of the electrolyte by gelling when the liquid electrolyte is impregnated. In this way, and a solubility parameter of 15 to 45 MPa ^1/2 is preferably a polymer, more preferably from 15 to 25 MPa ^1/2, and 30 to 45 MPa ^1/2 range. Therefore, hydrophilic polymers having more polar groups than hydrophobic polymers such as polyolefins are preferable. 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 binder polymers that can be used include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, Polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer, polyethylene oxide ( polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol Cyanoethylcellulose (cyanoeth ylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide or these And mixtures thereof. In addition, any material can be used singly or in combination as long as it contains the above-described properties.

The organic / inorganic composite porous film of the present invention may further include other additives in addition to the above-described inorganic particles and polymers.

When preparing the organic / inorganic composite porous film of the present invention using a mixture including inorganic particles and a binder polymer, three embodiments can be largely made, but not limited thereto.

The first is to form an organic / inorganic composite porous film alone using a mixture of inorganic particles and a polymer. The second is to form an organic / inorganic composite porous film by coating the mixture on a porous substrate having pores, wherein the film coated on the porous substrate has a surface of the porous substrate or a portion of the pores of the substrate of the inorganic particles and the polymer. It will comprise an active layer coated with a mixture. Third, an organic / inorganic composite porous film may be prepared by coating the mixture on the positive electrode and / or the negative electrode, wherein the prepared film is integrated with the electrode.

In the embodiment of the organic / inorganic composite porous film of the present invention, the porous substrate coated with the mixture containing the inorganic particles and the polymer is not particularly limited as long as it is a porous substrate including pores, and particularly, a heat resistant porous material having a melting temperature of 200 ° C. or higher. It is preferable that it is a base material. This is to improve the thermal safety of the organic / inorganic composite porous film which may be caused by external and / or internal heat stimulation. Non-limiting examples of the porous base material having the pore portion and the melting temperature of 200 ℃ or more include polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfidro, polyethylenenaphthalene (polyethylenenaphthalene) or mixtures thereof, and other heat-resistant engineering plastics can be used without limitation.

The thickness of the porous substrate is not particularly limited, but is preferably in the range of 1 to 100 μm, more preferably in the range of 5 to 50 μm. If it is less than 1㎛ it is difficult to maintain the mechanical properties, if it exceeds 100㎛ acts as a resistive layer.

Pore size and porosity of the porous substrate is not particularly limited, porosity is preferably 5 to 95%. The pore size (diameter) is preferably 0.01 to 50 µm, more preferably 0.1 to 20 µm. When the pore size and porosity are less than 0.01 μm and 10%, respectively, it acts as a resistive layer, and when the pore size and porosity exceeds 50 μm and 95%, it becomes difficult to maintain mechanical properties.

The porous substrate may be in the form of fibers or membranes, and in the case of fibers, a nonwoven fabric forming a porous web, and may be in the form of spunbond or melt blown composed of long fibers. desirable.

The spawn bond method is a single continuous process, receives heat and melts to form long fibers, and is stretched by hot air to form a web. The melt blown process is a process of spinning a polymer capable of forming a fiber through a spinneret formed of hundreds of small orifices. It is a three-dimensional fiber with a spider-web structure.

Organic / inorganic composite porous film that can be prepared in various embodiments according to the present invention is characterized in that it comprises a microstructured pore structure. First, the organic / inorganic composite porous film of the present invention prepared using only a mixture of inorganic particles and a polymer alone has micro pores due to the interstitial volume between the inorganic materials serving as a spacer and a spacer. The structure is formed. In addition, the organic / inorganic composite porous film of the present invention formed by coating the mixture on the porous substrate also includes pores in the porous substrate itself, and also due to the empty space between the inorganic particles formed on the substrate and the active layer All will form a pore structure. In addition, in the case of coating the mixture on the electrode surface, as in the electrode active material particles in the electrode to form a pore structure, due to the interstitial volume between the inorganic particles to achieve a uniform pore structure. Therefore, the organic / inorganic composite porous film of the present invention may exhibit an effect of increasing the diffusion and conductivity of lithium ions by increasing the space for the electrolyte solution through the pores of the formed micro-units, which is described above The performance of the battery can be improved.

The pore size and porosity of the organic / inorganic composite porous film mainly depend on the size of the inorganic particles. For example, when using inorganic particles having a particle diameter of 1 μm or less, the pores formed also exhibit 1 μm or less. The pore structure is filled with the electrolyte solution to be poured later, the electrolyte thus filled serves to transfer the ion. Therefore, the pore size and porosity are important influence factors for controlling the ionic conductivity of the organic / inorganic composite porous film. The pore size and porosity of the organic / inorganic composite porous film of the present invention is preferably in the range of 0.001 to 10㎛, 5 to 95%, respectively.

In addition, the thickness of the organic / inorganic composite porous film of the present invention is not particularly limited, and may be adjusted in consideration of battery performance. It is preferably in the range from 1 to 100 μm, more preferably in the range from 2 to 30 μm. By adjusting the thickness range, battery performance can be improved.

In the organic / inorganic composite porous film formed on the electrode according to the present invention, the composition of the inorganic particles and the polymer is not particularly limited, and may be adjusted according to the thickness and structure of the final film.

The organic / inorganic composite porous film of the present invention may be applied to a battery using a microporous separator, such as a polyolefin-based separator, depending on the characteristics of the final cell.

Organic / inorganic composite porous film according to the present invention can be prepared according to conventional methods known in the art, for example, (a) dissolving a polymer in a solvent to prepare a polymer solution; (b) adding and mixing the inorganic particles to the polymer solution prepared in step (a); And (c) coating and drying the mixture of step (b) on the substrate and then detaching the substrate.

First, 1) the polymer is dissolved in a suitable organic solvent to prepare a polymer solution.

As the solvent, the solubility index is similar to that of the binder polymer to be used, and the boiling point is preferably low. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone ( N-methyl-2-pyrrolidone, NMP), cyclohexane, water or a mixture thereof.

2) Inorganic particles are added and dispersed in the prepared polymer solution to prepare inorganic particles and polymer mixture.

It is preferable to grind | pulverize an inorganic particle after adding an inorganic particle to a polymer solution. In this case, the crushing time is suitably 1 to 20 hours, and the particle size of the crushed inorganic particles is preferably 0.001 to 10 탆 as mentioned above. As the shredding method, a conventional method can be used, and a ball mill method is particularly preferable.

The composition of the mixture consisting of inorganic particles and polymers is not particularly limited, and thus the thickness, pore size and porosity of the organic / inorganic composite porous film of the present invention can be adjusted.

That is, as the ratio (ratio = I / P) of the inorganic particles (I) to the polymer (P) increases, the porosity of the organic / inorganic composite porous film of the present invention increases, which is the same solid content (inorganic particle weight + Binder polymer weight), resulting in an increase in the thickness of the organic / inorganic composite porous film. In addition, the pore size of the inorganic particles increases, so that the pore size increases. At this time, as the size (particle diameter) of the inorganic particles increases, the interstitial distance between the inorganic particles increases, thereby increasing the pore size.

3) After coating and drying the prepared mixture of inorganic particles and polymer on the substrate (substrate), the organic / inorganic composite porous film of the present invention can be obtained by desorbing the substrate.

The substrate is preferably a teflon sheet or a similar film commonly used in the art, but is not particularly limited thereto.

In addition, the method of coating the mixture of the inorganic particles and the polymer on the substrate may use a conventional coating method known in the art, for example, dip coating, die coating, roll coating, Various methods, such as a comma coating or a mixing method thereof, can be used.

In the above step, when using a porous substrate having a pore or a pre-made electrode as a substrate, the organic / inorganic composite porous film of the above-described various embodiments can be prepared. In this case, the mixture of the inorganic particles and the polymer is coated by penetrating not only the surface of the porous substrate having pores, the surface of the electrode, but also a part of the pores of the substrate. In addition, a manufacturing process of desorption from the substrate is not required.

The organic / inorganic composite porous film of the present invention prepared as described above may be used as a separator of an electrochemical device, preferably a lithium secondary battery. In addition, it is possible to use a separator by coating a conventional polymer known in the art, such as an electrolyte impregnable polymer, on one or both surfaces of the organic / inorganic composite porous film.

In this case, when a gelable polymer is used when the liquid electrolyte solution is impregnated with the binder polymer component of the film, after the battery is assembled using the separator, the injected electrolyte and the polymer react with each other to form a gel-type organic / inorganic composite electrolyte. have.

The gel-type organic / inorganic composite electrolyte of the present invention is easier to manufacture than the gel polymer electrolyte of the prior art, and due to the micro-pore structure, a large amount of space to be filled with the injected liquid electrolyte provides high ionic conductivity and electrolyte impregnation rate. It can improve battery performance.

In addition, the present invention (a) a positive electrode; (b) a cathode; (c) the organic / inorganic composite porous film of the present invention interposed between the positive electrode and the negative electrode; And (d) provides an electrochemical device comprising an electrolyte.

Electrochemical devices include all devices that undergo an electrochemical reaction, and specific examples thereof include all kinds of primary, secondary cells, fuel cells, solar cells, or capacitors. In particular, 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 secondary batteries is preferable.

The organic / inorganic composite porous film included in the electrochemical device plays the role of a separator as in the present invention, and also plays a role of an electrolyte when using a gelable polymer when the liquid electrolyte is impregnated with a polymer among the film components.

In this case, in addition to the organic / inorganic composite porous film, a fine pore separation membrane may be additionally used. The micro pore separator may be a polyolefin-based separator or polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, With polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfidro and polyethylenenaphthalene It may be a porous substrate having a melting temperature of at least one selected from the group consisting of 200 ° C or more.

The electrochemical device may be manufactured according to conventional methods known in the art, and for example, an electrolyte may be injected after assembling the organic / inorganic composite porous film described above between an anode and a cathode. It can be manufactured by.

The electrode to be applied together with the organic / inorganic composite porous film of the present invention is not particularly limited, and according to a conventional method known in the art, the electrode active material may be prepared in a form bound to the electrode current collector. Non-limiting examples of the positive electrode active material of the electrode active material may be a conventional positive electrode active material that can be used for the positive electrode of the conventional electrochemical device, in particular lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide or Lithium intercalation materials such as composite oxides formed by combination are preferred. Non-limiting examples of the negative electrode active material may be a conventional negative electrode active material that can be used in the negative electrode of the conventional electrochemical device, in particular lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, Lithium adsorbents such as graphite or other carbons are preferred. Non-limiting examples of the positive electrode current collector is a foil produced by aluminum, nickel or a combination thereof, and non-limiting examples of the cathode current collector by copper, gold, nickel or copper alloy or a combination thereof Foils produced.

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 ) Salts containing ions consisting of anions such as ₃ ^- or combinations thereof include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC) , Dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethylcarbonate (EMC), gamma butyrolactone (γ-butyrolactone Or dissolved in an organic solvent consisting of a mixture thereof, but is not limited thereto.

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

In the process of applying the organic / inorganic composite porous film of the present invention as a battery, a lamination (stacking) and folding (folding) process of the separator and the electrode may be performed in addition to the general winding process.

When the organic / inorganic composite porous film of the present invention is applied to the lamination process in the above process, the thermal safety improvement effect of the battery becomes remarkable. This is due to the heat shrinkage of the separator in the battery produced by the lamination and folding process is more severe than the battery produced by the general winding process. In addition, the lamination (lamination, stack) process has the advantage that can be easily assembled due to the excellent adhesive properties of the polymer in the organic / inorganic composite porous film of the present invention. At this time, the adhesion properties may be controlled by the content of the inorganic particles and the polymer or the physical properties of the polymer, in particular, the more polar the polymer, the glass transition temperature (T _g ) or melting temperature (melting) The lower the point, Tm), the better the adhesion between the organic / inorganic composite porous film and the electrode of the present invention.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

Reference Example . Ion Conductivity Variation with Changes in Inorganic Particle Content

The change of the ionic conductivity according to the content change of the inorganic particles used in the organic / inorganic hybrid system of the present invention was observed.

The organic / inorganic composite porous film prepared according to the present invention is ethylene carbonate / propylene carbonate / diethyl carbonate in which 1 M lithium hexafluorophosphate (LiPF ₆ ) is dissolved (EC / PC / DEC = 30: 20: 50 wt% After impregnation with) -based electrolyte solution, the film impregnated with the electrolyte solution was measured using a Metrohm 712 instrument. At this time, the measurement temperature was 25 degreeC.

As shown in FIG. 7, it could be seen that as the content of the inorganic particles is increased, the ionic conductivity is improved. In particular, when the inorganic particles are used at 50 wt% or more, the ionic conductivity is remarkably improved.

[ Example  1 ~ 7. Organic / inorganic composite porous film and lithium secondary battery manufacturing using same]

Example  One

1-1. Organic / Inorganic Composite Porous Film ( PVdF - HFP  Of BaTiO ₃ ) Produce

A polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) polymer was added to tetrahydrofuran (THF) about 5% by weight, and then dissolved at a temperature of 50 ° C. for about 12 hours or more to prepare a polymer solution. . BaTiO ₃ powder having a particle size of about 400 nm was added to this polymer solution at 20 wt% of total solids and dispersed to prepare a mixed solution (BaTiO ₃ / PVdF-HFP = 80: 20 (weight ratio)). The mixed solution prepared using the doctor blade method was coated on a Teflon sheet substrate. After coating, THF. After drying, it was detached from a Teflon sheet to obtain a final organic / inorganic composite porous film (see FIG. 1). The final film thickness was about 30 μm. As a result of measuring by a porosimeter, the pore size and porosity of the final organic / inorganic composite porous film were 0.4 μm and 60%, respectively.

1-2. Lithium secondary battery manufacturing

(Anode manufacturing)

A positive electrode mixture slurry was prepared by adding 94 wt% of LiCoO ₂ as a cathode active material, 3 wt% of carbon black as a conductive agent, and 3 wt% of PVdF as a binder to N-methyl-2 pyrrolidone (NMP) as a solvent. . The positive electrode mixture slurry was coated and dried on a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, which is a positive electrode current collector.

(Cathode production)

A negative electrode mixture slurry was prepared by adding carbon powder as a negative electrode active material, PVdF as a binder, and carbon black as a conductive agent at 96 wt%, 3 wt%, and 1 wt%, respectively, to NMP as a solvent. The negative electrode mixture slurry was coated and dried on a thin film of copper (Cu), which is a negative electrode current collector having a thickness of 10 μm, to prepare a negative electrode.

(Battery manufacturing)

The positive electrode, the negative electrode, and the organic / inorganic composite porous film prepared in Example 1-1 were assembled using a stacking method, and 1M lithium hexafluorophosphate (LiPF ₆ ) was dissolved in the assembled battery. An ethylene carbonate / propylene carbonate / diethyl carbonate (EC / PC / DEC = 30: 20: 50% by weight) based electrolyte was injected to prepare a lithium secondary battery.

Example  2

The BaTiO ₃ powder instead of BaTiO ₃ / Al ₂ O ₃ is used for the inorganic particle powder mixing ratio 20: 80% by weight of organic / inorganic composite porous film, except that the Preparation _{(PVdF - Al 2 O 3 -} HFP / BaTiO 3) Then, it carried out similarly to Example 1, and manufactured the lithium secondary battery. As a result of measuring the porosity, the final organic / inorganic composite porous film had a thickness of 25 μm, and the pore size and porosity were 0.3 μm and 57%, respectively.

Example  3

Use PMNPT powder instead of BaTiO ₃ powder, the organic / inorganic composite porous film was prepared, and the lithium secondary battery in the same manner as in Example 1 except that the Preparation (PVdF HFP / PMNPT). As a result of measuring by the porosity measuring device, the final organic / inorganic composite porous film thickness was 30㎛, pore size and porosity were 0.3㎛ and 60%, respectively.

Example  4

Carboxyl Methyl Cellulose (CMC) polymer was added to water instead of PVdF-HFP and dissolved in water at a temperature of 60 ° C. for at least 12 hours to prepare a polymer solution. A lithium secondary battery was manufactured in the same manner as in Example 1, except that the inorganic / inorganic composite porous film ( CMC / BaTiO ₃ ) was prepared. As a result of measuring by the porosity measuring device, the thickness of the final organic / inorganic composite porous film was 25 μm, and the pore size and porosity were 0.4 μm and 58%, respectively.

Example  5

BaTiO ₃ powder in place of using the PZT powder, organic / inorganic composite porous film (PVdF - HFP / PZT) was manufactured in the same manner as in Example 1, except that a lithium secondary battery was prepared. As a result of measuring by the porosity measuring device, the final organic / inorganic composite porous film thickness was 25 μm, and the pore size and porosity were 0.4 μm and 62%, respectively.

Example  6

A lithium secondary battery was manufactured in the same manner as in Example 1, except that an organic / inorganic composite porous film ( PVDF - HFP / PLZT) was manufactured using PLZT powder instead of BaTiO ₃ powder. As a result of measuring by the porosity measuring device, the final organic / inorganic composite porous film thickness was 25㎛, pore size and porosity were 0.3㎛ and 58%, respectively.

Example  7

Organic / Inorganic Composite Porous Films ( PVDF - HFP) using HfO ₂ powder instead of BaTiO ₃ powder / HfO ₂ ) was prepared in the same manner as in Example 1, except that a lithium secondary battery was prepared. As a result of measuring by the porosity measuring device, the final organic / inorganic composite porous film thickness was 28㎛, pore size and porosity were 0.4㎛ and 60%, respectively.

[ Comparative example  1 to 3]

Comparative example  One

A lithium secondary battery was manufactured in the same manner as in Example 1, except that a conventional PP / PE / PP separator (see FIG. 3) was used.

Comparative example  2

An organic / inorganic composite porous film and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that the composition ratio of BaTiO ₃ and PVdF-HFP was used in a 20:80 wt% ratio. As a result of measuring the prepared BaTiO ₃ / PVdF-HFP by the porosity measuring device, the pore size of the organic / inorganic composite porous film was less than 0.01㎛, porosity was 10% level.

Comparative example  3. Preparation of Porous Film Using Plasticizer

After selecting dimethyl carbonate (DMC) as a plasticizer, the composition ratio of PVdF-HFP was 30: 70% by weight, and THF was used as a solvent to prepare a porous film. To prepare a final porous film and a lithium secondary battery comprising the same. As a result of measuring the prepared PVdF-HFP porous film with a porosity measuring device, the pore size was 0.01 μm or less, and the porosity was 30% (see FIG. 4).

Experimental Example  1. Surface analysis of organic / inorganic composite porous film

In order to analyze the surface of the organic / inorganic composite porous film prepared according to the present invention, the following experiment was performed.

As a sample, a PVdF-HFP / BaTiO ₃ film prepared in Example 1 was used, and a PP / PE / PP separator of Comparative Example 1 and a porous film using a plasticizer in Comparative Example 4 were used as controls.

As a result of confirming the surface by Scanning Electron Microscope (SEM), the PP / PE / PP separator of Comparative Example 1 and the porous film of Comparative Example 4 showed a conventional microporous structure (see FIGS. 3 and 4). . In particular, it could be seen that the porous film of Comparative Example 4 had a dense pore structure formed separately from the inorganic particles present on the surface of the film, which was determined by artificial plasticizer extraction.

In contrast, it can be seen that the organic / inorganic composite porous film of the present invention has micropores formed by inorganic particles, for example, inorganic particles having high dielectric constant. In addition, it was confirmed that the polymer is coated on the surface of the inorganic particles (see FIG. 2).

Experimental Example  2. Heat Shrinkage Analysis of Organic / Inorganic Composite Porous Films

In order to compare the organic / inorganic composite porous film prepared according to the present invention with a conventional separator, the following experiment was performed.

As a sample, a PVdF-HFP / BaTiO ₃ film prepared in Example 1 was used, and a PP / PE / PP separator and a PE separator were used as controls.

After leaving each of the samples at a temperature of 150 ° C. for 1 hour and collecting and confirming them, when 1 hour had elapsed at a temperature of 150 ° C., they showed different aspects. As a control group, the PP / PE / PP separator showed shrinkage due to high temperature and almost remained in shape, and the PE separator showed a significant shrinkage of about 1/10. In comparison, the organic / inorganic composite porous film of the present invention showed a good state in which no heat shrinkage was observed (see FIG. 5).

As a result, it was confirmed that the organic / inorganic composite porous film of the present invention has excellent thermal stability.

Experimental Example  3. Safety Evaluation of Lithium Secondary Battery

In order to evaluate the safety of the lithium secondary battery including the organic / inorganic composite porous film prepared in the present invention, it was performed as follows.

The lithium secondary batteries prepared in Examples 1 to 7 were used, and the BaTiO ₃ / PVdF-HFP film consisting of a battery of Comparative Example 1 using a commercially available PP / PE / PP separator as a control and a ratio of 20:80 wt% was used as a separator. The battery of Comparative Example 2 used was used.

3-1. Hot Box  Experiment

Each cell was stored at 150 ° C. and 160 ° C. for 1 hour, respectively, after which the state of the cell is shown in Table 1 below.

As a result, the battery of Comparative Example 1 using a commercialized PP / PE / PP separator exhibited an explosion phenomenon of the battery when stored for 1 hour at a temperature of 160 ℃. This means that severe thermal contraction and melt fracture of the polyolefin-based separator proceeded by high temperature storage, causing internal short circuits of the positive electrode and the negative electrode of the battery. In comparison, the lithium secondary battery including the organic / inorganic composite porous film prepared in the present invention showed no ignition and combustion even at a high temperature of 160 ° C., and showed a safe state (see Table 1).

As a result, it was confirmed that the lithium secondary battery including the organic / inorganic composite porous film of the present invention had excellent thermal safety.

Hot Box Experiment Conditions 150 ℃ / 1 hour 160 ℃ / 1 hour Example 1 O O Example 2 O O Example 3 O O Example 4 O O Example 5 O O Example 6 O O Example 7 O O Comparative Example 1 O X Comparative Example 2 O O

3-2. Overcharge Experiment

Each battery was charged under the conditions of 6V / 1A and 10V / 1A, and then the state of the battery is described in Table 2 below.

As a result, the battery of Comparative Example 1 using a commercialized PP / PE / PP separator exhibited an explosion phenomenon (see Figure 6). This indicates that overcharging of the battery causes short-circuits of the electrodes due to shrinkage of the polyolefin-based separator and a decrease in safety of the battery. In comparison, the lithium secondary battery including the organic / inorganic composite porous film prepared in the present invention showed a safe state during overcharging (see Table 2 and FIG. 6).

Overcharge Experiment Conditions 6V / 1A 10V / 1A Example 1 O O Example 2 O O Example 3 O O Example 4 O O Example 5 O O Example 6 O O Example 7 O O Comparative Example 1 X X Comparative Example 2 O O

Experimental Example  4. Performance Evaluation of Lithium Secondary Battery

In order to measure the charge and discharge capacity of the lithium secondary battery including the organic / inorganic composite porous film prepared in the present invention, it was performed as follows.

The lithium secondary batteries prepared in Examples 1 to 7 were used, and the BaTiO ₃ / PVdF-HFP film consisting of a battery of Comparative Example 1 using a commercially available PP / PE / PP separator as a control and a ratio of 20:80 wt% was used as a separator. The battery of Comparative Example 3 using the PVdF-HFP porous film prepared using the battery of Comparative Example 2 and the plasticizer used as a separator was used.

Each battery having a battery capacity of 760 mAh was cycled at a discharge rate of 0.5 C, 1 C, and 2 C, and their discharge capacities are shown in Table 3 by plotting C-rate characteristics.

As a result, the battery of Comparative Example 2 using an organic / inorganic composite porous film having a composition ratio of high dielectric constant inorganic particles and a binder polymer in a ratio of 20: 80% by weight was used in the organic / inorganic composite porous film prepared in all Examples of the present invention. And it was shown that the capacity for each discharge rate is significantly reduced compared to the battery using a conventional polyolefin-based separator (see Table 3). This means that the amount of the inorganic particles is relatively smaller than that of the polymer, so that the pore size and porosity formed by the void space between the inorganic particles significantly decrease, resulting in deterioration of the battery performance. In addition, the battery of Comparative Example 3 using a porous film having an artificial pore structure formed by using a plasticizer as a separator also showed that the capacity for each discharge rate was significantly reduced, similar to the battery of Comparative Example 2.

In contrast, the lithium secondary battery having the organic / inorganic composite porous film of the present invention showed high-rate discharge (C-rate) characteristics comparable to the conventional polyolefin-based separator up to a discharge rate of 2C (see Table 3).

Discharge rate (mAh) 0.5C 1C 2C Example 1 757 746 694 Example 2 756 748 693 Example 3 756 744 691 Example 4 758 747 694 Example 5 759 750 698 Example 6 755 742 690 Example 7 758 747 694 Comparative Example 1 758 746 693 Comparative Example 2 695 562 397 Comparative Example 3 698 585 426

As described above, the organic / inorganic composite porous film of the present invention is connected and fixed between the inorganic particles due to the binder polymer, and due to the interstitial volume between the inorganic particles, the main component of the film, Since the pore structure is formed to increase the space to be filled with the electrolyte solution to improve the electrolyte impregnation rate and lithium ion conductivity, the lithium secondary battery using this as a separator can improve thermal safety and performance.

Claims (17)

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), An organic / inorganic composite porous film containing at least one inorganic particle composed of hafnia (HfO ₂ ) and used as a battery separator. The method of claim 1, wherein the organic / inorganic composite porous film (a) inorganic particles; And (b) a binder polymer coating layer formed on part or all of the surface of the inorganic particles, An inorganic / organic composite porous film, wherein the inorganic particles are connected and fixed by the binder polymer, and micropores are formed due to an interstitial volume between the inorganic particles. delete The organic / inorganic composite porous film of claim 1, wherein the inorganic particles have a size ranging from 0.001 to 10 μm. The organic / inorganic composite porous film of claim 2, wherein the content of the inorganic particles is 50 to 99 wt% per 100 wt% of the mixture including the inorganic particles and the binder polymer. The organic / inorganic composite porous film of claim 2, wherein the binder polymer has a glass transition temperature (T _g ) of −200 to 200 ° C. 4. The organic / inorganic composite porous film of claim 2, wherein the binder polymer has a solubility parameter in the range of 15 to 45 MPa ^1/2 . The method of claim 2, wherein the binder polymer is polyvinylidene fluoride-hexafluoropropylene (polyvinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride-co-trichloroethylene (polyvinylidene fluoride-co-trichloroethylene), Polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer, polyethylene oxide (polyethylene oxide), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol ), Cyanoethylcellulose, Selected from the group consisting of cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer and polyimide At least one organic / inorganic composite porous film. The organic / inorganic composite porous film of claim 1, wherein the pore size of the organic / inorganic composite porous film is in a range of 0.001 to 10 μm. The organic / inorganic composite porous film of claim 1, wherein the porosity of the organic / inorganic composite porous film is in a range of 5 to 95%. The organic / inorganic composite porous film of claim 1, wherein the organic / inorganic composite porous film has a thickness in a range of 1 to 100 μm. (a) an anode; (b) a cathode; (c) an organic / inorganic composite porous film according to any one of claims 1, 2, and 4 to 11, interposed between the positive electrode and the negative electrode; And (d) electrolyte Electrochemical device comprising a. The electrochemical device of claim 12, wherein the electrochemical device is a lithium secondary battery. The electrochemical device of claim 12, wherein the electrochemical device further comprises a microporous separator. 15. The method of claim 14, wherein the microporous separator is a polyolefin-based separator or polyethylene terephthalate (polyethyleneterephthalate), polybutylene terephthalate (polybutyleneterephthalate), polyester (polyester), polyacetal, polyamide, polyamide, poly Consists of carbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfidro and polyethylenenaphthalene An electrochemical device which is a porous substrate having a melting temperature of at least 200 ° C. selected from the group. delete delete

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