阅读说明：本技术 多孔隔板和包括所述多孔隔板的锂二次电池 (Porous separator and lithium secondary battery comprising same ) 是由 崔雄喆 崔净勋 姜龙熙 张民哲 尹锡逸 孙炳国 于 2019-10-11 设计创作，主要内容包括：本发明涉及一种多孔隔板和一种包括所述多孔隔板的锂二次电池,所述多孔隔板包括：多孔层和形成在所述多孔层的任一表面上的金属层,所述多孔层包含多个板状无机颗粒和位于所述板状无机颗粒的部分或全部表面上以连接和固定所述板状无机颗粒的第一粘合剂聚合物。(The present invention relates to a porous separator and a lithium secondary battery including the same, the porous separator including: and a metal layer formed on either surface of the porous layer, the porous layer comprising a plurality of plate-like inorganic particles and a first binder polymer located on a part or all of the surface of the plate-like inorganic particles to attach and fix the plate-like inorganic particles.)

1. A porous separator comprising a porous layer and a metal layer formed on either surface of the porous layer, the porous layer comprising a plurality of plate-like inorganic particles and a first binder polymer located on a part or all of the surface of the plate-like inorganic particles to bind and fix the plate-like inorganic particles.

2. The porous separator according to claim 1, further comprising a ceramic coating layer formed on the other surface of the porous layer.

3. The porous separator according to claim 1, wherein the plate-like inorganic particles are alumina, silica, zirconia, titania, magnesia, ceria, yttria, zinc oxide, iron oxide, barium titanium oxide, alumina-silica composite oxide, or a mixture of two or more thereof.

4. The porous separator according to claim 1, wherein the plate-like inorganic particles have an aspect ratio of 5 to 100.

5. The porous separator according to claim 1, wherein the plate-like inorganic particles have an aspect ratio of 50 to 100.

6. The porous separator of claim 1, wherein the metal layer comprises Li capable of reacting with lithium to form Li_xMetal (M) of an alloy (alloy) of M (x ═ 1 to 2.25).

7. The porous separator of claim 1, wherein the metal layer comprises at least one metal selected from the group consisting of Al, In, Au, Ni, and Mg.

8. The porous separator of claim 1, wherein the metal layer has a thickness of 0.01 μ ι η to 1 μ ι η.

9. The porous separator of claim 2, wherein the ceramic coating has a dielectric constant of 20 to 1000.

10. The porous separator of claim 2, wherein the ceramic coating comprises a material selected from the group consisting of HfO₂、ZrO₂、BaSrTiO₃And PbLaZrTiO₃At least one inorganic particle of the group consisting of.

11. The porous separator of claim 1, wherein the porous layer further comprises spherical inorganic particles.

12. A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is the porous separator of claim 1.

13. The lithium secondary battery according to claim 12, wherein the anode and the metal layer of the porous separator are in contact with each other.

14. The lithium secondary battery according to claim 12, wherein the lithium secondary battery comprises lithium metal or a lithium alloy in the anode.

Technical Field

This application claims priority to korean patent application No. 10-2018-0122101, filed on 12.10.2018, the entire contents of which are incorporated herein by reference.

The present invention relates to a porous separator capable of blocking lithium ion dendrites and having improved high-temperature safety due to excellent thermal properties, and a lithium secondary battery including the same.

Background

Recently, there has been an increasing interest in energy storage technology. As its application field is expanded to energy sources of mobile phones, camcorders, notebook computers, and even electric vehicles, research and development work on electrochemical devices is being carried out more and more specifically. In this regard, electrochemical devices are the most interesting field, and development of secondary batteries capable of charging/discharging among electrochemical devices is a focus of attention. Recently, in developing these batteries, research and development on novel electrode and battery designs have been conducted to improve capacity density and specific energy.

Among the currently used secondary batteries, the lithium secondary battery developed in the early 90 s of the 20 th century received much attention because of its advantage of having higher operating voltage and energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries using an electrolyte solution in the form of an aqueous solution. However, the lithium ion battery has safety problems such as ignition and explosion due to the use of an organic electrolyte solution, and has disadvantages in that it is difficult to manufacture.

Recent lithium ion polymer batteries are considered as one of the next-generation batteries by improving the disadvantages of such lithium ion batteries, but the capacity of such batteries is still relatively low, particularly the discharge capacity at low temperature is insufficient, as compared with lithium ion batteries, and improvement thereof is urgently required.

The electrochemical devices as described above are produced by many companies, but their safety characteristics exhibit different aspects. It is very important to evaluate the safety of these electrochemical devices and to ensure the safety thereof. The most important consideration is that the electrochemical device should not cause injury to the user in the event of a failure. For this reason, safety standards strictly regulate ignition and smoking in electrochemical devices. In the safety feature of the electrochemical device, if the electrochemical device is overheated and thus shows thermal runaway, or the separator is punctured, there is a high risk of causing explosion. In particular, a polyolefin-based porous substrate, which is generally used as a separator of an electrochemical device, exhibits extreme thermal shrinkage behavior at a temperature of 100 ℃ or more due to material characteristics and characteristics of a manufacturing process including stretching, thereby causing a short circuit between a positive electrode and a negative electrode.

In order to solve the safety problem of the electrochemical device as described above, a separator having a porous organic-inorganic coating layer formed by coating an excess mixture of inorganic particles and a binder polymer on at least one side of a polyolefin-based porous substrate having a plurality of pores has been proposed.

In this case, however, the porous layer may have coating defects (defects) on the surface due to cracks generated in a manufacturing process such as a drying process. Therefore, when a secondary battery is assembled or when the battery is used, the organic/inorganic composite porous layer may be easily peeled off from the polyolefin-based porous substrate, which results in a reduction in the safety of the battery. Further, in order to form the porous layer, the slurry for forming the porous layer applied to the polyolefin-based porous substrate has the following problems: the degree of compaction of the particles increases during drying, resulting in a densely packed (packing) section and thus a reduction in air permeability.

Further, there are the following problems: heavy metal components inevitably mixed in the manufacturing process of the electrode plates of the battery and the preparation process of raw materials are deposited on the surface of the negative electrode by being redox during the activation of the battery, with the result that needle-shaped crystals (dendrites) of metallic lithium cause micro-short circuits (micro-short) on the positive electrode or the negative electrode, thereby causing a voltage drop of the battery.

Therefore, in terms of the characteristics of the battery industry requiring higher and higher stability, there is still a need for an improved separator capable of contributing to the stability of the battery.

(patent document 1) korean unexamined patent publication No. 10-2015-0099648, "a separator, a method of manufacturing the separator, a lithium polymer secondary battery including the separator, and a method of manufacturing a lithium polymer secondary battery using the separator".

Disclosure of Invention

Technical problem

Accordingly, a problem to be solved by the present invention is to provide a porous separator capable of preventing a short-circuit phenomenon between a positive electrode and a negative electrode due to dendrite growth and having improved high-temperature safety due to excellent thermal properties, and an electrochemical device including the same.

Technical scheme

In order to solve the above-described problems, the present invention provides a porous separator including a porous layer and a metal layer formed on either surface of the porous layer, the porous layer including a plurality of plate-like inorganic particles and a first binder polymer located on a part or all of the surface of the plate-like inorganic particles to attach and fix the plate-like inorganic particles.

Further, the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, wherein the separator is the above-mentioned porous separator.

Advantageous effects

According to the present invention, by providing the foundation layer containing the plate-like inorganic particles, the path between the positive electrode/negative electrode, so-called twist degree, can be increased, so that even if dendrites are generated in the battery, since the associated dendrites become difficult to reach from the negative electrode to the positive electrode, the reliability of dendrite short circuit can be further improved.

In addition, since the porous separator according to the present invention does not have a porous polymer substrate, there is an effect of reducing costs, the pore size and porosity of the entire separator can be controlled to achieve a uniform porous separator, and the thickness of the separator can be thinned to reduce weight. Further, there is no phenomenon such as heat shrinkage even when exposed to a high temperature of 120 ℃ or more, and thus there is an advantage of improving safety.

In addition, the porous separator according to the present invention has an advantage of suppressing Li dendrite growth by forming a metal having a low Li diffusion barrier (Li diffusion barrier) through an evaporation (evaporation) process or a sputtering (sputter) process on a portion contacting the negative electrode.

In addition, the porous separator according to the present invention has an advantage of improving output characteristics by coating a ceramic having a large dielectric constant on a portion contacting the positive electrode.

Drawings

Fig. 1 is a schematic diagram showing the degree of torsion in a porous layer composed of inorganic particles.

Fig. 2 is a schematic diagram showing the degree of torsion in a porous layer composed of spherical inorganic particles.

Fig. 3 is a schematic diagram showing the degree of torsion in a porous layer composed of plate-like inorganic particles.

FIG. 4 is a schematic view of a porous separator according to one embodiment of the invention.

FIG. 5 is a schematic view of a porous separator according to one embodiment of the invention.

FIG. 6 is a schematic view of a porous separator according to one embodiment of the invention.

Detailed Description

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the invention. The terms and words used in the present specification and claims should not be construed as limited to general terms or dictionary terms, but interpreted in a meaning and concept consistent with the technical idea of the present invention based on the principle that the inventor can appropriately define the concept of the term to describe his invention in the best possible manner.

In the drawings, portions irrelevant to the description of the present invention are omitted for clarity of illustration of the present invention, and like reference numerals are used for like portions throughout the specification. Further, the sizes and relative sizes of components shown in the drawings are not related to actual proportions, and may be reduced or enlarged for clarity of description.

Porous partition

A porous separator according to one embodiment of the present invention includes a porous layer including a plurality of plate-like inorganic particles and a first binder polymer on a part or all of surfaces of the plate-like inorganic particles to attach and fix the plate-like inorganic particles, and a metal layer formed on any one surface of the porous layer.

As described below, since the porous separator of the present invention can be used as a separator by being interposed between a positive electrode and a negative electrode, the porous separator may correspond to a porous separator (separator), and may also correspond to an organic-inorganic composite material because an organic material and an inorganic material are mixed in terms of components.

Since the organic-inorganic composite material is composed of only an inorganic material and a binder polymer without a porous polymer base material such as polyolefin, the separator does not exhibit thermal shrinkage even when exposed to a high temperature of 120 ℃ or more and does not decompose or break even if the temperature is raised to be close to the melting point of the polymer base material, as compared with a separator made of a conventional porous polymer base material, so that the possibility of short circuit between the positive electrode and the negative electrode can be fundamentally prevented, and the thickness of the separator can be reduced to reduce the weight.

On the other hand, in order to safely use an electrochemical device such as a secondary battery for a long time, foreign metal ions in the battery generated during charge/discharge form dendrites by being reduced at the surface of the negative electrode, it is necessary to suppress an internal short-circuit phenomenon caused by these dendrites. In addition, dendrites generated by the reduction of these metal ions during charge/discharge in the manufacturing process of the battery increase the defect rate in the manufacturing process of the battery in terms of quality in the manufacturing of the battery. In addition, if dendrites generated during the manufacturing process electrically connect the positive and negative electrodes to each other due to external pressure or vibration, safety and stability problems of the battery may be caused even during use, and the reduction of other metal ions generated during the use of the battery may also cause the formation of dendrites, which may seriously deteriorate the safety and stability of the battery. Therefore, in the lithium secondary battery as described above, it is necessary to suppress the formation and growth of dendrites that can electrically connect the positive electrode and the negative electrode inside the battery.

In the case of using a porous organic/inorganic layer having inorganic particles as a separator, pores of the porous organic/inorganic layer, i.e., the intervals and paths between the inorganic particles, may greatly affect the growth of dendrites and the short circuit phenomenon between the positive and negative electrodes. If the time required for the metal ions to pass through the separator and thus be transported to the negative electrode becomes long, or even if the metal ions pass through the separator and deposit dendrites on the surface of the negative electrode, if the path to the positive electrode on which the metal ions are deposited and grown is complicated or the time required for the metal ions to deposit and grow increases, the growth of dendrites formed by the reduction and deposition of the metal ions on the surface of the negative electrode can be suppressed or delayed.

The migration path in porous organic/inorganic layers with inorganic particles that affect the deposition and growth of these foreign metal ions can be explained by the tortuosity (tortuosity).

The degree of distortion is a value represented by quantifying the degree of curve bending or distortion. This degree of twist is commonly used to describe diffusion that typically occurs in porous materials. Referring to fig. 1, the degree of torsion τ may be defined as follows.

Wherein Δ ι: actual travel length, Δ χ: unit length.

That is, although the thickness of the porous layer composed of the plurality of particles 1 corresponds to Δ χ, the time taken to pass through the pores 2 of the porous layer from one side to the other side is proportional to the actual travel distance Δ ι.

Referring to fig. 2 and 3, it can be seen that the actual travel distance may vary greatly depending on the type of inorganic particles in the porous separator having the binder polymer and the inorganic particles. In the case where the shape of the inorganic particles 3 is spherical as shown in fig. 2, the degree of distortion of the path passing through the holes 4, 6 is small as compared with the case where the shape of the inorganic particles 5 is plate-like as shown in fig. 3, so that it is possible to pass from one side to the other side with a short travel length. It follows that in the case where the inorganic particles of the porous separator are in the shape of a plate, since the travel length is longer than that of a sphere, it takes more time, and dendrites formed on the surface of the negative electrode are difficult to grow, pass through the pores of the separator, and are connected to the positive electrode, thereby suppressing the growth of dendrites and the short circuit phenomenon caused thereby.

Accordingly, the present invention provides a porous separator including a porous layer having plate-shaped inorganic particles.

Referring to fig. 4, a porous separator 100 according to an embodiment of the present invention includes a porous layer 10, the porous layer 10 including a plurality of plate-shaped inorganic particles 11 and a first binder polymer (not shown) on a part or all of surfaces of the plate-shaped inorganic particles 11 to attach and fix the plate-shaped inorganic particles.

Further, according to an embodiment of the present invention, a metal layer formed on either surface of the porous layer may be included.

As the metal layer, a metal (M) having a low Li diffusion barrier (Li diffusion barrier) that can form Li by reacting with lithium can be used_xAn alloy (alloy) of M (x ═ 1 to 2.25). Here, "x is 1 to 2.25" means that x lithium meets with the metal (M) to form Li_xAn alloy of M (alloy).

The copper current collector does not undergo an alloying (alloy) reaction with lithium and therefore lithium plating occurs, which requires more energy than the metal undergoing the alloying (alloy) reaction. Therefore, in the case of using lithium metal as the negative electrode, the growth of lithium during charging is concentrated in the region where lithium is initially grown, thereby forming dendrites, and as a result, it is highly likely that the growth of lithium does not occur on the entire surface of the copper current collector, but the growth of lithium will be concentrated in a local region where lithium starts to grow.

However, if there is a metal layer having a low lithium diffusion barrier, the growth of lithium does not occur in a local region during charging, but occurs uniformly over a wide range, thereby producing an effect of suppressing dendrite formation.

Specific examples of the metal (M) having a low Li diffusion barrier (Li diffusion barrier) include Al, In, Au, Ni, Mg, or the like.

The thickness of the metal layer may be 0.01 μm to 1 μm. Since the metal layer is formed on either surface of the porous layer, the growth of dendrite due to the growth of lithium metal can be suppressed.

Referring to fig. 5, a porous separator 200 according to one embodiment of the present invention includes a porous layer 10 and a metal layer 20 on one surface of the porous layer as a base layer, the porous layer 10 including a plurality of plate-shaped inorganic particles 11 and a first binder polymer (not shown) on a part or all of the surface of the plate-shaped inorganic particles 11 to attach and fix the plate-shaped inorganic particles.

According to an embodiment of the present invention, the inorganic particles in the porous layer may consist of only the plate-like inorganic particles, or may comprise 50 wt% or more, particularly 50 to 90 wt% of the plate-like inorganic particles, based on the total weight of the inorganic particles in the porous layer. In the latter case, the porous layer may further include spherical inorganic particles as the inorganic particles of the porous layer.

Non-limiting examples of the plate-shaped inorganic particles may include alumina, silica, zirconia, titania, magnesia, ceria, yttria, zinc oxide, iron oxide, barium titanium oxide, alumina-silica composite oxide, or a mixture of two or more thereof.

Non-limiting examples of the spherical inorganic particles may include inorganic particles having a high dielectric constant of 5 or more, particularly 10 or more, inorganic particles having lithium ion transport ability, or a mixture thereof.

Non-limiting examples of the inorganic particles having a dielectric constant of 5 or more may include BaTiO₃、Pb(Zr,Ti)O₃(PZT)、Pb_1-xLa_xZr_1-yTi_yO₃(PLZT)、PB(Mg₃Nb_2/3)O₃-PbTiO₃(PMN-PT), hafnium oxide (hafnia, HfO)₂)、SrTiO₃、SnO₂、CeO₂、MgO、NiO、CaO、ZnO、ZrO₂、Y₂O₃、Al₂O₃、TiO₂、SiC、AlO(OH)、Al₂O₃·H₂O or mixtures thereof.

Further, the inorganic particles having lithium ion transport ability refer to inorganic particles containing a lithium element but having a function of moving lithium ions without storing lithium. Non-limiting examples of the inorganic particles having lithium ion transport ability include lithium phosphate (Li)₃PO₄) Lithium titanium phosphate (Li)_xTi_y(PO₄)₃,0<x<2,0<y<3) Lithium aluminum titanium phosphate (Li)_xAl_yTi_z(PO₄)₃,0<x<2,0<y<1,0<z<3) Such as 14Li₂O-9Al₂O₃-38TiO₂-39P₂O₅Like (LiAlTiP)_xO_yBase glass (0)<x<4，0<y<13) Lithium lanthanum titanate (Li)_xLa_yTiO₃,0<x<2,0<y<3) Such as Li_3.25Ge_0.25P_0.75S₄Like germanium lithium thiophosphate (Li)_xGe_yP_zS_w,0<x<4,0<y<1,0<z<1,0<w<5) Such as Li₃Lithium nitrides such as N (Li)_xN_y,0<x<4,0<y<2) Such as Li₃PO₄-Li₂S-SiS₂Like SiS₂Base glass (Li)_xSi_yS_z,0<x<3,0<y<2,0<z<4) Such as LiI-Li₂S-P₂S₅Like P₂S₅Base glass (Li)_xP_yS_z,0<x<3,0<y<3,0<z<7) Or mixtures thereof.

The aspect ratio of the plate-like inorganic particles may be 5 to 100, specifically 50 to 100. If the aspect ratio of the plate-like inorganic particles is less than 5, there is no effect as compared with the case where only spherical inorganic materials are used. If the aspect ratio of the plate-like inorganic particles is more than 100, there is a problem in that the surface quality of the separator (such as surface protrusions of the inorganic particles) is deteriorated.

The aspect ratio of the spherical inorganic particles may be 1 to 2, specifically 1 to 1.5.

Here, the aspect ratio refers to an average value of a ratio of a length in a major axis direction to a length in a minor axis direction of the inorganic particles (length in the major axis direction/length in the minor axis direction).

For example, the average value of the aspect ratio, that is, the ratio of the length of the inorganic particles in the major axis direction to the length in the minor axis direction can be obtained by image analysis of an image taken by a Scanning Electron Microscope (SEM). Further, the aspect ratio of the inorganic particles can also be obtained by image analysis of an image taken by SEM.

Further, the porous separator 300 according to an embodiment of the present invention shown in fig. 6 includes: a porous layer 10, the porous layer 10 comprising a plurality of plate-like inorganic particles 11 and a first binder polymer (not shown) on a part or all of the surface of the plate-like inorganic particles 11 to attach and fix the plate-like inorganic particles; a metal layer 20 on one surface of the porous layer; and a ceramic coating layer 30 formed on the other surface of the porous layer.

If the porous separator further includes a ceramic coating, output characteristics can be improved when the battery is manufactured.

For this, a compound having a dielectric constant of 20 to 1000 may be applied as a ceramic coating, and specifically, a coating such as HfO may be applied₂、ZrO₂、BaSrTiO₃Or PbLaZrTiO₃Or a mixture thereof.

The inorganic particles may be mixed with a binder (second binder polymer) to be uniformly dispersed in the coating layer.

In the porous separator according to an aspect of the present invention, a polymer having a glass transition temperature (Tg) of-200 ℃ to 200 ℃ may be used as the first binder polymer and the second binder polymer. This is because mechanical properties, such as flexibility and elasticity, of the finally formed porous separator can be improved.

Such a binder polymer faithfully serves as a binder for connecting and stably fixing the inorganic particles, thereby contributing to prevention of deterioration of mechanical properties of the porous separator.

In addition, the first binder polymer and the second binder polymer do not necessarily have ion conductivity, but when a polymer having ion conductivity is used, the performance of the electrochemical device may be further improved. Therefore, polymers having a high dielectric constant may be used as the first binder polymer and the second binder polymer. In fact, since the degree of dissociation of the salt in the electrolyte solution depends on the dielectric constant of the solvent of the electrolyte solution, the degree of dissociation of the salt in the electrolyte can be increased as the dielectric constant of the binder polymer becomes higher. The dielectric constant of the first binder polymer and the second binder polymer may be in the range of 1.0 to 100 (measurement frequency ═ 1kHz), particularly 10 or more. In addition to the above functions, the first and second binder polymers may have a characteristic of exhibiting a high degree of swelling (degree of swelling) caused by an electrolyte solution by gelation upon impregnation with a liquid electrolyte solution. Thus, the solubility parameter of the binder polymer, i.e., the Hildebrand solubility parameter, is in the range of 15 to 45MPa^{1 /2}Or 15-25MPa^1/2And 30-45MPa^1/2Within the range of (1). Thus, hydrophilic polymers with more polar groups may be more suitable than hydrophobic polymers (such as polyolefins).

The reason is that if the solubility parameter is less than 15MPa^1/2And greater than 45MPa^1/2It may be difficult to swell with a conventional liquid electrolyte solution for a battery (swelling).

In the porous separator, the inorganic particles are charged and bound by the first binder polymer and the second binder polymer contacting each other, and thus interstitial volumes (interstitial volumes) are formed between the inorganic particles, and the interstitial volumes (interstitial volumes) between the inorganic particles become empty spaces to form pores.

That is, the first binder polymer and the second binder polymer attach the inorganic particles to each other such that they remain bound together, e.g., the first binder polymer and the second binder polymer are connected and fixed between the inorganic particles. In addition, the pores of the porous separator are pores formed by vacant interstitial volumes between the inorganic particles, which are spaces defined by the inorganic particles substantially contacting each other by surfaces in a packed (closed packed or dense packed) structure.

The first binder polymer and the second binder polymer may be used without limitation as long as they satisfy the above weight average molecular weight and are generally used in the art, and examples of the first binder polymer and the second binder polymer may each independently be but are not limited to each of the following: polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene (polyvinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride-co-trichloroethylene (polyvinylidene fluoride-co-trichloroethylene), polyimide (polyimide), polymethyl methacrylate (polymethyl methacrylate), polybutyl acrylate (polybutyl acrylate), polyacrylonitrile (polyacrylonitrile), polyvinylpyrrolidone (polyvinylpyrrolidone), polyvinyl acetate (polyvinyl acetate), polyethylene-co-vinyl acetate (polyvinyl acetate), polyethylene oxide (polyethylene oxide), polyvinyl starch (polyacrylate), cellulose acetate (cellulose acetate), cellulose acetate (cellulose acetate ), cellulose acetate (cellulose acetate), cellulose acetate, cyanoethyl sucrose (cyanoethyl sucrose), pullulan (pullulan), carboxymethyl cellulose (carboxymethyl cellulose) and the like.

Further, the weight of the first binder polymer is 0.1 to 30 wt%, specifically 0.3 to 25 wt%, more specifically 0.5 to 20 wt%, relative to the total weight of the porous layer.

Furthermore, the weight of the second binder polymer is 0.1 to 30 wt. -%, in particular 0.3 to 25 wt. -%, more in particular 0.5 to 20 wt. -%, relative to the total weight of the ceramic coating.

When the weight of each of the first binder polymer and the second binder polymer satisfies these ranges, an excessive amount of the binder polymer may be present in the pores of the porous separator to be formed to prevent the problem of the reduction in pore size and porosity, and the inorganic particles may be stably fixed by the binder polymer without being separated during the manufacturing stage of the porous separator or the storage or operation of an electrochemical device having such a porous separator.

The porous separator according to an aspect of the present invention may further include other additives in addition to the inorganic particles and the binder polymer described above.

As the additive, conventional additives used in the art may be used.

The porous separator according to one embodiment of the present invention may be prepared by: first, a base layer composition including plate-shaped inorganic particles and a first binder polymer is prepared, the composition is applied to one surface of a release substrate, and dried, and then the release substrate is removed. Further, by applying the composition for forming a porous separator directly on one side of an electrode layer (such as a positive electrode or a negative electrode) and drying, the porous separator can be manufactured as a composite of an electrode porous layer directly bonded to the electrode layer.

First, a base layer composition may be prepared by dissolving a first binder polymer in a solvent, and then adding and dispersing plate-shaped inorganic particles. The plate-like inorganic particles may be added in a state of being pulverized in advance to have a predetermined average particle diameter, or may be dispersed by: inorganic particles are added to the binder polymer solution, and then the inorganic particles are pulverized by using a ball milling method while controlling them to have a predetermined average particle diameter.

The method of coating the base layer composition on the release substrate or the electrode layer is not particularly limited, but preferably slit coating, comma coating, curtain coating, micro-gravure coating, spin coating, roll coating, or dip coating is used.

The slot coating may control the thickness of the coating layer according to the flow rate supplied from the metering pump so that the composition supplied through the slot die is applied to the front surface of the substrate. Further, dip coating is a method of dip coating and coating a substrate in a tank containing a composition, which is capable of adjusting the thickness of the coating layer according to the concentration of the composition and the speed of removing the substrate from the composition tank, and after soaking, post-measurement is performed again by a Mayer rod or the like, so as to more precisely control the thickness of the coating layer.

Therefore, the release substrate coated with the composition for forming a porous separator is dried at a temperature of, for example, 90 ℃ to 150 ℃ using a dryer such as an oven, and then the porous layer is prepared by removing the release substrate. As such a releasable substrate, a glass plate, a polyethylene-based film, a polyester-based film, or the like can be used, but not limited thereto. Optionally, the surface of the release substrate may be surface-modified by corona treatment (for example, treatment at a voltage of 0.5kV to 1.5kV for 10 seconds to 30 seconds) or the like.

Alternatively, when the base layer composition is directly coated on the electrode layer, it may be dried in the same manner and made into a composite of the electrode porous layer bonded to the electrode layer.

The coating thickness of the porous layer formed by coating in the above-described manner may be 5 μm to 20 μm, specifically 5 μm to 20 μm.

Next, the composition for forming a porous separator may be coated on at least one surface of the prepared porous layer, and then dried to further form a metal layer and a ceramic coating layer.

The ceramic coating layer may be prepared by dissolving the second binder polymer in a solvent and then adding and dispersing inorganic particles, and as another method, a method of manufacturing the base layer composition may be similarly applied. The coating thickness of the ceramic coating layer formed by coating in the above-described manner may be 1 μm to 20 μm, specifically 1 μm to 5 μm.

In the present invention, the porosity is measured using a Capillary flow porosimeter (Capillary flow porosimeter) device of the PMI company.

The metal layer may be formed of a metal having a low Li diffusion barrier (Li diffusion barrier) such as Al, In, Au, Ni, Mg, or the like, by an evaporation (evaporation) or sputtering (sputter) process. The coating thickness of the metal layer formed by coating in the above-described manner may be 0.01 μm to 1 μm.

According to one embodiment of the present invention, it is preferable that the plate-like inorganic particles in the porous layer are present in a form substantially parallel to the plane of the porous layer.

Lithium secondary battery

A lithium secondary battery according to one aspect of the present invention includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is the above-described porous separator according to one embodiment of the present invention.

The lithium secondary battery may include lithium metal or a lithium alloy in the negative electrode.

In addition, the metal layers of the anode and the porous separator may contact each other.

The porous separator of the present invention may be used for an electrochemical device including all devices that undergo an electrochemical reaction, and specific examples thereof include a capacitor (capacitor), such as various primary batteries, secondary batteries, fuel cells, solar cells, or supercapacitor devices. In particular, lithium secondary batteries including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries are preferable.

The two electrodes, the positive electrode and the negative electrode, used with the porous separator of the present invention are not particularly limited and may be prepared in the form of an electrode active material bonded to an electrode current collector according to a conventional method known in the art. Non-limiting examples of the cathode active material of the electrode active material may be conventional cathode active materials that may be used for a cathode of a conventional electrochemical device, and specifically, a lithium manganese oxide, a lithium cobalt oxide, a lithium nickel oxide, a lithium iron oxide, or a lithium composite oxide in a combination thereof is preferably used. Non-limiting examples of the negative active material may be a conventional negative active material that can be used for a negative electrode of a conventional electrochemical device, and particularly, preferably, lithium adsorbent such as lithium metal or lithium alloy, carbon, petroleum coke (petroleum coke), activated carbon (activated carbon), graphite (graphite), or other carbon. Non-limiting examples of the positive electrode current collector include foils made of aluminum, nickel, or a combination thereof. Non-limiting examples of the negative electrode current collector include copper, gold, nickel, or copper alloy, or a combination thereof.

The electrolyte solution that may be used in the electrochemical device of the present invention may be, but is not limited to, one obtained by forming a metal oxide such as structure A⁺B^-An electrolyte solution prepared by dissolving or dissociating a salt in an organic solvent, wherein A⁺Is an alkali metal cation, such as Li⁺、Na⁺Or K⁺Or ions composed of combinations thereof, and B^-Is an anion, such as PF₆ ^-、BF₄ ^-、Cl^-、Br^-、I^-、ClO₄ ^-、AsF₆ ^-、CH₃CO₂ ^-、CF₃SO₃ ^-、N(CF₃SO₂)₂ ^-Or C (CF)₂SO₂)₃ ^-Or ions composed of a combination thereof, and the organic solvent includes 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), Ethyl Methyl Carbonate (EMC), gamma-butyrolactone (γ -butyrolactone), or a mixture thereof.

The injection of the electrolyte solution may be performed at an appropriate step in the battery manufacturing process depending on the manufacturing process and the desired physical properties of the final product. That is, the injection of the electrolyte solution may be performed before the battery assembly or at the final stage of the battery assembly.

Hereinafter, the present invention will be described in detail by way of examples to describe the present invention in detail. However, the embodiment according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiment described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Examples

Example 1

< preparation of porous separator >

After mixing PVdF-HFP polymer binder (LBG Grade) from Arkema) and inorganic particles (alumina, NW-710Grade from T-cera, aspect ratio 67) in a ratio of 2:8, the mixture was mixed with solvent N-methyl-2-pyrrolidone (NMP) at a solid concentration of 40% to prepare a coating solution.

The prepared coating solution was coated on a corona surface-treated polyethylene terephthalate (PET) film (SKC corporation, RX12G 50 μm) with a 0.7Kw intensity using an Applicator (Applicator), and then dried in a Mathis oven at 130 ℃ for 5 minutes to prepare a PET film coated with a porous separator having a thickness of 100 μm.

The porous separator-coated PET film was rolled on a Roll press (CLP-2025H by CIS corporation) to form a porous separator having a thickness of 20 μm, and then the PET film was peeled.

Thereafter, using a Sputtering system (Sputtering Systems) from Novellus corporation, a 0.5 μm aluminum metal layer was formed on one surface of the porous separator under a vacuum of 10mTorr and 1kV in an Ar gas atmosphere.

< production of lithium Secondary Battery >

By using 96.7 parts by weight of LiCoO as a positive electrode active material₂1.3 parts by weight of graphite as a conductive agent, and 2.0 parts by weight of polyvinylidene fluoride (PVd) as a binderF) Mixing to prepare a positive electrode mixture. The obtained cathode mixture was dispersed in 1-methyl-2-pyrrolidone serving as a solvent to prepare a cathode mixture slurry. The slurry was coated, dried, and pressed on both sides of an aluminum foil having a thickness of 20 μm, respectively, to prepare a positive electrode.

As the negative electrode, a Li metal electrode (a Honzo corporation, japan) in which a 100% Li metal layer having a thickness of 20 μm was formed on a copper foil current collector was used.

Mixing LiPF₆A nonaqueous electrolyte solution was prepared by dissolving Ethylene Carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in an organic solvent obtained by mixing them in a composition of 1:2:1 (volume ratio) at a concentration of 1.0M, and dissolving 2 parts by weight of vinylene carbonate based on 100 parts by weight of the organic solvent.

A porous separator was interposed between the prepared cathode and anode, and an electrolyte solution was injected to prepare a lithium secondary battery in the form of a button cell. At this time, the metal layer of the porous separator is inserted to contact the negative electrode.

Example 2

By combining a PVdF-HFP polymer binder (LBG Grade from Arkema) with BaSrTiO₃The coating solution was prepared by mixing in a ratio of 1:9 and then mixing the mixture with a solvent of N-methyl-2-pyrrolidone (NMP) at a solid concentration of 20 wt%. A lithium secondary battery was prepared in the same manner as in example 1, except that: the coating solution was coated on the other surface of the porous separator prepared in example 1, on which the metal layer was not formed, in the same manner as in example 1 to prepare a porous separator having a ceramic coating layer.

Comparative example 1

A lithium secondary battery was prepared in the same manner as in example 1, except that: PVdF-HFP polymer binder (LBG Grade) from Arkema corporation) and inorganic particles (alumina, NW-710Grade (NW-710Grade) from Ticera corporation) were mixed in a ratio of 1:9, and no metal layer was formed.

Comparative example 2

A lithium secondary battery was prepared in the same manner as in example 1, except that: as the porous separator, CSP20 product from Optodot corporation was used.

Comparative example 3

A lithium secondary battery was prepared in the same manner as in example 1, except that: no metal layer is formed.

Test example 1: analysis of life characteristics of battery

The battery was charged with a Constant Current (CC) of 0.2C until it became 4.25V using a Small Cell cycle (Small Cell cycle) device of PNE dissolution, and then charged once with an off current of 5% with respect to 1C at a Constant Voltage (CV) of 4.25V, and then discharged with a constant current of 0.5C until it became 3V, which constituted 1 cycle. The loop is repeatedly executed.

The cycle performance according to the cycle characteristics and the 2C discharge capacity with respect to 0.2C were measured. The results are shown in table 1 below.

Table 1:

referring to table 1, it was found that the results of applying the porous inorganic separators of comparative examples 1 to 3 showed that fading (fading) began before 30 cycles, while the porous separators of examples 1 and 2 showed stable discharge capacity even at longer cycles and also showed better 2C discharge capacity with respect to 0.2C. The porous separators of analytical examples 1 and 2 have excellent characteristics of suppressing the growth of lithium dendrites.

Test example 2: high temperature stability analysis of separator

The separator was exposed to a temperature of 150 degrees for 30 minutes using a Convection oven (Convection oven). The high temperature stability of the separator was determined in a manner that the shrinkage rate was calculated by measuring the area of the separator before and after exposure.

As a result, 8% of the area was shrunk in the case of example 1, and 5% of the area was shrunk in the case of example 2. In contrast, 6% shrinkage occurred in comparative example 1, 80% shrinkage occurred in comparative example 2, and 10% shrinkage occurred in comparative example 3. It is considered that the high temperature stability is improved due to the coating of the inorganic particles and the metal layer on the surface of the porous separators of examples 1 and 2.

All simple modifications and variations of the present invention fall within the scope of the present invention, and the specific protection scope of the present invention will be clarified by the appended claims.