KR100999309B1 - A separator having porous coating layer and electrochemical device containing the same - Google Patents

Abstract

The separator according to the present invention comprises a porous substrate having a plurality of pores; And a porous coating layer coated on at least one surface of the porous substrate and formed of a mixture of a plurality of filler particles and a binder polymer, wherein the filler particles include electrode active material particles. The separator of the present invention uses the electrode active material particles which are subjected to the electrochemical oxidation and reduction reaction as the filler particles of the porous coating layer, so that not only the thermal stability of the separator due to the introduction of the porous coating layer but also the capacity of the battery can be simultaneously increased. .

Description

A separator having a porous coating layer and an electrochemical device having the same {A SEPARATOR HAVING POROUS COATING LAYER AND ELECTROCHEMICAL DEVICE CONTAINING THE SAME}

1 is a cross-sectional view schematically showing a separator on which a porous coating layer is formed,

2 is a photograph taken with a scanning electron microscope of the surface of the separator with a porous coating layer according to an embodiment of the present invention,

3 is a photograph taken after leaving the separator according to an embodiment of the present invention and a comparative example for 1 hour in an oven at 150 ℃,

4 is a graph measuring charge and discharge characteristics of a coin cell using a separator according to an embodiment of the present invention and a comparative example,

5 is a graph measuring the c-rate behavior of the coin cell using the separator according to the embodiment and comparative example of the present invention.

The present invention relates to a separator used in an electrochemical device such as a lithium secondary battery and an electrochemical device having the same, and more particularly, a separator having a porous coating layer formed of a mixture of filler particles and a binder polymer on a surface of a porous substrate, and a separator. It relates to an electrochemical device provided.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders, notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete. The electrochemical device is the most attracting field in this respect, and the development of a secondary battery capable of charging and discharging has been the focus of attention, and in recent years in the development of such a battery in order to improve the capacity density and specific energy The research and development of the design of the battery is progressing.

Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s have a higher operating voltage and greater energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use an aqueous electrolyte solution. I am in the spotlight. However, such lithium ion batteries have safety problems such as ignition and explosion due to the use of the organic electrolyte, and are difficult to manufacture. Recently, the lithium ion polymer battery has been considered as one of the next generation batteries by improving the weakness of the lithium ion battery, but the capacity of the battery is still relatively low compared to the lithium ion battery, and the discharge capacity is improved due to insufficient discharge capacity at low temperatures. This is urgently needed.

Such electrochemical devices are produced by many companies, but their safety characteristics show different aspects. It is very important to evaluate the safety and secure the safety of these electrochemical devices. The most important consideration is that an electrochemical device should not cause injury to the user in case of malfunction. For this purpose, safety standards strictly regulate the ignition and smoke in the electrochemical device. In the safety characteristics of the electrochemical device, there is a high possibility that an explosion occurs when the electrochemical device is overheated to cause thermal runaway or the separator penetrates. In particular, polyolefin-based porous substrates commonly used as separators for electrochemical devices exhibit extreme heat shrinkage behavior at temperatures of 100 degrees or more due to material characteristics and manufacturing process characteristics including stretching, and thus, a short circuit between the anode and the cathode. There is a problem that causes.

In order to solve the safety problem of the electrochemical device, Korean Patent Publication Nos. 10-2006-72065, 10-2007-231, etc., at least one surface of the porous substrate 1 having a plurality of pores, inorganic matter A separator 10 is proposed in which a porous coating layer of a mixture of filler particles 3 such as particles and a binder polymer 5 is formed (see FIG. 1). In the separator 10 in which the porous coating layer is formed, the filler particles 3 in the porous coating layer formed on the porous substrate 1 serve as a kind of spacer that can maintain the physical form of the porous coating layer, thereby increasing the porosity when the electrochemical device is overheated. The substrate is suppressed from heat shrinking. In addition, interstitial volumes exist between the filler particles to form micropores.

As such, the porous coating layer formed on the porous substrate contributes to the safety improvement of the electrochemical device. The filler particles used to form the porous coating layer according to the prior art include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), ZrO ₂ , SiO ₂ , Al ₂ O ₃ , TiO ₂ , lithium phosphate (Li ₃ PO _4). ), Lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3), etc., which are used to contribute to the capacity of the battery due to the electrochemical properties it's difficult. Therefore, when the porous coating layer is formed on a porous substrate having a conventional thickness, the separator becomes thick, thereby reducing the amount of electrode active material particles that can enter the unit volume, thereby reducing capacity per cell.

Accordingly, the technical problem to be achieved by the present invention is to solve the above problems, to provide an electrochemical device having a separator that can increase the capacity of the battery at the same time as well as improving the thermal stability of the separator according to the introduction of the porous coating layer.

In order to achieve the above technical problem, the separator according to the present invention comprises a porous substrate having a plurality of pores; And a porous coating layer coated on at least one surface of the porous substrate and formed of a mixture of a plurality of filler particles and a binder polymer, wherein the filler particles include electrode active material particles.

The separator of the present invention uses electrode active material particles which are electrochemically oxidized and reduced as filler particles of the porous coating layer. Accordingly, it is possible to improve the thermal stability of the separator according to the introduction of the porous coating layer, as well as to reduce the capacity of the battery even when using a porous substrate having a conventional thickness.

In the separator of the present invention, as the filler particles, in addition to the electrode active material particles, inorganic particles having a dielectric constant of 5 or more, inorganic particles having a lithium ion transfer ability, or mixtures thereof are preferably used.

Such a separator of the present invention may be used in an electrochemical device such as a lithium secondary electron or a supercapacitor device by interposing between an anode and a cathode and injecting an electrolyte solution.

Hereinafter, the present invention will be described in detail. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

The separator according to the present invention comprises a porous substrate having a plurality of pores; And a porous coating layer coated on at least one surface of the porous substrate and formed of a mixture of a plurality of filler particles and a binder polymer, wherein electrode active material particles are used as filler particles.

As described above, the filler particles used to form the porous coating layer according to the prior art BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), ZrO ₂ , SiO ₂ , Al ₂ O ₃ , TiO ₂ , lithium phosphate ( Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3), etc. are not particles that undergo oxidation and reduction reactions electrochemically, Contributes little to capacity improvement. However, when using 1 to 100% by weight of the electrode active material particles, which are particles that undergo electrochemical oxidation and reduction as filler particles according to the present invention, for example, based on the total weight of the filler particles, thermal separation of the separator according to introduction of the porous coating layer In addition to improving stability, battery capacity can be increased at the same time. Accordingly, even when a separator is manufactured by forming a porous coating layer on a porous substrate having a conventional thickness, the problem of decreasing capacity per cell can be improved.

In the separator of the present invention, the porous coating layer may be coated on one side or both sides of the porous substrate, wherein the electrode active material particles may be used alone or in combination with the positive electrode active material particles, negative electrode active material particles, respectively. Looking at the action of the electrode active material particles contained in the porous coating layer in more detail, as follows.

The positive electrode active material particles contained in the porous coating layer formed to face the positive electrode contribute to the increase of the capacity of the positive electrode, and the negative electrode active material particles contained in the porous coating layer formed to face the negative electrode contribute to the increase of the capacity of the negative electrode. On the other hand, the negative electrode active material particles contained in the porous coating layer formed to face the positive electrode does not contribute to the increase of the capacity of the positive electrode or the negative electrode, but serves only as a filler particle. On the contrary, the positive electrode active material particles contained in the porous coating layer formed to face the negative electrode do not contribute to the increase of the capacity of the negative electrode or the positive electrode, but only serve as filler particles.

Therefore, in order to increase the capacity of the positive electrode, it is preferable to form a porous coating layer containing only the positive electrode active material particles as the electrode active material particles only on one surface of the porous substrate so as to face the positive electrode. In addition, when only the capacity of the negative electrode is to be increased, it is preferable to form a porous coating layer containing only the negative electrode active material particles as the electrode active material particles on only one surface of the porous substrate so as to face the negative electrode. In addition, to increase the capacity of both the positive electrode and the negative electrode, a porous coating layer containing only positive electrode active material particles is formed on one surface of the porous substrate to face the positive electrode, and the porous coating layer containing only negative electrode active material particles is porous to face the negative electrode. It is preferable to form in the other surface of a base material.

However, when the porous coating layer is formed on both sides of the porous substrate by using a dip coating method, etc. in consideration of processability and productivity when forming the porous coating layer, the porous coating layer may be formed in the following manner.

First, when the purpose of increasing the capacity of the positive electrode, a porous coating layer containing only the positive electrode active material particles as electrode active material particles can be formed on both sides of the porous substrate.

Second, in order to increase the capacity of the negative electrode, a porous coating layer including only negative electrode active material particles as electrode active material particles may be formed on both sides of the porous substrate.

Third, in order to increase the capacity of both the positive electrode and the negative electrode, a porous coating layer including both the positive electrode active material particles and the negative electrode active material particles as electrode active material particles may be formed on both sides of the porous substrate.

The electrode active material particles described above are not particularly limited as long as they are conventional electrode active material particles which are subjected to electrochemical oxidation and reduction reactions. Non-limiting examples of the positive electrode active material particles of the electrode active material particles are LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiFePO ₄ , LiNiMnCoO ₂ , LiNi which are conventional positive electrode active material particles that can be used for the positive electrode of a conventional electrochemical device _1-xyz Co _x M1 _y M2 _z O ₂ (M1 and M2 are each independently selected from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo) , x, y and z, independently of each other, as the atomic fraction of the elements of the oxide composition are 0 ≤ x <0.5, 0 ≤ y <0.5, 0 ≤ z <0.5) and the like, these are each alone or Two or more of these can be mixed and used. In addition, non-limiting examples of the negative electrode active material particles of the electrode active material particles are natural graphite, artificial graphite, carbonaceous materials, LTO, silicon (Si), tin ( Sn) etc. are mentioned, These can be used individually or in mixture of 2 or more types of these, respectively.

In the separator of the present invention, the filler particles used for forming the porous coating layer include, in addition to the electrode active material particles, inorganic particles typically used as filler particles, that is, operating voltage range of the electrochemical device (for example, 0 based on Li / Li ⁺ ). At 5V), inorganic particles which do not undergo oxidation and / or reduction reaction may be further added and used. In particular, in the case of using the inorganic particles having the ion transport ability, it is possible to improve the performance by increasing the ion conductivity in the electrochemical device. In addition, when inorganic particles having a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolyte may be improved by contributing to an increase in the degree of dissociation of an electrolyte salt such as lithium salt in the liquid electrolyte.

For the above reasons, the filler particles, in addition to the electrode active material particles, it is preferable to further include a high dielectric constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more, inorganic particles having a lithium ion transfer capacity or a mixture thereof. Do. 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, where 0 <x <1, 0 <y <1), Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT), Hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO , NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO _2, SiC Or mixtures thereof.

In particular, BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT, wherein 0 <x <1, 0 <y <1) ), Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT) and hafnia (HfO ₂ ) particles not only show high dielectric constants with dielectric constants above 100 but also exhibit constant pressure. When applied to tension or compression, it has piezoelectricity that generates electric charges and a potential difference between both surfaces, thereby preventing internal short-circuiting of the positive electrode due to external impact, thereby improving safety of electrochemical devices. can do. In addition, synergistic effects of the high dielectric constant inorganic particles and the inorganic particles having lithium ion transfer ability may be doubled.

In the present invention, the inorganic particles having a lithium ion transfer capability refers to inorganic particles containing lithium elements but having a function of transferring lithium ions without storing lithium, and the inorganic particles having lithium ion transfer capability are inside the particle structure. Since lithium ions can be transferred and moved due to a kind of defect present in the battery, lithium ion conductivity in the battery is improved, thereby improving battery performance. Non-limiting examples of the inorganic particles having a lithium ion transfer capacity is lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3) , Lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ Such as (LiAlTiP) _x O _y series glass (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), Li _{3 .25} Ge _{0 .25} P _{0 .75} S ₄ Lithium germanium thiophosphate such as Li _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5), Li ₃ N, etc. Ride (Li _x N _y , 0 <x <4, 0 <y <2), Li ₃ PO ₄ -Li ₂ S-SiS ₂ SiS ₂ series glass such as Li _x Si _y S _z , 0 <x <3, 0 <y <2, 0 <z <4), LiI-Li ₂ SP ₂ S ₅ P ₂ S ₅ series glass (Li _x P _y S _z , 0 <x <3, 0 <y <3, 0 <z <7), or a mixture thereof.

In addition, the filler particles may include a carbon conductive material having an electrical conductivity of 1 ms / cm or more.

In the separator of the present invention, the filler particle size of the porous coating layer is not limited, but in order to form a coating layer having a uniform thickness and an appropriate porosity, it is preferably 0.001 to 10 μm. If the particle size is less than 0.001 μm, the dispersibility of the filler particles may be reduced. If the thickness is greater than 10 μm, the thickness of the porous coating layer may be increased, and thus the mechanical properties may be reduced. It increases the chance of something happening.

The composition ratio of the filler particles and the binder polymer of the porous coating layer formed on the porous substrate according to the present invention is preferably in the range of 50:50 to 99: 1, more preferably 70:30 to 95: 5. When the content ratio of the filler particles to the binder polymer is less than 50:50, the content of the binder polymer is increased, thereby improving the thermal safety of the separator. In addition, the pore size and porosity due to the reduction of the void space formed between the filler particles may be reduced, resulting in deterioration of final cell performance. When the content of the filler particles exceeds 99 parts by weight, the binder polymer content is too small, the peeling resistance of the porous coating layer may be weakened. The thickness of the porous coating layer composed of the filler particles and the binder polymer is not particularly limited, but is preferably in the range of 0.01 to 20 μm. In addition, pore size and porosity are also not particularly limited, pore size is preferably in the range of 0.001 to 10㎛, porosity is preferably in the range of 10 to 90%. Pore size and porosity depend mainly on the size of the filler particles. For example, when using filler particles having a particle diameter of 1 μm or less, the pores formed also exhibit approximately 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. When the pore size and porosity are less than 0.001 μm and 10%, respectively, the pore size and porosity may act as a resistive layer. When the pore size and porosity exceed 10 μm and 90%, respectively, mechanical properties may be degraded.

In the separator of the present invention, the binder polymer used for forming the porous coating layer may be a polymer commonly used in forming a porous coating layer in the art. In particular, it is preferable to use a polymer having a glass transition temperature (T _g ) of -200 to 200 ° C, because it can improve mechanical properties such as flexibility and elasticity of the finally formed porous coating layer. . Such a binder polymer faithfully plays a role of a binder for stably connecting and stably between filler particles, thereby contributing to preventing mechanical property degradation of the separator into which the porous coating layer is introduced.

In addition, the binder polymer does not necessarily have an ion conducting ability, but when a 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 degree of dissociation of the salt in the electrolyte depends on the permittivity constant of the electrolyte solvent, the higher the dielectric constant of the polymer, the higher the dissociation of salt in the electrolyte. The dielectric constant of the binder polymer may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), particularly preferably 10 or more.

In addition to the above-described function, the binder polymer may have a feature that can exhibit a high degree of swelling of the electrolyte by gelling upon impregnation of the liquid electrolyte. In this way, and a solubility parameter of 15 to 45 MPa ^1/2 is preferably a polymer, more preferably to to 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 such polymers include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl Methacrylate (polymethylmethacrylate), polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate), polyethylene oxide oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, Cyanoethylcellulose, poetry No-ethyl and the like sucrose (cyanoethylsucrose), pullulan (pullulan), carboxymethyl cellulose (carboxyl methyl cellulose).

In the separator of the present invention, in addition to the filler particles and the binder polymer including the electrode active material particles described above as the porous coating layer component, other additives such as a conductive agent may be further included.

In addition, in the separator of the present invention, any porous substrate commonly used in an electrochemical device such as a polyolefin-based porous substrate may be used as the porous substrate having a plurality of pores. The polyolefin-based porous substrate may be used as long as it is a polyolefin-based porous substrate commonly used as an electrochemical device, in particular, a separator of a lithium secondary battery. For example, a membrane formed of a polymer such as a high density polyethylene, a linear low density polyethylene, a low density polyethylene, an ultra high molecular weight polyethylene, a polyolefin-based polymer such as polypropylene, polybutylene, polypentene, etc., alone or in a mixture thereof. And nonwoven fabrics. The thickness of the porous substrate is not particularly limited, but is preferably 1 to 100 µm, more preferably 5 to 50 µm, and the pore size and pore present in the porous substrate are also not particularly limited, but 0.01 to 50 µm and 10, respectively. It is preferably from 95%.

The separator in which the porous coating layer including the electrode active material particles is formed according to the present invention may be manufactured by a conventional method, and a preferable manufacturing method is exemplified below, but is not limited thereto.

First, the binder polymer is dissolved in a solvent to prepare a binder polymer solution.

Next, filler particles are added and dispersed in a solution of the binder polymer. 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. It is preferable to grind | pulverize filler particle after adding filler particle to a binder polymer solution. In this case, the crushing time is suitably 1 to 20 hours, and the particle size of the crushed filler particles is preferably 0.001 to 10 μm as described above. As the shredding method, a conventional method can be used, and a ball mill method is particularly preferable.

Then, a solution of the binder polymer in which the filler particles are dispersed is coated on the porous substrate under a humidity condition of 10 to 80% and dried.

The method of coating the solution of the binder polymer in which the filler particles are dispersed on the porous substrate may use a conventional coating method known in the art, for example, dip coating, die coating, roll Various methods such as coating, comma coating, or a mixture thereof can be used.

The separator of the present invention prepared as described above may be used as a separator of an electrochemical device interposed between an anode and a cathode. In this case, when a gelable polymer is used when the liquid electrolyte solution is impregnated as the binder polymer component, the gel electrolyte may be formed by reacting and injecting the electrolyte solution and the polymer after the battery is assembled.

Electrochemical devices include all devices that undergo an electrochemical reaction, and specific examples include capacitors such as all kinds of primary, secondary cells, fuel cells, solar cells, or supercapacitor elements. 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 electrochemical device may be manufactured according to conventional methods known in the art, and for example, may be manufactured by injecting an electrolyte after assembling through the above-described separator between the positive electrode and the negative electrode.

The electrode to be applied together with the separator of the present invention is not particularly limited, and may be prepared by applying an electrode active material slurry to a current collector according to conventional methods known in the art. As the electrode active material particles and the negative electrode active material particles used for the electrode, conventional electrode active material particles that can be used for the positive electrode and the negative electrode of the conventional electrochemical device may be used, and specific examples are as described above.

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. As a process of applying the separator of the present invention to a battery, a lamination (stack) and folding process of a separator and an electrode may be performed in addition to the general winding process.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example  One

Separator  Produce

PVdF-CTFE (polyvinylidene fluoride-chlorotrifluoroethylene copolymer) and Cyanoethylpullulan (cyanoethyl pullulan) were added to acetone in a weight ratio of 10: 2, respectively, and dissolved at 50 ° C. for at least 12 hours. Was prepared. Group electrode active material to the prepared polymer solution powder _{(LiNi 1/3 Mn 1/} 3 Co 1/3 O 2) was added such that the polymer mixture / electrode active material powder = 10/90 weight ratio, and more than 12 hours using a ball mill method The electrode active material powder was crushed and dispersed to prepare a slurry. The particle size of the electrode active material particles of the slurry thus prepared may be controlled according to the size (particle size) and ball mill time of the beads used in the ball mill, but in Example 1, the slurry was pulverized to about 600 nm.

The slurry thus prepared was coated on a 12 μm thick polyethylene porous membrane (porosity 45%) by dip coating. The coating thickness was adjusted to about 4 μm. The pore size in the porous coating layer coated on the polyethylene porous membrane was 0.4 μm, and the porosity was 66%.

Manufacture of anode

92% by weight of lithium cobalt composite oxide as a positive electrode active material particle, 4% by weight of carbon black as a conductive material, and 4% by weight of PVDF as a binder are added to N-methyl-2 pyrrolidone (NMP) as a solvent to prepare a positive electrode active material. Slurry was prepared. The positive electrode active material slurry was applied to an aluminum (Al) thin film of a positive electrode current collector having a thickness of 20 μm and dried to prepare a positive electrode, and then roll press was performed.

Manufacture of batteries

A positive electrode coin half cell was manufactured using the positive electrode and the separator manufactured by the method described above, and then performance test was performed.

In the battery manufacturing, the Li foil, the positive electrode, and the separator were assembled in a coin cell form by stacking (stacking) method, and the electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 1/2) ), And 1 mole of lithium hexafluorophosphate (LiPF6) were injected to test battery performance.

Example  2

Separator  Produce

PVdF-CTFE (polyvinylidene fluoride-chlorotrifluoroethylene copolymer) and Cyanoethylpullulan (cyanoethyl pullulan) were added to acetone in a weight ratio of 10: 2, respectively, and dissolved at 50 ° C. for at least 12 hours. Was prepared. The electrode active material powder (LTO) was added to the prepared polymer solution so that the polymer mixture / electrode active material powder = 10/90 weight ratio, and the electrode active material powder was crushed and dispersed at 800 nm using a ball mill method for at least 12 hours to obtain a slurry. Prepared.

The slurry thus prepared was coated on a 12um thick polyethylene porous membrane by dip coating. The coating thickness was adjusted to about 4 μm. In Example 2, the dip coating method was used in the same manner as in Example 1.

Preparation of Cathode

N-methyl-2 pyrrolidone (NMP), which is 94% by weight, 3% by weight, and 3% by weight of the LTO anode active material particles, the polyvinylidene fluoride (PVdF) binder, and the carbon black conductive agent, respectively ) To prepare a negative electrode active material slurry. The negative electrode active material slurry was applied to a copper (Cu) thin film, which is a negative electrode current collector having a thickness of 10 μm, and dried to prepare a negative electrode, and then roll press was performed.

Manufacture of batteries

A negative electrode coin half cell was manufactured using the negative electrode and the separator manufactured by the method described above, and then performance test was performed.

Battery manufacturing was assembled by stacking (stacking) the Li foil, the negative electrode and the separator, and the electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 1/2 (volume ratio), lithium hexaflo 1 mole of low phosphate (LiPF6) was injected to test the cell performance.

Comparative example  One

A battery was manufactured in the same manner as in Example 1, except that a conventional polyolethylene porous membrane without a porous coating layer was used as a separator.

Comparative example  2

A battery was manufactured in the same manner as in Example 2, except that a conventional polyolethylene porous membrane without a porous coating layer was used as the separator.

Comparative example  3

The batteries of Comparative Examples 3-1 and 3-2 were prepared in the same manner as in Examples 1 and 2, except that BaTiO ₃ powder was used instead of the electrode active material particles used to form the porous coating layer of the separator.

Separator  Surface analysis

2 is a photograph taken of the surface of the separator prepared according to Example 1 and Example 2 with a scanning electron microscope. Referring to FIG. 2, in the separator of the present invention, a porous coating layer including electrode active material particles and a binder polymer is formed on a surface thereof, and a uniform pore structure is formed by the electrode active material particles.

Separator Heat shrinkage  evaluation

The thermal contraction rate after storing the separator of an Example and a comparative example at 150 degree | times for 1 hour was shown in Table 1 below.

As a result, a separator made of a conventional polyolethylene porous membrane (Comparative Examples 1 and 2) having no porous coating layer exhibited a heat shrinkage of 80% or more, while forming a porous coating layer using electrode active material particles according to the present invention. The separators (Examples 1 and 2) exhibit thermal shrinkage of less than 5%, like separators (Comparative Example 3) in which a porous coating layer was formed using conventional filler particles. 3 is a photograph photographing the separator after the above-described heat shrinkage evaluation experiment.

Condition Example 1 Example 2 Comparative Example 1,2 Comparative Example 3 Heat shrinkage <5% <5% > 80% <5%

Battery performance evaluation

0.5C discharge capacity of each battery having a positive electrode and a negative electrode capacity of 30mAh after 0.5C charge is shown in Table 2. Referring to the results of Table 2, the separator (Examples 1 and 2) in which the porous coating layer was formed using the electrode active material particles according to the present invention is a separator in which the porous coating layer was formed using conventional filler particles (Comparative Example 3). It can be seen that the discharge capacity is increased.

4 is a coin cell according to Example 2 and Comparative Example 2 when the charge and discharge curves of the coin cells according to Example 1 and Comparative Example 1, and the LTO cathode having the same capacity when the positive electrode having the same capacity is used. Graph showing charge and discharge behavior Referring to FIG. 4, a coin cell (Examples 1 and 2) having a separator in which a porous coating layer was formed using electrode active material particles, and a coin cell having a conventional separator in which no porous coating layer was formed (Comparative Examples 1 and 2). It can be seen that the capacity is increased from 2).

On the other hand, Figure 5 is a graph showing the c-rate behavior of the coin cell according to Examples 1-2 and Comparative Examples 1-2. Referring to FIG. 5, a coin cell (Examples 1 and 2) having a separator in which a porous coating layer is formed using electrode active material particles is a coin cell (comparative examples 1 and 2) having a conventional separator that does not form a porous coating layer. It can be seen that capacity is increased at lower charge and discharge than 2). This increase in capacity was the same at high speed charge and discharge.

Example 1
(mAh) Comparative Example 1
(mAh) Comparative Example 3-1
(mAh) Discharge capacity 4.3 3.9 3.9 Example 2
(mAh) Comparative Example 2
(mAh) Comparative Example 3-2
(mAh) Discharge capacity 1.75 1.5 1.5

The separator according to the present invention has the following effects by using the electrode active material particles as filler particles of the porous coating layer formed on the porous substrate.

First, as the porous coating layer is introduced into the separator, even when the electrochemical device is overheated, a short circuit between the positive electrode and the negative electrode can be suppressed, thereby greatly improving the safety of the electrochemical device.

Secondly, the porous coating layer including the electrode active material particles, which are particles which are electrochemically oxidized and reduced, contributes to an increase in capacity of the battery. Accordingly, even when a separator is manufactured by forming a porous coating layer on a porous substrate having a conventional thickness, the problem of decreasing capacity per cell can be improved.

Claims (21)

A porous substrate having a plurality of pores; And In the separator is coated on at least one side of the porous substrate, comprising a porous coating layer formed of a mixture of a plurality of filler particles and a binder polymer, The filler particles include electrode active material particles, The content of the electrode active material particles is a separator, characterized in that 1 to 100% by weight based on the total weight of the filler particles. delete The method of claim 1, The electrode active material particles are LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiFePO ₄ , LiNiMnCoO ₂ and LiNi _{1- xy- z} Co _x M1 _y M2 _z O ₂ (M1 and M2 are independently of each other Al, Ni , Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, and x, y and z independently of each other as the atomic fraction of the elements of the oxide composition 0 ≤ x <0.5 , 0 ≦ y <0.5, 0 ≦ z <0.5), any one of the positive electrode active material particles selected from the group consisting of or a mixture of two or more thereof. The method of claim 1, The electrode active material particles are any one of negative electrode active material particles selected from the group consisting of natural graphite, artificial graphite, carbonaceous material, LTO, silicon (Si) and tin (Sn), or a mixture of two or more thereof. . The method of claim 1, The filler particles have a size of 0.001 to 10 μm. The method of claim 1, The filler particles may further include inorganic particles selected from the group consisting of inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transfer ability, and mixtures thereof. The method of claim 6, The inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT, where 0 <x <1, 0 <y <1), Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT), Hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO And ZnO, ZrO ₂ , SiO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC, and any one inorganic particles selected from the group consisting of TiO ₂ or a separator, characterized in that a mixture of two or more thereof. The method of claim 7, wherein The inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT, where 0 <x <1, 0 <y <1), Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT) and hafnia (HfO ₂ ), any one piezoelectric inorganic particle selected from the group consisting of 2 The separator characterized by the above-mentioned mixture. The method of claim 6, The inorganic particles having a lithium ion transfer ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3), and lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), (LiAlTiP) _x O _y series glass (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO _{3 ,} 0 <x <2, 0 <y <3), lithium germanium thiophosphate (LixGeyPzSw, 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5), Lithium Nitride (LixNy, 0 <x <4, 0 <y <2), SiS ₂ (LixSiySz, 0 <x <3, 0 <y <2, 0 <z <4) any one inorganic particle selected from the group consisting of glass and P ₂ S ₅ (LixPySz, 0 <x <3, 0 <y <3, 0 <z <7) series glass or two of them The separator characterized by the above-mentioned mixture. The method of claim 1, The filler particles further comprise a carbon conductive material having an electrical conductivity of 1 ms / cm or more. The method of claim 1, Separator characterized in that the weight ratio of the filler particles and the binder polymer is 50:50 to 99: 1. The method of claim 1, The binder polymer is a separator, characterized in that the solubility parameter of 15 to 45 Mpa ^1/2. The method of claim 1, The polymer is polyvinylidene fluoride-co-hexafluoropropylene (polyvinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride-co-trichloroethylene (polyvinylidene fluoride-co-trichloroethylene), polymethyl methacrylate ( polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer, polyethylene oxide, cellulose acetate (cellulose acetate), cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose cyanoethylcellulose), cyanoethyl sucrose ( A separator, characterized in that any one of a binder polymer selected from the group consisting of cyanoethylsucrose, pullulan and carboxyl methyl cellulose or a mixture of two or more thereof. The method of claim 1, The thickness of the porous coating layer is a separator, characterized in that 0.01 to 20 ㎛. The method of claim 1, The porous substrate is a separator, characterized in that the polyolefin-based porous substrate. The method of claim 1, The thickness of the porous substrate is a separator, characterized in that 1 to 100 ㎛. The method of claim 1, The porous coating layer is coated on both sides of the porous substrate, the electrode active material particles, the separator, characterized in that the positive electrode active material particles. The method of claim 1, The porous coating layer is coated on both sides of the porous substrate, the electrode active material particles, the separator, characterized in that the negative electrode active material particles. The method of claim 1, The porous coating layer is coated on both sides of the porous substrate, the electrode active material particles, the separator, characterized in that the mixture of the positive electrode active material and negative electrode active material particles. In the electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, 20. The electrochemical device according to claim 1, wherein the separator is any one of claims 1 and 3 to 19. The method of claim 20, The electrochemical device is an electrochemical device, characterized in that the lithium secondary battery.

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