KR20100129471A - Organic/inorganic composite separator for electrochemical cell and electrochemical cell including the same - Google Patents

Abstract

PURPOSE: An organic/inorganic composite separator is provided to ensure excellent acid resistance, to secure stability from acid generated by moisture, and to improve performance and lifetime property of an electrochemical cell. CONSTITUTION: An organic/inorganic composite separator is a sheet type separation film with a porous structure capable of ion transfer while maintain an insulation state. A non-oxide inorganic powder is applied on the surface of the separation film. The non-oxidation inorganic powder is Si3N4, SiC, and AlN or WC.

Description

Organic / inorganic composite separator for electrochemical cell and electrochemical cell including the same}

The present invention relates to an organic-inorganic composite separator for an electrochemical cell and an electrochemical cell including the same, and more particularly, a sheet type having a porous structure capable of moving ions while maintaining an insulating state of electrodes facing each other on both sides. As a separator, by coating a non-oxide-based inorganic powder on the surface of the separator not only increases the mechanical strength of the separator, but also provides excellent acid resistance to the organic-inorganic composite separator for electrochemical cells having excellent performance and life characteristics of the separator and cells, and the like It relates to an electrochemical cell.

As technology development and demand for mobile devices increase, the demand for electrochemical cells capable of charging and discharging as energy sources is rapidly increasing. Accordingly, many studies on electrochemical cells capable of meeting various needs have been conducted. Representative examples of such electrochemical cells include secondary batteries.

For example, the lithium secondary battery has a structure in which a non-aqueous electrolyte containing lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode on which an active material is coated on a current collector. Lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium composite oxide, and the like are mainly used as the cathode active material, and carbonaceous materials are mainly used as the cathode oxide.

Such lithium secondary batteries cause acid (eg, hydrofluoric acid (HF)) by causing decomposition of the electrolyte when the moisture content increases in the battery, and the generated acid is a cathode solid electrolyte interface (SEI). Side reactions such as decomposition of the cation and dissolution of the positive electrode active material, and ultimately cause problems such as a decrease in battery capacity and an increase in internal resistance. That is, since the performance of the lithium secondary battery is greatly affected by the moisture content in the battery, it is important to prevent the penetration of moisture in the battery manufacturing process.

In this regard, in Patent Document 1, in order to impart mechanical strength to a nonwoven fabric or a woven fabric separation membrane made of an inorganic fibrous material, a silane-based compound is applied to form an inorganic particle layer in the separation membrane to improve adhesion to the inorganic particle layer and at the same time hydrophobic effect. Patent Document 2 discloses a technique of obtaining a silane-based compound before or after the coating of the inorganic coating in order to form an inorganic coating on the separation membrane having an asymmetric pore structure having a different internal pore size. . However, the above technique is not preferable because undesired unnecessary side reactions can occur in a secondary battery in which a complicated chemical reaction occurs by using a highly reactive substituent such as a methoxy group as a silane compound.

In addition, Patent Document 3 discloses a separator in which a clay mineral having affinity for a polar solvent is coated on the surface of the separator, and Patent Document 4 discloses a compound having low chemical reactivity so as to exhibit high water repellency on at least one surface of the separator. Disclosed is a separation membrane subjected to hydrophobic surface treatment. However, the above technique still has the above-mentioned problem.

Patent Document 1: Korean Patent Publication No. 2005-0035281

Patent Document 2: Korean Patent Publication No. 2005-0086877

Patent Document 3: Korean Unexamined Patent Publication No. 2008-0017110

Patent Document 4: Korea Patent Publication No. 2008-0025433

Accordingly, in the present invention, the surface of the separator for electrochemical cells is coated with a non-oxide inorganic powder so that the separator has overall acid resistance, thereby preventing dissolution of the separator from acid generated by adsorption and inflow of water during the battery manufacturing process. The present invention was completed based on this.

Accordingly, it is an object of the present invention to provide an organic-inorganic composite separator for an electrochemical cell that not only increases the mechanical strength of the separator, but also has excellent acid resistance.

Another object of the present invention to provide an electrochemical cell with improved long-term life of the cell including the organic-inorganic composite separator.

The organic-inorganic composite membrane for an electrochemical cell of the present invention for achieving the above object is a sheet-type separator having a porous structure capable of moving ions while maintaining the insulation state of the electrodes facing each other on both sides, a non-oxide on the surface of the separator It is characterized in that the inorganic powder is coated.

In the separator, the non-oxide inorganic powder is Si ₃ N ₄ , SiC, AlN, or WC characterized in that.

In the separation membrane, the non-oxide inorganic powder is characterized in that the nitride.

In the separator, the nitride is characterized in that Si ₃ N ₄ , or AlN.

Electrochemical cell comprising an organic-inorganic composite separator for an electrochemical cell for achieving another object of the present invention is characterized in that the sheet-like separator according to any one of the above-described embodiment comprises an electrode assembly interposed between the positive electrode and the negative electrode It is done.

In the electrochemical cell, the electrochemical cell is characterized in that the secondary battery or capacitor.

In the electrochemical cell, the secondary battery is characterized in that the lithium secondary battery.

In the electrochemical cell, the secondary battery is used as a unit cell in a battery pack of high output large capacity.

As described above, the separator according to the present invention is a porous separator in which at least one surface is coated with a non-oxide inorganic powder, and may have excellent acid resistance, so that it is stable from acid generated by moisture sucked in the manufacturing process of the battery. It is possible to improve the performance and life characteristics of the electrochemical cell containing it.

Looking at the present invention in more detail as follows.

In general, an electrochemical cell may be manufactured by mounting an electrode assembly including an anode, a cathode, and a separator interposed therebetween in a case, injecting a non-aqueous electrolyte, and then sealing the case. In such an electrochemical cell, an acid (eg, hydrofluoric acid (HF)) is generated by reacting water (H ₂ O) penetrated into an electrode mixture or electrolyte solution and an electrolyte solution (LiPF ₆ ), in particular, during electrode manufacturing. Acid dissolves the coated oxide-based inorganic powder in order to improve the mechanical strength of the separator, thereby reducing the mechanical strength and long life of the electrochemical cell.

Therefore, in the present invention, by coating the surface of the separator with a non-acid inorganic powder that is resistant to acid (acid), the production of acid generated by the moisture adsorbed or introduced into the battery during the electrode manufacturing process is suppressed. Thus, the high temperature storage characteristics can be improved by preventing side reactions caused by moisture in the electrochemical cell. Specifically, by coating the separator with a non-oxide inorganic powder, it is possible to prevent dissolution of the inorganic powder by hydrofluoric acid generated by the action of moisture in the cell, to prevent decomposition of the negative electrode SEI film, and to dissolve the positive electrode active material. This can minimize the phenomenon.

According to the present invention, examples of the non-oxide inorganic powder include Si ₃ N ₄ , SiC, AlN, or WC, and the like. More preferably, the non-oxide inorganic powder is nitride. Referring to Figure 1, the separator according to the present invention can be prepared by applying and drying the nitride ceramic powder on the separator. Examples of the nitrides include Si ₃ N ₄ , or AlN.

In the present invention, the method of coating the non-oxide inorganic powder on at least one surface of the separator is not particularly limited. Coating the solution of the binder polymer in which the inorganic particles are dispersed on the porous substrate may be 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. In addition, the porous active layer may be selectively formed on both surfaces or only one surface of the porous substrate.

The organic / inorganic composite separator of the present invention prepared as described above may be used as a separator of an electrochemical device, preferably a lithium secondary battery. In this case, when a gelable polymer is used as the binder polymer component when the liquid electrolyte is impregnated, the gel-organic organic / inorganic composite electrolyte may be formed by assembling the battery using the separator and then reacting the gel with the injected electrolyte and the polymer.

The present invention also provides an electrochemical device including an anode, a cathode, an organic / inorganic composite separator coated with the above-mentioned porous active layer interposed between the anode and the cathode, and 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. Particularly, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery is preferable.

The electrochemical device may be manufactured according to a conventional method known in the art, and according to one embodiment thereof, the electrolyte is injected after assembling the organic / inorganic composite separator described above between the positive electrode and the negative electrode. It can be manufactured by.

The electrode to be applied together with the organic / inorganic composite separator of the present invention is not particularly limited, and according to a conventional method known in the art, the electrode active material may be manufactured in a form bound to the electrode current collector.

The positive electrode active material of the electrode active material, for example, can be used 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 a combination thereof It is preferable to use one lithium composite oxide. As the negative electrode active material, for example, a conventional negative electrode active material that can be used for the negative electrode of the conventional electrochemical device can be used, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, Lithium adsorbents such as graphite or other carbons are preferred. The positive electrode current collector includes, for example, a foil made of aluminum, nickel, or a combination thereof, and the negative electrode current collector is, for example, copper, gold, nickel, or a copper alloy or a combination thereof. By foil.

Electrolyte that may be used in the present invention is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, K ^+, and contains the ion consisting of alkali metal cations or a combination of both 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 Salts containing ions consisting of anions such as SO ₂ ) ₃ ^- or a combination thereof are 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 (-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 organic / inorganic composite separator of the present invention to a battery, a lamination, stacking and folding process of the separator and the electrode may be performed in addition to the general winding process.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Experimental Example 1 Comparison of Acid Resistance of Membrane

Example 1

1-1. Preparation of Membrane

As a bare film of the separator, a porous polyolefin-based separator having a thickness of 20x10 ^-6 m was used, and the coating solution was dispersed in Sonicate for 20 minutes after adding 0.1 to 0.5 wt% of Si ₃ N ₄ and 0.1 to 1 wt% of PVdF to toluene. A slurry was prepared by preparing a slurry and coating Si ₃ N ₄ on both surfaces of the separator by a dip coating method.

Comparative Example 1

A separator was prepared in the same manner as in Example 1, except that the separator was coated with Al ₂ O ₃ .

In order to evaluate the acid resistance of the separators prepared in Example 1 and Comparative Example 1, 1M LiPF ₆ EC / EMC (1/2 wt / wt) of 5x5 cm ² prepared in Example 1 and Comparative Example 1, respectively The solution was stored in vial with electrolyte and 500 ppm HF (45 wt% aqueous solution) for 60 to 1 week. Since each electrolyte was measured by Si and Al content through ICP analysis. As a result, 5 (± 1) ppm was measured in the electrolyte solution in contact with the separator of Example 1, while Al of 730 (± 10) ppm was measured in the electrolyte solution in contact with the separator of Comparative Example 1. This is because the separation membrane of Comparative Example 1 has a chemical dissolution reaction of Al ₂ O ₃ by HF present in the electrolyte, whereas the separation membrane of Example 1 using Si ₃ N ₄ which is inert to HF dissolves Si ₃ N ₄ . It shows that the reaction occurred in a slight degree. That is, it can be seen that the separator of Example 1 according to the present invention has superior acid resistance than the separator of Comparative Example 2.

Experimental Example 2 Evaluation of High Temperature Storage Characteristics of Battery

Example 2

2-1. Manufacture of anode

LiCoO ₂ was used as a positive electrode active material, and 95% by weight of LiCoO ₂ , 2.5% by weight of Super-P (conductor), and 2.5% by weight of PVdF (binder) were added to N-methyl-2-pyrrolidone (NMP) as a solvent. To prepare a positive electrode mixture slurry, and then coated, dried, and pressed on a long sheet aluminum foil to prepare a positive electrode.

2-2. Preparation of Cathode

Artificial graphite was used as the negative electrode active material, and 95% by weight of artificial graphite, 2.5% by weight of Super-P (conductive material), and 2.5% by weight of PVdF (binder) were added to NMP as a solvent to prepare a negative electrode mixture slurry. The negative electrode was prepared by coating, drying and pressing on a long sheet copper foil.

2-3. Manufacture of batteries

1M LiPF ₆ EC / EMC (1/2 wt / wt) containing 200 ppm of HF (45 wt% aqueous solution) interposed between the separator of Example 1 and the cathode and cathode of 2-1 and 2-2. An electrolyte solution was injected to prepare a coin-type lithium secondary battery.

Comparative Example 2

A coin-type lithium secondary battery was manufactured in the same manner as in Example 2, except that the separator of Comparative Example 1 was used.

In order to evaluate the high temperature storage characteristics of the electrodes prepared in Example 2 and Comparative Example 2, the batteries prepared in Example 2 and Comparative Example 2, respectively, after storing for 60 to 2 weeks in a fully charged state, 1 C Dose was measured and shown in Table 1 as a ratio to the initial dose.

battery  Capacity before high temperature preservation Capacity after high temperature storage  Retention rate Example 2  5.4 mAh  4.8 mAh  90.6% Comparative Example 2  5.3 mAh  3.1 mAh  58.5%

As shown in Table 1, the battery of Example 2 using the excellent acid resistance separator according to the present invention was very high as the ratio of the capacity to the initial capacity after storage at 90% or more. That is, by using a non-oxide inorganic powder, it can be confirmed that the capacity storage characteristics are improved by suppressing side reactions inside the battery due to the acid component of the electrolyte during high temperature storage. On the other hand, the battery of Comparative Example 2 using a separator having relatively low acid resistance has a higher capacity than the initial capacity after high temperature storage as a result of chemical dissolution reaction of the oxide inorganic powder and the resulting by-products causing various side reactions. It is estimated to have decreased in width.

1 is a schematic view showing a separator coated with a nitride ceramic powder according to an embodiment of the present invention.

Claims (8)

A sheet-type separator having a porous structure capable of moving ions while maintaining the insulation state of electrodes facing each other on both sides, and an organic-inorganic composite separator for an electrochemical cell, wherein a non-oxide inorganic powder is coated on the surface of the separator. . The method according to claim 1, The organic-inorganic composite separator for an electrochemical cell, wherein the non-oxide inorganic powder is Si ₃ N ₄ , SiC, AlN, or WC. The method according to claim 2, The organic-inorganic composite separator for an electrochemical cell, wherein the non-oxide inorganic powder is nitride. The method according to claim 3, The organic-inorganic composite separator for an electrochemical cell, wherein the nitride is Si ₃ N ₄ , or AlN. An electrochemical cell comprising an organic-inorganic composite separator for an electrochemical cell, characterized in that the sheet separator according to any one of claims 1 to 4 comprises an electrode assembly interposed between the anode and the cathode. The method according to claim 5, The electrochemical cell is an electrochemical cell, characterized in that the secondary battery or capacitor. The method according to claim 6, The secondary battery is an electrochemical cell, characterized in that the lithium secondary battery. The method according to claim 6, The secondary battery is an electrochemical cell, characterized in that used as a unit cell in a high-capacity battery pack.

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