KR101686598B1 - Separator for adsorbing metal ion and secondary battery comprising same, and method for preparing separator - Google Patents

Abstract

The present invention provides a separator for a secondary battery comprising an Mn scavenger capable of adsorbing Mn ions. The Mn scavenger includes a core part made of ceramic fine particles and a shell part made of a polymer electrolyte and coating the core part. The secondary battery separator according to the present invention can combine with Mn ions leaking from the Mn-based anode to mitigate the degeneration of the anode active material, and can maintain excellent battery performance and improve the life of the battery.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a separation membrane capable of adsorbing metal ions, a secondary battery including the separation membrane, and a method of manufacturing the separation membrane.

The present invention relates to a separator capable of adsorbing metal ions, a secondary battery comprising the same, and a process for producing the separator.

Recently, interest in energy storage technology is increasing. The development of rechargeable secondary batteries, especially lithium secondary batteries, has become a focus of attention as the application fields of cell phones, camcorders, laptops and even electric vehicles expand.

However, the porous separator of the secondary battery exhibits extreme heat shrinkage behavior at a temperature of about 100 캜 or more due to the characteristics of the manufacturing process including material properties and elongation, thereby causing a short circuit between the anode and the cathode. In order to solve the safety problem of such a battery, for example, Korean Patent Laid-Open Publication No. 2007-0083975 and Korean Patent Publication No. 2007-0019958 disclose a method in which a porous coating layer formed of a mixture of insulating filler particles and a binder polymer is formed on a porous substrate , And a material having a shut-down function is added to the porous coating layer.

However, for example, when the secondary battery is overcharged, excessive transition ions (metal ions) are emitted from the positive electrode and excess transition ions are inserted into the negative electrode, whereby a transition metal having a high reactivity is precipitated on the surface of the negative electrode, and the positive electrode is thermally unstable , The concern about safety such as overheat, ignition and explosion is not completely solved due to a rapid exothermic reaction due to the decomposition reaction of an organic solvent used as an electrolytic solution. Therefore, it is necessary to remove such excessive metal ions There is still a need for a battery having a novel component.

Accordingly, an object of the present invention is to provide a separation membrane having a new porous coating layer capable of adsorbing and removing metal ions, and a secondary battery comprising the same. It is also to be easily understood that the objects and advantages of the present invention can be realized by the means or method described in the claims, and the combination thereof.

The present invention provides a separation membrane for a secondary battery to solve the above-described technical problems. The separator includes a Mn scavenger capable of reducing Mn ions, and the Mn scavenger includes a core portion containing inorganic fine particles and a shell portion containing a polymer resin and coating the surface of the core portion .

Here, the Mn scavenger may have an average particle diameter of 0.1 mu m to 3 mu m.

Here, the inorganic fine particles may be electrochemically stable within an operating voltage range of the secondary battery.

The inorganic fine particles may be one or a mixture of two or more selected from the group consisting of alumina (Al ₂ O ₃ ), boehmite (AlOOH), silica (SiO ₂ ) and titanium dioxide (TiO ₂ ).

Here, the polymer resin may have a cation exchange functional group.

Here, the shell portion may have a thickness of 1 nm to 20 nm.

Here, the shell portion may include a first layer containing a polymer resin and coating the surface of the inorganic fine particles; And a second layer coating the surface of the first layer.

Here, the first layer includes a polymer resin having an anion exchange functional group, and the second layer may include a polymer resin having a cation exchange functional group.

Here, the Mn scavenger may be distributed on at least one surface of the secondary battery separator.

Here, the Mn scavenger may be distributed on the negative electrode facing surface of the separator for a secondary battery.

Here, the Mn scavenger may be uniformly dispersed in the separator for the secondary battery and on the surface thereof.

The separation membrane may further comprise: a) a separation membrane including at least one porous polymer film; Inorganic composite porous coating layer formed on at least one side surface of the substrate, and b) a separation membrane base material comprising one or more porous polymer films and an organic / inorganic composite porous coating layer formed on at least one side surface of the base material.

Here, the organic / inorganic composite porous coating layer of b) above may include a polymeric binder resin having an adhesion property and an inorganic particle.

Also, the present invention provides an electrode assembly including a cathode, a cathode, and a separator interposed between the anode and the cathode, wherein the separator is the separator according to the present invention.

The separator for a secondary battery of the present invention having a porous coating layer capable of capturing Mn on at least one surface of the porous substrate can be combined with Mn ions leaking from the Mn-based anode to relax the deterioration of the anode active material, And the life of the battery can be improved. According to an aspect of the present invention, the filler particles in the separation membrane coating layer are inert in the normal operating temperature range of the battery, but the excessive metal ions in the battery are adsorbed to maintain the safety of the battery in the range exceeding the operating temperature.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. On the other hand, the shape, size, scale or ratio of the elements in the drawings incorporated herein can be exaggerated to emphasize a clearer description.
Fig. 1 shows one specific embodiment of the Mn capturing agent according to the present invention.
Figure 2 shows an embodiment in which the shell portion is made up of multiple layers.

Hereinafter, the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor may designate the concept of a term appropriately in order to describe its own invention in the best way possible. It should be interpreted as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

The present invention relates to a separator for a secondary battery comprising an Mn scavenger capable of reducing Mn ⁺ ions. The Mn capturing agent utilizes the ion exchange property of the polymer resin, and the polymer resin can adsorb Mn ⁺ ions generated from the anode to precipitate Mn metal from the surface of the Mn capturing agent.

According to a particular embodiment of the present invention, the Mn scavenger is in the form of fine particles comprising a core part and a shell part coating the surface of the core part, wherein the core part comprises inorganic fine particles , And the shell portion includes a polymer resin. The polymer resin is a polymer compound in which a substantial part of the constituent unit contains an ionic or ionizable functional group. The polymeric compound may be formed by a non-flowable back bone by an ionic or ionizable functional group and may contain a flowable ion for neutralizing the charge of the backbone.

The polymer resin is not particularly limited as long as it is electrochemically stable in an electrochemical device using a manganese-based anode and adsorbs Mn ⁺ ions by ion exchange and precipitates Mn on the surface of the Mn adsorbent. According to one embodiment of the present invention, the polymer resin is a cation exchange resin. Examples of the cation exchange resin include poly sodium styrene sulfonate (PSS) and polyacrylic acid, and they can be used alone or in combination of two or more.

According to a specific embodiment of the present invention, the Mn capturing agent may be coated on at least one surface of the separator disposed between the anode and the cathode, or may be dispersed evenly in the inside and the outside of the separator. Thereby, the Mn capturing agent first comes into contact with the manganese ions, and at the contacting surface, the manganese ions bind with the anions of the shell portion of the Mn capturing agent, and the bonding has such affinity that the manganese does not move to the surface of the active material. Since the manganese ions preferentially bind to the surface of the Mn capturing agent, the manganese captures the manganese in the lithium secondary battery containing the manganese-based cathode active material and binds to the Mn capturing agent film, not the carbon surface of the cathode. And inhibits the degradation of the hair. Therefore, excellent battery performance can be maintained and the life of the battery can be improved.

The specific working principle is that Mn ²⁺ is stabilized by ionic bonding with anions on the surface of the ion exchange resin, and when it is deposited directly on the surface of the negative electrode active material, the phenomenon of accelerating electrolyte decomposition and increasing the resistance can be suppressed.

According to a specific embodiment of the present invention, the Mn capturing agent has an average particle diameter of 0.1 mu m to 3 mu m. When the average particle diameter of the Mn trapping agent is less than the above-mentioned range, it is buried in the pores of the porous layer separately formed for the purpose of improving the heat resistance property on the surface of the porous substrate or separation membrane used as the separation membrane and the porosity and coating property Can be degraded. In addition, if it exceeds the above-mentioned range, the adhesion between the electrode and the separation membrane can be lowered.

In the present invention, the inorganic fine particles are not particularly limited as long as they are electrochemically stable within the operating voltage range of the secondary battery. Specific examples of the inorganic fine particles include alumina (Al ₂ O ₃ ), boehmite (AlOOH), silica (SiO ₂ ), and titanium dioxide (TiO ₂ ). In the present invention, alumina and / or boehmite may be used as the inorganic fine particles. Alumina and / or boehmite are electrochemically very stable, so that the possibility of side reactions is low and the outer surface is negatively charged, which makes it possible to easily coat with alumina and / or boehmite.

In a specific embodiment of the present invention, the shell portion has a thickness of 1 nm to 20 nm. Generally, the single-layer polymer resin coating layer has a thickness of approximately 1 nm. Thus, the shell portion may have a thickness of at least about 1 nm. Also, as will be described later, in one specific embodiment of the present invention, the shell portion may be formed of multiple layers, and the shell portion may be formed to a thickness of up to about 30 nm, preferably 20 nm.

According to a specific embodiment of the present invention, the shell portion may be in the form of a multilayer composed of two or more layers. For example, the shell portion may comprise a double layer of a first layer coating the surface of the core portion and a second layer coating the surface of the first layer. Fig. 2 shows an embodiment in which the shell portion is made of a double layer. Here, the first layer is preferably a polymer resin having an anion exchange functional group. The inorganic fine particles such as alumina or boehmite forming the core in the Mn capturing agent of the present invention have anions such as OH < ^- > In addition, polymeric resins such as poly sodium styrene sulfonate (PSS) having a cation exchanger forming a shell part of the Mn capturing agent contain a functional group for cation exchange so that they are anionic. For this reason, when a fine particle core is directly coated using a polymer resin such as PSS having a cation exchanger, a coating is difficult to form due to the repulsion between anions. Therefore, in order to prevent this, the core, which is an inorganic fine particle, is first coated with a polymer resin including an anion exchange functional group to form a first layer, and then a core portion having the first layer formed is coated with a polymer resin containing a cation exchange functional group .

According to another specific embodiment of the present invention, the shell part may be formed in the form of a multilayer in which a first layer made of the anion exchange resin and a second layer made of a cation exchange resin are alternately laminated. 3 shows a shell part in the form of a multilayer in which a first layer and a second layer are alternately laminated.

As described above, when the shell portion having the first layer using the polymer resin having the anion exchange functional group and the second layer having the cation exchange functional group is formed in the inorganic fine particle core, the bonding strength between the core portion and the shell portion, And the surface area of the second layer formed on the surface of the first layer is larger than the area of the second layer formed directly on the core portion, so that the Mn capture rate is increased.

The anion exchange resin is not particularly limited as long as it has an anion exchange functional group and is electrochemically stable in an electrochemical device and has an effect of enhancing the bonding strength between the inorganic fine particle core portion and the outer layer of the shell portion. Non-limiting examples of the anion exchange resin include PAH (polyallylamine) and PEDOT (poly (3,4-ethylenedioxythophene), and one or more of them may be used in combination.

The shell portion may be formed by a layer-by-layer process of a polymer resin. When the shell portion is a double layer of anion exchange resin and cation exchange resin, the layer-by-layer production method is as follows.

First, a polymer resin, which is an anion exchange resin, is added to a solvent and mixed, followed by impregnation with an inorganic fine particle. Thereafter, the excess polymer resin and the solvent are washed and removed by centrifugation. Next, the polymer resin as the anion exchange resin is added to the solvent and mixed, and the inorganic fine particles coated with the anion exchange resin obtained in the previous step are impregnated. Thereafter, the excess polymer resin and the solvent are washed and removed by centrifugation. This process was performed to form a shell part composed of a first layer and a second layer on the surface of the inorganic fine particles. Further, according to a specific embodiment of the present invention, it is possible to repeat the above process to fabricate the shell portion into four or more layers. Preferably until the thickness of the shell portion is 30 nm, more preferably 20 nm. According to a specific embodiment of the present invention, in order to capture Mn ⁺ ions, the outermost surface portion of the shell portion is preferably coated with a cation exchange resin.

In the present invention, the method of forming the shell portion is not limited to the layer-by-layer method, and various lamination methods may be used within the scope of the present invention.

The present invention also provides a separation membrane for an electrochemical device comprising the Mn capturing agent. In the present invention, examples of the electrochemical device include a primary cell, a secondary battery, and a lithium ion secondary battery. However, the present invention is not limited thereto.

According to a specific embodiment of the present invention, the separator for electrochemical devices is distributed on the surface portion of the separator, and / or on one surface of the separator, which faces the negative electrode. The method of distributing the Mn capturing agent to the inside and / or the surface portion of the separating membrane is not particularly limited as long as the Mn capturing agent can be uniformly distributed in the inside and / or the surface portion of the separating membrane and / .

In one specific embodiment of the present invention, the separation membrane may be, for example, the following a) or b).

a) a separation membrane comprising at least one porous polymer film

b) a composite membrane comprising a separation membrane substrate comprising at least one porous polymer film and an organic / inorganic composite porous coating layer formed on at least one side of the substrate

In one specific embodiment of the present invention, the Mn capturing agent may be incorporated into the composition for preparing a porous film and uniformly distributed on the inside and the surface of the film. For example, when a polymer resin such as a polypropylene and / or a polyethylene resin is melted / extruded to produce the porous polymer film, the Mn capturing agent described above is added to the melt of the resin and stirred / It is possible to uniformly distribute the Mn capturing agent to the inside and the surface portion of the porous film. Here, the content of the Mn capturing agent contained in the composition for separator base material is not particularly limited, but is preferably 15% by weight to 30% by weight based on 100% by weight of the porous film.

According to another aspect of the present invention, a separation membrane including an Mn capturing agent can be formed by coating a porous film. For example, a method may be employed in which a mixed solution prepared by dispersing the Mn capturing agent in an appropriate solvent is prepared, and then a predetermined separation membrane prepared is coated with the mixed solution. The coating method is not particularly limited, and various methods such as dip coating, roller coating, spray coating and flow coating can be applied.

In one embodiment of the present invention, the separation membrane may be a composite separation membrane having a porous coating layer formed on the surface of the porous film to improve heat resistance and shrink resistance.

The porous coating layer comprises a mixture of binder polymer resin and inorganic particles having an adhesive property such as acrylate resin or PVdF, and the pores formed by the interstitial volume by the inorganic particles filled with the inorganic particles Lt; / RTI >

In one specific embodiment of the present invention, the inorganic particles may include high-permittivity inorganic particles having a dielectric constant of 5 or more, or 10 or more, inorganic particles having lithium ion-transporting ability, or a mixture thereof. Nonlimiting examples of such inorganic particles 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 <<y<1 _{Im), 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 , SiC, TiO _2, and the like.

The porous coating layer may contain inorganic particles in an amount of 50 to 99% by weight, particularly 60 to 95% by weight, based on 100% by weight of the porous coating layer. The Mn capturing agent according to the present invention may include Or it is possible to substitute all of them. Preferably, the Mn capturing agent may be replaced by inorganic particles in an amount of 30 wt% to 50 wt% in 100 wt% of the inorganic particles. If the Mn capturing agent is excessively substituted by more than 50% by weight of the inorganic particles, a problem of side reaction during cell driving may occur. On the other hand, when the amount of the Mn capturing agent is less than 30 wt%, it is difficult to achieve the desired Mn trapping effect.

In this case, the Mn trapping agent may be dispersed in the composition for preparing a porous coating layer to uniformly distribute the Mn trap in the porous coating layer. First, a polymer binder resin, an inorganic particle and an Mn scavenger are added to an appropriate solvent to prepare a uniform slurry composition. Next, the slurry prepared above is applied to the surface of the prepared porous film and dried. The slurry coating can be carried out by a conventional coating method known in the art, for example, die coating, roll coating, dip coating and the like. In this case, the porous film may contain an Mn capturing agent.

The present invention also provides a positive electrode containing a manganese-based lithium metal oxide, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a secondary battery comprising the electrolyte.

In a specific embodiment of the present invention, the separation membrane is such that the above-mentioned Mn capturing agent is uniformly distributed on the surface or uniformly dispersed in the separation membrane.

It is preferable that the separation membrane is a porous substrate which can be used in a secondary battery and prevents short-circuiting of the electrode and has high ion mobility. As the porous substrate, a polyolefin-based porous substrate can be used, and the polyolefin-based porous substrate can be formed of any one selected from the group consisting of polyethylene, polypropylene, polybutylene, and polypentene.

According to one specific embodiment of the present invention, it is preferable to use a positive electrode containing a manganese-based lithium metal oxide, and there is no particular limitation on both electrodes of the positive electrode and the negative electrode. According to a conventional method known in the art The electrode active material can be produced in the form bound to the electrode current collector. The cathode active material is a lithium manganese oxide having a spinel structure or a lithium manganese oxide having a spinel structure and other cathode active materials. In order for the Mn capturing agent to function in accordance with the present invention, it is preferable that the cathode contains at least 30 wt% of the manganese spinel-based cathode active material.

As a non-limiting example of the negative electrode active material, a conventional negative electrode active material that can be used for a negative electrode of an electrochemical device can be used. In particular, lithium metal or a lithium alloy, carbon, petroleum coke, activated carbon, Lithium-adsorbing materials such as graphite or other carbon-based materials and the like are preferable. Non-limiting examples of the positive current collector include aluminum, nickel, or a combination thereof. Examples of the negative current collector include copper, gold, nickel, or a copper alloy or a combination thereof Foil to be manufactured, and the like.

Electrolyte that may be used in the secondary battery of the present invention is A ⁺ B ^- A salt of the structure, such as, A ⁺ comprises Li ^+, Na ^+, an alkali metal cation or an ion composed of a combination thereof, such as K ⁺ and B ^- is _{^{PF 6 -, BF 4 -,}} Cl -, Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C ( CF ₂ SO _{2) 3} ^- anion, or a salt containing an ion composed of a combination of propylene carbonate (PC like), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DMP), dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone Butyrolactone), or a mixture thereof, but the present invention 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 required properties of the final product. That is, it can be applied before assembling the cell or at the final stage of assembling the cell.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments 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 embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Preparation Example: Preparation of Mn capturing agent

50 g of PAH was added to 100 ml of a 0.5 molar NaCl solution and mixed to prepare a first mixture. Then, 10 g of alumina was impregnated into the first solution, and then the excess polymer resin and NaCl were washed and removed through centrifugation (5000 rpm, 5 minutes) to complete the first coating process. Next, 50 g of PSS was added to 100 ml of a 0.5 molar NaCl solution and mixed to prepare a second mixture. Then, 10 g of the PAH-coated alumina particles were impregnated into the second mixture, and the excess polymer resin and NaCl were washed and removed through centrifugal separation (5000 rpm, 5 minutes) to complete the secondary coating process. Then, the first coating process and the second coating process were repeated 15 times to obtain an Mn capturing agent. The average particle diameter of the Mn capturing agent was 0.5 mu m.

Example: Preparation of a separation membrane having a porous coating layer containing Mn capturing agent

4.5 g of PVdF-CTFE (polyvinylidene fluoride-chlorotrifluoroethylene copolymer) was added to 85.5 g of acetone and dissolved at 50 DEG C for about 12 hours or more to prepare 90 g of a binder polymer solution. 8 g of the Mn capturing agent obtained in the above Preparation Example and 10 g of alumina particles (particle diameter 500 nm) were added to the prepared binder polymer solution and uniformly mixed to prepare a composition for separator coating. A polyethylene porous membrane substrate (10 cm x 10 cm) was dip coated with the above composition and dried to prepare a separation membrane having a porous coating layer.

Comparative Example

4.5 g of P VdF-CTFE (polyvinylidene fluoride-chlorotrifluoroethylene copolymer) was added to 85.5 g of acetone and dissolved at 50 ° C for about 12 hours or more to prepare 90 g of a binder polymer solution. 18 g of alumina particles (particle diameter: 500 nm) was added to the prepared binder polymer solution and uniformly mixed to prepare a composition for separator coating. A polyethylene porous membrane substrate (10 cm x 10 cm) was dip coated with the above composition and dried to prepare a separation membrane having a porous coating layer.

Experimental Example

The separation membrane prepared in Examples and Comparative Examples was cut into 50 mm * 50 mm and impregnated into 200 ml of DEC (diethylene carbonate) solution containing 50 ppm of Mn ions. After 7 days, the separation membrane was taken from the solution and dried. ICP measurement results were as follows. The amount of Mn obtained was quantified with respect to the weight of the membrane and expressed in mg / g. As a result, the amount of Mn of 1.8 mg / g was obtained in the separator of the Example, while the amount of Mn of 0.20 mg / g was analyzed in the separator of Comparative Example.

Claims (14)

A separator for a secondary battery, comprising: a Mn scavenger capable of reducing Mn ions, wherein the Mn scavenger comprises a core portion containing inorganic fine particles and a polymer resin, and coating the surface of the core portion And a shell portion.
The method according to claim 1,
Wherein the Mn scavenger has an average particle diameter of 0.1 mu m to 3 mu m.
The method according to claim 1,
Wherein the inorganic fine particles are electrochemically stable within an operating voltage range of the secondary battery.
The method according to claim 1,
Wherein the inorganic fine particles are one kind or a mixture of two or more kinds selected from the group consisting of alumina (Al ₂ O ₃ ), boehmite (AlOOH), silica (SiO ₂ ) and titanium dioxide (TiO ₂ ) .
The method according to claim 1,
Wherein the polymer resin has a cation exchange functional group.
The method according to claim 1,
Wherein the shell portion has a thickness of 1 nm to 20 nm.
The method according to claim 1,
Wherein the shell portion comprises a first layer comprising a polymer resin and coating the surface of the inorganic fine particles; And a second layer coating the surface of the first layer.
8. The method of claim 7,
Wherein the first layer comprises a polymer resin having an anion exchange functional group and the second layer comprises a polymer resin having a cation exchange functional group.
The method according to claim 1,
Wherein the Mn scavenger is distributed on at least one surface of the separator for a secondary battery.
10. The method of claim 9,
Wherein the Mn scavenger is distributed on a negative electrode facing surface of the separator for a secondary battery.
11. The method of claim 10,
Wherein the Mn scavenger is uniformly dispersed in the inside and the surface of the separator for a secondary battery. The method according to claim 1,
Wherein the separation membrane is the following a) or b):
a) a separation membrane comprising at least one porous polymer film
b) a separator for a secondary battery comprising a separator substrate including at least one porous polymer film and an organic / inorganic composite porous coating layer formed on at least one surface of the substrate.
13. The method of claim 12,
Wherein the organic / inorganic composite porous coating layer of b) comprises a polymeric binder resin having an adhesive property and inorganic particles.
An electrode assembly comprising an anode, a cathode, and a separation membrane interposed between the anode and the cathode, wherein the separation membrane is the separation membrane according to any one of claims 1 to 13.

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