KR101512170B1 - Solid electrolyte based Nonwoven separator for lithium Secondary Battery and its making method - Google Patents

Abstract

The present invention relates to a composite nonwoven fabric separator for a lithium secondary battery and a method of manufacturing the same, and more particularly, to a nonwoven fabric separator used for a lithium secondary battery, which has a high heat conductivity, Which is free from precipitation of metal ions in a lithium secondary battery, and a method for producing the same.
The nonwoven fabric separator for a lithium secondary battery according to the present invention is a non-woven fabric separator of polyacrylonitrile (PAN), which has a LAGP (lithium-aluminum-germanium-for-state) The present invention relates to a method for producing a solid electrolyte composite nonwoven fabric separating membrane, which comprises separating a LAGP sample and a PAN sample into a solvent, and then dispersing the solution in a solvent is applied to one side of a previously prepared PAN separator by electrospinning Followed by squeezing at a high temperature.

Description

Technical Field [0001] The present invention relates to a solid electrolyte based nonwoven fabric separator for a lithium secondary battery,

The present invention relates to a composite nonwoven fabric separator for a lithium secondary battery and a method of manufacturing the same, and more particularly, to a nonwoven fabric separator used for a lithium secondary battery, which has a high heat conductivity, Which is free from precipitation of metal ions in a lithium secondary battery, and a method for producing the same.

It is desirable to use a lithium secondary battery having a high energy density accompanied with the recent spread of various portable electronic devices and high performance. In addition, although a number of automobiles conscious of environmental response such as hybrid automobiles have been developed, a lithium secondary battery having a high energy density has attracted much attention as one of the power sources to be mounted. Most of the lithium secondary batteries are composed of an anode, an electrolyte, a separator, and a cathode. Separator The main function is to prevent shorting of the positive electrode and the negative electrode. However, the required characteristics are the mobility, strength and durability of lithium ion.

In the current separator used in lithium secondary batteries, polyolefin such as polyethylene is generally used. Polyolefin is widely used because it satisfies the required characteristics of a lithium secondary battery and also has a function of preventing a heat congestion by shutting off a current from the occlusion of a hole due to a high temperature and a shut down function as a stabilizing function at a high temperature . However, even if the hole is closed due to the temperature rise and the current is cut off, the temperature of the battery becomes higher than the melting point (130 ° C) of the polyethylene constituting the porous film and the heat resistance is exceeded, the shot down function is lost. As a result, thermal congestion of the battery may occur due to a short circuit between the electrodes, which may cause accidents due to ignition. For this reason, a separator capable of maintaining a shot down function even at a high temperature is required in order to secure new stability.

In accordance with such industrial requirements, a separator in the form of a nonwoven fabric instead of a conventional polyolefin-based porous separator has been actively studied. The non-woven separator made by thermal bonding has excellent overall battery reliability due to the relatively large porosity as compared with the porous separator manufactured by the dry / wet process, and the shrinkage ratio at high temperature is small Thermal stability can be ensured and attention is paid to the use of a large-capacity battery such as an electric vehicle battery. However, in the case of the nonwoven fabric separator, the metal ions eluted from the anode migrate to the cathode due to an excessively large pore size and uneven surface, and metal precipitation occurs, thereby causing internal short circuit due to dendrite formation.

In order to improve the technical problems of such a nonwoven fabric separator, for example, JP-A 60-52 (1985. 1.5)], a separator in which polyethylene powder is adhered to a polypropylene nonwoven fabric has been proposed. Polypropylene) has a melting point near 165 ° C. and does not show a shot down function, the nonwoven fabric may be melted and shrunk to cause a new thermal runaway. In addition, the particle diameter of polyethylene (Polyethyiene) And the like, there is a problem such as internal resistance and the like, and it can not be said that sufficient battery characteristics can be expressed.

For example, Japanese Unexamined Patent Application Publication No. 2004-115980 (Apr. 4, 2004) discloses a method of using a nonwoven fabric mainly composed of a low melting point resin component and a high melting point resin component as a separator It has been proposed that, when the temperature inside the battery rises, the low-melting-point resin component is melted and a small hole between the fibers is closed, thereby exhibiting a shot down function.

However, in the same separator, in order to develop the strength of the nonwoven fabric, it is necessary to melt the low-melting-point resin component and sufficiently knit the fibers, but the difference between the temperature required for the strength development and the shutdown temperature is small, , It is difficult to control the pore size or the small pore size between the fibers. In addition, when the shot down function is not sufficiently developed, there is a disadvantage that the nonwoven fabric itself may melt and shrink.

Although the additive coating composite separator thus far studied has improved mechanical strength and heat shrinkability, it has been unable to exhibit sufficient cell characteristics due to the problem of deterioration of ionic conductivity and inhibition of reactivity at high voltage.

It is an object of the present invention to provide a nonwoven fabric separator which maintains heat resistance and heat shrinkability at a current nonwoven fabric separator level, a shut down function, further increases ion conductivity, It is an object of the present invention to provide a solid electrolyte composite nonwoven fabric separator which can be used as a separator for a lithium secondary battery having a function as a separator.

The objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood from the following description.

The nonwoven fabric separator for a lithium secondary battery according to the present invention is characterized in that a solid electrolyte is attached to a surface facing a positive electrode and a solid electrolyte is not attached to a surface facing the negative electrode, Is a solid electrolyte composite nonwoven fabric separator.

Preferably, the solid electrolyte is LAGP (lithium-aluminum-germanium-perovskite), more preferably LAGP has the formula [Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ].

The nonwoven fabric separator for a lithium secondary battery according to the present invention is a non-woven fabric separator of polyacrylonitrile (PAN), which has a LAGP (lithium-aluminum-germanium-for-state) LAGP-bonded layer separated by a layered structure of a solid electrolyte composite nonwoven fabric.

The method for producing a nonwoven fabric separator for a lithium secondary battery according to the present invention comprises dispersing a LAGP sample and a PAN sample in a solvent and then dispersing the solution in the solvent by electrospinning one side of a PAN separator prepared in advance and then pressing it at a high temperature.

According to a preferred embodiment, the LAGP has the formula [Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ], and the solvent is DMF (N, N-dimethylformamide).

As described above, the solid electrolyte composite nonwoven fabric separator (separator) of the present invention maintains the heat resistance, heat shrinkability and shut down function of the nonwoven fabric separator at present, further enhances the ion conductivity and precipitates metal ions in the counter electrode It is possible to use it as a separator for a battery having a function of blocking the battery. Therefore, the solid electrolyte composite nonwoven fabric separator of the present invention is preferably a lithium secondary battery with high performance and high energy density.

The solid electrolyte composite nonwoven fabric separator according to the present invention is advantageous in that a simple method of electrospinning can be attached to one surface (a surface facing the anode) of the separator, thereby simplifying the manufacturing process and increasing the working efficiency.

FIG. 1 is a diagram illustrating the structure and electrospinning process of a composite separator according to a preferred embodiment of the present invention.
Fig. 2 shows a component construction diagram of a pouch cell to which a separator is applied and an assembling process of the pouch cell.
3 is an SEM photograph of a PE separator, a PAN separator, and a composite separator of Example 1, respectively.
4 is a graph showing the electrochemical charge / discharge cycle characteristics at full temperature and at high temperature for a full cell manufactured using a PE separator and a full cell manufactured by the embodiment.
5 is a graph showing a high rate discharge characteristic of a battery with respect to a full cell made of a pouch separator to which a PE separator is applied and a full cell manufactured according to an embodiment.
FIG. 6 shows the result of analyzing the EDS composition on the cathode surface (SEM BS-image) after continuously filling the pouch full cell to which the PAN separator was applied and the pouch full cell prepared in the example.
Fig. 7 is a photograph showing the heat shrinkage behavior of the PE separator and the composite separator produced by the embodiment. Fig.
8 is a graph showing results of an ARC (Accelerated Calorimetry) experiment to determine the relative thermal stability of a pouch pull cell equipped with a PE separator and a pouch pull cell manufactured according to an embodiment.

In order to solve the problems of conventional PE (polyethylene, polyethyiene) separator and PAN (poly acrylonitrile) separator, the present inventors have proposed a LAGP (lithium-aluminum-germanium- In particular, Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ] was mixed with PAN (polyacrylonitrile) samples and electrospinning on a conventional PAN separator to develop a composite separator with a solid electrolyte LAGP on one side only Respectively.

That is, the solid electrolyte composite separator of the present invention is a composite nonwoven fabric separator having a LAGP having a high ionic conductivity attached to one side of the PAN nonwoven fabric separator facing the anode.

In the method for producing a solid electrolyte composite separator of the present invention, a sample (powder) of LAGP [Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ] used as a solid electrolyte and a PAN sample (powder) Then, one surface of the PAN separator prepared in advance is subjected to electrospinning, and then compressed at a high temperature as a whole to complete a composite separator having LAGP attached on one surface facing the anode.

1 shows a structure of a composite separator according to a preferred embodiment of the present invention.

The composite separator of the present invention has a double structure consisting of a portion made only of the PAN separator and a portion made of the PAN separator having the LAGP attached thereto. The part made only of the PAN separator faces the negative electrode, and the part made of the PAN separator having the LAGP is the part facing the positive electrode.

The reason for having the double structure in the present invention is that if the solid electrolyte LAGP is formed on the surface facing the negative electrode, the lithium in the positive electrode moves to the negative electrode through the separator and the solid electrolyte In the LAGP, the bond of Ge-oxygen is further reacted to reduce the conductivity of Ge due to the reduction of Ge, and the function of the function is lost.

Therefore, in the solid electrolyte composite nonwoven fabric separator of the present invention, a solid electrolyte is attached to the surface facing the anode, but a solid electrolyte is not attached to the surface facing the anode.

LAGP (lithium-aluminum-germanium-for-state) is a sample used as a solid electrolyte, and a solid electrolyte of a battery can be divided into an inorganic type having high ionic conductivity and durability and a polymer type having high productivity.

The mineral series is again divided into the sulfide series and the oxide series. Among them, the solid electrolytes showing the most progress are sulfide series materials having an ionic conductivity of 10 ^-3 S / cm at the electrolyte level are being developed.

A representative example is a solid electrolyte having a structure of NASICON-Na Super Ionic Conductor having conductivity of sodium ion. Due to the three-dimensional interstitial structure, lithium ion migration is easy in all directions and high ion conductivity can be expected. It has been studied extensively and is easier to handle than the sulfide-based solid electrolyte, and has excellent thermal stability and chemical stability.

NaM ₂ (PO ₄ ) ₃ structure can be represented by A _{1 + x} M _x M ' _1-x (PO ₄ ) ₃ instead of Na and M in place of other materials. Since the Ge-O bond such as Li which improves the high grain boundary resistance of the nacicon structure has a strong covalent bond, in the present invention, LAGP (lithium-aluminum-germanium-phosphorous) is used as a solid electrolyte capable of increasing ion conductivity Respectively.

Therefore, in the present invention, the ion conductivity of the separator (separator) is increased by manufacturing the separator using LAGP (lithium-aluminum-germanium-for-state) having the highest ionic conductivity and having the nacicon structure, It is possible to prevent the precipitation of

The composite separator of the present invention is produced by mixing and dispersing a sample (powder) of LAGP (Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ] used as a solid electrolyte and a PAN sample (powder) in a solvent, (Electrospinning) on one side of the substrate. That is, only one side of the PAN separator prepared beforehand (the side facing the anode) is electrospinning to fabricate a separator, and then the battery is produced facing the counter electrode.

In other words, the nonwoven fabric separator of the present invention has a double structure. One side of the nonwoven fabric separator faces the negative electrode with a previously prepared PAN separator portion, and the other side is a newly added portion by electrospinning. The PAN separator portion And this portion is a portion facing the anode.

Then, after the electric discharge, the mixture is compressed at a high temperature of 80 degrees to complete the composite separator of the present invention. Here, the reason for squeezing at a high temperature is to stabilize a polymer material such as evaporation of water.

Example 1. Fabrication of composite separator

For the preparation of the composite separator of the present invention, a primary separation membrane for the composite membrane was prepared by using a polyacrylonitrile (PAN) powder sample and a LAGP solid electrolyte in a solvent, N, N-dimethylformamide. That is, the LAGP sample and the PAN sample were measured in DMF solution as a solvent at 70:30 (wt%) and dispersed for 1 hour through a ball-milling process. The dispersed solution was sprayed on one side of a conventional PAN separator using an electrospinning machine and pressed at a high temperature of 80 占 폚 to 30 占 퐉 to prepare a composite separator.

Example 2. Manufacture of pouch cell

The positive electrode, the anode and the electrolyte were selected before preparing the full cell using the composite separator. The core part of the anode active material is made of natural graphite and the surface modified layer is made of core-shell type graphite material coated with amorphous carbon material and SBR / CMC aqueous binder is applied. The anode was made of Li (Ni _1/3 Co _1/3 Mn _1/3 ) O ₂ , which is a typical high-output active material, and Super-P was used as a conductive material and PVdf binder was used as a binder. Electrolyte composition consisted of 1M LiPF ₆ , EC / EMC = 1: 2 (v / v) + VC2wt.%. Assembly of the pouch pull cell of the lithium secondary battery was performed according to a conventional method.

FIG. 2 is a view illustrating a part configuration of a pouch cell to which a separator is applied. In the pouch pull cell assembly, as shown in FIG. 2, Electrode → Electrode punching → Cathode and anode → Tab welding → Stacking → Laminated film forming → Electrode insertion → Electrolyte filling and vacuum sealing . As will be readily appreciated by those skilled in the art.

On the other hand, as a performance comparative group, a separator for PE base general lithium secondary battery (manufactured by Celguard) and a nonwoven fabric separator for PAN (poly acrylonitrile) lithium secondary battery (manufactured by Finetex EnE) And the pouch full cells prepared in the same manner as in Example 2 were also evaluated for comparison.

Experimental Example 1 (SEM photograph)

The PE separator, the PAN separator, and the composite separator of Example 1 were each photographed by SEM. 3 is an SEM photograph of each separator in Fig. 3. (A) is a SEM photograph of a PE separator, (B) is an SEM photograph of a PAN separator, and (C) is an SEM photograph of the composite separator produced in Example 1. (B) and (C) show relatively excellent porosity as a nonwoven fabric separator, and (C) it can be confirmed that a solid electrolyte, LAGP, is attached.

Experimental Example 2 (Electrochemical Charge / Discharge Cycle Characteristics)

In order to investigate the capacity degradation behavior due to the continuous charge and discharge at 25 ° and 45 ° for the pouch full cell with PE separator and the pouch full cell manufactured according to the example, a 1C / 1C charge / discharge rate The characteristics of the electrochemical charge and discharge cycle were investigated.

FIG. 4 shows the electrochemical charge / discharge cycling characteristics of the full cell prepared by the PE separator and the full cell prepared by the example.

Referring to FIG. 4, in the case of a room temperature (25 degrees) lifetime, the composite separator manufactured by the example shows good life characteristics as compared with the conventional PE separator, and the lifetime As a result of evaluation, the application of the composite separator manufactured according to the embodiment exhibited improved life characteristics as compared with the case where the conventional PE separator was applied. That is, in the pouch full cell to which the composite separator of the present invention manufactured by the example was applied at room temperature as well as at high temperature, more improved life characteristics were exhibited.

Experimental Example 3 (High Rate Discharge Characteristics of Battery)

The high rate discharge characteristics of the battery were examined with respect to the full cell of the pouch with PE separator and the full cell manufactured by the example. The results are shown in Fig.

Referring to FIG. 5, it can be seen that the composite separator according to the embodiment exhibits a relatively high high-rate characteristic as compared with the case of the PE-based separator.

Experimental Example 4 (EDS Composition Analysis)

EDS composition was analyzed on a cathode surface (SEM BS-image) after continuous filling of the pouch full cell with PAN separator and the pouch full cell prepared according to the example. The results are shown in Fig.

In the case of a cell to which the PAN separator was applied, it was observed that the metal particle precipitation of Co and Ni progressed after continuous charging for each full cell for several hours. However, in the case of the battery using the composite separator according to the embodiment There was no phenomenon of metal particle precipitation due to metal ion migration into the counter electrode.

Experimental Example 5 (Comparison of heat shrinkage behavior)

The PE separator and the composite separates prepared according to the examples were heated to a certain temperature and then the heat shrinkage behavior was compared. That is, for each of the PE separator and the composite separator produced according to the examples, the temperature was raised to 150 ° C. and 180 ° C. at a rate of 5 ° C. per minute, and then the shrinkage of the separator was measured after 12 hours at each temperature.

Figure 7 shows the result. Referring to FIG. 7, in the case of the composite separator manufactured according to the embodiment, the shrinkage rate at 150 degrees is close to 0%, whereas in the case of the PE-based separator, the shrinkage rate is 10% I could observe. Also, it was confirmed that the shrinkage percentage of 4% in the case of the composite separator according to the example after 180-degree maintenance, and the shrinkage percentage of 25% or more in the case of the PE separator were confirmed. Therefore, it was confirmed that the composite separator according to the Example had excellent heat resistance as compared with the PE separator.

Experimental Example 6 (Comparison of ARC behavior)

In order to investigate the effect of the above heat shrinkage on the actual pouch full cell, an ARC (Accelerated Calorimetry) experiment was conducted to confirm the relative thermal stability. That is, the ARC behaviors of the pouch pull cell with the PE separator and the pouch pull cell manufactured with the example were compared.

Compared with the full cell to which the conventional PE separator was applied, in the case of the full cell using the composite separator according to the embodiment of the present invention, the battery thermal stability due to the heat shrinkage characteristics was excellent.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention may be embodied otherwise without departing from the spirit and scope of the invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the scope of the present invention, but are intended to be illustrative, and the scope of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of the claims should be construed as being included in the scope of the present invention.

Claims (8)

In the nonwoven fabric separator for a lithium secondary battery,
Wherein a solid electrolyte of LAGP (lithium-aluminum-germanium-perovskite) is attached to the surface facing the anode, but the LAGP is not attached to the surface facing the anode. Nonwoven membrane. delete The method according to claim 1,
Wherein the LAGP has a chemical formula of [Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ]. In the nonwoven fabric separator for a lithium secondary battery,
In a non-woven fabric separator of polyacrylonitrile (PAN), LAGP (lithium-aluminum-germanium-for-state) is attached to the surface facing the anode, but LAGP is not attached to the surface facing the anode. Wherein the solid electrolyte composite nonwoven fabric separator comprises: 5. The method of claim 4,
Wherein the LAGP has a chemical formula of [Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ]. A method for producing a nonwoven fabric separator for a lithium secondary battery,
A method for producing a nonwoven fabric separator for a lithium secondary battery, comprising the steps of dispersing a LAGP sample and a PAN sample in a solvent, and then dispersing the solution in a solvent, electrospinning one side of a PAN separator prepared in advance, The method according to claim 6,
Wherein the LAGP has a chemical formula of Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ . The method according to claim 6,
Wherein the solvent is DMF (N, N-dimethylformamide).

Images