JPH07130349A - Manufacture of separator for battery - Google Patents

Abstract

PURPOSE:To prepare a precise separator extremely easily within a short time by combining a porous film and a low molecular weight polyolefine with optional melting point; wherein the fine pores of the film in the separator can be closed at optional temperature. CONSTITUTION:A charged porous film 12 is sent to a heater roller 3 set at the temperature lower by 0.5 to several degrees than the melting point of low molecular weight polyolefine-based wax fine particles 13 which are to be thermally pressed to the film, and then the porous film 12 charged by the heater roller 3 is sent to a wax fine particle stirring tank 4 filled with the wax fine particles 13 through an open mouth part 4a. As a result, the wax fine particles 13 adhere to the charged porous film 12 due to electrostatic force and the wax fine particles 13 are immediately softened and stuck to the porous film 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a battery separator using a porous film.

[0002]

2. Description of the Related Art Recent remarkable advances in electronic technology have made electronic devices smaller and lighter one after another. Along with this, batteries, which are used as mobile power sources, are required to be smaller and lighter and have high energy density.

As one of the methods for coping with this, the separator, which is a constituent element of the battery, has been improved. That is, there is a method of using a porous film as a battery separator in order to meet the demands for improving battery performance and reducing battery thickness by increasing the amount of active material and reducing internal resistance. For example, a method of impregnating a liquid electrolyte or a semi-solid electrolyte using a microporous polyethylene or polypropylene film as a separator has been reported.

[0004]

However, in the case where the microporous polyethylene or polypropylene film shown in such an example is used as a separator, inconvenience occurs when an accident occurs in the battery. For example, if an unexpected accident causes the ion current control between the positive and negative electrodes inside the battery to become impossible, a short circuit occurs through the fine holes of the separator, and a chemical reaction involving a rapid increase in battery temperature occurs inside the battery, The contents of the battery may squirt outside or even explode.

In order to deal with this problem, conventionally, a method of melting at an arbitrary temperature to close the fine pores of the separator, that is, a so-called fuse agent is attached to the surface of the separator, and a porous separator itself is used. As a property, research is progressing by two types of methods, that is, a method in which crystal melting occurs when the temperature rises and a material that closes the micropores is used.

[0006] For example, as a method of using the former fuse agent, the fuse agent itself is porous and is combined with a surfactant to form a geometric pattern on the separator by a method such as printing, A method of defining the coverage of this fuse agent, forming a fusible non-woven fabric on this separator by a so-called melt blow method, and crimping with a hot press, sandwiching fusible particles from both sides with a porous film,
There is a method of pressing and crimping.

On the other hand, as the latter method of melting the separator itself by heat to close the fine pores, a non-woven fabric formed by a so-called melt blow method or flash yarn preventing method is subjected to hot press film formation to reduce the fine pore diameter of the separator. There are a control method and a so-called gel stretching method using polyethylene as a material.

However, the former method using a fuse agent requires a very complicated and highly accurate manufacturing process, though this method is very effective for preventing battery accidents. In addition, since some special materials are required, the yield is low, the manufacturing cost is significantly increased, and the reliability of the product is seriously problematic.

Further, in the latter method in which the separator itself is heat-melted to close its fine pores, in the case of using the above-mentioned non-woven fabric, since the base material is a non-woven fabric, the micro-pore diameter is large,
It takes time to heat-melt and block the micropores, and it is hard to say that the blockage is sufficient. Further, in the case of the gel drawing method, since the material polyethylene has a low melting point, the material strength at ordinary use temperature is not sufficient, and there is a problem that elastic modulus relaxation occurs in this temperature range.

The present invention has been made in view of the above-mentioned various problems, and an object of the present invention is to combine a porous film and a low molecular weight polyolefin having an arbitrary melting point to obtain the porous material at an arbitrary temperature. It is possible to manufacture a separator that closes the micropores of a quality film very simply and precisely in a short time, greatly reducing the manufacturing cost and greatly improving the yield and reliability of the product. Another object of the present invention is to provide a method for manufacturing a battery separator that becomes

[0011]

In the present invention, a low-molecular-weight polyolefin fine particle is electrostatically adhered onto a porous film and thermocompression bonded to produce a battery separator.

In this case, polypropylene is used as a material for the porous film.

[0013]

In the method for manufacturing a battery separator according to the present invention, static electricity is charged on a porous film made of polypropylene, which has a very stable elastic modulus relaxation strength at around room temperature using a charging roller, and then a low molecular weight is used. Since the polyolefin fine particles are attached to the porous film by using the electrostatic force charged by using a heater roller, and then the polyolefin fine particles are thermocompression-bonded by using a pressure-bonding roller, a battery separator is prepared. When an unexpected accident occurs in the battery and the temperature of the battery exceeds a predetermined value, the polyolefin fine particles that are pressure-bonded onto the separator are melted to close the micropores of the battery separator, thereby positive and negative electrodes of the battery. Thus, the separator that cuts off the short circuit between and can be manufactured extremely easily and reliably, and in a short time.

[0014]

EXAMPLES Examples of a method for manufacturing a battery separator according to the present invention will be described below with reference to the drawings.

A non-aqueous electrolyte secondary battery is an example of a high-performance battery using a battery separator.
This non-aqueous electrolyte secondary battery uses a substance capable of doping and dedoping lithium ions, such as lithium and a lithium alloy, and further a carbon material, as a negative electrode, and a positive electrode such as a lithium cobalt composite oxide. A composite oxide is used. This battery has a high battery voltage, a high energy density, and excellent cycle characteristics.

Taking the case where the battery has a cylindrical shape as an example, the electrodes of the non-aqueous electrolyte secondary battery described above include a negative electrode made of KH carbon, which is a carbon material capable of doping / dedoping lithium, and a lithium electrode. L, which is a complex oxide of
An electrode portion composed of a positive electrode made of iCoO ₂ is wound around the winding core body a plurality of times via a separator to form a winding electrode body.

By the way, an unexpected accident occurs in the battery, a short circuit occurs between the positive and negative electrodes inside the battery through the fine holes of the separator, and an uncontrollable chemical reaction occurs inside the battery accompanied by a rapid rise in the battery temperature. May cause a danger such as battery explosion. As one of suitable measures against this, when an unexpected accident occurs in the battery and the temperature of the battery exceeds a predetermined value, the polyolefin fine particles are melted to close the micropores of the battery separator to close the battery. There is a method in which a separator for blocking a short circuit generated between the positive electrode and the negative electrode is used as a battery separator.

The present embodiment is a preferred manufacturing method for manufacturing this separator.

In the method for manufacturing a battery separator according to this embodiment, the manufacturing apparatus used for manufacturing the battery separator includes a separator delivery roller 1 and a charging high-voltage charging roller 2 as shown in FIG. A heater roller 3, a wax fine particle stirring tank 4 having a stirring gear 11, a cooling tank 5 installed in contact with the lower portion of the wax fine particle stirring tank 4, a pressure bonding roller 6, and a separator winding roller. 7 and 7.

The method for producing the battery separator according to this embodiment uses the wax fine particles of low molecular weight polyolefin described below, and combines the porous fine film described later with the wax fine particles by the production apparatus shown in FIG. A separator is produced.

That is, in the above embodiment, first, the porous film 12 to be described later is loaded into the separator delivery roller 1.
The porous film 12 is further fed, and then the fed porous film 12 is charged by the charging high-voltage charging roller 2 charged to 1 to several kV.

Then, wax fine particles 1 of a low molecular weight polyolefin, which will be described later, are thermocompression bonded onto the porous film 12.
The charged porous film 12 is sent to the heater roller 3 set to a temperature lower than the melting temperature of 3 by 0.5 to several degrees Celsius, and the charged porous film 12 is filled with the wax fine particles 13 by the heater roller 3. By being fed into the wax fine particle stirring tank 4, the wax fine particles 13 are electrostatically attached to the charged porous film 12, and the wax fine particles 13 are immediately softened and fused on the porous film 12. .

Here, in the wax fine particle stirring tank 4,
The stirring gear 11 rotates to keep the wax in a uniform state at all times. Further, the cooling tank 5 installed in contact with the lower part of the wax fine particle stirring tank 4 is for keeping the temperature of the wax in the wax fine particle stirring tank 4 constant and constantly maintaining it at a constant temperature.

Then, the wax fine particles 13 are pressure-bonded onto the porous film 12 by the pressure-bonding roller 6 so as to be smoothed and sent to the separator take-up roller 7, whereby the battery separator is completed.

Now, the material of the porous film 12 will be described. As a material of the porous film 12,
Two types are considered: polyethylene and polypropylene. Therefore, as Experimental Example 1, a battery separator made of each of these two materials was manufactured by the method for manufacturing a battery separator according to the above-described example, and the temperature dependence of each elastic modulus was examined.

The results of Experimental Example 1 are shown in FIGS. 2 and 3. In these FIGS. 2 and 3, the elastic modulus E ′ and elastic modulus relaxation strength E ″ when the complex elastic modulus E is expressed as E = E ′ + iE ″ (both are measured values, the scale in the figure is logarithmic display. And the unit is Pa), and the elastic modulus E ′ on the complex plane
Elastic modulus t which is the gradient of the elastic modulus relaxation strength E ″ with respect to
an δ (calculated value calculated from the above measured value).

First, as for the porous film made of polyethylene, as shown in FIG. 2, the increase rate of the elastic loss rate is very large at room temperature (around 25 ° C.). It will suddenly lose its elasticity. On the other hand, a porous film made of polypropylene (trade name Celgard 250, manufactured by Hoechst-Ceraneze Co., Ltd.
Regarding 2), unlike the above polyethylene, as shown in FIG. 3, the change rate of the elastic loss rate is small at room temperature, and therefore, even if the temperature is further changed at room temperature, the elastic modulus hardly changes.

From the above results, it is understood that polypropylene is preferable as the material of the porous film 12.

In Example 1, the wax fine particles 13 are selected from the waxes shown in Table 1 below.

[0030]

[Table 1]

In Table 1, A is a molecular weight, B is a viscosity (cps), C is a DSC sub-peak temperature (° C.), and D is a DS.
C main peak temperature (° C.), E shows softening point temperature (° C.), and F shows visual melting temperature (° C.). Further, in the table, S represents the product name Sun Wax manufactured by Sanyo Kasei Co., Ltd., and B represents Viscol (for example, S-131P represents the sun wax 131P). Here, the molecular weight, the viscosity, and the softening point temperature are the values published by the manufacturer. Further, the trade name Sun Wax is ethylene-based, and the trade name Viscose is propylene-based.

Here, the ion current blocking characteristics when the temperature rises (that is, the wax fine particles 13 on the porous film 12 of the battery separator manufactured according to the above-mentioned example.
Melts to block the micropores of the porous film 12 and block the ionic current in the electrolytic solution (hereinafter referred to as SD characteristic).
Experimental Example 2 in which is examined will be described. In Experimental Example 2, the ionic current interruption characteristic was measured as a change in electric resistance value of the separator with respect to a temperature change.

In this Experimental Example 2, the porous film 12 of the sample of the battery separator prepared in the above-mentioned Example
For example, the product name Celguard 2502 manufactured by Hoechst-Celanies Co., Ltd. and the product name Celguard 25 having a different film thickness
00 (film thickness 25 μm) was used, and the wax fine particles 13 were made of the above-mentioned polypropylene. Also,
In Experimental Example 2, as a comparative example with respect to the sample, the resistance value at each temperature was measured as the battery separator using only the trade name Celguard 2502 described above.

The results of Experimental Example 2 are shown in FIGS. 4 and 5 (resistance values are shown in logarithm in the figures). As for the sample, as shown in FIG. 4, the resistance value drastically increases when the temperature exceeds 120 ° C., and at 155 ° C., the resistance value rises by almost five orders of magnitude over the resistance value at room temperature. From this, the wax fine particles 13 on the porous film 12 melt around the temperature exceeding 120 ° C. and start to close the fine pores of the porous film 12, and as the temperature further rises, the fine pores almost certainly exist. You can see that it will be blocked.

On the other hand, in the above comparative example, as shown in FIG. 5, there was almost no change in the resistance value up to around 155 ° C.
Even if the temperature exceeds 60 ° C, the increase is about two orders of magnitude. This indicates that the porous film 12 alone does not sufficiently close the micropores of the porous film 12 at a high temperature, and it is difficult to obtain high SD characteristics.

From the above, it can be seen that the battery separators manufactured according to the above-mentioned examples exhibit extremely high SD characteristics.

In the method for manufacturing a battery separator according to this example, static electricity is charged by using the charging roller 1 on the porous film 12 made of polypropylene, which has a very stable elastic modulus relaxation strength at around room temperature. After that, the wax fine particles 13 which are low molecular weight polyolefin fine particles are attached to the porous film 12 by using the electrostatic force charged by using the heater roller 3, and then the wax fine particles 13 are thermocompression bonded by using the pressure bonding roller 5. Since the battery separator is produced by the above, when the accident of the battery occurs and the temperature of the battery exceeds a predetermined value, the wax fine particles 13 pressure-bonded on the separator are melted and The separator that closes the micropores and blocks the short-circuiting ionic current generated between the positive electrode and the negative electrode of the battery is extremely simple and Indeed, addition and thus made in a short time.

Therefore, the yield can be increased and the reliability of the product can be greatly improved.

Next, a modification of the above embodiment will be described with reference to the drawings. The same reference numerals are given to those corresponding to FIG.

This modification has substantially the same structure and function as the above-mentioned embodiment, but differs in that a plurality of manufacturing apparatuses are used in the manufacturing process of the battery separator.

That is, in this modification, as shown in FIG. 6, a plurality of manufacturing apparatuses shown in FIG. 1 (three in the illustrated example) are provided, and each manufacturing apparatus has the above-mentioned Table 1.
Different ones of the waxes listed in 1 above are fused on the porous film 12. That is, in the modified example, the porous film 12 is passed through each of the manufacturing apparatuses, so that the porous film 12 has a plurality of different types (3 in the illustrated example).
The wax fine particles 13 of (seed) are fused.

It should be noted that the wax fine particles 13 arranged in each of the above-mentioned manufacturing apparatuses have a melting temperature lower toward the right in the figure.

Also in this modification, as in the above-described embodiment, the charging roller 1 is used to electrostatically charge the porous film 12 made of polypropylene, which has a very stable elastic modulus relaxation strength at around room temperature, and then charges. Wax fine particles 13 which are low molecular weight polyolefin fine particles are attached to the porous film 12 by using an electrostatic force charged by using a heater roller 3, and then the wax fine particles 13 are thermocompression bonded by using a pressure bonding roller 5. Since the battery separator is manufactured by the method described above, when the battery accidentally occurs and the temperature of the battery exceeds a predetermined value, the wax fine particles 13 pressure-bonded onto the separator are melted so that the battery separator becomes fine. The separator that closes the hole and blocks the short circuit between the positive electrode and the negative electrode of the battery is extremely simple, reliable, and in a short time. And thus to be prepared.

Therefore, the yield can be increased and the reliability of the product can be significantly improved. In addition, since it is possible to fuse plural kinds of wax fine particles 13 onto the porous film 12, it becomes possible to synergistically improve the SD characteristics.

[0045]

EFFECT OF THE INVENTION According to the method for producing a battery separator of the present invention, the low-molecular-weight polyolefin fine particles are electrostatically adhered onto the porous film and thermocompression bonded to produce the battery separator. By combining a porous film and a low-molecular-weight polyolefin having an arbitrary melting point, a separator that closes the micropores of the porous film at an arbitrary temperature can be produced very simply and precisely in a short time. It is possible to significantly reduce the cost and significantly improve the product yield and reliability.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a method for manufacturing a battery separator according to an example of the present invention.

FIG. 2 is a characteristic diagram showing temperature dependence of elastic modulus of a polyethylene porous film.

FIG. 3 is a characteristic diagram showing temperature dependence of elastic modulus of a polypropylene porous film used in this example.

FIG. 4 is a characteristic diagram showing temperature dependence of electric resistance of the battery separator manufactured according to this example.

FIG. 5 is a characteristic diagram showing the temperature dependence of the electrical resistance of the battery using only the porous film used in this example as a battery separator.

FIG. 6 is a schematic view showing a modified example of the method for manufacturing the battery separator according to the example of the present invention.

[Explanation of symbols]

 1 ... Separator feeding roller 2 ... Charging roller 3 ... Heater roller 4 ... Wax fine particle stirring tank 5 ... Cooling tank 6 ... Crimping roller 7 ... Separator take-up roller 12 ... ..Porous film 13 ... Wax fine particles

Claims (2)

[Claims] 1. A method for producing a battery separator, characterized in that low-molecular-weight polyolefin fine particles are electrostatically adhered onto a porous film and thermocompression bonded. 2. The method for manufacturing a battery separator according to claim 1, wherein the porous film is made of polypropylene.