JP2002037911A - Porous formed body of polycarbodiimide, separator for battery and battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a separator for a battery, capable of controlling the self discharge of a battery. SOLUTION: This porous formed body of a polymer containing a carbodiimide unit of formula (I) (R is an organic group; n is an integer of 1-10,000) in the molecule. This separator for a battery comprises the porous formed body of a polycarbodiimide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polycarbodiimide porous molded article, a porous sheet and a method for producing the same.
The present invention also relates to a battery separator made of the porous sheet and a battery using the same.

[0002]

2. Description of the Related Art In recent years, secondary batteries such as nickel-metal hydride batteries and nickel-cadmium (nickel) batteries are expected to be used not only as small batteries for electric / electronic devices but also as power sources for electric vehicles. Such a secondary battery generally includes a positive electrode, a negative electrode, and a separator. Among them, the separator is to prevent short-circuiting of both electrodes inside the battery and to transmit ions, and requires hydrophilicity, chemical resistance, and mechanical strength. Conventionally, a hydrophilic nonwoven fabric using a polyamide resin or the like has been known as a separator.
However, such separators do not have sufficient chemical resistance (alkali, acid). For this reason, polyolefin nonwoven fabric separators subjected to various treatments are also known. That is, there has been proposed a separator obtained by subjecting a polyolefin-based nonwoven fabric to hydrophilic treatment such as surfactant impregnation, plasma treatment, graft treatment, or sulfonation treatment.
(JP-A-4-167355, JP-A-11-238496, etc.).

Further, since a polyamide-based nonwoven fabric has an amide bond, the self-discharge of the battery is larger than that of an electrochemically inactive polyolefin nonwoven fabric, and a battery using this as a separator is inferior in battery characteristics. On the other hand, batteries with polyolefin-based nonwoven fabric treated as a separator by using a specific treatment have better overall battery characteristics than those using polyamide-based separators, but have a sufficiently satisfactory self-discharge characteristic. Not something to do.

That is, a separator obtained by treating a polyolefin-based nonwoven fabric with a surfactant shows an effective hydrophilic property in the early stage of use, but once immersed in water, taken out and dried, and immersed in water again, the hydrophilic property is reduced. The self-discharge characteristics are not satisfactory, and the self-discharge characteristics are not satisfactory.

[0005] Further, the polyolefin-based nonwoven fabric subjected to the plasma treatment is immersed in water and then dried once to form a hydrophilic group bonded by covalent bonds on the surface of the base material.
Keep wet enough even if immersed in water again, wet-dry revers
ible. However, when immersed in a high-concentration alkaline aqueous solution, it is washed with water, dried, and then immersed again in water, and does not wet with water. This is presumed to be due to the fact that the boundary layer, which is formed on the surface of the base material by the plasma treatment and is hydrophilic but has low adhesion, comes into contact with the high-concentration aqueous alkali solution and peels off. Such separators do not have a significant improvement in self-discharge suppression.

In the case of a grafted polyolefin-based nonwoven fabric, a water-soluble monomer is firmly bonded to a substrate by a covalent bond. However, in a grafting process using acrylic acid or methacrylic acid, a strong oxidizing atmosphere is used because the carboxylic acid type is used. There is a risk of oxidative decomposition below, and the battery separator is limited and used.

In addition, the sulfonated polyolefin-based nonwoven fabric has a function of maintaining hydrophilicity and suppressing self-discharge of a battery because a sulfonic acid group is firmly bonded to a substrate by a covalent bond. However, the process involves
A post-cleaning step is required.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a separator capable of effectively suppressing self-discharge of a battery. Further, a molded article suitable for such a separator is provided.

[0009]

According to the present invention, there is provided the following formula (I):

[0010]

Embedded image (In the formula, R represents an organic group, and n represents an integer of 1 to 10,000.) The present invention provides a porous molded article of a polymer having a carbodiimide unit represented by the following formula: Examples of the porous molded body include those obtained by perforating a polymer sheet of the formula (I). Further, a powder of the polymer of the formula (I) sintered at a temperature equal to or higher than its melting point, or a material obtained by sintering the polymer particles of the formula (I) and the polyolefin particles at a temperature equal to or higher than the melting point of the polyolefin particles, particularly a sheet The molded article is preferably When the molded article is in the form of a sheet, it is preferable to cut the porous molded article into a sheet. This porous sheet is preferable as a battery separator, and a battery using this separator suppresses self-discharge.

(Production of polycarbodiimide) The polycarbodiimide used in the present invention is represented by the above formula (I). Here, examples of the organic group R include aromatic or aliphatic organic groups. (i) As the aromatic organic group,

[0012]

Embedded image (In the formula, p is an integer of 0 to 10, and q means an integer of 0 to 5.).

In the above formula, X is

[0014]

Embedded image It is. X may be the same or different in the repeating unit. a, b, c and d are _{-H, -CH 3, -OCH 3,} -CF 3 or -OCF
_3, which may be the same or different. (ii) As the aliphatic organic group,

[0015]

Embedded image (In the formula, r represents an integer of 0 to 10.). In the above formula, Y is

[0016]

Embedded image It is. Y may be the same or different in the repeating unit. a, b, c and d are-
H, —CH ₃ , —OCH ₃ , —CF ₃ or —OCF _3, which may be the same or different.

In the formula (I), n is 1 to 10,000. If n exceeds 10,000, the gelation time is short at room temperature, and the workability is undesirably reduced. n is preferably 5
-100, more preferably 10-50.

In order to obtain such a polycarbodiimide, a known method can be used. For example, T. W. Ca
mpbell et a1. 0rg. Chem., 28, 2069 (l963);
M. A1berino et al., J.A. App1. Po1ym. Sci., 21, 1999
(l977), JP-A-2-292316, JP-A-4-275359, and the like, and can be easily obtained by reacting an organic diisocyanate in an organic solvent in the presence of a carbodiimidization catalyst.

Specific examples of the organic diisocyanate used in the synthesis of the above polycarbodiimide include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1-methoxyphenyl-2,4-diisocyanate, and 4,4 ′. -Diphenylmethane diisocyanate, 3,
3'-dimethoxy-4,4'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 3,3'-dimethyl-4,4'-diphenyl ether diisocyanate , Hexamethylene diisocyanate, xylylene diisocyanate, 2,2-bis [4- (4-isocyanatophenoxy) phenyl] hexafluoropropane, 2,2-bis [4- (4-isocyanatophenoxy) methyl] propane, , 2-dimethyl-
1,3-bis (4-isocyanatophenoxy) propane and the like can be used. These can be used alone or in combination of two or more (a copolymer is obtained). For the purpose of imparting hydrophobicity, an organic diisocyanate partially substituted with a fluorine group may be used.

Examples of the organic solvent include halogenated hydrocarbons such as toluene, xylene, tetrachloroethylene, 1,2-dichloroethane and chloroform; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; and tetrahydrofuran. And dioxane and other cyclic ethers can be used, and these can be used alone or in combination of two or more.

Further, as the carbodiimidization catalyst,
Specifically, 3-methyl-1-phenylphospholene-1
-Oxide, 1-phenyl-2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, 1
Phosphorene oxide such as -ethyl-2-phospholene-1-oxide or 3-phospholene isomer thereof can be used. These can be used alone or in combination of two or more.

The terminal blocking treatment may be carried out by adding a monoisocyanate at any of the last stage, the middle stage, the initial stage or the whole of the polymerization reaction. As such a monoisocyanate, phenyl isocyanate, ρ-nitrophenyl isocyanate, ρ- and m-tolyl isocyanate, ρ-formylphenyl isocyanate, ρ-isopropylphenyl isocyanate and the like can be used. The polycarbodiimide solution thus obtained is excellent in storage stability of the solution.

The obtained polycarbodiimide solution is cast on a glass plate, dried and peeled to obtain a sheet. Further, particles or powder can be obtained by vacuum-drying the above solution and, if necessary, crushing it.

The solvent used for preparing the polycarbodiimide solution is not particularly limited as long as it can dissolve the polycarbodiimide. Examples of the solvent include hydrocarbons such as toluene and xylene; and hydrocarbons such as tetrachloroethylene, 1,2-dichloroethane and chloroform. Halogenated hydrocarbons;
Examples include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; and cyclic ethers such as tetrahydrofuran and dioxane. These may be used alone or in combination of two or more. The concentration of the polycarbodiimide may be appropriately adjusted to a viscosity that facilitates handling, and is preferably, for example, 3 to 20% by weight.

(Porous Polycarbodiimide Sheet) A first embodiment of the separator of the present invention is a porous sheet comprising a polycarbodiimide compound of the formula (I). Such a sheet
The polycarbodiimide sheet may be made porous by perforation, etching, or the like. The production of such a porous sheet,
(i) forming a sheet from a polycarbodiimide solution and perforating the sheet with a needle or a laser, (ii)
There is a method of adding particles, powder, or fibrous material to a polycarbodiimide solution to form a sheet, and then extracting the particles, powder, or fibrous material. Further, (iii) the porous sheet may be obtained by chemical etching.

As a specific example of the chemical etching method, for example, a metal wire (copper wire or the like) is coated with a polycarbodiimide solution, and this is densely and multiplely wound on a core so as to have a predetermined diameter. I do. Next, the polycarbodiimide is heated to above the softening point (preferably above the melting point) to remove the solvent and unify the coated metal wires. After cooling, the tubular integrated body is sliced in a direction perpendicular to the metal wire to obtain a sheet having a predetermined thickness, and the metal wire is removed from the sheet using an etching solution such as hydrochloric acid or sulfuric acid. The heating condition in this chemical etching method is usually a temperature of 140 to 200 ° C., a time of 0.5 to 5 hours, and an etching solution concentration of 0.1 to 10 mol / L. The porous separator thus obtained usually has a thickness of 10 to 300 μm, a porosity of 20 to 80%, and a pore diameter of 1 to 500 μm.

Incidentally, a surfactant may be applied to the porous sheet in order to improve the initial wettability of the electrolytic solution.

(Sintered Sheet) Another form of the porous sheet of the present invention can be obtained by forming a polycarbodiimide particle or a porous molded product obtained by blending a polyolefin with the polycarbodiimide particle. Such a molded article is preferably in the form of a sheet. For molding, polycarbodiimide particles and polyolefin as needed are mixed, filled into a shape retainer, the hot air drying furnace and the shape retainer are placed in a pressure-resistant container, and after the air in the container is exhausted, hot air, steam, etc. To obtain a sheet-like porous sintered body. Alternatively, a porous sintered body may be obtained using a cylindrical shape retainer, and then the porous molded body may be cut to a predetermined thickness.

The polycarbodiimide particles or powder can be obtained by vacuum drying the solution. If desired, the carbodiimide may be crosslinked. The polycarbodiimide powder can be sintered alone to obtain a porous sintered body sheet. The sintering temperature is defined by the melting point and the thermal decomposition temperature of polycarbodiimide. Heat treatment is performed at a temperature not lower than the melting point and not higher than the thermal decomposition temperature. The melting point of polycarbodiimide is
It is affected by the molecular structure, molecular weight and the like of the obtained polycarbodiimide. However, the sintering temperature is often 140
~ 200 ° C. The sintering time is preferably 1 to 24 hours. If the treatment time is shorter than this, it is difficult to obtain a porous sintered body having a strong bond. If the time is longer than this, the productivity may decrease. As described above, the sintering temperature and time are appropriately adjusted in order to obtain a desired porosity of the porous sintered body.

The processing temperature when a polycarbodiimide particle is mixed with a polyolefin to produce a sintered body is determined by the melting point and molecular weight of the polyolefin, depending on the mixing ratio. When the blending amount of the polycarbodiimide particles is 1 to 20% by weight based on the total amount of the mixture, the sintering conditions substantially depend on the melting point and molecular weight of the polyolefin. The sintering temperature is preferably from 140 to 200C. If the temperature is lower than 140 ° C., it is difficult to obtain a porous sintered body in which the particles are tightly bound as described in sintering of polycarbodiimide alone. 2
If the temperature exceeds 00 ° C., cracks are likely to occur in the sintered body, especially when a polyolefin having a smaller molecular weight than the ultrahigh molecular weight polyolefin is applied. The sintering time is
1 to 24 as in the case of the polycarbodiimide alone.
Time is preferred. If it is shorter than 1 hour, it is difficult to obtain a porous sintered body in which the particles are firmly bound. If it exceeds 24 hours, it is not preferable in terms of productivity. When the blending amount of polycarbodiimide exceeds the above range, the same sintering conditions as in the case of using polycarbodiimide alone can be used.

The polyolefins include ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-
Examples include olefin homopolymers and copolymers such as hexene, and blends thereof. Among these, polypropylene and polyethylene are preferable, and particularly, the ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more (UHPE)
Is preferred.

The porous sheet thus obtained is
Usually, the thickness is preferably 30 to 500 μm, the porosity is 25 to 60%, and the pore diameter is preferably 10 to 100 μm.

With respect to the self-discharge suppressing function, when a film made of carbodiimide is brought into contact with ammonia gas, the disappearance of the carbodiimide group can be confirmed by infrared absorption spectrum. Therefore, the ammonia gas trapping function of carbodiimide group (Weith W., Ber., 7, 10 (1874)).

The structure of a battery using the separator of the present invention may be the same as that of a conventional battery, and has a positive electrode, a negative electrode, and a separator disposed between these two electrodes. In addition, other materials constituting the battery, such as an electrolyte solution and a battery container, may be the same as the conventional product. FIG. 1 is a schematic sectional view showing an example of a button battery using the separator of the present invention. As shown in FIG. 1, a Ni net 2 and a Ni current collector 3 are provided in an inner case 1 of a battery, a negative electrode 4, a separator 5, and a positive electrode 6 are laminated, and an outer lid 8 is attached via a packing 7. Further, the battery of the present invention may be any of a cylindrical battery in which an electrode and a separator are overlapped and wound, and a rectangular battery in which the electrode and the separator are overlapped and housed in a case.

[0035]

Next, the present invention will be described more specifically with reference to examples and comparative examples. The evaluation of the battery was performed as follows.

(Evaluation of Battery) First, the discharge capacities of the batteries obtained in Examples and Comparative Examples were measured. Next, after full charge 4
After storing at 5 ° C. for 1 week to allow self-discharge, the discharge capacity was measured, and the discharge capacity was measured again after full charge. Table 1 shows the results
It was shown to. The discharge rate was 0.2 C ₅ A, and the capacity retention was determined by the following equation.

Capacity retention [%] = (discharge capacity after self-discharge
[Ah] / ((discharge capacity before self-discharge [Ah] + discharge capacity after self-discharge and full charge [Ah]) / 2) × 100

[Example I-1] Takenate 80 (manufactured by Takeda Pharmaceutical Co., Ltd .: 2,4-tolylene diisocyanate, 2,
100 g of 6-tolylene diisocyanate mixture) were put into 500 g of toluene together with 0.06 g of a carbodiimidation catalyst (3-methyl-1-phenylphospholene-1-oxide) and 10 g of isopropylphenylisocyanate, and reacted at 100 ° C. for 6 hours. Thus, a polycarbodiimide solution was obtained. The molecular weight was measured by GPC (gel permeation chromatography), and n was determined.
Met. This solution was cooled to room temperature, cast on glass, heated at 90 ° C. for 30 minutes, and peeled off to a thickness of 100 μm.
Was obtained. The film was pierced with 40,000 holes per 1 cm ² having a diameter of 30 μmφ to give a porosity of 28 μm.
%, A separator having a thickness of 100 μm.

On the other hand, 100 parts by weight of nickel hydroxide powder,
10 parts by weight of cobalt powder, polytetrafluoroethylene
(PTFE) 10 parts by weight of powder and 20 parts by weight of water were mixed to prepare a dispersion for forming a positive electrode. This liquid is foamed nickel (Ni)
The resulting Ni plate was pressed into a sheet and pressed into a sheet to form a positive electrode. 100 parts by weight of a hydrogen storage alloy (Misch metal type), 10 parts by weight of PTFE powder, and 20 parts of water
The dispersion was mixed with parts by weight to form a dispersion for forming a negative electrode, which was pressed into a foamed Ni plate, dried and pressed to form a sheet, thereby forming a negative electrode.

In producing a button-type nickel-metal hydride battery (2032 size: diameter 20 mm, height 3.2 mm), the separator was previously immersed in a 7.2 kmol / m ³ potassium hydroxide electrolytic solution to perform vacuum impregnation. . A Ni net and a Ni current collecting plate were placed in the can for current collection, and laminated with a negative electrode, a separator, a positive electrode, and an outer lid.

Example I-2 The polycarbodiimide solution obtained in Example I-1 was coated on a copper wire having a diameter of 18 μm to obtain a coated copper wire having a diameter of 52 μm. Next, the core was densely wound around a core having a diameter of 60 cm, and was wound in multiple layers until the diameter became 70 cm, and the core was heated at 160 ° C. for 2 hours to obtain a fused tubular integrated body. After cooling, 80 μm in the direction perpendicular to the copper wire
The sheet was sliced thick to obtain a sheet. 1 mol of the sheet
The conductive wire was removed by immersion in / L hydrochloric acid to obtain a separator (porosity: 28%, thickness: 80 µm) having holes with a diameter of 18 µmφ. Using this separator, a battery was manufactured in the same manner as in Example I-1.

Example I-3 A polycarbodiimide solution was obtained in the same manner as in Example I-1 except that 4,4'-diphenylmethane diisocyanate was used instead of Takenate 80 (n = 408 by GPC) to produce a battery. did.

[Example I-4] Example I- except that 2,2'-dimethyl-1.3-bis (4-isocyanatophenoxy) phenyl] propane was used instead of Takenate 80
A polycarbodiimide solution was obtained in the same manner as in Example 1 (n = 18 by GPC) to produce a battery.

Example I-5 Example I-5 was repeated, except that 2,2'-bis [4- (4-isocyanatophenoxy) phenyl] hexafluoropropane was used instead of Takenate 80.
1 to obtain a polycarbodiimide solution (GPC
According to n = 30) a battery was manufactured.

[Comparative Example I-1] A nonwoven fabric made of polyethylene and polypropylene fibers (having a basis weight of 60 g) was used as a porous sheet without using a polycarbodiimide separator.
/ M ² ) 2.5 sodium dodecylbenzenesulfonate
A battery was prepared in the same manner as in Example I-1, except that the battery was immersed in a wt% aqueous solution and then dried to obtain a battery separator.

[0046]

From the above results, it can be seen that the use of the polycarbodiimide separator can improve the self-discharge suppressing function.

Example II-1 A polycarbodiimide solution was obtained in the same manner as in Example I-1 (n by GPC was 2
5). After the solution was cooled to room temperature, it was vacuum dried and ground in a mortar. The obtained coarse powder was used to remove coarse particles using a 60-mesh sieve. The polycarbodiimide particles are placed in a sheet retainer and placed in a hot-air drying oven for 145.
Sintering was performed at 2 ° C. for 2 hours, taken out of the furnace and cooled to obtain a porous sintered body sheet (thickness: 300 μm, porosity: 30%, pore diameter: 80 μm). This porous sintered body sheet is previously
It was immersed in kmol / m ³ potassium hydroxide electrolyte to perform vacuum impregnation, and the electrolyte was introduced into the holes to produce a 2032 size button-type nickel-metal hydride battery. The same positive electrode, negative electrode, Ni mesh, Ni plate and can lid were used as in Example I-1.

Example II-2 UHPE powder (weight average molecular weight 4.5 million, melting point 135 ° C., average particle size 106 μm
(Mesh classified product)) 1.8 kg and 1.2 kg of the carbodiimide powder prepared in Example II-1 were transferred to a cylindrical wire mesh basket.
A cylindrical wire mesh basket having an outer diameter of 4 cm was disposed at the center of the inner diameter (15 cm), and the donut-shaped portion of the void was filled in a shape retainer consisting of a mold having a polytetrafluoroethylene porous sheet adhered inside.

This mold was placed in a heat-resistant and pressure-resistant container made of metal (including a steam introduction pipe and an opening / closing valve thereof), and the atmospheric pressure was adjusted to 1.3 kPa by a vacuum pump. Then, the pump was stopped, and after leaving it for 30 minutes, the valve was opened, steam was introduced, the temperature was raised to 120 ° C. in 10 minutes, and the temperature was maintained for 30 minutes. Thereafter, the steam pressure was increased to 0.4 MPa and the temperature was increased to 1
After heating and sintering at 45 ° C. for 3 hours, the valve was closed and naturally cooled to obtain a cylindrical porous body. The obtained porous body was cut to a thickness of 200 μm with a cutting lathe to obtain a film-shaped separator having a porosity of 50% and a hole diameter of 70 μm. A button-type battery was produced in the same manner as in Example II-1, except that this separator was used.

Comparative Example II-1 In Example II-2,
A porous sheet having a thickness of 200 μm, a porosity of 43%, and a pore diameter of 70 μm was obtained using only UHPE powder without using polycarbodiimide powder. The obtained porous sheet is previously immersed in an electrolytic solution to perform vacuum impregnation, and the electrolytic solution is introduced into the pores.
032 size button type nickel metal hydride battery (Positive electrode active material:
Nickel hydroxide (Ni), a negative electrode active material: a hydrogen storage alloy, and an electrolytic solution: a potassium hydroxide aqueous solution) were produced.

[0052]

From the above results, it is understood that the carbodiimide powder and the porous sintered body sheet and the porous sheet comprising the carbodiimide powder and the polyolefin particles can improve the self-discharge suppressing function.

[0054]

The porous molded article of the present invention is preferable as a battery separator. By using this battery separator, a battery with less self-discharge can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a button battery using a separator of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inner case 2 Ni net 3 Ni current collector 4 Negative electrode 5 Separator 6 Positive electrode 7 Packing 8 Outer lid

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[Procedure amendment]

[Submission date] July 3, 2001 (2001.7.3)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0022

[Correction method] Change

[Correction contents]

The terminal blocking treatment may be carried out by adding a monoisocyanate at any of the last stage, the middle stage, the initial stage or the whole of the polymerization reaction. As such a monoisocyanate, phenyl isocyanate, p -nitrophenyl isocyanate, p- and m-tolyl isocyanate, p -formylphenyl isocyanate, p -isopropylphenyl isocyanate and the like can be used. The polycarbodiimide solution thus obtained is excellent in storage stability of the solution.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H01M 10/30 H01M 10/30 Z B29K 79:00 B29K 79:00 B29L 7:00 B29L 7:00 C08L 79:00 C08L 79:00 (72) Inventor Yutaka Kishi 1-1-2 Shimozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Takashi Yamamura 1-1-2 Shimohozumi, Ibaraki-shi, Osaka No. Nitto Denko Corporation (72) Inventor Masao Abe 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Sadahito Misumi 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Inside Electric Works Co., Ltd. (72) Inventor Fumiki Asai 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Electric Works Co., Ltd. F-term (reference) 4F074 AA56 CA10 CC12Z CC28X CD08 DA02 DA 23 DA49 4F212 AA03 AA40 AG01 AG20 UA11 UW24 UW25 5H021 BB01 BB04 CC08 EE02 EE04 EE20 EE23 HH06 HH07 5H028 AA05 BB05 EE06 HH08

Claims (8)

[Claims] (1) The following formula (I): (In the formula, R represents an organic group, and n represents an integer of 1 to 10,000.) A porous molded article of a polymer having a carbodiimide unit represented by the following formula: 2. The porous molded article according to claim 1, wherein the porous molded article is obtained by perforating a polymer sheet of the formula (I). 3. The porous molded article according to claim 1, wherein the porous molded article is obtained by sintering a polymer powder of the formula (I) at a temperature not lower than its melting point. 4. The porous molded article according to claim 1, wherein the porous molded article is obtained by sintering the polymer particles of the formula (I) and the polyolefin particles at a temperature not lower than the melting point of the polyolefin particles. 5. The porous molded article according to claim 3, which is in the form of a sheet. 6. A method for producing a sheet-like porous molded article, comprising cutting the porous molded article of claim 3 or 4 into a sheet. 7. A battery separator comprising the porous sheet according to claim 2. 8. A battery using the battery separator according to claim 7.