`
`(19) —
`
`(12)
`
`Europaisches Patentamt
`
`EuropeanPatentOffice
`
`Office européen des brevets
`
`(11)
`
`EP 1 315 220 Al
`
`EUROPEANPATENT APPLICATION
`published in accordancewith Art. 158(3) EPC
`
`(43) Date of publication:
`28.05.2003 Bulletin 2003/22
`
`(51)
`
`Int cl.7; HOIM 4/62
`
`(86)
`
`International application number:
`PCT/JP01/02917
`
`(87)
`
`International publication number:
`WO 01/075994 (11.10.2001 Gazette 2001/41)
`
`* KIl, Keisuke c/o NITTO DENKO CORPORATION
`lbaraki-shi, Osaka 567-8680 (JP)
`¢ KISHII, Yutaka
`c/o NITTO DENKO CORPORATION
`
`lbaraki-shi, Osaka 567-8680 (JP)
`* YAMAMURA, Yutaka
`c/o NITTO DENKO CORPORATION
`
`lbaraki-shi, Osaka 567-8680 (JP)
`* ABE, Masao c/o NITTO DENKO CORPORATION
`lbaraki-shi, Osaka 567-8680 (JP)
`¢ MISUMI, Sadahito
`c/o NITTO DENKO CORPORATION
`
`lbaraki-shi, Osaka 567-8680 (JP)
`* ASAI, Fumiteru
`c/o NITTO DENKO CORPORATION
`
`lbaraki-shi, Osaka 567-8680 (JP)
`
`(74) Representative: Griinecker, Kinkeldey,
`Stockmair & Schwanhausser Anwaltssozietat
`Maximilianstrasse 58
`
`80538 Miinchen (DE)
`
`(21) Application number: 01917822.7
`
`(22) Date offiling: 04.04.2001
`
`(84) Designated Contracting States:
`AT BE CH CY DE DK ES FI FR GB GRIE IT LILU
`MC NL PT SE TR
`
`Designated Extension States:
`AL LT LV MK ROSI
`
`(30) Priority: 05.04.2000 JP 2000103445
`05.04.2000 JP 2000103446
`05.04.2000 JP 2000103447
`05.04.2000 JP 2000103448
`05.04.2000 JP 2000103449
`05.04.2000 JP 2000103450
`05.04.2000 JP 2000103451
`05.04.2000 JP 2000103452
`05.04.2000 JP 2000103453
`26.10.2000 JP 2000327159
`17.11.2000 JP 2000350559
`
`(71) Applicant: NITTO DENKO CORPORATION
`lbaraki-shi, Osaka 567-8680 (JP)
`
`Inventors:
`(72)
`« URAIRI, Masakatsu
`c/o NITTO DENKO CORPORATION
`
`lbaraki-shi, Osaka 567-8680 (JP)
`
`(54)
`
`BATTERY
`
`
`
`(wherein R means an organic group and n means an
`(57)~~Abattery highly inhibited from suffering self-dis-
`integer of 1 to 10,000).
`charge.
`The battery is characterized by containing a built-in
`polymer which has in the molecule a carbodiimide unit
`represented by the following formula (I):
`
`-[-R-N=C=N-],-
`
`0)
`
`EP1315220A1
`
`Printed by Jauve, 75001 PARIS (FR)
`
`(Cont. next page)
`
`JLab/Cambridge, Exh. 1012, p. 1
`
`JLab/Cambridge, Exh. 1012, p. 1
`
`

`

`EP 1 315 220 Al
`
`
`
`JLab/Cambridge, Exh. 1012, p. 2
`
`JLab/Cambridge, Exh. 1012, p. 2
`
`

`

`EP 1 315 220 Al
`
`Description
`
`Technical Field
`
`[0001] The present invention relates to a battery containing built-in polycarbodiimide. According to the invention,
`battery self-discharge is inhibited and the battery life is prolonged.
`
`Background Art
`
`Secondary batteries such as nickel-hydrogen cells and nickel-cadmium (Ni-Cd) cells are recently expected
`[0002]
`to be used as powersourcesfor electric cars as well as small batteries for electrical/electronic appliances. Such a
`secondary battery is generally constituted of a positive electrode, a negative electrode, and a separator. Among these,
`the separator serves to prevent the cell from short-circuiting between the electrodes and enable ions to pass there-
`through, and is required to have hydrophilicity, chemical resistance, and mechanical strength. Conventionally known
`as a separator is a hydrophilic nonwoven fabric formed from a polyamide resin or the like. However, this separator has
`insufficient resistance to chemicals (alkalis and acids). Because of this, separators comprising polyolefin nonwoven
`fabrics which have undergone various treatments are also known. Specifically, separators obtained by subjecting a
`polyolefin-based nonwovenfabric to a hydrophilizing treatment, e.g., impregnation with a surfactant, plasma treatment,
`grafting treatment, sulfonation treatment, or the like, have been proposed (Unexamined Published Japanese Patent
`Applications Nos. 4-167355 and 11-238496, etc.).
`[0003]
`Furthermore, since the polyamide-based nonwoven fabric has amide bonds, batteries employing this as a
`separator show a higher degree of self-discharge than batteries employing an electrochemically inert polyolefin non-
`woven fabric and have poor battery properties. In contrast, batteries employing a separator obtained by subjecting a
`polyolefin-based nonwovenfabric to a specific treatment cannot be regarded asfully satisfactory in self-discharge
`characteristics, although superior in overall battery properties to batteries employing the polyamide-based separator.
`[0004]
`Specifically, the separator obtained by treating a polyolefin-based nonwoven fabric with a surfactant shows
`effective hydrophilicity in the initial stage of use. However, when this separator is once immersed in water, taken out
`therefrom, dried, and reimmersedin water, then the hydrophilicity decreases considerably. In addition, this separator
`is unsatisfactory in self-discharge characteristics.
`[0005]
`Furthermore, the polyolefin-based nonwoven fabric which has undergone a plasma treatment has hydrophilic
`groups bondedto the substrate surface by covalent bonding and henceretains sufficient wettability even when it is
`immersed in water, dried once, and reimmersed in water. Namely,it is wet-dry reversible. However, in the case where
`this nonwoven fabric is immersed in an aqueousalkali solution having a high concentration, it is not wetted by water
`when it is washed with water, dried, and reimmersedin water. It is presumed that the hydrophilic but weakly adherent,
`interfacial layer formed on the substrate surface by the plasma treatment was peeled off upon cantact with the high-
`concentration aqueous alkali solution. This separator also is ineffective in greatly improving the inhibition of self-dis-
`charge.
`Inthecaseof the polyolefin-based nonwoven fabric which has undergone a grafting treatment, a water-soluble
`[0006]
`monomeris tenaciously bonded to a substrate by covalent bonding. However, the polyolefin treated by grafting with
`acrylic acid or methacrylic acid has the possibility of undergoing oxidative decomposition in a strongly oxidizing atmos-
`phere because this polyolefin is of the carboxylic acid type. Consequently, this nonwoven fabric is used as a battery
`separator in limited applications.
`[0007]
`Furthermore, the polyolefin-based nonwoven fabric which has undergone a sulfonation treatment has sulfo
`groups tenaciously bonded to the substrate by covalent bonding. Consequently, this nonwoven fabric retains long-
`lasting hydrophilicity and functions to inhibit a battery from suffering self-discharge. However, the treatment necessi-
`tates a post-washing step.
`[0008]
`Anobject of the invention is to provide a battery which is sufficiently inhibited from suffering self-discharge
`and has excellent battery properties. The present inventors made extensive investigations on the self-discharge of
`batteries. As a result, it has unexpectedly been found thatthe self-discharge of a battery is considerably inhibited by
`causing polycarbodiimide to be presentin the battery. The invention has thus been completed.
`
`Disclosure of the Invention
`
`[0009] The invention provides a battery containing a built-in polymer which hasin the molecule a carbodiimide unit
`represented by the fallowing formula (1):
`
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`JLab/Cambridge, Exh. 1012, p. 3
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`JLab/Cambridge, Exh. 1012, p. 3
`
`

`

`EP 1 315 220 Al
`
`{-R-N=C=N-],-
`
`(1)
`
`(wherein R means an organic group and n means anintegerof 1 to 10,000).
`[0010] The battery of the invention can beinhibited from suffering self-discharge due to the built-in pelycarbodiimide
`represented by general formula (I), which is disposedin any of various forms such as sheet, powder, and particlesin
`or on an electrode or the separator or in other inner part of the battery.
`[0011] The built-in polycarbociimide may be disposed in any desired position within the battery. Furthermore, the
`battery is not particularly limited in steps for the production thereof. In the case wherethe polycarbodiimideis particulate
`or powdery, it may be placed in a bag madeof a net or porous material having an opening diameter smaller than the
`particles, so as to prevent the polycarbodiimide from scattering. In the case wherethe polycarbodiimideis particulate
`or powdery, it may be present on the surface of or in an inner part of a porous separator substrate. It may have been
`deposited on the surface of the separator by coating. The polycarbodiimide may be present on the surface of or in an
`inner part of an electrode. It may also be present between the separator and an electrode. Incidentally, the polycarbo-
`diimide may be crosslinked if desired.
`
`Brief Description of the Drawings
`
`[0012]
`[0013]
`[0014]
`[0015]
`
`(Fig. 1] A schematic sectional view illustrating one embodimentof the battery of the invention.
`[Fig. 2] A schematic sectional viewillustrating another embodimentof the battery of the invention.
`(Fig. 3] Aschematic sectional viewillustrating still another embodimentof the battery of the invention.
`(Fig. 4] Aschematic sectional viewillustrating a further embodimentof the battery of the invention.
`
`Detailed Description of the Invention
`
`[0016] The battery of the invention is not limited at all as long asit has built-in polycarbodiimide. The battery has a
`positive electrode, a negative electrode, and a separator interposed between the two electrodes. The other materials
`constituting the battery, including the electralytic solution and battery case, may be conventionally known ones. Fig. 1
`is a schematic sectional view of a battery (button type cell) of the invention. As shownin Fig. 1, a nickel wire gauze 2
`and a nickel collector 3 are disposedin a cell inner case 1. Furthermore, a negative electrode 4, a separator 5 having
`polycarbodiimide, and a positive electrode 6 are superposed thereon and an outer cover 8 is attached through a packing
`7. Figs. 2 to 4 are schematic sectional viewsillustrating other embodiments of the battery of the invention. In these
`embodiments, a polycarbadiimidefilm 9 is disposed in respective inner positionsin the batteries. The battery according
`to the invention maybe either a cylindrical cell containing electrodes and a separator which have been superposed
`and spirally wound or a prismatic cell comprising electrodes and a separator which have been superposed and packed
`in a case,
`
`[0017] The separator or the porous sheet to be used as a separator substrate is not particularly limited in material.
`However, for use in applications where the separator is used in a strongly oxidizing or reducing atmosphere, e.g., like
`the separators for alkaline secondary batteries, the material thereof is preferably a polyolefin or the like having no
`specific functional groups.
`[0018] Examples of the polyolefin to be used as the separator (or separator substrate) include homopolymers or
`copolymers of olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene, blends of these pol-
`ymers, and the like. Preferred of these are polypropylene and polyethylene. Especially preferred for use in a strongly
`oxidizing or reducing atmosphereas, e.g., the separator of an alkaline secondary battery or the like is ultrahigh-mo-
`lecular polyethylene (hereinafter abbreviated as UHPE) having a weight average molecular weight of 1,000,000 or
`higher.
`[0019] With respect to the form of the porous sheet, it is preferably a porous film or a nonwoven fabric. The porous
`sheetis not particularly limited in pore diameter or porosity.
`
`(Application to Separator)
`
`In the case where polycarbodiimide is applied to a separator, particles or a powder of the polycarbodiimide
`[0020]
`is disposed in pores of a porous sheet substrate. In producing such a separator, a sheet substrate is immersed in a
`dispersion of particles or a powder of the polycarbodiimide, or the dispersion is applied to the substrate, whereby the
`polycarbodiimide is infiltrated into pores of the porous substrate. Due to the incorporation of the particles or powder in
`poresof the separator, the separator has a substantially increased surface area and a reduced pore diameter, whereby
`the function of inhibiting self-discharge and liquid retentivity are improved. The dispersion is more preferably one in
`
`10
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`25
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`30
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`JLab/Cambridge, Exh. 1012, p. 4
`
`JLab/Cambridge, Exh. 1012, p. 4
`
`

`

`EP 1 315 220 Al
`
`which the dispersion medium is a polycarbodiimide solution. Upon drying, the solution forms a coating film on the
`surface of the fibers or particles constituting the separator, whereby not only the surface area of polycarbodiimideis
`increased but also the particles or powder is prevented from falling from the separator. The particles or powder of
`carbodiimide can be obtained by vacuum-drying a polycarbodiimide solution and optionally conducting pulverization.
`[0021]
`Furthermore, use may be made of a separator obtained by coating at least part of the surface of a porous
`sheet substrate with polycarbodiimide. It is especially preferred to use as the sheet substrate a porous sheet obtained
`by sintering a powder of UHPE. The coating may be accomplished by immersing a sheet substrate in a polycarbodiimide
`solution and then evaporating the solvent by drying. If desired, the polycarbodiimide may be crosslinked.
`[0022]
`Inthecaseof using a porous sheet substrate consisting of a UHPE powderbonded to one another,this porous
`sheet usually preferably has a thickness of from 10 to 300 im, a porosity of from 20 to 80%, and a pare diameter of
`from 1 to 500 um. A UHPE porous sheet which can be usedin the invention is obtained, for example, in the following
`manner. A UHPE powder is packed into a shape-retaining tool, and this shape-retaining tool is placed in a pressure
`vessel. The air present in the vessel is discharged. Subsequently, the powderis sintered in a water vapor atmosphere
`heated to a temperature not lower than the melting point of the UHPE and then cooled to thereby obtain a porous
`material in a block form. Thereafter, this porous material is sliced into sheets of a given thickness.
`[0023] A polycarbodiimide-coated separator can be obtained by immersing a porous sheet substrate in a polycar-
`bodiimide solution and then evaporating the solvent by drying. If desired, the polycarbodiimide may be crosslinked.
`[0024]
`Furthermore, a porous sheetof polycarbodiimide which has been made porous byperforation, etching, or the
`like may be used as the separator. Examples of methods for producing this porous sheetinclude (i) a method in which
`a sheetis formed fram a polycarbodiimide solution and this sheetis perforated with needlesor a laser; and (ii) a method
`which comprises adding a particulate, powdery, or fibrous material to a polycarbodiimide solution, forming the mixture
`into a sheet, and then extracting the particulate, powdery,or fibrous material. It is also possible (iii) to obtain a porous
`sheet through chemical etching. Examples of methodsfor this chemical etching include the following method. A metal
`wire (copperwire, etc.) is coated with a polycarbodiimide solution, and this coated wireis tightly wound repeatedly on
`a core until the resultant structure comes to have a given diameter. Subsequently, the resulting structure is heated to
`a temperature not lower than the softening point (preferably not lower than the melting point) of the polycarbodiimide
`to thereby remove the solvent and simultaneously unite the loops of the coated metal wire. After cooling, this united
`tubular structureis sliced in a direction perpendicular to the metal wire to obtain a sheet having a given thickness. The
`metal wire is removed from this sheet with an etchant such as hydrochloric acid or sulfuric acid.
`In the case of using
`this chemical etching method, heating conditions usually include a temperature of from 140 to 200°C, atime period of
`from 0.5 to 5 hours, and an etchant concentration of from 0.1 to 10 mol/L. The porous separator thus obtained usually
`has a thickness of from 10 to 300 um, a porosity of from 20 to 80%, and a pore diameter of from 1 to 500 um.
`[0025] Forthe purposeof improving initial wettability by an electrolytic solution, the porous sheet may be coated with
`a surfactant beforehand.
`
`[0026] As the separator may also be used a sheet having a given thickness obtainedbyslicing either a porous sinter
`obtained by sintering a polycarbodiimide powderat a temperature not lower than the melting point thereof or a porous
`sinter obtained by sintering polycarbodiimide and polyolefin particles at a temperature not lower than the melting point
`of the polyolefin particles. As this polyolefin may be used the aforementioned polyolefins. Especially preferred is UHPE.
`Such a porous film in which UHPE has been blended can be produced, for example, in the following manner.
`[0027]
`Particles of a polymer having carbodiimide units in the molecule are mixed with UHPE according to need,
`and this mixture is packed into a shape-retaining tool. The powder mixture packedis sintered by heating in a hot-air
`drying oven at a temperature not lower than the melting point of the UHPE. Alternatively, the shape-retaining tool is
`placed in a pressure vessel and, after the discharge of the air present in the vessel, the powder mixtureis sintered in
`a water vapor atmosphere heated to a temperature not lower than the melting point of the UHPE. The resultant sintered
`powder mixture is cooled to obtain a porous sinter. Thereafter, this porous sinteris sliced into a given thickness, whereby
`a porous sheet can be produced.
`[0028]
`Furthermore, a porous sheet produced by aggregating coated polymerparticles obtained by forming a coating
`layer of polycarbodiimide on the surface of core particles madeof a polyolefin resin or the like may be used as the
`separator. This porous sheet can be produced, for example, by forming a coating layer of the polycarbodiimide on the
`surface of core particles and sintering the coated polymerparticles at a temperature not lower than the melting point
`of the core particles.
`[0029]
`Incidentally, if n in formula (I) exceeds 10,000, the polycarbodiimideis insoluble in solvents and the desired
`polycarbodiimide-coated polymer particles cannot be obtained. From the standpointof obtaining evenly coated polymer
`particles, n is preferably from 5 to 100, more preferably from 10 to 50.
`[0030]
`For forming the core particles to be used for the coated polymerparticles, either a thermoplastic or a thermo-
`setting resin is used. Preferred are polyolefin resins such as polypropylene and polyethylene and fluororesins because
`these resins have excellent resistanceto alkaline electrolytic solutions. Especially preferred is UHPE.
`[0031] Acoated polymeris producedin the following manner. Whenthe polycarbodiimideis solid, it is dissolved in
`
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`JLab/Cambridge, Exh. 1012, p. 5
`
`JLab/Cambridge, Exh. 1012, p. 5
`
`

`

`EP 1 315 220 Al
`
`it may be diluted to a given concentration so as to be easily handled. To the
`In the case of a solution,
`a solvent.
`polycarbodiimide solution thus prepared are added core polymer particles in such an amount asto result in a core
`particle concentration of about from 20 to 50% by weight. The resultant mixture is stirred with a mixer to obtain a slurry.
`This slurry is stirred with heating at a temperature lower than the melting point of the core particles to conduct a solvent
`elimination treatment. In the case where the resultant coated polymer particles are in an aggregatedstate, a treatment
`for reducing the aggregate is suitably conducted using a stirrer, pulverizer, etc.
`[0032] The polycarbodiimide-coated polymer particles described above are packed, for example, into a cylindrical
`metal vessel, heated and sintered, subsequently cooled, and then taken out from the vessel to thereby obtain a porous
`sinter. Furthermore, this sinter is sliced into a given thickness with a lathe to obtain a porous sheet. Alternatively, a
`porous sheetis obtained also by a method in which the coated polymerparticles are compressed at ordinary temper-
`ature in a mold having a certain gap to obtain a sheet-form molding and this sheet is heated and sintered.
`
`(Application to Electrode)
`
`In one embodimentof the battery of the invention, at least one of the positive electrode and negative electrode
`[0033]
`of the battery contains polycarbodiimide. This electrode is produced from an electrode-forming dispersion containing
`polycarbodiimide. The polycarbodiimide compound may be in a powder form or solution form. In this case, a conven-
`tional production apparatus can be used without modifying the production steps. In another embodiment, polycarbo-
`diimide is disposed on the surfaceofat least one of the positive electrode/negative electrode. In this case, the electrode
`is produced by scattering particulate or powdery polycarbodiimide on the surface of an electrode and then uniting the
`polycarbodiimide with the electrode by pressing, etc.
`
`(Application to Other Parts of Battery)
`
`In other embodiments of the invention, particles or a powderof polycarbodiimide may be sprinkled on a part
`[0034]
`other than the separator and the electrodes, e.g., between the separator and an electrode. This can be accomplished
`by merely disposing the particles or powder between an electrode and the separator during battery fabrication, and a
`conventional apparatus can be usedtherefor without necessitating a considerable modification in the production steps.
`Furthermore, a layer of particles is substantially formed and the amountof the liquid retained by the spaces among
`the particles or powderis increased.
`
`(Production of Polycarbodiimide)
`
`10
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`20
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`[0035] The polycarbodiimide to be caused to be present asafilm, a powder, or particles in or on an electrode or the
`35
`separator or in other parts in a can in the invention is represented by formula (|) described above.
`In formula (I),
`examples of the organic group R include aromatic or aliphatic organic groups.
`
`(i) Examples of the aromatic organic groups include substituents represented by
`
`40
`
`45
`
`50
`
`55
`
`(wherein p is an integer of 0 to 10 and q means anintegerof 0 to 5).
`In the formula given above, X is
`
`-O-,
`
`-S~, CHo-,
`
`CH;
`|
`-C=,
`
`CF;
`|
`-C-
`
`CH3
`
`CF3
`
`or
`
`0
`|
`-S-
`
`0
`
`JLab/Cambridge, Exh. 1012, p. 6
`
`JLab/Cambridge, Exh. 1012, p. 6
`
`

`

`EP 1 315 220 Al
`
`and the X's in the repeating units may be the same or different; and a, b, c, and d are -H, -CH3, -OCH3, -CFor
`-OCF3 and may be the same or different.
`(ii) Examplesof the aliphatic organic groups include substituents represented by
`
`-CH,-(-Y-),-
`
`(wherein r means an integerof 0 to 10).
`
`[0036]
`
`In the formula given above, Y is
`
`-0O-, -S-, CHo-,
`
`CH3
`i
`-C-,
`
`\
`CH3°
`
`CF,
`|
`-C-
`
`|
`CF;
`
`0
`i
`or a
`
`|
`a)
`
`and the Y's in the repeating units may be the same or different; and a, b, c and d are -H, -CHg, -OCHs, -CF, or -OCF3
`and may be the same or different.
`[0037]
`In formula (I), nis 1 to 10,000. If n exceeds 10,000, the polycarbodiimide undesirably has a reduced gelation
`time at room temperature, resulting in impaired workability.
`[0038]
`For obtaining such a polycarbodiimide, a known method can be used. For example, the polycarbodiimide can
`be easily obtained by reacting an organic diisocyanatein an organic solventin the presenceof a carbodiimide synthesis
`catalyst in the manner described in T.W. Campbell et al., J. Org. Chem., 28, 2069(1963), L.M. Alberino et al., J. Appi.
`Polym. Sci., 21, 1999(1977), Unexamined Published Japanese Patent Applications Nos. 2-292316 and 4-275359, etc.
`[0039] As the organic diisocyanate for use in the polycarbodiimide synthesis can be used, for example, 2,4-tolylene
`diisocyanate, 2,6-tolylene diisocyanate, 1-methoxyphenyl 2,4-diisocyanate, 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,
`2,2-dimethyl-1 ,3-bis(4-isocyanatophenoxy)propane, or the like. These may be used alone or may be usedin combi-
`nation of two or more thereof (to obtain a copolymer). For the purposeof imparting hydrophobicity, an organic diiso-
`cyanate substituted with one or more fluorine groups may be partly used.
`[0040] As the organic solvent can be used, for example, toluene, xylene, a halogenated hydrocarbon such astetra-
`chloroethylene, 1,2-dichloroethane, or chloroform, a ketone such as acetone, methyl ethyl ketone, methyl isobutyl
`ketone, or cyclohexanone, a cyclic ether such as tetrahydrofuran or dioxane, or the like. These may be used alone or
`in combination of two or more thereof.
`
`Furthermore, as the carbodiimide synthesis catalyst can be used, for example, a phospholene oxide such as
`[0041]
`3-methyl-1-phenylphospholene 1-oxide, 1-phenyl-2-phospholene 1-oxide, 1-ethyl-2-phospholene 1-oxide, 1-ethyl-
`2-phospholene 1-oxide, or the 3-phospholene isomer of any of these. These may be used alone or in combination of
`two or morethereof.
`
`In anyof the final, middle, and initial stages of the polymerization reaction or throughoutthe reaction, a chain-
`[0042]
`terminating treatment may be conducted by adding a monaisocyanate. As such a manoisocyanate can be used phenyl
`isocyanate, p-nitrophenyl isocyanate, p- and m-tolyl isocyanates, p-formylphenyl isocyanate, p-isopropylphenyl isocy-
`anate, or the like. The polycarbodiimide solution thus obtained has excellent storage stability.
`[0043] The polycarbodiimide solution obtained is cast on a glassplate, dried, andpeeledoff, whereby a film can be
`obtained. On the other hand, particles or a powder can be obtained by vacuum-drying the solution described above
`and optionally pulverizing the resultant particles.
`[0044] With respect to the function of inhibiting self-discharge, this function is presumed to be attributable to the
`ammonia gas trapping function of carbodiimide groups (W. Weith, Ber., 7, 10 (1874)), because the fact that carbodiimide
`groups disappear whena film formed from carbodiimide is brought into contact with ammonia gas can be ascertained
`from an infrared absorption spectrum.
`
`Examples
`
`[0045]
`
`The invention will be explained below in moredetail by means of Examples and Comparative Examples. Cells
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`JLab/Cambridge, Exh. 1012, p. 7
`
`JLab/Cambridge, Exh. 1012, p. 7
`
`

`

`EP 1 315 220 Al
`
`were evaluated in the following manner.
`
`(Evaluation of Cell)
`
`[0046] Thecells obtained in the Examples and the Comparative Examples werefirst examinedfar discharge capacity.
`Subsequently, the cells were fully charged and then stored for 1 week at 45°C to causeself-discharge. Thereafter, the
`cells were examined for discharge capacity, fully recharged, and then examined for discharge capacity. The results
`are shownin Table 1. The discharge rate was regulated to 0.2 C,A, and the capacity retention was determined using
`the following equation.
`[0047] Capacity retention [%] = (discharge capacity after self-discharge [Ah] / ((discharge capacity before self-dis-
`charge [Ah] + discharge capacity after full recharge after self-discharge [Ah])/2)x100
`
`10
`
`[EXAMPLE I-1]
`
`15
`
`25
`
`To 500 g of toluene was added 100 g of Takenate 80 (manufactured by Takeda ChemicalIndustries, Ltd.; a
`[0048]
`2,4-tolylene diisocyanate/2,6-tolylene diisocyanate mixture) together with 0.06 g of a carbodiimide synthesis catalyst
`(3-methyl-1-phenylphospholene 1-oxide) and 10 g of isopropylphenyl isocyanate. This mixture was reacted at 100°C
`for 6 hours to obtain a polycarbodiimide solution (solution A). The molecular weight thereof was measured by GPC
`(gel permeation chromatography) to determine n, which was thus found to be 25. This solution was cast on a glass
`20
`plate, subsequently dried at 90°C for 30 minutes, and peeled off to obtainafilm (thickness, 100 um).
`[0049] Anonwovenfabric composedof polypropylene and polyethylene fibers (basis weight, 60 g/m?) was immersed
`ina2.5 wt% aqueous solution of sodium dodecylbenzenesulfonate and dried. This fabric was used as a separator.
`[0050]
`On the other hand, 100 parts by weight of a nickel hydroxide powder was mixed with 10 parts by weight of a
`cobalt powder, 10 parts by weight of a polytetrafluoroethylene (PTFE) powder, and 20 parts by weight of water to
`preparea dispersion for positive-electrode formation. This liquid was forced into a foamed nickel(Ni) plate. The resultant
`nickel plate was dried and then pressedinto a sheet to obtain a positive electrode. Furthermore, 100 parts by weight
`of a hydrogen-occluding alloy (mischmetal type) was mixed with 10 parts by weight of a PTFE powder and 20 parts
`by weight of water to prepare a dispersion for negative-electrode formation, which was forced into a foamed nickel
`plate. This plate was dried and then pressed into a sheet to obtain a negative electrode.
`[0051]
`In fabricating a button type nickel-hydrogen cell (2032 size: diameter, 20 mm; height, 3.2 mm), the separator
`described above was immersed beforehand in a 7.2 kmol/m®electrolytic solution of potassium hydroxide to conduct
`vacuum impregnation. The polycarbediimidefilm described above was subjected to punching to obtain a film piece of
`12 mm® (12.9 mg), which wasplaced in a can. A nickel wire gauze for current collection and a nickel collector were
`placed thereon, and the negative electrode, the separator, the positive electrode, and an outer cover were superposed
`thereon.
`
`30
`
`35
`
`[EXAMPLE I-2]
`
`40
`
`45
`
`50
`
`55
`
`[0052] The polycarbodiimide solution (solution A) obtained in Example |-1 was vacuum-dried and the resultant solid
`waspulverized to obtain a powder. A button type cell similar to that in Example |-1 was produced in the same manner
`as in Example |-1, except that 10 mg of the powder was usedin place of the polycarbodiimide film.
`
`[EXAMPLES I-3 AND I-4]
`
`[0053] A polycarbodiimide solution (solution B) was obtained (n determined by GPC was 408) and cells were pro-
`duced in the same manner as in Example I-1 and Example I-2, respectively, except that 4,4'-diphenylmethane diiso-
`cyanate was used in place of Takenate 80.
`
`[EXAMPLES I-5 and |-6]
`
`[0054] A polycarbodiimide solution (solution C) was obtained (n determined by GPC was 18) and cells were produced
`in the same manner as in Example |-1 and Example |-2, respectively, except that 2,2'-dimethyl-1,3-bis(4-isocyanat-
`ophenoxy)-phenyl]propane was usedin place of Takenate 80.
`
`[EXAMPLES I-7 AND I-8]
`
`[0055] Apolycarbodiimide solution (solution D) was obtained (n determined by GPC was30) and cells were produced
`in the same manneras in Example |-1 and Example |-2, respectively, except that 2,2'-bis[4-(4-isocyanatophenoxy)
`
`JLab/Cambridge, Exh. 1012, p. 8
`
`JLab/Cambridge, Exh. 1012, p. 8
`
`

`

`EP 1 315 220 Al
`
`phenyl]-hexafluoropropane was usedin place of Takenate 80.
`
`[COMPARATIVE EXAMPLE I-1]
`
`[0056] Acell was produced in the same manneras in Example |-1, except that the polycarbodiimide was not used.
`
`(Application to Separator (1))
`
`[EXAMPLE II-1]
`
`[0057] A polycarbodiimide solution (solution A) was obtained in the same manner as in Example |-1 (n determined
`by GPC was 25). The solution was cooled to room temperature and then vacuum-dried. The polymerdried was pul-
`verized with a mortar. The resulting particles were sieved with a sieve having an opening size of 31 tum. Ten parts by
`weight of the polycarbodiimide powder which had passed the sieve was mixed with 10 parts by weight of the solution
`A described above and 10 parts by weight of toluene to prepare a dispersion.
`[0058] A nonwovenfabric composed of polypropylene and polyethylene fibers (basis weight, 60 g/m?) was immersed
`as a separator in the dispersion described above and dried at 80°C for 30 minutes to obtain a separator. The separator
`was immersed beforehand in a 7.2 kmol/m®electrolytic solution of potassium hydroxide to conduct vacuum impreg-
`nation and thereby incorporate the electrolytic solution into the pores. A button type nickel-hydrogen cell of the 2032
`size was produced. The positive electrode, negative electrode, nickel wire gauze, nickel plate, and the can cover used
`were the same as in Example |-1.
`
`[EXAMPLE II-2]
`
`[0059] Twokilograms of a UHPE powder (weight average molecular weight, 4,500,000: melting point, 135°C; average
`particle diameter, 106 um (sieved product)) was packedinto a shape-retaining tool comprising a mold formed by placing
`a cylindrical metal gauze cage having an outer diameter of 4 cm in the centerof a cylindrical metal gauze cage (inner
`diameter, 15 cm) and applying a porous polytetrafluoroethylene film to the inside of the resultant doughnut space. This
`mold wasplacedin a heat-resistant pressure vessel made of metal (equipped with a water vapor introduction pipe and
`a switch valve therefor), and the ambient pressure was adjusted to 1.3 kPa with a vacuum pump. Subsequently, the
`pump was stopped, and the pressure vessel was allowed to