United States Patent (19)
`Kawakami
`
`USOO5853914A
`Patent Number:
`11
`(45) Date of Patent:
`
`5,853,914
`*Dec. 29, 1998
`
`54 RECHARGEABLE LITHIUM BATTERY
`HAVING ASPECIFIC PRESSURE MEANS
`COMPRISING A POLYMER GEL MATERIAL
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`75 Inventor: Soichiro Kawakami, Nara, Japan
`73 Assignee: Canon Kabushiki Kaisha, Tokyo,
`Japan
`
`*
`
`Notice:
`
`This patent issued on a continued pros
`ecution application filed under 37 CFR
`1.53(d), and is subject to the twenty year
`patent term provisions of 35 U.S.C.
`154(a)(2).
`
`21 Appl. No. 709,448
`22 Filed:
`Sep. 6, 1996
`30
`Foreign Application Priority Data
`Sep. 6, 1995
`JP
`Japan .................................... 7-2S2O68
`(51) Int. Cl. ................................................ HO1M 2/10
`52 U.S. Cl. ............................. 429/66; 429/142; 429/186
`58 Field of Search .............................. 429/66, 186, 190,
`429/142
`
`2,499,239 2/1950 Williams ................................... 429/66
`2,723,301 11/1955 West et al. .............................. 429/190
`5.244,754 9/1993 Bohmer et al.
`... 429/66 X
`5,605,549 2/1997 Zucker ................................ 429/190 X
`OTHER PUBLICATIONS
`Journal of the Electrochemical Society, “The Electrochem
`nical Decomposition of Propylene Carbonate on Graphite,”
`Dey, et al., vol. 117, No. 2, pp. 222-224, Feb. 1970.
`Primary Examiner Stephen Kalafut
`Attorney, Agent, or Firm-Fitzpatrick, Cella, Harper &
`Scinto
`ABSTRACT
`57
`A rechargeable lithium battery comprising at least a cathode,
`a separator, an anode, and an electrolyte or electrolyte
`Solution integrated in a battery housing, characterized in that
`Said rechargeable lithium battery is provided with a preSSure
`means comprising a polymer gel for pressing Said anode and
`cathode.
`
`29 Claims, 7 Drawing Sheets
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`U.S. Patent
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`Dec. 29, 1998
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`Sheet 1 of 7
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`U.S. Patent
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`Dec. 29, 1998
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`Sheet 2 of 7
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`U.S. Patent
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`Dec. 29, 1998
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`Sheet 3 of 7
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`5,853,914
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`U.S. Patent
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`Dec. 29, 1998
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`U.S. Patent
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`Dec. 29, 1998
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`Sheet 5 of 7
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`U.S. Patent
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`Dec. 29, 1998
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`U.S. Patent
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`Dec. 29, 1998
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`Sheet 7 of 7
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`5,853,914
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`1
`RECHARGEABLE LITHIUM BATTERY
`HAVING ASPECIFIC PRESSURE MEANS
`COMPRISING A POLYMER GEL MATERIAL
`
`BACKGROUND OF THE INVENTION
`
`2
`ion batteries having Such configuration, which are practi
`cally usable. In these lithium ion rechargeable batteries, the
`carbonous material Serving as a host for allowing lithium
`ions as a guest to intercalate (or insert) into or deintercalate
`(or release) from the six-membered network layer planes of
`the carbonous material is used as the anode active material
`to prevent the growth of a lithium dendrite so that the
`charging and discharging cycle life is prolonged.
`In the conventional rechargeable lithium batteries includ
`ing these lithium ion batteries, Since lithium deposited upon
`charging is readily reactive with moisture, there is generally
`used a nonaqueous Solvent as the Solvent for the electrolyte
`used. Particularly, in the case of a nonaquecuS Series elec
`trolyte Solution prepared by dissolving a given electrolyte in
`a nonaqueous Solvent, its ion electrical conductivity is lower
`than that of an aqueous Series electrolyte Solution.
`Therefore, in the case of a rechargeable lithium battery in
`which Such a nonaqueous Series electrolyte Solution is used,
`in order to reduce the battery impedance, the distance
`between the cathode and anode is narrowed by pressing the
`cathode and anode. Whether or not the electrode impedance
`can be reduced greatly influences the battery characteristics.
`If a desirable reduction in the electrode impedance should be
`attained, an improvement can be attained in not only the
`charge-and-discharge efficiency but also the charging and
`discharging cycle life. For instance, in the case of a spiral
`wound rechargeable lithium battery comprising a Stacked
`body (comprising an anode, a separator, and a cathode)
`wound in multiple on a predetermined axis, the distance
`between the anode and cathode can be easily narrowed by
`applying a desired tension in a spiral State upon winding the
`Stacked body in multiple. However, in the case of a large
`rectangular prismatic rechargeable lithium battery produced
`by laminating a rectangular cathode and a rectangular anode,
`an appropriate preSSure means capable of uniformly narrow
`ing the distance between Said rectangular cathode and anode
`is not available at the present time. Therefore, it is difficult
`to attain a practical employable large capacity rechargeable
`lithium battery which is high enough in charge-and
`discharge efficiency and long enough in charging and dis
`charging cycle life.
`Separately, for the conventional lithium ion battery, there
`is a problem in that a lithium dendrite is often generated
`upon overcharging to cause internal-shorts between the
`anode and cathode, where a large electric current Suddenly
`flows causing temperature rise in the battery whereby the
`organic Solvent of the electrolyte Solution is decomposed to
`increase the internal preSSure of the battery. In order to
`prevent the occurrence of this problem, the use of a Safety
`means is known. AS Such safety means, there is known to
`employ a Separator comprising a polyethylene or polypro
`pylene capable of fusing to fill micropores upon temperature
`rise. Besides this, it is known to install a PTC (positive
`temperature coefficient) element in the battery. Further, it is
`known to install a overcharge preventive circuit in the
`battery. The use of these Safety means unavoidably makes
`the resulting lithium ion battery to be high in production
`COSt.
`Hence, there is an increased demand for simplifying the
`Structure of, particularly, a rechargeable lithium battery
`having a large battery capacity especially in terms of the
`Safety means.
`
`1. Field of the Invention
`The present invention relates to a highly reliable recharge
`able lithium battery using intercalation and deintercalation
`reactions of lithium ions in charging and discharging.
`The rechargeable lithium battery using intercalation and
`deintercalation reactions of lithium ions in charging and
`discharging will be hereinafter simply referred to as
`rechargeable lithium battery. And the rechargeable lithium
`battery in the present invention is meant to include a lithium
`ion battery.
`More particularly, the present invention relates to an
`improved, highly reliable rechargeable lithium battery pro
`Vided with a specific pressure means comprising a polymer
`gel material for pressing the anode and the cathode arranged
`therein, which is low in internal impedance, and has an
`improved charge-and-discharge efficiency and a prolonged
`charging and discharging cycle life.
`2. Related Background Art
`In recent years, global warming from the So-called green
`house effect has been predicted due to increased level of
`atmospheric CO. To prevent this warming phenomenon
`from further developing, there is a tendency to prohibit the
`construction of new Steam-power generation plants which
`exhaust a large quantity of CO.
`Under these circumstances, proposals have been made to
`institute load leveling in order to effectively utilize power.
`Load leveling involves the installation of rechargeable bat
`teries at general locations to Serve a Storage for Surplus
`power unused in the night, known as dump power. The
`power thus stored is available in the day time when the
`power demand is increased, leveling the load requirements
`in terms of power generation.
`Separately, there is an increased Societal demand for
`developing a high performance rechargeable battery with a
`high energy density for an electric Vehicle which would not
`exhaust air polluting Substances. There is further increased
`Societal demand for developing a miniature, lightweight,
`high performance rechargeable battery usable as a power
`Source for portable instruments Such as Small personal
`computers, word processors, Video cameras, and pocket
`telephones.
`In order to attain Such a miniature and light weight
`rechargeable battery, various Studies have been made of a
`rechargeable lithium battery which would allow the appli
`cation of a high Voltage and which would excel in energy
`density. For instance, a lithium-graphite intercalation com
`pound as an anode active material in a rechargeable battery
`has been proposed (see, Journal of the Electrochemical
`Society, 117, 222, (1970)).
`Since then, public attention has focused on a rocking chair
`type lithium ion battery. And various Studies have been made
`in order to develop Such a rocking chair type lithium ion
`battery. The rocking chair type lithium ion battery is typi
`cally configured Such that a carbonous intercalation material
`is used as an anode active material and another intercalation
`compound intercalated with lithium ions is used as a cathode
`active material, and lithium ions are intercalated into the
`Six-membered network layer planes provided by carbon
`atoms to Store in the battery reaction upon charging.
`Presently, there are known Several rocking chair type lithium
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`SUMMARY OF THE INVENTION
`A principal object of the present invention is to eliminate
`the foregoing problems found in the prior art and to provide
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`3
`a highly reliable rechargeable lithium battery which is free
`of Such problems.
`A further object of the present invention is to provide an
`improved, highly reliable rechargeable lithium battery par
`ticularly having a large capacity which is provided with a
`Specific pressure means comprising a polymer gel material
`for pressing the anode and cathode and which has a high
`energy density and a prolonged charging and discharging
`cycle life.
`A typical embodiment of a rechargeable lithium battery
`which attains the above objects of the present invention
`comprises at least an anode, a separator, a cathode, and an
`electrolyte (or an electrolyte Solution) integrated in a battery
`housing, characterized in that the rechargeable lithium bat
`tery is provided with a Specific pressure means comprising
`a polymer gel material for pressing the anode and cathode.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a Schematic view illustrating an example of the
`constitution of a rechargeable lithium battery provided with
`preSSure means comprising a polymer gel material according
`to the present invention.
`FIG. 2 is a Schematic diagram illustrating the mechanism
`for a polymer gel material sheet as a preSSure means used in
`a rechargeable lithium battery to exhibit pressing by way of
`Swelling in the present invention.
`FIGS. 3(A) through 3(D) are schematic views respec
`tively illustrating a polymer gel material in the form of a
`film-like shape or sheet-like shape which constitutes a
`principal part of a pressure means used in a rechargeable
`lithium battery in the present invention.
`FIG. 4 is a schematic perspective view illustrating an
`example of the constitution of a prismatic rechargeable
`lithium battery according to the present invention.
`FIG. 5 is a Schematic croSS-Sectional view illustrating an
`example of a single-layer System flat rechargeable lithium
`battery according to the present invention.
`FIG. 6 is a Schematic croSS-Sectional view illustrating an
`example of a spiral-wound cylindrical rechargeable lithium
`battery according to the present invention.
`FIG. 7 is a Schematic croSS-Sectional view illustrating an
`example of a prismatic rechargeable lithium battery accord
`ing to the present invention.
`FIG. 8 is a Schematic cross-sectional view illustrating
`another example of a rectangular prismatic rechargeable
`lithium battery according to the present invention.
`
`DESCRIPTION OF THE INVENTION AND
`PREFERRED EMBODIMENTS
`AS previously described, the present invention provides a
`highly reliable rechargeable lithium battery comprising at
`least an anode, a separator, a cathode and an electrolyte or
`electrolyte Solution integrated in a battery housing, charac
`terized in that Said rechargeable lithium battery is provided
`with a Specific pressure means comprising a polymer gel
`material for pressing the anode and cathode. The pressure
`means enables control of the distance between the anode and
`cathode as desired So as to attain a desirably adjusted
`internal impedance of the battery.
`In a preferred embodiment, the pressure means for press
`ing the anode and cathode comprises a polymer gel material
`capable of being expanded or shrunk depending upon the
`concentration of a Solvent. In this case, by adding an
`appropriate Solvent into the polymer gel material of the
`
`4
`preSSure means disposed in a fabricated rechargeable lithium
`battery, uniform preSSure can be attained between the anode
`and the cathode. This situation enables construction of a
`largeSize rechargeable lithium battery. By this, there can be
`attained a large capacity rechargeable lithium battery having
`an increased charge-and-discharge efficiency, a prolonged
`charging and discharging cycle life, and a high energy
`density.
`In the present invention, the Separator itself interposed
`between the anode and the cathode may be designed to also
`exhibit a pressing performance for the anode and cathode by
`providing a layer comprising a polymer gel material capable
`of being expanded or shrunk depending upon the concen
`tration of a solvent (this layer will be hereinafter referred to
`as polymer gel material layer) at the separator Such that the
`Separator is covered by the polymer gel material layer. In
`this case, when the electrolyte Solution is also incorporated
`into the polymer gel material layer covering the Separator,
`the polymer gel material layer is expanded or shrunk by
`virtue of the solvent contained in the electrolyte solution to
`attain a close relationship between the anode and the cathode
`through the Separator having the electrolyte Solution therein.
`AS a result a desirable reduction in the internal impedance of
`the battery is attained and the electrolyte Solution is immo
`bilized in the polymer gel material layer to prevent the
`electrolyte Solution from being decomposed particularly
`upon operating charging. Also, the generation of a lithium
`dendrite on the Surface of the anode upon operating charging
`is effectively prevented. And if said lithium dendrite should
`be generated, the lithium dendrite is prevented from growing
`while preventing it from being Separated. This situation
`prolongs the charging and discharging cycle life of the
`rechargeable lithium battery.
`In the present invention, the polymer gel material capable
`of being expanded or shrunk depending upon the concen
`tration of a Solvent, which is used as the preSSure means for
`the anode and cathode, may preferably comprise a polymer
`gel material excelling in rigidity which is prepared using a
`Side chain-bearing monomer, or an ionic polymer gel mate
`rial having a group capable of dissociating to convert into an
`ion in a Solvent. Any of these polymer gel materials is
`advantageous in that it is discontinuously expanded and
`shrunk.
`Further, in the present invention, the polymer gel material
`capable of being expanded or shrunk depending upon the
`concentration of a Solvent, which is used as the preSSure
`means for the anode and cathode, may preferably comprise
`a polymer gel material capable of being shrunk upon tem
`perature rise. In this case, the preSSure means performs Such
`that it releases the pressure between the anode and the
`cathode upon temperature rise to increase the internal
`impedance of the battery thereby controlling the electric
`current flown in the battery. By this, the rechargeable lithium
`battery is always maintained in a Safe State. Particularly,
`when the Separator itself interposed between the anode and
`the cathode is constituted by at least a polymer gel material
`capable of being shrunk upon temperature rise So that it also
`exhibit a performance of releasing the pressure between the
`anode and the cathode upon temperature rise, there is
`provided an advantage in that when the temperature of the
`battery is raised due to internal-shorts or the like inside of
`the battery, the Separator is shrunk to increase the internal
`impedance of the battery thereby preventing the electrolyte
`Solution from being decomposed. Accordingly an improve
`ment is attained in the Safety of the rechargeable lithium
`battery. When the above polymer gel material capable of
`being shrunk upon temperature rise comprises a polymer gel
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`material excelling in rigidity which is prepared using a side
`chain-bearing monomer, or an ionic polymer gel material
`having a group capable of dissociating to convert into an ion
`in a Solvent, any of these polymer gel materials is readily
`shrunk upon temperature rise. Hence, it is desired to use any
`of these polymer gel materials as the pressure means which
`releases the pressure between the anode and cathode upon
`temperature rise.
`In the present invention, the pressure means comprising
`the foregoing polymer gel material for pressing the anode
`and the cathode may be configured Such that preSSure means
`comprises a polymer gel material shaped into a sheet-like
`form (this will be hereinafter referred to as polymer gel
`sheet). In this case, there are provided advantages in that the
`Volume occupied by the pressure means in the rechargeable
`lithium battery is minimized, and a uniform pressure is
`applied against the anode and the cathode.
`In the case where the polymer gel sheet is of a configu
`ration formed by Subjecting a powdery polymer gel material
`to preSS-molding or by dispersing a polymer gel material on
`or in a Support member, the size of the polymer gel sheet can
`uniformly controlled as desired upon the preparation
`thereof. The use of Such a polymer gel sheet applies a
`uniform pressure against the anode and the cathode. This
`Situation makes the rechargeable lithium battery have uni
`form battery characteristics.
`The rechargeable lithium battery according to the present
`invention may be configured Such that a plurality of lami
`nates each comprising the anode, the Separator (having the
`electrolyte Solution retained therein) and the cathode are
`respectively housed in a heat-shrinkable tubing in a plurality
`of unit cells. The plurality of unit cells are Stacked into a
`Stacked body, and the Stacked body is placed in the battery
`housing Such that the Stacked body is Sandwiched between
`a pair of the pressure means comprising the foregoing
`polymer gel material in the battery housing. This configu
`ration has advantages Such that there is no occasion for the
`anode and the cathode to be Stacked in a deviated State upon
`the fabrication of a rechargeable lithium battery, the Stacked
`body can be readily inserted into the battery housing, and the
`rechargeable lithium battery has improved uniform battery
`characteristics. Further, in the case where an end portion of
`each of the above heat-shrinkable tubings, where the power
`outputting and inputting terminals of the anode and cathode
`are not present, is Sealed, the electrolyte Solution retained in
`the Separator is not diffused into the polymer gel material of
`the pressure means. Because of this, the polymer gel mate
`rial of the pressure means does not Suffer from phase change
`of an influence due to a certain factor other than the
`temperature, where the pressure means desirably exhibit a
`pressing performance against the Stacked body.
`In the case where the polymer gel material as the pressure
`means in the present invention comprises a powdery poly
`mergel material, the powdery polymer gel material allows
`a Solvent to readily penetrate thereinto thereby making phase
`change readily occur in the pressure means So that an
`improvement is provided in the expanding and shrinking
`efficiency of the pressure means. In this case, the powdery
`polymer gel material of the pressure means can be readily
`combined with other polymer material. This situation pro
`vides a polymer gel sheet having a thickness excelling in
`uniformity and which is expanded and shrunk in an
`improved uniform State. Hence, there can be attained a
`sheet-like Shaped pressure means having an improved uni
`form thickness.
`In the following, the present invention is further described
`while referring to FIGS. 1 to 3.
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`FIG. 1 is a conceptual view of a rechargeable lithium
`battery according to the present invention. The rechargeable
`lithium battery comprises a Stacked body Sandwiched
`between a pair of preSSure means 100 each including a layer
`comprising the foregoing polymer gel material which is
`supported on a support member 101. The stacked body
`comprises a plurality of laminates each comprising at least
`an anode 102, a separator 104 having an electrolyte solution
`retained therein and a cathode 103. Reference numeral 105
`indicates a battery housing (which is not expressly shown in
`the figure for simplification).
`The preSSure means herein uses a property of the polymer
`gel material at expanding depending upon the concentration
`of a Solvent. By configuring the polymer material into a
`sheet (that is, the layer) on the support member 101 as shown
`in FIG. 1, after the above stacked body is inserted into the
`battery housing, the Stacked body can readily be pressed
`from the opposite sides by the pair of the preSSure means.
`According to the configuration of FIG. 1, the fabrication of
`a rechargeable lithium battery can be efficiently conducted
`and the Stacked body can be uniformly pressed.
`FIG. 2 is a conceptual view for explaining an example of
`the mechanism for the preSSure means 100 comprising the
`polymer gel material shown in FIG. 1 to exhibit a pressing
`performance by way of Swelling the polymer gel material by
`virtue of a given solvent. In FIG. 2, reference numeral 200
`indicates a polymer gel material sheet (corresponding to the
`polymer gel material layer as the pressure means 100 in FIG.
`1), reference numeral 201 a Support member (corresponding
`to the Support member 101 in FIG. 1), reference numeral 205
`a battery housing, and reference numeral 206 volume Swell
`(or Volume expansion). Now, as shown in FIG. 2, by adding
`a given Solvent (capable of being adsorbed by the polymer
`gel material to Swell the polymer gel material) into the
`polymer gel material sheet 200, the polymer gel material
`sheet is expanded in terms of the Volume as indicated by the
`numeral reference 206 in FIG. 2. Therefore, by arranging the
`polymer gel material sheet 200 in the battery housing 205
`Such that it is in parallel to the Side plane of the Stacked body
`(see, FIG. 1, not shown in FIG. 2), a uniform pressure can
`applied against the respective anodes and cathodes of the
`Stacked body, where the distance of each pair of the anode
`and cathode in the Stacked body can be uniformly shortened
`to result in a reduction in the internal impedance of the
`battery. Herein, it is required for the polymer gel Sheet to be
`designed Such that it is expanded to cause a pressure in the
`direction perpendicular to the plane without causing a pres
`Sure in the direction parallel to the plane. In order to attain
`this, it is possible to employ a construction wherein the
`polymer gel material sheet is prepared by drying a given
`polymer gel material and press-molding the dried polymer
`gel material in the plane direction to be pressed or a
`construction wherein the size of the polymer gel material
`sheet is appropriately adjusted in advance while having a
`due care about the size thereof upon the Volume expansion.
`For the mechanism for the polymer gel sheet as the
`preSSure means to be shrunk upon temperature rise to release
`the pressure between the anode and cathode, it can be easily
`understood from the description of FIG. 2.
`FIGS. 3(A) to 3(D) are schematic views respectively
`illustrating a polymer gel material in the form of a film-like
`shape or sheet-like shape prior to Swelling, which constitutes
`a principal part of the pressure means used in a rechargeable
`lithium battery according to the present invention.
`Particularly, FIG. 3(A) is a schematic view illustrating a
`preSSure means comprising a polymer gel material 300 only.
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`FIG. 3(B) is a schematic view illustrating a pressure means
`comprising a polymer gel material 301 implanted in a
`nonwoven member (e.g., a nonwoven fabric) as a Support
`member. FIG. 3(C) is a schematic view illustrating a pres
`Sure means comprising a powdery polymer gel material 302
`dispersed in another polymer material 303. FIG. 3(D) is a
`Schematic view illustrating a pressure means comprising a
`polymer gel material 304 held on a support member 305.
`The pressure means shown in FIG.3(A) may be prepared
`in a manner wherein a polymer gel material is directly
`formed from an appropriate monomer by way of polymer
`ization and crosslinking reaction or in a manner wherein a
`polymer gel material is formed by polymerizing an appro
`priate monomer to obtain a polymer and Subjecting the
`polymer to crosslinking.
`The pressure means shown in FIG.3(B) may be prepared
`in a manner wherein an appropriate nonwoven member as a
`Support member is immersed in a Solution of an appropriate
`monomer and the resultant is Subjected to crosslinking to
`convert the monomer held on the nonwoven member into a
`polymer gel material or in a manner wherein an appropriate
`nonwoven member as a Support member is immersed in a
`Solution of an appropriate polymer and the resultant is
`Subjected to crosslinking to convert the polymer held on the
`nonwoven member into a polymer gel material.
`The pressure means shown in FIG.3(C) may be prepared
`in a manner wherein a powdery polymer gel material is
`formed from an appropriate monomer by way of polymer
`ization and crosslinking reaction and the powdery polymer
`gel material is dispersed in a Solution of an appropriate
`polymer to Solidify the powdery polymer gel material in the
`polymer.
`The pressure means shown in FIG.3(D) may be prepared
`in a manner (a) wherein a Solution of an appropriate polymer
`is cast onto the Surface of an appropriate Support member
`and the resultant is Subjected to crosslinking to convert the
`polymer Solution held on the Support member into a polymer
`gel material or in a manner (b) wherein a Solution of an
`appropriate monomer is cast onto the Surface of an appro
`priate Support member and the resultant is Subjected to
`polymerization and/or crosslinking to convert the monomer
`Solution held on the Support member into a polymer gel
`material. For the thickness of the polymer gel material 304
`in the pressure means shown in FIG. 3(D), it may be the
`thickness of the polymer gel material obtained in the any of
`the above while appropriately adjusting the concentration of
`the Solution for the polymer gel material as desired.
`Alternatively, it may be appropriately adjusted as desired by
`drying the polymer gel material formed on Support member
`in any of the above and Subjecting the resultant to preSS
`treatment to attain a uniform thickneSS for the polymer gel
`material.
`The thickness of the polymer gel material may be appro
`priately adjusted as desired by adjusting the kind and
`concentration of a Solvent used or the depth of a reaction
`vessel used.
`For the expansion coefficient of the polymer gel material,
`it may be appropriately adjusted by appropriately adjusting
`the related factorS Such as the kind, polymerization degree,
`or crosslinking degree of a monomer used, the kind and
`concentration of a Solvent used, the concentration of an
`electrolyte contained in a Solvent used, and the like.
`The nonwoven member as the Support member used in the
`pressure means shown in FIG. 3(B) can include nonwoven
`members of polyolefins Such as polypropylene, nonwoven
`members made of glass, and nonwoven members made of
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`5,853,914
`
`8
`metallic materials. Specific preferable examples are non
`woven members made of metals. Such as nickel, copper, or
`the like; nonwoven members made of metal alloys Such as
`Stainless Steel; and nonwoven members made of ceramics
`Such as alumina, or the like.
`Specifically, the formation of a film-like or sheet-like
`shaped polymer gel material (for example, of the configu
`ration shown in FIG. 3(A) or 3(C)) may be conducted, for
`example, by means of liquid casting process wherein a
`polymer Solution obtained by dissolving a given polymer in
`a Solvent is cast onto an even Surface of a metallic Support
`member while rotating the metallic Support member to
`covert the polymer Solution into a film on the metallic
`Support member, a melt extrusion process wherein a poly
`mer liquid obtained by heat-fusing a given polymer is
`Subjected to T-die eXtrusion to convert the polymer liquid
`into a film; or a calendering process wherein a given
`polymer material is passed between two or more rolls to
`calender the polymer material into a film.
`In a detailed embodiment of the liquid casting process, for
`instance, a polymer gel material film is formed by using a
`polymer Solution containing a given powdery polymer gel
`material dispersed therein, or a polymer gel material film is
`formed by converting a given noncrosslinked polymer Solu
`tion into a film and Subjecting the film to crosslinking. In a
`detailed embodiment of the melt extrusion process, for
`instance, a polymer gel material film is formed by convert
`ing a given noncrosslinked polymer liquid into a film and
`Subjecting the film to crosslinking. In a detailed embodiment
`of the calendering process, for instance, a polymer gel
`material film is formed by using a dried polymer gel
`material.
`In the present invention, as previously described, the
`preSSure means for applying a pressure against the anode
`and the cathode So that the distance between the anode and
`the cathode is shortened to reduce the internal impedance of
`the battery may preferably to comprise a polymer gel
`material capable of expanding and shrinking depending
`upon the concentration of a Solvent and capable of Shrinking
`upon temperature rise. In order for the pressure by the
`preSSure means to be uniformly applied against the anode
`and the cathode So as to shorten the distance between the two
`electrodes as desired and also in order for the preSSure means
`to be readily introduced into the battery housing, the pres
`Sure means may preferably be shaped in a sheet-like form as
`pre