US005853914A
`5,853,914
`[11] Patent Number:
`[15
`United States Patent
`Kawakami
`[45] Date of Patent:
`*Dec. 29, 1998
`
`
`[54] RECHARGEABLE LITHIUM BATTERY
`HAVING A SPECIFIC PRESSURE MEANS
`COMPRISING A POLYMER GEL MATERIAL
`
`[56]
`
`References Cited
`US. PATENT DOCUMENTS
`2/1950 Williams w....sssssssssssssccssesecee 429/66
`2,499,239
`
`......
`wee 429/190
`11/1955 West etal.
`2,723,301
`9/1993 Bohmeret al.
`.
`.. 429/66 X
`5,244,754
`[73] Assignee: Canon Kabushiki Kaisha, Tokyo, 5,605,549=2/1997 Zucker ..eeceecceseeceeeeeees 429/190 K
`
`Japan
`OTHER PUBLICATIONS
`
`(75]
`
`Inventor: Soichiro Kawakami, Nara, 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
`
`154(a)(a provisions of 35 U.S.C.
`
`o
`
`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
`
`[21] Appl. No.: 709,448
`
`Filed:
`Sep. 6, 1996
`(22]
`oo. .
`,
`Foreign Application Priority Data
`[30]
`Sep. 6, 1995
`[IP]
`Japan vaesssccsscsetensssssesseentens 7-252068
`[SL]
`Lint. C0e
`aecccccecccccsseecesecccssseeeeceesnneeseennnnees HOIM 2/10
`
`... 429/66; 429/142; 429/186
`[52] U.S. Cl.
`......
`[58] Field of Search oo. 429/66, 186, 190,
`429/142
`
`[57]
`
`ABSTRACT
`
`Arechargeablelithium battery comprising at least a cathode,
`a separator, an anode, and an electrolyte or electrolyte
`Solution integrated in a battery housing, characterizedin that
`said rechargeable lithium battery is provided with a pressure
`means comprising a polymergelfor 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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`5,853,914
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`PRESSURE=201
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`3
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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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`FIG. 3(A)
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`U.S. Patent
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`Dec. 29, 1998
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`Sheet 4 of 7
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`5,853,914
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`FIG. 4
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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 6 of 7
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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
`
`1
`RECHARGEABLE LITHIUM BATTERY
`HAVING A SPECIFIC PRESSURE MEANS
`COMPRISING A POLYMER GEL MATERIAL
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present inventionrelates 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 lithtum 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 meantto includea lithium
`ion battery.
`invention relates to an
`the present
`More particularly,
`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 cyclelife.
`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-
`eries 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 demandis 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
`elephones.
`In order to attain such a miniature and light weight
`echargeable 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 lithtum-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 anotherintercalation
`compoundintercalated 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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`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 guestto 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 nonaqueoussolventas the solventfor the electrolyte
`used. Particularly, in the case of a nonaquecusseries elec-
`trolyte solution prepared by dissolving a givenelectrolyte in
`a nonaqueoussolvent, 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 nonaqueousseries 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. Whetheror 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 safcty
`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 cspecially in terms of the
`safety means.
`
`SUMMARYOF THE INVENTION
`
`A principal object of the present invention is to eliminate
`the foregoing problems foundin the prior art and to provide
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`5,853,914
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`a highly reliable rechargeable lithium battery whichis 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
`cyclelife.
`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 shect-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 viewillustrating an
`example of a single-layer system flat rechargeable lithium
`battcry according to the present invention.
`FIG.6 is a schematic cross-sectional viewillustrating an
`example of a spiral-wound cylindrical rechargeable lithium
`battery according to the present invention.
`FIG.7 is a schematic cross-sectional viewillustrating 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
`meansenablescontrol of the distance between the anode and
`cathode as desired so as to attain a desirably adjusted
`internal impedanceof the battery.
`In a preferred embodiment, the pressure meansfor 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
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`pressure meansdisposed 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. Bythis, 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 polymergel 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
`scparator 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. Andif 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 conecn-
`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 cise to increase the internal
`impedance of the battery thereby controlling the electric
`current flown in the battery. Bythis, the rechargeable lithium
`battery is always maintained in a safe state. Particularly,
`whenthe separator itself interposed between the anode and
`the cathodeis constituted by at least a polymer gel material
`capable of being shrunk upon temperature rise so that it also
`exhibit a performance ofreleasing 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 ofthe 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 polymergel
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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
`temperaturerise.
`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 advantagesin that the
`volume occupied by the pressure meansin 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 polymergel 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 bodyis 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 lithiumbattery, 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 prescnt, is scaled, the electrolyte solution retained in
`the separator is not diffused into the polymer gel material of
`the pressure means. Becauseofthis, the polymer gel mate-
`rial of the pressure means doesnot suffer from phase change
`of an influence due to a certain factor other than the
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`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-
`mer gel material, the powdery polymer gel material allows
`a solventto 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
`shect-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 (whichis not expressly shown in
`the figure for simplification).
`The pressure meansherein 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(thatis, the layer) on the support member 101 as shown
`in FIG. 1, after the above stacked bodyis 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 polymergel material by
`virtue of a given solvent. In FIG. 2, reference numeral 200
`indicates a polymer gel material sheet (corresponding to the
`polymergel 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 volumeswell
`(or volume expansion). Now, as shownin 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
`shect is expandedin terms of the volumeas indicated by the
`numeral reference 206 in FIG. 2. Therefore, by arranging the
`polymer gel material sheet 200 in the battery housing 205
`suchthatit is in parallel to the side planeof 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 meansto be shrunk upon temperatureriseto 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 ofa 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 viewillustrating a
`pressure means comprising a polymergel material 300 only.
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`5,853,914
`
`7
`FIG. 3(B) is a schematic viewillustrating 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 shownin 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
`olymer to crosslinking.
`The pressure means shown in FIG. 3(B) may be prepared
`in a manner wherein an appropriate nonwoven memberas 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 memberinto 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 memberinto a polymer gel material.
`The pressure means shownin 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
`polymerto solidify the powdery polymergel material in the
`polymer.
`The pressure means shownin 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
`polymersolution held on the support memberinto a polymer
`gel material or in a manner (b) wherein a solution of an
`appropriate monomeris 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. Kor the thickness of the polymer gel material 304
`in the pressure means shown in FIG. 3(D), it may be the
`hickness of the polymer gel material obtained in the any of
`he above while appropriately adjusting the concentration of
`he 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-
`reatment to attain a uniform thickness for the polymer gel
`material.
`
`The thickness of the polymer gel material may be appro-
`priatcly 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
`electralyte contained in a solvent used, and the like.
`The nonwoven memberas the support memberused in the
`pressure means shownin FIG. 3(B) can include nonwoven
`membersof polyolefins such as polypropylene, nonwoven
`members made of glass, and nonwoven members made of
`
`
`
`
`10
`
`15
`
`45
`
`50
`
`55
`
`60
`
`65
`
`12
`
`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 TIG. 3(A) or 3(C)) may be conducted, for
`example, by means of liquid casting process wherein a
`polymersolution 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 cmbodimentof the liquid casting process, for
`instance, a polymer gel material film is formed by using a
`polymer solution containing a given powdery polymergel
`material dispersed therein, or a polymer gel material film is
`formed by converting a given noncrosslinked polymersolu-
`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.
`
`the
`In the present invention, as previously described,
`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 cathodeso as to shorten the distance betweenthe two
`electrodesas desired andalso 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
`previously described. A polymer gel material sheet as such
`a sheet-like shaped pressure means may be prepared also in
`a manner(a) of providing a given sheet-like shaped polymer
`material and subjecting the sheet-like shapedto crosslinking
`or in a manner(b) of providing a given polymer gel material
`and subjecting the polymer gel material to press-molding.
`In the case where the pressure means takes such a
`configuration comprising a polymer gel material layer held
`on a support member as shownin FIG. 3(D),
`there are
`advantages such that the size of the pressure means can be
`readily controlled as desired, and the pressure means can be
`casily handled. The support member in this case can include
`members made of metallic materials, members made of
`ceramics, glass members, and members madeofplastics.
`The support member may be shaped in a plate-like form,
`punching metal form, woven fabric form, or nonwoven
`fabric form.
`
`The polymer gel material in this case may be formed on
`the support memberin accordance with the foregoing liquid
`casting process, melt extrusion process, calendering process,
`manner(a), or manner(b). Particularly, for instance, it may
`
`
`
`12
`
`

`

`10
`with the irradiation of light under condition with the addition
`of a photo sensitizer.
`In the case of crosslinking between polymerchains, there
`can be employed a construction wherein cellulose or polvi-
`nyl alcohol having hydroxyl groups is crosslinked by way of
`chemical reaction with aldehyde. N-methylol compound,
`carboxylic acid, or bisepoxide; a construction wherein an
`aminoacid group-bearing polymeris gellated with aldehyde
`or glycidyl group; a constructi