a2) United States Patent
`US 6,372,387 Bl
`(10) Patent No.:
`
` Kawakamietal. (45) Date of Patent: Apr.16, 2002
`
`
`US006372387B1
`
`(54) SECONDARY BATTERY HAVING AN ION
`CONDUCTIVE MEMBER AND
`MANUFACTURING PROCESS THEREOF
`
`(75)
`
`Inventors: Soichiro Kawakami, Tomoya
`Yamamoto, both of Nara; Hironao
`Kimura, Suwa,all of (JP)
`
`(73) Assignee: Canon Kabushiki Kaisha, Tokyo (JP)
`
`(*) Notice:
`
`Subject to anydisclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/282,417
`
`Filed:
`
`Mar. 31, 1999
`
`(22)
`
`(30)
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,786,277 A * 11/1988 Powers et al... 604/20
`5,280,078 A *
`1/1994 Gregor etal.
`....... 525/328.5
`5,609,974 A
`B/L99T SUM wee cc ecc teens 429/192
`OTIIER PUBLICATIONS
`
`A. N. Dey et al., “The Electrochemical Deposition of
`Propylene Carbonate on Graphite,” J. Electrochem. Soc.,
`vol. 117, No. 2, pp. 222-224 (1970).
`* cited by examiner
`
`Primary Examiner—Gabrielle Brouillette
`Assistant Examiner—Angela J. Martin
`(74) Attorney, Agent, or Firm—Fitzpatrick, Cella, Harper &
`Scinto
`
`Foreign Application Priority Data
`
`(57)
`
`ABSTRACT
`
`Mar. 31, 1998
`Mar. 19, 1999
`
`(IP) veeeeeececccsesesesseneseeseneeens 10-086197
`(IP)
`eesececsecssesesessenseeeseenesees 11-075466
`
`TMB, C1 cece eececee cece cece cece eesneceneeseesnens HOIM 6/16
`(SV)
`(52) U.S. Cl.
`429/303; 429/304; 429/306;
`429/314; 429/317; 429/322; 429/324; 429/188
`(58) Field of Search .....0.000ee 429/304, 306,
`429/303, 314, 317, 322, 324
`
`A secondary battery comprises a negative electrode and a
`positive electrode which oppose each other and an ion
`conductive member which includes a layered or columnar
`structure Gon channels) in ils matrix and which is sand-
`wiched between the negative electrode and the positive
`electrode.
`
`34 Claims, 8 Drawing Sheets
`
`607
`—__oo
`608 609
`
`
`
`eeIXNN
`U0Lilli
`600\AN“\ 5s
` SNSNNAANN
`~\\AN\SINININININISN
`NNSNNSNNSN
`RRRRRR)
`Keeeee
`KELLLLL
`
`603 602
`WO
`601
`
`
`
`610
`
`606 605
`Ne
`604
`
`APPLE-1024
`
`1
`
`APPLE-1024
`
`

`

`U.S. Patent
`
`Apr. 16, 2002
`
`Sheet 1 of 8
`
`US 6,372,387 B1
`
`
`
`FIG. 1B
`
`101
`
`rrr
`TLL
`v7
`(LILLLALLLLLLELLALLLOCLCLLLOCIIN Lh Zit
`TADLd
`aa
`
`LLkLdedhddiiidiididioidécacccvlverrrr asc
`
`
`2
`
`

`

`U.S. Patent
`
`Apr. 16, 2002
`
`Sheet 2 of 8
`
`US 6,372,387 B1
`
`FIG. 2A
`
`RSsS&&&w
`
`SSSV@_aaaw
`
`RSS“004
`
`
`
`
`
` eeR&SGO
`
`
`
`
`
`
`
`RSXSou
`
`SSS“oo
`
`Wa
`
`
`
`
`RSS Q—9wws
`
`MIs
`
`RSsao
`
`WWTeYi
`
`
`3
`
`

`

`US 6,372,387 BI
`
`uo
`
`U.S. Patent
`
`Apr.16, 2002
`
`Sheet 3 of 8
`
`p
`
`Oe
`EV
`LAXSS
`SS
`LS
`
`ES
`(OS
`Lo
`AVE
`
`yrUp
`
`NSS
`
`\~
`Ld
`
`4
`
`
`

`

`U.S. Patent
`
`Apr. 16, 2002
`
`Sheet 4 of 8
`
`US 6,372,387 B1
`
`FIG.5
`
`
`Wierrane AAMMAMWNMY
`
`
`NAABABABAAHABBABBBAAW-
`IAA AA BAYA
` 500
`
`
`
`5
`
`

`

`U.S. Patent
`
`Apr. 16, 2002
`
`Sheet 5 of 8
`
`US 6,372,387 B1
`
`FIG. 6
`
`607
`—.
`608
`609
`
`|
`
`
`
`
`of»IZANNALLL
`VLU,
`SISASSENEEEEUEN v
`eeNYesNINN
`NNSNNNSSNNSSNN/
`
`
`x610
`—ERRKEKEEKERGR
`
`603 602
`606 605
`Vs
`Ls
`601
`604
`
`
`
`
`
`FIG. /
`
`
`
`6
`
`

`

`U.S. Patent
`
`Apr. 16, 2002
`
`Sheet 6 of 8
`
`FIG. 8
`
`re
`‘Tocy
`»LL
`
`\
`
`7
`
`
`
`

`

`U.S. Patent
`
`Apr. 16, 2002
`
`Sheet 7 of 8
`
`US 6,372,387 B1
`
`FIG. 9
`
`WN
`\S\
`
`YY;
`Yy
`
`C|
`
`aeo2
`
`te:
`
`901
`
`FIG. 10
`
`20.0KV (x500)
`
`8
`
`
`
`
`
`
`

`

`FIG. 11AP
`
`
`
`
`
`
`
`
`
`
`
`
`
`SLom?Pe
`SSSEK
`
`Ca
`
`
`
`
`
`
`
`~~
`
`
`9
`
`

`

`US 6,372,387 B1
`
`1
`SECONDARY BATTERY HAVING AN ION
`CONDUCTIVE MEMBER AND
`MANUFACTURING PROCESS THEREOF
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`2
`In order to prevent the secondary battery from degrading
`as stated above, the battery is sometimes furnished with an
`overcharge prevention circuit, a PTC (Positive Temperature
`Coefficient) element whose resistance increases withthe rise
`of temperature or the like. This contrivance, however,
`increases cost.
`
`Besides, in order to solve the drawbacks of the decom-
`position and deterioration of the electrolyte solution in the
`secondary battery which utilizes the charge and discharge
`reactions based on lithium ions, U.S. Pat. No. 5,609,974 has
`proposed a secondary battery which adopts a solid polymer
`electrolyte, obtained in such a way that monomersofthree
`types—a diacrylate type, a monoacrylate type, and an acry-
`late type including a carbonate group—are copolymerized in
`the presence of both an organic solvent and a supporting
`electrolyte and in which coke anda lithium cobalt oxide are
`respectively applied to a negative electrode and a positive
`electrode. The solid polymerelectrolyte, however, exhibits
`an ionic conductivity which is below 4% as compared with
`that of a liquid electrolyte in which a supporting electrolyte
`is dissolved in a solvent. Consequently, a current density in
`the secondarybattery is limited, and an energy density is
`also low.
`
`On the other hand, an electrolyte solidifying technique
`which prevents liquid leakage while avoiding degradation in
`performance to the extent possible has been required also of
`a high-performance alkaline storage battery (secondary
`battery) which uses a hydrogen-occlusion alloy or the like
`for a negative electrode.
`SUMMARY OF THE INVENTION
`
`The present invention has been made in view of the
`problemsstated above, and it hasfor its object to provide an
`electrolyte for use in a secondary battery, which is immune
`against deterioration and decomposition in the charge and
`discharge reactions of the secondary battery and a novel
`secondary battery which employs the electrolyte.
`The first mode of the present invention consists of a
`secondary battery wherein an ion conductive member is
`arranged between a positive electrode and a negative elec-
`trode which are disposed in opposition to each other, char-
`acterized in that said ion conductive member has its ion
`
`channels oriented so as to have a higher ionic conductivity
`in a direction ofjoining a planeof said positive electrode and
`that of said negative clectrode. Herein, the secondarybattery
`shall cover a contrivance wherein said ion conductive mem-
`ber has a layered structure or a columnarstructure.
`The second mode of the present invention consists of a
`process for producing a secondary battery wherein an ion
`conductive memberis arranged between a positive electrode
`and a negative electrode which are disposed in oppositionto
`each other, characterized by orienting ion channels of said
`ion conductive memberso that said ion conductive member
`
`may have a higher ionic conductivity in a direction of
`joining a plane of said positive electrode and that of said
`negative electrode. Herein, the process for producing the
`sccondary battcry shall cover a contrivance wherein said ion
`conductive member is endowed with a layered structure or
`a columnarstructure.
`The ion conductive member which constitutes the sec-
`
`ondary battery according to the present invention can be
`endowed with the layered or columnar structure. In that
`case, ion conducting paths (ion channels) along which the
`migrating distances of ions become substantially the shortest
`are formed in a direction parallel or perpendicular to the
`layered or columnarstructure. Therefore, the ionic conduc-
`
`10
`
`15
`
`30
`
`35
`
`invention relates to a secondary battery
`The present
`having an ion conductive member, and a manufacturing
`process thereof. More particularly, it relates to a secondary
`battery in which the decomposition ofan electrolyte solution
`attributed to the repetition of charge and discharge is sup-
`pressed.
`2. Related Background Art
`Since the quantity of carbon dioxide gas contained in the
`atmosphereis currently increasing, the warming of the earth
`is predicted to increase due to the greenhouseeffect. It has,
`therefore, become difficult
`to build new thermal power
`stations which emit carbon dioxide gas in large quantities. In
`this regard, for the purpose of effectively utilizing electric ,,
`power generated by a dynamoofa thermal powerstation or
`the like, so-called “load leveling” has been proposed,
`wherein night power is stored in secondary batteries
`installed in general households and is used in the daytime
`whenlarge power consumption is required, thereby leveling ,
`a station load. Meanwhile, the development of a secondary
`battery of higher energy density has been expected in the
`field of electric vehicles, which features the emission of no
`air-pollutive substances. Further, it is of urgent necessity to
`develop high-performance secondary batteries which are
`smaller in size and lighter in weight for use in the power
`sources of portable apparatuses such as notebook type
`personal computers, word processors, video cameras and
`pocket telephones.
`As the high-performance secondary battery of smaller
`size and lighter weight, an example wherein a lithium-
`graphite interlayer compound is applied to the negative
`electrode of a secondary battery was reported in JOURNAL
`OF THE ELECTROCHEMICAL SOCIETY, 117, 222
`(1970). Since then, by way of example, a rocking chair type
`secondary battery, i.e., a so-called “lithium ion battery” has
`been developed wherein a carbonaceous material
`is
`employed as a negative-electrode active material, while an
`interlayer compounddoped with lithium ions is employed as
`a positive-electrode active material, and wherein lithium is
`introduced and kept between the layers of the carbonaceous
`material by a charge reaction. Somearticles ofthis type are
`being put into practical use. With the lithium ion battery, the
`carbonaceous material as a host material which is interca-
`
`40
`
`45
`
`lated between the layers using lithium as a guest is applied
`to the negative electrode, thereby suppressing the growth of
`the dendrite of lithium during charge and achieving a longer
`litetime in charge and discharge cycles.
`However, an organic solvent is used as the solvent of an
`electrolyte solution in the secondary battery utilizing gal-
`vanic reactions (charge and discharge reactions) based on
`lithium ions, such as the lithium-ion secondary battery.
`Therefore, when the battery is overcharged, the solvent is
`decomposed thereby producing carbonic acid gas,
`hydrocarbons,etc., and it is not restored to its original state
`by a recombination reaction. It is accordingly believed that
`the electrolyte solution will deteriorate thereby increasing
`the internal impedance of the secondary battery. Further, the
`overcharge of the secondary battery causes internal short
`circuiting thereof, along with the generation of heat and
`promotion of a reaction which rapidly decomposes the
`solvent, which can lead to the breakage of the battery.
`
`50
`
`55
`
`60
`
`65
`
`10
`
`10
`
`

`

`US 6,372,387 B1
`
`3
`tivity of the ion conductive member becomesthe highest in
`the paths, and the ion conductive member exhibits an
`anisotropic conductivity. In this regard, according to the
`secondary battery of the present invention, the direction in
`which the ionic conductivity of the 1on conductive member
`is higheris brought into agreement with the direction which
`is perpendicular to the planes of the negative and positive
`electrodes opposing one another. Thus, the secondary bat-
`tery of the present invention can haveits internal resistance
`lowered, and it is permitted to be charged and dischargedat
`a higher efficiency and a higher current than any secondary
`battery which does not adopt the ion conductive memberof
`such a structure.
`
`In addition, the ion conductive memberof the layered or
`columnar structure should preferably be a polymer gel
`electrolyte which is formed in such a way that a polymer
`serving as the matrix of the specified structure is caused to
`absorb an electrolyte solution (a solution obtained by dis-
`solving a supporting electrolyte in a solvent).
`The process for producing a secondary battery in the
`second mode of the present invention can be performed by
`sandwiching the ion conductive member endowed with the
`layered or columnar structure between the negative and
`positive electrodes. The ion conductive member is fabri-
`cated in such a way that a cross-linked polymer material
`having the layered or columnarstructure is prepared and is
`thereafter caused to absorb an electrolyte solution, or that a
`cross-linked polymer material having the layered or colum-
`nar structure is prepared in the presence of an electrolyte.
`The cross-linked polymer material having the layered or
`columnar structure can be obtained in such a way that the
`molecules of a cross-linking polymer are arrayed into a
`regular arrangementbyat least one operation selected from
`the group consisting of irradiation with light, application of
`a magnetic field, application of an electricfield, and heating,
`whereupon the resulting molecules are cross-linked.
`Alternatively, the polymer of the specified structure can be
`obtained in such a way that a compound which has a
`molecular structure serving as a template is employed in the
`operation of preparing the cross-linked polymer.
`
`BRIEF DESCRIPTION OF‘THE DRAWINGS
`
`FIGS. 1A and 1B are schematic views each showing an
`example of an ion conductive member which is adopted for
`the present invention;
`FIGS. 2A and 2B are schematic views for explaining the
`structure and operation of an ion conductive member which
`is adopted for the present invention;
`FIGS. 3A and 3B are schematic views for explaining the
`structure and operation of an ion conductive memberin the
`prior art;
`FIG. 4 is a schematic view showing another example of
`an ion conductive member whichis adopted for the present
`invention;
`FIG. 5 is a schematic view showing the structure of a
`secondary battery according to the present invention;
`FIG. 6 is a sectional view showing an aspect of a
`coin-type battery of the present invention;
`FIG. 7 is a sectional view showing an-aspect of a cylin-
`drical battery of the present invention;
`FIG. 8 is a schematic view showing a system which serves
`to measure the impedance of an ion conductive member in
`an embodiment;
`FIG. 9 is a schematic view showing a system for prepar-
`ing a polymer gel electrolyte which serves to verify the
`
`10
`
`15
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`anisotropy of the ionic conduction of an ton conductive
`member in an embodiment;
`FIG. 10 is a schematic view showing an image which was
`obtained when an ion conductive member (a polymer gel
`electrolyte) in Experiment 2 was observed with an electron
`microscope; and
`FIGS. 11A and 11Bare schematic views each showing an
`image which was obtained when an ion conductive member
`(a polymer gel electrolyte) in Experiment 4 was observed
`with the electron microscope. FIG. 11AP is a partially
`enlarged viewof FIG. 11A.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`Now,the aspects of performance of the present invention
`will be described with reference to the drawings.
`First, ion conductive members having a layered structure
`or a columnarstructure as can be employedfor the second-
`ary battery of the present invention will be explained with
`reference to FIGS. 1A and 1B.
`
`FIGS. LA and 1B are perspective views each showing the
`schematic sectional structure of the ion conductive member
`
`101 in the shape of a sheet by way of example. The structure
`101 in FIG. 1A is such that the columnarstructure or layered
`structure has grown in a direction perpendicularto the plane
`of the sheet-like ionically conductive structure. On the other
`hand, the structure 101 in FIG. 1B is such that the layered
`structure has grownin a direction parallel to the plane of the
`sheet-like ionically conductive structure. With the ion con-
`ductive member shown in FIG. 1A or FIG. 1B,ion conduct-
`ing paths (ion channels) along which the migrating distances
`of ions become substantially the shortest are formed in a
`direction parallel or perpendicular to the layered or colum-
`nar structure. Therefore, the ionic conductivity of the ion
`conductive member becomes the highest in the paths, and
`the ion conductive member exhibits an anisotropic conduc-
`tivity. In the secondary battery of the present invention, the
`ion conductive member having the layered structure or
`columnarstructure as shown in FIG. 1A or FIG. 1B, which
`should preferably have a thickness of 500 um or below, more
`preferably a thickness of 100 wm or below, and the ionic
`conductivity of which is higher in a direction perpendicular
`to the planes of a negative electrode and a positive electrode,
`may be sandwiched between the negative and positive
`electrodes which oppose each other.
`‘The ion conductive member having the layered structure
`or columnar structure can be fabricated by preparing a
`cross-linked polymer which has the layered or columnar
`structure and which absorbs an electrolyte solution (a solu-
`tion obtained by dissolving a supporting electrolyte in a
`solvent). In addition, the layered or columnarstructure ofthe
`cross-linked polymer can be attained in such a waythat
`molecules constituting a cross-linking polymer are arrayed
`into a regular arrangementbyat least one operation selected
`from the group consisting of irradiation with light, applica-
`tion of a magnetic field, application of an electric field, and
`heating, or that molecules constituting a cross-linking poly-
`merare arrayed using a template. Mentioned as an example
`of such an ion conductive memberis a polymer material of
`the specified structure (a polymergel electrolyte) which has
`been brought into a gelatinous state by absorbing an elec-
`trolyte solution in which a supporting electrolyte such as
`lithium salt
`is dissolved in an organic solvent. In this
`example, it is possible to form the ton conductive member
`whoseionic conductivity in the direction of the higher ionic
`conduction exceeds, at
`least, 3x10-? Sem7? or 5x10-3
`Sem7}.
`
`11
`
`11
`
`

`

`US 6,372,387 B1
`
`6
`5
`elements 402 can be worked into the shape of a layer or film
`the ion conductive member having the
`Alternatively,
`
`layered structure or columnar structure can be formed in or a sheet by using a polyethylene oxide oralike resin as a
`such a way that, under the application of an electric field
`binder. Besides, in a case where the matrix of the granular
`and/or a magnetic field, an inorganic oxide such as tonically
`ionic conduction elements 402 is a cross-linked organic
`conductive glass is vapor-deposited with a cluster ion beam
`polymer material, these elements 402 can be processed into
`or electron beam or by sputtering.
`the shape of a film or sheet by a processing method such as
`calendering.
`Next, the features of an anisotropic ionically conductive
`structure will be explained with reference to FIGS. 2A and
`Next, the aspects of the secondary battery of the present
`2B and FIGS. 3A and 3B. FIG. 2A is a schematic view
`invention will be schematically explained with reference to
`FIG. 5 and FIG. 6.
`
`10
`
`FIG. 5 illustrates the general configuration of the second-
`ary battery of the present invention. In the secondary battery
`500 shown in the figure, an ion conductive member 501
`having the shortest ion channels 502, which are arrayed in
`a direction perpendicular to a negative electrode 504 and a
`positive electrode 505 opposing each other within the matrix
`503 of the ion conductive member as shown in FIG. 1A,
`FIG. 1B or FIG. 2A, is sandwiched between the negative
`electrode 504 and the positive electrode 505, and the result-
`ing structure is accommodatedin a battery jar (housing) 506.
`By way of example, such a secondarybattery 500 is a square
`battery whose section in a direction normal to the drawing
`sheet is rectangular. Terminals 507 and 508 for external
`connection are respectively connected to the negative elec-
`trode 504 and the positive electrode 505, and they are
`connected to an external load or a power source. With the
`secondary battery 500 thus constructed, the ion conductive
`member 501 employed has its ion channels 502 oriented
`along a layered or columnar structure in the direction
`perpendicular to the planes of the opposing negative elec-
`trode 504 and positive electrode 505. Accordingly,
`the
`migrating distances of ions between the negative electrode
`504 and the positive electrade 505 become the shortest, and
`the substantial migrating velocity thercof heightens, so that
`the impedance of the secondary battery is lowered. It is,
`therefore, possible to realize the secondary battery which
`can be charged and discharged at higher current densities
`and which has a higher charge and discharge efficiency.
`FIG. 6 illustrates a practicable configuration in which the
`secondary battery of the present invention is applied to a
`sheet-like battery. In the secondary battery 600 shownin the
`figure, an ion conductive member 601 is sandwiched as a
`scparator between a negative clectrode 604 including an
`active material layer 605 on a collector 606 and a positive
`electrode 607 including an active material layer 608 on a
`collector 609. The ion conductive member 601 has the
`
`shortest ion channels 602 which are formed along a layered
`or columnarstructure and which are arrayed in a direction
`perpendicular to the opposing negative electrode 604 and
`positive electrode 607 within the matrix 603 of the ion
`conductive member as shown in FIG. 1A, FIG. 1B or FIG.
`2A, the matrix 603 being oriented in a direction perpendicu-
`lar to the planes of the positive and negative electrodes and
`beingfilled with an electrolyte therein. Besides,the resulting
`laminated body of the “negative electrode/ion conductive
`member/positive electrode” has input/output terminals (not
`shown)led out of the collectors of the respective electrodes
`and is covered with a sheathing material 610.
`Such a secondary battery 600 is charged by connecting an
`unshown external power source to the input/output
`terminals, and it accumulates electricity due to electro-
`chemical reactions (migrations of ions between the
`electrodes) which arise through the ion conductive member
`601. Besides, when an unshown external load is connected
`to the input/output
`terminals, electrochemical reactions
`(migrations of ions between the electrodes) arise through the
`ion conductive member 601 inside the battery, and the
`battery is discharged.
`
`showing the ion conductive member 201. In the matrix 203
`of the ion conductive member 201, ion conducting paths (ion
`channels) 202 being the shortest are so formedthat they are
`arrayed, namely, oriented in a direction parallel
`to the
`layered or columnarstructureorin a direction perpendicular
`to the layered structure. Here in the illustration of FIG. 2B,
`the ion conductive member 201, in which the direction of the
`shortest ion conducting paths (ion channels) 202 agrees with
`a direction perpendicular to the planes of electrodes 204 and
`205, is arranged between the electrodes 204 and 205, and
`these electrodes 204 and 205 are connected to a supply ,,
`voltage source 206.
`in an ion conductive member 301
`On the other hand,
`shownin FIG. 3A, ion conducting paths (ion channels) 302
`are formed in random directions within the matrix 303 of the
`structure 301. In the illustration of FIG. 3B, the ion con-
`ductive member301is arranged betweenelectrodes 304 and
`305, which are connected to a supply voltage source 306.
`Whenthe ion conductive members 201 and 301, respec-
`tively shown in FIG. 2B and FIG. 3B, are compared, the
`channel length of the former 201 in the direction in which
`the ion channels 202 are oriented is substantially shorter
`than that of the latter 301. Therefore, in a case where the
`numbers of tons and the mobilities thereof in the ton
`conductive members 201 and 301 are the same, an electric
`field is applied across the ion conductive members 201 and
`301 (between the electrodes 204 and 205, and betweenthe
`electrodes 304 and 305) so as to cause the ions to migrate in
`the directions in which the ion channels 202 and 302 are
`oriented, and an electric field intensity (applied voltage/
`channel length) becomeshigherto afford a higher migrating
`ionic velocity (mobilityof ions)x(electric field intensity)) in
`the ion conductive member 201 of the shorter ion channels
`
`15
`
`5
`
`30
`
`35
`
`40
`
`corresponding to the present invention. Herein, since the
`ionic conductivity of each structure at issue increases in
`proportion to the concentration of the ions and the migrating
`velocity thereof, the ion conductive member 201 exhibits a
`higher ionic conductivity. Besides,
`in the ion conductive
`member 201 shown in FIGS. 2A and 2B, the shortest ion
`channels are arrayed in the direction perpendicular to the
`planes of the opposing electrodes, and the ionic conductivity
`in this direction is selectively higher than in any other
`direction. Therefore, the ion conductive member 201 exhib-
`its an anisotropy in ion conduction.
`FIG. 4 illustrates another aspect of the ion conductive
`memberof the present invention. The ion conductive mem-
`ber 401 shownin the figure is an aggregate including a large
`numberof granular ionic conduction elements 402 in each of
`which ion channels are regularly arranged along a layered or
`columnar structure 403. Since the shortest
`ion channels
`arranged regularly in a certain direction are formed in each
`granular
`ionic conduction element 402,
`a substantially
`higher ionic conductivity is attained. Incidentally, numeral
`404 designates a layer (material) which binds up the granu-
`lar tonic conduction elements 402. An organic polymer gel,
`a granular inorganic oxide gel (for example, granular silica
`gel), or the like can be employed for the granular ionic
`conduction elements 402. The granular ionic conduction
`
`45
`
`50
`
`55
`
`60
`
`65
`
`12
`
`12
`
`

`

`US 6,372,387 B1
`
`7
`As in the case of the battery shown in FIG. 5, according
`to the sheet-like battery, the characteristics of the ion con-
`ductive member 601 create the shortest migrating distances
`of ions between the negative electrode 604 and the positive
`electrode 607 and heighten the substantial migrating, veloc-
`ity of the ions.
`It
`is,
`therefore, possible to realize the
`secondary battery whose internal resistance is lower, which
`can be charged and discharged at higher current densities,
`and which has a higher charge and discharge efficiency.
`Further,
`the ion conductive member 601 sandwiched
`between the electrodes is a solid structure or a solidified
`
`structure. Unlike a battery including a liquid electrolyte
`between negative and positive electrodes, accordingly, the
`sheet-like battery undergoes no liquid leakage even upon
`damage of the sheathing material 610, and the decomposi-
`tion of a solvent
`in the electrolyte on the occasion of
`overcharge is suppressed. Therefore, a safety mechanism
`such as a safety valve is dispensed with, the thickness of the
`battery can be decreased, and an overcharge circuit having
`been complicated can be replaced with a simple circuit.
`Moreover, the sheet-like battery can have its shape designed
`at will, and it can minimize the installation space of a power
`source in the application thereof to the power source of an
`apparalus.
`By the way, the single pair of electrodes—the positive
`electrode 607 and the negative electrode 604—are included
`in the sheet-like battery shown in FIG. 6. It is also possible,
`however, to construct a secondary battery in a configuration
`in which a plurality of pairs of electrodes are disposed to
`form a laminated body consisting of, for example,
`the
`“negative electrode/ion conductive member/positive
`electrode/ion conductive member/negative electrode/ion
`conductive member/positive electrode”, and in which cell
`units each consisting of the “negative electrode/ion conduc-
`tive member/positive electrode” are connected in parallel or
`in series inside the laminated body.It is further possible that
`the cell units each consisting of the “negative electrode/ion
`conductive member/positive electrode” are assembled into
`the battery housing of a battery in a shape as will be stated
`later, such as a coin-shaped battery, a cylindrical battery or
`a square battery.
`Now, members constituting the secondary battery of the
`present invention and processes for producing them will be
`described in detail.
`ION CONDUCTIVE MEMBER(101 shownin FIG. 1A and
`1B, 201 shown in FIGS. 2A and 2B, 501 shown in FIG. 5,
`or 601 shown in FIG. 6)
`The ion conductive member for use in the secondary
`battery of the present invention can have a layered structure
`or a columnarstructure. In the case of such a configuration,
`ion conducting paths (ion channcls) along which the migrat-
`ing distances of ions become substantially the shortest are
`formed in a direction parallel to the layered or columnar
`structure or in a direction perpendicular to the layered
`structure. Therefore, the ionic conductivity of the ion con-
`ductive member becomes the highest in the paths, and the
`ion conductive memberexhibits an anisotropic conductivity.
`The secondary battery of the present
`invention can be
`constructed in such a waythat the ion conductive member,
`which has the layered structure or columnar structure and
`whose ionic conductivity is higher in a direction perpen-
`dicular to the planes of a negative electrode and a positive
`electrode opposing each other, is sandwiched between the
`negative electrode and the positive electrode.
`The material of the ion conductive member having the
`layered structure or columnarstructure for use in the present
`Invention may be any of, for example, an organic or inor-
`
`10
`
`15
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`
`
`8
`ganic gelatinous polymer and anionically conductive glass,
`each of which is endowed with a specified molecular ori-
`entation. In addition, the glass transition temperature of the
`ion conductive member for use in the secondary battery of
`the present invention should preferably be minus 20° C. or
`below, more preferably be minus 30° C. or below, much
`more preferably be minus 50° C. or below. The glass
`transition temperature can be found by the thermal analysis
`of a measurement based on a compressive load method
`employing a thermomechanical analyzer, a measurement
`employing a differential scanning calorimeter, or the like.
`The process for producing the ion conductive member
`made from a polymer gel will now be explained using
`examples of a process for producing an ion conductive
`member in which a polymer material having the layered
`structure or columnarstructure is filled with an electrolyte
`(electrolyte solution), that is, a structure which contains a
`polymer gel electrolyte.
`(a) There are mixed, at least, a monomer which forms a
`polymer by a polymerizing reaction, a cross-linking
`agent which forms a polymer gel, and a compound
`which has a molecular structure serving as a template.
`Next, the polymerizing reaction and a cross-linking
`reaction are induced in the resulting mixed solution,
`hereby preparing a cross-linked polymer having a
`ayered or columnarstructure. In the preparation of the
`cross-linked polymer, a solvent is mixed as may be
`needed. Subsequently, the resulting cross-linked poly-
`meris caused to absorb and carry an electrolyte solu-
`ion in which a supporting electrolyte is dissolved in a
`solvent, thereby forming a polymergel electrolyte. If
`possible, the compound for the template should desir-
`ably be removed aftcr the preparation of the cross-
`inked polymer. Alternatively, a polymer gel ionically
`conductive structure filled with the electrolyte solution
`may well be fabricated at a stroke by adding the
`electrolyte solution before the polymerizing reaction.
`(b) There are mixed,at least, a polymer material, a solvent
`which dissolves the polymer, a cross-linking agent, and
`a compound which has a molecular structure serving as
`a template. Next, a cross-linking reaction is induced in
`the resulting mixed solution, thereby preparing a cross-
`linked polymer having a layered or columnarstructure.
`Subsequently,
`the prepared cross-linked polymer is
`caused to absorb and carry an electrolyte solution in
`which a supporting electrolyte is dissolved in a solvent,
`thereby forming a polymer gel electrolyte. The com-
`pound for the template should desirably be removed
`after
`the preparation of the cross-linked polymer.
`Alternatively, a polymergel ionically conductive struc-
`ture filled with the electrolyte solution may well be
`fabricated at a stroke by adding the electrolyte solution
`before the cross-linking reaction.
`The ion conductive member made from the polymergel
`as fabricated in the above example (a) or (b) canbe directly
`brought into the shape of a film or a sheet by fixing it to a
`supporting material such as unwovenfabric or by utilizing
`a technique suchas casting. On this occasion,it is preferable
`that the columnarstructure or layered structure grows in a
`direction perpendicular to the plane of the film or sheet (in
`the direction of the thicknessof the film or sheet) or that the
`layered structure growsin a direction parallel to the plane of
`the film or sheet. Thus, it is desirable that paths for con-
`ducting ions (ion channels) grow in the direction perpen-
`dicular to the plane of the film or sheet.
`(c) The preparation of the cross-linked polymer in the
`process of the above example(a) or(b) is performed by
`
`13
`
`13
`
`

`

`US 6,372,387 B1
`
`9
`suspension polymerization or emulsion polymerization
`so as to obtain a granular cross-linked polymer.
`Alternatively, the cross-linked polymer prod