United States Patent (19)
`McCullough
`
`III III IIII
`USOO5518836A
`11
`Patent Number:
`5,518,836
`(45. Date of Patent:
`May 21, 1996
`
`(54) FLEXIBLE CARBON FIBER, CARBON
`FIBER ELECTRODE AND SECONDARY
`ENERGY STORAGE DEVICES
`76) Inventor: Francis P. McCullough, 104 Fir Dr.,
`Lake Jackson, Tex. 77566
`
`21 Appl. No.: 372,446
`i-
`22 Filed:
`Jan. 13, 1995
`Int. Cl. ................................ HO1M 6/48; D01F 9/12
`(51
`52 U.S. Cl. ............................ 429/94; 429/194; 429/210;
`429/218; 423/447.2
`58) Field of Search .............................. 429/94, 194, 218,
`429/223, 224; 42.3/447.1, 447.2
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,830,938 5/1989 McCullough et al............... 429/210 X
`4,865,931 9/1989 McCullough et al................... 429/194
`5,032,473 7/1991 Hoge .......................
`429/210 X
`5,082,594
`1/1992 Tsuzuki et al. ..................... 429/210 X
`5,209,975 5/1993 Miyazaki et al. .................... 423f447.1
`
`5,227,237 7/1993 Saruyama et al. ................... 423f447.2
`Primary Examiner-Anthony Skapars
`Attorney, Agent, or Firm-Nis H. Juhl
`(57)
`ABSTRACT
`A novel flexible carbon fiber is disclosed which has a
`generally non-circular or tubular cross-sectional shape, a
`Young's modulus of from greater than 1 MM psi (6.9 GPa)
`to 55MM psi (380 GPa), and a bending strain value of from
`greater than 0.01 to less than 50%. The invention also
`resides in an electrode for a secondary energy storage device
`utilizing the carbon fibers of the invention and containing a
`non-aqueous electrolyte. The invention further resides in a
`secondary energy storage device comprising a water imper
`meable housing having at least two cells containing at least
`one shared bipolar electrode made of the flexible carbon
`fibers of the invention. Also disclosed is a pseudo bipolar
`electrode and terminal electrode for use in a lithium ion
`battery in which the fibers or a portion of the carbon fibers
`are coated with an ion active lithium salt of a metal oxide.
`Also disclosed is a novel battery stack and a method of
`manufacture of the secondary energy storage device.
`33 Claims, 7 Drawing Sheets
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`5,518,836
`
`1.
`FLEXIBLE CARBON FIBER, CARBON
`FBERELECTRODE AND SECONDARY
`ENERGY STORAGE DEVICES
`
`FIELD OF THE INVENTION
`The present invention relates to an electrically conductive
`carbon fiber derived from a stabilized polymeric precursor
`material, said fiber having a generally non-circular or tubular
`cross-sectional shape, a Young's modulus of from greater
`than 1 MM psi (6.9 GPa) to 55 MM psi (380 GPa), and
`wherein said carbon fiberis flexible and has a bending strain
`value of from greater than 0.01% to less than 50%.
`The invention also relates to different types of electrodes,
`including bipolar electrodes and pseudo bipolar electrodes,
`made from a multiplicity of said flexible carbon fibers. The
`invention further relates to several different types of batter
`ies employing at least one of said flexible carbon fiber
`electrodes and to a process for the manufacture of the
`flexible carbon fibers. The invention further resides in a
`lithium ion battery utilizing a pseudo bipolar electrode
`having a portion thereof coated with a lithium salt of a metal
`oxide.
`
`O
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`2
`are described in Table 2-9 on pages 52 and 53 and include
`tubular, triangular, irregular striated, oval, etc.
`It is now well understood in this art that the carbon
`electrodes for secondary electrical energy storage devices
`require a special type of carbon or graphite, particularly
`when used as the positive electrode in nonaqueous battery
`systems due to destructive intercalation of large anions from
`the electrolyte entering between the planar graphite layers.
`These large anions which enter between the planar graphite
`layers (usually referred to as "d-spacing' in the art) cause
`spalling or flaking of the carbon or graphite layers and can
`thus bring about a rapid degradation of the electrode when
`Subjected to repeated electrical charging and discharging
`cycles. Accordingly, destructive intercalation of large anions
`between the carbon or graphite layers of an electrode and
`electrolyte instability becomes a particular problem with
`rechargeable batteries, that operate with a nonaqueous elec
`trolyte and that have a cell voltage of greater than 2.5 volts.
`Such batteries require exacting standards during their manu
`facture and operation to prevent the introduction of gaseous
`water or water vapor into the batteries since the introduction
`of only minute quantities of water into a battery, i.e. in the
`range of parts per million (ppm), results in the electrolysis
`of the water molecule. Electrolysis of water molecules can
`take place during electrical charging of the battery at a
`potential of greater than 2.5 V, during storage in the charged
`state, or during discharge of the battery, forming O, OH and
`H" ions with the OHT ions migrating to the positively
`charged cathode where electrolysis to O and O, takes place.
`Species such as OH and H cause a breakdown of such
`commonly used nonaqueous electrolyte materials such as
`propylene carbonate through catalysis, while highly reactive
`O and O. destroy the surface of the carbon or graphite
`electrode due to destructive intercalation. McCullough et al
`report that their battery is capable of operating with a water
`content of up to 300 ppm but that it will have a somewhat
`reduced cycle life. McCullough et all also report that, if the
`water content should become onerous, the battery can be
`disassembled, dried and reassembled in a dried state without
`Substantial damage to its continued operation.
`
`BRIEF DESCRIPTION OF THE INVENTION
`The invention particularly resides in an electrically con
`ductive carbon fiber derived from a stabilized polymeric
`precursor material having a generally non-circular or tubular
`cross-sectional shape, a Young's modulus of from greater
`than 1 MM psi (6.9 GPa) to 55 MM psi (380 GPa), and
`wherein said carbon fiberis flexible and has a bending strain
`value of from greater than about 0.01 to less than 50%,
`preferably, the carbon fiber has a bending strain value of
`from about 0.1 to about 30%.
`It is a particular object of the invention to make electrodes
`from a multiplicity of flexible carbon fibers each having a
`generally noncircular shape when viewed in cross-section
`such as, for example, a multilobal, crescent, star, or the like.
`The surface contour of the fibers can be smooth or rough,
`and regular or irregular as, for example, in a trilobal, regular
`and symmetrical, smooth surface contour, or an irregular
`striated contour so long as the surface structural integrity is
`maintained and the fiber surface is contiguous and remains
`substantially free of pits and surface pores. By substantially
`free of pits and surface pores, it is meant that the fiber
`surface may still have some micropores provided, however,
`that these micropores do not represent more than 5% of the
`total surface area of the fiber.
`
`BACKGROUND OF THE INVENTION
`Electrical energy storage devices, particularly batteries,
`which employ fibrous carbon or graphite electrodes and
`which operate in a nonaqueous electrolyte at ambient tem
`perature are known from U.S. Pat. No. 4,865,931, issued
`Sep. 12, 1989 to F. P. McCullough et al, the subject matter
`of which is, in its entirety, incorporated herein by reference.
`The patent generally discloses a secondary battery compris
`ing a housing having at least one cell positioned in the
`housing, each cell comprising a pair of electrodes made of
`a multiplicity of electrically conductive carbon fibers, a
`foraminous electrode separator for electrically insulating the
`electrodes from contact with each other, and an electrolyte
`comprising an ionizable salt in a nonaqueous fluid in each
`cell.
`A similar electrical storage device is disclosed in U.S. Pat.
`No. 4,830,938 to F. P. McCullough et al, issued May 16,
`1989, the subject matter of which is incorporated herein, in
`its entirety, by reference. This patent discloses a fibrous
`carbonaceous electrode which is characterized as having a
`Young's modulus of greater than 1 MM psi (6.9 GPa) and a
`surface area with respect to the fibrous material of at least
`0.1 m/g, most preferably less than 5 m/g. The patent
`additionally discloses a shared bipolar carbonaceous elec
`trode which is capable of carrying a current from one cell to
`an adjacent cell without a current collector frame associated
`therewith and, when employed as the electrode in a series of
`adjacent cells of a battery, having a pair of terminal elec
`trodes each provided with a collector frame at the terminal
`cells of the battery. The useable capacities of the circular
`cross-section fiber electrodes of these batteries was less than
`1 Liper 6 carbons on the anode (negative electrode) side and
`less than 1 anion per 12 carbons on the cathode (positive
`electrode) side.
`The physical shape of nongraphitic and electrically non
`conductive polymeric fibers is described in Modem Textiles,
`second edition, 1982, by D. S. Lyle, John Wiley & Sons. In
`the chapter entitled "Fiber Properties', pp. 41 to 63, various
`natural and polymeric fibers are described having different
`surface contours, i.e. smooth, rough, serrated, etc. which are
`said to influence cohesiveness, resiliency, loft, and thick
`ness. Polymeric fibers having various cross-sectional shapes
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`It has been found that the substantially contiguous and
`uniform surface structure presented by the carbon fibers of
`the present invention further provides a solution to the
`problem of destructive anion intercalation typically found
`with porous and adsorptive carbon when used as the active
`positive electrode material. The carbon fibers of the inven
`tion, optionally, can have a generally tubular cross-sectional
`shape or can be provided with at least two interior passage
`ways extending along the length of each fiber when viewed
`in cross-section.
`The generally noncircular carbon fibers of the invention
`have a substantially higher surface area to unit mass ratio as
`well as a substantially contiguous conductive surface and,
`therefore, have a substantially greater practically useable
`electrical storage capacity per unit weight and significantly
`enhanced performance as compared to fibers having a sub
`stantially circular cross-section.
`The flexible carbon fibers of the invention are essentially
`continuous, i.e. they can be made to any desired length, are
`not chopped or crimped, and possess a high degree of
`flexibility which manifests itself in a bending strain of from
`greater than 0.01 to less than 50%, preferably from about 0.1
`to about 30%, that allow the fibers to be formed into a
`variety of complex electrode shapes and configurations for
`use in many types of applications for energy storage devices
`in use today. In contrast, the bending strain of conventional
`carbon fibers is substantially less than 0.01% and often less
`than 0.001% for extremely high modulus graphitic fibers.
`Moreover, the noncircular cross-sectional shape of the fibers
`of the invention increases the effective electron storage
`capacity per unit weight of the electrode. Presently, conven
`30
`tional carbon and graphite electrodes made from high modu
`lus fibers with a Young's modulus of greater than 1 MM psi,
`typically from 30 to 55 MM psi. are limited in their
`applications in view of their extreme brittleness which
`makes their handling during fabrication difficult, resulting in
`excessive breakage of the fibers. Due to their generally
`circular cross-section, these stiff and brittle fibers also suffer
`from a comparatively reduced effective electrical storage
`capacity per unit weight of the electrodes.
`The invention further resides in a high performance
`secondary energy storage device containing a terminal elec
`trode comprising a collector frame formed of an electrically
`conductive material. The collector frame is coated with a
`lithium salt of a metal oxide (lithiated metal oxide) of the
`empirical formula Li(MO) in which M is a metal selected
`45
`from groups VIIb and VIIIb of the periodic table. The
`storage device also includes a pseudo bipolar electrode
`formed of a multiplicity of the flexible carbon fibers of the
`invention and having a portion thereof coated with a metal
`oxide (MO) in which M is a metal selected from groups
`VIIb and VIIIb of the periodic table. Preferably, the metal
`oxide coating of the terminal and the portion of the pseudo
`bipolar electrode is selected from the group consisting of
`CoO, NiO and MnO.
`The invention also resides in a flexible carbon fiber and
`electrode that can be made more easily and at a substantially
`lower manufacturing cost from an unfiltered polymeric
`precursor material such as, for example, an acrylic or
`sub-acrylic polymer that can contain from about 0.0001 to
`about 5% by weight particulate matter having a diameter of
`less than about 0.1 microns. Sub-micron particles are natu
`rally present in any polymeric material and thus will also be
`present in polymeric precursor materials that are extruded to
`form fibers for use in the manufacture of textile articles, for
`example. These particles are generally organic or inorganic
`materials which are insoluble in the polymeric precursor
`melt or dope.
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`It is also contemplated and within the scope of the
`invention to introduce an additional quantity of sub-micron
`particulate matter, such as, for example, fumed silica, cal
`cium oxide and various other inorganic materials such as
`silicates into the polymeric precursor material. It has been
`found that the addition of these sub-micron particles into the
`polymeric precursor material will reduce the formation of a
`high degree of order or crystallinity in the spun precursor
`fiber material. When the polymeric precursor fibers are
`subsequently heated and carbonized in a non-oxidizing
`atmosphere, they lack the stiffness, brittleness and high
`modulus that is normally associated with traditional carbon
`and graphitic fibers, while still exhibiting a low electrical
`resistivity and good uniform and contiguous surface struc
`ture, free from the voids, pores and pitting normally asso
`ciated with adsorptive carbon materials. These characteris
`tics differentiate the flexible carbon fibers of the invention
`from high surface area absorptive carbon materials. It is
`known in the art and an accepted standard, imposed by the
`Federal Trade Commission, that the term "acrylic' applies to
`any long chain synthetic polymers composed of at least 85
`mole percent by weight of acrylonitrile units andless than 15
`mole percent of another polymer. Carbon fibers made from
`acrylic precursor materials are generally wet spun and are
`limited to fibers having a circular cross-section.
`In accordance with a further embodiment of the invention,
`it has been discovered that flexible carbon fibers and elec
`trodes can be made from a polymeric precursor material that
`is derived from a sub-acrylic polymer and that is character
`ized by containing less than 85 mole percent acrylonitrile
`units and greater than 15 mole percent of another polymer,
`particularly a plasticizer such as a vinyl unit. More specifi
`cally, less than 85 mole percent acrylonitrile units can be
`blended with more than 15 mole percent, and as much as 35
`mole percent of a plasticizer to render the blend more easily
`melt extrudable through an extrusion nozzle or nozzles
`while the polymer blend is in a heat softened condition. The
`so extruded, heat softened filament can be stretched and
`attenuated, while under tension, to form a finer denier
`filament (i.e. in which the unit length of the fiber is increased
`with respect to the weight) having a relatively smaller
`diameter as compared to extruded fibers made from a
`standard acrylic resin. The sub-acrylic resin of the invention
`can also be advantageously employed in extruding filaments
`having a noncircular or tubular cross-section.
`The invention further resides in electrodes assembled
`from a multiplicity of the flexible carbon fibers of the
`invention, particularly for use in secondary electrical energy
`storage devices.
`The invention additionally resides in a secondary energy
`storage device comprising a pair of electrodes and wherein
`at least the positive electrode comprises a multiplicity of
`electrically conductive, flexible carbon fibers of the inven
`tion. The non-circular shape of the fiber electrodes of the
`invention surprisingly give significantly higher useful
`capacities for both electrodes as compared to the circular
`cross-section fibers of McCullough et al. The useable
`capacities of the non-circular cross-section fibers of these
`batteries is 1 Li per 2 to 4 carbons on the anode side
`(negative electrode) and 1 anion per 6 to 10 carbons on the
`cathode side (positive electrode). This represents an increase
`of over 25% over the prior art in terms of the capacities with
`similar improvements in other performance aspects such as
`power density.
`The invention further resides in a high performance
`secondary energy storage device comprising at least a pair of
`cells wherein the storage device contains at least one bipolar
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`5,518,836
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`5
`electrode formed of a multiplicity of the electrically con
`ductive, flexible carbon fibers of the invention.
`The invention further resides in a high performance
`Secondary energy storage device comprising at least a pair of
`cells with one of the terminal cells containing a terminal
`electrode comprises a collector frame formed of an electri
`cally conductive material. The collector frame is coated with
`a lithium salt of a metal oxide. Preferably, the metal oxide
`coating is selected from the group consisting of CoO, NiO,
`and Mn2O4. The storage device also includes at least one
`pseudo bipolar electrode comprising a multiplicity of the
`flexible carbon fibers of the invention having a portion
`thereof coated with said lithium salt of a metal oxide.
`The invention also resides in a composite pseudo bipolar
`electrode comprising a multiplicity of the flexible carbon
`fibers of the invention, wherein a portion of the carbon fibers
`is coated with an ion conductive lithium salt of a metal oxide
`which serves as the initial source of lithium ions on charging
`the cell. Preferably, the metal oxide coating is selected from
`the group consisting of CoO, NiO2 and Mn2O.
`The invention additionally resides in a process of making
`flexible carbon fibers having a non-circular or tubular cross
`sectional shape with a Young's modulus of from greater than
`1 MM psi (6.9 GPa) to 55 MM psi (380 GPa), and a bending
`strain of from about greater than 0.01 to less than 50%,
`preferably from about 0.1% to 30%.
`The invention also resides in secondary battery stack
`comprising at least two batteries that are electronically
`connected by means of a bipolar or pseudo bipolar carbon
`fiber electrode of the invention.
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`meric precursor materials that are usefully employed in the
`manufacture of flexible carbon fibers of the invention can
`contain from about 0.0001 to about 5% by weight particulate
`matter in which the particles have a diameter of less than
`about 0.1 microns, preferably less than 0.001 microns.
`The term "sub-acrylic resin' used herein applies to a long
`chain polymer which is selected from the group consisting
`of copolymers and terpolymers, wherein the copolymers and
`terpolymers contain less than 85 mole percent acrylic units
`but more than 15 mole percent of one or more plasticizer
`units, such as vinyl units, copolymerized therewith.
`The term "polymeric blends' applies to polymeric pre
`cursor materials that are suitable for forming the flexible
`carbon fibers of the invention and that are blended with other
`polymers, preferably plasticizers, which in the case of
`sub-acrylic polymeric materials are present at levels of
`greater than 15%, generally from greater than 15% up to
`35%, preferably from greater than 15% to about 25% by
`weight.
`The term "polymeric material' or "polymeric precursor
`material' used herein includes any polymers that are capable
`of being carbonized to form the flexible electrically conduc
`tive carbon fibers of the invention. Polymeric materials that
`can be suitably employed are well known in the art and are
`exemplified by copolymers and terpolymers of polyacety
`lene, polyphenylene, polyvinylidene chloride, polyacryloni
`trile, and the like. Mesophase pitch (petroleum or coal tar)
`containing particulate impurities or additives can also suit
`ably be employed. Preferably, the polymeric precursor mate
`rial of the invention is a polyacrylonitrile or sub-acrylic
`polymer (as hereinbefore defined) in the form of fibers in
`which the fibers are subsequently carbonized in accordance
`with the procedure described in U.S. Pat. No 4,837,076,
`issued Jun. 6, 1989 to McCullough et al.
`The term "plasticizer” or “polymeric plasticizer' used
`herein applies to any organic compound that can be added to
`or blended with a high polymer to facilitate processing and
`to increase the flexibility and toughness of the final product
`by internal modification (solvation) of the polymer mol
`ecule. Suitable plasticizers include, for example, vinyl chlo
`ride, methyl acrylate, methyl methacrylate, polyvinyl chlo
`ride and cellulose esters, phthalates, adipates, and sebacate
`esters, polyols such as ethylene glycol and its derivatives,
`tricresyl phosphate, caster oil, etc.
`The term "bending strain” as used herein is as defined in
`Physical Properties of Textile Fibers by W. E. Morton and J.
`W. S. Hearle. The Textile Institute, Manchester, pages
`407-409. The percent bending strain on a fiber can be
`determined by the equation S=(r/R) x100 where S is the
`percent bending strain, r is the effective cross sectional fiber
`radius and R is the radius of curvature of the bend. That is,
`if the neutral plane remains in the center of the fiber, the
`maximum percentage tensile strain, which will be positive
`on the outside and negative on the inside of the bend, equals
`(r/R)x100 in a circular cross section of the fiber.
`The term "effective cross-sectional diameter' as it applies
`to a fiber having a generally circular cross-section, is the
`distance from one point along the outer surface of the fiber
`through the center of the fiber to an opposite point on its
`outer surface. In the case of a fiber having a generally
`non-circular cross-section, the effective cross-sectional
`diameter is the distance extending across a generally circular
`region where the core material of the fiber is solid and
`uninterrupted (see reference no.32 in FIG. 2A). By the term
`"generally circular cross-section of a fiber', it is also meant
`that the diameter of the generally circular in cross-section
`
`DEFINITIONS
`
`The term "non-circular' or "non-circular in cross-section'
`use herein generally refers to a fiber having a surface contour
`that can be smooth or rough, or regular or irregular in texture
`or shape. For example, a fiber can be multi-lobal, e.g.
`trilobal, in cross-section and have a regular and symmetrical
`cross-sectional shape as well as a smooth surface contour
`Alternatively, a fiber can have an irregular striated, crinkled,
`or the like contour. Other cross-sectional shape that can be
`usefully employed are fibers having, for example, a dog
`bone, crescent, star, or the like cross-sectional shape. It
`would also be advantageous to make a tubular fiber or a fiber
`having 2 or more passageways extending along the longi
`tudinal axis of the fiber.
`The term "electrode structure' used herein applies to a
`multiplicity of fibers, fibertows, a non-woven web or felt, or
`a woven, knit, or non-woven fabric made from continuous
`flexible carbon fibers or staple carbon fibers.
`Although the term "Carbon fibers' is generally known to
`apply to fibers having a carbon content of greater than 92%
`by weight, while the term "Graphite fibers' is generally
`known to apply to fibers having a carbon content of greater
`than 98% by weight, it is intended herein that the term
`"carbon fibers' should apply to fibers having a carbon
`content of greater than 85% and up to 99% by weight.
`Accordingly, the term "carbon fibers' used herein is
`intended to be inclusive of "carbon' and "graphitic fibers'.
`Preferably, the fibers of the invention have a carbon content
`of from about 95% to about 98% by weight.
`The term “unfiltered” used herein applies to polymeric
`precursor materials which, when in a melt phase and during
`manufacture, are not subjected to the usual micro-filtration
`procedure to remove impurities, such as non-polymeric
`inclusions, from the precursor material. Unfiltered poly
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`

`

`7
`fiber can vary in its circularity due to the fact that during
`extrusion of the fiber the hot melt extrudate has a tendency
`to flow until it is sufficiently cooled to set. Thus, the
`cross-section of the fiber is not generally in the shape of a
`perfect circle but contains some slight variations in its
`circularity. The same applies to the non-circular fibers of the
`invention. For example, the hot polymer that is extruded
`through a tri-lobal die will continue to flow until the polymer
`is cooled sufficiently thus forming a tri-lobal fiber in which
`the individual lobes are not perfectly symmetrical.
`The term "flexible' used herein is specifically applicable
`to carbon fibers having a bending strain value of from
`greater than about 0.01 to less than 50%, preferably from
`about 0.1 to 30%.
`The term "stabilized' used herein applies to polymeric
`precursor fibers or tows which have been oxidized in an
`oxidizing atmosphere such as oxygen or air, at a specific
`temperature, typically less than about 350° C. for PAN
`(polyacrylonitrile) fibers, provided it is understood that in
`20
`some instances the fibers can be oxidized by chemical
`oxidants at lower temperatures.
`The term "energy storage device' used herein applies to
`electrical storage devices including those that are recharge
`able such as, for example, secondary batteries, accumula
`tors, capacitors, fuel cells, and the like.
`The term "aspect ratio” is defined herein as the length to
`diameter (l/d) ratio of a fiber. The term "pseudo bipolar
`electrode' used herein is applicable to a carbon fiber elec
`trode in which at least a portion thereof is coated with a
`lithium salt of a metal oxide. Optionally, the carbon fibers of
`the electrode can initially be coated with a conductive metal
`coating such as, for example, nickel, followed by a coating
`of a lithium salt of a metal oxide or lithiated metal oxide as
`it is sometimes referred to. The initial metal coating serving
`the purpose of providing a lower contact resistance and more
`secure bond for the metal oxide coating to the carbon fibers.
`All percentages given herein are in "percent by weight'
`unless otherwise specified.
`
`10
`
`15
`
`25
`
`30
`
`35
`
`40
`
`5,518,836
`
`8
`In FIG. 5, there is illustrated a planar cross sectional end
`view of a lithium ion battery which is similar in construction
`to the battery illustrated in FIG. 3, except that one of the
`terminal electrodes consist of an electrically conductive
`collector frame having a lithium salt of a metal oxide coating
`(in the fully discharged state) and a pseudo bipolar com
`posite electrode is provided having a portion of the carbon
`fibers coated with a metal oxide coating.
`In FIG. 5A, there is illustrated an enlarged cross sectional
`view of a pseudo bipolar carbon fiber electrode in which a
`portion of the carbon fibers are coated with a lithium salt of
`a metal oxide coating.
`In FIG. 5B, there is illustrated an enlarged cross sectional
`view of the metal oxide coated portion of the pseudo bipolar
`electrode of FIG. 5, when viewed along cross-sectional lines
`SB-5B.
`In FIG. 6 there is illustrated a planar cross-sectional end
`view of a stacked battery assembly, i.e. in which one battery
`is stacked upon a second battery, with a bipolar electrode
`extending from a terminal cell in said one battery into a
`terminal cell of the second battery.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`In accordance with one embodiment of the present inven
`tion, as particularly illustrated in FIG. 1, there is provided a
`secondary battery 10 comprising a housing 12 having a
`generally rectangular or prismatic configuration. It will be
`apparent that the housing can have any other desired shape,
`such as a generally planar board where the length, width and
`thickness can be adjusted to a particular end use and to
`accommodate any desired number of cells. Accordingly, the
`battery of the invention can be constructed of any other
`symmetrical or non-symmetrical configuration. For
`example, the housing of the battery can consist of an air and
`water vapor impervious polymer or a metal/plastic laminate
`that can be molded or pressed into any desired shape to form
`a housing which could then be inserted into or form the roof,
`door, or floor panel of an automobile, the wall or panel of a
`portable computer, etc. Moreover, the battery perse can be
`in the form of a flexible container or pouch that can be
`contained in a garment or that can be used for medical
`applications such as a light weight power unit for a Holter
`Monitor (an EKG monitoring device), a portable insulin
`pump, an in vivo portable defibrillator unit, i.e. TENS (Trans
`Electro Neuro Stimulator), etc.
`The battery housing 12 consists of a bottom wall 14 and
`a top wall 16, a pair of side walls 18 and 20, and a pair of
`end walls (not illustrated) connecting the top and bottom
`walls to form an internal chamber 22. A pair of generally
`planar electrodes 24A and 24B, constructed in accordance
`with the teachings of the present invention, are positioned in
`the chamber in a facing relationship. An electrically non
`conductive, ion permeable planar, sheet like electrode sepa
`rator 26 is positioned between the electrodes to prevent short
`circuiting between the electrodes while permitting ions to
`travel between the electrodes. It will be understood by
`persons skilled in the art that a planar sheet l