(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY(PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`(43) International Publication Date
`19 December 2002 (19.12.2002)
`
`
`
`PCT
`
`(10) International Publication Number
`WO 02/101856 A2
`
`(72) Inventor; and
`(75) Inventor/Applicant
`(for US only): ZENG, Shuming
`(21) International Application Number:=PCT/US02/17746
`[CN/US], 34 Chester Street, Brookfield, CT 06804 (US).
`
`(51) International Patent Classification’:
`
`HOIM 4/62
`
`(22) International Filing Date:
`
`6 June 2002 (06.06.2002)
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`(30) Priority Data:
`09/880,651
`
`English
`
`English
`
`13 June 2001 (13.06.2001)
`
`US
`
`(63) Related by continuation (CON)or continuation-in-part
`(CIP) to earlier application:
`US
`Filed on
`
`09/880,651 (CON)
`13 June 2001 (13.06.2001)
`
`(71) Applicant (for all designated States except US): THE
`GILLETTE COMPANY [US/US]; Prudential Tower
`Building, Boston, MA 02199 (US).
`
`(74) Agents: RICHARDS, John etal.; Ladas & Parry, 26 West
`61st Sreet, New York, NY 10023 (US).
`
`(81) Designated States (national): AK, AG, AL, AM, AT, AU,
`AZ, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CO, CR, CU,
`CZ, DE, DK, DM, DZ, EC, EE, ES, FI, GB, GD, GE, GH,
`GM,HR,HU,ID,IL, IN,IS, JP, KE, KG, KP, KR, KZ, LC,
`LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, Mw,
`MX, MZ, NO, NZ, OM,PH,PL, PT, RO, RU, SD, SE, SG,
`SI, SK, SL, TJ, TM, TN, TR, TT, TZ, UA, UG, US, UZ,
`VN, YU, ZA, 2M, ZW.
`
`(84) Designated States (regional): ARIPO patent (GH, GM,
`KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZM, ZW),
`Eurasian patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM),
`European patent (AT, BE, CH, CY, DE, DK, ES, FI, FR,
`
`[Continued on next page]
`
`(54) Title: ALKALINE CELL WITH IMPROVED CATHODE
`
`cell
`electrochemical
`alkaline
`An
`(37) Abstract:
`having a cathode comprising manganese dioxide and
`conductive graphitized mesophase pitch-based carbon
`fibers having an increased BET surface area of between
`about 10 and 60 m7/g, desirably beetween about 10
`and 50 m*/g, preferably between about 30 and 50
`m’/g by heat treatment between 800 and 1200°C with
`potassium hydroxide. The treated graphitized mesophase
`pitch-based carbon fibers can comprise between about |
`and 100 percent by weight of the total graphite material
`in the cathode, typically between about 5 and 50 percent
`by weight of the total graphite. The total graphite in
`the cathode desirably comprises between about 4 and 10
`percent by weight of the cathode. The graphite can be the
`mixtures of the graphilized mesophase pitch-based carbon
`fibers with flaky crystalline graphites including expanded
`graphites. The graphitized mesophase pitch-based carbon
`fibers have a mean average diameter typically between
`about 1 and 10 micron. The use of said carbon fibers in
`
`the cathode increasescathode conductivity and results in
`improvedcell performance.
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`WO 02/101856 A2
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`—_[IMITIMTTIIIATAINATATOA
`
`For two-letter codes and other abbreviations, refer to the "Guid-
`GB, GR,IE, IT, LU, MC, NL, PT, SE, TR), OAPI patent
`(BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, ML, MR,—ance Notes on Codes andAbbreviations" appearing at the begin-
`NE, SN, TD, TG).
`ning ofeach regular issue ofthe PCT Gazelle.
`
`Published:
`— without international search report and to be republished
`upon receipt of that report
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`ALKALINE CELL WITH IMPROVED CATHODE
`This invention relates to an improved cathode mixture comprising
`manganese dioxide andcarbon fibers, particularly graphitized mesophasepitch-based
`carbon fibers.
`
`Conventionalalkaline electrochemicalcells are formed of a cylindrical
`casing. The casingis initially formed with an enlarged open end and opposing closed
`end. After the cell contents are supplied, an end cap with insulating plug is inserted
`into the open end. Thecell is closed by crimping the casing edge over an edge of the
`insulating plug and radially compressing the casing aroundthe insulating plug to
`providea tight seal. A portion ofthe cell casing at the closed end forms the positive
`terminal.
`
`Primary alkaline electrochemicalcells typically include a zinc anode
`active material, an alkaline electrolyte, a manganese dioxide cathode active material,
`and an electrolyte permeableseparatorfilm, typically of cellulose or cellulosic and
`polyvinylalcoholfibers. The anodeactive material can include for example, zinc
`particles admixed with conventionalgelling agents, such as sodium carboxymethyl]
`cellulose or the sodium salt of an acrylic acid copolymer, and anelectrolyte. The
`gelling agent serves to suspend thezincparticles and to maintain them in contact with
`one another. Typically, a conductive metal nail inserted into the anode active material
`serves as the anode currentcollector, whichis electrically connected to the negative
`terminal end cap. Theelectrolyte can be an aqueoussolution ofan alkali metal
`hydroxide for example, potassium hydroxide, sodium hydroxide orlithium hydroxide.
`The cathode typically includes particulate manganese dioxideas the electrochemically
`active material admixed with an electrically conductive additive, typically graphite
`material, to enhanceelectrical conductivity. Optionally, polymenc binders, and other
`additives, such as titanium-containing compoundscan be addedto the cathode.
`Since manganese dioxide typically exhibits relatively low electric
`conductivity, an electrically conductive additive is needed to improve the electric
`conductivity between individual manganese dioxideparticles. Such electrically
`conductive additive also improveselectric conductivity between the manganese
`dioxideparticles and the cell housing, whichalso serves as cathode current collector.
`Suitable electrically conductive additives can include, for example, conductive carbon
`powders, such ascarbonblacks, including acetylene blacks,flaky crystalline natural
`graphite, flaky crystalline synthetic graphite, including expandedor exfoliated
`graphite.
`.
`It is desirable for a primary alkaline battery to have a high discharge
`capacity(i.e., long service life). Since commercial cell sizes have been fixed,it is
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`knownthat the useful service life of a cell can be enhanced bypacking greater amounts
`of the electrode active materials into the cell. However, such approachhaspractical
`limitations such as, for example, if the electrode active material is packed too densely
`in the cell, the rates of electrochemical reactions during cell discharge can be reduced,
`in turn reducingservice life. Other deleterious effects such as cell polarization can
`occur as well. Polarization limits the mobility of ions within both the electrolyte and
`the electrodes, which in turn degradescell performance andservicelife. Although the
`amountofactive material included in the cathodetypically can be increased by
`decreasing the amountof non-electrochemically active materials such as polymeric
`binder or conductive additive, a sufficient quantity of conductive additive must be
`maintained to ensure an adequate level of bulk conductivity in the cathode. Thus, the
`total active cathode material is effectively limited by the amount of conductive
`additive required to provide an adequate level of conductivity.
`Further, it is highly desirable to enhance the performanceof an alkaline
`cell at high rates of discharge. Typically, this is accomplished by increasing the
`fraction of conductive additive in the cathode in order to increase overall (bulk)
`electric conductivity of the cathode. The fraction of conductive additive within the
`cathode mustbe sufficient to form a suitable network of conductiveparticles.
`Typically, when the conductive additive is a conductive carbon, about3 to 15,
`desirably between 4 to 10 weight percent of the total mixture are required. However,
`an increase in the amount of conductive carbon produces a corresponding decrease in
`the amountof active cathode material, giving lower service life. Conventional
`powdery conductive carbonssuch as acetylene black have large volumeinacertain
`weight but lowerelectric conductivity than the flaky, crystalline natural or synthetic
`graphite, which possess a three-dimensional crystal structure as described below. The
`less conductive nature of carbon blacksleads to high carbon content in cathode
`electrode and less electrochemically active material, in turn, to the shorter servicelife
`of electrochemicalcells.
`To increase the electric conductivity of carbonaceous materials, a
`thermal process knownasgraphitization is applied to convert carbons into graphite
`material or graphite product. Such a graphitic product is characterized by a distinctive
`three-dimensional graphitic crystal structure. The crystalline structure is composed of
`individual unit cells which are repeatable in the "a" and "c" directions. The graphite
`crystalline structure has a unit cell which is generally of a three dimensional hexagonal
`(six sided) shape. The baseof the hexaganol unit is defined by a hexaganol plane of
`sides "a" of equal size and separated from each other by 120 degrees. The hexaganol
`plane defines the "a" direction of the crystalline structure. The thicknessof the unit
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`cell is defined by the heightofthe unit cell defined by the axis "c" whichis
`perpendicularto said hexagonal plane lying in the "a" direction. A reference to such
`hexaganolunit cells using the same standard nomenclature can be found, for example,
`in F. Daniels and R. Alberty, Physical Chemistry, 2" Edition, John Wiley & Sons
`(1961), pp. 622-623. The unit cells are repeatable in the "a" direction and "c" direction
`up to a point where they abruptly change orientation. This defines the bounds ofthe
`crystalline structure in the "a" and “c" directions. Different graphites have different
`numberof repeatable unit cell in the "a" and "c" direction. (The size of each repeatable
`unit cell for graphites will be the same). The size ofthe crystalline structure
`(crystalline size) for a specific graphite can be defined by the distance Laof the
`crystalline structure in the "a" direction which spansthe total number ofrepeat units in
`the "a" direction, and the distance Lc in the "c" direction which spans the total number
`of repeat units in the "c" direction. The number ofunit cells in the "a" direction can be
`determined by dividing the distance Labythe size ofthe unit cell in the "a" direction.
`Conversely, the numberofunit cells in the "c" direction can be determined by dividing
`the distance Lcbythe size of the unit cell in the "c" direction.
`In most graphitic products, for example, natural graphite, the Lc and La
`distances definingthe crystalline size as measuredby x-ray diffraction are typically in
`the range of 1000 to 3000 Angstrom. Expanded graphite, a typical exfoliated graphite,
`can have a large La of about 500 to 1000 buttypically a smaller Lc of about 300 to
`1000, typically between about 400 to 600 Angstrom due to chemical exfoliation in this
`direction. Due to the anisotropy of graphite in the "a" and “c" directions of the crystal
`unit cell, the La normally contributesto electric and thermal conductivity of a graphite
`more than Lc does.
`In order to provide good electric conductivity, it is desirable to use
`graphite including natural and synthetic graphite that have a La greater than 100, more
`typically between 100 to 300 Angstromin the cathode ofan alkaline cell.
`Conventional powdery conductive carbons suchas acetylene black have small La,
`typically in the range below 100 Angstrom. These materials, therefore, have low
`electric conductivity.
`After graphitization the crystal unit cell sizes such as Le and La of
`carbon increase. Physical properties, for example,the electric conductivity can be
`improved significantly. Some carbon materials, depending on their molecular
`structure cannot be completely converted to graphite or only partially converted to
`graphite. Such materials are classified as non-graphitizable or hard carbons, while
`those carbonsthat can be easily graphitized are termed graphitizable. The graphitized
`carbons normally have higherelectric conductivity than the nongraphitized hard
`carbons.
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`Carbonfibers (not graphites) are synthetic carbon materials taking the
`forms of fibers or thin strands of carbon material. Such carbonfibers can beclassified
`into four types based on the precursors and processes used duringtheir manufacture:
`1) rayon based carbonfibers, 2) polyacrylonitrile (PAN) based carbonfibers, 3)
`pitch-based carbon fibers (PCF), and 4) catalyzed vapor growth carbonfibers (VGCF).
`The pitch-based carbonfibers (PCF) can further be classified into isotropic pitch-based
`and the mesophase pitch-based carbon fiber (MPCF). Most carbonfibers are not
`graphitizable. However, mesophasepitch-based carbon fiber (MPCF) and vapor
`growth carbon fiber (VGCF)are graphitizable. The graphitized mesophase
`pitch-based carbon fibers (GMPCF)generally have a muchhigherelectrical
`conductivity than MPCF, the non-graphitizable form such asisotropic pitch-based
`carbon fiber and other carbonfibers such as rayon or polyacrlonitrile (PAN)-based
`carbon fibers. The diameter of carbon fibers can vary from aboutless than 1 micron (1
`x 10° meter), e.g., in the case of vapor growth carbonfibers to about 5 to 10 micron (5
`or 10 x10meter) and even up to 100 micron (100 x 10° meter), e.g. in the case of
`mesophasepitch carbonfibers. Mesophase pitch-based carbon fibers (MPCF) and
`graphitized mesophasepitch-based carbon fibers (GMPCF), typically have a diameter
`between about 5 and 10 micron, moretypically between about 5 and 7 microns.
`Conventional mesophase pitch-based carbon fibers and graphitized mesophase
`pitch-based carbonfibers have a BET surface area between about 0.2 and 5.0 m*/g,
`moretypically 0.5 to 3 m’/g.
`Typically, natural and synthetic graphite materials including expanded
`graphite are in a flaky crystalline form. They can have averageparticle sizes ranging
`from about 2 to 50 microns. A suitable flaky natural crystalline graphite having an
`average particle size of about 12 to 15 microns is commercially available underthe
`tradename "MP-0702X" or "NdG-15" from Nacional de Grafite. Suitable expanded
`graphites typically have average particle sizes ranging from 0.5 to 40 microns. As
`described hereinabove, expanded graphite canbe natural graphite or synthetic graphite
`wherein the graphite crystal lattice has been uniaxially expanded. Such expansion
`reduces the crystalline sizes of expanded graphite particles in c-axis direction, butstill
`maintains large crystalline dimensionin a-axis direction. The expanded graphite thus
`can exhibit a much higheraspectratio (i.e., ratio of thickness to diameter) in term of
`crystalline size. Meanwhile, expansionin c-direction creates large volumewithin the
`graphite particles, resulting in increase in bulk volumeandparticle size. The large
`particle size and high aspectratio of expanded graphite relative to flaky natural or
`synthetic graphites suggest that expanded graphite can providean increase in the
`numberof points and/or surfaces that contact each other and as well with the
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`manganese dioxideparticles. This in turn can provide enhanced conductivity in
`cathodes formed from mixtures thereof. Suitable expanded graphites are available
`commercially, for example, from Chuetsu Graphite under the tradename "DCN-2",
`Timcal AG underthe tradename "BNB90", and Superior Graphite under the tradename
`"ABG-40. Cathode containing expanded graphite usually has better electric
`conductivity than that with small particle flaky natural graphite.
`The use of expanded graphite as a conductive additive in cathodes of
`conventionalalkaline primary cells is known and disclosed for example, in U.S. Patent
`No. 5,482,798. A suitable expanded graphite having an average particle size ranging
`from 0.5 to 15 microns, preferably from 2 to 6 micronsts disclosed in U.S. Patent
`5,482,798. The smaller averageparticle size of expanded graphite relative to
`conventional natural or synthetic crystalline graphite (e.g., 15 to 30 microns) was
`hypothesizedto facilitate the formation of a conductive network typically at a lower
`volumefraction of graphite. An expanded graphite having an averageparticle size
`greater than about30 microns was disclosed to provide no performance advantage in
`alkaline cells compared to a conventional non-expandednatural graphite having a
`comparable particle size. U.S. Patent No. 5,482,798also discloses that suitable
`amounts of expanded graphite can range from about 2 to 8 weight percent, and
`preferably from about 3 to 6 weight percentof the total cathode, Further, for expanded
`graphite contents ofgreater than about 10 weight percent no performance advantageis
`provided relative to equivalent amounts of unexpanded graphite particles in alkaline
`primary cells.
`
`Various methodsfor preparing mixtures of manganese dioxide and
`graphite are knownto providesuitable levels of electric conductivity in cathodes of
`alkaline cells. Typically, graphite can be mixed dry or wet with manganese dioxide
`using any ofa variety of conventional blending, mixing or milling equipment. For
`example, U.S. Patent No. 5,482,798 discloses the use of a twin cylinder mixer or a
`rotary tumbling mixer to dry mix graphite and manganese dioxide.
`In a subsequent
`step disclosed in U.S. Patent No. 5,482,798 the formed mixture was wet-pulverized,
`preferably in water, using a horizontal media mill suchas a ball mill or bead mill to
`decrease average manganesedioxide particle size to less than 10 microns.
`Manganesedioxidessuitable for use in alkaline cells include both
`chemically produced manganese dioxide knownas "chemical manganesedioxide"
`commonly referenced in the art as "CMD"and electrochemically produced manganese
`dioxide knownas "electrolytic manganese dioxide” commonly referenced as "EMD".
`CMDcan be produced economically and in high purity, for example, by the methods
`described by Welsh et al. in U.S. Patent No. 2,956,860. EMD is manufactured
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`commercially by the direct electrolysis of a bath containing manganese sulfate
`dissolved in a sulfuric acid solution. Manganese dioxide produced by
`electrodeposition typically has high purity and high density. Processes for the
`manufacture of EMD andrepresentative properties thereofare described in "Batteries",
`edited by Karl V. Kordesch, Marcel Dekker, Inc., New York, Vol. 1, 1974, pp.
`433-488. EMDisthe preferred type of manganese dioxide for use in alkaline cells.
`One consequenceofthe electrodeposition processis that the EMD typically retains a
`high level of surface acidity from the sulfuric acid ofthe electrolysis bath. This acidity
`in residual surface can be neutralized for example, by treatment with an aqueousbase
`solution. Suitable aqueous bases include: sodium hydroxide, ammoniumhydroxide
`(i.e., aqueous ammonia), calcium hydroxide, magnesium hydroxide, potassium
`hydroxide, lithium hydroxide, and any combinations thereof. Typically, commercial
`EMDis neutralized with a strong base such as sodium hydroxide becauseit is both
`highly effective and economical.
`Thus, even though considerable effort has been expended to improve
`cathode conductivity, as evidenced bythepriorart cited hereinabove, the conductive
`carbon and/or graphite employed therein require additional refinementin order to
`improve substantially the discharge performanceandservicelife of alkaline
`electrochemical cells.
`It is a principal objective of the present invention to produce an
`improved cathode comprising manganesedioxide and graphite material comprising
`treated graphitized mesophasepitch-based carbon fibers (GMPCF)to provide an
`improvementin cathode conductivity and discharge performance.
`An aspectofthe present invention is directed to producing an alkaline
`primarycell having increased servicelife as well as improved discharge performance
`at high rate of discharge, e.g. between about 0.5 and 1-Watt or 0.5 to 2-Amps.
`The present invention provides a conductive cathode consisting of
`predominantly manganese dioxide admixed with a small amountofelectrically
`conductive graphitized mesophase pitch-based carbon fibers (GMPCF). The
`graphitized mesophasepitch-based carbonfibers are preferably chemically treated
`before admixing with the MnO,to producethe treated graphitized mesophase
`pitch-based carbon fibers (treated GMPCF). Preferably the graphitized mesophase
`pitch-based carbonfibers are treated with potassium hydroxide (KOH)at high
`temperature before admixing with MnO,. The treated graphitized mesophase
`pitch-based carbon fibers when used in admixture with particulate manganese dioxide
`to form a cathode mixture results in higher conductivity of the cathode mixture for a
`given amount of carbon. Thetreated graphitized mesophase pitch-based carbonfibers
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`also function as a binder for the particulate manganese dioxide. Such treated
`graphitized mesophasepitch-based carbonfibers have a higher BET surface area and
`are softer and thusless resilient than the untreated graphitized mesophase pitch-based
`carbon fibers during the compressing process of making the cathode.
`It is theorized
`that this combinationof factors leadsto the higher electric conductivity of cathodes
`comprising MnO,and the treated graphitized mesophasepitch-based carbonfibers.
`Such cathodes are more easily compacted. The softer carbon fibers and higher BET
`surface area ofthe fibers appearto result in better intimate contact betweenthe fibers
`with each other and with the MnO,particles, in turn leading to higher conductivity.
`Thetreated graphitized mesophase pitch-based carbonfibers (treated
`GMPCF)ofthe invention have a mean average BETsurface area of between about 10
`and 60 m’/g, preferably between about 10 and 50 g/m’. Desirably, the treated
`graphitized mesophase pitch-based carbonfibers have a mean average BETsurface
`area of between about 30 and 60 m’/g, advantageously between about30 and 50 m’/g.
`Such treated graphitized mesophase pitch-based carbon fibers havea length typically
`of between about 20 and 200 micron, with a mean average length of between about 40
`and 150 micron, and a mean average diameter between about | and 10 micron,
`typically between about 4 and 7 micron. The treated graphitized mesophase
`pitch-based carbonfibers (treated GMPCF)also have a crystal unit cell size Le in the
`"co" direction of between about 50 and 300 Angstrom, for example, between about 50
`and 250 Angstrom, more typically between about 100 and 200 Angstrom in the "c"
`direction (crystal thickness), and a crystal unit cell size La of between about 100 and
`300 Angstrom,typically about 200 Angstrom in the "a" direction. (The crystal unit
`cell size Lc in the "c" direction of the treated mesophase pitch-based carbon fibers of
`the invention have been determined to be smaller than the crystal size Le of untreated
`mesophasepitch-based carbonfibers).
`The weightratio of graphite material to MnO,in an alkalinecell
`cathode, irrespective of the percent by weight of MnO,in the cathode, is between
`about 0.05 (1:20) and 0.085 (1:12). The total graphite material in a representative
`In
`alkaline cell cathode is between about 4 and 10 percent by weightof the cathode.
`accordance with a specific aspect of the invention the total graphite material can be
`composedentirely ofthe treated graphitized mesophase pitch-basedcarbonfibers of
`the invention or entirely of a mixture of treated graphitized mesophase pitch-based
`carbonfibers and graphite including natural and expanded graphite. Alternatively, the
`treated graphitized mesophasepitch-based carbon fibers can make upa fraction ofthe
`total graphite material, for example, between about 1 and 100 percent by weight,
`desirably between about 5 and 50 percent by weight of the total graphite material in the
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`cathode. In such case the remainder of the graphite material can be composedofother
`graphites for example,natural or expanded graphites or mixtures thereof.
`The treated graphitized mesophase pitch-based carbon fibers also have
`the property that makes a cathode mixture comprising MnO,, treated graphitized
`mesophasepitch-based carbonfibers and aqueous KOHeasier to compact. The
`cathode mixture can be prepared wet by mixing the MnO,,treated and untreated
`graphitized mesophasepitch-based carbon fibers together with aqueous potassium
`hydroxide (KOH). The wet mixture can then be compacted andinserted into the cell
`casing or the wet mixture can be inserted into the cell and compacted while in the cell.
`Such cathode comprising the graphitized mesophase pitch-based carbonfibers exhibits
`increased conductivity and high bulk density of the MnO, (EMD), allowingfor a high
`loading of manganese dioxide (EMD)in the cell.
`Alternatively, a mixture of MnO,and treated graphitized mesophase
`pitch-based carbon fibers can be mixed while dry andtheresulting dry mixture
`compacted into the cell. Aqueous potassium hydroxide solution can then be added to
`the compacted dry mixture in the cell. The aqueous KOHis readily absorbed into the
`dry mixture to form the cathode. This can result in a cathode ofincreased conductivity
`and high bulk density resulting in even higher loading of MnO,therein. Also the
`compacted dry mixture of MnO,andtreated graphitized mesophasepitch- based
`carbon fibers can absorb the aqueouspotassium hydroxide solution quickly and in a
`large amount, due to the porousstructure of treated graphitized mesophase pitch-based
`carbon fiber. This can result in a cathode of increased electrolyte absorption and
`resulting in even higher performancefor high rate discharge.
`Definitions
`
`The term "graphite" or "graphite material" as used herein shall include
`natural and synthetic graphites, expanded graphites, graphitized carbon, and
`graphitized carbon fibers. The term "graphitized carbon fibers” shall mean carbon
`fibers which have a basic graphite crystalline structure as defined bythe International
`Committee for Characterization and Terminology of Carbon (ICCTC, 1982) as
`published in the Journal Carbon, Vol 20, p. 445. Such graphitized carbonfiber can be
`obtained by subjecting carbonfiber to a graphitization process, which normally
`involves heating carbonorcarbonfibers at very high temperatures, typically between
`about 2500°C and 3000°C to obtain the characteristics of the basic graphite structure
`which is a three-dimensionalcrystalline structure comprised of ordered layers of
`hexagonally arranged carbon atomsstacked parallel to each other as referenced in the
`International Committee for Characterization and Terminology of Carbon (ICCTC,
`1982).
`It will be appreciated that such graphitized carbon fibers can be broadly
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`classified as such despite that their average BET surface area and crystalline size (La
`and Lc) can be altered by the methodsdescribed herein. The term "natural crystalline
`graphite" shall mean graphite that is minimally processed,i.e., essentially in its
`geologically occurring natural crystalline form. The term "synthetic graphite" as used
`herein shall mean synthetically prepared or processed graphite. Synthetic graphite can
`have crystal structure and morphological properties that are the sameor similar to
`natural graphite or can have a different structure. The term "synthetic graphite" as
`used herein unless further qualified is also intended to include various expanded forms
`of graphite (including expanded graphite that has been exfoliated). The term
`“expanded graphite" is a recognized term ofart, for example, the form of graphite
`generally as referenced in U.S. Patent No. 5,482,798. Further, expanded graphite as
`used herein can be formed fromnatural and/or synthetic non-expanded graphite
`processed so as to have a uniaxially expanded crystal lattice. The extent of uniaxial
`expansion can be sufficiently large such that the expanded graphite particles can
`completely exfoliate (i.e., separate into thin laminae). The term "flaky" as commonly
`used in connection with graphites, (i.e., natural or synthetic flaky graphites) is intended
`to reflect that such graphites havea plate-like, non-expandedparticle form.
`The term "carbon fiber" shall mean elongated strands of carbon having
`a length to diameter ratio greater than about4, typically greater than 8 andup to about
`30 or more. Mesophasepitch-based carbonfibers is a known and commercially
`available type of carbon fiber.
`It is made by thermally treating "pitch". Pitch is a well
`known material which is a carbonaceoustackytar residue, typically a petroleum tar
`residue as defined, for example, in Hawley, Condensed Chemical Dictionary, Tenth
`Edition. Mesophasepitch is made by chemically treating pitch as described,for
`example,in U.S. Patent 4,005,183, Japanese Patent 57-42924 (correspondsto U.S.
`Patent 4,303,631), U.S. Patent 4,208,267, Japanese Patent 58-18421, Japanese Patent
`63-120112 (correspondsto U.S. Patent 4,822,587), or in the references Mochida,
`
`Carbon, Vol. 13, p. 135 (1975), Park and Mochida, Carbon, Vol. 27, p. 925 (1989),
`
`and Mochida, Carbon, Vol. 27, p. 843 (1989). The mesophasepitchis an intermediate
`phase which is a liquid crystal. The mesophase liquid crystal can be formedintaror
`pitch by heating such material at elevated temperatures, typically between about 350°C
`and 450°C. The mesophase tar or mesophasepitch resulting from heating such
`material was first reported and described in Taylor, G.H., "Developmentof Optical
`Properties of Coke During Carbonization", Fuel, Vol. 40, p. 465 (1961). Mesophase
`pitch characteristically have molecules which are highly oriented in one direction
`which makesthe material more readily graphitizable. Such molecular orientation of
`the mesophasepitchis described in Brooks, J.D. and Taylor, G.H., Chemistry and
`
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`15
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`20
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`25
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`30
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`PCT/US02/17746
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`Physics of Carbon, Vol. 4, p. 243 (1968). Thus, the term mesophasepitch shall have
`the ordinary and accepted meaningasusedin the art as applied to pitch which has been
`heattreated to obtain the mesophaseliquid crystalline phase structure with respect to
`such pitch material. The mesophasepitch can be made into mesophase pitch-based
`carbon fiber (MPCF)by first thermal extruding the mesophasepitch material at
`elevated temperature of about 200 to 350°C as, for example, as described in Otani U.S.
`Patent 4,016,247. The extruded mesophasepitch fiber, by way of non-limiting
`example,is then typically subjected to oxidation, preferably by reheating the material
`in air at 250 to 350°C to oxidize the extruded material as described for examplein
`Otani, Carbon, Vol. 3, p.31 (1965). This material can then be subjected to heat
`treatment at temperature between 1000 to 1800°C,typically 1000°C to 1200°C in the
`
`presenceofan inert gas such argon as described for example in Otani, Carbon, Vol. 3,
`p. 31 (1965). The end product is mesophasepitch-based carbonfiber, whichis a
`recognizeable type of carbon fiber known and referenced in the art by such name.
`Thus, the term "mesophasepitch-based carbon fiber" as usedin this application is
`intended to refer to such materialas it is ordinarily known andreferencedin theart.
`The mesophasepitch-based carbon fiber can then be graphitized by
`conventional methodsusedto graphitize carbon. The graphitization process normally
`involves heatingthe fiber at very high temperaturestypically between about 2500°C
`and 3000°C as is knownin the art. Such graphitization processes, by way of non-
`limiting example, can involve treating the carbon fibers with heat to a temperature of
`above 2500°C, more desirably between 2800°C and 3000°C,or at temperature
`sufficient to obtain the characteristics of an ordered three-dimensional graphite
`crystalline structure consisting of layers of hexagonally arranged carbon atomsstacked
`parallel to each otheras defined by the International Committee for Characterization
`and Terminology of Carbon (ICCTC, 1982), published in the Journal Carbon, Vol. 20,
`p. 445. The graphite is further characterized by ordered d-spacing between graphite
`layers (ordered layers), and crystalline sizes Le and La in the c and adirections of the
`crystalline structure, respectively. Thus, the term graphitized mesophase pitch-based
`carbon fibers (GMPCF)is a type of graphite material and shall mean mesophase
`pitch-based carbonfibers that have been subjected to such conventional graphitization
`
`processes.
`
`The term "treated graphitized mesophase pitch-based carbonfibers"
`(treated GMPCF) shall mean graphitized mesophase pitch-based carbon fibers th