(12) United States Patent
`(10) Patent N0.:
`US 6,287,719 B1
`
`Bailey
`(45) Date of Patent:
`Sep. 11, 2001
`
`U5006287719B1
`
`(54) BATTERY INCLUDINGA NON-AQUEOUS
`MULTI-CELL SPIRAL-WOUND ELECTRODE
`
`............................ 429/164
`5,849,431 * 12/1998 Kita et al.
`5,856,037 *
`1/1999 Casale et al.
`.......................... 429/82
`
`ASSEMBLY
`
`FOREIGN PATENT DOCUMENTS
`
`(75)
`
`Inventor:
`
`John C. Bailey, Columbia Station, OH
`(US)
`
`(73) Assignee: Eveready Battery Company, Inc., St.
`LOUIS, MO (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/094,820
`
`(22)
`
`Filed:
`
`Jun. 15, 1998
`
`0 533 576 A
`0 602 976 A
`HE15-54895
`W0 95/31836
`A
`
`3/1993 (EP)
`6/1994 (EP)
`3/1993 (JP) .
`
`............................... H01M/4/82
`............................... H01M/6/40
`
`11/1995 (W0) ............................. H01M/6/46
`OTHER PUBLICATIONS
`
`Vinal, George Wood, “Dry Cells—Material Production,”
`Primary Batteries, John Wiley & Sons, Inc., pp. 53—56.
`Vincent, Colin A., “Primary Aqueous Electrolyte Cells,”
`Modern Batteries, Edward Arnold (Publishers) Ltd. pp.
`68—75.
`
`7
`
`Int. Cl.
`(51)
`(52) US. Cl.
`
`.................................................... H01M 10/04
`.............................. 429/94; 429/99; 429/164;
`429/159
`
`* cited by examiner
`
`Primary Examiner—Gabrielle Brouillette
`Assistant Examiner—M. Wills
`
`(58) Field of Search ................................ 429/94, 99, 164,
`429/159, 120, 29/623
`
`(74) Attorney, Agent, or Firm—Russell H. Toye, Jr.; Robert
`W. Welsh
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`2,661,388
`12/1953 Warner ................................. 136/100
`4,051,304
`9/1977 Snook .....
`429/94
`
`
`4,709,472 * 12/1987 Machida eta.
`29/623
`
`5/1990 Catotti .............
`4,929,519 *
`429/94
`
`..
`4,963,445 * 10/1990 Marple etal.
`429/94
`
`.. 429/120
`5,034,290 *
`7/1991 Sands et al.
`6/1993 Kaun ...........
`5,219,573
`429/32
`
`2/1994 Klein .......
`5,288,564
`429/94
`
`...... 429/152
`5,300,373
`4/1994 Shackle
`
`...... 429/152
`5,498,489
`3/1996 Dasgupta
`4/1996 MacKay ............ 429/152
`5,503,948
`
`8/1996 Kagawa ............ 429/149
`5,547,780
`
`........ 429/99
`5,578,392 * 11/1996 Kawamura ..
`
`...... 429/127
`5,582,931
`12/1996 Kawakami
`..
`5/1997 Miller ..........
`5,633,097
`429/94
`
`
`5,637,416 *
`6/1997 Yoshii et al.
`429/94
`.......................... 29/6232
`5,693,105
`12/1997 Kawakami
`
`ABSTRACT
`(57)
`A battery construction is disclosed that includes a housing
`and a spiral-wound electrode assembly disposed in the
`housing and defining at least two electrochemical cells that
`are electrically connected in series. Both of the cells include
`wound layers of a positive electrode, a negative electrode,
`and a polymer electrolyte provided between the positive and
`negative electrode layers. The layers of each successive
`electrochemical cell are wound around the layers of the
`previous cell and are preferably separated therefrom by an
`insulating layer. By utilizing a polymer electrolyte, the need
`for expensive microporous separator layers is eliminated as
`is the need for providing separate sealed containers to
`construct a multi-cell battery. Thus, a less-expensive and
`space-efficient multi-cell spiral-wound electrode construc-
`tion may be obtained.
`
`24 Claims, 6 Drawing Sheets
`
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`
`JLab/Cambridge, Exh. 1010, p. 1
`
`JLab/Cambridge, Exh. 1010, p. 1
`
`

`

`US. Patent
`
`Sep. 11,2001
`
`Sheet 1 0f 6
`
`US 6,287,719 B1
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`JLab/Cambridge, Exh. 1010, p. 2
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`JLab/Cambridge, Exh. 1010, p. 2
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`

`

`US. Patent
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`Sep.11,2001
`
`SheetZ 0f6
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`US 6,287,719 B1
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`US. Patent
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`Sep.11,2001
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`Sheet3 0f6
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`US 6,287,719 B1
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`JLab/Cambridge, Exh. 1010, p. 4
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`JLab/Cambridge, Exh. 1010, p. 4
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`

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`US. Patent
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`Sep. 11,2001
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`US. Patent
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`Sep. 11,2001
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`Sheet 5 0f 6
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`US 6,287,719 B1
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`JLab/Cambridge, Exh. 1010, p. 6
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`JLab/Cambridge, Exh. 1010, p. 6
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`

`

`US. Patent
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`Sep. 11,2001
`
`Sheet 6 0f 6
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`US 6,287,719 B1
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`
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`Fig. 7
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`JLab/Cambridge, Exh. 1010, p. 7
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`JLab/Cambridge, Exh. 1010, p. 7
`
`

`

`US 6,287,719 B1
`
`1
`BATTERY INCLUDING A NON-AQUEOUS
`MULTI-CELL SPIRAL-WOUND ELECTRODE
`ASSEMBLY
`
`BACKGROUND OF THE INVENTION
`
`The present invention generally relates to batteries having
`one or more electrochemical cells. The present invention
`further generally relates to batteries including an electro-
`chemical cell having a spiral-wound electrode assembly in
`which the positive and negative electrodes of the electro-
`chemical cell are wound about a mandrel in a spiral manner.
`Batteries are known that include an electrochemical cell
`
`in which the positive and negative electrodes are wound into
`a spiral-wound electrode assembly (also known as a jelly
`roll assembly). The positive and negative electrodes in these
`types of batteries are typically constructed of elongated
`conductive foil strips made of aluminum or copper that have
`a mixture of materials including active electrochemical
`materials coated on both sides. The positive and negative
`electrodes are wound by a mandrel with layers of a separator
`material disposed between the electrode layers so as to
`prevent any physical contact between the positive and
`negative electrodes. After the spiral-wound electrode assem-
`bly has been wound about the mandrel, the spiral-wound
`electrode assembly is removed and inserted into an open end
`of a cylindrical or prismatic metal cell housing.
`Subsequently, an electrolyte is dispensed into the open end
`of the cell housing. The liquid electrolyte flows around and
`within the spiral-wound electrode assembly and is absorbed
`into the separator layers between the positive and negative
`electrodes so as to enable the transport of ions between the
`positive and negative electrodes.
`After the electrolyte has been dispensed within the cell
`housing,
`the cell housing is sealed by inserting a cover
`assembly into the open end such that the cover assembly is
`electrically connected to one of the electrodes, and crimping
`the cell housing to hold the cover assembly in place. The
`cover assembly is also preferably electrically insulated from
`the cell housing so that the cover assembly and the cell
`housing each serve as electrical contact terminals having
`opposite polarities.
`Such spiral-wound electrode-type cells are typically used
`in combination in rechargeable battery packs for video
`cameras, cellular telephones, and portable computers.
`Because battery packs of these types require high output
`voltages, the cells used typically have cell voltages at or in
`excess of 3 volts. The components used to construct these
`electrochemical cells are typically more expensive and
`require more stable electrolytes and binders, which bind the
`active electrochemical materials to the conductive electrode
`
`strips.
`A further problem with the construction of spiral-wound
`electrode-type electrochemical cells constructed as
`described above, results from the use of the microporous
`separators. Such microporous separators are one of the more
`expensive components of the electrochemical cell. Further,
`these separators typically increase the internal resistance of
`the cell and, as a consequence, may decrease the high-rate
`performance of the cell. Moreover,
`the separators them-
`selves are not electrochemically active components and
`consume space within the cell housing that could otherwise
`be filled with electrochemically active components.
`It is known in the art of alkaline batteries to construct a
`
`high-voltage battery using a plurality of lower voltage
`electrochemical cells coupled in series. For example, con-
`ventional 9-volt batteries are constructed by coupling six
`
`10
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`55
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`60
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`2
`1.5 -volt cells in series. Such multi-cell batteries are typically
`constructed using electrochemical cells that have separate
`sealed housings so as to keep the liquid electrolyte contained
`therein separate from each of the other cells. If the liquid
`electrolyte were allowed to flow freely between the cells,
`inter-cell leakage current would result. Because of the space
`that would be required within the battery housing for includ-
`ing separate sealed cells, such batteries make poor use of the
`total battery volume. As a result, low-voltage cells are poor
`candidates for high-voltage battery construction.
`
`SUMMARY OF THE INVENTION
`
`Accordingly, it is an aspect of the present invention to
`solve the above problems by providing a battery having a
`multi-cell, spiral-wound electrode-type construction that
`does not require separate sealed containers for each of the
`cells. An additional aspect of the present invention is to
`provide a battery having a spiral-wound electrode-type
`construction that does not require the use of expensive
`separators. It is yet another aspect of the present invention
`to provide a battery that
`is capable of generating cell
`voltages of 3 or more volts while enabling the use of
`less-expensive lower voltage components. A further aspect
`of the present invention is to provide a multi-cell construc-
`tion that is relatively easy to manufacture using conventional
`electrode winding equipment.
`To achieve these and other aspects and advantages, a
`battery constructed in accordance with the present invention
`comprises a housing and a spiral-wound electrode assembly
`disposed in the housing and defining at least two concentric
`electrochemical cells that are electrically connected in
`series. Each of the cells includes wound layers of a positive
`electrode, a negative electrode, and a polymer electrolyte
`provided between the positive and negative electrode layers.
`Preferably,
`the cells are electrically insulated from one
`another by providing an insulating layer that
`is wound
`between electrode layers of the cells that are otherwise
`adjacent to one another.
`By utilizing a polymer electrolyte, the electrolyte cannot
`flow between the cells and thereby create an inter-cell
`leakage current. Thus, the need for separate sealed contain-
`ers is eliminated. By eliminating the need for sealed con-
`tainers within the battery housing, the electrochemical cells
`may be disposed in the battery housing in the most space-
`efficient manner. Also, by utilizing a polymer electrolyte, the
`need for microporous separator layers is eliminated since the
`polymer electrolyte prevents physical contact between the
`positive and negative electrode layers. The term “polymer
`electrolyte” as used herein means a material which has ionic
`conductivity but is substantially physically immobile and
`hence remains positioned between the anode and cathode.
`The composition of such polymer electrolytes can range
`from a salt dissolved in a high molecular weight polymer
`with no low molecular weight plasticizer to compositions
`containing electrolyte salt, a large amount of one or more
`low molecular weight solvents, and only sufficient polymer
`to immobilize (gel) the low molecular weight solvent.
`In addition, by enabling the creation of a multi-cell,
`spiral-wound electrode assembly, higher voltage batteries
`may be constructed that utilize lower voltage cells that in
`turn may utilize less-expensive lower voltage components.
`
`These and other features, advantages, and objects of the
`present invention will be further understood and appreciated
`by those skilled in the art by reference to the following
`specification, claims, and appended drawings.
`
`JLab/Cambridge, Exh. 1010, p. 8
`
`JLab/Cambridge, Exh. 1010, p. 8
`
`

`

`US 6,287,719 B1
`
`3
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the drawings:
`FIG. 1 is a perspective view of a battery constructed in
`accordance with the present invention;
`FIG. 2 is a cross section of the battery shown in FIG. 1
`taken along the plane II—II;
`FIG. 3 is a simplified cross-sectional view of a spiral-
`wound electrode assembly constructed in accordance with
`the present invention as it would appear if taken along plane
`III—III of the battery shown in FIG. 2;
`FIG. 4 is an enlarged cross-sectional view of the portion
`of the spiral-wound electrode assembly identified as FIG. 4
`in the cross section shown in FIG. 3;
`FIG. 5 is a partially-exploded perspective view of a
`spiral-wound electrode assembly constructed in accordance
`with the present invention;
`FIG. 6 is a partially-exploded perspective view of a
`spiral-wound electrode assembly constructed in accordance
`with the present invention as viewed from a side opposite
`that shown in FIG. 5; and
`FIG. 7 is a perspective view of an unsealed prismatic
`battery constructed in accordance with the present invention.
`
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`A battery 5 constructed in accordance with the present
`invention is shown in FIGS. 1 and 2. As shown, battery 5
`includes a housing 10 having a closed end 12 and an open
`end 14. Housing 10 is preferably constructed of a structur-
`ally rigid material that is chemically inert and electrically
`conductive. Housing 10 may be cylindrical or prismatic. As
`will be described in more detail below, battery 5 includes a
`spiral-wound electrode assembly 30 disposed within hous-
`ing 10 and having at least a first electrochemical cell 50 and
`a second electrochemical cell 80 separated by an insulator
`layer 45. As also described further below, first and second
`cells 50 and 80 are constructed of wound layers of a positive
`electrode, a negative electrode, and a polymer electrolyte
`disposed between the alternating layers of positive and
`negative electrodes. After spiral-wound electrode assembly
`30 has been wound and deposited within the open end 14 of
`housing 10, a core pin 40 may optionally be inserted into the
`middle of spiral-wound electrode assembly 30 so as to
`decrease the likelihood of an internal short circuit in the
`
`event housing 10 is crushed.
`As used herein, the term “electrochemical cell” or simply
`“cell” shall refer to the basic functional unit providing a
`source of electrical energy by direct conversion of chemical
`energy which includes an assembly of electrodes and
`electrolyte/separator. As described in more detail below,
`each “cell” of the multi-cell construction does not include its
`
`own container. As also used herein, the term “battery” shall
`refer to an assembly of cells disposed in a battery housing
`that provides two external contact terminals.
`Housing 10 may then have a circumferential bead 16
`formed proximate open end 14. Bead 16 is formed to
`provide a ledge upon which a cover assembly 20 may rest
`when inserted into open end 14. Once inserted, cover
`assembly 20 may be crimped in place using any conven-
`tional technique.
`As shown in FIG. 3, spiral-wound electrode assembly 30
`includes a first cell 50 that is formed by winding a positive
`electrode 52 and a negative electrode 60 about a mandrel to
`form alternating layers of the positive and negative elec-
`
`10
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`15
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`35
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`40
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`4
`trodes that spiral outward. After first cell 50 has been wound,
`an electrical insulating layer 45 is wound about the outer
`layers of first cell 50. Subsequently, second cell 80, which
`includes alternating layers of a positive electrode 90 and a
`negative electrode 82, are wound about the mandrel over
`insulating layer 45.
`As illustrated in FIG. 4, first negative electrode layer 60
`includes a conductive foil strip 61 having a mixture coated
`on one or more of its sides 65 and 66, and second negative
`electrode 82 includes a conductive foil strip 81 having a
`mixture coated on one or more of its sides 83 and 85. The
`
`mixture coated on conductive foils 61 and 81 may include
`any electrochemically active material conventionally used
`on similar types of negative electrodes as well as any
`conventional binder and conductive agent used with such
`active materials. Positive electrodes 52 and 90 also each
`
`include an elongated strip of a conductive foil 51 and 91 that
`has a mixture coated on one or more of its sides 53 and 55,
`and 95 and 96, respectively. The mixture coated on conduc-
`tive foils 51 and 91 may include any electrochemically
`active materials conventionally used on similar types of
`positive electrodes as well as any suitable conventional
`binder and conductive agent. Preferred coatings for the
`positive and negative electrodes are described in further
`detail below following the remainder of the description of
`the physical construction of the battery of the present
`invention.
`
`As shown in FIG. 3, a leading end 54 of the metal foil of
`positive electrode 52 is left uncoated and exposed such that
`a conductive tab 56 may be welded thereto which, as shown
`in FIGS. 5 and 6, extends from one end of spiral-wound
`electrode assembly 30. Conductive tab 56 is preferably
`configured so as to be electrically coupled to an exterior
`contact terminal of cover assembly 20. Similarly, a trailing
`end 84 of the conductive foil of negative electrode 82 is also
`left exposed such that a second conductive tab 86 may be
`welded thereto. As shown in FIGS. 5 and 6, second con-
`ductive tab 86 extends from an opposite end of spiral-wound
`electrode assembly 30 so as to be electrically connected to
`closed end 12 of housing 10.
`In this manner, contact
`terminals may be provided at opposite ends of battery 5 that
`are connected to electrodes of opposite polarity within
`housing 10. Further, by providing an electrical connector
`strip 47 to electrically couple the exposed conductive foil 63
`of negative electrode 60 of first cell 50 to the exposed
`conductive foil 93 of positive electrode 90 of second cell 80,
`first and second cells 50 and 80 may be electrically coupled
`in series. In this manner, with the negative electrode 82 of
`second cell 80 coupled to a negative contact terminal of
`battery 5 through conductive tab 86 and housing 10, and
`positive electrode 90 coupled to a positive external contact
`terminal of battery 5 through conductive tab 56 and cover
`assembly 20,
`the voltage appearing between the exterior
`positive and negative terminals of battery 5 will be equal to
`the sum of the cell voltages of first cell 50 and second cell
`80.
`
`the layers of polymer
`For purposes of simplification,
`electrolyte material that are disposed between the negative
`and positive electrodes of cells 50 and 80 are not shown in
`FIG. 3. However, as best shown in FIG. 6, first cell 50 is
`constructed using first and second layers of polymer elec-
`trolyte 70 and 72 that are provided in the form of elongated
`strips that are wound about the mandrel along with positive
`and negative electrodes 52 and 60. Electrolyte layers 70 and
`72 are preferably slightly wider than positive and negative
`electrodes 52 and 60 so as to prevent any inadvertent contact
`therebetween in the event there is any misalignment of the
`
`JLab/Cambridge, Exh. 1010, p. 9
`
`JLab/Cambridge, Exh. 1010, p. 9
`
`

`

`US 6,287,719 B1
`
`5
`layers during the winding process. As shown in FIGS. 4—6,
`positive electrode 52 is preferably coated with the active
`material mixture over its entire length with the exception of
`leading end 54 (FIG. 3). Negative electrode 60 is preferably
`coated with the active material mixture over its entire length
`on both sides with the exception of one side of its trailing
`end 62. This exposed conductive foil 63 is provided to
`enable electrical contact with electrical connector strip 47. In
`a similar manner, positive electrode 90 includes an exposed
`foil portion 93 on a leading end thereof for contacting
`connector strip 47. In this manner, the conductive foil of
`negative electrode 60 of first cell 50 may be electrically
`connected to the conductive foil of positive electrode 90 of
`second cell 80. Although the use of a separate connector
`strip 47 is disclosed, it will be appreciated by those skilled
`in the art that the conductive foils of the electrodes may be
`provided in direct contact without using a separate element
`to make the series connection.
`
`As shown in FIGS. 4—6, connector strip 47 may be formed
`on or adhered to a portion of electrical insulating layer 45.
`As shown in FIGS. 4—6, insulating layer 45 having connec-
`tor strip 47 assembled thereon may be inserted between
`positive electrode layer 90 and a polymer electrolyte layer
`99 so that connector strip 47 contacts exposed region 93 of
`the foil of positive electrode 90. With a portion of connector
`strip 47 extending out beyond the leading edges of positive
`electrode 90 and a second polymer electrolyte layer 97,
`insulating layer 45 may be applied over negative electrode
`60 of first cell 50 with the portion of connector strip 47
`extending beyond the leading edges of the layers of second
`cell 80 being aligned with exposed foil region 63 of negative
`electrode 60. Preferably,
`insulating layer 45 is slightly
`longer than the circumference of first cell 50. In this manner,
`insulating layer 45 will be completely wound about the
`outermost layers of first cell 50 prior to the winding of any
`of the layers of second cell 80.
`It will be appreciated by those skilled in the art that first
`cell 50 may be wound about the mandrel prior to applying
`insulating layer 45 or any of the layers of second cell 80.
`Alternatively, insulating layer 45 may be attached to the
`trailing end of the layers of first cell 50 and to the leading
`end of second cell 80 prior to winding such that the winding
`process need not be halted until the complete spiral-wound
`electrode assembly has been wound.
`Although only two cells have been disclosed for the
`construction of spiral-wound electrode assembly 30, it will
`be appreciated by those skilled in the art that additional cells
`could be included by connecting the negative or positive
`electrodes of one cell with the positive or negative elec-
`trodes of a subsequent cell in the same manner as described
`above. It will further be appreciated that the arrangement of
`the layers within the spiral-wound electrode may also be
`varied so long as electrolyte layers are wound between each
`of the positive and negative electrode layers. Further, the
`manner by which the cells are insulated from one another
`within the spiral-wound electrode assembly and the manner
`by which the cells are electrically coupled in series may vary
`from the specific example illustrated above without depart-
`ing from the spirit and scope of the present invention.
`As noted above, the use of polymer electrolytes is attrac-
`tive because such solid or semi-solid electrolytes can elimi-
`nate the need for a microporous separator and provide a final
`product which is free from liquid electrolyte. Thus, by
`eliminating the microporous separators, the overall cost of
`the battery may be reduced. Further, the increase in internal
`resistance of the cell caused by such separators may also be
`reduced and, as a consequence, so may the resultant
`decrease in the high-rate performance of the cell.
`
`10
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`55
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`60
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`6
`Although the above battery construction has been
`described with respect
`to a cylindrical battery having a
`cylindrical housing and having a cylindrical spiral-wound
`electrode assembly disposed therein, the present invention
`may also be implemented in prismatic batteries or the like,
`such as prismatic battery 100 shown in FIG. 7. As shown in
`FIG. 7, prismatic battery 100 includes a battery housing 110
`having a plurality of flat surfaces. The spiral-wound elec-
`trode assembly 130 may be wound about a paddle-shaped
`mandrel
`to more efficiently fit within the shape of the
`prismatic battery housing 110. Thus, with this construction,
`the spiral-wound electrode assembly would have a non-
`cylindrical shape.
`The above multi-cell battery construction may be used to
`construct both primary and secondary (rechargeable) batter-
`ies utilizing any electrochemical system for which polymer
`electrolytes are suitable. Examples of types of electrochemi-
`cal systems with which this invention may be used include
`alkaline manganese dioxide, nickel cadmium, nickel metal
`hydride and Zinc air systems having aqueous electrolytes,
`and lithium and lithium ion types with nonaqueous electro-
`lytes. Lithium batteries are preferred primary batteries, in
`which lithium and alloys thereof are preferred negative
`electrode active materials and MnOz, FeSz, (C2F)n, (CF2)n,
`CuS and CuS2 are preferred positive electrode active mate-
`rials. Lithium ion batteries are preferred secondary batteries,
`in which lithium-intercalable/intercalated materials are used
`as negative and positive electrode materials. Preferred mate-
`rials for the negative electrode are carbonaceous materials
`such as graphite, amorphous carbon and mesophase carbon,
`transition metal oxides and sulfides, and amorphous metal
`oxides containing silicon and/or tin. Preferred materials for
`the positive electrode are lithiated metal oxides, especially
`those containing cobalt, nickel or manganese. Examples
`include LiCoO2 and LiMn204. Electrolyte salts typically
`used for lithium and lithium ion cells include LiPFG, LiAsFG,
`LiBF4, LiClO4, LiCF3SO3, Li(CF3SOz)2N and Lil. Pre-
`ferred electrolyte solvents are nonaqueous solvents in which
`the electrolyte salt is soluble and which also serve as a
`plasticizer for the polymer electrolyte separator, as disclosed
`below.
`
`Electrodes for use in this invention may be made by any
`known method suitable for producing electrodes which may
`be spirally wound into an electrode assembly. Such methods
`include coating, laminating or impregnating a flexible, elec-
`trically conductive substrate, such as a metal foil, screen or
`foam, a perforated metal sheet, or an expanded metal sheet,
`with active electrode material. Rollcoating a slurry of active
`material and binder onto a thin metal foil is a preferred
`method of making electrodes for lithium and lithium ion
`cells. For both primary and rechargeable cells, the foil on
`which the negative electrode is formed is preferably made of
`copper, and the foil for the positive electrode is preferably
`made of aluminum. In some cell constructions, one of the
`negative or positive electrode may be formed without uti-
`lizing a conductive foil.
`In such an event, the connector strip 47 would directly
`contact the active material of such an electrode.
`
`Suitable polymer electrolyte materials are disclosed in
`US. Pat. No. 5,409,786. The preferred polymer electrolyte
`materials are discussed below.
`
`There are several important considerations in the manu-
`facture of polymer electrolyte cells. These include (1)
`obtaining suitable positive electrode packing, (2) providing
`an electrolyte/separator which has suitable ionic conductiv-
`ity but is mechanically stable, and (3) avoiding the safety
`
`JLab/Cambridge, Exh. 1010, p. 10
`
`JLab/Cambridge, Exh. 1010, p. 10
`
`

`

`US 6,287,719 B1
`
`7
`problems associated with assembling live high area cells
`without a prior continuity check for shorts.
`With respect
`to packing positive electrodes, common
`methods of preparing such polymer electrolyte cell positive
`electrodes include casting a mixture of the positive electrode
`active material, electronic conductor (for example carbon
`black, graphite, metal powder, or similar material), and the
`polymer electrolyte in a volatile solvent. This mixture can be
`applied to a suitable metallic carrier and dried by removal of
`the volatile solvent.
`
`Although a positive electrode of suitably high packing
`can,
`in principle, be prepared this way,
`in practice,
`the
`integrity of the positive electrode is often low due to the
`formation of “mud cracks” as the solvent evaporates.
`Further,
`the recovery of large volumes of toxic and/or
`flammable solvent may be required. Aprocess which avoids
`the “mud cracking” and solvent problems is to prepare a
`mixture of the polymer electrolyte monomers, the electro-
`lyte salt, the polymer plasticizers, the electric conductor, and
`the positive electrode active material. This mixture can be
`applied to a metallic carrier by extrusion or other methods
`capable of converting a highly viscous paste into a thin,
`positive electrode film. Once the paste has been applied to
`the carrier, it can be polymerized in place by heating using
`an electron beam or similar high energy radiation. However,
`positive electrodes produced by this method require high
`levels of electrolyte in order to keep the paste viscosity low
`enough to process. For this reason, the packing of positive
`electrode active material is usually limited to 40 percent by
`volume or lower. Packing of 55 percent or higher is desirable
`for a higher energy density cell.
`These positive electrode problems can be avoided by the
`use of a modified version of a roll coating process currently
`used to produce the positive electrode of AA-sized Li/FeS2
`cells. In this process, a mixture of a polymer binder, for
`example, polypropylene, polyethylene-polypropylene
`copolymer, polyethylene oxide, etc., the positive electrode
`active material, an electronic conductor, and a volatile
`solvent (to reduce the viscosity of the mixture) is prepared.
`This mixture is roll coated onto aluminum foil, dried to
`remove the volatile solvent, then rolled to produce a smooth
`uniform electrode. The positive electrodes made with this
`process have active material volumes of 55 percent or more
`and are suitable for the manufacture of high energy density
`cells. It has been found that positive electrodes suitable for
`a high energy density polymer electrolyte cell can be made
`by preparing the above positive electrode mixture but sub-
`stituting a combination of electrolyte polymers and mono-
`mers for the binder, substituting a suitable polymer electro-
`lyte plasticizer for at
`least
`the majority of the volatile
`solvent, and finally, including a thermal initiator so that the
`monomers can be polymerized during the heating step.
`Suitable monomers include polyethylene glycol acrylates,
`diacrylates, and triacrylates which contain 8—10 polyethyl-
`ene glycol units. An example of a suitable thermal polymer-
`ization initiator is 2,2'-azobisisobutyronitrile. Plasticizers
`which are chemically compatible with the lithium system
`include the solvents which are commonly used to prepare
`lithium and lithium ion battery liquid electrolytes. For
`example, any one or a combination of diglyme (diethylene
`glycol dimethyl ether), tetraglyme (tetraethylene glycol dim-
`ethyl ether), ethylene carbonate, dimethyl carbonate, diethyl
`carbonate, dimethoxyethane, methylethyl carbonate, propy-
`lene carbonate and the like may be used. The electrolyte salt
`may be included in the roll coating mixture, but is preferably
`omitted and introduced into the cell after assembly in order
`to prevent cell activation immediately upon combining the
`negative electrode, positive electrode and polymer
`electrolyte/separator layer.
`Another important consideration in producing a polymer
`electrolyte cell, is applying the polymer electrolyte layer
`
`10
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`15
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`20
`
`25
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`30
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`35
`
`40
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`45
`
`50
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`55
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`60
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`65
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`8
`between the negative and positive electrode layers. The
`polymer electrolyte layer must have both sufficient ionic
`conductivity to enable the cell to function at high rates yet
`have mechanical properties so that the negative and positive
`electrode layers remain physically and electrically sepa-
`rated. Electrolytes which have high ionic conductivity often
`contain 50 volume percent or more plasticizer (solvent) and
`have the physical properties more like a gel than a plastic
`film. At
`the other extreme, polymer films with reduced
`plasticizer levels and good physical properties generally
`have ionic conductivities 2—3 orders of magnitude below
`that of organic liquid electrolytes and the highly-plasticized
`polymer electrolytes.
`Polymer electrolyte cells may be made by manufacturing
`a positive electrode as described above and mating it to the
`negative electrode with a polymer electrolyte layer therebe-
`tween. The cell is then instantly activated as it is assembled.
`Any flaws in the components or malfunction of the cell
`assembling machinery may result in an electrical short. The
`shorted cell will heat rapidly and may catch fire.
`Both the mechanical properties of the electrolyte and the
`safety problem associated with assembling a live cell may be
`avoided by omitting the majority of the electrolyte plasti-
`cizer and preferably all the electrolyte salt from the polymer
`electrolyte/separator layer. Without
`the high volume of
`plasticizer, the electrolyte will have properties more like a
`plastic film than a gel. Further, without the electrolyte salt,
`this film will have substantially no ionic