(12) United States Patent
`US 6,443,999 B1
`(10) Patent N0.:
`Cantave et al.
`
`@5)l)ate(n’Patent: Sep.3,2002
`
`US006443999B1
`
`(54)
`
`(75)
`
`LITHIUM CELL WITH HEAT FORMED
`SEPARATOR
`
`Inventors: Reynald A. Cantave, Bridgewater;
`Fred J. Berkowitz, Hudson; William
`T. McHugh, Westwood; Jane A. Blasi,
`Acton; Ernesto Figueira, Brighton, all
`of MA (US)
`
`(73)
`
`Assignee: The Gillette Company, Boston, MA
`(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)
`
`(22)
`
`(51)
`(52)
`(58)
`
`(56)
`
`Appl. No.: 09/527,508
`
`Filed:
`
`Mar. 16, 2000
`
`Int. Cl.7 ................................................. H01M 2/18
`US. Cl.
`....................... 29/623.1; 429/133; 429/247
`Field of Search ............................... 429/52—56, 94,
`429/247, 129, 131, 140, 133; 29/6231
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`7/1981 Moses
`4,279,972 A
`1/1986 Matsuo ...................... 29/6234
`4,565,002 A *
`1/1986 Goebel
`........................ 429/94
`4,565,753 A *
`11/1987 McVeigh
`4,707,421 A
`5/1990 Yoshinaka ................... 429/54
`4,929,518 A *
`6/1990 Moses
`4,937,154 A
`5,458,993 A * 10/1995 Terao .......................... 429/94
`
`5,595,835 A *
`1/1997 Miyamoto ..
`....... 429/56
`5,714,278 A *
`2/1998 Mallinson ................... 429/126
`5,776,629 A
`7/1998 Degan
`
`FOREIGN PATENT DOCUMENTS
`
`JP
`JP
`JP
`JP
`JP
`
`01—122574 A
`01—307176 A
`63—136383
`03—025865 A
`11096982
`
`5/1989
`12/1989
`* 12/1989
`2/1991
`4/1999
`
`*
`
`.......... H01M/10/40
`
`............ H01M/2/08
`
`* cited by examiner
`
`Primary Examiner—Patrick Ryan
`Assistant Examiner—Mark Ruthkosky
`(74) Attorney, Agent, or Firm—Barry D. Josephs; Paul I.
`Douglas; Thomas G. Krivulka
`
`(57)
`
`ABSTRACT
`
`A primary lithium cell having a wound electrode assembly.
`The electrode assembly comprises an anode comprising
`lithium, a cathode comprising a manganese dioxide and an
`electrolyte permeable separator therebetween. The electrode
`assembly comprises a cathode sheet, an anode sheet and
`electrolyte permeable separator sheet
`therebetween. The
`sheets are wound into a spiral roll. An exposed edge of each
`revolution of the separator sheet is then heat treated, for
`example, by applying a heated platen thereto to mold said
`exposed edge into a continuous separator membrane. The
`continuous separator membrane, so formed, covers and seals
`off said edge of adjacent revolutions of the cathode sheet and
`thus provides electrical insulation therefor. The electrode
`assembly can then be inserted into the cell casing so that the
`continuous separator membrane abuts a surface of the casing
`and provides electrical insulation between the casing and the
`wound cathode sheet. This reduces the total amount of
`
`electrical insulation needed between the cell casing and
`wound electrodes and thereby frees up void volume which
`can be used for additional active material, for example, by
`making the anode and cathode sheets wider.
`
`4 Claims, 7 Drawing Sheets
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`10\
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`35
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`JLab/Cambridge, Exh. 1016, p. 1
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`JLab/Cambridge, Exh. 1016, p. 1
`
`

`

`US. Patent
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`Sep. 3, 2002
`
`Sheet 1 0f 7
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`US 6,443,999 B1
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`FIG. 1
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`JLab/Cambridge, Exh. 1016, p. 2
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`JLab/Cambridge, Exh. 1016, p. 2
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`

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`US. Patent
`
`Sep.3,2002
`
`SheetZ 0f7
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`JLab/Cambridge, Exh. 1016, p. 3
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`

`

`US. Patent
`
`Sep.3,2002
`
`Sheet3 0f7
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`US 6,443,999 B1
`
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`

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`
`Sep. 3, 2002
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`Sheet 4 0f 7
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`JLab/Cambridge, Exh. 1016, p. 5
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`

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`US. Patent
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`Sep. 3, 2002
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`Sheet 5 0f 7
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`US 6,443,999 B1
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`
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`JLab/Cambridge, Exh. 1016, p. 6
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`JLab/Cambridge, Exh. 1016, p. 6
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`

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`US. Patent
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`Sep. 3, 2002
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`Sheet 6 0f 7
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`US 6,443,999 B1
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`FIG. 4
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`JLab/Cambridge, Exh. 1016, p. 7
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`JLab/Cambridge, Exh. 1016, p. 7
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`

`

`US. Patent
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`Sep.3,2002
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`Sheet7 0f7
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`US 6,443,999 B1
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`

`

`US 6,443,999 B1
`
`1
`LITHIUM CELL WITH HEAT FORMED
`SEPARATOR
`
`FIELD OF THE INVENTION
`
`The invention relates to spirally wound lithium cells
`having an anode comprising lithium and a cathode compris-
`ing a manganese dioxide with a separator therebetween.
`
`BACKGROUND
`
`Primary (non-rechargeable) electrochemical cells having
`an anode comprising lithium are known and are in wide-
`spread commercial use. The anode is comprised essentially
`of lithium metal. Such cells typically have a cathode com-
`prising manganese dioxide, and electrolyte comprising a
`lithium salt such as lithium trifluoromethane sulfonate
`
`(LiCF3SO3) dissolved in a nonaqueous solvent. The cells are
`referenced in the art as primary lithium cells (primary
`Li/MnO2 cells) and are generally not
`intended to be
`rechargeable. Alternative primary lithium cells with lithium
`metal anodes but having different cathodes are also known.
`Such cells, for example, have cathodes comprising iron
`disulfide (FeSz). These cells are commonly in the form of
`button cells or cylindrical cells having about 2/3 the height of
`a conventional AA size alkaline cell. (Alkaline cells as
`referenced herein shall be understood to be conventional
`
`commercial alkaline cells having an anode comprising zinc,
`a cathode comprising manganese dioxide, and an electrolyte
`comprising potassium hydroxide.) The Li/MnO2 cells have
`a voltage of about 3.0 volts which is twice that of conven-
`tional Zn/MnO2 alkaline cells and also have higher energy
`density (watt-hrs per cm3 of cell volume) than that of
`alkaline cells. Primary lithium cells are in widespread use as
`a power source for many conventional photographic flash
`cameras, which require operation at higher voltage and at
`higher power than is supplied by individual alkaline cells.
`Primary lithium cells (other than button cells) are con-
`ventionally formed of an electrode composite comprising an
`anode formed of a sheet of lithium, a cathode formed of a
`coating of cathode active material comprising manganese
`dioxide on a conductive metal substrate (cathode substrate)
`and a sheet of electrolyte permeable separator material
`therebetween. The separator sheet is typically placed on
`opposite sides of the lithium anode sheet and the cathode
`sheet is placed against one of the separator sheets, thereby
`separating the anode and the cathode sheets. The electrode
`composite is spirally wound and inserted into the cell casing,
`for examples, as shown in US. Pat. No. 4,707,421. The
`cathode substrate is typically a stainless steel expanded
`metal foil. A portion of the anode sheet is typically electri-
`cally connected to the cell casing which forms the cell’s
`negative terminal. The cell is closed with an end cap which
`is insulated from the casing. The cathode sheet can be
`electrically connected to the end cap which forms the cell’s
`positive terminal. The casing is typically crimped over the
`peripheral edge of the end cap to seal the casing’s open end.
`The primary lithium cell is typically provided with PTC
`(positive thermal coefficient) device located under the end
`cap and connected in series between the cathode and end
`cap. Such device protects the cell from discharge at a current
`drain higher than a predetermined level. Thus, if the cell is
`drained at an abnormally high current, e.g., higher than
`about 2 Amp, the PTC device expands and heats causing its
`resistance to increase dramatically, thus shutting down the
`abnormally high drain.
`The primary lithium cell is a nonaqueous cell. The man-
`ganese dioxide powder used to form the cathode active
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`material can be conventionally heat treated at temperatures
`of between about 200—350 ° C. in vacuum as taught in US.
`Pat. No. 4,133,856 (Ikeda). It is preferable to heat the MnOz,
`for example, electrolytic MnO2 (EMD) in two steps once to
`temperatures above 250 ° C.
`to drive off non-crystalline
`water during which step gamma MnO2 is gradually con-
`verted to gamma-beta structure. The heated MnO2 can then
`be heated at higher temperatures between 250 and 350 ° C.
`as described in US. Pat. No. 4,133,856 prior to insertion of
`the MnO2 into the cell. The treatment results in better cell
`performance and higher capacity. The second heating helps
`to prevent electrolyte leakage. The treated MnO2 is mixed
`with suitable binders,
`for example,
`tetrafluoroethylene
`(Teflon) binders, and conductive agents, for example, carbon
`black and graphite. The cathode mixture can be coated onto
`a metallic substrate such as a stainless steel expanded metal
`foil.
`
`The anode can be formed by coating a layer of lithium on
`a metallic substrate such as copper. However, it is preferable
`that the anode is formed of a sheet of lithium without any
`substrate.
`
`The electrolyte used in a primary lithium cell is formed of
`a lithium salt dissolved in an organic solvent. Typically, the
`salt
`is lithium perchlorate (LiClO4) or
`lithium trifluo-
`romethanesulfonate (LiCF3SO3). Other salts which are con-
`ventionally used include LiPFG, LiAsF6 and LiCF3CO2 and
`LiBF4. Organic solvents can typically include ethylene
`carbonate/propylene carbonate (EC/PC) dimethoxyethane
`(DME), dioxolane, gamma-butyrolactone, and diglyme.
`Recently electronic devices, such as digital cameras, fully
`featured photographic flash cameras, as well as some high
`power toys and electronic games have appeared in the
`commercial market. These devices, require sustained load
`voltages of at the level of between about 2.5 and 3 Volt and
`demand high power which can be satisfied with the use of
`primary lithium cells. Although present commercial primary
`lithium cells can be used to power many of these devices, it
`is desirable to increase the cell’s capacity where possible in
`order to make the lithium cell even more attractive for such
`
`application.
`It
`is desirable to increase the lithium cell’s capacity
`(mAmp-hr) for a given cell size, where technically and
`economically feasible provided that there is no significant
`sacrifice in the cell’s power output.
`SUMMARY OF THE INVENTION
`
`The invention is directed to improvements in spirally
`wound primary lithium cells to increase the electrochemical
`capacity (mAmp-hr) of a cell of any given size and shape
`without changing the basic cell chemistry or thickness of the
`individual sheets comprising the spirally wound electrode
`assembly therein. The spirally wound electrode assembly
`within the cell casing is formed by spirally winding an
`electrode composite comprising an anode sheet of lithium, a
`cathode sheet comprising a manganese dioxide and a sepa-
`rator of electrolyte permeable material therebetween. The
`manganese dioxide can include any form of manganese
`dioxide useful as cathode active material in primary lithium
`cells, for example, manganese dioxide, heat treated electro-
`lytic manganese dioxide (EMD) and lithiated manganese
`dioxide. The cell casing, typically a cylindrical metal casing,
`has an open end and a closed end. After the electrode
`composite is spirally wound it is inserted into the open end
`of the metal casing until it comes to rest against the casing
`closed end. Electrolyte can then be added.
`A principal aspect of the invention is directed to forming
`improved electrical insulation around the spiral electrode
`
`JLab/Cambridge, Exh. 1016, p. 9
`
`JLab/Cambridge, Exh. 1016, p. 9
`
`

`

`US 6,443,999 B1
`
`3
`assembly of a primary lithium cell. The improved insulation
`is accomplished by reshaping an edge of the separator layer,
`as by heat forming, and using said reshaped portion of the
`separator layer to also function as a continuous electrical
`insulation layer between the positive cathode sheet and the
`cell casing, particularly at the closed end of the casing.
`An aspect of the invention involves first forming a spirally
`wound electrode assembly with the bottom edge of the
`wound separator sheet extending beyond the bottom edge of
`the wound anode and cathode sheets thereby exposing the
`bottom edge of the wound separator sheet. At this stage of
`formation, the bottom edge of the separator sheet is aligned
`parallel to the bottom edge of the cathode sheet and therefore
`there are gaps between each revolution of the bottom edge
`of the separator sheet and the bottom edge of the cathode
`sheet. (The term “bottom edge”, as used herein, is defined as
`that edge of the spiral electrode assembly which abuts the
`casing closed end when the spiral electrode assembly is
`inserted into the casing.)
`In accordance with a principal aspect of the invention a
`heat source, preferably a heated platen, can be applied to the
`exposed bottom edge of the separator sheet extending from
`the bottom of the spirally wound electrode assembly. The
`separator sheet
`is electrolyte permeable and heat
`deformable, preferably of thermoplastic material. A desir-
`able electrolyte permeable sheet having such properties is
`microporous polypropylene. Alternatively, the separator can
`be of microporous polyethylene or laminates of polyethyl-
`ene and polypropylene. The exposed bottom edge of sepa-
`rator softens or melts upon contact with the heat source
`thereby reshaping the edge by thermoforming. When the
`heat source is removed, the bottom edge of the separator
`sheet, upon cooling, solidifies into a continuous
`(thermoformed) separator membrane which covers the
`exposed bottom edge of the cathode sheet. Thus, when the
`electrode assembly is inserted into the cell casing the
`continuous (thermoformed) separator membrane forms a
`continuous electrical insulation layer between the bottom
`edge of the cathode sheet and the inside surface of the closed
`end of the casing.
`Since the continuous separator membrane also lies flush
`against the bottom edge of the cathode sheet, void space
`normally present between the bottom of the spirally wound
`electrode assembly and the closed end of the casing is
`eliminated.
`(The term “void space” as used herein is
`intended to mean space not occupied with electrochemically
`active anode or cathode material.) Also the formation of
`such a continuous separator membrane covering and elec-
`trically insulating the bottom edge of the cathode sheet
`makes it possible to eliminate the electrical insulating disk
`which is normally inserted between the bottom edge of the
`electrode assembly and the inside surface of the closed end
`of the casing. The space saved by eliminating such void
`volume can now be utilized by increasing the amount of
`anode and cathode active material in the cell, for example,
`by making the electrode sheets wider thereby increasing cell
`capacity.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The invention will be better understood with reference to
`
`the drawings in which:
`FIG. 1 is an isometric view of an embodiment of the cell
`of the invention.
`
`FIG. 2A is a partial cross sectional elevation view of the
`cell taken through sight lines 2—2 of FIG. 1 to show the top
`and interior portion of the cell.
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`FIG. 2B is a partial cross sectional elevation view of the
`cell taken through sight lines 2—2 of FIG. 1 to show a
`spirally wound electrode assembly wherein the bottom edge
`of the separator has not been heat treated.
`FIG. 2C is a partial cross sectional elevation view of the
`cell taken through sight lines 2—2 of FIG. 1 to show a
`spirally wound electrode assembly wherein the bottom edge
`of the separator has been reshaped (thermoformed) by the
`heat treatment process of the invention.
`FIG. 3 is a cross sectional view (taken perpendicular to
`the cell’s longitudinal axis) of the spiral electrode assembly.
`FIG. 4 is a schematic showing the placement of the layers
`comprising the electrode assembly.
`FIG. 5 is a plan view of the electrode assembly of FIG. 4
`with each of the layers thereof partially peeled away to show
`the underlying layer.
`FIG. 6 is a schematic view showing a heated platen used
`to reshape (thermoform) the bottom edge of the separator
`sheet within the spirally wound electrode assembly.
`DETAILED DESCRIPTION
`
`Specific embodiments of a primary (non rechargeable)
`cell having an anode comprising lithium and a cathode
`comprising a manganese dioxide are shown in the Figures.
`A preferred embodiment of the invention is shown in FIG.
`2C. The term “manganese dioxide” as used herein is
`intended to include all forms of manganese dioxide, for
`example, electrolytic manganese dioxide (EMD), heat
`treated manganese dioxide, and lithiated manganese dioxide
`used as cathode active material in primary lithium cell. The
`electrodes are in spiral configuration. The cell is preferably
`cylindrical. Although the invention is described with respect
`to a cylindrical cell,
`this is intended as a nonlimiting
`example, since other cell shapes, for example, prismatic
`cells, are possible. The invention is also not intended to be
`limited to cell size. For example, the invention is specifically
`applicable to conventional 2/3 A size cells (2/3 the height of an
`A cell) typically employed with spirally wound primary
`lithium cells. The invention, however, is also applicable to
`conventional AAAA, AAA, AA, C and D size cells.
`The preferred shape of the cell casing (housing) 20 is
`cylindrical as shown in FIG. 1. Casing 20 is preferably
`formed of nickel plated steel. The cell casing 20 (FIG. 1) has
`a continuous cylindrical surface 20. The spiral wound elec-
`trode assembly 70 (FIG. 3) comprising anode 40 and cath-
`ode composite 62 with separator 50 therebetween can be
`prepared by spirally winding a flat electrode composite 13.
`The electrode composite 13 (FIGS. 4 and 5) can be made in
`the following manner: A cathode mixture 60 comprising
`manganese dioxide can be prepared and coated onto a
`substrate sheet 65 of stainless steel expanded metal foil to
`form a cathode composite sheet 62 (FIG. 4). The cathode
`coating 60 can be prepared have the following desirable
`formulation: manganese dioxide (electrolytic manganese
`dioxide, EMD), 90.9 wt.%,
`tetrafluoroethylene (Teflon
`polymer), 3.0 wt.%, Shawinigan carbon black, 4.1 wt. %,
`and particulate graphite, 2.0 wt.%. The manganese dioxide
`was heat treated in conventional manner to remove non-
`
`crystalline water therefrom before the cathode coating 60
`was prepared. The cathode mixture can be mixed in a
`conventional electric blender at room temperature until a
`homogeneous mixture is obtained. The cathode mixture 60
`can be coated on one side of a cathode substrate 65 to form
`
`cathode composite sheet 62. The cathode substrate 65 is
`preferably a stainless steel expanded metal foil (EXMET
`stainless steel foil from Exmet Company) having a basis
`
`JLab/Cambridge, Exh. 1016, p. 10
`
`JLab/Cambridge, Exh. 1016, p. 10
`
`

`

`US 6,443,999 B1
`
`5
`
`weight of about 0.024 g/cm2. It appears as a porous mesh or
`screen. Alternatively,
`the cathode substrate 65 can be a
`stainless steel foil. The cathode coating 60 on the substrate
`65 desirably has a thickness of between about 0.38 and 0.42
`mm, preferably about 0.4 mm. The stainless steel substrate
`65 secures the cathode coating 60 and functions as a cathode
`current collector during cell discharge. The composite sheet
`62 can desirably have a thickness of about 0.4 mm.
`The anode 40 can be prepared from a solid sheet of
`lithium metal. The anode 40 is desirably formed of a
`continuous sheet of lithium metal
`(99.8 % pure).
`Alternatively, the anode 40 can be an alloy of lithium and an
`alloy metal, for example, an alloy of lithium and aluminum.
`In such case the alloy metal,
`is present
`in very small
`quantity, preferably less than 1 percent by weight of the
`lithium alloy. Upon cell discharge the lithium in the alloy
`thus functions electrochemically as pure lithium. Thus, the
`term “lithium or lithium metal” as used herein and in the
`claims is intended to include such lithium alloy. The lithium
`sheet forming anode 40 does not require a substrate. The
`lithium anode 40 can be advantageously formed from an
`extruded sheet of lithium metal having a thickness of
`desirably between about 0.15 and 0.20 mm desirably
`between about 0.16 and 0.17 mm, preferably about 0.165
`mm.
`
`Individual sheets of electrolyte permeable separator mate-
`rial 50, preferably of microporous polypropylene having a
`thickness of about 0.025 mm is inserted on each side of the
`
`lithium anode sheet 40 (FIGS. 4 and 5). The first (top)
`separator sheet 50 (FIG. 4) can be designated the outer
`separator sheet and the second sheet (FIG. 4) can be desig-
`nated the inner separator sheet. The cathode composite sheet
`62 comprising cathode coating 60 on conductive substrate
`65 is then placed against the inner separator sheet 50 to form
`the flat electrode composite 13 shown in FIG. 4. The flat
`composite 13 (FIG. 4) is spirally wound to form electrode
`spiral assembly 70 (FIG. 3). The winding can be accom-
`plished using a mandrel to grip an extended separator edge
`50b of electrode composite 13 and then spirally winding
`composite 13 to form wound electrode assembly 70. When
`the winding is completed separator portion 50b appears
`within the core 98 of the wound electrode assembly 70
`(FIGS. 2A and 2B). As may be seen from FIG. 3 the
`electrode spiral 70 has separator material 50 between anode
`sheet 40 and cathode composite 62. The spirally wound
`electrode assembly 70 has a configuration (FIG. 3) conform-
`ing to the shape of the casing body. The spirally wound
`electrode assembly 70 is inserted into the open end 30 of
`casing 20. As wound, the outer layer of the electrode spiral
`70 comprises separator material 50 shown in the figures. An
`additional insulating layer 72, for example, a plastic film
`such as polyester tape, can desirably be placed over the outer
`separator layer 50, before the electrode composite 13 is
`wound. In such case the spirally wound electrode 70 will
`have insulating layer 72 in contact with the inside surface of
`casing 20 (FIG. 2A and 2B) when the wound electrode
`composite is inserted into the casing. Alternatively,
`the
`inside surface of the casing 20 can be coated with electri-
`cally insulating material 72 before the wound electrode
`spiral 70 is inserted into the casing. Also an electrical
`insulating material 74 (FIG. 2B), for example in the form of
`an insulating disk 74 can be inserted into casing 20 to line
`the bottom (closed end 35) of the casing before the spirally
`wound electrode composite 70 is inserted into the casing.
`Insulating material 74 can be employed to prevent cathode
`material from inadvertently contacting the casing bottom 35
`and thus provides additional assurance that the cell will not
`short.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`Electrolyte can be added to the wound electrode spiral 70
`after it is inserted into the cell casing 20. The electrolyte
`desirably has the following composition: Lithium salts of
`lithium trifiuoromethanesulfonate (LiCF3SO3), 9.3 wt.%,
`LiNO3, 500 ppm, solvents ethylene carbonate/propylene
`carbonate (EC/PC) 34.5 wt.%, dimethoxyethane (DME),
`56.2 wt.%.
`
`An end cap 18 forming the cell’s positive terminal has a
`metal tab 25 (cathode tab) which can be welded on one of
`its sides to inside surface of end cap 18. Metal tab 25 is
`preferably of stainless steel. A portion of the cathode sub-
`strate 65 is flared along its top edge forming a an extended
`portion 64 extending from the top of the wound spiral as
`shown in FIG. 2A and 5. The flared cathode substrate portion
`64 can be welded to the exposed side of metal tab 25 before
`the casing peripheral edge 22 is crimped around the end cap
`18 to close the cell’s open end 30. Alternatively, the end cap
`18 can be welded along its peripheral edge to the inside
`surface of the casing peripheral edge 22. In such case the
`terminal 17 is desirably an integral part of end cap 18.
`Alternatively, terminal 17 can be formed as the top of an end
`cap assembly of the type described in US. Pat. No. 5,879,
`832 which assembly can be inserted into an opening in the
`surface of end cap 18 and then welded thereto.
`A metal tab 44 (anode tab), preferably of nickel can be
`pressed into a portion of the lithium metal anode 40. Anode
`tab 44 can be pressed into the lithium metal at any point
`within the spiral, for example,
`it can be pressed into the
`lithium metal at the outermost layer of the spiral as shown
`in FIG. 2B. Anode tab 44 can be embossed on one side
`
`forming a plurality of raised portions on the side of the tab
`to be pressed into the lithium. The opposite side of tab 44
`can be welded to the inside surface of the casing either to the
`inside surface of the casing side wall 24 as illustrated in FIG.
`2B. It is even more desirable to weld the anode tab 44 to the
`
`inside surface of close end 35 of casing 20. It is preferable
`to weld anode tab 44 to the inside surface of the casing
`closed end 35, since this is readily accomplished by inserting
`an electrical spot welding probe (an elongated resistance
`welding electrode) into the cell core 98. If an insulator disk
`74 is used at the bottom of casing 20 then such insulator can
`be provided with a central aperture 75 (FIG. 2B). The anode
`tab 44 can be located so that it lies under aperture 75. Thus,
`as the spot welding probe (not shown) is inserted into core
`98 its tip passes through aperture 75 and contacts the portion
`of anode tab 44 underlying the aperture. The spot welding
`probe can then be activated in order to securely weld tab 74
`to the inside surface of the casing closed end 35 of the
`casing. Alternatively, anode tab 44 can be spot welded to the
`inside surface of the casing side wall 24. In practice it has
`been determined to be more convenient to weld anode tab 44
`
`to the inside of the casing closed end 35 as above described
`since core 98 provides a convenient entry for an electrical
`welding probe. However, one difficulty encountered with
`inserting the welding probe into the cell core passage 98 is
`that there is normally a piece 50b of separator 50 located
`within the center of core 98 and vertically aligned within
`core 98 as shown in FIG. 2B. This is because the electrode
`
`spiral 70 is typically formed by employing a wrapping
`mandrel (as above describe) which conveniently grips onto
`an exposed starter edge 50b of separator 50 in order to wind
`electrode composite 13. When the electrode spiral 70 is
`formed and the mandrel is removed from the spiral the
`starter edge 50b is left behind and appears within the center
`axis of core 98. This can interfere with the insertion of the
`
`spot welding probe into core 98. Thus the starter edge 50b
`of the separator can be an obstacle towards obtaining the
`
`JLab/Cambridge, Exh. 1016, p. 11
`
`JLab/Cambridge, Exh. 1016, p. 11
`
`

`

`US 6,443,999 B1
`
`7
`desired welding of anode tab 44 to the inside surface of the
`casing closed end 35.
`The electrode spiral 70 can be formed so that the cathode
`bottom edge 60a extends beyond the anode bottom edge
`40a. Such configuration assures that essentially all of the
`anode active material is depleted during cell discharge. In
`order to accomplish this the cathode active material is in
`excess. This is conveniently accomplished by forming the
`cathode sheet 60 so that the cathode edge 60a extends below
`anode edge 40a. In the embodiment of the spirally wound
`electrode assembly 70 shown in FIG. 2B the bottom edge
`50a of each revolution of separator sheet 50 extends beyond
`the bottom edge 60a of cathode sheet 60. This provides a
`measure of electrical insulation between the bottom edge
`60a of the cathode sheet (positive) and the casing 20
`(negative). Also, in the embodiment shown in FIG. 2B it has
`been determined desirable to include a separate electrically
`insulating disk 74 against the inside surface of the casing
`closed end 35 to provide additional protection against the
`possibility that any portion of the cathode sheet 60 could
`contact the casing 20. In particular insulating disk 74 pro-
`tects against the possibility of such contact within the casing
`inside corner 23 at closed end 35.
`
`The extension of bottom edge 50a of the separator sheet
`beyond the bottom edge 60a of the cathode sheet and
`inclusion of insulator disk 74 therefore protect against
`possible electrical shorting of the cell in the region of the
`casing closed end 35. However, such design has the disad-
`vantage in that it creates void space, that is, uses up space
`which could otherwise be used to increase the total amount
`of anode and cathode active material in the cell.
`
`In accordance with the present invention a way has been
`found to increase the cell capacity of spirally wound primary
`lithium cells without changing the basic cell chemistry and
`electrode thickness. Specifically, it has been determined that
`an improved structural design for the separator bottom edge
`50a provides the required electrical
`insulation and also
`results in an increase in cell capacity. The electrode com-
`posite 13 can be made as above described and then spirally
`wound to form spiral electrode assembly 70 in the manner
`above described. However, before the spiral electrode
`assembly 70 is inserted into the casing 20, a heated platen
`can be applied to the exposed bottom edge 50a of separator
`50 in order to heat form or mold (thermoform) the edge 50a
`into a flat continuous membrane 55 which covers and lies
`
`flush against the cathode sheet bottom edge 60a.
`In such heat forming the bottom edge 50a of each
`revolution of separator 50 is reshaped so that it forms a
`continuous membrane 55 which forms about a 90 degree
`angle with the separator body 50C as shown in FIG. 2C. That
`is, the heat forming reshapes the bottom edges 50a of the
`separator sheets 50 into a continuous flat membrane 55
`which covers cathode bottom edge 60a and is aligned
`parallel to the casing closed end 35 as shown best in FIG.
`2C. The membrane 55 could be formed with one or more
`
`opening therein if desired, but a continuous membrane
`without openings is preferred. The heat
`forming
`(thermoforming) can be accomplished by applying a heat
`source, preferably a heated platen or die 110 (FIG. 6) to the
`bottom edges 50a of each revolution of the separator 50 after
`the spiral electrode assembly 70 has been formed. Platen 110
`may of metal, for example, steel or other heat conductive
`material that can be heated to the desired temperature level.
`Platen 110 has a cavity preferably in the form of an annular
`region 115 desirably circumventing an elongated member
`(center pin) 120. The elongated member 120 extends verti-
`cally upwards from the body of platen 110 (FIG. 6) and
`
`8
`desirably terminates in a tapered or pointed end 122. Other
`forms of heat treatment could also be used in place of the
`heated platen. For example, bottom edge 50a of the sepa-
`rator can be heat formed using hot air or infrared light.
`In accomplishing the heat forming process of the inven-
`tion an electrode spiral 70 is first formed having the con-
`figuration as shown in FIG. 2B. However, instead of insert-
`ing the electrode spiral