(19)
`
`(12)
`
`Europäisches Patentamt
`
`European Patent Office
`
`Office européen des brevets
`
`*EP000829105B1*
`EP 0 829 105 B1
`
`(11)
`
`EUROPEAN PATENT SPECIFICATION
`
`(45) Date of publication and mention
`of the grant of the patent:
`21.05.2003 Bulletin 2003/21
`
`(21) Application number: 97908519.8
`
`(22) Date of filing: 27.03.1997
`
`(51) Int Cl.7: H01M 10/40, H01M 10/04
`
`(86) International application number:
`PCT/JP97/01040
`
`(87) International publication number:
`WO 97/036338 (02.10.1997 Gazette 1997/42)
`
`(54) NON-AQUEOUS ELECTROLYTE SECONDARY BATTERIES
`
`NICHTWÄSSRIGE ELEKTROLYT SEKUNDÄRBATTERIE
`
`BATTERIES AUXILIAIRES COMPORTANT UN ELECTROLYTE NON AQUEUX
`
`(84) Designated Contracting States:
`DE FR GB
`
`(30) Priority: 28.03.1996 JP 7352996
`
`(43) Date of publication of application:
`18.03.1998 Bulletin 1998/12
`
`(73) Proprietor: MATSUSHITA ELECTRIC INDUSTRIAL
`CO., LTD.
`Kadoma-shi, Osaka 571 (JP)
`
`(72) Inventors:
`• OKOCHI, Masaya
`Osaka-shi, Osaka 535 (JP)
`• KITAGAWA, Masaki
`Katano-shi, Osaka 576 (JP)
`• TAKEUCHI, Takashi
`Kadoma-shi, Osaka 571 (JP)
`• INOUE, Kaoru
`Moriguchi-shi, Osaka 570 (JP)
`• KOSHINA, Hizuru
`Neyagawa-shi, Osaka 572 (JP)
`
`(74) Representative: Crawford, Andrew Birkby et al
`A.A. Thornton & Co.
`235 High Holborn
`London WC1V 7LE (GB)
`
`(56) References cited:
`EP-A- 0 655 793
`GB-A- 2 225 153
`US-A- 4 622 277
`
`WO-A-96/10273
`US-A- 4 385 101
`US-A- 5 322 746
`
`• PATENT ABSTRACTS OF JAPAN vol. 017, no.
`683 (E-1477), 15 December 1993 & JP 05 234620
`A (SONY CORP), 10 September 1993,
`• PATENT ABSTRACTS OF JAPAN vol. 096, no.
`004, 30 April 1996 & JP 07 320770 A (SANYO
`ELECTRIC CO LTD), 8 December 1995,
`
`Remarks:
`The file contains technical information submitted
`after the application was filed and not included in this
`specification
`
`Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give
`notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in
`a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art.
`99(1) European Patent Convention).
`
`Printed by Jouve, 75001 PARIS (FR)
`
`EP0 829 105B1
`
`Eve Energy Co., Ltd v. Varta Microbattery Gmbh
`
`Eve Ex. 1021, p. 1
`
`

`

`EP 0 829 105 B1
`
`Description
`
`Technical Field
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`[0001] The present invention relates to a non-aqueous electrolyte secondary battery having an electrode group com-
`posed of a thin positive electrode and a thin negative electrode with separator material sandwiched therebetween. and
`more particularly to its safety.
`
`Background Art
`
`[0002] Conventionally, non-aqueous electrolyte secondary batteries, using chalcogenide, such as an oxide, sulfide
`or selenide of a transition metal as positive active material. For example, manganese dioxide, molybdenum disulfide,
`titanium selenide, or metal lithium sheet is used as a negative active material.
`[0003] An organic electrolyte composed of an organic solvent solution of lithium salt is typically used as a non-
`aqueous electrolyte,, Such batteries are typically referred to as lithium secondary batteries, and are aimed at producing
`batteries of high voltage, large capacity, and high energy density. In such lithium secondary batteries, however, although
`an intercalation compound having excellent charging and discharging characteristics may have been selected as the
`positive active material, the charging and discharging characteristics of the negative electrode was not always excellent,
`and it was difficult to assure a long cycle life.
`[0004] Furthermore, accidents such as fire and rupture due to an internal short circuit were likely to occur, raising
`serious safety concerns.
`[0005] The metal lithium in the negative active material in this battery is dissolved as lithium ions in the organic
`electrolyte due to discharge. When charging, the dissolved lithium ions deposit on the surface of the negative electrode
`as metal lithium, but all of them do not deposit smoothly as in the initial state. Some of them deposit as dendrites or
`mossy, active. metallic crystals. Such active metallic crystals react with the organic solvent in the electrolyte, causing
`their surface to be covered with a passivation film, making them inactivate, and unable to contribute to discharge.
`Therefore, the negative electrode capacity drops as the charging and discharging cycles are repeated. Accordingly,
`when manufacturing the cells, it was necessary to set the negative electrode capacity extremely larger than that of the
`positive electrode. Besides, active lithium metallic crystals are likely to form an internal short circuit by penetrating
`through the separator and contacting with the positive electrode. By such an internal short circuit, the cell may suddenly
`generate heat, causing a cell rupture or accidental fire.
`[0006] Accordingly, the so-called lithium ion secondary batteries using a material for intercalating and deintercalating
`lithium ions by charging and discharging as the negative material have been proposed, intensively researched and
`developed globally, and are now already in a practical stage. The lithium ion secondary battery, as long as it is not
`overcharged, does not deposit active metallic lithium crystals on the negative electrode surface when charging, and
`enhancing safety. Its demand is growing rapidly in recent years because it is superior to the conventional lithium sec-
`ondary battery in high-rate charge and discharge characteristics and life cycle. In the lithium ion secondary battery,
`lithium is the active material, and thus, the battery may be regarded as a kind of lithium secondary battery. It can be
`distinguished, however, from the lithium secondary battery that uses conventional metallic lithium as the negative
`electrode.
`[0007] As the positive active material of the lithium ion secondary battery, a double oxide of lithium and a transition
`metal, such as LiCoO2, LiNiO2, LiMnO2, or LiMn2O4 in discharged state, is used. As the negative active material,
`graphite or other carbon material similar in potential to the metallic lithium as charged is used in most systems, but in
`other systems of low voltage operation, in part, a double oxide of lithium and transition metal is used in the negative
`electrode.
`[0008] When the lithium ion secondary battery is charged and discharged, the positive active material can reversibly
`repeat deintercalation and intercalation of lithium ions, and the negative active material, can reversibly repeat interca-
`lation and deintercalation of lithium ions, so that the cycle life is extremely long.
`[0009] Moreover, because of high voltage and/or large capacity, a battery of high energy density is provided.
`[0010] However, these lithium ion secondary batteries, like the conventional lithium secondary batteries, employ
`organic electrolytes of relatively low ionic conductivity.
`[0011] Accordingly, a thin positive electrode and negative electrode are fabricated by thinly forming an active material
`layer or a mixture layer of active material and conductive agent on a metal foil of current collector. An electrode group
`is composed by setting the positive electrode and negative electrode oppositely to each other separated by a thin
`microporous polyolefin resin membrane separator. By increasing the opposing surface areas of the positive electrode
`and negative electrode, a practical high-rate charge and discharge characteristic is maintained to expand conformity
`to many applications. For example, the positive electrode and negative electrode, each piece in a thin and long strip
`form sandwiching a separator therebetween, may be spirally wound or plated like an accordion, or a plurality of positive
`
`2
`
`Eve Energy Co., Ltd v. Varta Microbattery Gmbh
`
`Eve Ex. 1021, p. 2
`
`

`

`EP 0 829 105 B1
`
`electrodes and negative electrodes may be laminated alternately with a separator therebetween to form the electrode
`group.
`[0012]
`In these lithium ion secondary batteries, a separator capable of closing fine pores and thus decreasing the
`ion conductivity when raised to a specified temperature is used to cut off current. Moreover an electronic protection
`circuit in the battery pack is used to control each cell to prevent fatal deterioration due to overcharge and over discharge.
`Therefore, when used normally, safety is assured, but in abnormal use, it is hard to guarantee safety. For example,
`when a battery pack in a fully charged state is crushed by a strong external force, such as being run over by an
`automobile, or when overcharged due to malfunction of the protection circuit as described above, the separator in the
`cell may be broken, and the positive and negative electrodes are sorted. Such shorted electrodes generate heat by
`Joule heat or reaction heat, and when the decomposition temperature of the positive active material is reached active
`oxygen is generated. The active oxygen, violently oxidizes the solvent in the organic electrolyte or the other material
`in the cell, causing a state of thermal runaway. As a result, the cell temperature rises sharply in an instant, possibly
`leading to a cell rupture or accidental fire. The risk of such accident is also present when the charged battery pack is
`disposed of with common household refuse.
`[0013] To prevent such accidents, usually, in each cell, a temperature fuse, PTC device, other temperature rise
`preventive means, and an explosion-proofsafety valve are provided, but may not be sufficient to cope with sudden
`temperature rise due to a thermal runaway. It was therefore proposed to provide a cell capable of preventing a sudden
`rise in cell temperature, thus preventing cell rupture and accidental fire as experienced hitherto, when the positive
`electrode and negative electrode are short-circuited. Such as when the separator is broken due to the cell being crushed
`or overcharged. A typical example is disclosed in document WO 96/10273 which was published on 4th April 1996,
`relating to a laminate electrode assembly (electrode group) comprising a positive electrode and a negative electrode,
`each comprising an active material layer at least on one side of a metal foil which is a collector positioned opposite to
`each other with a separator therebetween. The confronting portions of the metal foils of the collector of the positive
`electrode and the negative electrode are exposed at least on one side, over at least one turn or one outermost portion,
`or intermediate portion.
`[0014]
`In such cell a composition, when the side surface is pressed, -the cell is crushed, the separator is torn, and
`the positive electrode and negative electrode contact each other, the short-circuit current flows selectively between
`the exposed metal foil portions of the collector of the positive electrode and the negative electrode, which are higher
`in electronic conductivity than the active material layer, and the positive and negative active materials in a charged
`state are discharged and consumed in a short time, so that the cell temperature may not be raised to a critical state.
`Moreover, in order to short-circuit securely between exposed portions of the metal foil of the positive and negative
`electrode collectors, this same publication also discloses means for selectively tearing the separator between the
`exposed portions of the positive and negative metal foils by interposing a part made of a rigid or elastic body at least
`in one of the exposed portions of the positive and negative electrode metal foils.
`[0015] As a result of close studies of these proposed cell compositions, the present invention proposes a cell com-
`position having an electrode group for selectively short-circuiting in a position of high electronic conductivity between
`the metal foil of the positive electrode collector and the negative electrode, easily releasing heat in the cell without
`sacrificing the cell capacity or increasing the number of parts more than necessary. By employing such a cell compo-
`sition, it is intended to present a non-aqueous secondary battery high in reliability and enhanced in safety, capable of
`securely preventing accidents such as rupture or fire, even in the event of the abnormality of crushing the cell.
`[0016] Document GBA 2225153 discloses an electrochemical cell having spirally wound electrodes and an electrolyte
`which enhances plating of the anode metal during voltage reversal. The safety of such cells is improved by concentrating
`the current, during voltage reversal, between an outer segment of the anode and a metal sheet connected to the
`cathode whereby anode metal onto the cathode is avoided.
`
`Disclosure of Invention
`
`[0017] The invention relates to a non-aqueous electrolyte secondary battery, comprising an electrode group com-
`posed by sandwiching a separator between a thin positive electrode and a thin negative electrode. Each electrode
`comprises a metal foil, which is a collector, having a thin coating thereon, the coating comprising an active material
`layer or a mixture layer of active material and conductive agent. The electrode group is spirally coiled such that the
`negative electrode is positioned outwardly relative to the positive electrode, and a portion of exposed metal foil, which
`is electrically connected to the positive electrode and has no active material layer or no mixture layer of active material
`and conductive agent thereon, covers the outer side of the negative electrode with a separator therebetween. The
`outermost side of the exposed metal foil is also covered with a separator. The electrode group so constructed is put
`in a negative polarity cell container together with non-aqueous electrolyte. Thus, the exposed metal foil connected to
`the positive electrode collector covers the entire surface of the outer side of the electrode group, having one side facing
`the negative electrode and the other side facing the inner side wall of the negative polarity cell container. Therefore, if
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`3
`
`Eve Energy Co., Ltd v. Varta Microbattery Gmbh
`
`Eve Ex. 1021, p. 3
`
`

`

`EP 0 829 105 B1
`
`the cell side surface is pushed by a strong external force and the cell is crushed, the separator on one side or both
`sides of the metal foil of the positive electrode collector positioned outside of the electrode group is first broken, and
`the metal foil for the positive electrode short-circuits with at least one of the negative electrode and the inner wall of
`the negative polarity cell container. The positive and negative materials in a charged state are thus discharged and
`consumed in a short time, and because the short-circuit position is adjacent to the cell container, the heat is released
`easily, thereby preventing a sudden rise in cell temperature. As a result, cell rupture, fire or other accidents may be
`prevented, so that the reliability and safety are successfully enhanced without increasing the number of parts or sac-
`rificing the cell capacity more than necessary.
`
`5
`
`10
`
`Brief Description of Drawings
`
`[0018]
`
`15
`
`20
`
`Fig. 1 is a sectional view of a cylindrical non-aqueous electrolyte secondary battery according to an embodiment
`of the invention.
`
`Fig. 2 shows the positive electrode having exposed surfaces on both sides of the metal foil of the collector over a
`sufficient length for covering at least the outermost periphery of the electrode group in a cylindrical cell in an
`embodiment of the invention.
`
`Fig. 3 show comparative examples 1, 2, 3 of the positive electrode for cylindrical cell.
`
`Fig. 4 shows a prior art of positive electrode for cylindrical cell.
`
`25
`
`Best Mode for Carrying Out the Invention
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`[0019] Referring now to the drawings and table below, a preferred embodiment of the invention is described specif-
`ically below.
`[0020] Fig. 1 is a sectional view of a lithium ion secondary cylindrical cell (overall height 70mm, diameter 20mm) in
`an embodiment of a non-aqueous secondary battery of the invention.
`[0021]
`In Fig. 1, an electrode group is constructed by spirally winding a positive electrode 1 of 57mm in width and
`520mm in length, and a negative electrode 2 of 59mm in width, 550mm in length, and 0.2mm in thickness,with a
`separator 3 therebetween. The separator is made of a microporous polypropylene membrane.
`[0022] The positive electrode 1 is fabricated by first preparing a positive electrode paste by adding and mixing an
`artificial graphite as a conductive agent to an active material made of a double oxide (LiCOO2) of lithium and cobalt
`prepared by baking a mixture of lithium carbonate (Li2CO3) and cobalto-cobaltic oxide (Co3O4) in air at 900°C. A 5 wt.
`% dispersion solution of polytetrafluoroethylene (PTFE) is added and mixed into the paste as a binder. Both sides of
`an aluminum (Al) foil 1a are coated with this positive electrode paste, dried, and pressed by rolling, forming a mixture
`layer 1b of active material and conductive agent. According to the invention, a 57mm portion of positive electrode 1
`(corresponding to the length of at least one periphery of the outer circumference of the spiral electrode group) has the
`Al foil of the collector exposed, without any mixture layer Al of the active material and conductive agent on either side,
`as shown in Fig. 2. A positive electrode lead piece 1c is spot-welded to the another exposed portion of Al foil at the
`end of the positive electrode opposite Al foil exposed portion 1a.
`[0023] The negative electrode 2 is fabricated by mixing 5 wt. % of styrenebutadiene rubber as a binder to the active
`material, which comprises artificial graphite powder with an average particle size of 3 µm. This negative electrode
`paste is then dispersed in carboxymethyl cellulose (CMC) aqueous solution and applied to both sides of the copper
`(Cu) foil of the collector. The paste; is then dried, and the electrode is pressed by rolling, and cut. A negative electrode
`lead piece 2c is spot welded to an exposed portion of the Cu foil at one end of the cut negative electrode 2.
`[0024] The electrode group is then spirally wound, starting with the separator 3 at the winding core, and ending with
`at least one turn of the exposed portion 1a of the positive electrode 1 covering the negative electrode 2, which is on
`the outer circumference. Separator 3 is sandwiched between exposed foil portion 1a and negative electrode 2 and
`also, covers the outermost circumference of the exposed foil. The outside diameter of the electrode group was 18mm.
`[0025] Afterwards, the upper surface and lower surface of the electrode group are heated by hot air, and any portions
`of the separators 3 extending past the upper end and lower end of the electrode group are shrunk. A bottom insulating
`plate 4 is fitted and put in a cell container 5, and a negative electrode lead piece 2c is spot welded to the inner bottom
`surface of the cell container 5. An upper insulating plate 6 is mounted on the electrode group, a groove is cut in a
`specified position of the opening of the cell container 5, and a proper amount of non-aqueous electrolyte is poured in.
`The non- aqueous electrolyte comprises I mole of lithium hexafluorophosphate (LiPF6) dissolved in a mixed solvent of
`
`4
`
`Eve Energy Co., Ltd v. Varta Microbattery Gmbh
`
`Eve Ex. 1021, p. 4
`
`

`

`EP 0 829 105 B1
`
`ethylene carbonate (EC) and diethyl carbonate (DEC) at volume ratio of 1:1. 1 liter of organic electrolyte was prepared.
`Later, a terminal plate 7a and a cover plate 7b are crimped into one body, a gasket 7c is fitted in the peripheral edge,
`and a positive electrode lead piece 1c is spot welded to the cover plate 7b of the lower side of this assembled cover.
`The assembled cover is fitted into the opening of the cell container 5, and the upper edge of the cell container 5 is
`curved inward to seal. This embodiment is listed as cell A in the table below.
`[0026] Fig. 3A, B and C show comparative examples 1, 2 and 3 fabricated for confirming the effect of the invention.
`[0027]
`In comparative example 1, the length of the exposed portion of the Al foil of positive electrode is 30mm long,
`as compared with the length of 57mm in the exposed portion of the Al foil of the positive electrode of the invention.
`When the electrode group is composed by using the positive electrode of the comparative example 1, the entire outer
`circumference of the electrode cannot be covered with the exposed portion of Al foil.
`[0028]
`In comparative example 2, the positive electrode has an exposed portion of Al foil over a length of 57mm at
`the winding core side of the electrode group to which the positive electrode lead piece 1c is welded.
`[0029]
`In comparative example 3, the positive electrode is 30mm long in the exposed portion of the Al foil at the
`winding core side.
`[0030]
`In the prior art shown in Fig. 4, there is no exposed portion of Al foil, unlike the positive electrodes in the
`invention and in the comparative examples.
`[0031] Using the positive electrodes of comparative examples 1, 2, 3 and prior art, cells were fabricated by construct-
`ing the rest of the electrode group and the rest of the cell in same manner as cell A, with all the same mother parts,
`materials and methods. These cells are respectively called B, C, D and E.
`50 cells each of the fabricated cells A, B, C, D and E, were charged for 2.0 hours at 20°C, at constant current
`[0032]
`of 800 mA and constant voltage of 4.2V per cell. All charged cells were presented for a crushing test, and the number
`of cells breaking out in fire was counted. The results are summarized in Table 1. In the crushing test, a cylindrical metal
`rod of 10 mm in diameter of steel or the like was placed so as to be vertical to the cell axial line, at the cell outer wall
`side of the middle of the overall height of each cell, and the cell .was pressed and crushed by a pressing machine until
`the diameter became half the diameter prior to crushing.
`
`Cell
`
`Positive Electrode
`
`Number of Cells breaking out in fire
`
`A
`
`B
`
`C
`
`D
`
`E
`
`Invention
`
`Comparative example 1
`
`Comparative example 2
`
`Comparative example 3
`
`Prior art
`
`0/50
`
`3/50
`
`4/50
`
`3/50
`
`7/50
`
`[0033] As is clear from the results in Table 1, fire took place in 7of cells E of the prior art, while no fire was caused
`in cells A of the invention. In cells B, C and D using the positive electrodes having exposed portions of Al foil in the
`outer circumference or winding core portion of the electrode group, the number of cells breaking out fire was about
`half that of cells E, but was not zero.
`[0034]
`In cell A of the invention, as mentioned above, the entire outer circumference of the electrode group is wound
`at least one turn in metal foil that conducts electrically with the positive electrode, with separator on either side of the
`metal foil. In other words. the metal foil for the positive electrode is wound at least one turn around the outer circum-
`ference of the electrode group, with one side facing the negative electrode with separator therebetween, and the other
`side facing the inner wall of the negative polarity cell container, with separator therebetween. When the cell is crushed
`in this state, first the separator closer to the outer side in the cell is torn, and the metal foil of the positive electrode
`collector selectively short-circuits with at least one of the cell container or the negative electrode of the outermost
`circumference. As mentioned above, since the outer circumference of the electrode group is covered by at least one
`turn of the exposed metal foil conducting electrically to the positive electrode, if any position of the cell side surface is
`crushed by pressing, short-circuit occurs as stated above, and no fire results in the cell.
`[0035] By contrast, in the cell B, as mentioned above, since the entire outer circumference of the electrode group is
`not covered with the exposed portion of the Al foil of the positive electrode, the metal rod used in the crushing test may
`not always press the exposed portion of the Al foil. This explains why fires cannot be completely eliminated in the cell B.
`[0036]
`In the cells having the exposed portion of the Al foil of the positive electrode collector at the winding core side
`of the electrode group, as in the cells C and D, the separator adjacent the exposed portion of the metal foil is not always
`torn. When the positive and negative active materials contact directly with each other due to breakage of separator,
`thermal runaway may occur in certain cells.
`[0037] The electrode group compositions in C and D are advantageous in that the cell capacity is hardly sacrificed,
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`5
`
`Eve Energy Co., Ltd v. Varta Microbattery Gmbh
`
`Eve Ex. 1021, p. 5
`
`

`

`EP 0 829 105 B1
`
`as disclosed in WO 96/10273, but accidental cell fires cannot be eliminated completely, which is a problem in the aspect
`of reliability. The same publication proposed separator breakage parts made of metal bars inserted into the winding
`core. These cells were evaluated in a crushing test, and it was confirmed that the cell fires could be nearly eliminated,
`In such cell compositions, however, since the number of parts increases, the cell manufacturing cost and weight are
`increased, and hence it is not an optimal solution.
`[0038] As mentioned above, according to the proposal disclosed in WO 96/10273, the cell is constructed by disposing
`the confronting portions of the metal foils of the positive electrode and negative electrode collectors having at least
`one side exposed and separator therebetween, over a length of one turn or one layer, in any one of the outermost side,
`innermost side, and the intermediate portion of the electrode group. In the present invention, the exposed portion of
`metal foil is only on the positive electrode the entire outer surface of the electrode group has the negative electrode
`positioned at the outer side and covered with the exposed metal foil portion of the electrode with separator therebe-
`tween, the outermost side of the foil is wrapped with separator, and the electrode group is put in a negative polarity
`cell container. In the present invention, the exposed portion is not provided in the metal foil of the negative electrode
`collector because the active material in the charged state of the lithium ion secondary battery and lithium secondary
`battery is highly conductive. For example, the carbon material in which the lithium is inserted, expressed as C6Li, and
`the metallic lithium are both highly conductive. If short-circuited, an active oxygen generation source is not obtained
`unless there is direct contact with the positive active material. Therefore, in the cell composition of the invention, the
`capacity of negative electrode or cell is not sacrificed. It is a benefit of the invention that the entire outer surface of the
`electrode group is covered with a very thin metal foil connected to the positive electrode collector and with a separator.
`In such cell composition, the cell capacityis slightly sacrificed, but the higher reliability in cell crushing and improved
`safety are considered more important.
`[0039] So far, a cylindrical cell has been described as the embodiment. The invention, however, is not limited to the
`cylindrical cell alone. It may also be applied to an oval cell using an oval section electrode group. Such an oval section
`electrode group is formed using thin and long positive electrode and a thin and long negative electrode configured in
`a flat plate in the winding core portion with a separator therebetween, and then plaiting down in one direction and
`winding up. This is similar to a prismatic cell using an electrode group by plaiting down a thin and long positive electrode
`and thin and long negative electrode in an accordion form with a separator therebetween, or a prismatic cell using an
`electrode group comprising a plurality of positive electrodes and negative electrodes alternately laminated with sepa-
`rators therebetween. Of the cells of these shapes, however, such as in the prismatic cell, where the electrode plate
`comprises the positive electrode and negative electrode plaited into an accordion form with separator therebetween,
`the exposed portion of metal foil must be provided at both ends of the positive electrode. In the case of the electrode
`group composed by alternately laminating a plurality of positive electrodes and negative. electrodes with separators
`therebetween, one more negative electrode is used than positive electrodes. The negative electrode is thus positioned
`at the outer side, and two metal foils connected to the positive electrode collectors are disposed at the outer side as
`dummy plates, with a separator between each foil and the respective negative electrode. The outermost sides of the
`foil are also wrapped with separator. In this case, of course, the negative electrodes are connected electrically in
`parallel, and the positive electrode and dummy plates are connected electrically in parallel.
`[0040]
`In the embodiment described herein, the active material was LiCoO2 in the positive electrode, and carbon in
`the negative electrode, but the invention is not limited to these systems alone. For example, as the positive active
`material, a double oxide of lithium and transition metal expressed as LiMO2 or LiM2O4, where M is one selected from
`the group consisting of Mn, Fe, Co, and Ni, may be used. As the negative active material,metallic lithium, Nb, Ti, and
`other transition metal oxides may be used as an alternative to carbon.
`[0041]
`In the embodiment described herein, a microporous polypropylene membrane is used as the separator. De-
`pending on the purpose, however, the membrane separator may be made of polyolefin such as polyethylene or mixture
`of polyethylene and polypropylene.
`[0042] The non-aqueous electrolyte of the invention is not limited to the organic electrolyte. The technology may be
`sufficiently applied to polymer solid electrolyte, too.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`Claims
`
`1. A non-aqueous electrolyte secondary battery comprising:
`
`55
`
`an electrode group formed by
`a positive electrode (1) and a negative electrode (2) spirally coiled together with a separator material sand-
`wiched there between, said positive electrode comprising a conductive metal foil having a first portion (1b)
`provided with a coating, the coating comprising an active material or a mixture of an active material and a
`conductive agent, and a second portion (1a) without said coating;
`
`6
`
`Eve Energy Co., Ltd v. Varta Microbattery Gmbh
`
`Eve Ex. 1021, p. 6
`
`

`

`EP 0 829 105 B1
`
`wherein the outermost portion of the negative electrode is positioned outwardly of the outermost first portion
`of the positive electrode, said second portion (1a) of the metal foil is positioned outwardly of the negative electrode
`outermost portion and extends around the entire circumference of the outermost portion of said negative electrode
`and said separator material is positioned between the second portion of the metal foil and the negative electrode
`outermost portion and covers the outermost side of the second portion of the metal foil; and
`a negative polarity cell container (5) in which said electrode group is housed together with a non-aqueous
`electrolyte.
`
`2. A non-aqueous electrolyte secondary battery according to claim 1, wherein said electrode group has an oval cross-
`section with said positive electrode, said negative electrode, and said separator material there between, configured
`in a flat plate in a central winding core; in which said second metal foil is electrically connected to an outer circum-
`ferential end of the positive electrode and wherein the negative polarity cell container has an oval geometry.
`
`3. A non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode group comprises a thin
`long positive electrode and negative electrode and a separator plated in an accordion form, and wherein a metal
`foil forming a positive electrode collector is electrically connected to both ends of the positive electrode.
`
`4. A non-aqueous electrolyte secondary battery according to any one of the preceding claims, wherein the first and
`second metal foil portions are integral with each other.
`
`5. A non-aqueous electrolyte secondary battery according to any one of the preceding claims, wherein said electrode
`group is adapted to fail upon application of a crushing force by at least one failure mode selected from the group
`consisting of:
`
`the separator material on the outermost side of said second metal foil breaking first so that the second metal
`foil short-circuits with an inner wall of said cell container;
`the separator material between said second metal foil and said negative electrode breaking first so that the
`second metal foil short-circuits with said n