(12) United States Patent
`Matsumoto
`
`USOO6800399B2
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,800,399 B2
`Oct. 5, 2004
`
`(54) NON-SINTERED THIN ELECTRODE FOR
`BATTERY, BATTERY USING SAME AND
`PROCESS FOR SAME
`
`(76) Inventor: Isao Matsumoto, 3-8-10, Ueshio,
`Tennoji-ku, Osaka-shi, Osaka-fu (JP),
`543-OOO2
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 181 days.
`
`(21) Appl. No.: 09/870,257
`(22) Filed:
`May 30, 2001
`(65)
`Prior Publication Data
`US 2002/0025475A1 Feb. 28, 2002
`Foreign Application Priority Data
`(30)
`Aug. 30, 2000
`(JP) ...
`... 2000-261780
`(JP) ....................................... 2000-318407
`Oct. 18, 2000
`(51) Int. Cl. .......................... H01M 4/66; H01 M 4/72;
`HO1 M 4/78
`(52) U.S. Cl. ....................... 429/241; 429/239; 429/243;
`429/245; 429/218.2
`(58) Field of Search .............................. 429/241, 218.2,
`429/223, 233, 239, 243, 245
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,251,603 A
`2/1981 Matsumoto et al.
`8/1996 Yanagihara et al.
`5,543.250 A
`5,824,435 A
`10/1998 Kawano et al.
`5,840,441 A 11/1998 Hirofumi et al.
`5,840,444 A 11/1998 Takeshima et al.
`6,444,366 B1
`9/2002 Kawano et al. ............. 429/241
`FOREIGN PATENT DOCUMENTS
`
`JP
`WO
`
`2000-48823
`WO 99/63608
`
`2/2000
`* 12/1999
`
`- - - - - - - - - - - - HO1M/4/70
`
`OTHER PUBLICATIONS
`Ikoma et al., “Self-Discharge Mechanism of Sealed-Type
`Nickel/Metal-Hydride Battery,” Journal of the Electro
`chemical Society, vol. 143, No. 6 (Jun. 1996).
`
`
`
`Matsumoto et al., “Ni-Fe Battery,” extended abstract from
`ECS Detroit Meeting (1982), no month.
`Ikoma et al., “Study on Self-Discharge of a Metal Hydride
`Rechargeable Battery System Employing MmNiM
`Alloy,” extended abstract from 174th Chicago (Fall) Meet
`ing (1988), no month.
`Yuasa et al., “Study on a Charge Characteristics of a
`Nickel/Hydride Battery System,” extended abstract from
`178th Seattle (Fall) Meeting (1990), no month.
`Fujiwara et al., “Development of a Hydrogen Absorbing
`Alloy for the Negative Electrode of Sealed Nickel-Hydride
`Battery System,” extended abstract from 180th Phoenix
`(Fall) Meeting (1991), no month.
`Matsumoto et al., “A Sealed Ni/MH Battery System for EV,”
`extended abstract from 183rd Honolulu (Spring) Meeting
`(1993), no month.
`Matsumoto et al., "Foamed Nickel Positive Electrode for a
`High Performance Cylindrical Ni-Cd Battery,” Power
`Sources 12, pp. 203-220 (1988), no month.
`Ogawa et al., Metal Hydride Electrode for High Density
`Sealed Nickel-Metal Hydride Battery, Power Sources 12,
`pp. 393-410 (1988), no month.
`Matsumoto et al., Ni-Fe Battery, ECS Fall Meeting, Detroit,
`Abstract 10 (1981), no month.
`
`* cited by examiner
`
`Primary Examiner Tracy Dove
`(74) Attorney, Agent, or Firm Merchant & Gould, P.C.
`(57)
`ABSTRACT
`An electrode Substrate is formed by mechanically processing
`a nickel foil So as to be made three dimensional through the
`creation of concave and convex parts, and then, this Sub
`strate is filled with active material or the like So that an
`electrode is manufactured, wherein the above described
`concave and convex parts are rolling pressed So as to incline
`in one direction. Furthermore, an electrode for Secondary
`battery is formed by using the above described method.
`
`9 Claims, 13 Drawing Sheets
`
`APPLE 1022
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`1
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`

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`U.S. Patent
`U.S. Patent
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`Oct. 5, 2004
`Oct. 5, 2004
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`Sheet 1 of 13
`Sheet 1 of 13
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`US 6,800,399 B2
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`Fig.1
`Fig.1
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`2
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`U.S. Patent
`U.S. Patent
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`Oct. 5, 2004
`Oct. 5, 2004
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`Sheet 2 of 13
`Sheet 2 of 13
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`US 6,800,399 B2
`US 6,800,399 B2
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`Fig.2
`Fig.2
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`3
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`

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`U.S. Patent
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`Oct. 5, 2004
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`Sheet 3 of 13
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`US 6,800,399 B2
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`Fig.3
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`
`
`?zzzzzzzzzzzzzzzzz
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`? % %
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`
`
`TOE --~~~~
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`4
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`

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`U.S. Patent
`U.S. Patent
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`Oct. 5, 2004
`Oct. 5, 2004
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`Sheet 4 of 13
`Sheet 4 of 13
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`US 6,800,399 B2
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`Fig.4
`Fig.4
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` TTLaIODC 12
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`5
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`U.S. Patent
`U.S. Patent
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`Oct. 5, 2004
`Oct. 5, 2004
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`Sheet 5 of 13
`Sheet 5 of 13
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`US 6,800,399 B2
`US 6,800,399 B2
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`Fig.5
`Fig.5
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`O O
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`O O O O O O O O O O O O O O O O O O O O O > ?^\O • O • O •
`
`
`(a)
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`
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`6
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`U.S. Patent
`U.S. Patent
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`Oct. 5, 2004
`Oct. 5, 2004
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`Sheet 6 of 13
`Sheet 6 of 13
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`Fig.6
`Fig.6
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`7
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`U.S. Patent
`U.S. Patent
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`Oct. 5, 2004
`Oct. 5, 2004
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`Sheet 7 of 13
`Sheet 7 of 13
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`US 6,800,399 B2
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`Fig.7
`Fig.7
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`
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`eho
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`727)
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`8
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`

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`U.S. Patent
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`Oct. 5, 2004
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`Sheet 8 of 13
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`US 6,800,399 B2
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`Fig.8
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`l, 4
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`l 2
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`, 0
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`0, 8
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`0, 6
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`O
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`-----------
`5
`O
`Discharge Rate C
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`9
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`U.S. Patent
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`Oct. 5, 2004
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`Sheet 9 of 13
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`US 6,800,399 B2
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`Fig.9
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`OO
`s
`s
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`s: 50
`5:
`SS
`ES
`so
`3
`d
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`C
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`O
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`O
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`OO
`500
`300
`OO
`Number of The Charge and Discharge Cycles (A)
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`10
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`

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`U.S. Patent
`U.S. Patent
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`Oct. 5, 2004
`Oct. 5, 2004
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`Sheet 10 of 13
`Sheet 10 of 13
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`US 6,800,399 B2
`US 6,800,399 B2
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`Fig.10
`Fig.10
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` ALTETIIITITIZILIEITEZITA
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`11
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`U.S. Patent
`U.S. Patent
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`Oct. 5, 2004
`Oct. 5, 2004
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`Sheet 11 of 13
`Sheet 11 of 13
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`US 6,800,399 B2
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`Fig.11
`Fig.11
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`12
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`U.S. Patent
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`Oct. 5, 2004
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`Sheet 12 of 13
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`US 6,800,399 B2
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`Fig 12
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`490
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`300
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`200
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`tOO
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`- - - - -
`O
`2S
`50
`75
`100
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`Capacity vs Theoretical Capacity f'6
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`13
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`

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`U.S. Patent
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`Oct. 5, 2004
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`Sheet 13 of 13
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`US 6,800,399 B2
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`Fig. 1 3
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`400
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`200
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`DO
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`O
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`25
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`50
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`100
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`Capacity vs Theoretical Capacity l%
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`14
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`

`US 6,800,399 B2
`
`1
`NON-SINTERED THIN ELECTRODE FOR
`BATTERY, BATTERY USING SAME AND
`PROCESS FOR SAME
`
`FIELD OF INVENTION
`The present invention relates to a paste type thin electrode
`for a battery, in which the cost is reduced and the high rate
`discharge characteristics and the cycle life are improved, and
`to a Secondary battery using this electrode.
`BACKGROUND OF THE INVENTION
`At present electrodes for batteries, used commercially for
`Secondary batteries, are broadly categorized as Sintered type
`electrodes and non-sintered type electrodes. In the Sintered
`type electrodes, active material is filled into a highly porous
`three dimensional Substrate where metal powder is sintered
`to have a large porosity on both Sides of a two dimensional
`metal Substrate. In the non-sintered type electrodes, the
`active material powder with a binder is coated on a two
`dimensional metal Substrate or grid, or filled into a three
`dimensional Substrate, Such as foamed nickel, metal bag or
`tube, without employing a sintered Substrate.
`In general, the former exhibits excellent characteristics in
`electronic conductivity (high-rate charge and discharge
`characteristics) due to a large amount of metal used in the
`Sintered plaque and has a long cycle-life with excellent
`mechanical Strength and Stability in the Shedding of active
`material, while it has the defect that the electrode is heavy
`and has a Small Volumetric energy density due to a Small
`amount of active material impregnated therein because of a
`large Volume of the electrode Substrate.
`On the contrary, a representative and Simple non-sintered
`type electrode is inexpensive and light weight, and has a
`large Volumetric energy density because of using an inex
`pensive Substrate of a Small Volumetric amount in the
`electrode, which is easy to manufacture, through the coating
`or direct filling process of active material powder, while it
`entails the problem that the entire electrode is inferior in
`current collection ability as a whole, in the mechanical
`Strength and in the holding of the active material. These are
`Significant problems in Secondary batteries where charging
`and discharging is repeated and, therefore, a variety of ideas
`are incorporated into respective battery Systems.
`AS a result, non-sintered types have a variety of Substrates
`to improve the above problems, as represented by a paste
`type or an application type, wherein active material powder
`is mixed with conductive material or a binder which is then
`mixed together with a Solution and the obtained paste or
`Slurry is coated on a two dimensional Substrate of a variety
`of shapes, or in Some cases the active material powders are
`filled in a pocket type or a tube type Substrate which has
`innumerable Small pores for electrochemical reactions.
`AS examples of non-sintered type electrodes, which are of
`the former type, a cadmium negative electrode, a metal
`hydride negative electrode for alkaline Storage batteries, the
`positive and negative electrodes for lithium ion batteries and
`the positive and negative electrodes for lead acid batteries
`are cited. Non-sintered type batteries which are of the latter
`type are, for example, employed in part of the nickel positive
`electrode for large Scale alkaline Storage batteries or for
`certain types of lead acid batteries. AS a Substrate of the
`electrodes described herein, punching metal, a metal Screen,
`foamed metal, a metal grid or the like are individually
`utilized according to the battery Systems or the purpose.
`However, recently, new types of electrodes in which a
`paste of active materials is filled into a foamed nickel porous
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`Substrate or into a nickel fiber Substrate, which have a three
`dimensional structure, in the high density (hereinafter abbre
`viated as 3DM type), have started being employed as
`proposed in U.S. Pat. No. 4,251,603, which belongs to
`another non-sintered type in classification. However, though
`these types of electrodes have a high capacity and a high
`reliability and are easily made to have higher capacity and
`to be lighter weight compared with the Sintered type, due to
`a Small amount of metal employed in the Substrate, they
`have the technical problems that the mechanical Strength is
`low and the electronic conduction of the entire electrode is
`inferior due to a large pore diameter within the Substrate and,
`in addition, have the technical problem that the cost of the
`Substrate is high.
`Since the present invention of paste type electrode relates
`to an improvement of the three dimensional Substrate used
`in the above described 3DM system, in particular for alka
`line Storage battery System currently, for the convenience of
`the detail technological description of prior art, a nickel
`positive electrode for a small sealed cylindrical Ni/MH
`batteries is focused on thereafter.
`AS for the nickel positive electrode for alkaline Storage
`batteries, the Sintered type electrode, which was developed
`in Germany during the Second World War, has a high
`performance and is durable, which replaced the previous
`non-sintered type electrode, that is to Say, the pocket type
`electrode, and, therefore, a Sintered type electrode Started to
`be used for rectangular Ni/Cd batteries requiring high per
`formance and high reliability. AS for the negative electrode,
`a similar conversion to the Sintered type has occurred. AS for
`the electrodes of sealed cylindrical Ni/Cd batteries devel
`oped afterwards, Sintered type positive and negative elec
`trodes have become the most popular because they are easily
`processed into thin electrodes. The Small Sealed cylindrical
`batteries represented by this nickel-cadmium battery (Ni/Cd
`battery) have achieved a dramatic growth as a power Supply
`for portable compact electronic equipments, Such as cam
`corders or CD players, which have achieved a remarkable
`growth in Japan starting in the 1980's. However, in the
`1990's, a new type of nickel-metal hydride storage battery
`(Ni/MH battery) and a lithium ion battery successively have
`been put into practical use So as to begin expansion into the
`market of nickel-cadmium batteries.
`And, as for a new market, applications for power Supplies
`as power tools, applications for mobile power Supplies, that
`is to say, for electrical vehicles (EVs), hybrid electrical
`vehicles (HEVs), electric power assisted bicycles or the like
`have newly started growing in recent years, and for those
`power supplies mainly Ni/MH batteries have started being
`used. A nickel positive electrode is employed for the positive
`electrodes of the above described Ni/Cd batteries and
`Ni/MH batteries for which the growth recently has been
`remarkable and the sintered types and 3DM types are used
`respectively, according to the applications under the present
`circumstances.
`As for the structure of this nickel positive electrode for a
`mass-production level, the non-sintered type was limited
`only to the pocket type, due to the electrode mechanical
`Stability. The pocket type electrode has a structure wherein
`active material powder is filled into a electrolyte proof metal
`bag with innumerable Small pores to prevent the Shedding of
`active metal powders as described above. The Sintered type
`adopts a structure wherein a Solution of active material Salt
`is impregnated into the Space of a three dimensional Sintered
`plaque, followed by the process of conversion to the active
`material with alkaline Solution. Naturally, the active material
`in this case is not in a powder condition.
`
`15
`
`

`

`3
`Another non-sintered 3DM type, which is different from
`the pocket type, is reported as a nickel positive electrode
`employing foamed nickel in the ECS Fall Meeting (Detroit)
`Abstract No. 10 in 1981. This electrode has a structure using
`a foamed nickel porous body as a Substrate, into which
`active material powder is filled.
`Though a light weight nickel positive electrode with a
`high capacity is realized by using this foamed nickel as a
`Substrate, it has the problems that the high power drain of the
`entire active material is not Sufficient due to the large
`diameter of the internal spherical Space, which is approxi
`mately 450 um in the case of even the Smallest diameter, and
`it is expensive. Therefore, batteries using a sintered type
`nickel positive electrode which exhibit excellent character
`istics in high-rate discharge are still the most popular for
`applications requiring high power drain.
`However, the following shortcomings of the Sintered type
`electrodes for those applications have been increasing, as
`problems in practical use, while applications are expanding,
`and, therefore, the introduction of the paste type electrodes
`are desirable. The shortcomings are: Small energy density;
`heavy weight; large Self-discharge due to the well-known
`Shuttle reaction between nitride and nitrate ions, which is not
`present in the non Sintered type. Since those applications
`require a high-rate discharge, thin electrodes are, in general,
`employed to increase the electrode Surface area in order to
`have a large active area, which also increases the area of the
`Substrates of the electrodes. Accordingly, a two dimensional
`Substrate or a three dimensional Substrate of low cost are
`particularly required and also light weight is a prerequisite
`for these high-power uses.
`Therefore, new structures of three dimensional substrates
`to replace expensive foamed nickel Such as in the 3DM type,
`which is a kind of the paste type of light weight, are
`proposed as follows:
`(1) One sheet of electrode is formed by overlapping a
`plurality of extremely thin electrodes wherein active mate
`rial powder is coated on the porous Substrate, Such as thin
`punched metal and foamed metal.
`(2) Innumerable pieces of metal in the form of bristle or
`whisker are attached to a porous Substrate, Such as metal foil
`and punched metal (U.S. Pat. No. 5,840,444).
`(3) Burrs are provided on a metal plate in the direction of the
`thickness of the plate (U.S. Pat. No. 5,543.250).
`(4) A metal plate is processed to have a three dimensional
`corrugated form. Holes with burrs are provided on the crests
`of the corrugated form So as to increase the three dimen
`sional shape (U.S. Pat. No. 5.824,435).
`The structures or the substrates in the above described (1)
`to (4), however, have not solved all of the problems. In (1),
`there still remains the problem of the active mass Shedding
`of each thin electrode due to the Swelling of the active
`material during charge and discharge cycles, which essen
`tially cannot be prevented. In (2), the thickness of the paste
`layer lackS uniformity due to the low binding Strength
`between the metal fiber in bristle or whisker, or due to the
`non-uniformity of the holes of the substrate itself with
`respect to its characteristics and, additionally, it costs more
`than the conventional Substrates. In (3), the structure is
`basically not three dimensional and, therefore, it has prob
`lems in the Shedding of the active material powders follow
`ing a decay in charge and discharge characteristics. In (4),
`though the above described problems have been improved to
`Some extent and low cost can be expected, there still remains
`the problem that a desired three dimensional Substrate shape
`is difficult to maintain. Because, the Substrate of the corru
`gated form is easily expanded in the direction of the wave
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`form during the electrode press work, which leads to the
`problem that the active material is easily peeled off from the
`Substrate when it is wound into an electrode of a spiral form
`or when charging and discharging are repeated.
`In addition, power Supplies for electric power tools are
`desired, derived from how power tools are used, to have
`high-rate discharge characteristics, and the batteries for
`power-use, Such as electric vehicles (EVs), hybrid electric
`vehicles (HEVs) and electric power assisted bicycles are
`desired to have improved high-rate discharge characteristics,
`particularly desired to be Smaller and to be lighter in order
`to Secure Space within the vehicles and in order to improve
`fuel efficiency respectively, that is to Say, to increase Volume
`energy density (Wh/l) and gravimetric energy density (Wh/
`kg).
`
`SUMMARY OF THE INVENTION
`The present inventor solved the above described problems
`by forming an electrode for alkaline Storage batteries as an
`application example as follows:
`(a) Forming a conductive electrode Substrate from a metal
`foil which is provided with innumerable concave and con
`VeX hollow parts or forming the same shape metal Substrate
`by the metal deposition through an electrolytic method;
`(b) Adjusting the thickness of the above described electrode
`Substrate to Substantially the same thickneSS as that of the
`electrode,
`(c) For limiting the above described substrate to become two
`dimensional, partially or as a whole, by the electrode press
`work after filling the paste of active material powders as the
`main material, arranging the position of Said concave and
`convex parts of the conductive electrode Substrate to main
`tain the current collection ability of the whole electrode; and
`(d) Preventing the peeling of the active material powders
`layer from the Substrate through the Spirally winding process
`of the electrode and also the Shedding of active material
`powders that formed the electrode through the repetitive
`charging and discharging afterwards, by bending the walls
`of the concave and convex hollow parts into one direction
`Specifically in the vicinity of the edge, just as to wrap the
`Space between the concave and the next concave or the
`conveX and the next conveX in order to prevent the Shedding
`of the active material powders.
`In addition, by maintaining all the active material powder,
`within 150 um in the distance from the nearest conductive
`electrode Substrate, the charging and discharging reaction,
`particularly the high rate discharge reaction, of the active
`material powder is enhanced and by using a cylindrical
`battery case wherein a ratio (t/t) of the thickness (t) of the
`bottom to the thickness (t) of the side walls is 1.5 or more,
`that is to Say, by using a case of which the Side walls have
`become thinner, the Secondary battery is further made lighter
`and made larger in capacity.
`Though the present invention is not particularly limited to
`a nickel positive electrode, in the case of application for a
`nickel positive electrode, in particular, a thinner nickel
`positive electrode is provided in which the thickness is 500
`tim or less for alkaline Storage batteries, and the electrode
`uses an inexpensive, light weight and conductive metal
`Substrate that can be formed only through mechanical opera
`tions on a metal foil or only through electrolytic metal
`deposition on the same pattern, without Sintering or plating,
`resulting in excellent characteristics in charge and discharge
`characteristics, restraining the Shedding of active material
`powder and light weight. Therefore, an inexpensive, light
`weight Sealed cylindrical or prismatic nickel-metal hydride
`battery (Ni/MH battery) that shows excellent characteristics
`of high-rate charge/discharge and long cycle-life is
`achieved.
`
`16
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`

`

`S
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIGS. 1(a) and 1(b) are schematic cross section views of
`a nickel positive electrode according to one mode of the
`present invention;
`FIG. 2 shows a nickel positive electrode according to one
`embodiment of the present invention. The croSS Section view
`along A-A is shown in FIG. 1;
`FIG. 3 shows a sealed cylindrical Ni/MH battery (AA
`Size) construction according to one mode of the present
`invention;
`FIG. 4 shows an electrode Substrate in a wide belt-like
`form utilized for the nickel positive electrode according to
`one mode of the present invention;
`FIGS. 5(a) and 5(b) show two examples of patterns for
`unevenneSS processing;
`FIG. 6 shows a pressing process for the nickel positive
`electrode according to one mode of the present invention;
`FIG. 7 is a cross section view of the electrode after filling
`the paste of active material powder into the Substrate;
`FIG. 8 shows high-rate discharge characteristics of a
`sealed cylindrical Ni/MH battery (AA size) using a nickel
`positive electrode according to one embodiment of the
`present invention;
`FIG. 9 shows cycle-life characteristics of a sealed cylin
`drical Ni/MH battery (AA size) using a nickel positive
`electrode according to one mode of the present invention.
`FIG. 10 shows a Stroking and Squeezing Step;
`FIG. 11 is an enlarged croSS Section view of a battery case
`manufactured through the Stroking and Squeezing step;
`FIG. 12 shows high-rate discharge characteristics of the
`nickel positive electrode according to one mode of the
`present invention (half cell); and
`FIG. 13 shows high-rate discharge characteristics of the
`nickel positive electrode according to one mode of the
`present invention (half cell).
`DESCRIPTION OF PREFERRED
`EMBODIMENTS
`In the following, in reference to the drawings, a Sealed
`cylindrical nickel-metal hydride battery is described as an
`example wherein an electrode obtained by winding a nickel
`positive plate 1, whose main material is nickel hydroxide
`powder and whose electrode thickneSS is 500 um or less, and
`an alloy negative plate 2, whose main material is hydrogen
`absorption alloy powders and of which electrode thickneSS
`is much thinner than that of the positive electrode, together
`with a separator 3 made of non-woven sheet of polyolefin
`type Synthetic resin fiber, is inserted into a cylindrical metal
`case and then an alkaline electrolyte Solution is poured in the
`case, which is then Sealed.
`Here, an electrode obtained by filling the paste 10, that has
`been obtained by mixing the main material and the like, into
`a conductive electrode Substrate 9 which is made three
`dimensional through a preSS work applied to a nickel foil of
`a thickness of 20 to 50 um between the upper and the lower
`plate dies, wherein an innumerable number of concavities
`and convexities are mutually provided So as to engage each
`other and, then, by pressing after drying, is used as the
`positive electrode. From the viewpoint of cost-effectiveness
`and ease for producing the same type of a Substrate, par
`ticularly in the case where the thickness close to 20 um, the
`method of electrolytic nickel deposition is available as well.
`In this case, the nickel deposition of about 20 um is carried
`out on the cathode, the Surface of which has innumerable
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`hollow concavities and convexities of a desired pattern, in
`the conventional electrolysis bath of pH 2.0 containing
`mainly nickel Sulfate. And, this method can also can provide
`a long Strip of Substrate with innumerable hollow concavi
`ties and convexities by employing a rotary drum as the
`cathode. After the Said Substrate is annealed at approxi
`mately 850 C. to have much more mechanical strength, it
`can be used for the electrode Substrate.
`Long cycle-life electrodes with excellent charge/
`discharge characteristics can be obtained through the three
`dimensional Structure of the Substrate, which is made as a
`three dimensional model to almost the same thickneSS as the
`electrode, particularly, through a structure wherein the
`shapes of the hollow concavities and convexities bend, in
`one direction, to a greater extent in relation to proximity to
`the edges So as to wrap the Space of the Substrate. The
`resultant Structure is excellent in current collection and
`wraps the active mass tightly in a manner not inferior to that
`in the sintered type or 3DM type.
`Long cycle-life electrodes with excellent charge/
`discharge characteristics can be obtained because the above
`described conductive electrode Substrate has a structure
`which is excellent in current collection performance and the
`wrapping of the active material powder is not inferior to that
`of sintered type or 3DM type, since it is made to be a three
`dimensional Structure of approximately the Same thickness
`as the final electrode, particularly, to be a structure wherein
`the closer to the edges of the hollow unevenness the Stronger
`they become and the more bent they are in one direction So
`as to enclose the Space areas in the Substrate. In addition,
`Since this Substrate can be manufactured only by passing
`between dies which engage with each other through the
`unevenness, it becomes inexpensive because of the Simple
`process and when it is wound to an electrode of a spiral
`wound form, the electrode is not broken apart. As a result,
`Ni/MH batteries are obtained that are easy to process and
`which are inexpensive with high performance and high
`reliability.
`Since the alloy negative electrode is improved in the
`electric current collection performance due to the thickness
`which is approximately 72 of the positive electrode, it can
`withstand a high-rate discharge of approximately 20 C.
`discharge at room temperature. However, in the case that a
`much higher rate discharge is necessary, it is preferable to
`adopt a three dimensional nickel electrode Substrate accord
`ing to the present invention for the alloy negative electrode.
`Here, though, Ni/MH batteries are described for the
`convenience of the description above, the present invention
`can be applied in the same way to electrodes for Ni/Cd
`batteries or Li Secondary batteries which need a high-rate
`discharge.
`FIG. 1 shows a croSS Section view taken along line A-A
`in FIG. 2 of the nickel positive electrode 1 according to the
`present invention. In FIG. 1, a nickel metal part forming a
`three dimensional nickel Substrate is denoted as 9, and
`mixed powder mainly containing nickel hydroxide powder
`filled into this Substrate is denoted as 10 and a hollow area
`is denoted as 11. The walls of the convex part B or B' and
`of the concave part C or C" in the three dimensional substrate
`processed from a nickel foil have a contour while tilting to
`one side and the edge D or D' of nickel part is leSS thick and
`further more tilting to the side. This contour and the tilt of
`the edges limit the Shedding of the fillings Such as the active
`material powder from the substrate. The tilt of the edges do
`not cause microscopic short circuit with the opposite elec
`trode by becoming an electrode whisker and, therefore, this
`
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`US 6,800,399 B2
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`15
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`25
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`7
`also has the effect of making the Shortest distance from the
`nickel Substrate to the active material powder grain (in the
`vicinity of M in the figure) which is farthest away to be
`shorter than in the case of not bending (in the vicinity of M"),
`that is to Say, the effect of enhancing the current collection
`ability of the entire electrode is provided. In the case of a
`nickel positive electrode, when the commercially available
`active material powder is used and the distance from the
`conductive electrode Substrate becomes more than 150 um,
`the deterioration of Voltage at high-rate discharge occurs and
`the rate of utilization of the active material is lowered.
`Therefore, it is preferable to use a metallic plate wherein the
`conductive electrode Substrate of a thin electrolyte-proof
`metal foil has a three dimensional Structure by forming
`innumerable concave and convex parts and the shortest
`distance between a majority of Said powders and the Said
`conductive electrode substrate is maintained within 150 lum.
`In addition, unlike the electrode Substrate which has electric
`conductivity, the active material has very little electric
`conductivity since it is mainly composed of Ni(OH).
`Therefore, it is preferable to add about 5 wt % of a powder
`with electric conductivity and cobalt oxide in the active
`material powder paste in order to enhance current collection
`characteristics. Further, in the case where further improve
`ment of high-rate discharge characteristics is desired with
`the requirement of higher power as a battery, it is preferable
`to use the active materials in the active material layer on a
`Substrate having a three dimensional Structure by forming
`concave and convex parts with the shortest distance between
`a majority of Said powders and the Said conductive electrode
`substrate being maintained within 150 lum. This is because
`when the amount of a powder with electric conductivity and
`cobalt oxide added in the active material powder in order to
`enhance current collection characteristics is increased, the
`amount of the active materials contained is decreased. When
`35
`the Specific explanation is made using the Figure, it is
`preferable to decide the size of the concavities and convexi
`ties as well as the pitch so that the distance between the M'
`in FIG. 1 and the closest conductive electrode Substrate is
`maintained within 150 lum.
`FIG. 2 shows an overall view of a nickel positive elec
`trode 1 which has a structure as shown in FIG. 1, which is
`a thin nickel positive electrode whose the thickness is 500
`tim or less.
`FIG. 3 is a Schematic diagram of a Sealed cylindrical
`Ni/MH battery construction of AA size which is obtained by
`the combination of a thin nickel positive electrode in FIG. 2
`and a thin alloy negative electrode wherein MmNi5 type
`hydrogen absorbing alloy powder is coated on punched
`metal in the same way as in a prior art. With respect to each
`of the components other than electrodes of the battery,
`basically they are the same as those in a conventional battery
`Structure.
`The conductive electrode Substrate according to the
`present invention may be any material as long as it has a
`conductivity and the proceSS for providing the unevenneSS
`and for contour and tilts of the walls is possible after the
`filling of the active material powder and is not limited
`particularly. However, the material of the conductive elec
`trode Substrate is properly used at least on the Surface of the
`conductive electrode Substrate by Selecting one kind or more
`from a group consisting of nickel, copper, aluminum, lead
`and alloys whose main components are those metals, which
`are employed in a variety of electrodes for batteries at
`present. Particularly, it is preferable for materials used as a
`nickel electrode for an alkaline Storage battery to be Selected
`at least one from a group consisting of cobalt, calcium,
`
`8
`titanium, Silver, yttrium, lanthanide, carbon and/or their
`oxides, which are arranged on the major part of the Surface,
`from the View point of easiness of processing. The thickness
`of the conductive electrode Substrate which is made three
`dimensional with the hollow concave and convex parts of
`the conductive electrode Substrate according to the present
`invention is the thickneSS which is approximately the same
`as the final electrode which is pressed after the powder
`mainly containing the active material powder or pseudo
`active material powder is filled in or coated on the electrode
`and, more concretely, it is preferable for the above descri