DESCRIPTION
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`NONAQUEOUS ELECTROLYTE SECONDARY BATTERY AND
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`SECONDARY BATTERY MODULE
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`CROSS REFERENCE TO RELATED APPLICATION
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`This application claims priority to Japanese Patent Application No. 2020-046539
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`filed on March 17, 2020, which is incorporated herein by reference in its entirety including
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`the specification, claims, drawings, and abstract.
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`TECHNICAL FIELD
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`Thepresent disclosure relates to a technique for a nonaqueouselectrolyte secondary
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`battery and to a secondary battery module.
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`BACKGROUND
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`10
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`15
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`A nonaqueouselectrolyte secondary battery, such as a lithium ion secondary battery,
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`typically includes an electrode body and electrolyte. The electrode body includesa positive
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`electrode having a positive electrode active material layer, and a negative electrode having
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`a negative electrode active material layer, in which these electrodes are laminated via a
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`20
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`separator.
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`Such anonaqueouselectrolyte secondary battery is, for example, a battery to be
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`charged or discharged with charge carriers (for example, lithium ions) in the electrolyte
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`moving back and forth between the respective electrodes.
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`For example, Patent Document
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`| describes use of a negative electrode in a
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`nonaqueous electrolyte secondary battery,
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`the negative electrode including a negative
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`25
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`electrode collector and a negative electrode active material layer, in which the negative
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`electrode active material layer includesa first layer and a second layer sequentially formed
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`from a side with the negative electrode collector, the first layer includes first carbon-based
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`active material particles with a 10% proof stress of 3 MPa or less, and the second layer
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`-|l-
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`

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`includes second carbon-based active material particles with a 10% proof stress of 5 MPa or
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`greater. According to Patent Document 1, use of the negative electrode active material
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`layer including the above-mentioned first layer and second layer enables provision of a
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`nonaqueouselectrolyte secondary battery superior in output characteristics.
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`CITATION LIST
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`Patent Literature
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`Patent Document 1: WO 2019/187537 Al
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`10
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`SUMMARY
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`As a safety evaluation test for evaluating the tolerance of a battery against internal
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`short-circuiting, for example, a nailing test is available in which a battery is stabbed with a
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`nail
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`to simulate occurrence of internal short-circuiting to observe the amount of heat
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`generation of the battery for safety evaluation of the battery.
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`As for a nonaqueous
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`15
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`electrolyte secondary battery including a negative electrode active material layer having a
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`laminated structure including a first layer and a second layer, as is described in Patent
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`Document 1, there is room for improvement, in that the amount of heat generation in the
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`battery in a nailing test can be reduced.
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`In view of the above, it is an object of the present disclosure to reduce the amount
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`20
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`of heat generation of a battery in a nailing test with respect to a nonaqueouselectrolyte
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`secondary battery and a secondary battery module, each including anegative electrode active
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`material layer having a laminated structure including a first layer and a secondlayer.
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`According to one aspect of this disclosure, there is provided a secondary battery
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`module including at least one nonaqueouselectrolyte secondary battery, and an elastic body
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`25
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`disposed together with the nonaqueouselectrolyte secondary battery, for receiving a load
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`from the nonaqueouselectrolyte secondary battery in a direction in which the nonaqueous
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`electrolyte secondary battery and the elastic body are disposed, wherein the nonaqueous
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`electrolyte secondary battery includes an electrode body including a laminate of a positive
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`-2-
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`

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`electrode, a negative electrode, and a separator disposed between the positive electrode and
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`the negative electrode, and an enclosure for storing the electrode body therein, the elastic
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`body has a compressive elastic modulus of 5 MPa to 120 MPa, the positive electrode includes
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`a positive electrode collector containing Al and an element other than Al, the positive
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`electrode collector has a thermal conductive rate of 65 W/(m-K) to 150 W/(m-K), the
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`negative electrode includes a negative electrode collector and a negative electrode active
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`material layer includinga first layer and a second layer sequentially formed from a side with
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`the negative electrode collector, the first layer contains negative electrode active material
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`particles containing first carbon-based active material particles with a 10% proofstress of 3
`
`10
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`MPaorless, and the second layer contains negative electrode active material particles
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`containing second carbon-based active material particles with a 10% proof stress of 5 MPa
`
`or greater.
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`According to another aspect of this disclosure, there is provided a nonaqueous
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`electrolyte secondary battery including an electrode body including a laminate ofa positive
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`15
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`electrode, a negative electrode, and a separator disposed betweenthe positive electrode and
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`the negative electrode, an elastic body for receiving a load from the electrode body in a
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`lamination direction of the electrode body, and an enclosure for storing the electrode body
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`and the elastic body therein, wherein the elastic body has a compressive elastic modulus of
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`5 MPa to 120 MPa,the positive electrode includes a positive electrode collector containing
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`20
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`Al and an element other than Al, the positive electrode collector has a thermal conductive
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`rate of 65 W/(m:K) to 150 W/(m:K), the negative electrode includes a negative electrode
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`collector and a negative electrode active material layer including a first layer and a second
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`layer sequentially formed from a side with the negative electrode collector, and thefirst layer
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`contains negative electrode active material particles containing first carbon-based active
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`25
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`material particles with a 10% proof stress of 3 MPaor less, and the second layer contains
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`negative electrode active material particles containing second carbon-based active material
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`particles with a 10% proofstress of 5 MPaor greater.
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`Accordingto one aspect of the present disclosure, it is possible to reduce the amount
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`-3-
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`

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`of heat generation of a battery in a nailingtest.
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`BRIEF DESCRIPTION OF DRAWINGS
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`Embodiment(s) of the present disclosure will be described based on the following
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`figures, wherein:
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`FIG.
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`1
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`is a perspective view of a secondary battery module according to an
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`embodiment;
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`FIG. 2 is an exploded perspective view of the secondary battery module according
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`to the embodiment;
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`10
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`FIG. 3 is a schematic cross sectional view of the nonaqueous electrolyte secondary
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`battery in expansion;
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`FIG. 4 is a schematic cross sectional view illustrating the condition of an electrode
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`body in a nailingtest;
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`FIG. 5 is a schematic cross sectional view of an elastic body disposed in an
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`15
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`enclosure;
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`FIG.6 is a schematic perspective view of a cylindrical winding electrode body;
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`FIG.7 is a schematic cross sectional view of a negative electrode;
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`FIG. 8 is a schematic perspective view of one example of an elastic body; and
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`FIG. 9 is aschematic cross sectional view of a part of an elastic body held between
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`20
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`an electrode body and an enclosure.
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`DESCRIPTION OF EMBODIMENTS
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`One example of an embodiment will now be described in detail. The drawings to
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`be referred to in description of the embodiment are only schematically illustrated, and the
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`25
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`dimensionsandratios of the structural components illustrated in the drawings may differ
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`from those of the corresponding actual components.
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`FIG.
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`1
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`is a perspective view of a secondary battery module according to an
`
`embodiment.
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`FIG. 2 is an exploded perspective view of the secondary battery module
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`-4.-
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`

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`according to the embodiment. A secondary battery module | includes, as one example, a
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`stacked body 2, a pair of binding members 6, and a cooling plate 8. The stacked body 2
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`includes a number of nonaqueouselectrolyte secondary batteries 10, a numberofinsulation
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`spacers 12, anumberofelastic bodies 40, and a pair of end plates 4.
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`Each nonaqueous
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`electrolyte
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`secondary battery
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`10
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`is,
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`for
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`example,
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`a
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`chargeable/dischargeable secondary battery, such as a lithium ion secondary battery. A
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`nonaqueouselectrolyte secondary battery 10 in this embodimentis a so-called rectangular
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`battery, and includes an electrode body 38 (refer to FIG. 3), electrolyte, and a flat rectangular
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`parallelepiped enclosure 13. The enclosure 13 includes an outer can 14 and a sealing plate
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`10
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`16. The outer can 14 has a substantially rectangular opening on its one surface, so that the
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`electrode body 38, the electrolyte, and so forth are inserted into the outer can 14 through the
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`opening. The outer can 14 is desirably coated with an insulation film, not illustrated, such
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`as a shrink tube. To the opening of the outer can 14, the sealing plate 16 is provided to
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`
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`cover the openingto thereby seal the outer can 14. Thesealing plate 16 constitutesafirst
`
`15
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`surface 13a of the enclosure 13. The sealing plate 16 is connected to the outer can 14, for
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`example, by meansoflaser, friction stir joining, or brazing.
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`The enclosure 13 may be a cylindrical case, for example, and may be an outer body
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`made of a laminated sheet including a metal layer and a resin layer.
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`The electrode body 38 has a structure including a number of sheet positive
`
`20
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`electrodes 38a and a number of sheet negative electrodes 38b alternately laminated via
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`separators 38d (refer to FIG. 3).
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`Specifically, the positive electrode 38a, the negative
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`
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`electrode 38b, and the separator 38d are laminated inafirst direction X. Thatis, thefirst
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`direction X corresponds to the lamination direction of the electrode body 38.
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`The
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`electrodes disposed at the respective end sides of the electrode body 38 in the lamination
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`25
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`direction are opposed to the respective longerlateral surfaces, to be described later, of the
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`enclosure 13. Note that the illustrated first direction X, a second direction Y, and a third
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`direction Z are directions orthogonal to one another.
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`The electrode body 38 may be a cylindrical winding electrode body formed by
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`-5-
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`

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`winding a laminate including a band-shapedpositive electrode and a band-shaped negative
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`electrode laminated via a separator. Alternatively, the electrode body 38 may bea flat
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`winding electrode body formed by flattening a cylindrical winding electrode body. For a
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`flat winding electrode body, a rectangular parallelepiped outer can is usable, whereas for a
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`cylindrical winding electrode body, a cylindrical outer can is desirably used.
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`Onthe sealing plate 16; that is, on the first surface 13a of the enclosure 13, an output
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`terminal 18 for electrical connection to the positive electrode 38a of the electrode body 38
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`is formed at a position closer to one end in the longitudinal direction, and an output terminal
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`18 for electrical connection to the negative electrode 38b of the electrode body 38 is formed
`
`10
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`at a position closer to the other end. Note that the output terminal 18 for connection to the
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`positive electrode 38a will be hereinafter referred to as a positive electrode terminal 18a, and
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`the output terminal 18 for connection to the negative electrode 38b as a negative electrode
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`terminal 18b.
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`In the case where no polarity distinction between the pair of output terminals
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`18 is necessary, the positive electrode terminal 18a and the negative electrode terminal 18b
`
`15
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`will be collectively referred to as output terminals 18.
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`The outer can 14 has a bottom surface opposedto the sealing plate 16.
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`In addition,
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`the outer can 14 has four lateral surfaces connecting the opening and the bottom surface.
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`Two out of the four lateral surfaces are a pair of longer lateral surfaces connected to two
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`respective opposed longer edges of the opening. Each longerlateral surface is a surface
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`20
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`having the largest area, or the main surface, among the surfaces of the outer can 14. Each
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`longer lateral surface is a lateral surface expanding in a direction intersecting the first
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`direction X (for example, being orthogonal). Meanwhile, the two lateral surfaces other
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`than the two longerlateral surfaces are a pair of shorter lateral surfaces connected to the
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`respective shorter edges of the opening andthose of the bottom surface of the outer can 14.
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`25
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`The bottom surface, the longer lateral surfaces, and the shorter lateral surfaces of the outer
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`can 14 respectively correspond to the bottom surface, the longer lateral surfaces, and the
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`shorter lateral surfaces of the enclosure 13.
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`In the description of this embodiment, for convenience, the first surface 13a of the
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`-6-
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`

`

`enclosure 13 is defined as the upper surface of the nonaqueouselectrolyte secondary battery
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`10.
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`In addition, the bottom surface of the enclosure 13 is defined as the bottom surface of
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`the nonaqueouselectrolyte secondary battery 10; the longer lateral surfaces of the enclosure
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`13 as the longer lateral surfaces of the nonaqueouselectrolyte secondary battery 10; and the
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`shorter lateral surfaces of the enclosure 13 as the shorter lateral surfaces of the nonaqueous
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`electrolyte secondary battery 10. As to the secondary battery module 1, the surface on a
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`side of the upper surface of the nonaqueous electrolyte secondary battery 10 is defined as
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`the upper surface of the secondary battery module 1; the surface on a side of the bottom
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`surface of the nonaqueous electrolyte secondary battery 10 as the bottom surface of the
`
`10
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`secondary battery module 1; and the surfaces on the respective sides of the shorter lateral
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`surfaces of the nonaqueouselectrolyte secondary battery 10 as the lateral surfaces of the
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`secondary battery module 1.
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`In addition, the direction toward the upper surface of the
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`secondary battery module 1 is defined as the upward direction in the vertical direction; and
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`the direction toward the bottom surface of the secondary battery module 1 as the downward
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`15
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`direction in the vertical direction.
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`The numberof nonaqueouselectrolyte secondary batteries 10 are aligned in parallel
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`at predetermined intervals such that the longer lateral surfaces of the adjacent nonaqueous
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`electrolyte secondary batteries 10 are opposed to each other.
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`In this embodiment, the
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`output terminals 18 of the respective nonaqueous electrolyte secondary battery 10 are
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`20
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`disposed directed in the same direction, although these may be disposed directed in different
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`directions.
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`Two adjacent nonaqueouselectrolyte secondary batteries 10 are disposed (stacked)
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`such that the positive electrode terminal 18a of one nonaqueouselectrolyte secondary battery
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`10 is disposed adjacent to the negative electrode terminal 18b of the other nonaqueous
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`25
`
`electrolyte secondary battery 10, and the positive electrode terminal 18a and the negative
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`electrode terminal 18b are serially connected to each other via a busbar (not illustrated).
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`Alternatively, the output terminals 18 of the same polarity of the number of adjacent
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`nonaqueouselectrolyte secondary batteries 10 may be connected in parallel via a busbar to
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`-7-
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`

`

`thereby form a nonaqueous electrolyte secondary battery block, and the nonaqueous
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`electrolyte secondary battery blocks may beserially connected to each other.
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`The insulation spacer 12 is disposed between two adjacent nonaqueouselectrolyte
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`secondary batteries 10 for electrical insulation between the two nonaqueouselectrolyte
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`secondary batteries 10. The insulation spacer 12 is made of insulation resin, for example.
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`Examples of the resin for formation of the insulation spacer 12 include polypropylene,
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`polybutylene terephthalate, and polycarbonate.
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`The number of nonaqueous electrolyte
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`secondary batteries 10 and the numberofinsulation spacers 12 are alternately stacked. The
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`insulation spacer 12 is disposed also between the nonaqueouselectrolyte secondary battery
`
`10
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`10 and the endplate 4.
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`The insulation spacer 12 includes a planar portion 20 and a wall portion 22. The
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`planar portion 20 intervenes between the opposed longerlateral surfaces of two adjacent
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`nonaqueous electrolyte secondary batteries 10.
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`This arrangement ensures insulation
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`between the outer cans 14 of the adjacent nonaqueouselectrolyte secondary batteries 10.
`
`15
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`The wall portion 22 extends from the outer edge of the planar portion 20 in a
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`direction in which the nonaqueouselectrolyte secondary batteries 10 are aligned, and covers
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`a part of the upper surface, the lateral surface, and a part of the bottom surface of the
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`nonaqueous electrolyte secondary battery 10. This ensures some distance, for example,
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`between the adjacent nonaqueous electrolyte secondary batteries 10 or between a
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`20
`
`nonaqueouselectrolyte secondary battery 10 and the end plate 4 on the lateral side. The
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`wall portion 22 has a notch 24 where the bottom surface of the nonaqueous electrolyte
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`secondary battery 10 is exposed.
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`In addition, the insulation spacer 12 has an urging force
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`receiving portion 26 formed upward on each end portion of the insulation spacer 12 in the
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`second direction Y.
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`25
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`Theelastic bodies 40 are disposedin the first direction X together with the number
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`of nonaqueous electrolyte secondary batteries 10.
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`That is, the first direction X is the
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`lamination direction of the electrode body 38, as described above, and also a direction in
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`which the nonaqueous electrolyte secondary batteries 10 and the elastic bodies 40 are
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`-8-
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`

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`disposed, or a disposition direction.
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`The elastic body 40 is shaped like a sheet, and
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`intervenes, for example, between the longerlateral surface of each nonaqueouselectrolyte
`
`secondary battery 10 and the planar portion 20 of each insulation spacer 12.
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`Theelastic
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`body 40, disposed between two adjacent nonaqueouselectrolyte secondary batteries 10, may
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`be one sheet or a laminate including a numberof sheets laminated. The elastic body 40
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`may be secured on the surface of the planar portion 20 with adhesive agent or the like.
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`Alternatively, a recess may be formed on the planar portion 20, so that the elastic body 40
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`may be fitin the recess.
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`Still alternatively, the elastic body 40 andthe insulation spacer 12
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`may be formed integrally.
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`Still alternatively, the elastic body 40 may serve also as the
`
`10
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`planar portion 20.
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`The number of nonaqueous electrolyte secondary batteries 10, insulation spacers
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`12, and elastic bodies 40, which are aligned in parallel to one another, are held between the
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`pair of end plates 4 in the first direction X. Each end plate 4 is made of a metal plate or a
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`resin plate, for example. Each end plate 4 has a screw hole 4a that penetrates the end plate
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`15
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`4 in the first direction X, so that a screw 28is inserted into the screw hole 4a.
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`Eachofthe pair of binding members6 is a longitudinal member whoselongitudinal
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`direction correspondsto the first direction X. The pair of binding members6 are disposed
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`opposed to each other in the second direction Y._ Between the pair of binding members6,
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`the stacked body 2 is disposed. Each binding member6 includes a main portion 30, a
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`20
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`support portion 32, anumberof urging portions 34, and a pair of fixture portions 36.
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`The main portion 30 is arectangular portion extendingin thefirst direction X. The
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`main portion 30 extends parallel to the lateral surfaces of the respective nonaqueous
`
`electrolyte secondary batteries 10. The support portion 32 extendsin thefirst direction X,
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`and projects in the second direction Y from the lower end of the main portion 30. The
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`25
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`support portion 32 is a plate member continuing in the first direction X, and supports the
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`stacked body 2.
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`The number of urging portions 34 are connected to the upper end of the main
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`portion 30, and project in the second direction Y. The support portion 32 is opposed to the
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`-9.-
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`

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`urging portion 34 in the third direction Z. The number of urging portions 34 are disposed
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`at predeterminedintervalsin the first direction X. Each of the urging portions 34 has a leaf
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`spring shape, for example, and urges the nonaqueous electrolyte secondary batteries 10
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`toward the support portion 32.
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`Each of the pair of fixture portions 36 is a plate member formed on the respective
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`end portion of the main portion 30 in thefirst direction X and projecting in the second
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`direction Y. The pair of fixture portions 36 is opposed to each otherin the first direction
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`X.
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`Eachfixture portion 36 has a through hole 36afor insertion of a screw 28 therethrough.
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`The pair of fixture portions 36 have the binding member6 secured to the stacked body 2.
`
`10
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`The cooling plate 8 is a mechanism for cooling the number of nonaqueous
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`electrolyte secondary batteries 10. The stacked body 2, being bundled with the pair of
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`binding members6, is placed on the main surface of the cooling plate 8, and secured onto
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`the cooling plate 8 with a fastening member(not illustrated), such as a screw, penetrating a
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`through hole 32a of the support portion 32 and a through hole 8a ofthe coolingplate 8.
`
`15
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`FIG. 3 is a schematic cross sectional view of nonaqueous electrolyte secondary
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`batteries in expansion.
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`In FIG. 3, a lower number of nonaqueouselectrolyte secondary
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`batteries 10 than the numberof the nonaqueouselectrolyte secondary batteries 10 actually
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`provided areillustrated; the inside structure of the nonaqueouselectrolyte secondary battery
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`10 is illustrated more simply; and the insulation spacer 12 is not illustrated.
`
`Asillustrated
`
`20
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`in FIG. 3, each nonaqueouselectrolyte secondary battery 10 incorporates the electrode body
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`38 (the positive electrode 38a, the negative electrode 38b, and the separator 38d). The outer
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`can 14 of the nonaqueous electrolyte secondary battery 10 expands and shrinks due to
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`expansion and shrinkageofthe electrode body 38 through charging and discharging. Once
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`the outer can 14 of each nonaqueouselectrolyte secondary battery 10 expands, a load G1
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`25
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`directed outwardin thefirst direction X is applied to the stacked body 2.
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`Thatis, the elastic
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`body 40, disposed together with the nonaqueouselectrolyte secondary battery 10, receives a
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`load directed in the first direction (or the disposition direction of the nonaqueouselectrolyte
`
`secondary battery 10 and the elastic body 40, which is also the lamination direction of the
`
`- 10 -
`
`

`

`electrode body 38) from the nonaqueouselectrolyte secondary battery 10. Meanwhile, a
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`load G2 corresponding to the load G1 is applied to the stacked body 2 by the endplate 4.
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`FIG. 4 is a schematic cross sectional view of an electrode body in a nailingtest.
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`Asillustrated in FIG. 4, the positive electrode 38a includesa positive electrode collector 50
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`and a positive electrode active material layer 52 formed on the positive electrode collector
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`50, while the negative electrode 38b includes a negative electrode collector 54 and anegative
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`electrode active material layer 56 formed on the negative electrode collector 54. Note that
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`the negative electrode active material layer 56 includesa first layer 56a and a second layer
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`56b sequentially formed from a side with the negative electrode collector 54, as to be
`
`10
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`described later (refer to FIG. 7).
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`Asillustrated in FIG. 4, when a nonaqueouselectrolyte
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`secondary battery is stabbed with a nail 58 in a nailing test until the nail 58 fully penetrates
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`the positive electrode 38a and the separator 38d to reach the negative electrode 38b, internal
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`short-circuiting is caused, and a short-circuit current flows. This leads to heat generation
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`in the nonaqueouselectrolyte secondary battery.
`
`15
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`Here, the positive electrode collector 50 in this embodiment is a low thermal
`
`conductive Al-containing positive electrode collector that contains Al and an element other
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`than Al and whose thermal conductive rate is 65 W/(m:K) to 150 W/(m:K).
`
`In such alow
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`thermal conductive Al-containing positive electrode collector, as heat likely concentrates in
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`a short-circuited portion (a portion of the positive electrode collector in direct contact with
`
`20
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`the nail), a short-circuited portion of the positive electrode collector 50 melts acceleratingly.
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`This leads to a shorter period of time after occurrenceof internal short-circuiting until fusing
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`of the positive electrode collector 50 in a nailingtest.
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`The elastic body 40 in this embodimentis an elastic body having a compressive
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`elastic modulus of 5 MPa to 120 MPa._Since such an elastic body having a compressive
`
`25
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`elastic modulus of 5 MPa to 120 MPa modifies the load G1 directed outward in the first
`
`direction X and the load G2 corresponding to the load G1, excessive approach between the
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`positive electrode 38a and the negative electrode 38b is prevented. This prevents increase
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`in area of a short-circuited portion of the positive electrode collector 50 in a nailing test, as
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`-ll-
`
`

`

`compared with a case in which the above-mentioned low thermal conductive Al-containing
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`positive electrode collector is used but an elastic body with a compressive elastic modulus
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`of 5 MPa to 120 MPais not disposed or an elastic body with a compressive elastic modulus
`
`in excess of 120 MPa is disposed. Hence, the period of time after occurrence of internal
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`short-circuiting until fusing of the positive electrode collector 50 is further shortened in a
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`nailing test.|Note here that a nonaqueous electrolyte secondary battery including the
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`negative electrode active material layer 56 having a laminated structure includingthe first
`
`layer 56a and the second layer 56b, to be described later, prevents drop in output of a battery
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`in a charge/discharge cycle, but still causes large heat generation due to a large short-
`
`10
`
`circuiting current when internal short-circuiting occurs in a nailingtest.
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`In such a
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`nonaqueouselectrolyte secondary battery 10 as well, use of the elastic body 40 having the
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`above-mentioned compressiveelastic modulus and the positive electrode collector 50 having
`
`the above-mentioned thermal conductive rate shortens the period of time after occurrence of
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`internal short-circuiting until fusing of the positive electrode collector 50 in a nailingtest,
`
`15
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`and thus reduces the amount of heat generation in a nailingtest.
`
`FIG. 5 is aschematic cross sectional view of an elastic body that is disposed inside
`
`an enclosure. The elastic body 40 is not necessarily disposed along with the nonaqueous
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`electrolyte secondary battery 10, as described above; that is, disposed outside the enclosure
`
`13, but can be disposed inside the enclosure 13. The elastic body 40 illustrated in FIG. 5
`
`20
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`is disposed on each end side of the electrode body 38 in the lamination direction (thefirst
`
`direction X) of the electrode body 38, and held between the inside wall of the enclosure 13
`
`and the electrode body 38.
`
`When the electrode body 38 expands through charging and discharging of the
`
`nonaqueouselectrolyte secondary battery 10, a load directed outward inthefirst direction X
`
`25
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`is generated in the electrode body 38.
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`Thatis, the elastic body 40 inside the enclosure 13
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`receives a load directed in thefirst direction (the lamination direction of the electrode body
`
`38) from the electrode body 38. Hence, provided that the elastic body 40 has a compressive
`
`elastic modulus of 5 MPa to 120 MPa andthat the positive electrode collector 50 is a low
`
`-12-
`
`

`

`thermal conductive Al-containing positive electrode collector containing Al and an element
`
`other than Al and having a thermal conductive rate of 65 W/(m:K) to 150 W/(m:K), the
`
`same operational effect as that described above can be obtained.
`
`The elastic body 40 in the enclosure 13 can be disposed anywhere, provided that
`
`the elastic body 40 can receive a load from the electrode body 38 in the lamination direction
`
`of the electrode body 38.
`
`For example, in the case where the electrode body 38 is a
`
`cylindrical winding electrode body 38 illustrated in FIG. 6, for example, the elastic body 40
`
`may be disposed at a winding core portion 39 of the cylindrical winding electrode body 38.
`
`Note that the lamination direction of the cylindrical winding electrode body 38 corresponds
`
`10
`
`to the diameter direction (R) of the electrode body 38. As the electrode body 38 expands
`
`or shrinks, a load directed in the lamination direction (the diameter direction (R) of the
`
`electrode body 38) is generated with respect to the electrode body 38, and the elastic body
`
`40 inside the winding core portion 39 receives the load in the lamination direction of the
`
`electrode body 38.
`
`In the case where a numberofelectrode bodies 38 are disposed inside
`
`15
`
`the enclosure 13, which is not described by reference to the drawings, the elastic body 40
`
`may be disposed between adjacent electrode bodies 38.
`
`In the case of a flat winding
`
`electrode body 38 as well, an elastic body may be similarly disposed at the middle of the
`
`electrode body.
`
`Thepositive electrode 38a, the negative electrode 38b, the separator 38d, the elastic
`
`20
`
`body 40, and the electrolyte will now be describedin detail.
`
`The positive electrode 38a includes the positive electrode collector 50, and the
`
`positive electrode active material layer 52 formed on the positive electrode collector 50.
`
`The positive electrode collector 50 contains Al and an element other than Al and has a
`
`thermal conductive rate in the range of 65 W/(m-K) to 150 W/(m:K). Al and the element
`
`25
`
`other than Al may or may notbe alloyed.
`
`The Al content of the positive electrode collector 50 is preferably in excess of 50
`
`wt%, more preferably 75 wt% or greater, and further preferably 90 wt% or greater, for
`
`example, in view of prevention of increase of the resistance value of the positive electrode
`
`- 13-
`
`

`

`collector 50. The upper limit of the Al content of the positive electrode collector 50 is, for
`
`example, 98 wt% orless.
`
`The element other than Al contained in the positive electrode collector 50 can be
`
`any element, provided that the element allows adjustment of the thermal conductive rate into
`
`the above-described range. Examples of the element include Mg, Si, Sn, Cu, Zn, and Ge.
`
`Amongthese elements, Mg,in particular, is preferable in view of easiness in adjustment of
`
`the thermal conductive rate of the positive electrode collector 50. The Mgcontent of the
`
`positive electrode collector 50 is preferably 1.5 wt% or greater, and more preferably 3 wt%
`
`or greater, in view of adjustment of the thermal conductive rate of the positive electrode
`
`10
`
`collector 50 to 150 W/(m:K) or less. The higher the Mg content of the positive electrode
`
`collector 50, the harder the positive electrode collector 50.
`
`In general, with a harder
`
`positive electrode collector,
`
`in the case of a nonaqueous electrolyte secondary battery
`
`employing a flat winding electrode body, for example, expansion and shrinkage of the
`
`electrode body through charging and discharging leads to application of a stress to a corner
`
`15
`
`portion (where the electrode and the separator are curved) of a flat winding electrode body,
`
`which may break the positive electrode collector at a corner portion of the electrode body.
`
`In this embodiment, however, since the elastic body 40 of 5 MPa to 120 MPa modifies the
`
`stress applied to the comer portion of the flat winding electrode body, breakage of the
`
`positive electrode collector 50 can be prevented despite increase of the Mg content of the
`
`20
`
`positive electrode collector 50. The upper limit of the Mg content of the positive electrode
`
`collector 50 is preferably less than 50 wt%, for example, more preferably 10 wt% orless,
`
`and further preferably is 6 wt% orless in consideration of the resistance valueofthe positive
`
`electrode collector 50.
`
`While an acceptable thermal conductive rate of the positive electrode collector 50
`
`25
`
`is in the rage of 65 W/(m-K) to 150 W/(m:K), a preferred range of the thermal conductive
`
`rates is a range from 85 W/(m: K) to 130 W/(m-K), and more preferred is a range from 95
`
`W/(m:K) to 120 W/(m-K), in view of further reduction in amount of heat generation of a
`
`battery in a nailingtest.
`
`- 14 -
`
`

`

`<Method for Measuring Thermal Conductive Rate>
`
`Thermaldiffusivity, specific heat, and density of the positive electrode collector 50
`
`are measured using the following method, and then substituted into the expression (1) below
`
`to obtain the thermal conduction rate (W/m: K) of the positive electrode collector 50.
`
`-
`
`thermal diffusivity: measured at 25°C, using a Xenon Flash Analyzer (registered
`
`trademark: LFA 467HT Hyper Flash, manufactured by Netzsch Japan K.K.).
`
`- specific heat: measured through comparison with sapphire reference material, using a
`
`differential scanning calorimeter (DSC).
`
`10
`
`- density: measured based on Archimedes’ principle.
`
`- thermal conductive rate = (thermal diffusivity) < (spe