DESCRIPTION
`
`TITLE OF INVENTION: NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY
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`TECHNICALFIELD
`
`[0001]
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`The present disclosure relates to a non-aqueouselectrolyte secondary battery.
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`BACKGROUND ART
`
`10
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`[0002]
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`A non-aqueouselectrolyte secondary battery including a carbon material used as a
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`negative electrode active material is widely used as a secondary battery having a high
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`energy density.
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`[0003]
`
`15
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`For example, Patent Literature 1 discloses a non-aqueouselectrolyte secondary
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`battery including densified carbon used as a carbon material, the densified carbon having a
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`porosity due to closed pores of 5% orless.
`
`10004}
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`For example, Patent Literature 2 discloses a non-aqueouselectrolyte secondary
`
`20
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`battery including carbon materials including a carbon material A having a porosity due to
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`closed pores of 1%or more and less than 23% and a carbon material B having a porosity
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`due to closed pores of 23% or more and 40%orless.
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`CITATION LIST
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`25
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`PATENT LITERATURE
`
`[0005]
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`PATENT LITERATURE 1: Japanese Unexamined Patent Application Publication No. H-
`
`320600
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`

`

`PATENT LITERATURE 2: Japanese Unexamined Patent Application Publication No.
`
`2014-67638
`
`SUMMARY
`
`[0006]
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`In view of improvedreliability of a non-aqueous electrolyte secondary battery,
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`suppression of deterioration in charging/discharging cyclic characteristics is required.
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`{0007|
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`A negative electrode of a non-aqueous electrolyte secondary battery is obtained by
`
`10
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`applying a slurry including a carbon material as a negative electrode active material io a
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`negative electrode current collector, drying the resulting coating, and compressing the
`
`resulting coating (negative electrode active material layer). However, there is a problem:
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`specifically, itis necessary to carry out the cornpression a plurality of times according to
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`the porosity due to closed pores of the carbon material, for obtaming a negative electrode
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`15
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`active material layer having a high packing density. The increase in the number of times
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`of the compression may lead to reduction in productivity ofbatteries.
`
`[0008]
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`It is an advantage of the present disclosure to provide a non-aqueouselectrolyte
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`secondary battery that can be produced without an increase in the number of times of the
`
`20
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`compression in manufacturing the negative electrode and can also achieve suppression of
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`deterioration in charging/discharging cyclic characteristics.
`
`[0009]
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`A non-aqueous electrolyte secondary battery of one aspect of the present disclosure
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`comprises a negative electrode having a negative electrode active material laver, the
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`25
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`negative electrode active material layer including graphite particles A and graphite
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`particies B each as a negative electrode active material,
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`wherein the graphite particles A have a porosity due to closed pores of 5%orless,
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`and the graphite particles B have a porosity due to closed pores of 8%to 20%, and
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`-2-
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`

`

`a mass ratio between the graphite particles A and the graphite particles B is 70:30to
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`90:10.
`
`[0010]
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`According to one aspect of the present disclosure, there can be provided a non-
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`aqueouselectrolyte secondary battery that can be produced without an increase inthe
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`number oftimes of the compression in manufacturing the negative electrode and can also
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`achieve suppression of deterioration in charging/discharging cyclic characteristics.
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`BRIEF DESCRIPTION OF DRAWING
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`10
`
`[0011]
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`FIG. 1 is asectional view illustrating a non-aqueous electrolyte secondary battery of
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`an exemplary embodiment.
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`FIG. 2 is aschematic enlarged view showing the section of a graphite particle in the
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`negative electrode active materiallayer.
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`15
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`DESCRIPTION OF EMBODIMENTS
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`[0012]
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`(Basic Findings of Present Disclosure)
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`Breakage of graphite particles due to charging/discharging cycles and a subsequent
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`20
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`decomposition reaction of a non-aqueouselectrolyte, for example, are prevented in the
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`graphite particles having a small porosity due to closed poresto result in a tendency to
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`suppress deterioration in charging/discharging cyclic characteristics of a non-aqueous
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`electrolyte secondary battery, as compared to graphite particles having a large porosity due
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`to closed pores. However, graphite particles having a small porosity due to closed pores
`
`25
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`are difficult to collapse by compression; accordingly, it is necessary to carry out the above-
`
`described compression a plural times in manufacturing the negative electrode, for
`
`obtaining a negative electrode active material laver having a high packing density. Then,
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`the present inventors have studied diligently, and as a resuli, have found that for providing
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`-3-
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`

`

`a non-aqueous electrolyte secondary battery that can be produced using graphite particles
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`having a small porosity due to closed pores without an increase in the number oftimes of
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`the compression in manufacturing the negative electrode and that can also achieve
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`suppression of deterioration in charging/discharging cyclic characteristics, it is necessary
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`to mix the graphite particles having a small porosity due to closed pores with graphite
`
`particles having a large porosity due to closed pores in a specific ratio. Thus, the present
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`imventors have reached the non-aqueous electrolyte secondary battery of the aspect shown
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`below.
`
`f0013]
`
`10
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`The non-aqueous electrolyte secondary battery of one aspect of the present
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`disclosure comprises a negative electrode having a negative electrode active material layer,
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`the negative electrode active material layer including graphite particles A and sraphite
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`particles B each as a negative electrode active material,
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`wherein the graphite particles A have a porosity due to closed pores of 5%or less,
`
`15
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`andthe graphite particles B have a porosity due to closed pores of &%to 20%, and
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`a mass ratio between the graphite particles A and the graphite particles B is 70:30 to
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`30:10.
`
`10014}
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`When the negative electrode active material laver including the graphite particles A
`
`20
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`having a porosity due to closed pores of 8%orless and the graphite particles B having a
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`porosity due to closed pores of 8%to 20% in a mass ratio of 70:30 to 90:10 1s compressed
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`with a mill rol or the like in the manufacturing process, the sraphite particles B are
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`moderately collapsed so that the graphite particles B are present in voids between the
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`graphite particles A, which are difficult to collapse, and thus, the packing density easily
`
`25
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`becomes high without an increase in the number of times of the compression.
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`Uf the ratio
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`of the graphite particles A is higher than the above described range, an increase in the
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`numberof times of the compression is necessary for reducing the voids between the
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`graphite particles A, and accordingly a high packmeg density cannot be obtained. The
`
`-4.-
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`

`

`presence of the graphite particles A, which have a porosity due to closed pores of 5% or
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`less, in the above-described ratio in the negative electrode active material layer suppresses
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`deterioration in charging/discharging cyclic characteristics.
`
`It is possible that not only the
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`presence of the graphite particles A, which have a porosity due to closed pores of 5%or
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`less, but also increase in the contact rate of the graphite particles (A, B) with each other
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`due to the presence of the graphite particles B in the voids between the graphite particles A
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`are causes of the suppressing effect on deterioration in charging/discharging cyclic
`
`characteristics.
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`Furthermore, the graphite particies B, which have a porosity due to closed
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`pores of 8%to 20%, retain a large amount of a non-aqueous electrolyte, accordingly, a
`
`10
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`certain amount of a non-aqueous electrolyte is retained in the negative electrode active
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`material layer due to the presence of the graphite particles B in the negative electrode
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`active material layer, and the contact of the graphite particles (A, B) with the non-aqueous
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`electrolyte is sufficiently ensured.
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`It is possible that this is also one of the causes of the
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`suppressing effect on deterioration in charging/discharging cyclic characteristics.
`
`ffthe
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`15
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`ratio of the graphite particles B is higher than the above descnbed range, breakage of the
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`graphite particles in charging/discharging cycles and the subsequent decomposition
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`reaction of the non-aqueous electrolyte abundantly occur, for example, and it is thus
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`difficult to sufficiently suppress deterioration in charging/discharging cyclic
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`characteristics.
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`20
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`[0015]
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`Hereinafter, exemplary embodiments will be described in detail with reference to
`
`drawings.
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`However,
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`the non-aqueous electrolyte secondary battery of the present
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`disclosure is not limited to the embodiments described hereinbelow. The drawings which
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`are referred in the description of the embodiments are schematically illustrated.
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`25
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`[0016]
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`FIG.
`
`1
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`is a sectional view of a non-aqueous electrolyte secondary battery of an
`
`exemplary embodiment. The non-aqueouselectrolyte secondary battery 10 shown in FIG.
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`1 comprises: an electrode assembly 14 having a woundstructure in which a positive
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`-5-
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`

`

`electrode 11 and a negative electrode 12 are woundtogether with a separator 13 interposed
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`therebetween; a non-aqueous electrolyte; insulating plates 18 and 19 respectively disposed
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`on the upper and lowersides of the electrode assembly 14; and a battery case 15 housing
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`these members. The battery case 15 is constituted of a cylindrical case body 16 having a
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`closed-end and a sealing assembly 17 for closing the opening of the case body 16.
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`Alternatively to the electrode assembly 14 having a woundstructure, an electrode assembly
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`in another form may beapplied, including an electrode assembly having a laminate structure
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`in which positive electrodes and negative electrodes are laminated alternately with separators
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`interposed therebetween. Examples of the battery case 15 include a metallic package can
`
`10
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`having a cylindrical shape, a rectangular shape, a coin shape, a button shape, or another
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`shape, and a package pouch formed by laminating a metal sheet with a resin sheet.
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`[0017]
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`The case body 161s, for example, a cylindrical metallic package having a closed-end.
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`A gasket 28 is provided between the case body 16 and the sealing assembly 17 to ensurethat
`
`15
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`the battery case is tightly sealed. The case body 16 includesa projecting portion 22 formed
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`by, for example, pressing the lateral surface from outside to support the sealing assembly 17.
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`The projecting portion 22 is preferably formed annularly along the circumferential direction
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`of the case body 16, and the upper surface thereof supports the sealing assembly 17.
`
`[0018]
`
`20
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`The sealing assembly 17 includesthe filter 23, a lower vent member24, an insulating
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`member 25, an upper vent member 26, and a cap 27, these membersbeingpiled in this order
`
`from the electrode assembly 14 side.
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`Each of the members constituting the sealing
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`assembly 17 has, for example, a disk or ring shape, and the members other than the insulating
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`member25 are electrically connected to each other. The lower vent member 24 and the
`
`25
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`upper vent member 26 are connected to each otherat their middle portions and the insulating
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`member25is interposed between their circumferences.
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`If the internal pressure of the non-
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`aqueouselectrolyte secondary battery 10 increases by heat generation due to, for example,
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`internal short, the lower vent member 24 changes its shape so as to, for example, push up
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`-6-
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`

`

`the upper vent member 26 toward the cap 27, and the lower vent member 24 thus ruptures
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`to break the electrical connection between the lower vent member 24 and the upper vent
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`member 26.
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`If the internal pressure further increases, the upper vent member26 ruptures
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`to discharge gas through the opening of the cap 27.
`
`[0019]
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`In the non-aqueous electrolyte secondary battery 10 shown in FIG. 1, a positive
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`electrode lead 20 attached to the positive electrode 11 passes through a through-hole in the
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`insulating plate 18 and extends toward the sealing assembly 17, and a negative electrode
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`lead 21 attached to the negative electrode 12 extends on the outside of the insulating plate
`
`10
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`19 to the bottom side of the case body 16. The positive electrode lead 20 is connected to
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`the lower surface of the filter 23, which is the bottom board of the sealing assembly 17, by
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`welding or the like, and the cap 27, which is the top board of the sealing assembly 17 and
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`electrically connected to the filter 23, serves as a positive electrode terminal. The negative
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`electrode lead 21 is connected to the inner surface of the bottom of the case body 16 by
`
`15
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`welding or the like, and the case body 16 serves as a negative electrode terminal.
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`[0020]
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`Component elements of the non-aqueous electrolyte secondary battery 10 will be
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`described in detail below.
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`[0021]
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`20
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`[Negative Electrode]
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`The negative electrode 12 comprises metal foil or the like as a negative electrode
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`current collector and a negative electrode active material layer formed on the current
`
`collector. As the negative electrode current collector, foil of a metal that is stable in the
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`electric potential range of the negative electrode, such as copper, a film with such a metal
`
`25
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`disposed as an outer layer, or the like is used. The negative electrode active material layer
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`includes a negative electrode active material including graphite particles. The negative
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`electrode active material layer preferably includes a binderorthelike.
`
`[0022]
`
`

`

`FIG. 2 is aschematic enlarged view showing the section of a graphite particle in the
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`negative electrode active material layer. As shown in FIG.2, the graphite particle 30
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`includes a pore 34 that is closed and does not reach any particle surface from the inner part
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`of the particle (hereinafter, referred to as a closed pore 34), and a pore 36 which reaches a
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`particle surface from the innerpart of the particle (hereinafter, referred to as an open pore
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`36) in the sectional view of the graphite particle 30.
`
`[0023]
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`The graphite particles 30 in the present embodimentinclude graphite particles A
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`having a porosity due to closed pores of 5% or less and graphite particles B having a
`
`10
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`porosity due to closed pores of 8% to 20%.
`
`In view of, for example, suppression of
`
`deterioration in charging/discharging cyclic characteristics, the graphite particles A have a
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`porosity due to closed pores of 5% or less, preferably 1% to 5%, and morepreferably 3%
`
`to5%.
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`In view of, for example, ease of compression of the negative electrode active
`
`material layer, the graphite particles B have a porosity due to closed pores of 8% to 20%,
`
`15
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`preferably 10% to 18%, and morepreferably 12% to 16%. The porosity due to closed
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`pores of the graphite particles is a two-dimensional value, andis the ratio of the area ofthe
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`closed pores 34 in the graphite particles to the area of the cross section of the graphite
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`particles. The porosity due to the closed pores in the graphite particles can be determined
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`in the following manner.
`
`20
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`[0024]
`
`<Method for determination of porosity due to closed pores>
`
`(1) A cross section of a negative electrode active material is exposed. The method for
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`exposing the cross section may be, for example, a method including cutting out a part of a
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`negative electrode and processing the resultant with an ion-milling machine(e.g.,
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`25
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`IM4000PLUS, manufactured by Hitachi High-Tech Corporation) to expose a cross section
`
`of the negative electrode active material layer.
`
`

`

`(2) A backscattered electron imageof the exposed cross section of the negative electrode
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`active material layer is taken using a scanning electron microscope. The magnification
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`for taking the backscattered electron imageis 3000x to 5000x.
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`(3) The obtained imageofthe cross section is imported into a computer, and a binarization
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`process is carried out using an imageanalysis soft (e.g., ImageJ, manufactured by National
`
`Institutes of Health, US) to obtain a binarized image in whichthe color of the cross
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`sections of particles and the color of pores present in the cross sections of the particles in
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`the imageofthe cross section are converted to black and white, respectively.
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`(4) Graphite particles A, B having a particle size of 5 um to 50 um are selected in the
`
`10
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`binarized image andthe area of the cross section of the graphite particle and the area of the
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`closed pores present in the cross section of the graphite particle are calculated. The area
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`of the cross section of a graphite particle here refers to the area of the region surrounded by
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`the outer circumference of the graphite particle, i.e., the whole area of the cross section of
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`the graphite particle. Among pores present in the cross section of a graphite particle, a
`
`15
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`pore having a width of 3 um or less may bedifficult to identify as either a closed pore or
`
`an open pore in the imageanalysis, and therefore, a pore having a width of 3 umorless
`
`may be regarded as aclosed pore. Then, from the area of the cross section of a graphite
`
`particle and the area of the closed pores in the cross section of the graphite particle
`
`calculated, the porosity due to closed pores of the graphite particle (the area of the closed
`
`20
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`pores in the cross section of the graphite particle x 100 / the area of the cross section of the
`
`graphite particle) is calculated. The average of ten particles of the graphite particles A
`
`and the average of ten particles of the graphite particles B are taken as the porosity due to
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`the closed pores of the graphite particles A and that of the graphite particles B,
`
`respectively.
`
`25
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`[0025]
`
`The graphite particles A, B are manufactured in the following manner, for example.
`
`<Graphite Particles A with Porosity Due to Closed Pores of 5%orless>
`
`

`

`For example, coke (precursor) as a main rawmaterial is crushed into a
`
`predetermined size, and the resultant in an aggregated state with a binderis fired at a
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`temperature of 2600°Cor higherto graphitize, followed by sieving to thereby obtain
`
`graphite particles A having a desired size. The porosity due to closed pores can be
`
`controlled to 5%or less bv, for example, the particle size of the precursor after crushing
`
`and the particle size of the precursor in an aggregated state.
`
`For example, the average
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`particle size (median diameter DS0) of the precursor after crushing is preferably within a
`
`range from 12 umto 20 um.
`
`For asmaller porosity due to closed pores withm a range of
`
`5%or less, the particle size of the precursor after crushing is preferably larger.
`
`10
`
`<Graphite Particles B with Porosity Due to Closed Pores of 8%to 20%>
`
`For example, coke (precursor) as a main raw material is crushed into a predetermined
`
`size, and the resulting coke is aggregated with a binder. The resultant is further press-
`
`moldedinto a block shapeandfired at a temperature of 2600°C or higher to graphitize. The
`
`molded product in a block shape after graphitization is crushed and sieved to thereby obtain
`
`15
`
`graphite particles B having a desired size.
`
`The porosity due to closed pores can be
`
`controlled to 8% to 20% by the amount of the volatile components included in the molded
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`product in a block shape.
`
`In the case where a part of the binder added to the coke
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`(precursor) volatilizes upon firing,
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`the binder can be used as a volatile component.
`
`Examples of such a binderincludepitch.
`
`20
`
`[0026]
`
`Examples of the graphite particles A and B used in the embodimentincludes, but
`
`not particularly limited to, natural graphite andartificial graphite, and artificial graphiteis
`
`preferred in view of, for example, ease of controlling the porosity due to closed pores.
`
`For the graphite particles A and B used in the embodiment,the lattice spacing (doo2) of
`
`25
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`(002) plane in wide-angle X-ray diffraction is preferably 0.3354 nm or more, more
`
`preferably 0.3357 nm or more, and preferably less than 0.340 nm, more preferably 0.338
`
`nm or less, for example.
`
`For the graphite particles A and B used in the embodiment, the
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`crystallite size (Lc(002)) determined by X-ray diffraction is preferably 5 nm or more, more
`
`- 10 -
`
`

`

`preferably 10 nm or more, and preferably 300 nm orless, more preferably 200 nm orless,
`
`for example.
`
`In the case wherethelattice spacing (doo2) and the crystallite size (Lc(002))
`
`are within the respective ranges described above, the battery capacity of the non-aqueous
`
`electrolyte secondary battery tends to be larger as compared to the case where they are out
`
`of the above-described ranges.
`
`[0027]
`
`For example, the negative electrode 12 can be produced by preparing a negative
`
`electrode mixture slurry including a negative electrode active material including the
`
`graphite particles A and B, a binder, and other components, applying the negative electrode
`
`10
`
`mixture slurry to a negative electrode current collector, drying the resultant coatings to
`
`form negative electrode active material layers, and then carrying out compression by
`
`compressing the negative electrode active material layers with a mill roll or the like.
`
`In
`
`the present embodiment, the negative electrode active material includes the graphite
`
`particles A and graphite particles B in a mass ratio of 70:30 to 90:10. The negative
`
`15
`
`electrode active material layer including the graphite particles A and graphite particles B in
`
`a massratio within the above described rangeis likely to have a high packing density
`
`through compression with a mill roll or the like, as described hereinbefore, and thus can
`
`prevent an increase in the number of times of the compression in manufacturing the
`
`negative electrode. The mass ratio between the graphite particles A and graphite particles
`
`20
`
`B is preferably 70:30 to 85:15, and more preferably 70:30 to 80:20, in view of obtaining a
`
`high packing density without an increasein the number of times of the compressionin
`
`manufacturing the negative electrode, for example.
`
`(0028]
`
`The packing density ofthe negative electrode active material layer is preferably 1.2
`
`25
`
`g/cr® to 1.7 g/erm?, and more preferably 1.5 g/cm’ to 1.7 g/cm’, in viewof securing the
`
`strengih of the negative electrode active material layer and obtaming favorable battery
`
`characteristics, for example.
`
`If the mass ratio, graphite particles A/graphite particles B, is
`
`more than 90/10, itis necessary to increase the number of times of the compression of the
`
`-ll-
`
`

`

`negative electrode active material layer comparedto the case of the mass ratio of 90/10 or
`
`less, for obtaming the negative electrode active material layer having the packing density
`
`within the range described above.
`
`If the mass ratio, graphite particles A/graphite particles
`
`B, is less than 70/30, a negative electrode active material layer having a packing density
`
`within the above-described range can be obtained without any increase in the number of
`
`times of the compression ofthe negative electrode active material layer compared to the
`
`case of the mass ratio of 70/30 or more, but charging/discharging cyclic characteristics are
`
`deteriorated.
`
`[0029]
`
`10
`
`The negative electrode active material may include other material that can
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`reversibly intercalate and deintercalate lithium ions in addition to the graphite particles A
`
`and B used in the present embodiment, and specifically, may include, for example, a metal
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`that can be alloyed with lithium, such as silicon (Si) and tin (Sn), or and an alloy or oxide
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`that includes a metal element such as Si or Sn.
`
`If the content of the other materialis
`
`15
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`large, the preventing effect on deterioration in charging/discharging cyclic characteristics
`
`of the non-aqueouselectrolyte secondary battery may not be provided sufficiently, and
`
`thus, the content of the other material is desirably 10 mass% or less based on the mass of
`
`the negative electrode active material, for example.
`
`(0030]
`
`20
`
`Examples of the binder include a fluororesin, PAN,a polyimideresin, an acrylic
`
`resin, a polyolefin resin, styrene-butadiene rubber (SBR), carboxymethyl] cellulose (CMC)
`
`or a Salt thereof, polyacrylic acid (PAA) or a salt thereof (e.g., PAA-Na and PAA-K which
`
`may be a partially neutralized salt), and polyvinyl alcohol (PVA). These may be used
`
`singly or in combinations of two or morethereof.
`
`25
`
`[0031]
`
`[Positive Electrode]
`
`The positive electrode 11 comprises metal foil or the like as a positive electrode
`
`current collector and a positive electrode active material layer formed on the positive
`
`-12-
`
`

`

`electrode current collector. As the positive electrode current collector, foil of a metal that
`
`is stable in the electric potential range of the positive electrode, such as aluminum, a film
`
`with such a metal disposed as an outer layer, or the like may be used. The positive
`
`electrode active material layer includes, for example, a positive electrode active material, a
`
`binder, a conductive agent, and other components.
`
`10032}
`
`For example, the positive electrode 11 can be produced by applyinga positive
`
`electrode mixture slurry including a positive electrode active material, a binder, a
`
`conductive agent, and other components to a positive electrode current collector, drying the
`
`10
`
`resultant coatings to form positive electrode active material layers, and then carrying out
`
`compression by compressingthe positive electrode active material layers with a mill roll or
`
`the like.
`
`[0033]
`
`Examples of the positive electrode active material include a lithium/transition metal
`
`15
`
`oxide, which contains a transition metal element such as Co, Mn, or Ni. Examples of the
`
`lithium/transition metal oxide include LixCoQ2, LixNiO2, LixMnO2, LixCoyNi1-+O2,
`
`LixCoyM1-yOz, LixNityMyOz, LixMn204, LixMino-+¥MyO4, LIMPO4, LizMPO«F (M:;at least
`
`one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0<x<1.2, 0<y<0.9,
`
`2.0<7<2.3). These may be used singly or two or more thereof may be mixed and used.
`
`20
`
`The positive electrode active material preferably include a lithium/nickel complex oxide
`
`such as LixNiO2, LixCoyNi1yO2, LixNi1-yMyOz(M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co,
`
`Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0<x<1.2, 0<y<0.9, 2.0<7<2.3), in view of obtaining a high
`
`capacity of a non-aqueouselectrolyte secondary battery.
`
`[0034]
`
`25
`
`Examples of the conductive agent include carbon particles such as carbon black (CB),
`
`acetylene black (AB), Ketjenblack, and graphite.
`
`These may be used singly or in
`
`combinations of two or morethereof.
`
`[0035]
`
`- 13-
`
`

`

`Examples of the binder include fluororesins, such as polytetrafluoroethylene (PTFE)
`
`and poly(vinylidene fluoride) (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic
`
`resins, and polyolefin resins. These may be used singly or in combinations of two or more
`
`thereof.
`
`[0036]
`
`[Separator]
`
`For example, an ion-permeable and insulating porous sheet is used as the separator
`
`13.
`
`Specific examples of the porous sheet include a microporous thin film, woven fabric,
`
`and nonwoven fabric.
`
`Suitable examples of the material for the separator include olefin
`
`10
`
`resins such as polyethylene and polypropylene, and cellulose. The separator 13 may be a
`
`laminate including a cellulose fiber layer and a layer of fibers of a thermoplastic resin such
`
`as an olefin resin.
`
`The separator 13 may be a multi-layered separator including a
`
`polyethylene layer and a polypropylene layer, and a surface of the separator to be used may
`
`be coated with a material such as an aramid resin or ceramic.
`
`15
`
`[0037]
`
`[Non-aqueousElectrolyte]
`
`The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt
`
`dissolved in the non-aqueous solvent. The non-aqueouselectrolyte is not limited to aliquid
`
`electrolyte (electrolyte solution), and may be a solid electrolyte using a gel polymeror the
`
`20
`
`like. Example of the non-aqueoussolvent to be used includeesters, ethers, nitriles such as
`
`acetonitrile, amides such as dimethylformamide, and mixed solvents of two or morethereof.
`
`The non-aqueous solvent may include a halogen-substituted product formed by replacingat
`
`least one hydrogen atom of any of the above solvents with a halogen atom suchas fluorine.
`
`[0038]
`
`25
`
`Examples of the esters include cyclic carbonate esters, such as ethylene carbonate
`
`(EC), propylene carbonate (PC), and butylene carbonate; chain carbonate esters, such as
`
`dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC),
`
`methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic
`
`- 14 -
`
`

`

`carboxylate esters such as y-butyrolactone and y-valerolactone; and chain carboxylate esters
`
`such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl
`
`propionate, and y-butyrolactone.
`
`[0039]
`
`Examples of the ethers include cyclic ethers such as 1,3-dioxolane, 4-methyl-1,3-
`
`dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide,
`
`1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, and crown
`
`ethers; and chain ethers such as, 1,2-dimethoxyethane, diethyl ether, dipropyl ether,
`
`diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methy]
`
`10
`
`phenyl!ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene,
`
`benzyl ethyl ether, diphenyl!ether, dibenzy] ether, o-dimethoxybenzene, 1,2-diethoxyethane,
`
`1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether,
`
`diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane,
`
`triethylene
`
`glycol dimethyl]ether, and tetraethylene glycol dimethyl.
`
`15
`
`[0040]
`
`Preferable examples of the halogen-substituted product for use include a fluorinated
`
`cyclic carbonate ester such as fluoroethylene carbonate (FEC), a fluorinated chain carbonate
`
`ester, a fluorinated chain carboxylate ester such as methyl fluoropropionate (FMP).
`
`[0041]
`
`20
`
`The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include
`
`LiBFs, LiClOs, LiPFe, LiAsFe, LiSbFe, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CQO2,
`
`Li(P(C204)F4), LiPFo-x(CnF2n+1)x (where 1 < x < 6, and nis 1 or 2), LiBioChio, LiCl, LiBr,
`
`Lil, chloroborane lithium, lithium short-chain aliphatic carboxylates; borate salts such as
`
`
`
`
`
`
`
`LixBsO7, imide=saltsLi(B(C204)F2); and such as LiN(SQoCF3)2 and
`
`
`
`
`
`
`
`
`
`25
`
`LiN(CiF21+1802)(CmF2m+18O2) (where | and m are integers of 1 or more). These lithium
`
`salts may be used singly or two or more thereof may be mixed and used. Among these,
`
`LiPFé is preferably used in view of ionic conductivity, electrochemical stability, and other
`
`properties. The concentration ofthe lithium saltis preferably 0.8 to 1.8 mol per L of solvent.
`
`- 15 -
`
`

`

`EXAMPLES
`
`[0042]
`
`Hereinafter, the present disclosure will be described in more details by way of
`
`Examples, but the present disclosure is not limited thereby.
`
`10043}
`
`<Example 1>
`
`[Production of Positive Electrode]
`
`90 parts by massof lithium cobalt oxide as a positive electrode active material, 5
`
`10
`
`parts by mass of graphite as a conductive agent, and 5 parts by mass of a powder of
`
`poly(vinylidene fluoride) as a binder were mixed, and an adequate amount of N-methy1-2-
`
`pyrrolidone (NMP) was further added thereto to prepare a positive electrode mixture
`
`slurry. This slurry was applied to both sides of aluminum foil (thickness: 15 um) as a
`
`current collector by doctor blade method, and the coatings were dried and then compressed
`
`15
`
`with a mill roll, to thereby produce a positive electrode having positive electrode active
`
`material layers formed on the both respective sides of the positive electrode current
`
`collector.
`
`[0044]
`
`[Production of Graphite Particles A]
`
`20
`
`Coke was crushed to an average particle size (median diameter D50) of 15 um.
`
`Pitch as a binder was addedto the crushed coke, and the coke was allowed to aggregate to
`
`an average particle size (median diameter D50) of 17 um. This aggregate was fired at a
`
`temperature of 2800°C for graphitization, and sieving the graphitized product was then
`
`carried out with 250-mesh sieve to obtain graphite particles A having an averageparticle
`
`25
`
`size (median diameter D50) of 23 um.
`
`[0045]
`
`[Production of Graphite Particles B]
`
`- 16 -
`
`

`

`Coke was crushed to an average particle size (median diameter D50) of 15 um.
`
`Pitch as a binder was addedto the crushed coke to aggregate, and an isotropic pressure was
`
`then applied to the resultant to form a molded product having a block shape and a density
`
`of 1.6 g/cm? to 1.9 g/cem?. The molded product having a block shape wasfired at a
`
`temperature of Z800°Cfor graphitization, and the resulting molded product having a block
`
`shape was crushed.
`
`Sieving the crushed product wascarried out with 250-meshsieve to
`
`obtain graphite particles B having an averageparticle size (median diameter D50) of 2