(12) ENTERNATIONAL APPLICATION PUBLISHED USDER THE PATENT COOPERATION TREATY CT)
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`(1) World tntellectual Property
`Organization
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`international Hereaut
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`AN
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`(10) International Publication Number
`WO 2016/020737 Al
`
`(43) International Publication Date
`1h February 2016 (102.2616) WHEPOLPCT
`
`(51) Luternational Patent Classification:
`HBIM 2°76 2086.03)
`HOIM100567 (ANOOV
`FOTN 2734 Q006. 01}
`HOIMT0423 (2006.01)
`AIM FRVGS2 TSG OAN)
`
`
`
`(21) International AppBoation Nuxber:
`
`POTERION SAMOS298
`
`(22)
`
`laternational fiting Date
`
`AG, AT, ALY Ad, BA, BB, BG, BA, BN, BR. BW, BY,
`Be, CA, CH, CL, CN, CO, CR, CU, CZ, DE, DE, DM,
`BO, D2, 8C, SEL BG, BS FL GB, GID, GE, GH, GM, CFP,
`HS, HR. HU, Ho, TL. BN, ER, ES, RE, KG, RN, RP, RR,
`Ke, LA, Li, LK, ER, 08, DLL LY, MA, MR, MEL MG,
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`MW, MX, MY_LM4, NA, 8G NE NO, NZ, OM,
`PAPE PG, PIL PL, PT, OA, RD, RS, REL RW, SA, SC,
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`Gi, SK, SL, SM, ST. SV,
`SY, TH. TL TM, TN,
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`TR, TT TZ, UA, UG, US, DZ, VO, VN, ZA, ZM, ZW.
`3 Aupust 2015 (83.68, 2015)
`(4) Designated States funesy ontcmwise didicated, for creny
`English
`£25) Filing Language:
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`of regione! protection available), ARIPO (BW GH,
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`GM. KE, LR, LS, MW. MZ, NA, RW, SD, SL, ST. Si,
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`ZM, ZW), Eurasian (AM, AZ, BY, RG KZ, RU,
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`(30) PriovityData:
`TL FM). Excopesm CAL, AT, BE, BC, CH, OF, C2. DR,
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`70} Applicant: TOYOTA dIDOSHA KABUSHIRY KABS-
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`SML TRA OAPT (BE. BL, cP, CcGi, Ch CML, GA, aN, GQ,
`A HIPYPE 1, Tovola-cho, Toyota-shi, Aichi-hen, 47 1-
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`CAV EM, MEL, MRLNE, SN, PPL PO.
`8577 CE}.
`73) dnventer: FPO. Yuichi of TOYDTA HDOSHA BA- Published:
`BUSHIRT KAISHA, of 1, Toyetaecho, Toycdaeshi, Aichi
`kea, $7 1-857 1 GP}.
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`se
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`with buernetional search report (lee 283}
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`interposed
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`betwwen the pos
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`electrode: a monaeous clectralyte
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`tery case that accommestates the eh
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`WO 2016/020737
`
`PCTAB201S461298
`
`NONAQUEOUS ELECTROLYTE SECONDARY BATTERY
`
`BACKGROUND OF THE INVENTION
`
`5
`
`1. Field of the Invention
`
`{0001}
`
`The present
`
`invention relates to a nonaqueous electrolyte secondary
`
`battery.
`
`Specifically, the invention relates to a nonaqueous electrolyte secondary battery
`
`mcluding a current interrupt device which operates in response to an increase in the
`
`intemal pressure of a battery.
`
`10
`
`2. Deseription of Related Art
`
`{0002}
`
`Typically, a nonaqueous electrolyte secondarybattery such as a lithiumion
`
`secondary battery 1s used in a state where the voltage 18 controlled to be in a predetermined
`
`region Gor example, 3.0 V to 4.2 V). However, when an excessively high current is
`
`15
`
`supplied to the battery due to malfunction or the like, the battery may be overcharged to
`
`higher than a predetermined voltage. When the overcharge progresses, for example, the
`
`imtemnal
`
`temperature af the battery may increase due to heat generation of an active
`
`material, or the battery may be swollen due to gas produced by the decomposition of a
`
`the progress of the overcharge is not
`nonagueous electrolyte, Due to these problems,
`preferable. Therefore, in orderto prevent these problems, a configuration is widely used,
`
`20.
`
`in which a battery case includes a pressure-operated current interrupt device (CID), and a
`nonaqueous electrolyte contains a compound (hereinafter, also referred to as “gas
`
`producing agent”) which is decomposed to produces gas during the overcharge of a battery
`
`(refer to Japanese Patent Application Publication No. 2014-082098 (IP 2014-082098 A).
`
`bo or Whena battery having this configuration is overcharged, the gas producing agent reacts on
`
`a positive electrode ta prodece hydrogen ions, and hydrogen pas (H2) is produced fromthe
`
`hydrogen ions on a negative electrode. Due to this hydrogen gas, the internal pressure of
`
`_a battery case rapidly increases. Therefore, the charging current to the battery can be
`
`interrupted in an early stage of overcharge, and the progress of overcharge can be stopped.
`
`CONFIRMATION COPY
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`

`

`WO 2016AR0737
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`PCT/ABZO TSA 298
`
`{HO03]
`
`However, according to the investigation, the present inventors found that
`
`the above-described technique has room for further improvement. That is, it was found
`
`that, after the battery is exposed to severe conditions fora long periodof time (for example,
`
`after the battery is stored or used in a high-temperature environment of 30°C or higher for
`
`a long period of time),
`
`the reactivity of the gas producing agent during overcharge
`
`decreases; as a result, the production of hydrogen gas may be slowed, or the amount of
`
`hydrogen gas produced may decrease.
`
`In this case,
`
`the time required to operate the
`
`current interrupt device may increase, and overcharge resistance is likely to decrease.
`
`10
`
`SUMMARYOF THEINVENTION
`
`{8064}
`
`The present invention provides a nonaqueous electrolyte secondary battery
`
`including a current interrupt device (pressure-operated type) that operates in response to an
`
`increase in the internal pressure of a battery, in which overcharge resistance is superior
`
`even, when being exposed ta severe conditions (for example,
`
`a high-temperature
`
`environment of SO°C or higher) for a long period oftime.
`
`{9005]
`
`The present
`
`inventors investigated the reason for a decrease in the
`
`reactivity of a gas producing agent from various aspects, As @ result, %¢ was found that,
`even when a battery is exposed to the above-described severe condition for a long period
`of time, a fluorine-containing compound (for example, LiPF, as a supporting electrolyte)
`
`contained in a nonaqueous electrolyte is gradually decomposed (typically, being reduced
`
`and decomposed on a negative electrode}
`
`and hydrofluoric acid is produced, By
`
`hydrofluoric acid being deposited on a surface of a positive electrode as a
`
`film
`
`{fluorine-containing film) containing fhiorine, the reaction of a gas producing agent during
`
`overcharge maybe inhibited, and hydrogen gas is not likely to be produced.
`
`|
`
`[O06]
`
`In
`
`order
`
`to
`
`suppress
`
`the
`
`above-described
`
`production
`
`of
`
`a
`
`fluorine-containing film on a surface of a positive electrode, as a result of further thorough
`
`investigation, the present invertors completed the invention. According to an aspect of
`
`the invention, a nonaqueous electrolyte secondary battery includes: an electrode badyin
`
`which a positive electrode and a negative electrode are disposed to be opposite to each
`
`

`

`WO DONGAN2O737
`
`PCTIB261 SAN 298
`
`other with a separator interposed between the positive electrode and the negative electrode;
`
`a nonaqueous electrolyte; and a battery case that accommodstes the electrode body and the
`
`nonaqueous electrolyte. The battery case includes a current interrupt device{CID) that
`
`operates im response fo an increase im an interna] pressure of the battery case. The
`
`least contains a fluorine-containing compound and a gas
`nonaqueous clectrolyte at
`producing agent, and the separator includes a hydrofluoric acid rapping layer containing
`
`an inorganic phosphate compoundon a surface of the separator.
`
`(0607)
`
`In the battery having the above-described configuration, the hydrofluoric
`
`acid trapping layer can trap (or consume} hydrofluoric acid produced bythe decomposition
`
`10
`
`of the flnorine-containing compound.
`
`Therefore, even under severe conditions (for
`
`example, in a high-temperature environment of about 50°C to 70°C), the production of a
`
`fluorine-containing film on the serface of the positive electrode can be suppressed.
`Accordingly, the reaction field of the gas producing agent (contact area betweenthe gas
`
`producing agent and the surface of the positive clectrade) can be widely secured. As a
`
`result, the gas producing agent can be oxidized and decomposed at once during overcharge,
`
`and hydrogen gas can be rapidly produced therefrom. That is, even when being exposed
`
`to severe conditions for a long period of time, a nonaqueous electrolyte secondary battery
`
`having hugh overcharge resistance (reliability) can be realized.
`
`In this specification,
`
`“fluorine-containing compound” refers to all
`
`the compounds containing at
`
`least one
`
`20
`
`fluorine atom as a constituent atom.
`
`In addition, when being ionized (HF) in a
`
`nonaqueons electrolytic solution, the fluorine-containing compound can be present in the
`
`form ofa flueride ton.
`
`fQ008}]
`
`Japanese
`
`Patent Application
`
`Publication No.
`
`2009-146610 GP
`
`2009-146610 A} describes a buffer laver including an organic compound and an inorganic
`
`20
`
`compound on a surface of a separator substrate, in which the buffer layer functions as a
`superior cushioning material so as to avoid and suppress a rapid shrinkage or rupture of a
`
`separator.
`
`In addition, Japanese Patent Application Publication No. 2014-103098 GP
`
`2014-103098 A) describes that battery deterioration can be suppressed by a positive
`
`electrode active material layer containing an inorganic phosphate. However, these patent
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`WO 2016AR0737
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`PCT/ABZO TSA 298
`
`documents have no descriptions regarding a current interrupt device or a gas producing
`
`agent and thus do net deal with the object of the invention, The technique disclosed
`
`herein is clearly distinguished fromthe technical ideas of the techniques in the related art.
`
`{0009}
`
`In the nonaqueous electrolyte secondarybattery, the separator may include
`
`or
`
`the hydrofluoric acid trapping layer on a surface on a side opposite the positive electrode.
`
`According to the investigation by the present inventors, by disposing the hydroflueric acid
`
`trapping layer at a position near the positive electrode (ypically in contact with the
`
`positive electrode), the hydrofluoric acid trapping ability of the hydrofluoric acid trapping
`
`layer can be improved, and the effects ofthe invention can be exhibited at a higher level.
`
`1
`
`0
`
`MOI}
`
`In the nonaqueous electrolyte secondary battery, in the separator, a porous
`
`heat resistance layer may be laminated on a surface of a separator substrate, and the
`
`hydrofluone acid trapping layer may be laminated on a surface of the porous heat
`
`resistance layer.
`
`fOO14]
`
`In the nonaqueouselectrolyte secondarybattery, a ratio of the mass of the
`
`i
`
`a
`
`inorganic phosphate compound to the total mass of the hydrofluoric acid trapping layer
`
`may be 70 mass%to 99 mass%.
`
`f0012}
`
`In the nonaqueous electrolyte secondary battery, a ratio of the mass of a
`
`binder to the total mass of the hydrofluoric acid trapping layer may be 1 mass%to 20
`
`mass%.
`
`20
`
`{0013}
`
`In the nonaquecus electrolyte secondary battery, the postive electrode
`
`may contain a positive electrode active material, and a content ofthe inorganic phosphate
`
`compound may be I part by mass or more with respect to 10) parts by mass of the mass of
`
`the positive electrode active material. As a result, hydrofluoric acid can be more stably
`
`trapped, and the effects of the invention can be exhibited at a higher level.
`
`In addition, in
`
`another aspect, the content of the inorgame phosphate compoundis 5 parts by massor less
`
`with respect to 100 parts by mass of the mass of the positive clectrade active material. As
`a result,
`the battery resistance can be maintained to be low, and superior battery
`performance can be exhibited dering normal use.
`In other words, baitery characteristics
`
`(for example, input and output characteristics) during normal use and overcharge resistance
`
`

`

`WO 2016AR0737
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`PCT/ABZO TSA 298
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`can be simultaneously realized at a mgh level,
`
`{0014] As
`
`the
`
`inorganic phosphate compound,
`
`for example, a phosphate
`
`containing an alkali metal element or a Group 2 element can be adopted. Specifically, for
`
`example, LisPO,, NasPOs, K3PO., Mg3(POgh, or Cas{POs}, can be adopted. Among
`
`these, a compound (for example,
`
`lithium phosphate (for example,
`
`im a lithtam ion
`
`secondary battery, LisPOs{LPO))) having the same cation (charge carrying ion) as that ofa
`
`supporting electrolyte may also be used.
`
`[0015]
`
`In the nonaqueouselectrolyte secondarybattery, an average particle size of
`
`the inorganic phosphate compound maybe 10 pm orless,
`
`10
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0016]
`
`Features, advantages, and the technical and industrial significance of
`
`exemplary embodiments of the invention will be described below with reference to the
`
`accompanying drawings, in which Ike numerals denote like elements, and wherein:
`
`FG. 1
`
`is a graph showing a relationship between the amount of gas produced during
`
`overcharge and the fluoride ion content of a positive electrode, after a predetermined
`period ofstorage in a high-temperature environment of 60°C;
`FIG. 2 is a vertical cross-sectional view schematically showing a nonaqueous
`
`|
`
`electrolyte secondary battery according to an embadiment ofthe invention;
`
`20
`
`FIG. 3 is a schematic view showing a configuration of a wound electrode body of FIG.
`
`FIG 4 is a cross-sectional view taken alone line [V-IV of the wound electrode body
`
`of FIG. 3;
`
`FIG, 3A is
`
`a graph showing battery characteristics after being subjected to
`
`25
`
`high-temperature storage, in which the amount of gas produced during overcharge and the
`
`fluoride ion content of a positive electrode are shawn;
`
`a graph showing battery characteristics afler being subjected - to
`FIG. SB is
`high-temperature storage, in which the battery resistance is shown; and
`
`FIG. 6 is a graph showing a relationship between the addition amount of lithium
`
`

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`WO 2016AR0737
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`PCT/ABZO TSA 298
`
`6
`
`phosphate, the amount of gas produced during overcharge, and the resistance increaserate.
`
`DETAILED DESCRIPTION OF EMBODIMENTS
`
`FOOL]
`
`Preferred embodiments of the invention are described below. Matters
`
`(for example, a general manufacturing process of a battery which is not 4 characteristic of
`
`the invention} necessary to practice this invention other than those specifically referred to
`in this specification may be understood as design matters based on the related art in the
`
`pertinent field fer 8 person of ordinary skills in the art. The invention can be practiced
`
`based on the contents disclosed in this specification and common technical knowledge in
`
`10
`
`the subject field.
`
`{AGES}
`
`A nonaqueous electrolyte secondary battery disclosed herein includes: an
`
`electrode body in which a positive electrode and a negative clectrode are disposed to be
`
`opposite cach other with a separater interposed between the positive electrode and the
`
`negative electrode; a nonaqueous electrolyte; and a battery case that accommodates the
`
`electrode body and the nonaqueous electrolyte, Hereinafter, the respective components
`
`will be sequentially described.
`
`{0019}
`
`{Positive Electrode]
`
`Typically, the positive electrode of the battery disclosed herein includes: a positive
`
`electrode current collector; and a positive electrode active material layer that contains a
`
`positive electrode active material attached to the positive clectrode current collector. As
`
`the positive electrodes current collector, a conductive member formed of highly conductive
`
`metal (for example, aluminum, nickel, or titanium) is preferably used. The positive
`
`electrode active material layer includes at least a positive electrode active material. As
`
`the positive electrode active material, one kind or two or more kinds may be used among
`
`various materials which can be used as a positive electrode active material of a nonaqueous
`
`Preferable examples of the positive electrode active
`electrolyte secondary battery.
`material include layered or spinel type lithium transitian metal composite oxide materials
`
`(fer example, LiNiQ,, LiCoQ,, LiMn2O,, LiFeO., LINIpasCoe33Mitte3302, LiNip.sMiny sO.
`
`and LiCrMnQO,) and olivine type materials (for example, LiFePO,). Among these, a
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`

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`WO 2016AR0737
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`PCT/ABZO TSA 298
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`lithium nickel cobalt manganese composite oxide having a layered structure which
`
`contains Li, Ni, Co, and Mnas constituent elements is preferable from the viewpoints of
`
`heatstability and energydensity.
`
`{0020}
`
`The positive electrode active material is typically particulate (powder-like).
`
`The average particle size is, for example, 0.1 uum or more, preferably 0.5 um or more, and
`
`more preferably 5 em or more and is, for example, 20 pm or less, preferably 15 yimor less,
`
`and more preferably 10 pm or less.
`fn addition, the specific surface area is, for example,
`0.1 m’’g or more and preferably 0.5 m°/g or more andis, for example, 20 m’/g or less,
`typically 10 m’/g ot less, preferably 5 m*/g or less, and more preferably 2 m’/g or less, A
`
`10
`
`positive electrode active material satisfying one or two among the above-described
`
`characteristics can maintain an appropriate porosity and superior conductivity in the
`
`positive electrode active material layer. Accordingly, during normal use, superior battery
`characteristics (for example,
`input and output characteristics} can be exhibited.
`In
`
`addition, even if a part of a surface of the positive electrode is covered with a film, a
`
`reaction field of a gas producing agent can be maintained. As a result, during overcharge,
`
`most parts of the gas producing agent can berapidly and stably oxidized and decomposed
`to produce gas, Due to the produced gas, a CID can be rapidly operated.
`In this
`
`specification, “average particle size” refers to a particle size (also referred to as “Deg
`
`20
`
`particle size” or “median size”) corresponding to a cumulative value of 30 volin order
`from the smallest particle size in a volume particle size distribution based on a general
`laser diffraction scattering method.
`In this specification, “specitic surface area” refers to
`
`a specific surface area (BET specific surface area) which is measured with a BET method
`
`(for example, a multi-point BET method) using nitrogen gas.
`
`{GO2E}
`
`In addition to the positive electrode active material, the positive electrode
`
`active material layer may optionally contain one material or two or more materials which
`
`can be used as components of a positive electrode active material layer in a general
`
`nonaqueous electrolyte secondary battery, Examples of the material include a conductive
`material and a binder. Examples of the conductive material include carbon materials such
`
`as Various carbon blacks (for example, acetylene black and Ketjen black), activated carbon,
`
`

`

`WO 2016AR0737
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`PCT/ABZO TSA 298
`
`graphite, and carbon fiber which are preferably used. Examples of the binder, include
`
`vinyl halide resins such as polyvinylidene fluoride (PVdF); and polyalkylene oxides such
`
`as polyethylene oxide (PEO),
`
`In addition, the positive electrode active material layer may
`
`flrther contain various additives (for example, a dispersant ora thickener) within a range
`
`of
`
`where the effects of the invention do not significantly deteriorate.
`
`10022}
`
`The average thickness of the positive electrode active material layer per
`
`single surface maybe, for example, 20 pm or more (typically 40 um or more, preferably
`
`50 pam or more} and maybe, for example, 100 um or less (typically 80 umor less}. The
`
`porosity of the positive electrode active material layer maybe, for example, 10 vol%to 50
`
`1
`
`0)
`
`val% {typically 20 vol% to 40 vol%), The density of the positive clectrode active
`material layer may be, for example, 1.5 giom? or more (typically 2 g/em* or more) and may
`be, for example, 4 g/om’ orless (typically 3.5 g/cm’ or less). Bysatisfying one or two or
`
`more among the above-described characteristics, batiery performance (for example, high
`
`. energy density or high input and output densities} and overcharge resistance can be
`
`tn
`
`simultancouslyrealized at a higher level.
`In thts specification, “porosity” refers to a value
`which is obtained by dividing a total pore volume (em) by the apparent volume (om) of
`
`an active material laver and multiplying the divided value by 100, the total pore volume
`
`being obtained by measurement using a mercury porosimeter.
`
`In this specification,
`
`“density” refers to a value obtained by dividing the mass (g) of an active material layer by
`the apparent volume (cm) thereof. The apparent volume can be calculated as the product
`
`20)
`
`ofthe area (om’) in a plan view and the thickness (cm).
`
`{0023}
`
`[Negative Electrode}
`
`Typically, the negative electrode of the battery disclosed herein includes: a negative
`electrode current collector; and a negative electrode active material layer that contains a
`
`negative electrode active material attached to the negative electrode current collector. As
`
`the negative electrode current collector, a conductive member formed of highly conductive
`
`metal (for example, copper, nickel, titanium, or stainless steel) is preferable.
`
`jo024]
`
`The negative electrode active material layer includes at least a negative
`
`electrode active material, As the negative electrode active material, one kind or two or
`
`

`

`WO 2016AR0737
`
`PCT/ABZO TSA 298
`
`more kinds may be used among various materials which can be used as a negative
`
`electrode active material of a nonaqueous electrolyte secondary battery.
`
`Preferable
`
`examples of the negative electrode active material include various carbon materials such as
`
`i
`rc
`
`graphite, non-graphitizable carbon (hard carbon), graphitizable carbon {soft carbon),
`
`carbon nanotube, and a combination thereof, Among these, from the viewpoint ofenergy
`density, a graphite-based material containing 30 mass% or more of graphite with respect to
`
`the total mass of the negative electrode active material
`
`is preferable. The negative
`
`electrode active material is typically particulate (powder-Hke). The average particle size
`
`maybe, for example, 20 jum ar less, typically 0.5 pm to 15 um, and preferably 1 pm to 10
`
`10
`
`um. By satisfving the above-described characteristics, the reduction decomposition of the
`
`nonaguemis electrolyte, for example,
`
`in a high-temperature environment can be more
`
`efficiently suppressed, and the effects of the invention can be exhibited ai a higher level.
`
`[0025]—_In addition to the negative electrode active material, the negative electrode
`
`active material layer may optionally contain one matenal or two or more materials which
`
`can be used as components of a negative electrode active material layer in a general
`
`nonaqueous electrolyte secondary battery. Examples of the material include a binder and
`
`various additives.
`
`Examples of the binder inchide styrene-butadiene rubber (SBR),
`
`polyvinylidene fluoride (PVdF), and polytetrafluorocthylene (PTFE). Moreover,
`
`the
`
`negative electrode active material layer mayfurther appropriately contain various additives
`
`20
`
`such as a thickener, a dispersant, or a conductive material. Examples of the thickener
`
`include celluloses such as carboxymethyl cellulose (CMC) and methyl! cellulose (MC).
`{0026}
` <Separator>
`|
`
`The separator of the battery disclosed herein includes a hydrofluorie acid trapping
`
`layer containing an inorganic phosphate compound that is formed on a surface of the
`
`separator.
`In other words, the separator includes the hydrofhioric acid trapping layer so as
`to be tn contact with the positive electrode active material layer and the negative electrode
`active material layer.
`In a typical example, the separator includes at least a separator
`
`substrate and a hydrofluoric acid trapping layer.
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`{0027}
`
`in a preferred aspect,
`
`the hydrofluoric acid trapping layer is directly
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`attached to the surface of the separator substrate. The separator substrate mayinsulate the
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`positive electrode and the negative clectrade from each other and have a function of
`
`holding the nonagueous electrolyte or a so-called shutdown function.
`
`Preferable
`
`examples of the separator include a perous resin sheet (film) formed of a resin such as
`
`polyethylene (PE), polypropylene (PP), polyester, cellalose, or polyamide. The porous
`
`resin sheet may have a single-layer structure or a muliilayer structure meluding two or
`
`more layers (fer example, a three-layer structure in which a PP layer is laminated on both
`
`surfaces of a PE layer; thatis PP/PE/PP), The average thickness of the separator substrate
`
`may be, for example, 10 pm to 40 jam from the viewpoint ofsuppressing battery resistance
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`10
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`to be low while stably exhibiting the above-described fimctions.
`
`In addition, the porosity
`
`of the separator substrate may be, for example, 20 vol%to 90 vale (typically 30 vol%to
`
`80 voland preferably 40 velte 60 vel} from the viewpoints of simultancously
`
`realizing the permeability of charge carrying ions and mechanical strength at a high level.
`
`{0028}
`
`The hydrofluoric acid trapping layer contains at
`
`least an inorganic
`
`15
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`phosphate compound. As the inorganic phosphate compound, any compound containing
`at
`least one phosphate ion (POs-) can be used without any particular himitahon.
`
`Preferable examples of the inorganic phosphate compound inchide a known inorganic solid
`
`electrolyte material which can function as a solid electrolyte material of an all-salid-state
`
`battery.
`
`Specific examples of the inorganic phosphate compound inchide Li;sPQO4, LiPON
`
`(uthium phosphate oxynitride), LAGP (ithtam aluminum geranium phosphate) a
`
`phosphoric acid-based lithium ion conductor such as LiysAlosGe;5 (POQg)3); and a
`
`NASICON type Hthtum ion conductor
`
`such as Li; sAlosGe;< (PO4)s).
`
`In
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`the
`
`above-described example, the charge carrying ion is a lithium jon (Li) but may be other
`
`*,
`“on
`BS
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`CHK
`
`cations (typically, an alkali metal jon such as Na” or K"), a Group 2 element ion such as
`Mg"or Ca™™ (typically, an alkali carth metal ion}}. Among these, a phosphate containing
`an alkali metal element or a Group 2 element, fer example, LisPQy, NasPOg, K3POx,
`
`Megx(PO,)s, or Ca;(PO4), is preferable due to its high hydrofluoric acid trapping ability.
`
`In particular, a compound (for example, Uthiam phosphate (for example, mm a lithium ton
`
`secondary battery, hthtum phosphate (Lij;PO,} having the same cation as that of a
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`sapporting electrolyte described belowis preferable.
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`{0029}
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`The hydrofluoric acid trapping ability of the inorganic phosphate
`
`compound can be verified using the following method. First, the inorganic phosphate
`compound as an evaluation target
`is added to an hydrochloric acid aqueous solution
`
`adjusted to 0.01 mol/L (pH=2}. Next, a change over time in the pH of the aqueous
`
`solution is measured under stirring. A compound having a value (ApH=pH,-pH,) of 0.5
`
`or more (preferably | or more and more preferably 3 or more} can be estimated to have
`
`high hydrofluoric acid trapping ability when the value is obtained by subtracting the pH
`
`{oHy: here pH,=2) of the hydrochloric acid aqueous solution used from the pH (pH,)
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`10
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`thereof after 6G minutes. For example, when the initial pH is adjusted to 2.0, the pH ofa
`
`compound after 60 minutes is preferably 2.5 or higher (more preferably 3.0 or higher and
`
`sti more preferably 5.0 or higher}, The pH value refers to a value at a solution
`
`temperature of 25°C.
`
`J0030}
`
`The characteristics of the inorganic phosphate compound are not
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`15
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`particularly limited. However, from the viewpoint of securing a wide contact area with
`
`the nonagueous electrolyte,
`the inerganic phosphate compound may be particulate
`fpowder-like), and the average particle size thereof may be about 15 um or less (typically
`10 wm or less; for example, Spm oriess).
`From the viewpoints of handleability during
`work and quality stability,
`the average particle size may be about O.O1 pum or more
`
`20
`
`{typically 0.03 um or more; for example, | pm or more).
`
`In the above-described particle
`
`size range, the effects ofthe invention can be exhibited at a higher level.
`
`In addition due
`
`to the same reason, the specific surface area of the inorganic phosphate compound maybe
`about § m’/g to 50 m’/g (typically, 10 m’/g to 40 m’/g; for example 20 m’/g to 30 m/g),
`
`[G031}
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`In addition to the above-described inorganic phosphate compound,
`
`optionally, the hydrofluoric acid trapping layer may further contain one material or two or
`
`more materials. Examples of the material inclade a binder and various additives. As the
`
`binder, for example, exemplary compounds which are described above as a constituent
`
`material of the positive electrode active material layer or the negative electrode active
`
`material
`
`layer
`
`can be
`
`considered.
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`Specific
`
`examples of
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`the binder
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`include
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`styrene-butadiene (PVdF),9andrubber (BR), polyvinylidene fluoride
`
`
`
`
`
`
`
`
`
`
`
`polytetrafluoroethylene (PTFE). Examples of the additives include an inorganic filer
`
`such as alumina, boehmite, silica, titania, calcia, magnesia, zirconia, boron nitride, or
`
`aluminumnitride can be preferablyused.
`
`[8032]
`
`The addition amount of the inorganic phosphate compound may vary
`
`depending on, for example, the kind and characteristics (for example, average particle size
`
`or specific surface area} of the positive electrode active material. However, in a preferred
`
`example, the addition amount of the inorganic phosphate compound may be about 0.1 parts
`
`by mass or more {typically 0.5 parts by mass or more and preferably 1 parts by mass or
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`16
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`more; for example, 2 parts by mass or more) with respect to 100 parts by mass of the
`
`positive electrade active material from the viewpointofsufficiently obtaining the efects of
`
`the invention.
`
`In another preferred embodiment, the addition amount of the inorganic
`
`phosphate compound may be about 8 parts by mass or less (preferably S parts by mass or
`
`less; for example, 4 parts by mass or less) with respect to 100 parts by mass of the positive
`
`electrode active material from the viewpoint of reducing battery resistance. A ratio of the
`
`mass of the organic phosphate compound to the total mass of the hydrofluoric acid
`
`trapping layer is suitably about 50 mass% or more and is usually preferably about 70
`
`mass® to 99 mass% (for example, 85 mass% to 95 mass), When the binder is used, a
`
`ratio of the mass of the binder to the total mass of the hydrofluoric acid trapping layeris,
`
`for example, about | massto 30 mass% and is usually preferably about 1 mass% to 20
`
`mass.
`
`{0033}
`
`A method of preparing the separator having the above-described aspect is
`
`not particularly Hmited.
`
`For example, first,
`
`the inorganic phosphate compound and
`
`optionally used materials are dispersed in an appropriate solvent to prepare a paste-like or
`
`be on
`
`sturry-hke composition (slurry for forming the hydrofluoric acid trapping layer). The
`surface of the separator substrate is coated with this slurry using an arbitrary method and
`
`dried. As a result, a separator including the hydrofluoric acid trapping layer that
`
`is
`
`formed on the surface of the separator substrate can be prepared. As the solvent, either an
`
`aqueous solvent or an organic solvent can be used. For example, N-methyl-2-pyrrolidone
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`(NMP) can be used.
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`In addition, the coating of the slurry can be performed using an
`
`appropriate coater such as a gravure coater, a slid coater, a die coater, a comma coater, or a
`
`dip coater. Altematively, the coating of the slurry can be performed using means such as
`
`Spray coating.
`
`In addition, the drying can be performed using general drying means (for
`
`example, drying by heating or vaceum drying).
`
`[0034]
`
`The separator of the battery disclosed herein may include the hydrofluoric
`
`acid trapping layer on only a single surface or both surfaces of the separator substrate.
`
`From the viewpoint of reducing battery resistance, the aspect of including the hydrofluoric
`
`acid trapping layer on only the single surface can he preferably adopted.
`
`In addition,
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`10
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`when the positive electrode and the negative clectrode are dispased to be opposite with the
`
`separator interposed therebetween, the hydrofluoric acid trapping layer may be opposite
`
`the positive electrode, may be opposite the negative electrode, er may be oppasite both the
`
`positive electrode and the negative electrode.
`
`In a preferred embodiment, the separator
`
`includes the hydrofluoric acid trapping layer that is formed on a surfaces on a side opposite
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`15
`
`at least the positive electrode.
`
`In a case where the hydroflu