(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`23 June 2011 (23.06.2011) OUT AUIA AMOMOA
`
`(43) International Publication Date
`
`(10) International Publication Number
`WO 2011/073798 A2
`
`
`G1)
`
`International Patent Classification:
`HOIM 10/0562 (2010.01)
`
`QD
`
`International Application Number:
`
`PCT/IB2010/003404
`
`(81)
`
`(22)
`
`(25)
`
`(26)
`
`(30)
`
`(71)
`
`(72)
`(75)
`
`International Filing Date:
`15 December 2010 (15.12.2010)
`
`Filing Language:
`
`Publication Language:
`
`Priority Data:
`2009-285275 16 December 2009 (16.12.2009)
`
`English
`
`English
`
`JP
`
`Applicant (for ail designated States except US): TOY-
`OTA JIDOSHA KABUSHIKI KAISHA [JP/JP];
`1,
`Toyota-cho, Toyota-shi, Aichi-ken, 471-8571 (JP).
`
`(84)
`
`Inventors; and
`Inventors/Applicants (for US only): OHTOMO, Taka-
`masa [JP/JP]; c/o TOYOTA JIDOSHA KABUSHIKI
`KAISHA, of
`1, Toyota-cho, Toyota-shi, Aichi-ken,
`471-8571 (JP). KAWAMOTO, Koji [JP/JP]; c/o TOY-
`OTA JIDOSHA KABUSHIKI KAISHA, of 1, Toyota-
`cho, Toyota-shi, Aichi-ken, 471-8571 (JP). HAMA,
`Shigenori [JP/JP]; c/o TOYOTA JIDOSHA KABUSHI-
`KI KAISHA, of 1, Toyota-cho, Toyota-shi, Aichi-ken,
`
`471-8571 (JP). KATO, Yuki [JP/JP]; c/o TOYOTA JI-
`DOSHA KABUSHIKI KAISHA, of 1, Toyota-cho, Toy-
`ota-shi, Aichi-ken, 471-8571 (JP).
`
`Designated States (unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`AO, AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ,
`CA, CH, CL, CN, CO, CR, CU, CZ, DE, DK, DM, DO,
`DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT,
`HN, HR, HU, ID, IL, IN, IS, KE, KG, KM, KN, KP, KR,
`KZ, LA, LC, LK, LR, LS, LT, LU, LY, MA, MD, ME,
`MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO,
`NZ, OM,PE, PG, PH, PL, PT, RO, RS, RU, SC, SD, SE,
`SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM, TN, TR, TT,
`TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW.
`
`Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LR, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG,
`ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU,TJ,
`TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, DK,
`EE, ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU,
`LV, MC, MK,MT, NL, NO, PL, PT, RO, RS, SE, SL SK,
`SM, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ,
`GW, ML, MR,NE,SN, TD, TG).
`
`[Continued on next page]
`
`(54) Titles METHOD OF PRODUCING A SULFIDE SOLID ELECTROLYTE MATERIAL, SULFIDE SOLID ELEC-
`TROLYTE MATERIAL, AND LITHIUM BATTERY
`
`STARTING MATERIAL COMPOSITION
`
`FIRST VITRIFICATION PROCESS
`
`(57) Abstract: A mcthod of producing a sulfide solid clec-
`trolyte material includes: forming an intermediate having
`FIG.1
`crosslinking sulfur but no Li2S, by vitrifying, inafirst vitri-
`fication process, a starting material composition obtained
`by mixing LipS and a sulfide ofa group 14 or group 15 ele-
`ment such that a proportion of Li,S with respect to the sum
`total of the LixS and the sulfide of a group 14 or group 15
`element is smaller than a proportion of Li.S required for the
`sulfide solid electrolyte material to obtain an ortho compo-
`sition; and eliminating the crosslinking sulfur by vitrifying,
`in a secondvitrification process, an intermediate-containing
`composition resulting from mixing a bond cleaving com-
`pound, which cleaves a bond of the crosslinking sulfur,
`with the intermediate.
`
`
`
`
`
`WoO2011/073798A2|IMIMITMINTARTANATANAAIAAATT
`
`Q
`
`
`
`
`
`
`
`
`
`INTERMEDIATE
`
`
`
`INTERMEDIATE~CONTAINING COMPOSITION
`
`SECOND VITRIFICATION PROCESS
`
`SULFIDE SOLID ELECTROLYTE MATERIAL
`
`

`

`WO 2011/073798 A2fMRI HIATT TATCAETAR
`
`Published:
`
`—_without international search report and to be republished
`upon receipt of that report (Rule 48.2(g))
`
`

`

`WO 2011/073798
`
`PCT/1IB2010/003404
`
`1
`
`METHOD OF PRODUCING A SULFIDE SOLID ELECTROLYTE MATERIAL,
`
`SULFIDE SOLID ELECTROLYTE MATERIAL, AND LITHIUM BATTERY
`
`BACKGROUND OF THE INVENTION
`
`1.
`
`Field ofthe Inverition
`
`[0001]
`
`The invention relates to a method of producing a sulfide solid electrolyte
`
`material that generates an extremely small amountof hydrogensulfide.
`
`2.
`
`Description of the Related Art
`
`10
`
`[0002]
`
`The rapid diffusion of information-related devices and communication
`
`15
`
`20
`
`25
`
`devices such as personal computers, video cameras, cell phones andthe like in recent
`years has been accompanied by efforts directed at developing batteries to be used as
`power sources in the foregoing devices. Meanwhile, high-output and high-capacity -
`batteriesfor electric automobiles and hybrid automobiles are the subject of ongoing
`research in the automotive industry.
`- At present, lithium batteries are predominant
`
`among various types of battery, thanks to their high energy density.
`- [0003)
`Current commercially available lithium batteries use electrolyte solutions
`that contain combustible organic solvents. Asa result,safety devices that suppress rises
`in temperature during short-circuits must be fitted to the battery, and also improvements
`in production and materials are called for in order to prevent short-circuits. By contrast,
`lithium batteries that are all-solid-state batteries, by changing the electrolyte solution into
`a solid electrolyte layer, employ no combustible organic solvent inside the battery, and
`arguably make for simpler safety devices, while being superior in terms of production
`costs and productivity. Sulfide solid electrolyte materials are conventional solid
`electrolyte materials that are employed in such solid electrolyte layers.
`|
`{0004}
`Sulfide solid electrolyte materials are useful for achieving higher battery
`outputs thanksto their high lithium (Li) ion conductivity, and research is being conducted
`on related technologies. For instance, Nobuya Machidaet al., “Mechano-chemical
`Synthesis ofLithium. lon’ConductingMaterials. inthe SystemLigO-LizS-P2S5”,J. Jpn.
`
`

`

`wo 2011/073798
`
`PCT/1IB2010/003404
`
`2
`
`Soc. Powder Metallurgy Vol. 51, No. 2, 91-97 disclose a glassy Li ion conductive
`material wherein part of LigS in 75Li2S-25P2Ssis replaced by Li,O. Also, R. Prasada
`Rao etal., “Oxysulfide glasses xLi,O-(1-x)(0.6Li2S-0.4P2S5)”, Journal of Power Sources
`159 (2006) 258-262, discloses a glassy Li ion conductive body represented by
`40Li20-36Li2S-24P28s5 (in this composition, the material satisfies x=40 in
`In both
`xLi,0-(1-x\(60Li,S-40P,Ss)) and that is produced by mechanical milling.
`technologies, a Li ion conductive body is producedin onesingle vitrification process
`(mechanical milling process).
`|
`[0005]
`Sulfide solid electrolyte materials are advantageousin terms of high Li
`ion conductivity, but, on the other hand, are problematic in that they generate hydrogen
`_ Sulfide when coming into contact with water (such as moisture, likewise hereafter).
`Against this background, the inventors have found that the amountofgenerated hydrogen
`‘sulfide can be reduced by adjusting the composition of a sulfide solid electrolyte material
`to an ortho composition. The term ortho composition denotes ordinarily the most highly
`hydrated oxoacid from among the oxoacids that are obtained through hydration of one
`same oxide. In the sulfide solid electrolyte material having LizS, however,the ortho
`composition denotes a composition having a crystal composition with the greatest
`amount-of LizS added amongthe sulfides.
`Ina LigS-P2Ss material, for instance, LizsPS4
`corresponds to the ortho composition, suchthat a sulfide solid electrolyte material of
`ortho composition is obtained when mixing starting materials in a proportion
`LigS:P2Ss=75:25, on a molar basis. Although a sulfide solid electrolyte material having
`an ortho composition has a lower amount of generated hydrogen sulfide than a sulfide
`solid electrolyte material otherthanof ortho composition, the sulfide solid electrolyte
`material releases nonetheless small amounts of hydrogen sulfide,and drops in Li ion
`conductivity have been observed. Therefore, hydrogen sulfide generation must be
`reduced furtherstill in order to increase the stability of the sulfide solid electrolyte
`
`10
`
`15
`
`20
`
`25
`
`material.
`
`_. SUMMARY. OF THE.INVENTION:.-
`
`

`

`WO 2011/073798
`
`PCT/1IB2010/003404
`
`3
`
`The invention provides a method of producing a sulfide solid electrolyte
`[0006].
`material that generates a very small amountof hydrogen sulfide.
`[0007]
`A first aspect of the invention relates to a method of producing a sulfide
`solid electrolyte material, characterized by including: forming an intermediate having
`crosslinking sulfur but no LiyS, by vitrifying, in a first vitrification process, a starting
`‘material composition obtained by mixing LigS and a sulfide of a group 14 or group 15
`element such that a proportionof Lips with respectto the sum total of the LigS and the
`' sulfide of a group 14 or group 15 element is smaller than a proportion of Li2S required
`for the sulfide solid electrolytematerial to obtain an ortho composition; and eliminating
`the crosslinking sulfur by vitrifying, in a second vitrification process, an
`intermediate-containing composition resulting from mixing a bond cleaving compound,
`which cleaves a bond of the crosslinking sulfur, with the intermediate.
`[0008]
`In the above configuration, an intermediate from which Li2S is removed
`is formed in the first vitrification step,while crosslinking sulfur in the intermediate is
`removed in the secondvitrification step. A sulfide solid electrolyte material can‘be
`obtained as a result that is free of bothLins and crosslinking sulfur.
`It becomespossible
`thereby to obtain a highly safesulfide solid electrolyte material that generates a very
`small amount Of hydrogen sulfide.
`[0009]
`In the production method according to the present aspect, the proportion
`in which the bond cleaving compoundis mixed with the intermediate may be a
`proportion at which a sulfide solid electrolyte material substantially free of crosslinking
`| sulfur is obtained. This feature allows suppressing generation of hydrogen sulfide
`caused by reaction betweenthe crosslinking sulfur and water.
`[0010]
`In the production method according to the present aspect, the bond
`cleaving compound may be LizO. By virtue of the abovefeature, the oxygen (O)
`_ element in Li2O can cleave with goodefficiency the crosslinking sulfur in the
`intermediate. Also, hydrogen sulfide is not generated even in the presence of unreacted
`LizO having been added in excess.
`—
`(OOL1}- Intheproduction-method-aceording to thepresent aspect,.the sulfide of a -
`
`10
`
`15
`
`20
`
`25
`
`

`

`WO 2011/01073798
`
`PCT/1IB2010/003404
`
`4
`
`‘ group 14 or group 15 element may be P2Ss; and in thestarting material composition, the
`proportionof theLizS with respect to the sum total of the LigS and the P2S5 may be
`smaller than 75%, on a molarbasis..
`{0012}
`Inthe production method according to the present aspect, the proportion
`of the sum total of the LizS and the LizO with respect to the sum total of the Li2S, the
`P2Ss and the Li2O inthe intermediate-containing composition may be not smaller than
`75%, on a molar basis. The above feature allows obtaining a sulfide solid electrolyte
`material substantially free of crosslinking sulfur.
`[0013]
`In the production method according to the present aspect, the sulfide of a
`group 14 or group 15 element may be GeS2; and in the starting material composition, the
`proportion of the LizS with respectto the sum total of the LizS and the GeS, may be
`- gmaller than 66.“Te, on a molar basis.
`{0014]
`“In the production method according to the present aspect, the proportion
`of the sum total of the LizS and the LizO with respect to the sum total of the LigS, the
`GeS> and the Li,O in the intermediate-containing composition may be not smaller than
`66.7%, on a molar basis. The above featureallows obtaining a sulfide solid electrolyte
`_ material substantially freeof crosslinking sulfur.
`|
`{0015}
`In the productionmethod according to the present aspect, the sulfide of a
`group 14 or group 15 element may be SiS2; and inthe starting material composition,the
`proportionof the Lies with respect tothe sum total of the LizS and the SiS2may be
`smaller than 66.7%, on a molarbasis..
`* [0016]
`In theproduction method according to the present aspect, the proportion
`of the sum total of the Li2S and the Li,O with respect to the sum total of the Li.S, the
`SiS, and the LizO in the intermediate-containing composition may be not smaller than
`66.7%, on amolar basis.
`. The.above feature allows obtaining a sulfide solid electrolyte
`material substantially free of crosslinking sulfur,
`[0017]
`In the production method according to the present aspect, the first
`_ vitrification process may be mechanical milling. The above feature enables processing
`at normal temperature and allows streamliningthe production process.
`
`10,
`
`~15
`
`"20
`
`25 ©
`
`

`

`WO 2011/073798
`
`PCT/1IB2010/003404
`
`5
`
`In the production method according to the present aspect, the second
`[0018]
`vitrification process may be mechanical milling. The above feature enables processing
`at normal temperature and allows streamlining the production process.
`.
`[0019].
`A second aspect of the invention relates to a sulfide solid electrolyte
`material that contains Li, a group 14 or group 15 element, O andS,is substantially free of
`crosslinking sulfur, and has a Li2S content no greater than 1 mol%.
`_
`(0020)
`In the above configuration, LizS content islow. Asulfide solid
`electrolyte material that generates a very small amount of hydrogen sulfide can be
`obtained as aresult.
`|
`.
`[0021]
`— “In the sulfide solid electrolyte material according to the present aspect,
`the group 14 or group 15 element may be P, and the sulfide solid electrolyte material
`according to the present aspect may beproduced by vitrifying Li2S, P2Ss and Li,O.
`[0022]
`In the sulfide solid electrolyte material according to the present aspect,
`LiO may form aphase. This feature allows obtaining a sulfide solid electrolyte
`
`material having yet better Li ion conductivity.
`[0023]
`A third aspectof the inventionrelates to a lithium battery that has a
`positive electrode active material layer containing a positive electrode active material; a
`negative electrode active material layer containing a negative electrode active material,
`and an electrolyte layer formed betweenthe positive electrode active material layer and
`the negativeelectrode active material Jayer.
`In the lithium battery, at least one from
`amongthe positive electrode active material layer, the negative electrode active material
`layer and the electrolyte layer contains.a sulfide solid electrolyte material that contains Li,
`a group 14 or group 15 element, O and §S,is substantially free of crosslinking sulfur, and
`has a Li2S content no greater than 1 mol%.
`(0024]
`Through the use ofthe above-described sulfide solid electrolyte material,
`the above configurationallows obtaining a lithium battery that generates a very small
`amountof hydrogen sulfide.
`.
`.
`[0025]
`The invention allows thus obtaining a sulfide solid electrolyte material
`that generates.a very small. amount of hydrogen sulfide.
`
`10
`
`15
`
`20
`
`25
`
`

`

`WO 2011/073798
`
`PCT/1IB2010/003404
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The foregoing and further objects, features and advantages of the
`[0026]
`invention will become apparent from the following description of example embodiments
`with reference to theaccompanying drawings, wherein like numerals are used to
`represent like elements and wherein:
`
`10
`
`15
`
`20
`
`25
`
`FIG. lisa flowchart illustrating as an example a method of producing a sulfide
`solid electrolyte material according to an embodimentof the invention;
`FIGs. 2A and 2B are explanatory diagrams for explaining a method of producing a
`sulfide solid electrolyte material accordingto related technologies, and a method of
`producinga sulfide solid electrolyte material according to an embodimentof the
`- invention;
`|
`FIG. 3 is a schematic cross-sectional diagram illustrating an example of a power
`generation elementin a lithium battery according to the an embodimentof the invention;
`FIG. 4 shows measurement results of amount of hydrogen sulfide generated by
`sulfide solid electrolyte materials obtained in Examples 1 to 3;
`FIG. 5 shows measurementresults of amount of hydrogen sulfide generatedby
`sulfide solid electrolyte materials obtained in Comparative examples 1 to 4;
`FIG. 6 shows measurementresults of X-ray diffraction of sulfide solid electrolyte
`materials obtained in Exarnples 1 to 4;
`FIG. 7 shows measurementresults of X-ray diffraction of sulfide solid electrolyte
`materials obtained in Comparative examples 1 to 3;
`FIG. 8 shows measurement results of X-ray diffraction of a sulfide solid electrolyte
`material obtained in Comparative example 4;
`|
`|
`FIG. 9 shows measurementresults of Li ion conductivity of sulfide solid electrolyte
`materials obtained in Examples 1 to 3 and Comparative examples 1 to4;
`FIG. 10 shows measurementresults of X-ray photoelectron spectroscopy ofa
`sulfide solid electrolyte material obtained in Comparative example 1;
`_
`
`

`

`_ WO 2011/073798
`
`PCT/IB2010/003404
`
`7
`
`FIG. 11 shows measurementresults of X-ray photoelectron spectroscopy of a sulfide |
`
`solid electrolyte material obtained in Comparative example 2;
`|
`FIG. 12 shows measurementresults of X-ray photoelectron spectroscopy of a
`sulfide solidelectrolyte material obtained in Comparative example 3; and
`|
`FIG. 13 shows measurementresults of X-ray photoelectron spectroscopy ofa
`
`sulfide solid electrolyte material obtained in Comparativeexample 4.
`
`10
`
`15
`
`20
`
`25
`
`DETAILED DESCRIPTION OF EMBODIMENTS
`[0027] Asa result of diligent research directed at solving the above problems,
`the inventors foundthat the reasons whya sulfide solid electrolyte material having an
`ortho composition generates small amounts of hydrogen sulfide were as follows.
`Specifically, the inventors foundthat an ortho composition can be obtained in a LigS-P2Ss5
`material in a case where starting materials are mixed in a proportion of LizS:P2Ss=75:25,
`on a molar basis, but when the proportion of LizS is low, even by a little, a small] ammount
`of SsP-S-PS; units (P2S7 units) is formed and the crosslinking sulfur in the units reacts
`with water to generate hydrogen sulfide. Conversely, when the proportion of LiaS is
`high, even bya little, there remains a small amount of Li2S, whichreacts with waterto
`generate hydrogen sulfide. Therefore, the inventors found that adjusting the starting
`material composition is extremely difficult in terms of obtaining a sulfide solid
`electrolyte material that generates a very smalJ.amount of hydrogen sulfide.
`- [0028].
`The inventors foundalso the following. Achieving a completely
`uniform composition of a glassy sulfide solid electrolyte material is difficult in a
`LipS-P2Ss material, even after having adjusted the starting material composition to an
`jdeal proportion (LigS:P2Ss=75:25, on a molar basis). Thus, small amounts of the
`above-described LiS and crosslinking sulfur remain, and can react with water to generate
`hydrogen sulfide. _ The inventors foundalso that even after adjustmentof the starting
`|
`|
`materialcomposition to an ideal proportion, there may be generated about 10% of
`Li4gP2S¢ units having a non-stoichiometric composition, which mayresult in the presence
`of residual Lis.
`
`

`

`WO 2011/073798
`
`PCT/IB2010/003404
`
`8
`
`Regarding related technologies, the present inventors found that
`[0029]
`a sulfide solid electrolyte material that generates a very small amount of hydrogen-sulfide,
`and being free of both LizS and crosslinking sulfur, can be obtained by dividing into two
`- stages the production of the sulfide solid electrolyte material that was carried out in one
`single vitrification process, such that, in a first vitrification process, there is produced an
`intermediate that may have crosslinking sulfur, since LizS is completely eliminated (Li2S
`is caused to be completely incorporated into the structure of the intermediate), and in a
`second vitrification process, a compound for cleaving crosslinking sulfur bondsis added
`to the intermediate, to remove thereby the crosslinking sulfur.
`[0030]
`A detailed explanation follows next on the method-of producing a sulfide
`~ solid electrolyte material, a sulfide solid electrolyte material and a lithium battery
`according to an embodimentof the invention. The term ortho composition denotes
`ordinarily the most highly hydrated oxoacid from among the oxoacids that are obtained
`through hydration of onc same oxide.
`In the sulfide solid electrolyte material having
`Li2S according to the present embodiment, however, the ortho composition denotes a
`composition having a crystal composition with the greatest amount of Li2S added among
`the sulfides.
`Ina Li2S-P2Ss5 material, for instance, LisPS4 correspondsto the ortho
`composition, such that a sulfidesolidelectrolyte material of ortho composition is
`obtained when mixing starting materials in a proportion Li2S:P2Ss=75:25, ona molar
`basis.
`|
`A method of producing a sulfide solid electrolyte material of an
`[0031]
`embodiment of the invention will be explained first. The method of producing a sulfide
`solid electrolyte material according the present embodimentis characterized by having a
`first vitrification step of vitrifying, by way of a first vitrification process, a starting
`material composition that is obtained by mixing LizS and a sulfide of a group 14 or group
`15 element in such a mannerthat the proportion.of LizS with respect to the sum total of
`LiS plus the. sulfide of a group 14 or group 15 element is smaller than the proportion of
`LigS at which an ortho composition isobtained, to form as a result an intermediate having
`crosslinking sulfur but no LigS; and a secondvitrification step of eliminating the
`
`10
`
`15
`
`20
`
`25
`
`

`

`WO 2011/073798
`
`PCT/1IB2010/003404
`
`9
`
`crosslinking sulfur by vitrifying an intermediate-containing composition resulting from
`mixing a bond cleaving compound which cleaves a bondofthe crosslinking sulfur, with
`
`the intermediate.
`
`In the present embodiment, an intermediate from which LigS is removed
`[0032]
`is formed in the first vitrification step, while the crosslinking sulfur in the intermediate is
`removedin the secondvitrification step. A sulfide solid electrolyte material can be
`obtained as a result that is free of both Lis and crosslinking sulfur.
`It becomes possible
`thereby to obtain a highly safe sulfide solid electrolyte material that generates a very
`small amount ofhydrogen sulfide. As pointed out in thesection on related art, adjusting
`a starting material composition was extremely difficult, as described above, when
`producinga sulfide solid electrolyte material in one single vitrification process, and there
`were also limits as to how low the amount of generated hydrogen sulfide could be
`_ brought. The present embodiment, by contrast, allowsobtaining easily a sulfide solid
`electrolyte material that generatesa very small amount of hydrogen sulfide, by dividing
`
`10
`
`15
`
`20
`
`the vitrification process into two stages.
`[0033]
`FIG. 1 is a flowchart illustrating as an example a method of producing a
`sulfide solid electrolyte material according to the present embodiment.
`In FIG. 1, there
`are preparedfirstly LigS and P2Ss5 (sulfide of a group 14 or group 15 element). The
`foregoing are then mixedtoaratio Li2S:P2Ss=70:30 (molar basis), to yield a starting
`material composition. The proportion of LigS with respect to the sum total of LizS and
`P2S; is smaller than the proportion (75%) at whichthe ortho composition is obtained..
`Next, the starting material compositionis vitrified (frst vitrification process) by
`mechanical milling, to yield a 7O0LizS-30P28s glass (intermediate). As described below,
`the intermediate has crosslinking sulfurbut no Li2S. Next, the 70Li2S:30P2Ss5 glass is
`mixed with Li,O (bond cleaving compound), to yield an intermediate-containing
`composition.
`‘Next, the intermediate-containing composition is vitrified (second
`vitrification process) by mechanical milling, to yield a sulfide solid electrolyte material.
`.
`{0034]
`In Nobuya Machida et al., “Mechano-chemical Synthesis of Lithium Jon
`Conducting Materials in theSystem LigO-LizS-P2S5”, J. Jpn. Soc. Powder Metallurgy Vol.
`
`25
`
`

`

`WO 2011/073798
`
`PCT/1IB2010/003404
`
`10
`
`51, No. 2, 91-97 and R. Prasada Rao etal., “Oxysulfide glasses
`xLizO-(1-x)(0.6LizS-0.4P2Ss)”, Journal of Power Sources 159 (2006) 258-262 cited
`above, a sulfide solid electrolyte material is produced by single mechanical milling using
`a mixture of Li2S, P2Ss and LizO.
`In this case, as illustrated in FIG. 2A, LizgO and P2Ss
`react at the sametime that Li2S and P2Ss react.
`Asa result, there isa high likelihood
`that a small amount of LizS remains in the obtained sulfide solid electrolyte material, and
`thus a smal] amount of hydrogen sulfide may be generated, as described in the
`comparative examples below.
`In the present embodiment, by contrast, firstly a
`LigS:P3Ss glass is produced by reacting Li2S and P2Ss, as illustrated in FIG. 2B. At this
`time, the proportionbetween LizS and P2Ss is adjusted to cause Lis to disappear
`completely(to cause the LigS to be completely incorporatedinto the structure of an
`intermediate). Asa result there is produced a LizS:P2S85 glass that may have crosslinking
`sulfur (for instance, the below-described P2S; units). Thereafter, the crosslinking sulfur
`in the LigSPSs glass ismade to react with LizO. Asa result there can be obtained a
`sulfide solid electrolyte material free of both Li2S and crosslinking sulfur, so that the
`amount of generated hydrogen sulfide can be kept very small.
`[0035]
`A formula of the reactionthat takes place when crosslinking sulfur (for
`instance, P2S7 units) in the intermediate is cleaved by a bond cleaving compound (for
`instance, Li2O), is given below as an example. As the reaction formula below indicates,
`the crosslinking sulfur $ in the PS1 unit reacts with Li,O to form a PS3;OLi unit and a
`PS,Li unit, whereuponthe crosslinking sulfur disappears. Although omitted in the
`reaction formulabelow, the single-bond S in each unit is S’ that has a Li* counter ion.
`
`[0036]
`
`Formula 1
`s
`.
`(Ss
`S.
`$s—P—S—-P—S + Lf \ oo S—P—OLi +
`Ss
`Ss
`Ss
`[0037] Amethodof producing a sulfide solid electrolyte material of an
`embodimentof the present embodiment willbe explained step by step.
`In the present
`
`Ss
`LIS —P-—S
`S
`
`- 10
`
`15
`
`20
`
`25
`
`

`

`WO 2011/073798
`
`PCT/1IB2010/003404
`
`11
`
`10
`
`_
`
`~
`
`embodiment, the below-described steps are all carried out ordinarily in an inert gas
`atmosphere (for instance, an Ar gas atmosphere).
`[0038]
`‘Thefirst vitrification step in the present embodimentis a step of
`vitrifying, by way ofafirst vitrification process, a starting material composition that is
`obtained by mixing Li,S and a sulfide of a group 14 or group 15 element in such a.
`manner that the proportion of LigS with respect to the sum total of LigS plus the sulfide of
`a group 14 or group 15 elementis smaller than the proportion ofLizS at which an ortho
`compositionis obtained, to form as a result an intermediate having crosslinking sulfur but
`no LiS.
`In the present embodiment, Li,S is completely eliminated in the first
`[0039]
`vitrification step (Li2S 1iscaused to be completely incorporated into the structure of the
`intermediate), as a result of which there is producedan intermediate that may have
`crosslinking sulfur. As usediin the present embodiment, the term °‘crosslinking sulfur”
`denotes a crosslinking sulfur in acompoundresulting from reacting Li2S and a sulfide of
`a group 14 or group 15 element. For example, the crosslinking sulfur in S3P-S-PS; units
`‘obtained by reacting Li,SandP2Ss.is. a case in point. Such crosslinking sulfur tends to
`react with water and to generate readily hydrogen sulfide as aresult. The feature
`“having crosslinking sulfur” can be checked based on measurements of Raman
`spectroscopy spectra.
`In the case, for instance, of a sulfide solid electrolyte materialof a
`Li2S-P2Ss material, the peaks of S;P-S-PS;units appear ordinarily at 402 cm?
`' Accordingly,the presence or absence of the crosslinking sulfur can be determined on the
`basis ofthatpeak.
`In sulfide-solid electrolyte materials other than LioS-P2Ss material,
`the presence or absence of crosslinking sulfur can be determined by identifying units
`having a crosslinking sulfur, and by measuring peaks of suchunits.
`[0040]
`Thestarting material composition of the present embodimentis
`explained next. The starting material composition of the present embodimentis a
`mixture of LipS and.a sulfide of a group 14 or group 15 element. Preferably, the LizS in
`the starting material composition may have few impurities, since side reactions can be
`suppressed in that case. Examplesof LiyS synthesis methodsare disclosed in, for
`
`15
`
`20
`
`25
`
`

`

`WO 2011/073798
`
`PCT/IB2010/003404
`
`12
`
`instance, Japanese Patent ApplicationPublication No. 7-330312 JP-A-7-330312).
`Preferably, LizS may be purified jn accordancewith, for instance, the methodset forth in
`
`WO 2005/040039.
`[0041]
`~ The starting material composition has a sulfide ofa group 14 or group 15
`element. The group 14 or group 15 elementis not particularly limited, buy may be, for
`- instance, P, Si, Ge, As, Sb or the like. Among the foregoing, preferably, the group 14 or
`group 15 element maybeP, Si or Ge,in particular P, since in this case there can be
`obtained a sulfide solid electrolyte material that generates a small amount of hydrogen
`sulfide and that has high Li ion conductivity. The sulfide of a group 14 or group 15
`element maybe, specifically, P2S3, P2Ss, SiS2, GeS2, As2S;3 or Sb2S3.
`|
`, [0042]
`Inthe present embodiment, the proportions in the starting material
`composition are adjusted in order to produce an intermediate having crosslinking sulfur
`but no LigS. Specifically, the proportion of LisS with respect to the sum total of LigS
`‘and the sulfide of a group 14 of group 15 elementis adjusted to be smaller than the
`‘proportion of LigS at which the ortho composition is obtained.
`In a case where the
`sulfide of a group 14 or group 15 elementis for instance P2Ss, the proportion of LiS at
`which the ortho composition is obtained is 715% (LipS:P2S5s=75:25, on a molar basis).
`Accordingly, the proportion of LizS with respect to the sum total of LigS and P2Ss is
`adjusted to be smaller than 75%, on a molarbasis.
`In the present embodiment, some
`LioS may remain evenif the above Li2S portion is 75% on a molar basis. That is
`becauseit is difficult to achieve a perfectly uniform composition of the glassy sulfide .
`solid electrolyte material, even when adjusting the proportionsin the starting material
`composition tothe ideal proportion(Lis:PrSs==75:25, on a molarbasis), and there is a
`chance.than a small amount of LigS remains in the material.
`In the present embodiment,
`preferably, the proportion of Li2S with respect to the sum total of Li2S and P2S5 may be
`set to be no greater than 74%, more preferably no greater than 73% and in particular, no
`greater than 72%,.on a molarbasis, since an intermediate having no Li2S can be produced
`more reliably iin that case.
`[0043] if the sulfide of a group14 or group 15 element is GeS2, the proportion
`
`10
`
`15
`
`20
`
`25
`
`

`

`WwO 2011/073798
`
`PCT/1IB2010/003404
`
`13
`
`of LiyS at which the ortho compositionis obtained is 66.7% (LizS:GeS2=66.7:33.3, ona _
`molar basis). Accordingly, the proportion of LizS with respect to the sum total of LizS
`and GeSzis adjusted to be smaller than 66.7%, ona molar basis.
`In the present
`embodiment, preferably, the proportion of LigS with respect to the sum total of LigS and
`GeS2maybe set to be no greater than 66%, more preferably no greater than 65% andin
`particular, no greater than 64%, ona molar basis, since an intermediate havingno LieS
`can be produced more reliably in that case.
`If the sulfide of a group 14 or group 15
`element is SiS2, theproportion ofLigSat which the ortho composition is obtained iis
`66.7% (Li2S:SiS2=66.7:33.3, on a molar basis). A preferred Li2S proportion may be the
`sameas in the case of GeSo.
`[0044]
`In the present embodiment, the proportion of LizS with respectto the
`_ sum total of LipS and the sulfide of a group 14 or group15 element may be, preferably,
`not lower than the proportion of‘Li,S at which a pyro composition is obtained. That is
`because MS,that contributes to ion conductivity (M denotes a group 14 or group 15
`element) does not form. readily when the above proportion of Li2S is smaller than the
`proportionof LigS at which the pyro composition is obtained. Herein, the term pyro
`denotes ordinarily the second most hydrated oxoacid from among the oxoacids that are
`obtained through hydration of onesameoxide.
`Ina sulfide solid electrolyte material
`using LiS, however, the pyro composition denotes a composition having a crystal
`, composition with the second greatest amount of added Li2S, among the sulfides. The
`pyro composition can also be defined as a Structure resulting from removingone water
`molecule from the ortho composition, through dehydrative condensationof the o