WO2023053610A1 - 硫化物系固体電解質 - Google Patents
硫化物系固体電解質 Download PDFInfo
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- WO2023053610A1 WO2023053610A1 PCT/JP2022/024586 JP2022024586W WO2023053610A1 WO 2023053610 A1 WO2023053610 A1 WO 2023053610A1 JP 2022024586 W JP2022024586 W JP 2022024586W WO 2023053610 A1 WO2023053610 A1 WO 2023053610A1
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- solid electrolyte
- sulfide
- based solid
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- aldirodite
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- 239000002203 sulfidic glass Substances 0.000 title abstract 2
- 239000013078 crystal Substances 0.000 claims abstract description 113
- 150000001450 anions Chemical class 0.000 claims abstract description 62
- 229910001416 lithium ion Inorganic materials 0.000 claims abstract description 44
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims abstract description 43
- 229910052794 bromium Inorganic materials 0.000 claims abstract description 32
- 229910052801 chlorine Inorganic materials 0.000 claims abstract description 31
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 26
- 239000007784 solid electrolyte Substances 0.000 claims description 92
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 claims description 68
- 229910052731 fluorine Inorganic materials 0.000 claims description 12
- 229910052760 oxygen Inorganic materials 0.000 claims description 12
- 229910052740 iodine Inorganic materials 0.000 claims description 6
- 229910052710 silicon Inorganic materials 0.000 claims description 5
- 229910052718 tin Inorganic materials 0.000 claims description 4
- 239000000460 chlorine Substances 0.000 description 65
- 239000002994 raw material Substances 0.000 description 51
- 150000001875 compounds Chemical class 0.000 description 50
- 239000000203 mixture Substances 0.000 description 47
- 239000000843 powder Substances 0.000 description 40
- 238000005259 measurement Methods 0.000 description 33
- 238000010438 heat treatment Methods 0.000 description 31
- 239000007774 positive electrode material Substances 0.000 description 28
- 238000002441 X-ray diffraction Methods 0.000 description 27
- 238000002156 mixing Methods 0.000 description 25
- 239000012298 atmosphere Substances 0.000 description 24
- 239000002245 particle Substances 0.000 description 22
- 239000000155 melt Substances 0.000 description 20
- 239000011248 coating agent Substances 0.000 description 19
- AMXOYNBUYSYVKV-UHFFFAOYSA-M lithium bromide Chemical compound [Li+].[Br-] AMXOYNBUYSYVKV-UHFFFAOYSA-M 0.000 description 15
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 description 15
- 238000004519 manufacturing process Methods 0.000 description 15
- 238000000576 coating method Methods 0.000 description 13
- 238000004458 analytical method Methods 0.000 description 11
- 230000006866 deterioration Effects 0.000 description 11
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 10
- 238000001816 cooling Methods 0.000 description 10
- 238000003991 Rietveld refinement Methods 0.000 description 9
- 238000007599 discharging Methods 0.000 description 9
- GLNWILHOFOBOFD-UHFFFAOYSA-N lithium sulfide Chemical compound [Li+].[Li+].[S-2] GLNWILHOFOBOFD-UHFFFAOYSA-N 0.000 description 9
- 239000000463 material Substances 0.000 description 9
- 229910013641 LiNbO 3 Inorganic materials 0.000 description 8
- -1 Sulfide ions Chemical class 0.000 description 8
- 239000007789 gas Substances 0.000 description 8
- 230000014759 maintenance of location Effects 0.000 description 8
- 238000000034 method Methods 0.000 description 8
- 230000000694 effects Effects 0.000 description 7
- 239000012535 impurity Substances 0.000 description 7
- 239000012299 nitrogen atmosphere Substances 0.000 description 7
- CYQAYERJWZKYML-UHFFFAOYSA-N phosphorus pentasulfide Chemical compound S1P(S2)(=S)SP3(=S)SP1(=S)SP2(=S)S3 CYQAYERJWZKYML-UHFFFAOYSA-N 0.000 description 7
- 230000005855 radiation Effects 0.000 description 6
- 239000000126 substance Substances 0.000 description 6
- 238000012360 testing method Methods 0.000 description 6
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 5
- 238000009826 distribution Methods 0.000 description 5
- FUJCRWPEOMXPAD-UHFFFAOYSA-N lithium oxide Chemical compound [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 description 5
- 229910001947 lithium oxide Inorganic materials 0.000 description 5
- 239000011669 selenium Substances 0.000 description 5
- 230000005469 synchrotron radiation Effects 0.000 description 5
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 4
- 229910018091 Li 2 S Inorganic materials 0.000 description 4
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 4
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 4
- 239000011230 binding agent Substances 0.000 description 4
- 229910052736 halogen Inorganic materials 0.000 description 4
- 150000002367 halogens Chemical class 0.000 description 4
- 238000001483 high-temperature X-ray diffraction Methods 0.000 description 4
- 238000000465 moulding Methods 0.000 description 4
- 238000007254 oxidation reaction Methods 0.000 description 4
- 238000005191 phase separation Methods 0.000 description 4
- XHXFXVLFKHQFAL-UHFFFAOYSA-N phosphoryl trichloride Chemical compound ClP(Cl)(Cl)=O XHXFXVLFKHQFAL-UHFFFAOYSA-N 0.000 description 4
- 229910052711 selenium Inorganic materials 0.000 description 4
- JHJLBTNAGRQEKS-UHFFFAOYSA-M sodium bromide Chemical compound [Na+].[Br-] JHJLBTNAGRQEKS-UHFFFAOYSA-M 0.000 description 4
- 238000002216 synchrotron radiation X-ray diffraction Methods 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 229910013716 LiNi Inorganic materials 0.000 description 3
- 229910018584 Mn 2-x O 4 Inorganic materials 0.000 description 3
- VKCLPVFDVVKEKU-UHFFFAOYSA-N S=[P] Chemical class S=[P] VKCLPVFDVVKEKU-UHFFFAOYSA-N 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 238000001479 atomic absorption spectroscopy Methods 0.000 description 3
- 239000011324 bead Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 3
- 230000003993 interaction Effects 0.000 description 3
- 238000004255 ion exchange chromatography Methods 0.000 description 3
- 229910052744 lithium Inorganic materials 0.000 description 3
- 238000000634 powder X-ray diffraction Methods 0.000 description 3
- 239000002002 slurry Substances 0.000 description 3
- 235000002639 sodium chloride Nutrition 0.000 description 3
- 239000011780 sodium chloride Substances 0.000 description 3
- 239000011593 sulfur Substances 0.000 description 3
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 2
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- ILAHWRKJUDSMFH-UHFFFAOYSA-N boron tribromide Chemical compound BrB(Br)Br ILAHWRKJUDSMFH-UHFFFAOYSA-N 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 150000001768 cations Chemical group 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000002425 crystallisation Methods 0.000 description 2
- 230000008025 crystallization Effects 0.000 description 2
- XUCJHNOBJLKZNU-UHFFFAOYSA-M dilithium;hydroxide Chemical compound [Li+].[Li+].[OH-] XUCJHNOBJLKZNU-UHFFFAOYSA-M 0.000 description 2
- 238000007580 dry-mixing Methods 0.000 description 2
- 238000004993 emission spectroscopy Methods 0.000 description 2
- 229910052732 germanium Inorganic materials 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- PQXKHYXIUOZZFA-UHFFFAOYSA-M lithium fluoride Chemical compound [Li+].[F-] PQXKHYXIUOZZFA-UHFFFAOYSA-M 0.000 description 2
- 238000003701 mechanical milling Methods 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 239000007773 negative electrode material Substances 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 239000011574 phosphorus Substances 0.000 description 2
- 230000001376 precipitating effect Effects 0.000 description 2
- 239000011164 primary particle Substances 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- KHDSWONFYIAAPE-UHFFFAOYSA-N silicon sulfide Chemical compound S=[Si]=S KHDSWONFYIAAPE-UHFFFAOYSA-N 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 238000012916 structural analysis Methods 0.000 description 2
- 229910052720 vanadium Inorganic materials 0.000 description 2
- 229910052726 zirconium Inorganic materials 0.000 description 2
- 229910052582 BN Inorganic materials 0.000 description 1
- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 description 1
- CPELXLSAUQHCOX-UHFFFAOYSA-M Bromide Chemical compound [Br-] CPELXLSAUQHCOX-UHFFFAOYSA-M 0.000 description 1
- WKBOTKDWSSQWDR-UHFFFAOYSA-N Bromine atom Chemical compound [Br] WKBOTKDWSSQWDR-UHFFFAOYSA-N 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 1
- 238000005169 Debye-Scherrer Methods 0.000 description 1
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 1
- 229910005839 GeS 2 Inorganic materials 0.000 description 1
- 229910018119 Li 3 PO 4 Inorganic materials 0.000 description 1
- PHSPJQZRQAJPPF-UHFFFAOYSA-N N-alpha-Methylhistamine Chemical compound CNCCC1=CN=CN1 PHSPJQZRQAJPPF-UHFFFAOYSA-N 0.000 description 1
- 241001460678 Napo <wasp> Species 0.000 description 1
- 238000001237 Raman spectrum Methods 0.000 description 1
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 description 1
- 229910052581 Si3N4 Inorganic materials 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 229910020346 SiS 2 Inorganic materials 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- IARUYLAWANRWEY-UHFFFAOYSA-N [S-2].[S-2].[S-2].[V+3].[V+3] Chemical compound [S-2].[S-2].[S-2].[V+3].[V+3] IARUYLAWANRWEY-UHFFFAOYSA-N 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 239000006230 acetylene black Substances 0.000 description 1
- 229910000272 alkali metal oxide Inorganic materials 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 239000005354 aluminosilicate glass Substances 0.000 description 1
- 229910052787 antimony Inorganic materials 0.000 description 1
- 229910052789 astatine Inorganic materials 0.000 description 1
- 239000005388 borosilicate glass Substances 0.000 description 1
- GDTBXPJZTBHREO-UHFFFAOYSA-N bromine Substances BrBr GDTBXPJZTBHREO-UHFFFAOYSA-N 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000011362 coarse particle Substances 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000012790 confirmation Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- KZHJGOXRZJKJNY-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Si]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O KZHJGOXRZJKJNY-UHFFFAOYSA-N 0.000 description 1
- XQNIYBBHBZAQEC-UHFFFAOYSA-N diphosphorus trisulphide Chemical compound S=PSP=S XQNIYBBHBZAQEC-UHFFFAOYSA-N 0.000 description 1
- 239000002612 dispersion medium Substances 0.000 description 1
- JIRDGEGGAWJQHQ-UHFFFAOYSA-N disulfur dibromide Chemical compound BrSSBr JIRDGEGGAWJQHQ-UHFFFAOYSA-N 0.000 description 1
- PXJJSXABGXMUSU-UHFFFAOYSA-N disulfur dichloride Chemical compound ClSSCl PXJJSXABGXMUSU-UHFFFAOYSA-N 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- DWRNSCDYNYYYHT-UHFFFAOYSA-K gallium(iii) iodide Chemical compound I[Ga](I)I DWRNSCDYNYYYHT-UHFFFAOYSA-K 0.000 description 1
- YIZVROFXIVWAAZ-UHFFFAOYSA-N germanium disulfide Chemical compound S=[Ge]=S YIZVROFXIVWAAZ-UHFFFAOYSA-N 0.000 description 1
- 238000002847 impedance measurement Methods 0.000 description 1
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 1
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- 239000007788 liquid Substances 0.000 description 1
- 239000011244 liquid electrolyte Substances 0.000 description 1
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 1
- 150000002642 lithium compounds Chemical class 0.000 description 1
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 1
- INHCSSUBVCNVSK-UHFFFAOYSA-L lithium sulfate Inorganic materials [Li+].[Li+].[O-]S([O-])(=O)=O INHCSSUBVCNVSK-UHFFFAOYSA-L 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 238000010303 mechanochemical reaction Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 229910052752 metalloid Inorganic materials 0.000 description 1
- 239000011812 mixed powder Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 229910052863 mullite Inorganic materials 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 238000005121 nitriding Methods 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- RLOWWWKZYUNIDI-UHFFFAOYSA-N phosphinic chloride Chemical compound ClP=O RLOWWWKZYUNIDI-UHFFFAOYSA-N 0.000 description 1
- 150000003018 phosphorus compounds Chemical class 0.000 description 1
- UHZYTMXLRWXGPK-UHFFFAOYSA-N phosphorus pentachloride Chemical compound ClP(Cl)(Cl)(Cl)Cl UHZYTMXLRWXGPK-UHFFFAOYSA-N 0.000 description 1
- FAIAAWCVCHQXDN-UHFFFAOYSA-N phosphorus trichloride Chemical compound ClP(Cl)Cl FAIAAWCVCHQXDN-UHFFFAOYSA-N 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 1
- 229910010271 silicon carbide Inorganic materials 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- KKCBUQHMOMHUOY-UHFFFAOYSA-N sodium oxide Chemical compound [O-2].[Na+].[Na+] KKCBUQHMOMHUOY-UHFFFAOYSA-N 0.000 description 1
- 229910000162 sodium phosphate Inorganic materials 0.000 description 1
- 239000001488 sodium phosphate Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000011029 spinel Substances 0.000 description 1
- 229910052596 spinel Inorganic materials 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 150000004763 sulfides Chemical class 0.000 description 1
- FWMUJAIKEJWSSY-UHFFFAOYSA-N sulfur dichloride Chemical compound ClSCl FWMUJAIKEJWSSY-UHFFFAOYSA-N 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- RBTVSNLYYIMMKS-UHFFFAOYSA-N tert-butyl 3-aminoazetidine-1-carboxylate;hydrochloride Chemical compound Cl.CC(C)(C)OC(=O)N1CC(N)C1 RBTVSNLYYIMMKS-UHFFFAOYSA-N 0.000 description 1
- MJNHIYILRDOOTC-UHFFFAOYSA-N tetrachlorophosphanium Chemical compound Cl[P+](Cl)(Cl)Cl MJNHIYILRDOOTC-UHFFFAOYSA-N 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 1
- ALRFTTOJSPMYSY-UHFFFAOYSA-N tin disulfide Chemical compound S=[Sn]=S ALRFTTOJSPMYSY-UHFFFAOYSA-N 0.000 description 1
- 229910001887 tin oxide Inorganic materials 0.000 description 1
- TUTLDIXHQPSHHQ-UHFFFAOYSA-N tin(iv) sulfide Chemical compound [S-2].[S-2].[Sn+4] TUTLDIXHQPSHHQ-UHFFFAOYSA-N 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- FAQYAMRNWDIXMY-UHFFFAOYSA-N trichloroborane Chemical compound ClB(Cl)Cl FAQYAMRNWDIXMY-UHFFFAOYSA-N 0.000 description 1
- TWQULNDIKKJZPH-UHFFFAOYSA-K trilithium;phosphate Chemical class [Li+].[Li+].[Li+].[O-]P([O-])([O-])=O TWQULNDIKKJZPH-UHFFFAOYSA-K 0.000 description 1
- RYFMWSXOAZQYPI-UHFFFAOYSA-K trisodium phosphate Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])([O-])=O RYFMWSXOAZQYPI-UHFFFAOYSA-K 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
- H01M10/0562—Solid materials
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/14—Sulfur, selenium, or tellurium compounds of phosphorus
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C10/00—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/06—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances
- H01B1/10—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances sulfides
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0065—Solid electrolytes
- H01M2300/0068—Solid electrolytes inorganic
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention relates to a sulfide-based solid electrolyte used in lithium-ion secondary batteries.
- Lithium ion secondary batteries are widely used in portable electronic devices such as mobile phones and laptop computers.
- liquid electrolytes have been used in lithium-ion secondary batteries, but there are concerns about liquid leakage, ignition, and the like, and it has been necessary to increase the size of the case for safety design.
- improvements in the short battery life and narrow operating temperature range of lithium ion secondary batteries have been desired.
- Solid electrolytes are roughly classified into sulfide-based solid electrolytes and oxide-based solid electrolytes.
- Sulfide ions forming a sulfide-based solid electrolyte have a higher polarizability than oxide ions forming an oxide-based solid electrolyte, and exhibit high lithium ion conductivity.
- As sulfide-based solid electrolytes there are LGPS-type crystals such as Li 10 GeP 2 S 12 , aldirodite-type crystals such as Li 6 PS 5 Cl, and LPS crystallized glasses such as Li 7 P 3 S 11 crystallized glass. are known.
- Patent document 1 is cited as an example disclosing a sulfide-based solid electrolyte containing aldirodite-type crystals.
- Non-Patent Documents 1 and 2 the interface resistance can be reduced by coating the surface of LiCoO 2 , which is a positive electrode active material, with lithium niobate (LiNbO 3 ). It is disclosed that the performance of secondary batteries can be improved.
- the ideal thickness of the surface coating of the positive electrode active material with a coating agent such as LiNbO 3 is 7 to 10 nm, but it is difficult to apply such a very thin coating uniformly and with good reproducibility.
- a coating agent such as LiNbO 3
- spinel-type crystal LiNi x Mn 2-x O 4 or the like which is known as a high-potential positive electrode active material
- coating agents such as LiNbO 3 are not suitable for surface coating because they cannot withstand high electromotive force and decompose. Sometimes not.
- a sulfide-based solid electrolyte used in a lithium-ion secondary battery comprising an aldirodite-type crystal containing Li, P, S and Ha, wherein the Ha contains at least one of Cl and Br, F is at least one element selected from the group consisting of , Cl, Br, and I, and the aldirodite-type crystal has (A) free anion sites containing S, at least one of Cl and Br, and and (B) a portion of P at the 4b site and a portion of S at the 16e site adjacent to P at the 4b site are present, respectively substituted with another element, and the aldirodite-type crystal has free anion contents [S 2 ⁇ ], [O 2 ⁇ ], [Br ⁇ ], [Cl ⁇ ] and [F ⁇ ] and their electronegativities ⁇ (S) , ⁇ (O) , ⁇ (Br) , ⁇ (Cl) and
- the algyrodite-type crystal satisfies the above (A), and the content of the free anion is 0 ⁇ [Br ⁇ ]/([F ⁇ ]+[Cl ⁇ ]+[Br ⁇ ]) ⁇ 2, the sulfide-based solid electrolyte according to any one of the above [1] to [6].
- the sulfide-based solid electrolyte of the present invention it is possible to suppress deterioration of battery characteristics when charging and discharging are repeated without coating the surface of the positive electrode active material with LiNbO 3 or the like. Therefore, when the positive electrode active material is used in a lithium ion secondary battery, the sulfide-based solid electrolyte eliminates the need for a step of uniformly and reproducibly coating the surface of the positive electrode active material with a very thin coating. Also, when using spinel type crystal LiNi x Mn 2-x O 4 or the like known as a high-potential positive electrode active material, it can be applied without worrying about decomposition of the coating agent.
- 2 is an XRD pattern of the sulfide-based solid electrolyte of Example 8.
- FIG. 3 is a charge-discharge curve obtained in battery evaluation of Example 1.
- a sulfide-based solid electrolyte according to the present embodiment (hereinafter sometimes simply referred to as a "solid electrolyte") is used in a lithium ion secondary battery and contains aldirodite-type crystals containing Li, P, S and Ha. .
- Ha is at least one element selected from the group consisting of F, Cl, Br and I, including at least one of Cl and Br.
- the algyrodite-type crystal in this embodiment satisfies at least one of the following (A) and (B).
- (A) S, at least one of Cl and Br, and one or more elements different therefrom are present at free anion sites.
- (B) Part of P at the 4b site and part of S at the 16e site adjacent to P at the 4b site are replaced with other elements.
- the contents of free anions are [S 2 ⁇ ], [O 2 ⁇ ], [Br ⁇ ], [Cl ⁇ ] and [F ⁇ ], and The following relationships are satisfied when the electronegativities of anions are represented by ⁇ (S) , ⁇ (O) , ⁇ (Br) , ⁇ (Cl) and ⁇ (F) .
- the aldirodite-type crystal satisfies at least one of the above (A) and (B) and the anion parameter is 0.36 or less, charging and discharging can be performed without coating the surface of the positive electrode active material with LiNbO 3 or the like. It is possible to suppress the deterioration of the battery characteristics when repeating the above.
- the free anion site in (A) above refers to an anion that is not covalently bonded to a cation, and when the aldirodite-type crystal is cubic, the 4a site and 4d site correspond to it. Further, although the details will be described later, when the algyrodite-type crystal is a rhombohedral crystal, the 1a site and the 3b site correspond to free anion sites.
- the anions present at the free anion sites can be obtained by synchrotron radiation X-ray diffraction (XRD) measurement.
- XRD synchrotron radiation X-ray diffraction
- the pattern obtained by synchrotron radiation XRD measurement is subjected to structural refinement analysis by the Rietveld method to determine the occupied element and occupancy rate of each site.
- the content of each element and the total thereof are determined by composition analysis using ICP emission spectrometry, atomic absorption spectrometry, ion chromatography, etc. Based on the values, the crystal structure is refined by the Rietveld method. can be analyzed with higher accuracy.
- the one or more elements different from S, Cl, and Br present at the free anion site include, for example, O, F, Se, and I, which have high electronegativity and anion parameters is preferably at least one of O and F, and more preferably F.
- the content of free anions is 0 ⁇ [Br - ]/([F - ]+[Cl - ]+[Br - ]) ⁇ 2, and the value represented by ⁇ [Br ⁇ ]/([F ⁇ ]+[Cl ⁇ ]+[Br ⁇ ]) ⁇ is more preferably greater than 0.3, and 0.3. More than 5 is more preferable, less than 1.5 is more preferable, and less than 1.2 is even more preferable.
- the other element M substituted for part of P at the 4b site in (B) is at least one element selected from the group consisting of metal elements and metalloid elements of Groups 2 to 14 of the periodic table.
- Elements that form a MS 4 tetrahedral structure with an ionic radius larger than that of PS 4 3 ⁇ are preferred.
- Examples of the element M that forms an MS tetrahedral structure with a large ionic radius include Si, Sn, Al, V, Ti, Zr, Sb, and Ge. More preferred are Si, Sn, V, Ge and Zr.
- Other elements substituted for part of S at the 16e site in (B) above are preferably O, Se, etc., and more preferably O from the viewpoint of high electronegativity and small anion parameter.
- the element M that replaces part of P at the 4b site is preferably an element that forms an MS 4 tetrahedral structure with a larger ionic radius than PS 4 3- as described above, and the element M is Si and At least one of Sn is more preferable. That is, the MS 4 tetrahedral structure is more preferably at least one of SiS 4 4- and SnS 4 4- , and in this case, part of S is further substituted with O, Se, etc. to satisfy the above (B) is preferred.
- the average bond distance between the 4b site and the adjacent 16e site is preferably 2.07 ⁇ or more, more preferably 2.08 ⁇ or more, 2.10 ⁇ or more is more preferable. From the viewpoint of maintaining the crystal structure, the average bond distance is preferably 2.20 ⁇ or less, more preferably 2.17 ⁇ or less, and even more preferably 2.15 ⁇ or less.
- the average bond distance between the 4b site and the adjacent 16e site in the PS 4 3- structure is 2.04 ⁇ . Further, the average bond distance is obtained by synchrotron radiation XRD measurement and Rietveld analysis.
- the algyrodite-type crystal in the present embodiment preferably further contains at least one of O and F in addition to Li, P, S, and at least one of Cl and Br.
- O and F are preferable as elements contained in the free anion site, and F is more preferable.
- O it is preferable to include O as an element in which a part of S at the 16e site adjacent to P at the 4b site is substituted.
- the electronegativity is lower than the electronegativity ⁇ (S) of S, O, and the electronegativities ⁇ (Br) and ⁇ (Cl) of Br and Cl. It is preferred to include F that is also low.
- ⁇ (1/ ⁇ (S) ) ⁇ [S 2 ⁇ ]+(1/ ⁇ (O) ) ⁇ [O 2 ⁇ ]+(1/ ⁇ (Br) ) ⁇ [Br ⁇ ]+(1/ ⁇ ( Cl) ) ⁇ [Cl ⁇ ]+(1/ ⁇ (F) ) ⁇ [F ⁇ ] ⁇ is the ratio of free anion content and the electronegativity of each element. It is the sum of products with reciprocals. The lower the value of this anion parameter, the higher the electronegativity of the aldirodite-type crystal, the larger the gap between the upper end of the valence band and the lower end of the conductor. Oxidation reaction becomes difficult to occur.
- the value of the anion parameter may be 0.36 or less, preferably 0.35 or less, more preferably 0.34 or less. From the viewpoint of forming aldirodite-type crystals, the value of the anion parameter is preferably 0.30 or more, more preferably 0.32 or more.
- the crystal structure of the aldirodite type may be analyzed from the XRD pattern of a general-purpose device, but it is preferable to analyze from the synchrotron radiation XRD pattern from the viewpoint of precision of analysis.
- the arrangement of each element in the crystal structure can be specified by refining the crystal structure by the Rietveld method for the XRD pattern measured with synchrotron X-rays. Furthermore, the content of each element and their sum are obtained by composition analysis using ICP emission spectrometry, atomic absorption spectrometry, ion chromatography, etc. Based on the values, refinement of the crystal structure by the Rietveld method is performed. By doing so, the crystal composition can be obtained with higher accuracy.
- the ratio of the contents (at %) of the elements constituting the algyrodite-type crystal is 5 ⁇ 5 when the composition is represented by Li ⁇ PS ⁇ Ha ⁇ . Satisfying the relationships ⁇ 7, 3 ⁇ 6 and 0 ⁇ 2.5 is preferable because the crystal tends to be of the aldirodite type.
- Such an element ratio more preferably satisfies the relationships of 5.1 ⁇ 6.3, 3.5 ⁇ 5.3 and 0.7 ⁇ 2.0, and 5.2 ⁇ 6 .2, 3.7 ⁇ 5.2 and 0.8 ⁇ 1.9 are more preferably satisfied.
- ⁇ is preferably greater than 5, more preferably greater than 5.1, still more preferably greater than 5.2, preferably less than 7, more preferably less than 6.3, and even more preferably less than 6.2.
- ⁇ is preferably greater than 3, more preferably greater than 3.5, still more preferably greater than 3.7, preferably less than 6, more preferably less than 5.3, and even more preferably less than 5.2.
- ⁇ is preferably greater than 0, more preferably greater than 0.7, still more preferably greater than 0.8, preferably less than 2.5, more preferably less than 2.0, and even more preferably less than 1.9.
- the preferred crystal structure of the algyrodite-type crystal is a cubic crystal such as F-43m, but the rhombohedral crystal described above may also be used. Alternatively, triclinic crystals with lower symmetry may be present.
- the halogen element represented by Ha is at least one selected from the group consisting of F, Cl, Br, and I, but since the crystal tends to be aldirodite type, it contains at least one of Cl and Br, and contains Cl. Cl alone or a mixture of Cl and Br is more preferred.
- the content represented by (c1/c2) where c1 (at%) is the content of Cl and c2 (at%) is the content of Br in the aldirodite-type crystal is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more. Also, (c1/c2) is preferably 10 or less, more preferably 3 or less, and even more preferably 1.6 or less. When (c1/c2) satisfies the above range, the interaction between lithium ions and halide ions is weakened, and the lithium ion conductivity of the sulfide-based solid electrolyte tends to be good.
- ⁇ 1 is 0.1 or more. It is preferably 0.3 or more, still more preferably 0.5 or more, preferably 1.5 or less, more preferably 1.4 or less, and still more preferably 1.3 or less.
- ⁇ 2 is preferably 0.1 or more, more preferably 0.3 or more, still more preferably 0.5 or more, and preferably 1.9 or less, more preferably 1.6 or less, and still more preferably 1.4 or less.
- the abundance ratio of halide ions in the crystal is optimized, and stable aldirodite-type crystals are obtained while reducing the interaction between anions and lithium ions in the crystal. be done. This tends to improve the lithium ion conductivity of the sulfide-based solid electrolyte.
- the cycle characteristics of the lithium ion secondary battery are likely to be improved.
- ⁇ , ⁇ and ( ⁇ 1+ ⁇ 2) preferably satisfy the same relationships as those of ⁇ , ⁇ and ⁇ described above.
- the crystallite size of the crystals constituting the crystal phase is preferably smaller.
- the crystallite size is preferably 1000 nm or less, more preferably 500 nm or less, and even more preferably 250 nm or less.
- the lower limit of the crystallite size is not particularly limited, it is usually 5 nm or more.
- the crystallite size can be calculated by using the half width of the peak of the XRD pattern and the Scherrer equation. A more precise value for the crystallite size can be obtained by refining the crystal structure by the Rietveld method.
- the content of aldirodite-type crystals in all components constituting the sulfide-based solid electrolyte is preferably 50% by mass or more, more preferably 65% by mass or more, and 80% by mass or more. More preferred.
- the upper limit of the content is not particularly limited, and may be 100% by mass, but is generally 99% by mass or less.
- the ratio of aldirodite-type crystals can be calculated by adding an internal standard substance, measuring by XRD or neutron beam scattering, and comparing the peak intensity with that of the internal standard substance.
- the aldirodite-type crystal may contain two or more crystal structures.
- the content of aldirodite-type crystals is the content including elements other than S, Cl, and Br present at free anion sites, and other elements substituted with P at the 4b site and S at the 16e site.
- the content of each element and the total thereof can be determined by composition analysis using ICP emission analysis, atomic absorption spectroscopy, ion chromatography, or the like.
- the solid electrolyte may contain amorphous components that can be algyrodite-type, oxide anions, Li 3 PS 4 , Li 4 P 2 S 6 , Li 2 S, LiHa (Ha is an impurity crystal phase such as at least one halogen element selected from F, Cl, Br, and I).
- Impurity crystal phases such as Li 3 PS 4 , Li 4 P 2 S 6 , Li 2 S, and LiHa may be contained as long as they do not affect the lithium ion conductivity and battery characteristics. It may be 15% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, relative to the system solid electrolyte. If an impurity crystal phase is included, it is better to analyze the crystal structure by subtracting the impurity crystal phase, but if the content of the impurity crystal phase is small, it does not affect the analysis result much There is also
- the sulfide-based solid electrolyte preferably has a lithium ion conductivity of 1 mS/cm or more, more preferably 2 mS/cm or more, and even more preferably 4 mS/cm or more at 25° C. when pressure-molded at a pressure of 380 MPa. Higher is better. Lithium ion conductivity is determined from Nyquist plots obtained by AC impedance measurements.
- the sulfide-based solid electrolyte according to the present embodiment is used in a lithium ion secondary battery, a good SEI is formed without surface coating the positive electrode active material. A decrease in battery characteristics is suppressed.
- the initial characteristic represented by (1st cycle discharge capacity/1st cycle charge capacity) is preferably more than 0.60, more preferably 0.65 or more, and even more preferably 0.70 or more. , the higher the better.
- the capacity retention rate represented by (5th cycle discharge capacity/1st cycle discharge capacity) ⁇ 100 (%) is preferably more than 86%, more preferably 88% or more, and 90 % or more is more preferable, and the higher the more preferable.
- a sulfide-based solid electrolyte forms a solid electrolyte layer together with other components such as a binder as necessary when used in a lithium ion secondary battery. Conventionally known materials are used as the binder and other components.
- the content of the sulfide-based solid electrolyte is preferably 80% by mass or more, more preferably 90% by mass or more, relative to the entire solid electrolyte layer.
- the solid electrolyte layer can be formed by dispersing or dissolving the components constituting the solid electrolyte layer in a solvent to form a slurry, coating the slurry in a layer, that is, a sheet, drying, and optionally pressing. If necessary, heat may be applied to remove the binder.
- the thickness of the solid electrolyte layer can be easily adjusted by adjusting the coating amount of the slurry.
- the solid electrolyte layer may be formed by dry press-molding a powder of a sulfide-based solid electrolyte or the like on the surface of the positive electrode or the negative electrode.
- a solid electrolyte layer may be formed on another substrate and transferred onto the surface of the positive electrode, negative electrode, or the like.
- a sulfide-based solid electrolyte may be mixed with a positive electrode active material or a negative electrode active material and used as a positive electrode layer or a negative electrode layer.
- a positive electrode active material or negative electrode active material current collector, binder, conductive aid, etc. used in the positive electrode layer or negative electrode layer, conventionally known substances are used.
- LiCoO 2 , NMC, or the like the surface of which has been conventionally coated with LiNbO 3 or the like
- a positive electrode active material that operates at a higher potential than conventional ones, to which surface coating with LiNbO 3 or the like is difficult to apply is also preferable from the viewpoint that the effects of the present invention can be more enjoyed.
- positive electrode active materials generally called 5V class such as spinel-type crystal LiNi x Mn 2-x O 4 known as high-potential positive electrode active materials, are preferred.
- a sulfide-based solid electrolyte is preferably used in a lithium-ion secondary battery with an electromotive force of 4.3 V or more, as an indicator of a positive electrode active material that operates at a higher potential than before.
- a lithium ion secondary battery using a sulfide-based solid electrolyte includes the solid electrolyte layer, a positive electrode layer, and a negative electrode layer.
- Conventionally known materials can also be used for the material of the exterior body of the lithium ion secondary battery.
- the shape of the lithium ion secondary battery can also be a conventionally known one. can be selected as appropriate.
- the method for producing the sulfide-based solid electrolyte used in the lithium-ion secondary battery according to the present embodiment passes through a homogeneous intermediate compound before precipitating aldirodite-type crystals.
- a homogenous intermediate compound is not simply a mixture of a plurality of raw materials, but refers to a substance in which the raw materials react with each other and the structure becomes, for example, amorphous or melted to form a melt.
- the raw materials are mixed with a medialess pulverizer such as a mixer mill or pin mill, and then a media pulverizer such as a planetary ball mill, bead mill, or attritor (registered trademark) is used.
- a media pulverizer such as a planetary ball mill, bead mill, or attritor (registered trademark)
- a method of mechanically mixing with and causing a mechanochemical reaction can be mentioned.
- the raw materials are mixed with a mixer mill or pin mill and then dissolved, and the dissolved state can be called a homogeneous intermediate compound.
- the raw material may be once dissolved in an organic solvent or the like.
- the method for producing a sulfide-based solid electrolyte according to the present embodiment is not particularly limited as long as an aldirodite-type crystal is obtained through such a homogeneous intermediate compound.
- the following production method i and production method ii There are two methods.
- Step i-1 a step of mixing raw materials to obtain a raw material mixture
- Step i-2 A step of heating the raw material mixture to obtain a melt as an intermediate compound
- Step i-3 A step of cooling the melt to precipitate aldirodite-type crystals.
- Step ii-1 A step of mixing raw materials to obtain an amorphous intermediate compound
- Step ii-2 A step of heating and firing the intermediate compound to precipitate aldirodite-type crystals.
- the intermediate compound obtained in step ii-1 above is an amorphous intermediate compound in which no peak derived from the raw material is observed in powder XRD measurement.
- Step i-1 is a step of mixing raw materials to obtain a raw material mixture.
- Raw materials containing Li, P, S and Ha are used to obtain aldirodite type crystals.
- conventionally known materials for obtaining aldirodite type crystals containing Li, P, S and Ha can be used. Examples thereof include a mixture of a compound containing Li (lithium), a compound containing P (phosphorus), a compound containing S (sulfur), and a compound containing Ha (halogen).
- elements other than S, Cl, and Br present at free anion sites and raw materials that serve as sources of elements substituting for P at the 4b site and S at the 16e site are also mixed.
- Li-containing compounds examples include lithium sulfide (Li 2 S), lithium oxide (Li 2 O), lithium carbonate (Li 2 CO 3 ), lithium hydroxide (LiOH), and lithium sulfate (Li 2 SO 4 ). Lithium compounds and lithium metal simple substance etc. are mentioned.
- Examples of compounds containing P include phosphorus sulfides such as phosphorus trisulfide ( P2S3 ) and phosphorus pentasulfide ( P2S5 ), lithium phosphates ( LiPO3 , Li4P2O7 , Li 3 PO 4 ), sodium phosphate (NaPO 3 , Na 4 P 2 O 7 , Na 3 PO 4 ) and other phosphorus compounds and elemental phosphorus.
- Compounds containing S include the above lithium sulfide (Li 2 S), the above phosphorus sulfide (P 2 S 3 , P 2 S 5 ), hydrogen sulfide (H 2 S), and the like, and elemental sulfur can also be used.
- examples of compounds containing Cl include lithium chloride (LiCl), phosphorus trichloride (PCl 3 ), phosphorus pentachloride (PCl 5 ), phosphorus tetrachloride (P 2 Cl 4 ), phosphoryl chloride (POCl 3 ), sulfur dichloride (SCl 2 ), disulfur dichloride (S 2 Cl 2 ), sodium chloride (NaCl), boron trichloride (BCl 3 ) and the like.
- LiCl lithium chloride
- PCl 3 phosphorus trichloride
- PCl 5 phosphorus pentachloride
- P 2 Cl 4 phosphorus tetrachloride
- POCl 3 phosphoryl chloride
- SCl 2 sulfur dichloride
- S 2 Cl 2 disulfur dichloride
- NaCl sodium chloride
- BCl 3 boron trichloride
- Br (bromine)-containing compounds include, for example, lithium bromide (LiBr), phosphorus tribromide (PBr 3 ), phosphoryl chloride (POBr 3 ), disulfur dibromide ( S 2 Br 2 ), sodium bromide (NaBr), boron tribromide (BBr 3 ), and the like.
- LiBr lithium bromide
- PBr 3 phosphorus tribromide
- POBr 3 phosphoryl chloride
- S 2 Br 2 sodium bromide
- NaBr sodium bromide
- BBr 3 boron tribromide
- Elements other than S, Cl, and Br present at free anion sites and raw materials that serve as sources of elements substituting P at the 4b site and S at the 16e site include, for example, silicon oxide (SiO 2 ), tin oxide (SnO ), silicon disulfide (SiS 2 ), tin disulfide (SnS 2 ), germanium disulfide (GeS 2 ), vanadium (III) sulfide (V 2 S 3 ), sulfides such as zirconium disulfide (ZrS 2 ), Alkali metal oxides such as selenium (Se), lithium oxide (Li 2 O), lithium hydroxide (LiOH) and sodium oxide (Na 2 O); Fluoride etc. are mentioned.
- the raw materials used may be extremely unstable in the atmosphere and may react with water to decompose, generating hydrogen sulfide gas or oxidizing. In that case, it is preferable to mix in an inert atmosphere. Mixing may be carried out in the atmosphere unless raw materials that are unstable in the atmosphere are used.
- Mixing of raw materials can be performed by, for example, mixer mills, pin mills, powder stirrers, and medialess mixing such as airflow mixing.
- the raw materials may be partially amorphized by mixing prior to step i-2.
- Step i-2 is a step of heating the obtained raw material mixture to obtain a melt as an intermediate compound.
- a molten state means that no peak derived from the raw material is observed in high-temperature X-ray diffraction measurement.
- the aldirodite type crystal has, for example, a Li--P--S--Ha composition
- the melt mixes well, which means that it is a melt of a homogeneous compound different from the raw material.
- a simple confirmation method of whether or not the raw material is in a molten state it can be confirmed by observing the state of the raw material in the furnace. If no unmelted matter is observed, it is completely dissolved and can be said to be an intermediate compound.
- the high-temperature X-ray diffraction measurement is performed after setting the measurement temperature, holding time, atmosphere, etc. so that the heating conditions are the same as those for obtaining the melt.
- the high-temperature X-ray diffraction measurement while changing the measurement temperature, it is possible to follow changes in the crystal state such as phase transitions and estimate the heating temperature at which the intermediate compound can be obtained.
- the heating conditions for obtaining a melt differ depending on the raw materials used and the composition of the raw material mixture.
- the heating temperature may be at least the heating temperature at which a homogeneous amorphous intermediate compound as described above can be obtained.
- the heating temperature is preferably 950° C. or lower, more preferably 900° C. or lower, and even more preferably 850° C. or lower, from the viewpoint of suppressing composition deviation due to volatilization of components.
- the temperature may be changed stepwise within the above temperature range.
- the heating temperature can be lowered for a composition having a higher halogen content represented by [Ha]/[P] (atomic ratio).
- the heating time may be longer than the time required to obtain a homogeneous amorphous intermediate compound as described above, and although it varies depending on the scale, for example, it is preferably 2 minutes or longer, more preferably 5 minutes or longer, and 10 minutes. minutes or more is more preferable. Moreover, from the viewpoint of productivity, the heating time is preferably 360 minutes or less, more preferably 180 minutes or less, and even more preferably 120 minutes or less.
- the melt that becomes an amorphous intermediate compound can be made more homogeneous. Also, the more homogeneous the mixing in step i-1, the shorter the heating time in step i-2.
- the specific method for heating and melting is not particularly limited, but an example is a method of putting raw materials in a heat-resistant container and heating them in a heating furnace.
- heat-resistant containers include, but are not limited to, heat-resistant containers made of carbon, heat-resistant containers containing oxides such as quartz, quartz glass, borosilicate glass, aluminosilicate glass, alumina, zirconia, and mullite, and nitriding.
- Heat-resistant containers containing nitrides such as silicon and boron nitride
- heat-resistant containers containing carbides such as silicon carbide, and the like can be mentioned.
- these heat-resistant containers may be bulks formed of the above materials, or may be containers formed with a layer of carbon, oxide, nitride, carbide, or the like.
- the raw materials are preferably mixed in an inert atmosphere, and the melt is also preferably obtained by heating in the inert atmosphere.
- the inert atmosphere includes, for example, an Ar atmosphere, a nitrogen atmosphere, etc. From the viewpoint of production costs, a nitrogen atmosphere is more preferable.
- the melt may also be obtained by heating in a hydrogen sulfide gas atmosphere, a sulfur gas atmosphere, a sulfur dioxide gas atmosphere, a mixed gas atmosphere of these gases, or the like. Also, the raw material may be heated in a vacuum sealed state.
- the amorphous intermediate compound should not show peaks derived from the raw material in high-temperature X-ray diffraction measurement, but from the viewpoint of homogeneity, the melt is preferably a homogeneous melt without phase separation. .
- the melt mixes well without phase separation, but the presence or absence of phase separation can be visually confirmed. Alternatively, the presence or absence of phase separation may be confirmed by determining whether or not light is optically transmitted without being scattered.
- Step i-3 is a step of cooling the melt, which is an amorphous intermediate compound, to precipitate aldirodite-type crystals.
- the aldirodite-type crystals may contain impurities derived from raw materials or the like as long as they do not affect the lithium ion conductivity and elastic modulus of the solid electrolyte.
- the cooling conditions for precipitating crystals vary depending on the composition and the target crystallization rate.
- the cooling rate is not particularly limited as long as algyrodite-type crystals precipitate, but from the viewpoint of productivity, it is preferably 5°C/min or more, more preferably 10°C/min or more, and even more preferably 30°C/min or more. From the viewpoint of increasing the crystallization rate, the cooling rate is preferably 2000° C./min or less, more preferably 1000° C./min or less, and even more preferably 300° C./min or less.
- the residence time is more preferable to extend the residence time at 200 to 450° C. during cooling to carry out crystal growth or reconstruction of the crystal structure. Further, after once cooling to room temperature, heat treatment may be additionally performed at a temperature of 200 to 550°C.
- the atmosphere during cooling is preferably an inert atmosphere, similar to the mixing of raw materials and heating for obtaining a melt. Moreover, when the heating for obtaining the melt is performed in a vacuum-sealed state, the cooling may also be performed in the vacuum-sealed state.
- one or more elements different therefrom are added to the free anion site. be made to exist. Also, part of P at the 4b site and part of S at the 16e site adjacent to P at the 4b site can be replaced with other elements. Furthermore, the value of the anion parameter can be 0.36 or less. As a result, even if the surface of the positive electrode active material is not treated with a coating agent, it is possible to suppress deterioration of battery characteristics when charging and discharging are repeated.
- Preferred embodiments of the obtained solid electrolyte are the same as the preferred embodiments described in ⁇ Sulfide-Based Solid Electrolyte> above.
- Step ii-1 is a step of mixing raw materials to obtain a homogeneous amorphous intermediate compound.
- Raw materials containing Li, P, S and Ha are used in order to obtain algyrodite-type crystals, and these can be used under the same conditions as those described in step i-1 of production method i.
- elements other than S, Cl, and Br present at free anion sites, and raw materials that serve as sources of elements substituting for P at the 4b site and S at the 16e site are mixed, but these are also mixed in the process i of the production method i. -1 can be used under the same conditions.
- An amorphous intermediate compound can be obtained by adopting much stricter conditions than before in mixing these raw materials.
- Amorphous (amorphous) intermediate compound means that no peak derived from the raw material is observed in X-ray diffraction measurement, which means that it is a homogeneous compound different from the mixture of raw materials do.
- a rotating ball mill that imparts rotation motion to the container a vibrating ball mill that imparts vibration motion, a planetary ball mill that imparts revolution and rotation motion, a bead mill, and an attritor (registered trademark). etc., and all of them can be applied if the conditions for obtaining an amorphous intermediate compound are adopted.
- planetary ball mills and bead mills with higher mixing power and crushing power are preferable.
- the rotation speed varies depending on the type of ball mill used and other conditions, but is preferably 200 rpm or more, more preferably 300 rpm or more, and even more preferably 400 rpm or more.
- the upper limit of the rotation speed is not particularly limited, it is preferably 1000 rpm or less, more preferably 800 rpm or less, from the viewpoint of mechanical strength.
- multiple rotation speeds may be combined, such as initially mixing at a low rotation speed for a period of time and then increasing the rotation speed to a high rotation speed for a period of time.
- the mixing time varies depending on the type of ball mill used and other conditions, but is preferably 0.5 hours or longer, more preferably 2 hours or longer, and even more preferably 4 hours or longer.
- the upper limit of the mixing time is not particularly limited, it is preferably 50 hours or less, more preferably 20 hours or less, from the viewpoint of productivity.
- the particle size of the balls varies depending on the type of ball mill used and other conditions, but is preferably 20 mm or less, more preferably 10 mm or less, and even more preferably 5 mm or less.
- the lower limit of the particle diameter of the balls is preferably 0.3 mm or more, more preferably 1 mm or more, from the viewpoint of ease of handling. Also, two or more types of balls having different particle diameters may be used in combination.
- the amount of balls used varies depending on the type of ball mill used and other conditions, but from the viewpoint of mixing power and crushing power, the weight of the balls is preferably 20% or more, and preferably 50% or more, of the total weight of the raw materials. It is more preferably 100% or more, more preferably 1000% or less, more preferably 500% or less, and even more preferably 400% or less.
- the ball mill may be dry mixing or wet mixing using a dispersion medium, but dry mixing is preferable from the viewpoint of efficiently transmitting energy.
- the mixed powder is made amorphous to obtain a homogeneous amorphous intermediate compound.
- the obtained amorphous intermediate compound means that no XRD peak derived from the raw material is observed, but in the Raman spectrum, the peak at the position of the raw material completely disappears and a peak appears at another position. It can be considered that a more homogeneous intermediate was obtained.
- the intermediate compound preferably has a particle size of 30 nm or more from the viewpoint of distinguishing between a mixture of raw materials having very small particle sizes and an amorphous intermediate compound. From the viewpoint of powder handling, the particle size of the intermediate compound is preferably 100 nm or more, more preferably 1 ⁇ m or more.
- the particle size of the intermediate compound is preferably 50 ⁇ m or less, more preferably 10 ⁇ m or less, and even more preferably 5 ⁇ m or less, in order to increase the surface area of the powder and efficiently proceed with the subsequent reaction.
- the particle size of the intermediate compound in the present specification is the primary particle size obtained from the image obtained by scanning electron microscope (SEM) observation. An SEM measurement without exposure to air is carried out, observed at a magnification of 2000 and an acceleration voltage of 2 kV, the particle diameters of 20 particles reflected in a suitable field of view are measured, and the average value is determined as the primary particle diameter.
- Step ii-2 is a step of heating and sintering the amorphous intermediate compound obtained in step ii-1 to precipitate aldirodite-type crystals.
- impurities such as those derived from raw materials may be contained in the aldirodite-type crystal as long as they do not affect the lithium ion conductivity and elastic modulus of the solid electrolyte.
- Heating is preferably performed, for example, under an inert gas atmosphere, under a hydrogen sulfide gas atmosphere, under a sulfur gas atmosphere, or under a vacuum sealed tube.
- the heating temperature is preferably 350.degree. C. or higher, more preferably 400.degree.
- the heating temperature is preferably less than 600°C, more preferably 575°C or less.
- the heating time is preferably 1 hour or longer, more preferably 2 hours or longer, and even more preferably 4 hours or longer. Also, the heating time is preferably 100 hours or less, more preferably 50 hours or less, and even more preferably 24 hours or less.
- Example 1 Lithium sulfide powder (manufactured by Sigma, purity 99.98%) and diphosphorus pentasulfide powder (manufactured by Sigma, purity 99%) were prepared in a dry nitrogen atmosphere so as to achieve the composition ratio shown in Table 1. ), lithium chloride powder (manufactured by Sigma, purity 99.99%), lithium bromide powder (manufactured by Sigma, purity 99.995%) and lithium oxide powder (manufactured by Sigma, purity 97%) were weighed and Using a mixer (X-TREME (MX1100XTM) manufactured by WARING) in an atmosphere, the materials were mixed in High mode for 1 minute to obtain a raw material mixture.
- X-TREME MX1100XTM
- the obtained raw material mixture is placed in a heat-resistant container, heated at 300° C. for 1 hour in an atmosphere with a dew point of ⁇ 60° C., and then heated at 700° C. for 0.5 hour to form a melt. Obtained.
- a desired sulfide-based solid electrolyte containing aldirodite-type crystals was obtained.
- Example 2 to 7, 9 Sulfide-based solid electrolytes containing aldirodite-type crystals of Examples 2 to 7 and 9 were obtained in the same manner as in Example 1, except that the composition ratio was changed to that described in "Composition" in Table 1.
- F in which F is included in the composition, in addition to the lithium sulfide powder, diphosphorus pentasulfide powder, lithium chloride powder, lithium bromide powder, and lithium oxide powder, lithium fluoride powder (manufactured by Sigma, purity 99.98%) was weighed and used.
- the result of XRD measurement (SmartLab, manufactured by Rigaku Co., Ltd.) under the same conditions as in Example 1 is shown in the lower part of FIG. It was confirmed that
- Example 8 A sulfide-based solid electrolyte containing aldirodite-type crystals of Example 8 was obtained in the same manner as in Example 1, except that the composition ratio was changed to that shown in Table 1, "Composition”.
- the obtained sulfide-based solid electrolyte was subjected to XRD measurement (manufactured by Rigaku Corporation, SmartLab) under the following conditions.
- the XRD pattern obtained is shown in FIG. A peak was seen in . From the peak position, it was found to be a rhombohedral single-phase aldirodite type crystal.
- Example 10 Lithium sulfide powder (manufactured by Sigma, purity 99.98%) and diphosphorus pentasulfide powder (manufactured by Sigma, purity 99%) were prepared in a dry nitrogen atmosphere so as to achieve the composition ratio shown in Table 1. ) and lithium chloride powder (manufactured by Sigma, purity 99.99%) are weighed, mixed in a mixer in the same atmosphere, and then further mixed using a planetary ball mill (LP-M2, manufactured by Ito Seisakusho). A raw material mixture was obtained. Mixing by a planetary ball mill was performed at 400 rpm for 20 hours using balls with a particle size of 10 mm.
- Lithium sulfide powder manufactured by Sigma, purity 99.98%) and diphosphorus pentasulfide powder (manufactured by Sigma, purity 99%) were prepared in a dry nitrogen atmosphere so as to achieve the composition ratio shown in Table 2.
- lithium chloride powder manufactured by Sigma, purity 99.99%
- lithium bromide powder manufactured by Sigma, purity 99.995%
- lithium oxide powder manufactured by Sigma, purity 97%) were weighed and Using a mixer (X-TREME (MX1100XTM) manufactured by WARING) in an atmosphere, the materials were mixed in High mode for 1 minute to obtain a raw material mixture.
- the obtained raw material mixture is placed in a heat-resistant container, heated at 300° C. for 1 hour in an atmosphere with a dew point of ⁇ 60° C., and then heated at 700° C. for 0.5 hour to form a melt. Obtained. As it was, it was cooled to room temperature at a rate of 300°C/min. In addition to the dew point of ⁇ 60° C., the atmosphere was an N 2 atmosphere with an oxygen concentration of 100 ppm or less. After that, mixing by a planetary ball mill is performed at 400 rpm for 20 hours using balls with a particle diameter of 10 mm, and the obtained mixture is vacuum-sealed in a heat-resistant container, sealed, and heated and baked at 450° C. for 5 hours. Thus, a sulfide-based solid electrolyte containing aldirodite-type crystals was obtained.
- Example 13 Sulfide-based solid electrolytes containing aldirodite-type crystals of Examples 13 and 14 were obtained in the same manner as in Example 12, except that the composition ratio was changed to that described in "Composition" in Table 2.
- Example 13 containing Si in the composition in addition to the lithium sulfide powder, diphosphorus pentasulfide powder, lithium chloride powder, lithium bromide powder and lithium oxide powder, silicon disulfide (manufactured by American Elements, purity 99.9%) was weighed and used.
- tin disulfide manufactured by Kojundo Chemical Laboratory Co., Ltd., Purity 3 Nup
- RIETAN-FP software was used to refine the crystal structure by the Rietveld method.
- the structure with the lowest Rwp value was determined as the crystal structure of each example.
- the Rwp value is a reliability factor Rwp (R-weighted pattern) that is generally used as a standard for the entire analysis range in the fitting of structure refinement by Rietveld analysis. A lower Rwp value is better, and in this analysis, the lowest Rwp values were all less than 10%.
- Rwp reliability factor
- anion parameter From the ratio of free anions determined from the results of structural analysis, ⁇ (1/ ⁇ (S) ) ⁇ [S 2 ⁇ ]+(1/ ⁇ (O) ) ⁇ [O 2 ⁇ ]+(1/ ⁇ (Br) ) ⁇ [Br ⁇ ]+(1/ ⁇ (Cl) ) ⁇ [Cl ⁇ ]+(1/ ⁇ (F) ) ⁇ [F ⁇ ] ⁇ was calculated.
- the results are shown in "Anion parameters" in Tables 1 and 2, respectively.
- Li ion conductivity A sulfide-based solid electrolyte was pulverized in a mortar, coarse particles were removed by a mesh pass with an opening of 100 ⁇ m, and then 100 mg was measured. Then, the lithium ion conductivity of the measurement sample was measured using an AC impedance measuring device (manufactured by Bio-Logic Sciences Instruments, potentiostat/galvanostat VSP) while press-molding an area with a diameter of 10 mm at 380 MPa. Measurement conditions were measurement frequency: 100 Hz to 1 MHz, measurement voltage: 100 mV, and measurement temperature: 25°C. The results are shown in "Li ion conductivity (mS/cm)" in Tables 1 and 2, respectively.
- the sulfide-based solid electrolyte was dry-milled in a dry nitrogen atmosphere with a planetary ball mill (manufactured by Ito Seisakusho, Model No. LP-M2) using alumina balls with a particle size of 2 mm. Then, it was passed through a sieve with an opening of 43 ⁇ m to obtain a sulfide-based solid electrolyte powder having a particle size distribution with an average particle size D50 of 3 ⁇ m.
- the average particle diameter D50 was determined from the volume-based particle size distribution chart obtained by measuring the particle size distribution using a Microtrac laser diffraction particle size distribution analyzer MT3300EXII.
- layered rock salt type NMC811 powder (purchased from MTI Corporation, volume average particle size: 11.75 ⁇ m) was used, 34 parts by mass of the sulfide-based solid electrolyte powder prepared above, and 60 parts by mass of the positive electrode active material. and 6 parts by mass of a conductive aid (acetylene black, manufactured by Denka Co., Ltd., HS100) to prepare a positive electrode mixture.
- 80 mg of the sulfide-based solid electrolyte powder prepared above was put into a plastic cylinder with a diameter of 10 mm and pressure-molded to form a solid electrolyte layer.
- the charge/discharge test is a constant current charge/discharge test under the conditions of measurement temperature: 25°C, charge current density: 0.05C, discharge current density: 0.05C, charge/discharge potential range: 1.9 to 3.7V. carried out.
- the charge-discharge curves of Example 1 are shown in FIG. From the results of the charge/discharge test, the initial characteristics and the capacity retention rate (%) represented by the following formulas were obtained, respectively, and the battery characteristics of the all-solid-state lithium ion secondary battery were evaluated.
- Initial characteristics (1st cycle discharge capacity/1st cycle charge capacity)
- Capacity retention rate (%) (discharge capacity at 5th cycle/discharge capacity at 1st cycle) x 100
- Example 1 In Examples 1 and 4 to 8, O exists as an element other than S and at least one of Cl and Br at the free anion site of the aldirodite-type crystal. Further, Example 9 contains F as another element, and Examples 2 and 3 contain both O and F as other elements. Moreover, all of the anion parameters are 0.36 or less. All of them gave good battery evaluations, and resulted in suppression of deterioration in battery characteristics when charging and discharging were repeated. On the other hand, in Examples 10 and 11, the other elements were not present, and the deterioration of the battery characteristics was large when charging and discharging were repeated.
- Example 12 in which O is present as another element, the effect of the present invention is exhibited.
- the anion parameter values were the same, the result was that the deterioration of the battery characteristics when charging and discharging were repeated could be suppressed more remarkably.
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Abstract
Description
従来、リチウムイオン二次電池においては液体の電解質が使用されてきたが、液漏れや発火等が懸念され、安全設計のためにケースを大型化する必要があった。また、リチウムイオン二次電池は電池寿命の短さ、動作温度範囲の狭さについても改善が望まれていた。
[1] リチウムイオン二次電池に用いられる硫化物系固体電解質であって、Li、P、S及びHaを含むアルジロダイト型の結晶を含み、前記Haは、Cl及びBrの少なくとも一方を含む、F、Cl、Br、及びIからなる群より選ばれる少なくとも1種の元素であり、前記アルジロダイト型の結晶は、(A)遊離のアニオンサイトに、Sと、Cl及びBrの少なくとも一方と、それらとは異なる1種又は2種以上の元素と、が存在すること、及び、(B)4bサイトのPの一部と、前記4bサイトのPと隣り合う16eサイトのSの一部とが、それぞれ他の元素に置換されていること、の少なくとも一方を満たし、前記アルジロダイト型の結晶は、遊離しているアニオンの含有量[S2-]、[O2-]、[Br-]、[Cl-]及び[F-]、並びに、それらの電気陰性度χ(S)、χ(O)、χ(Br)、χ(Cl)及びχ(F)が、
{(1/χ(S))×[S2-]+(1/χ(O))×[O2-]+(1/χ(Br))×[Br-]+(1/χ(Cl))×[Cl-]+(1/χ(F))×[F-]}≦0.36、かつ
[S2-]+[O2-]+[Br-]+[Cl-]+[F-]=1の関係を満たす、硫化物系固体電解質。
[2] 前記アルジロダイト型の結晶が、O及びFの少なくとも一方をさらに含む、前記[1]に記載の硫化物系固体電解質。
[3] 前記遊離しているアニオンの含有量[S2-]、[O2-]、[Br-]、[Cl-]及び[F-]、並びに、それらの電気陰性度χ(S)、χ(O)、χ(Br)、χ(Cl)及びχ(F)が、
{(1/χ(S))×[S2-]+(1/χ(O))×[O2-]+(1/χ(Br))×[Br-]+(1/χ(Cl))×[Cl-]+(1/χ(F))×[F-]}≦0.34
の関係を満たす、前記[1]又は[2]に記載の硫化物系固体電解質。
[4] 前記アルジロダイト型の結晶は、前記(B)を満たし、前記4bサイトと、それと隣り合う前記16eサイトの平均結合距離が2.07Å以上である、前記[1]~[3]のいずれか1に記載の硫化物系固体電解質。
[5] 前記アルジロダイト型の結晶は、前記(B)を満たし、前記4bサイトのPの一部と置換される元素Mが、PS4 3-よりもイオン半径が大きなMS4四面体構造を形成する、前記[1]~[4]のいずれか1に記載の硫化物系固体電解質。
[6] 前記MS4四面体構造における前記元素MがSi及びSnの少なくとも一方である、前記[5]に記載の硫化物系固体電解質。
[7] 前記アルジロダイト型の結晶は、前記(A)を満たし、前記遊離しているアニオンの含有量が、0<{[Br-]/([F-]+[Cl-]+[Br-])}<2の関係を満たす、前記[1]~[6]のいずれか1に記載の硫化物系固体電解質。
[8] 前記リチウムイオン二次電池の起電力が4.3V以上である、前記[1]~[7]のいずれか1に記載の硫化物系固体電解質。
本実施形態に係る硫化物系固体電解質(以下、単に「固体電解質」と称することがある。)はリチウムイオン二次電池に用いられ、Li、P、S及びHaを含むアルジロダイト型の結晶を含む。Haとは、Cl及びBrの少なくとも一方を含む、F、Cl、Br、及びIからなる群より選ばれる少なくとも1種の元素である。
(A)遊離のアニオンサイトに、Sと、Cl及びBrの少なくとも一方と、それらとは異なる1種又は2種以上の元素と、が存在する。
(B)4bサイトのPの一部と、前記4bサイトのPと隣り合う16eサイトのSの一部とが、それぞれ他の元素に置換されている。
{(1/χ(S))×[S2-]+(1/χ(O))×[O2-]+(1/χ(Br))×[Br-]+(1/χ(Cl))×[Cl-]+(1/χ(F))×[F-]}≦0.36、かつ
[S2-]+[O2-]+[Br-]+[Cl-]+[F-]=1
以後、{(1/χ(S))×[S2-]+(1/χ(O))×[O2-]+(1/χ(Br))×[Br-]+(1/χ(Cl))×[Cl-]+(1/χ(F))×[F-]}を「アニオンパラメータ」と称することがある。
上記(A)の遊離のアニオンサイトとは、カチオンと共有結合していないアニオンのことを指し、アルジロダイト型の結晶が立方晶(Cubic)である場合には、4aサイトと4dサイトが該当する。また、詳細は後述するが、アルジロダイト型の結晶が菱面体晶(Rhombohedral)である場合には、1aサイトと3bサイトが遊離のアニオンサイトに該当する。
このような置換が行われると、アニオンパラメータは小さくなり、正極活物質の表面をLiNbO3等でコーティングしなくても電池特性の低下を抑制できるようになる。
表面がコーティングされていない正極活物質を用いたリチウムイオン二次電池の充放電を行うと、正極活物質と硫化物系固体電解質の界面では、成分が相互に拡散される。その結果、硫化物系固体電解質側では酸化反応、厳密には正極活物質の酸素と固体電解質の硫化物の反応等が起こる。酸化反応が生じる原因の一つは、特にS2-のような、遊離しているアニオン、すなわち、他の元素と共有結合していない不安定なイオンである可能性が考えられる。その遊離したアニオンを、可能な限り、電気陰性度が高い元素で構成することで、価電子帯の上端と伝導帯の下端とのギャップが大きくなり、高電位な状態で酸化反応が起こりにくくなること、そしてそれに伴い、正極活物質と硫化物系固体電解質の界面に良好なSEI(Solid Electrolyte Interface)が形成されることにより、電池特性の低下を抑制できるようになるのではないかと考えている。
上記(B)の4bサイトのPの一部と置換される他の元素Mとは、周期表の第2~14族の金属元素及び半金属元素からなる群より選ばれる少なくとも1種の元素が好ましく、PS4 3-よりもイオン半径が大きなMS4四面体構造を形成する元素がより好ましい。
イオン半径が大きなMS4四面体構造を形成する元素Mとしては、Si、Sn、Al、V、Ti、Zr、Sb、Ge等が挙げられ、中でも、価数が高くPと置き換え易い点から、Si、Sn、V、Ge、Zrがさらに好ましい。
PS4 3-構造とイオン半径が異なるMS4四面体構造が結晶構造内に入ることで、アルジロダイト型の結晶中の電荷分布がより均質なものとなる。その結果、特にS2-のような、他の元素と共有結合していない不安定なアニオンが安定化し、正極活物質と硫化物系固体電解質の界面に良好なSEIが形成されて、電池特性の低下を抑制できるようになるのではないかと考えている。
なお、PS4 3-構造における4bサイトと、それと隣り合う16eサイトの平均結合距離は2.04Åである。また、上記平均結合距離は、放射光XRD測定とリートベルト解析により求められる。
これは、上記(A)の観点からは、O、Fはいずれも、遊離のアニオンサイトに含まれる元素として好ましく、Fがより好ましい。
また、上記(B)の観点からは、4bサイトのPと隣り合う16eサイトのSの一部が置換されている元素として、Oを含むことが好ましい。
さらに、アニオンパラメータを小さくする観点からは、電気陰性度がSの電気陰性度χ(S)よりも低い値であるOや、BrやClの電気陰性度χ(Br)、χ(Cl)よりも低い値であるFを含むことが好ましい。
このアニオンパラメータの値が低いほど、アルジロダイト型の結晶が電気陰性度が高い元素で構成されていることとなり、価電子帯の上端と伝導体の下端とのギャップが大きくなり、高電位な状態で酸化反応が起こりにくくなる。
アニオンパラメータにおける各元素の電気陰性度は、χ(S)=2.5、χ(O)=3.5、χ(Br)=2.8、χ(Cl)=3.0、χ(F)=4.0である。
結晶構造中の各元素の配置は、放射光X線で測定したXRDパターンについてリートベルト法により結晶構造の精密化を行うことで、特定できる。
さらに、各元素の含有量やそれらの合計は、ICP発光分析、原子吸光法、イオンクロマトグラフ法などを用いた組成分析により求められ、その値を基にリートベルト法による結晶構造の精密化を行うと、結晶組成をより高精度に求められる。
すなわち、αについて、5超が好ましく、5.1超がより好ましく、5.2超がさらに好ましく、また、7未満が好ましく、6.3未満がより好ましく、6.2未満がさらに好ましい。
βについて、3超が好ましく、3.5超がより好ましく、3.7超がさらに好ましく、また、6未満が好ましく、5.3未満がより好ましく、5.2未満がさらに好ましい。
γについて、0超が好ましく、0.7超がより好ましく、0.8超がさらに好ましく、また、2.5未満が好ましく、2.0未満がより好ましく、1.9未満がさらに好ましい。
ここでα、β及び(γ1+γ2)は、上述のα、β及びγと同様の関係をそれぞれ満たすことが好ましい。
結晶子サイズは、XRDパターンのピークの半値幅とシェラーの式(Scherrer equation)を用いることにより算出できる。また、結晶子サイズは、リートベルト法により結晶構造の精密化により、更に精密な値を求められる。
アルジロダイト型の結晶の割合は、内部標準物質を含有させて、XRDや中性子線散乱により測定後、内部標準物質とのピーク強度を比較することにより算出が可能である。アルジロダイト型の結晶は、2種以上の結晶構造を含んでいてもよい。
アルジロダイト型の結晶の含有量とは、遊離のアニオンサイトに存在するS、Cl、Br以外の元素や、4bサイトのPや16eサイトのSと置換された他の元素をも含む含有量である。
また、各元素の含有量やそれらの合計は、ICP発光分析、原子吸光法、イオンクロマトグラフ法などを用いた組成分析により求められる。
Li3PS4、Li4P2S6、Li2S、LiHa等の不純物結晶相はリチウムイオン伝導率や電池特性に影響を与えない程度であれば、含んでいてもよく、例えば、硫化物系固体電解質に対して15質量%以下であればよく、10質量%以下が好ましく、5質量%以下がより好ましい。不純物結晶相が含まれる場合は、かかる不純物結晶相を差し引いた形で結晶構造解析を行った方が良いが、不純物結晶相の含有量が少量である場合はあまり解析結果に影響を与えない場合もある。
本実施形態に係る硫化物系固体電解質は、リチウムイオン二次電池に用いられるにあたり、正極活物質に対する表面コーティングを行わなくても、良好なSEIが形成されるため、充放電を繰り返した際の電池特性の低下が抑制される。
充放電試験において、(1サイクル目の放電容量/1サイクル目の充電容量)で表される初期特性は、0.60超が好ましく、0.65以上がより好ましく、0.70以上がさらに好ましく、高いほど好ましい。
また、充放電試験において、(5サイクル目の放電容量/1サイクル目の放電容量)×100(%)で表される容量維持率は、86%超が好ましく、88%以上がより好ましく、90%以上がさらに好ましく、高いほど好ましい。
固体電解質層全体に対して、硫化物系固体電解質の含有量は80質量%以上が好ましく、90質量%以上がより好ましい。
また、LiNbO3等による表面コーティングを適用しづらい、従来よりも高電位で作動する正極活物質も、本発明の奏する効果をより享受できる点から好ましい。具体的には、高電位正極活物質として知られるスピネル型結晶LiNixMn2-xO4等、一般に5V級と呼ばれる正極活物質が好ましい。
従来よりも高電位で作動する正極活物質の指標として、硫化物系固体電解質は、起電力が4.3V以上となるリチウムイオン二次電池に用いられることが好ましい。
リチウムイオン二次電池の外装体の材料も、従来公知の物を使用できる。リチウムイオン二次電池の形状も従来公知の物を使用できるが、例えば、コイン型、シート状(フィルム状)、折り畳み状、巻回型有底円筒型、ボタン型等が挙げられ、用途に応じて適宜選択できる。
本実施形態に係るリチウムイオン二次電池に用いられる硫化物系固体電解質の製造方法は、アルジロダイト型の結晶を析出する前に、均質な中間体化合物を経る。均質な中間体化合物とは、単に複数の原材料の混合物ではなく、原材料同士が反応して、構造が、例えばアモルファスになったり、溶けて融液になったものを指す。
工程i-1:原材料を混合して原料混合物を得る工程、
工程i-2:上記原料混合物を加熱して中間体化合物としての溶融物を得る工程、及び
工程i-3:上記溶融物を冷却し、アルジロダイト型の結晶を析出する工程、
を含む。
工程ii-1:原材料を混合してアモルファスな中間体化合物を得る工程、及び
工程ii-2:上記中間体化合物を加熱焼成してアルジロダイト型の結晶を析出する工程、
を含む。
上記工程ii-1で得られる中間体化合物は、粉末XRD測定において上記原材料に由来するピークが観測されない、アモルファスな中間体化合物である。
工程i-1は、原材料を混合して原料混合物を得る工程である。
アルジロダイト型の結晶を得るために、Li、P、S及びHaを含む原材料を用いる。これらは、Li、P、S及びHaを含むアルジロダイト型の結晶を得る材料として従来公知の物を使用できる。例えば、Li(リチウム)を含有する化合物と、P(リン)を含有する化合物と、S(硫黄)を含有する化合物と、Ha(ハロゲン)を含有する化合物との混合物が挙げられる。
また、遊離のアニオンサイトに存在するS、Cl、Br以外の元素や、4bサイトのPや16eサイトのSと置換する元素の源となる原材料も混合する。
Sを含有する化合物としては、上記硫化リチウム(Li2S)や上記硫化リン(P2S3、P2S5)や硫化水素(H2S)等が挙げられ、硫黄単体も使用できる。
Haを含有する化合物のうち、Cl(塩素)を含有する化合物としては、例えば、塩化リチウム(LiCl)、三塩化リン(PCl3)、五塩化リン(PCl5)、四塩化二リン(P2Cl4)、塩化ホスホリル(POCl3)、二塩化硫黄(SCl2)、二塩化二硫黄(S2Cl2)、塩化ナトリウム(NaCl)、三塩化ホウ素(BCl3)等が挙げられる。
Haを含有する化合物のうち、Br(臭素)を含有する化合物としては、例えば、臭化リチウム(LiBr)、三臭化リン(PBr3)、塩化ホスホリル(POBr3)、二臭化二硫黄(S2Br2)、臭化ナトリウム(NaBr)、三臭化ホウ素(BBr3)等が挙げられる。
中でも、硫化リチウムと、硫化リンと、塩化リチウム及び臭化リチウムの少なくとも一方と、の組み合わせが好ましい。
溶融状態とは、高温X線回折測定において、原材料に由来するピークが観測されないことを意味する。アルジロダイト型の結晶が、例えばLi-P-S-Ha組成の場合、融液はよく混ざり合うため、これは、原材料とは異なる均質の化合物の溶融物であることを意味する。また、溶融状態かどうかの簡易的な確認方法としては、炉内原料の様子を観察することでも確認できる。未融物が見られなければ、完全に溶解しており、中間体化合物といってよい。
また、測定温度を変化させながら高温X線回折測定を行うことで、相転移等の結晶状態の変化を追い、中間体化合物が得られるようになる加熱温度の見当を付けることが可能となる。
加熱温度は、上記のような均質なアモルファスな中間体化合物が得られるようになる加熱温度以上であればよく、例えば、550℃以上が好ましく、600℃以上がより好ましく、650℃以上がさらに好ましい。また、加熱温度は、成分の揮散による組成ズレ抑制の観点から、950℃以下が好ましく、900℃以下がより好ましく、850℃以下がさらに好ましい。また、上記温度範囲で、段階的に温度を変化させてもよい。また、[Ha]/[P](原子比)で表されるハロゲン含有量が多い組成ほど、加熱温度を低くすることが可能である。
しかしながら、中間体化合物が溶融物である製造方法iにおいては、中間体化合物の流動性が高いことから均質となりやすい。そのため、イオン半径の大きいBrも結晶構造中に入りやすくなるため、上記のような調整は必ずしも必要でない。
冷却速度は、アルジロダイト型の結晶が析出すれば特に限定されないが、生産性の観点から、5℃/分以上が好ましく、10℃/分以上がより好ましく、30℃/分以上がさらに好ましい。また、結晶化率を高める観点から、冷却速度は2000℃/分以下が好ましく、1000℃/分以下がより好ましく、300℃/分以下がさらに好ましい。
なお、得られる固体電解質の好ましい態様は、上記<硫化物系固体電解質>に記載された好ましい態様と同様である。
工程ii-1は、原材料を混合して均質なアモルファスな中間体化合物を得る工程である。
また、遊離のアニオンサイトに存在するS、Cl、Br以外の元素や、4bサイトのPや16eサイトのSと置換する元素の源となる原材料も混合するが、これらも製造方法iの工程i-1にて記載したものと同様のものを同様の条件で使用できる。
アモルファス(非晶質)な中間体化合物とは、X線回折測定において、原材料に由来するピークが観測されないことを意味するが、これは、原材料の混合物とは異なる均質の化合物であることを意味する。
回転数は、用いるボールミルの種類や他の条件によっても異なるが、200rpm以上が好ましく、300rpm以上がより好ましく、400rpm以上がさらに好ましい。回転数の上限は特に限定されないが、機械強度の観点から1000rpm以下が好ましく、800rpm以下がより好ましい。
また、初めは低回転数で一定時間混合し、次いで高回転数に上げて一定時間混合するなど、複数の回転数を組み合わせてもよい。
先述したように、得られるアモルファスな中間体化合物は、原材料に由来するXRDピークが観測されないことを意味するが、Ramanスペクトルにおいて、原材料の位置のピークが完全に消失し別の位置にピークが出ていることを確認できると、より、均質な中間体が得られたと考えてよい。
なお、本明細書における中間体化合物の粒子径とは、走査型電子顕微鏡(SEM)観察で得られる像より求められる一次粒子径である。大気非曝露のSEM測定を行い、倍率2000倍、加速電圧2kVで観察し、適当な視野内に映る粒子20個の粒子径を測定して、その平均値を一次粒子径として決定する。
加熱温度は、固相反応、すなわち結晶化を促進する観点から350℃以上が好ましく、400℃以上がより好ましく、450℃以上がさらに好ましい。また、熱分解を抑制する観点から、加熱温度は600℃未満が好ましく、575℃以下がより好ましい。
なお、得られる固体電解質の好ましい態様は、上記<硫化物系固体電解質>に記載された好ましい態様と同様である。
例1~例9及び例12~例14は実施例であり、例10及び例11は比較例である。
ドライ窒素雰囲気下で、表1の「組成」に記載の組成比となるように、硫化リチウム粉末(Sigma社製、純度99.98%)、五硫化二リン粉末(Sigma社製、純度99%)、塩化リチウム粉末(Sigma社製、純度99.99%)、臭化リチウム粉末(Sigma社製、純度99.995%)及び酸化リチウム粉末(Sigma社製、純度97%)を秤量し、同雰囲気中、ミキサー(WARING社製、X-TREME(MX1100XTM))を用いて、Highモードにて1分間混合することで原料混合物を得た。得られた原料混合物を、耐熱性の容器に入れ、露点-60℃の雰囲気下において、300℃で1時間加熱した後、温度を上げて、700℃で0.5時間加熱して溶融物を得た。そのまま、300℃/分の速度で室温まで冷却し、アルジロダイト型の結晶を析出することで、目的のアルジロダイト型の結晶を含む硫化物系固体電解質を得た。
得られたアルジロダイト型の結晶の、下記条件によるXRD測定(株式会社リガク製、SmartLab)の結果を図1の上段に示すが、得られた回折パターンから、結晶が立方晶であることを確認した。
(条件)
XRD測定の条件は下記のとおりである。
線源:CuKα線(λ=1.5418Å)、管球電圧:45kV、管球電流:200mA、走査角度:10~100°、走査速度:5°/分、ステップ数:0.01°/ステップ。
組成比を表1の「組成」に記載のものへと変更した以外は例1と同様にして、例2~例7、例9のアルジロダイト型の結晶を含む硫化物系固体電解質を得た。
なお、組成にFが含まれる例2、例3、例9については、上記硫化リチウム粉、五硫化二リン粉末、塩化リチウム粉末、臭化リチウム粉末及び酸化リチウム粉末に加えて、フッ化リチウム粉末(Sigma社製、純度99.98%)を秤量して用いた。組成にBrが含まれない例7は臭化リチウム粉末を用いなかった。組成にOが含まれない例9は酸化リチウム粉末を用いなかった。得られた例2のアルジロダイト型の結晶について、例1と同じ条件によるXRD測定(株式会社リガク製、SmartLab)の結果を図1の下段に示すが、得られた回折パターンから、結晶が立方晶であることを確認した。
組成比を表1の「組成」に記載のものへと変更した以外は例1と同様にして例8のアルジロダイト型の結晶を含む硫化物系固体電解質を得た。
得られた硫化物系固体電解質に対し、下記条件でXRD測定(株式会社リガク製、SmartLab)を行った。
(条件)
XRD測定の条件は下記のとおりである。
線源:CuKα線(λ=1.5418Å)、管球電圧:45kV、管球電流:200mA、走査角度:10~100°、走査速度:5°/分、ステップ数:0.01°/ステップ。
ドライ窒素雰囲気下で、表1の「組成」に記載の組成比となるように、硫化リチウム粉末(Sigma社製、純度99.98%)、五硫化二リン粉末(Sigma社製、純度99%)及び塩化リチウム粉末(Sigma社製、純度99.99%)を秤量し、同雰囲気中、ミキサーで混合した後、遊星ボールミル(伊藤製作所社製、LP-M2)を用いてさらに混合することで原料混合物を得た。遊星ボールミルによる混合は、粒径10mmのボールを用いて、400rpmで20時間行った。得られた原料混合物を、耐熱性の容器に真空封入して封管し、450℃で5時間加熱焼成することで、アルジロダイト型の結晶を析出し、アルジロダイト型の結晶を含む硫化物系固体電解質を得た。
例11については、上記硫化リチウム粉末、五硫化二リン粉末及び塩化リチウム粉末に加えて、臭化リチウム粉末(Sigma社製、純度99.995%)を秤量して用いた。
得られたアルジロダイト型の結晶は、下記条件でのXRD測定(株式会社リガク製、SmartLab)の結果から、立方晶であることを確認した。
(条件)
測定条件は下記のとおりである。
線源:CuKα線(λ=1.5418Å)、管球電圧:45kV、管球電流:200mA、走査角度:10~100°、走査速度:5°/分、ステップ数:0.01°/ステップ。
ドライ窒素雰囲気下で、表2の「組成」に記載の組成比となるように、硫化リチウム粉末(Sigma社製、純度99.98%)、五硫化二リン粉末(Sigma社製、純度99%)、塩化リチウム粉末(Sigma社製、純度99.99%)、臭化リチウム粉末(Sigma社製、純度99.995%)及び酸化リチウム粉末(Sigma社製、純度97%)を秤量し、同雰囲気中、ミキサー(WARING社製、X-TREME(MX1100XTM))を用いて、Highモードにて1分間混合することで原料混合物を得た。得られた原料混合物を、耐熱性の容器に入れ、露点-60℃の雰囲気下において、300℃で1時間加熱した後、温度を上げて、700℃で0.5時間加熱して溶融物を得た。そのまま、300℃/分の速度で室温まで冷却した。雰囲気は上記露点-60℃に加え、酸素濃度が100ppm以下のN2雰囲気で実施した。その後、遊星ボールミルによる混合を、粒径10mmのボールを用いて、400rpmで20時間行い、得られた混合物を、耐熱性の容器に真空封入して封管し、450℃で5時間加熱焼成することで、アルジロダイト型の結晶を含む硫化物系固体電解質を得た。
組成比を表2の「組成」に記載のものへと変更した以外は例12と同様にして、例13、例14のアルジロダイト型の結晶を含む硫化物系固体電解質を得た。
なお、組成にSiが含まれる例13については、上記硫化リチウム粉、五硫化二リン粉末、塩化リチウム粉末、臭化リチウム粉末及び酸化リチウム粉末に加えて、二硫化ケイ素(American Elements社製、純度99.9%)を秤量して用いた。組成にSnが含まれる例14については、上記硫化リチウム粉、五硫化二リン粉末、塩化リチウム粉末、臭化リチウム粉末及び酸化リチウム粉末に加えて、二硫化スズ(高純度化学研究所社製、純度3Nup)を秤量して用いた。
得られた硫化物系固体電解質のアニオンパラメータは、放射光XRD測定の結果を基に下記手順により求めた。
(放射光XRD測定)
例1、例3、例5、例11~例14に関して、下記条件で放射光X線回折測定を行った。
測定方法:粉末X線回折
測定に使用した光エネルギー:17.71keV
試料形状:直径0.3mmのキャピラリー
測定角度範囲:2θ=0.1~95°
ステップ幅(Δ2θ)=0.010°
検出器:デバイシェラー型カメラと二次元半導体検出器
放射光X線回折測定を行った例に関して、RIETAN-FPソフトウェアを用いてリートベルト法による結晶構造の精密化を行った。最もRwp値が低くなった構造を各例の結晶構造として判断した。Rwp値とは、リートベルト解析による構造精密化のフィッティングにおいて、解析範囲全体に対して一般的な目安とされる信頼性因子Rwp(R-weighted pattern)のことである。Rwp値は低い方が良く、本解析においては、最も低くなったRwp値は何れも10%未満であった。これにより、硫化物系固体電解質中のアルジロダイト型結晶の結晶構造を求めた。
構造解析の結果から求まる遊離のアニオンの割合より、各例のアルジロダイト型の結晶の{(1/χ(S))×[S2-]+(1/χ(O))×[O2-]+(1/χ(Br))×[Br-]+(1/χ(Cl))×[Cl-]+(1/χ(F))×[F-]}で表されるアニオンパラメータを算出した。なお、各アニオンの含有量は、[S2-]+[O2-]+[Br-]+[Cl-]+[F-]=1となるように規格化された値である。
アニオンパラメータにおける各元素の電気陰性度は、χ(S)=2.5、χ(O)=3.5、χ(Br)=2.8、χ(Cl)=3.0、χ(F)=4.0である。
なお、例2、例4、例6~例10に関しては、XRDパターンより単一相であることを確認したのち、上記で得られた例1、例3、例5の解析結果を参照して、下記式により求めた値である。
[S2-]={(表1又は表2のSの値)―(表1又は表2のPの値)×4}/規格化値
[O2-]=(表1又は表2のOの値)/規格化値
[Br-]=(表1又は表2のBrの値)/規格化値
[Cl-]=(表1又は表2のClの値)/規格化値
[F-]=(表1又は表2のFの値)/規格化値
上記規格化値とは、[S2-]+[O2-]+[Br-]+[Cl-]+[F-]=1となるように調整する値である。
結果を表1、表2の「アニオンパラメータ」にそれぞれ示す。
硫化物系固体電解質を乳鉢で粉砕し、目開き100μmのメッシュパスで粗粒を取り除いた後、100mg測り取った。次いで、直径10mmの面積を380MPaで加圧成型しながら測定サンプルに対し、交流インピーダンス測定装置(Bio-Logic Sciences Instruments社製、ポテンショスタット/ガルバノスタット VSP)を用いてリチウムイオン伝導率を測定した。
測定条件は、測定周波数:100Hz~1MHz、測定電圧:100mV、測定温度:25℃とした。
結果を表1、表2の「Liイオン伝導率(mS/cm)」にそれぞれ示す。
ドライ窒素雰囲気下で硫化物系固体電解質を遊星ボールミル(伊藤製作所社製、型番LP-M2)により粒径2mmのアルミナボールを用い乾式粉砕した。次いで、目開き43μmの篩を通して、平均粒径D50が3μmの粒度分布の硫化物系固体電解質粉末を得た。
なお、平均粒径D50は、Microtrac製レーザー回折粒度分布測定機MT3300EXIIを用いて粒度分布を測定し、得られた体積基準粒度分布のチャートから測定した。
正極活物質として、層状岩塩型NMC811粉末(MTI Corporation社より購入、体積平均粒子径:11.75μm)を用い、上記で作製した硫化物系固体電解質粉末を34質量部、正極活物質を60質量部、導電助剤(アセチレンブラック、デンカ株式会社製、HS100)を6質量部混合し、正極合材を作製した。
上記で作製した硫化物系固体電解質粉末80mgを直径10mmのプラスチック製の円筒に投入し、加圧成型して固体電解質層とした。次いで、同じ円筒に上記で作製した正極合材を6mg投入し再び加圧成型し、正極層を形成した。さらに正極合材とは反対側から、インジウム箔とリチウム箔を投入して負極層とした。このようにして全固体型リチウムイオン二次電池を作製し、拘束圧10kNにて、充放電試験を実施した。
充放電試験の結果から、以下の式で表される初期特性、容量維持率(%)をそれぞれ求め、全固体型リチウムイオン二次電池の電池特性を評価した。
初期特性=(1サイクル目の放電容量/1サイクル目の充電容量)
容量維持率(%)=(5サイクル目の放電容量/1サイクル目の放電容量)×100
◎:初期特性0.65以上、容量維持率88%以上、の両方を満たす。
○:初期特性0.60超、容量維持率86%超、の両方を満たし、かつ、初期特性0.65未満、容量維持率88%未満、の一方を満たす。
×:初期特性0.60以下、容量維持率86%以下、の少なくとも一方を満たす。
例12~例14に対し、PS4 3-構造における4bサイトと、それと隣り合う16eサイトの平均結合距離を、放射光XRD測定とリートベルト解析により求めた。結果を表2の「平均結合距離」に示す。
一方、例10、例11は、上記他の元素が存在せず、充放電を繰り返した際の電池特性の低下が大きかった。
Claims (8)
- リチウムイオン二次電池に用いられる硫化物系固体電解質であって、
Li、P、S及びHaを含むアルジロダイト型の結晶を含み、
前記Haは、Cl及びBrの少なくとも一方を含む、F、Cl、Br、及びIからなる群より選ばれる少なくとも1種の元素であり、
前記アルジロダイト型の結晶は、(A)遊離のアニオンサイトに、Sと、Cl及びBrの少なくとも一方と、それらとは異なる1種又は2種以上の元素と、が存在すること、及び、(B)4bサイトのPの一部と、前記4bサイトのPと隣り合う16eサイトのSの一部とが、それぞれ他の元素に置換されていること、の少なくとも一方を満たし、
前記アルジロダイト型の結晶は、遊離しているアニオンの含有量[S2-]、[O2-]、[Br-]、[Cl-]及び[F-]、並びに、それらの電気陰性度χ(S)、χ(O)、χ(Br)、χ(Cl)及びχ(F)が、
{(1/χ(S))×[S2-]+(1/χ(O))×[O2-]+(1/χ(Br))×[Br-]+(1/χ(Cl))×[Cl-]+(1/χ(F))×[F-]}≦0.36、かつ
[S2-]+[O2-]+[Br-]+[Cl-]+[F-]=1
の関係を満たす、硫化物系固体電解質。 - 前記アルジロダイト型の結晶が、O及びFの少なくとも一方をさらに含む、請求項1に記載の硫化物系固体電解質。
- 前記遊離しているアニオンの含有量[S2-]、[O2-]、[Br-]、[Cl-]及び[F-]、並びに、それらの電気陰性度χ(S)、χ(O)、χ(Br)、χ(Cl)及びχ(F)が、
{(1/χ(S))×[S2-]+(1/χ(O))×[O2-]+(1/χ(Br))×[Br-]+(1/χ(Cl))×[Cl-]+(1/χ(F))×[F-]}≦0.34
の関係を満たす、請求項1又は2に記載の硫化物系固体電解質。 - 前記アルジロダイト型の結晶は、前記(B)を満たし、前記4bサイトと、それと隣り合う前記16eサイトの平均結合距離が2.07Å以上である、請求項1~3のいずれか1項に記載の硫化物系固体電解質。
- 前記アルジロダイト型の結晶は、前記(B)を満たし、前記4bサイトのPの一部と置換される元素Mが、PS4 3-よりもイオン半径が大きなMS4四面体構造を形成する、請求項1~4のいずれか1項に記載の硫化物系固体電解質。
- 前記MS4四面体構造における前記元素MがSi及びSnの少なくとも一方である、請求項5に記載の硫化物系固体電解質。
- 前記アルジロダイト型の結晶は、前記(A)を満たし、前記遊離しているアニオンの含有量が、0<{[Br-]/([F-]+[Cl-]+[Br-])}<2の関係を満たす、請求項1~6のいずれか1項に記載の硫化物系固体電解質。
- 前記リチウムイオン二次電池の起電力が4.3V以上である、請求項1~7のいずれか1項に記載の硫化物系固体電解質。
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WO2020033809A1 (en) * | 2018-08-10 | 2020-02-13 | The Florida State University Research Foundation, Inc. | Solid electrolytes, electronic devices, and methods |
US20200087155A1 (en) * | 2018-09-19 | 2020-03-19 | Blue Current, Inc. | Lithium oxide argyrodites |
JP2021072288A (ja) * | 2019-11-01 | 2021-05-06 | 三星エスディアイ株式会社SAMSUNG SDI Co., LTD. | 固体イオン伝導体化合物、それを含む固体電解質、それを含む電気化学セル、及びその製造方法 |
JP2021162230A (ja) | 2020-03-31 | 2021-10-11 | 三菱電機株式会社 | 換気装置 |
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WO2015012042A1 (ja) | 2013-07-25 | 2015-01-29 | 三井金属鉱業株式会社 | リチウムイオン電池用硫化物系固体電解質 |
WO2020033809A1 (en) * | 2018-08-10 | 2020-02-13 | The Florida State University Research Foundation, Inc. | Solid electrolytes, electronic devices, and methods |
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