WO2022071324A1 - 二次電池 - Google Patents
二次電池 Download PDFInfo
- Publication number
- WO2022071324A1 WO2022071324A1 PCT/JP2021/035662 JP2021035662W WO2022071324A1 WO 2022071324 A1 WO2022071324 A1 WO 2022071324A1 JP 2021035662 W JP2021035662 W JP 2021035662W WO 2022071324 A1 WO2022071324 A1 WO 2022071324A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- layer
- negative electrode
- flame retardant
- secondary battery
- active material
- Prior art date
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- 239000003063 flame retardant Substances 0.000 claims abstract description 167
- RNFJDJUURJAICM-UHFFFAOYSA-N 2,2,4,4,6,6-hexaphenoxy-1,3,5-triaza-2$l^{5},4$l^{5},6$l^{5}-triphosphacyclohexa-1,3,5-triene Chemical compound N=1P(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP=1(OC=1C=CC=CC=1)OC1=CC=CC=C1 RNFJDJUURJAICM-UHFFFAOYSA-N 0.000 claims abstract description 162
- 239000007773 negative electrode material Substances 0.000 claims abstract description 144
- 125000005843 halogen group Chemical group 0.000 claims abstract description 34
- 239000002245 particle Substances 0.000 claims description 260
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 130
- 229910002804 graphite Inorganic materials 0.000 claims description 49
- 239000010439 graphite Substances 0.000 claims description 49
- PAZHGORSDKKUPI-UHFFFAOYSA-N lithium metasilicate Chemical compound [Li+].[Li+].[O-][Si]([O-])=O PAZHGORSDKKUPI-UHFFFAOYSA-N 0.000 claims description 46
- 229910052912 lithium silicate Inorganic materials 0.000 claims description 46
- 239000011856 silicon-based particle Substances 0.000 claims description 45
- 239000002041 carbon nanotube Substances 0.000 claims description 43
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 43
- 229910052799 carbon Inorganic materials 0.000 claims description 34
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Chemical compound [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 claims description 30
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 19
- 229910052744 lithium Inorganic materials 0.000 claims description 9
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 9
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 8
- 125000004122 cyclic group Chemical group 0.000 claims description 7
- BSWWXRFVMJHFBN-UHFFFAOYSA-N 2,4,6-tribromophenol Chemical compound OC1=C(Br)C=C(Br)C=C1Br BSWWXRFVMJHFBN-UHFFFAOYSA-N 0.000 claims description 4
- DYIZJUDNMOIZQO-UHFFFAOYSA-N 4,5,6,7-tetrabromo-2-[2-(4,5,6,7-tetrabromo-1,3-dioxoisoindol-2-yl)ethyl]isoindole-1,3-dione Chemical compound O=C1C(C(=C(Br)C(Br)=C2Br)Br)=C2C(=O)N1CCN1C(=O)C2=C(Br)C(Br)=C(Br)C(Br)=C2C1=O DYIZJUDNMOIZQO-UHFFFAOYSA-N 0.000 claims description 3
- DEIGXXQKDWULML-UHFFFAOYSA-N 1,2,5,6,9,10-hexabromocyclododecane Chemical compound BrC1CCC(Br)C(Br)CCC(Br)C(Br)CCC1Br DEIGXXQKDWULML-UHFFFAOYSA-N 0.000 claims description 2
- VEORPZCZECFIRK-UHFFFAOYSA-N 3,3',5,5'-tetrabromobisphenol A Chemical compound C=1C(Br)=C(O)C(Br)=CC=1C(C)(C)C1=CC(Br)=C(O)C(Br)=C1 VEORPZCZECFIRK-UHFFFAOYSA-N 0.000 claims description 2
- UGQQAJOWXNCOPY-UHFFFAOYSA-N dechlorane plus Chemical compound C12CCC3C(C4(Cl)Cl)(Cl)C(Cl)=C(Cl)C4(Cl)C3CCC2C2(Cl)C(Cl)=C(Cl)C1(Cl)C2(Cl)Cl UGQQAJOWXNCOPY-UHFFFAOYSA-N 0.000 claims description 2
- 125000004206 2,2,2-trifluoroethyl group Chemical group [H]C([H])(*)C(F)(F)F 0.000 claims 1
- 229910019142 PO4 Inorganic materials 0.000 claims 1
- 239000007983 Tris buffer Substances 0.000 claims 1
- 239000010452 phosphate Substances 0.000 claims 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 claims 1
- 239000010410 layer Substances 0.000 description 247
- 239000000203 mixture Substances 0.000 description 52
- 238000000034 method Methods 0.000 description 32
- 229910052710 silicon Inorganic materials 0.000 description 31
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 28
- 239000010703 silicon Substances 0.000 description 28
- 238000004519 manufacturing process Methods 0.000 description 21
- 239000000463 material Substances 0.000 description 21
- 239000011248 coating agent Substances 0.000 description 20
- 238000000576 coating method Methods 0.000 description 20
- 239000011255 nonaqueous electrolyte Substances 0.000 description 19
- 239000011230 binding agent Substances 0.000 description 17
- 239000011267 electrode slurry Substances 0.000 description 17
- 239000002994 raw material Substances 0.000 description 17
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 16
- 239000003575 carbonaceous material Substances 0.000 description 16
- 239000010408 film Substances 0.000 description 16
- 238000012360 testing method Methods 0.000 description 16
- 239000004020 conductor Substances 0.000 description 15
- 230000005856 abnormality Effects 0.000 description 14
- -1 alumina Chemical class 0.000 description 13
- 230000014759 maintenance of location Effects 0.000 description 13
- 229910003481 amorphous carbon Inorganic materials 0.000 description 12
- 239000008151 electrolyte solution Substances 0.000 description 12
- 150000001875 compounds Chemical class 0.000 description 11
- 238000002156 mixing Methods 0.000 description 11
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 10
- 239000002033 PVDF binder Substances 0.000 description 10
- 230000007423 decrease Effects 0.000 description 10
- 229910001416 lithium ion Inorganic materials 0.000 description 10
- 229910003002 lithium salt Inorganic materials 0.000 description 10
- 159000000002 lithium salts Chemical class 0.000 description 10
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 10
- 238000007789 sealing Methods 0.000 description 10
- 239000002002 slurry Substances 0.000 description 10
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 9
- 239000012298 atmosphere Substances 0.000 description 9
- 230000000694 effects Effects 0.000 description 9
- 229910052751 metal Inorganic materials 0.000 description 9
- 239000002184 metal Substances 0.000 description 9
- 229920003048 styrene butadiene rubber Polymers 0.000 description 9
- 239000011889 copper foil Substances 0.000 description 8
- 239000003792 electrolyte Substances 0.000 description 8
- 239000011734 sodium Substances 0.000 description 8
- 239000000126 substance Substances 0.000 description 8
- 238000006243 chemical reaction Methods 0.000 description 7
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
- 229910052782 aluminium Inorganic materials 0.000 description 6
- GDTBXPJZTBHREO-UHFFFAOYSA-N bromine Substances BrBr GDTBXPJZTBHREO-UHFFFAOYSA-N 0.000 description 6
- 229910052794 bromium Inorganic materials 0.000 description 6
- 239000006229 carbon black Substances 0.000 description 6
- 235000019241 carbon black Nutrition 0.000 description 6
- 239000006258 conductive agent Substances 0.000 description 6
- 238000007599 discharging Methods 0.000 description 6
- 238000011156 evaluation Methods 0.000 description 6
- 150000004706 metal oxides Chemical class 0.000 description 6
- 235000012239 silicon dioxide Nutrition 0.000 description 6
- 239000002904 solvent Substances 0.000 description 6
- WKBOTKDWSSQWDR-UHFFFAOYSA-N Bromine atom Chemical compound [Br] WKBOTKDWSSQWDR-UHFFFAOYSA-N 0.000 description 5
- 238000002441 X-ray diffraction Methods 0.000 description 5
- 239000002253 acid Substances 0.000 description 5
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 5
- 239000002131 composite material Substances 0.000 description 5
- IJKVHSBPTUYDLN-UHFFFAOYSA-N dihydroxy(oxo)silane Chemical compound O[Si](O)=O IJKVHSBPTUYDLN-UHFFFAOYSA-N 0.000 description 5
- 230000020169 heat generation Effects 0.000 description 5
- 238000002347 injection Methods 0.000 description 5
- 239000007924 injection Substances 0.000 description 5
- 150000002642 lithium compounds Chemical class 0.000 description 5
- 239000011159 matrix material Substances 0.000 description 5
- 229910044991 metal oxide Inorganic materials 0.000 description 5
- 239000003960 organic solvent Substances 0.000 description 5
- 239000007774 positive electrode material Substances 0.000 description 5
- 239000000377 silicon dioxide Substances 0.000 description 5
- 229910021384 soft carbon Inorganic materials 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 4
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 4
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 4
- 239000002174 Styrene-butadiene Substances 0.000 description 4
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 description 4
- 239000006230 acetylene black Substances 0.000 description 4
- 239000000654 additive Substances 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 4
- 239000003125 aqueous solvent Substances 0.000 description 4
- 239000001768 carboxy methyl cellulose Substances 0.000 description 4
- 239000000460 chlorine Substances 0.000 description 4
- 239000000470 constituent Substances 0.000 description 4
- 239000002612 dispersion medium Substances 0.000 description 4
- 238000000921 elemental analysis Methods 0.000 description 4
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 4
- FKRCODPIKNYEAC-UHFFFAOYSA-N ethyl propionate Chemical compound CCOC(=O)CC FKRCODPIKNYEAC-UHFFFAOYSA-N 0.000 description 4
- 229910052731 fluorine Inorganic materials 0.000 description 4
- 239000011737 fluorine Substances 0.000 description 4
- 239000011888 foil Substances 0.000 description 4
- 230000005484 gravity Effects 0.000 description 4
- 229910021385 hard carbon Inorganic materials 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 238000012986 modification Methods 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 238000000550 scanning electron microscopy energy dispersive X-ray spectroscopy Methods 0.000 description 4
- 235000019812 sodium carboxymethyl cellulose Nutrition 0.000 description 4
- 229920001027 sodium carboxymethylcellulose Polymers 0.000 description 4
- 238000004804 winding Methods 0.000 description 4
- 229910001928 zirconium oxide Inorganic materials 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 description 3
- 239000004114 Ammonium polyphosphate Substances 0.000 description 3
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 description 3
- 229910013870 LiPF 6 Inorganic materials 0.000 description 3
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 3
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 3
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical group OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 3
- 230000002159 abnormal effect Effects 0.000 description 3
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 3
- 235000019826 ammonium polyphosphate Nutrition 0.000 description 3
- 229920001276 ammonium polyphosphate Polymers 0.000 description 3
- 229910021383 artificial graphite Inorganic materials 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 238000005229 chemical vapour deposition Methods 0.000 description 3
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 3
- 239000011300 coal pitch Substances 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
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- 229910052748 manganese Inorganic materials 0.000 description 3
- 238000013507 mapping Methods 0.000 description 3
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 3
- 229910021382 natural graphite Inorganic materials 0.000 description 3
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- 150000003254 radicals Chemical class 0.000 description 3
- 229920005989 resin Polymers 0.000 description 3
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- 238000002076 thermal analysis method Methods 0.000 description 3
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- VAYTZRYEBVHVLE-UHFFFAOYSA-N 1,3-dioxol-2-one Chemical compound O=C1OC=CO1 VAYTZRYEBVHVLE-UHFFFAOYSA-N 0.000 description 2
- YAJYJWXEWKRTPO-UHFFFAOYSA-N 2,3,3,4,4,5-hexamethylhexane-2-thiol Chemical compound CC(C)C(C)(C)C(C)(C)C(C)(C)S YAJYJWXEWKRTPO-UHFFFAOYSA-N 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 2
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 2
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- CERQOIWHTDAKMF-UHFFFAOYSA-N Methacrylic acid Chemical compound CC(=C)C(O)=O CERQOIWHTDAKMF-UHFFFAOYSA-N 0.000 description 2
- RJUFJBKOKNCXHH-UHFFFAOYSA-N Methyl propionate Chemical compound CCC(=O)OC RJUFJBKOKNCXHH-UHFFFAOYSA-N 0.000 description 2
- 239000004372 Polyvinyl alcohol Substances 0.000 description 2
- 229910004298 SiO 2 Inorganic materials 0.000 description 2
- 229920002125 Sokalan® Polymers 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
- 229910026551 ZrC Inorganic materials 0.000 description 2
- OTCHGXYCWNXDOA-UHFFFAOYSA-N [C].[Zr] Chemical compound [C].[Zr] OTCHGXYCWNXDOA-UHFFFAOYSA-N 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 2
- 239000011149 active material Substances 0.000 description 2
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 2
- 239000012300 argon atmosphere Substances 0.000 description 2
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 2
- 150000001733 carboxylic acid esters Chemical class 0.000 description 2
- 229910052801 chlorine Inorganic materials 0.000 description 2
- 238000013329 compounding Methods 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- ZUOUZKKEUPVFJK-UHFFFAOYSA-N diphenyl Chemical compound C1=CC=CC=C1C1=CC=CC=C1 ZUOUZKKEUPVFJK-UHFFFAOYSA-N 0.000 description 2
- USIUVYZYUHIAEV-UHFFFAOYSA-N diphenyl ether Chemical compound C=1C=CC=CC=1OC1=CC=CC=C1 USIUVYZYUHIAEV-UHFFFAOYSA-N 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- STVZJERGLQHEKB-UHFFFAOYSA-N ethylene glycol dimethacrylate Chemical compound CC(=C)C(=O)OCCOC(=O)C(C)=C STVZJERGLQHEKB-UHFFFAOYSA-N 0.000 description 2
- 239000012757 flame retardant agent Substances 0.000 description 2
- GAEKPEKOJKCEMS-UHFFFAOYSA-N gamma-valerolactone Chemical compound CC1CCC(=O)O1 GAEKPEKOJKCEMS-UHFFFAOYSA-N 0.000 description 2
- 229910021469 graphitizable carbon Inorganic materials 0.000 description 2
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- 239000003273 ketjen black Substances 0.000 description 2
- AMXOYNBUYSYVKV-UHFFFAOYSA-M lithium bromide Chemical compound [Li+].[Br-] AMXOYNBUYSYVKV-UHFFFAOYSA-M 0.000 description 2
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 2
- 229910052808 lithium carbonate Inorganic materials 0.000 description 2
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 description 2
- 229910052749 magnesium Inorganic materials 0.000 description 2
- 239000011777 magnesium Substances 0.000 description 2
- 150000002736 metal compounds Chemical class 0.000 description 2
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- 229910052757 nitrogen Inorganic materials 0.000 description 2
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- SIWVEOZUMHYXCS-UHFFFAOYSA-N oxo(oxoyttriooxy)yttrium Chemical compound O=[Y]O[Y]=O SIWVEOZUMHYXCS-UHFFFAOYSA-N 0.000 description 2
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- FZYCEURIEDTWNS-UHFFFAOYSA-N prop-1-en-2-ylbenzene Chemical compound CC(=C)C1=CC=CC=C1.CC(=C)C1=CC=CC=C1 FZYCEURIEDTWNS-UHFFFAOYSA-N 0.000 description 2
- FBCQUCJYYPMKRO-UHFFFAOYSA-N prop-2-enyl 2-methylprop-2-enoate Chemical compound CC(=C)C(=O)OCC=C FBCQUCJYYPMKRO-UHFFFAOYSA-N 0.000 description 2
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- GEWWCWZGHNIUBW-UHFFFAOYSA-N 1-(4-nitrophenyl)propan-2-one Chemical compound CC(=O)CC1=CC=C([N+]([O-])=O)C=C1 GEWWCWZGHNIUBW-UHFFFAOYSA-N 0.000 description 1
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- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical group C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 1
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- 229910007562 Li2SiO3 Inorganic materials 0.000 description 1
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- 229910013684 LiClO 4 Inorganic materials 0.000 description 1
- 229910015746 LiNi0.88Co0.09Al0.03O2 Inorganic materials 0.000 description 1
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- 101150058243 Lipf gene Proteins 0.000 description 1
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- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 241000209094 Oryza Species 0.000 description 1
- 240000007594 Oryza sativa Species 0.000 description 1
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- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
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- 239000004698 Polyethylene Substances 0.000 description 1
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- XBDQKXXYIPTUBI-UHFFFAOYSA-M Propionate Chemical compound CCC([O-])=O XBDQKXXYIPTUBI-UHFFFAOYSA-M 0.000 description 1
- 238000001530 Raman microscopy Methods 0.000 description 1
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Images
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Definitions
- This disclosure relates to secondary batteries.
- Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have high output and high energy density. Therefore, non-aqueous electrolyte secondary batteries are used as power sources for small consumer applications, power storage devices, and electric vehicles.
- Patent Document 1 states that "the positive electrode has a positive electrode mixture layer containing a specific Li-containing transition metal oxide having Ni, Mn and the like as essential constituent elements, and the negative electrodes are Si and O.
- It has a negative electrode mixture layer containing a material containing the above (the atomic ratio x of O to Si is 0.5 ⁇ x ⁇ 1.5) and graphite as constituent elements, and in the negative electrode mixture layer, Si and O
- a non-aqueous secondary battery in which the ratio of the material containing Si and O as a constituent element is 3 to 20% by mass when the total of the material containing the above as a constituent element and graphite is 100% by mass is disclosed. There is.
- the secondary battery includes a positive electrode and a negative electrode, the negative electrode includes a first layer containing a negative electrode active material, and the first layer further contains a flame retardant containing a halogen atom.
- the secondary battery according to this embodiment includes a positive electrode and a negative electrode.
- the negative electrode includes a first layer containing a negative electrode active material.
- the first layer is usually arranged on the surface of the negative electrode current collector.
- the first layer further contains a flame retardant containing a halogen atom in addition to the negative electrode active material.
- the first layer may further contain carbon nanotubes.
- the flame retardant and the halogen atom may be referred to as "flame retardant (R)" and “halogen atom (Ha)", respectively.
- the secondary battery according to this embodiment may be referred to as a "secondary battery (S)” below.
- the secondary battery (S) may be a non-aqueous electrolyte secondary battery.
- the negative electrode active material may contain particles (P) and graphite.
- the particles (P) are the first particles containing silicon oxide represented by the formula of SiO X (0.5 ⁇ X ⁇ 1.6), the lithium silicate phase, and the silicon dispersed in the lithium silicate phase. It is at least one kind of particle selected from the group consisting of a second particle including particles and a third particle including a carbon phase and silicon particles dispersed in the carbon phase.
- the silicon particles contained in the second particle can be read as the silicon phase
- the silicon particles contained in the third particle can be read as the silicon phase.
- the particles (P) containing silicon (Si) As the negative electrode active material.
- the inventors of the present application have found that when the particles (P) are used, the battery temperature tends to rise at the time of abnormality (for example, during the nail piercing test). Furthermore, the inventors of the present application have found that by using a specific flame retardant, it is possible to suppress an increase in the battery temperature at the time of abnormality without significantly deteriorating the battery characteristics. This disclosure is based on these new findings.
- the lithium silicate phase of the second particle may contain a lithium silicate represented by the formula Li 2Z SiO (2 + Z) (0 ⁇ Z ⁇ 2). The details of the second particle will be described later.
- the content of particles (P) in the negative electrode active material may be 1% by mass or more. According to this configuration, it is possible to increase the capacity as compared with the case where the negative electrode active material is only graphite.
- the content of the particles (P) in the negative electrode active material may be 3% by mass or more.
- the content may be 50% by mass or less.
- the negative electrode active material may contain a plurality of types of particles selected from the group consisting of the first particle, the second particle, and the third particle.
- the particles (P) may be composed of two types of particles selected from them, or may include all three types of particles.
- the negative electrode active material may contain a first particle and a second particle, a first particle and a third particle, and a second particle and a third particle. It may contain particles.
- the negative electrode active material may include all of the first, second, and third particles.
- the graphite content in the negative electrode active material may be in the range of 50 to 99% by mass.
- the particles (P) contain graphite on the surface and / or inside, the graphite is not included in the graphite content.
- the graphite content is the graphite content not contained in the particles (P).
- the value of a may be 0.1 or more, 0.5 or more, or 1 or more.
- the value of a may be 10 or less, 5 or less, less than 5, or 3 or less. These lower and upper limits can be combined arbitrarily as long as there is no contradiction.
- the value of a may be in the range of 1 or more and 5 or less (or 1 or more and less than 5), and more preferably 1 or more and 3 or less. In this case, high capacity can be maintained while suppressing heat generation, and both high charge / discharge performance and high safety can be realized.
- the content ratio of the negative electrode active material in the first layer is obtained from the sample obtained by extracting only the negative electrode active material layer from the secondary battery in the discharged state. Specifically, first, the discharged secondary battery is disassembled and the negative electrode is taken out. Next, the negative electrode is washed with an organic solvent, further vacuum dried, and then only the negative electrode active material layer is peeled off to obtain a sample. By performing thermal analysis such as TG-DTA on the sample, the ratio of the binder component and the conductive material component other than the negative electrode active material can be calculated.
- the ratio of the flame retardant (R) to the negative electrode active material layer can be determined by elemental analysis such as SEM-EDX (Energy Dispersive X-ray Spectroscopy) with respect to the cross section of the negative electrode active material layer.
- the flame retardant (R) may be unevenly distributed on the surface side of the first layer.
- the first layer includes, for example, a second layer containing at least the negative electrode active material and a third layer arranged on the surface of the second layer and containing at least the flame retardant (R).
- the content of the flame retardant in the third layer is larger than the content of the flame retardant in the second layer.
- the content of the flame retardant means the number of moles of the flame retardant contained in the unit volume (apparent volume) of the second layer or the third layer, and the first layer (second layer and third layer).
- the second layer may be a negative electrode active material layer (negative electrode mixture layer) containing at least a negative electrode active material
- the third layer may be a flame retardant layer containing at least a flame retardant (R). ..
- the negative electrode active material layer which is the second layer, may contain carbon nanotubes as a conductive material.
- the negative electrode active material contained in the second layer which is the negative electrode active material layer, preferably satisfies at least one of the following conditions (i) and (ii).
- the negative electrode active material contains particles (P) and graphite.
- the particle (P) is at least one kind of particle selected from the group consisting of the first particle, the second particle, and the third particle described above.
- the negative electrode active material contains metallic lithium.
- the capacity of the battery can be increased by using the particles (P) containing silicon (Si) as the negative electrode active material.
- the particles (P) when used, the battery temperature at the time of abnormality (for example, during the nail piercing test) tends to rise. Therefore, suppressing the rise in battery temperature when the battery is abnormal becomes an important issue.
- the flame retardant layer on which the specific flame retardant is arranged on the surface of the negative electrode active material layer it is possible to suppress an increase in the battery temperature at the time of abnormality without significantly deteriorating the battery characteristics. ..
- the negative electrode active material may contain a plurality of types of particles selected from the group consisting of the first particle, the second particle, and the third particle.
- the particles (P) may be composed of two types of particles selected from them, or may include all three types of particles.
- the negative electrode active material may contain a first particle and a second particle, a first particle and a third particle, and a second particle and a third particle. It may contain particles.
- the negative electrode active material may include all of the first, second, and third particles.
- the content of the particles (P) in the negative electrode active material may be 1% by mass or more. According to this configuration, it is possible to increase the capacity as compared with the case where the negative electrode active material is only graphite.
- the content of the particles (P) in the negative electrode active material may be 3% by mass or more.
- the content may be 50% by mass or less.
- the third layer as the flame retardant layer contains a flame retardant (R) containing a halogen atom (Ha).
- the negative electrode having the third layer can suppress excessive heat generation at the time of abnormality. Further, since the flame retardant (R) does not have electron conductivity, in a secondary battery, a short circuit may occur inside the battery because the third layer is interposed between the negative electrode active material layer and the separator. Also, the third layer acts as a resistance layer that suppresses a short circuit. This can effectively suppress heat generation.
- the third layer is preferably arranged on the surface of the second layer so as to contact the surface of the negative electrode active material layer, which is the second layer of the negative electrode, and cover at least a part of the negative electrode active material layer.
- the third layer may contain a binder in addition to the flame retardant (R).
- the binding property of the flame retardant (R) particles to each other and the binding property of the flame retardant (R) to the second layer, which is the negative electrode active material layer can be enhanced. .. That is, the third layer can be brought into close contact with the second layer.
- the binder is not particularly limited, and examples thereof include polyvinylidene fluoride (PVdF), ethylene dimethacrylate, allyl methacrylate, t-dodecyl mercaptan, ⁇ -methylstyrene dimer, and methacrylic acid.
- PVdF polyvinylidene fluoride
- ethylene dimethacrylate, allyl methacrylate, t-dodecyl mercaptan, ⁇ -methylstyrene dimer, and methacrylic acid are used as binders, pressure and / or heat is applied to the third layer. By being added, the negative electrode can be adhered to the separator.
- the third layer may contain particles other than the flame retardant (R) and the binder.
- examples of other particles include inorganic particles containing metal oxides such as alumina, boehmite, and titania.
- Inorganic particles containing metal oxides function as spacers and can suppress the amount of flame retardant added.
- the average particle size of the inorganic particles is preferably 0.01 ⁇ m to 5 ⁇ m, and more preferably 1/2 or less of the average particle size of the flame retardant (R).
- the flame retardant (R) exists in the form of an aggregate in which the particles of the flame retardant (R) are aggregated, or an aggregate in which the particles of the flame retardant (R) are aggregated via a binder. Can be.
- the flame retardant layer (R) may partially cover the surface of the second layer, or the third layer may cover almost the entire surface of the negative electrode active material layer.
- the coverage (area standard) of the third layer on the surface of the second layer may be 5% or more, 10% or more, or 30% or more, and may be 50%, in terms of suppressing an increase in the battery temperature at the time of abnormality. The above is preferable.
- the coverage of the third layer with respect to the surface of the second layer is 100% and the surface of the second layer is completely covered by the third layer, the space between the particles of the third layer is reached. Since the gap is sufficiently large compared to the size of the lithium ion, the lithium ion can move through the gap and does not interfere with charging / discharging. However, from the viewpoint of suppressing an increase in battery resistance, the coverage of the third layer with respect to the surface of the second layer may be 90% or less or 80% or less.
- the coverage of the third layer on the surface of the second layer is 5% or more and 90% or less, 10% or more and 90% or less, 30% or more and 90% or less, 50% or more and 90% or less, or 50% or more and 80% or less. There may be.
- the coverage of the third layer is obtained by elemental mapping of the electrode surface with SEM-EDX or the like.
- the coverage of the third layer on the surface of the second layer can be calculated by elementally mapping the particles of the flame retardant (R) and the negative electrode active material by element mapping.
- the average particle size of the particles of the flame retardant (R) in the third layer may be 0.01 ⁇ m to 5 ⁇ m, and 0. It may be 05 ⁇ m to 3 ⁇ m.
- the average particle size of the flame retardant (R) is obtained as follows. First, 20 flame retardant (R) particles are randomly selected from the SEM image on the surface of the negative electrode. Next, after observing the grain boundaries of the selected 20 particles and specifying the outer shape of the particles, the major axis of each of the 20 particles is obtained, and the average value thereof is the average particle of the flame retardant (R) particles. The diameter. When the third layer contains particles other than the flame retardant (R), the average particle diameter of the other particles can be determined by the same method.
- the basis weight of the third layer is preferably 0.1 g / m 2 or more, and more preferably 0.3 g / m 2 or more or 1 g / m 2 or more, in terms of suppressing an increase in battery temperature at the time of abnormality.
- the basis weight of the third layer is preferably 10 g / m 2 or less in terms of suppressing an increase in battery resistance. These lower and upper limits can be combined arbitrarily as long as there is no contradiction.
- the basis weight of the third layer is the mass (g) of the third layer and the surface area of the second layer (negative electrode active material layer) on which the third layer is arranged (when the coverage is less than 100%, the second layer). The value divided by (including the area where the layer is exposed).
- the third layer can be formed by depositing a mixture containing at least the particles of the third layer and the binder on the surface of the negative electrode active material layer.
- the mixture may be a slurry containing particles of the flame retardant (R), a binder, and a solvent (dispersion medium).
- a third layer can be formed by spraying, dropping, or applying the slurry to the surface of the negative electrode active material layer and drying it. By adjusting the amount of the solvent and / or the coating amount of the slurry with respect to the amount of the particles of the flame retardant (R) in the slurry, the coating ratio and the basis weight (thickness) of the third layer can be controlled.
- the proportion of the flame retardant (R) in the entire third layer may be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more on a mass basis.
- the proportion of the flame retardant (R) in the entire third layer may be 100% or less or 95% or less on a mass basis.
- the thickness of the third layer is preferably 0.1 ⁇ m or more, and more preferably 1 ⁇ m or more or 3 ⁇ m or more, in terms of suppressing an increase in the battery temperature at the time of abnormality.
- the thickness of the third layer is preferably 10 ⁇ m or less in terms of suppressing an increase in battery resistance. These lower and upper limits can be combined arbitrarily as long as there is no contradiction.
- the thickness of the third layer is the average thickness in the region where the surface of the second layer (negative electrode active material layer) is covered with the third layer, and is obtained from the SEM image of the cross section of the negative electrode.
- the second layer containing at least the negative electrode active material may further contain carbon nanotubes.
- the first layer comprises a second layer containing at least a negative electrode active material and carbon nanotubes, and a third layer containing at least a flame retardant, and the third layer is a second layer, a positive electrode and a negative electrode. It is arranged between the separator and the separator. According to this embodiment, by arranging the flame retardant layer on which the specific flame retardant is arranged between the separator and the negative electrode active material layer, the increase in the battery temperature at the time of abnormality is suppressed without significantly deteriorating the battery characteristics. can.
- the flame retardant (R) exhibits a flame retardant effect by releasing a halogen atom (Ha) at a high temperature. Therefore, according to the secondary battery (S), excessive heat generation at the time of abnormality can be suppressed.
- the flame retardant (R) may satisfy at least one of the following conditions (1) and (2). However, it is preferable that the flame retardant (R) satisfies both of the following conditions (1) and (2).
- the flame retardant (R) contains a cyclic structure to which a halogen atom (Ha) is bonded.
- the cyclic structure may or may not be an aromatic ring. In this case, all halogen atoms (Ha) may be bonded to the cyclic structure, or only some halogen atoms (Ha) may be bonded to the cyclic structure.
- a structure in which a halogen atom (Ha) is bonded to a cyclic structure is preferable because it is easy to increase the content of the halogen atom.
- the proportion of the halogen atom (Ha) in the flame retardant (R) is 45% by mass or more. This ratio may be 60% by mass or more (for example, 70% by mass or more).
- the upper limit is not particularly limited, but may be 95% by mass or less (for example, 90% by mass or more). These lower and upper limits can be combined arbitrarily.
- Ethylene-1,2-bispentabromophenyl which is an example of the flame retardant (R), is shown below.
- the halogen atom (Ha) is not particularly limited, but examples of preferable halogen atoms (Ha) include bromine (Br), fluorine (F), and chlorine (Cl).
- the halogen atom (Ha) may be bromine and / or fluorine, or may be bromine, in that a flame-retardant effect can be expected from the initial stage of abnormal heat generation.
- the reaction at the negative electrode plays a major role in the exothermic reaction at the time of abnormality, and by adding a material exhibiting a flame retardant effect to the negative electrode, the exothermic reaction is effectively suppressed and safety is improved. Can be enhanced.
- the negative electrode having a larger reaction area than the positive electrode reacts preferentially with the electrolytic solution to generate H radicals, and the H radicals repeatedly react with other products at an accelerated rate.
- the flame retardant (R) containing a halogen atom (Ha) added to the negative electrode deactivates the H radical, so that the exothermic reaction is suppressed.
- the flame retardant (R) containing such a halogen atom (Ha) has a larger specific gravity than the conventionally used phosphorus-based flame retardant, the volume can be reduced with respect to the added weight. As a result, it is possible to maintain a high loading amount of the negative electrode active material while adding a sufficient amount of flame retardant, and it is possible to maintain a high capacity.
- the flame retardant (R) preferably contains bromine (Br) because of its high specific gravity. Further, the larger the number of halogen atoms (Ha) bonded to the flame retardant (R), the better.
- the flame retardant (R) tends to have a large specific gravity because a halogen atom (Ha) is bonded to the cyclic structure.
- the specific gravity of the flame retardant (R) may be, for example, 2.7 or more, preferably 3.0 or more.
- the flame retardant (R) preferably does not contain a water-generating moiety and / or a hydrophilic group in the structure of the compound.
- a secondary battery having excellent reliability because it is difficult for water to enter the battery in the manufacturing process of the secondary battery.
- the portion that generates water include a hydroxy group (-OH), a carboxyl group (-COOH), a carbonyl group (-CO-), and an oxo acid group such as a sulfo group and a phosphoric acid group.
- the hydrophilic group include an amino group and the like in addition to the above functional group.
- the halogen atom (Ha) contained in the flame retardant (R) reacts with Si to form a stable film on the surface of the negative electrode active material. .. As a result, high cycle characteristics can be maintained and high durability can be expected.
- the flame retardant (R) may release a halogen atom (Ha) at a temperature of 180 ° C. or higher (for example, 250 ° C. or higher).
- a halogen atom (Ha) may be released in a non-abnormal state, and the characteristics of the battery may be deteriorated. Therefore, it is preferable that the flame retardant (R) does not substantially emit a halogen atom (Ha) at a temperature of less than 180 ° C.
- the flame retardant (R) is ethylene-1,2-bispentabromophenyl, ethylenebistetrabromophthalimide, tetrabromobisphenol A, hexabromocyclododecane, 2,4,6-tribromophenol, 1,6,7, 8,9,14,15,16,17,17,18,18-dodecachloropentacyclo (12.2.1.16,9.02,13.05,10) octadeca-7,15-diene (commodity) Name: Declolan Plus), and Tris (2,2,2-trifluoroethyl) phosphate may be at least one selected from the group.
- these flame retardants (R) commercially available ones may be used.
- the flame retardant (R) may be synthesized by a known synthesis method.
- the first particle contains silicon oxide represented by the formula SiO X (0.5 ⁇ X ⁇ 1.6).
- the first particles may include silicon oxide particles and a carbon layer arranged around the silicon oxide particles.
- the average particle size of the first particles may be in the range of 1 ⁇ m to 25 ⁇ m (for example, in the range of 4 ⁇ m to 15 ⁇ m).
- the second particle contains a lithium silicate phase and silicon particles dispersed in the lithium silicate phase.
- the lithium silicate phase may contain a lithium silicate represented by the formula Li 2Z SiO (2 + Z) (0 ⁇ Z ⁇ 2), or may be composed of the lithium silicate. Z preferably satisfies the relationship of 0 ⁇ Z ⁇ 1.
- the lithium silicate phase may be composed of lithium silicate in which 50% by mass or more (for example, 60% by mass or more) satisfies 0 ⁇ Z ⁇ 0.5.
- the second particle may contain at least one element Me dispersed in the lithium silicate phase.
- At least one element Me is at least one element selected from the group consisting of rare earth elements and alkaline earth metal elements. Examples of alkaline earth metal elements include Mg, Ca, Sr, Ba and the like.
- the element Me may be dispersed as a Me oxide in the lithium silicate phase.
- the Me oxide may contain at least one selected from the group consisting of yttrium oxide, cerium oxide, calcium oxide, and magnesium oxide.
- the lithium silicate phase may contain zirconium oxide. Then, the element Me may be dispersed in zirconium oxide.
- the amount of elemental Me contained in the second particle is calculated assuming that the elemental Me forms a stoichiometric oxide regardless of the state of the elemental Me or the type of compound of the elemental Me.
- the amount (estimated Me oxide amount) can be used as an index.
- the estimated amount of Me oxide may be in the range of 0.001% by mass to 1.0% by mass with respect to the total of the lithium silicate phase and the silicon particles. By setting the estimated Me oxide amount to 0.001% by mass or more, the effect of reducing the reaction area and improving the hardness of the lithium silicate phase is enhanced. On the other hand, by setting the estimated Me oxide amount to 1.0% by mass or less, the decrease in the initial capacity can be suppressed.
- the lithium silicate phase may contain a metal compound such as a metal oxide, a metal carbide, a metal nitride, or a metal boride.
- Suitable metal compounds are metal oxides and metal carbides. Among them, it is preferable to use at least one selected from the group consisting of zirconium oxide (ZrO2), aluminum oxide (Al2O3), zirconium carbide (ZrC), tungsten carbide (WC), and silicon carbide (SiC).
- the amount of the compound of the metal element other than the element Me is in the range of 0.005% by mass to 15% by mass (for example, in the range of 0.01% by mass to 10% by mass) with respect to the total of the lithium silicate phase and the silicon particles.
- the amount of the compound of the metal element it may be in the range of 0.01% by mass to 1% by mass).
- the amount calculated on the assumption that the metal element forms a stoichiometric oxide may be obtained as in the case of the content of the element Me.
- the average particle size of the second particles may be in the range of 1 ⁇ m to 25 ⁇ m (for example, in the range of 4 ⁇ m to 15 ⁇ m). In such a range, it is easy to relieve the stress due to the volume change of the second particle due to charge / discharge, and it is easy to obtain good cycle characteristics. Further, the surface area of the second particle becomes appropriate, and the volume decrease due to a side reaction with the non-aqueous electrolyte is suppressed.
- the crystallite size of the silicon particles dispersed in the lithium silicate phase is, for example, 10 nm or more.
- Silicon particles have a particulate phase of elemental silicon (Si).
- Si elemental silicon
- the crystallite size of the silicon particle is calculated by Scherrer's equation from the half width of the diffraction peak attributed to the Si (111) plane of the X-ray diffraction (XRD) pattern of the silicon particle.
- the average particle size of the silicon particles in the second particles may be preferably 500 nm or less (more preferably 200 nm or less, still more preferably 50 nm or less) before the initial charge. After the initial charge, the average particle size of the silicon particles is preferably 400 nm or less (more preferably 100 nm or less). By refining the silicon particles, the volume change during charging and discharging becomes small, and the structural stability of the second particles is further improved.
- the content of silicon particles (elemental Si) in the second particles is in the range of 20% by mass to 95% by mass (for example, in the range of 35% by mass to 75% by mass) from the viewpoint of increasing the capacity and improving the cycle characteristics. It is preferable to be in. According to this range, the diffusivity of lithium ions is also good, and it becomes easy to obtain excellent load characteristics. Further, the surface of the silicon particles exposed without being covered with the lithium silicate phase is reduced, and the side reaction between the non-aqueous electrolyte and the silicon particles is suppressed.
- the second particle may contain a conductive material that covers at least a part of its surface. Since the lithium silicate phase has poor electron conductivity, the conductivity of the second particle also tends to be low. By covering the surface with a conductive material, the conductivity can be dramatically improved. It is preferable that the conductive layer is thin enough not to affect the average particle size of the second particles.
- the thickness of the conductive layer may be in the range of 1 nm to 200 nm (for example, in the range of 5 nm to 100 nm) from the viewpoint of ensuring conductivity and diffusing lithium ions. An example of the material of the conductive layer and an example of the forming method will be described later.
- the third particle includes a carbon phase and silicon particles dispersed in the carbon phase.
- the carbon phase of the third particle may be composed of amorphous carbon (ie, amorphous carbon).
- the amorphous carbon may be hard carbon, soft carbon, or other carbon.
- Amorphous carbon (amorphous carbon) generally refers to a carbon material having an average plane spacing d002 of (002) planes measured by an X-ray diffraction method of more than 0.34 nm.
- the third particle contains a carbon phase and silicon particles dispersed in the carbon phase.
- the carbon phase of the third particle has conductivity. Therefore, even if a void is formed around the third particle, the contact point between the third particle and its surrounding is likely to be maintained. As a result, the capacity decrease due to repeated charge / discharge cycles is likely to be suppressed.
- the average particle size of the third particle may be 3 ⁇ m or more and 18 ⁇ m or less, 6 ⁇ m or more and 15 ⁇ m or less, or 8 ⁇ m or more and 12 ⁇ m or less.
- the content of the silicon particles in the third particle may be 30% by mass or more and 80% by mass or less, or 40% by mass or more and 70% by mass or less. In such a range, a sufficiently high capacity of the negative electrode can be achieved, and the cycle characteristics can be easily improved.
- the average particle size of the silicon particles in the third particle may be, for example, 1 nm or more. Further, the average particle size of the silicon particles may be 1000 nm or less, 500 nm or less, 200 nm or less, 100 nm or less (further, 50 nm or less). The finer the silicon particles, the smaller the volume change of the third particle during charging and discharging, and the better the structural stability of the third particle.
- composition of the second and third particles and the content of the components can be analyzed by the method described in International Publication No. 2018/1796969.
- the content of each element contained in the particles (P) may be measured by, for example, inductively coupled plasma emission spectroscopy (ICP-AES). Specifically, the particles (P) are dissolved in a heated acid solution, carbon in the solution residue is removed by filtration, and then the obtained filtrate is analyzed by ICP-AES to determine the spectral intensity of each element. taking measurement. Subsequently, a calibration curve is prepared using a commercially available standard solution of each element, and the content of each element is calculated.
- ICP-AES inductively coupled plasma emission spectroscopy
- the second particle and the third particle each have a so-called sea-island structure.
- the silicon particles (islands) in the second and third particles are dispersed in a matrix (sea) of silicate phase and carbon phase, respectively, and are covered with a lithium ion conduction phase (silicate phase and carbon phase). ..
- the contact between the silicon particles and the electrolyte is restricted, so that side reactions are suppressed.
- the stress generated by the expansion and contraction of the silicon particles is relaxed by the matrix of the lithium ion conductive phase.
- graphite examples include natural graphite, artificial graphite, graphitized mesophase carbon particles and the like.
- known graphite used as a negative electrode active material may be used.
- Graphite means a material having a developed graphite-type crystal structure, and generally refers to a carbon material having an average plane spacing d002 of (002) planes measured by an X-ray diffraction method of 0.340 nm or less.
- the average particle size of graphite (graphite particles) contained in the negative electrode as an active material may be 13 ⁇ m or more and 25 ⁇ m or less.
- the average particle size of graphite is preferably larger than the average particle size of the particles (P).
- the particles (P) existing in the voids contribute to the maintenance of electronic contact between the graphite particles.
- the entire negative electrode is unlikely to expand / contract, so that deterioration due to the charge / discharge cycle is unlikely to occur.
- the average particle size of each of the particles (P), the silicon particles in the particles (P), and graphite in the negative electrode active material layer was measured by observing the cross section of the negative electrode active material layer using SEM or TEM. You may. In that case, the average particle size is determined by arithmetically averaging the maximum diameters of any 100 particles.
- a median diameter (D 50 ) at which the cumulative volume becomes 50% in the volume-based particle size distribution can be used.
- the median diameter can be determined using, for example, a laser diffraction / scattering type particle size distribution measuring device.
- the first particle may be produced, for example, by the following method. First, particles having a composition of SiO (silicon monoxide) are pulverized and classified to adjust the particle size. Next, the surface of the obtained particles is coated with carbon by a CVD method under an argon atmosphere. Then, by crushing and classifying this, a first particle represented as SiO X is prepared. As a method for coating SiO X particles with carbon, various well-known methods can be adopted. Further, the process of coating the SiO X particles with carbon may be omitted.
- SiO silicon monoxide
- the second particle may be produced by a method other than the production method described below.
- the second particle may be produced by the method described in International Publication No. 2018/179969.
- the second particle is generally synthesized through two processes, a pre-step for obtaining lithium silicate and a post-step for obtaining the second particle from lithium silicate and the raw material silicon.
- the element Me may be added to the raw material of lithium silicate in the previous step, but it is preferable to add the element Me in the subsequent step so as not to affect the synthesis of lithium silicate.
- the method for producing the second particle is a step (i) of mixing silicon dioxide and a lithium compound and firing the obtained mixture to obtain lithium silicate, and lithium silicate and raw material silicon (i).
- Step (ii) of obtaining a second particle containing a lithium silicate phase and silicon particles dispersed in the lithium silicate phase by further compounding with the element Me), if necessary. .. [Step (i)]
- Formula: Li 2Z The Z value of the lithium silicate represented by SiO 2 + Z may be controlled by the atomic ratio of silicon to lithium in the mixture of silicon dioxide and the lithium compound: Li / Si. In order to synthesize a high-quality lithium silicate with less elution of alkaline components, it is preferable to make Li / Si smaller than 1.
- Lithium carbonate, lithium oxide, lithium hydroxide, lithium hydride, etc. can be used as the lithium compound. These may be used individually by 1 type and may be used in combination of 2 or more type.
- the mixture containing silicon dioxide and the lithium compound is preferably heated in air at 400 ° C. to 1200 ° C., preferably 800 ° C. to 1100 ° C. to react the silicon dioxide with the lithium compound.
- the lithium silicate and the raw material silicon are combined.
- the mixture may be pulverized while applying a shearing force to the mixture of lithium silicate and the raw material silicon (which may further contain the element Me).
- the raw material silicon coarse particles of silicon having an average particle size of several ⁇ m to several tens of ⁇ m may be used. It is preferable to control the finally obtained silicon particles so that the crystallite size calculated by Scherrer's equation from the half width of the diffraction peak attributed to the Si (111) plane of the XRD pattern is 10 nm or more. ..
- oxides, oxalates, nitrates, sulfates, halides, carbonates and the like of the element Me may be used.
- Me oxide is preferable because it is stable and has good ionic conductivity. More specifically, CeO 2 , Sc 2 O 3 , Y 2 O 3 , Er 2 O 3 , Tm 2 O 3 , Yb 2 O 3 , Lu 2 O 3 and the like can be mentioned.
- compounds containing elements other than the element Me and oxygen such as yttria-stabilized zirconia, may be used. These may be used individually by 1 type and may be used in combination of 2 or more type.
- lithium silicate, raw material silicon, and (if necessary, a compound of element Me) may be mixed at a predetermined mass ratio, and the mixture may be stirred while being atomized using a crushing device such as a ball mill.
- a crushing device such as a ball mill.
- the compounding process is not limited to this.
- silicon nanoparticles, lithium silicate nanoparticles, and (a compound of the element Me, if necessary) may be synthesized and mixed without using a pulverizer.
- the finely divided mixture is heated at 450 ° C. to 1000 ° C. in an inert atmosphere (for example, an atmosphere of argon, nitrogen, etc.) and calcined.
- a sintered body of the mixture may be produced by firing while applying pressure to the mixture by hot pressing or the like.
- Lithium silicate is stable at 450 ° C to 1000 ° C and hardly reacts with silicon, so that the capacity decrease is slight even if it occurs.
- the silicate softens and flows to fill the gaps between the silicon particles. As a result, it is possible to obtain a dense block-shaped sintered body having the silicate phase as the sea portion and the silicon particles as the island portion.
- the sintered body may then be pulverized until it becomes granular to form second particles.
- the second particles having the average particle size in the above-mentioned range can be obtained.
- a step (iii) may be performed in which at least a part of the surface of the second particle is covered with a conductive material to form a conductive layer.
- the conductive material is preferably electrochemically stable, and preferably a carbon material.
- a CVD method using a hydrocarbon gas such as acetylene or methane as a raw material may be used.
- a method of mixing coal pitch, petroleum pitch, phenol resin, or the like with the second particles and then heating them may be used. Further, carbon black may be attached to the surface of the second particle.
- the step of washing the second particles with acid may be performed.
- the second particle may be washed with an acidic aqueous solution.
- an acidic aqueous solution By washing with an acid, a trace amount of a component such as Li2SiO3 that may occur when the raw material silicon and the lithium silicate are combined can be dissolved and removed.
- an aqueous solution of an inorganic acid such as hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, phosphoric acid or carbon dioxide, or an aqueous solution of an organic acid such as citric acid or acetic acid can be used.
- the third particle may be produced by a method other than the production method described below.
- the raw material silicon and the carbon source are mixed, and the mixture of the raw material silicon and the carbon source is crushed and compounded while being made into fine particles by using a crushing device such as a ball mill.
- An organic solvent may be added to the mixture and wet pulverized.
- the raw material silicon is finely pulverized to generate silicon particles.
- the silicon particles are dispersed in a matrix of carbon sources.
- Examples of the carbon source include water-soluble resins such as carboxymethyl cellulose (CMC), hydroxyethyl cellulose, polyacrylic acid salt, polyacrylamide, polyvinyl alcohol, polyethylene oxide and polyvinylpyrrolidone, sugars such as cellulose and sucrose, petroleum pitch, and coal pitch. , Tar and the like can be used, but are not particularly limited.
- CMC carboxymethyl cellulose
- hydroxyethyl cellulose polyacrylic acid salt
- polyacrylamide polyvinyl alcohol
- polyethylene oxide and polyvinylpyrrolidone sugars such as cellulose and sucrose
- petroleum pitch and coal pitch.
- Tar and the like can be used, but are not particularly limited.
- organic solvent alcohol, ether, fatty acid, alkane, cycloalkane, silicic acid ester, metal alkoxide and the like can be used.
- the composite of silicon particles and a carbon source is heated to 700 ° C to 1200 ° C in an inert gas atmosphere (for example, an atmosphere of argon, nitrogen, etc.).
- an inert gas atmosphere for example, an atmosphere of argon, nitrogen, etc.
- This heating carbonizes the carbon source to produce amorphous carbon.
- a third particle in which silicon particles are dispersed in a carbon phase containing amorphous carbon is obtained.
- the raw material silicon and the carbon material are mixed, and the mixture of the raw material silicon and the carbon material is pulverized and composited by using a pulverizing device such as a ball mill.
- An organic solvent may be added to the mixture and wet pulverized.
- the raw material silicon is finely pulverized to generate silicon particles. Silicon particles are dispersed in a matrix of carbon materials.
- a third particle in which silicon particles are dispersed in the carbon phase of amorphous carbon can be obtained.
- the third particle may then be heated to 700 ° C. to 1200 ° C. in an inert gas atmosphere.
- amorphous carbon is preferable, and graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon black and the like can be used.
- carbon black include acetylene black and ketjen black. Even when graphite is used as the carbon material, the crystal structure of graphite is almost lost when a composite of silicon particles and the carbon material is obtained by using a pulverizer, and a carbon phase of amorphous carbon is formed.
- the secondary battery (S) includes, for example, an exterior body (battery case) and a positive electrode, a negative electrode, an electrolyte, and a separator arranged inside the exterior body.
- the separator is arranged between the positive electrode and the negative electrode.
- the shape of the secondary battery (S) is not limited, and may be cylindrical, square, coin-shaped, button-shaped, or the like.
- the battery case is selected according to the shape of the secondary battery (S).
- the negative electrode includes a first layer containing a negative electrode active material.
- the negative electrode comprises a negative electrode current collector and a first layer disposed on the surface of the negative electrode current collector.
- the first layer may be a negative electrode active material layer (negative electrode mixture layer).
- the first layer contains the negative electrode active material and the flame retardant (R), and if necessary, contains other components other than the negative electrode active material and the flame retardant (R). Examples of other components include binders, conductive agents, thickeners and the like. As those other components, components used in known secondary batteries may be used.
- the first layer may contain carbon nanotubes as a conductive material.
- the first layer may have a laminated structure of a second layer (negative electrode active material layer) containing at least a negative electrode active material and a third layer (flame retardant layer) containing at least a flame retardant (R).
- the third layer is arranged on the surface of the second layer on the side not facing the negative electrode current collector.
- the second layer contains the negative electrode active material and, if necessary, other components. Examples of other components include conductive materials, binders, thickeners and the like. As those other components, components used in known secondary batteries may be used.
- both the second layer and the third layer may contain a flame retardant.
- the flame retardant contained in the second layer the compound listed as the above-mentioned flame retardant (R) may be used, or a known flame retardant other than the flame retardant (R) may be used.
- the flame retardant contained in the second layer is preferably a flame retardant (R) containing a halogen atom, like the flame retardant contained in the third layer.
- the flame retardant (R) contained in the second layer is a compound different from the flame retardant (R) contained in the third layer. It may be the same compound.
- a negative electrode slurry in which a negative electrode mixture is dispersed in a dispersion medium is applied to the surface of a negative electrode current collector to form a coating film, and then the coating film is dried. It can be formed by letting it. The dried coating film may be rolled if necessary.
- the dispersion medium include water, alcohol, ether, N-methyl-2-pyrrolidone (NMP), and a mixed solvent thereof.
- the ratio of the components in the negative electrode mixture can be adjusted by changing the mixing ratio of the materials of the negative electrode mixture.
- binder examples include fluororesin, polyolefin resin, polyamide resin, polyimide resin, vinyl resin, styrene-butadiene copolymer rubber (SBR), polyacrylic acid and derivatives thereof.
- conductive agents include carbon black, conductive fibers, carbon fluoride, organic conductive materials and the like.
- thickeners include carboxymethyl cellulose (CMC), polyvinyl alcohol and the like. For these components, one kind of material may be used alone, or two or more kinds of materials may be used in combination.
- the content ratio of the negative electrode active material in the negative electrode active material layer is obtained from the sample obtained by extracting only the negative electrode active material layer from the secondary battery in the discharged state. Specifically, first, the discharged secondary battery is disassembled and the negative electrode is taken out. Next, the negative electrode is washed with an organic solvent, further vacuum dried, and then only the negative electrode active material layer is peeled off to obtain a sample. By performing thermal analysis such as TG-DTA on the sample, the ratio of the binder component and the conductive material component other than the negative electrode active material can be calculated.
- the ratio of the flame retardant (R) to the negative electrode active material layer can be obtained by elemental analysis such as fluorescent X-ray analysis (XRF) for the negative electrode active material layer.
- Another aspect of the present disclosure relates to the negative electrode mixture constituting the first layer or the second layer as the negative electrode active material layer.
- Yet another aspect of the present disclosure relates to a negative electrode for a secondary battery having the first layer containing at least a negative electrode active material and a flame retardant (R).
- the first layer or the second layer as the negative electrode active material layer may further contain carbon nanotubes.
- the carbon nanotubes can be contained in the negative electrode active material layer as a conductive agent. Since carbon nanotubes have an extremely large aspect ratio (ratio of length to diameter), they can exhibit high conductivity even in a small amount. By using carbon nanotubes as the conductive material, it is possible to increase the proportion of the negative electrode active material in the negative electrode active material layer while maintaining high conductivity of the negative electrode active material layer. Therefore, the capacity of the secondary battery (S) can be increased.
- the first layer or the second layer as the negative electrode active material layer can contain at least one conductive carbon material selected from the group consisting of amorphous carbon and carbon fibers, in addition to carbon nanotubes.
- Amorphous carbon includes hard carbon and soft carbon.
- soft carbon include carbon blacks such as acetylene black and ketjen black. A plurality of kinds of these materials may be combined and used as a conductive material.
- the negative electrode active material layer may or may not contain a conductive material other than carbon nanotubes.
- the negative electrode active material layer preferably contains carbon black as a conductive material other than the carbon nanotubes in addition to the carbon nanotubes. However, if they are contained in a large amount, the ratio of the negative electrode active material to the negative electrode active material layer decreases. Therefore, the mass of the conductive material contained in the negative electrode active material layer other than the carbon nanotubes is 10 times or less (for example, 0 to 5 times, 0 to 1 times) the mass of the carbon nanotubes contained in the negative electrode active material layer. , Or in the range of 0 to 0.5 times).
- carbon nanotubes examples include carbon nanofibers. Since various carbon nanotubes are commercially available, commercially available carbon nanotubes may be used. Alternatively, the carbon nanotubes may be synthesized by a known synthesis method.
- the carbon nanotube may be a single layer (Single Wall), a double layer (Double Wall), or a multilayer (Multi Wall).
- Single-walled carbon nanotubes are preferable because they can obtain a large effect with a small amount.
- Carbon nanotubes having a diameter of 5 nm or less contain a large amount of single-walled carbon nanotubes.
- the single-walled carbon nanotubes may be 50% by mass or more of the total carbon nanotubes.
- the diameter of the carbon nanotube is not particularly limited and may be in the range of 0.001 to 0.05 ⁇ m.
- the length of the carbon nanotubes is not particularly limited, but may be 0.5 ⁇ m or more from the viewpoint of ensuring electron conduction in the negative electrode active material layer.
- the particle size of the negative electrode active material is generally 1 ⁇ m or more and 25 ⁇ m or less
- the length of the carbon nanotubes may be about the same. That is, the length of the carbon nanotubes may be, for example, 1 ⁇ m or more and 25 ⁇ m or less.
- the length of 50% or more (number ratio) of the carbon nanotubes may be 1 ⁇ m or more. It may be 1 ⁇ m or more and 25 ⁇ m or less.
- the length of 80% or more of the carbon nanotubes may be 1 ⁇ m or more, or 1 ⁇ m or more and 20 ⁇ m or less.
- the outer diameter and length of carbon nanotubes can be determined by image analysis using a scanning electron microscope (SEM).
- SEM scanning electron microscope
- the length is determined by arbitrarily selecting a plurality of (for example, 100 to 1000) carbon nanotubes, measuring the length and diameter, and averaging them.
- the negative electrode current collector As the negative electrode current collector, a non-perforated conductive substrate (metal foil, etc.) and a porous conductive substrate (mesh body, net body, punching sheet, etc.) are used. Examples of the material of the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy.
- Negative electrode active material a material capable of electrochemically occluding and releasing lithium ions is preferably used. Examples of such materials include carbonaceous materials and Si-containing materials. As the negative electrode active material, one type may be used alone, or two or more types may be used in combination.
- carbonaceous materials examples include graphite, graphitizable carbon (soft carbon), and non-graphitizable carbon (hard carbon).
- the carbonaceous material one kind may be used alone, or two or more kinds may be used in combination.
- Graphite is particularly preferable as the carbonaceous material because it has excellent charge / discharge stability and has a small irreversible capacity.
- Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.
- known graphite used as a negative electrode active material may be used.
- Si-containing material examples include Si alone, a silicon alloy, a silicon compound (silicon oxide, etc.), and a composite material in which a silicon phase is dispersed in a lithium ion conductive phase (matrix).
- silicon oxide examples include SiO X particles.
- X is, for example, 0.5 ⁇ X ⁇ 2, and may be 0.5 ⁇ X ⁇ 1.6 or 0.8 ⁇ X ⁇ 1.6.
- the lithium ion conducting phase at least one selected from the group consisting of a SiO 2 phase, a silicate phase and a carbon phase can be used.
- the negative electrode active material may contain a plurality of types of particles selected from the group consisting of the first particle, the second particle, and the third particle.
- the particles (P) may be composed of two types of particles selected from them, or may include all three types of particles.
- the negative electrode active material may contain a first particle and a second particle, a first particle and a third particle, and a second particle and a third particle. It may contain particles.
- the negative electrode active material may include all of the first, second, and third particles.
- the particles (P) are preferably used as a negative electrode active material in combination with graphite.
- the content of the particles (P) in the negative electrode active material may be 1% by mass or more. According to this configuration, it is possible to increase the capacity as compared with the case where the negative electrode active material is only graphite.
- the content of the particles (P) in the negative electrode active material may be 3% by mass or more.
- the content may be 50% by mass or less.
- the graphite content in the negative electrode active material may be in the range of 50 to 99% by mass.
- the particles (P) contain graphite on the surface and / or inside, the graphite is not included in the graphite content.
- the graphite content is the graphite content not contained in the particles (P).
- the positive electrode contains a positive electrode mixture.
- the positive electrode includes a positive electrode current collector and a positive electrode active material layer (positive electrode mixture layer) formed on the surface of the positive electrode current collector.
- the positive electrode mixture layer can be formed by applying a positive electrode slurry in which a positive electrode mixture is dispersed in a dispersion medium to the surface of a positive electrode current collector and drying it. The dried coating film may be rolled if necessary.
- the positive electrode mixture contains a positive electrode active material as an essential component, and may contain a binder, a conductive agent, and the like as optional components.
- a lithium composite metal oxide can be used as the positive electrode active material.
- the lithium composite metal oxide include Li a CoO 2 , Li a NiO 2 , Li a MnO 2 , Li a Co b Ni 1-b O 2 , Li a Co b M 1-b O c , and Li a Ni.
- Examples thereof include 1-b M b O c , Li a Mn 2 O 4 , Li a Mn 2-b M b O 4 , Li GPO 4 , and Li 2 GPO 4 F.
- M is at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B.
- G contains at least a transition element (eg, includes at least one selected from the group consisting of Mn, Fe, Co, Ni).
- a transition element eg, includes at least one selected from the group consisting of Mn, Fe, Co, Ni.
- the a value indicating the molar ratio of lithium increases or decreases depending on charging and discharging.
- the binder and the conductive agent the same ones as those exemplified for the negative electrode can be used.
- the conductive agent graphite such as natural graphite or artificial graphite may be used.
- the shape and thickness of the positive electrode current collector can be selected from the shape and range according to the negative electrode current collector.
- Examples of the material of the positive electrode current collector include stainless steel, aluminum, aluminum alloy, and titanium.
- an electrolytic solution containing a solvent and a solute dissolved in the solvent can be used.
- the solute is an electrolyte salt that ionically dissociates in the electrolytic solution.
- the solute may include, for example, a lithium salt.
- the components of the electrolytic solution other than the solvent and solute are additives.
- the electrolytic solution may contain various additives.
- a non-aqueous solvent is used as the solvent.
- a cyclic carbonate ester for example, a chain carbonate ester, a cyclic carboxylic acid ester, a chain carboxylic acid ester and the like are used.
- the cyclic carbonic acid ester include propylene carbonate (PC), ethylene carbonate (EC), vinylene carbonate (VC) and the like.
- the chain carbonate ester include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) and the like.
- the cyclic carboxylic acid ester include ⁇ -butyrolactone (GBL) and ⁇ -valerolactone (GVL).
- chain carboxylic acid ester examples include methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP) and the like.
- non-aqueous solvent one type may be used alone, or two or more types may be used in combination.
- non-aqueous solvent examples include cyclic ethers, chain ethers, nitriles such as acetonitrile, and amides such as dimethylformamide.
- lithium salt examples include a lithium salt of a chlorine-containing acid (LiClO 4 , LiAlCl 4 , LiB 10 Cl 10 , etc.) and a lithium salt of a fluorine-containing acid (LiPF 6 , LiPF 2 O 2 , LiBF 4 , LiSbF 6 , LiAsF 6 ).
- LiN (FSO 2 ) 2 LiN (CF 3 SO 2 ) 2 , LiN (CF 3 SO 2 ) (C 4 F 9 SO) 2 ), LiN (C 2 F 5 SO 2 ) 2 , etc.
- lithium halide LiCl, LiBr, LiI, etc.
- the lithium salt one kind may be used alone, or two or more kinds may be used in combination.
- the concentration of the lithium salt in the electrolytic solution may be 1 mol / liter or more and 2 mol / liter or less, or 1 mol / liter or more and 1.5 mol / liter or less.
- the lithium salt concentration is not limited to the above.
- the electrolytic solution may contain other known additives.
- the additive include 1,3-propanesarton, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, fluorobenzene and the like.
- a separator may be arranged between the positive electrode and the negative electrode.
- a member having high ion permeability and having appropriate mechanical strength and insulating property can be applied.
- a microporous thin film, a woven fabric, a non-woven fabric, or the like can be used.
- polyolefins such as polypropylene and polyethylene are preferable.
- An example of the secondary battery (S) includes an exterior body, an electrode group housed in the exterior body, and a non-aqueous electrolyte.
- the structure of the electrode group is not particularly limited.
- An example of the electrode group is formed by winding the positive electrode, the negative electrode, and the separator so that the separator is arranged between the positive electrode and the negative electrode.
- Another example of the electrode group is formed by laminating the positive electrode, the negative electrode, and the separator so that the separator is arranged between the positive electrode and the negative electrode.
- the form of the secondary battery (S) is not limited, and may be a cylindrical shape, a square shape, a coin shape, a button shape, a laminated shape, or the like.
- the manufacturing method of the secondary battery (S) is not particularly limited, and a known manufacturing method may be applied, or at least a part of the known manufacturing method may be modified and applied.
- FIG. 1 is a cross-sectional view showing a configuration example of a negative electrode (negative electrode for a secondary battery) 2 constituting the secondary battery according to the embodiment of the present disclosure.
- the negative electrode active material layer (second layer) 21 is arranged on the surface of the negative electrode current collector 20, and the flame retardant layer (third layer) 22 is arranged on the surface of the negative electrode active material layer 21.
- the flame retardant layer 22 contains the flame retardant (R).
- FIG. 1 is an example in which the flame retardant layer 22 is formed so as to cover the entire surface of the negative electrode active material layer 21.
- FIG. 2 is a schematic perspective view in which a part of the square secondary battery according to the embodiment of the present disclosure is cut out.
- the secondary battery 1 shown in FIG. 2 includes a bottomed square battery case 11, an electrode group 10 housed in the battery case 11, and an electrolyte (not shown).
- the electrode group 10 includes a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator that is interposed between them and prevents direct contact.
- the electrode group 10 is formed by winding a negative electrode, a positive electrode, and a separator around a flat plate-shaped winding core and pulling out the winding core.
- One end of the negative electrode lead 15 is attached to the negative electrode current collector of the negative electrode by welding or the like.
- One end of the positive electrode lead 14 is attached to the positive electrode current collector of the positive electrode by welding or the like.
- the other end of the negative electrode lead 15 is electrically connected to the negative electrode terminal 13 provided on the sealing plate 12.
- a gasket 16 is arranged between the sealing plate 12 and the negative electrode terminal 13 to insulate them.
- the other end of the positive electrode lead 14 is connected to the sealing plate 12 and electrically connected to the battery case 11 that also serves as the positive electrode terminal.
- a resin frame 18 is arranged on the upper part of the electrode group 10.
- the frame body 18 separates the electrode group 10 and the sealing plate 12, and also separates the negative electrode lead 15 and the battery case 11.
- the opening of the battery case 11 is sealed with a sealing plate 12.
- a liquid injection hole 17a is formed in the sealing plate 12. The electrolyte is injected into the battery case 11 from the injection hole 17a. After that, the liquid injection hole 17a is
- the secondary battery according to the present disclosure will be described in more detail by way of examples.
- Example 1 a plurality of types of secondary batteries were prepared and evaluated by the following procedure.
- the plurality of types of secondary batteries differ in the type of flame retardant and / or the ratio of substances in the negative electrode mixture layer.
- Graphite was used as the negative electrode active material.
- a negative electrode active material sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), water, and if necessary, a flame retardant were mixed at a predetermined mass ratio to prepare a negative electrode slurry. ..
- a coating film was formed by applying a negative electrode slurry to the surface of a copper foil (negative electrode current collector). The coating film was dried and then rolled. In this way, the negative electrode mixture layer was formed on both sides of the copper foil.
- LiNi 0.88 Co 0.09 Al 0.03 O 2 was used as the positive electrode active material.
- a positive electrode slurry was prepared by mixing the positive electrode active material, polyvinylidene fluoride, N-methyl-2-pyrrolidone (NMP), and acetylene black in a predetermined mass ratio.
- a positive electrode slurry was applied to the surface of the aluminum foil (positive electrode current collector) to form a coating film. After the coating film was dried, it was rolled to form a positive electrode mixture layer on both sides of the aluminum foil.
- LiPF 6 was added as a lithium salt to a mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3: 7, to prepare an electrolytic solution.
- the concentration of LiPF 6 in the non-aqueous electrolytic solution was 1.3 mol / liter.
- a lead tab was attached to each electrode.
- the positive electrode and the negative electrode were spirally wound via the separator so that the lead was located at the outermost peripheral portion.
- the electrode group was prepared in this way.
- the electrode group was inserted into the exterior body made of a laminated film having an aluminum foil as a barrier layer, and vacuum dried.
- a non-aqueous electrolytic solution was injected into the exterior body to seal the opening of the exterior body. In this way, a secondary battery was obtained.
- a plurality of secondary batteries (batteries A1 to A12, B1, B2, C1) were manufactured by changing the type of the flame retardant and the ratio of the substances in the negative electrode mixture layer.
- the batteries B1 and B2 are comparative examples, and a flame retardant different from the flame retardant (R) containing a halogen atom was added.
- Battery C1 is a reference example, and no flame retardant was added.
- the ratio of substances was changed by changing their mixing ratio when preparing the negative electrode slurry. Some of these ratios are shown in Table 1 below. The types of flame retardants will be described later.
- the discharge capacity of the manufactured secondary battery was measured by the following method. First, in an environment of 25 ° C., the battery was charged with a constant current of 0.5 CA until the battery voltage reached 4.2 V, and then charging was continued at a constant voltage until the current value reached 0.02 CA. After leaving the charged battery for 20 minutes, the battery was discharged at a constant current of 1.0 CA until the battery voltage reached 2.5 V. Then, it was left for 20 minutes. This operation (charging / discharging cycle) was repeated 100 times.
- Capacity retention rate (%) 100 x DC1 / DC0
- the measurement of the current value I of the short-circuit current and the measurement of the voltage V of the battery were continued for 1 second after the battery was short-circuited by the round nail. Then, the amount of heat generated per second was obtained by integrating the product (electric power) of the current value I and the voltage V over time.
- Table 1 shows some of the battery manufacturing conditions and the evaluation results.
- the a value (mass ratio) indicating the content of the flame-retardant agent indicates the mass of the flame-retardant agent when the mass of the negative electrode active material in the negative electrode active material layer is 100.
- the flame retardant r1 represents ethylene-1,2-bispentabromophenyl (SAYTEX®-8010 manufactured by Albemarle Japan Co., Ltd.).
- the flame retardant r2 shows ethylene bistetrabromophthalimide (halogen atom content 67% by mass).
- the flame retardant r3 indicates potassium citrate.
- the batteries A1 to A12 to which the flame retardant (R) was added the calorific value at the time of the nail piercing test was reduced with respect to the battery C1, and the decrease in the initial capacity and the capacity retention rate was suppressed. That is, the batteries A1 to A12 can reduce the amount of heat generated, and can achieve both high charge / discharge performance and high safety.
- the initial capacity and the capacity retention rate equal to or higher than those of the battery C1 to which the flame retardant was not added were obtained.
- the batteries A3, A4, A9, and A10 having an a value of 1 or more and less than 5 maintained the same initial capacity as the battery C1 while obtaining a remarkably low calorific value, and the capacity retention rate was improved as compared with the battery C1.
- the discharge capacity drops to about 70% of the initial capacity after 70 charge / discharge cycles, and the capacity retention rate after 100 charge / discharge cycles drops to almost 0%. I could't discharge.
- the decrease in the initial capacity and the capacity retention rate was suppressed even when compared with the battery C1. Therefore, when the flame retardant (R) was contained in the negative electrode active material layer, the function as a battery could be maintained even after 100 cycles of charging and discharging.
- Example 2 In this example, a plurality of non-aqueous electrolyte secondary batteries were prepared and evaluated. A non-aqueous electrolyte secondary battery was manufactured by the following procedure.
- the negative electrode active material graphite or a mixture of graphite and particles (P) was used.
- a negative electrode active material sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), water, and if necessary, a flame retardant were mixed at a predetermined mass ratio to prepare a negative electrode slurry. ..
- a coating film was formed by applying a negative electrode slurry to the surface of a copper foil (negative electrode current collector). The coating film was dried and then rolled. In this way, the negative electrode mixture layer was formed on both sides of the copper foil.
- the first particle was prepared by the following method. First, particles having a composition of SiO (silicon monoxide) were pulverized and classified to adjust the particle size. Next, the surface of the obtained particles was coated with carbon by a CVD method under an argon atmosphere. Then, by crushing and classifying this, a first particle represented as SiO X was prepared.
- SiO silicon monoxide
- the second particle was prepared by the following method. First, silicon dioxide and lithium carbonate are mixed so that the atomic ratio: Si / Li is 1.05, and the mixture is calcined in air at 950 ° C. for 10 hours, thereby being represented by the formula: Li 2 Si 2 O 5 . Obtained a lithium silicate. The obtained lithium silicate was pulverized so as to have an average particle size of 10 ⁇ m.
- the obtained lithium silicate, raw material silicon (3N, average particle size 10 ⁇ m), and yttrium oxide (Y2O3) were mixed at a mass ratio of 50:50: 0.0005.
- the mixture was milled at 200 rpm for 50 hours.
- the powdery mixture was taken out in the inert atmosphere and fired at 800 ° C. for 4 hours in a state where pressure was applied by a hot press machine in the inert atmosphere to obtain a sintered body (mother particles) of the mixture. Obtained.
- the sintered body was crushed, passed through a mesh of 40 ⁇ m, mixed with coal pitch (MCP250 manufactured by JFE Chemical Co., Ltd.), and the mixture was fired at 800 ° C. in an inert atmosphere to obtain the crushed particles.
- the surface was coated with conductive carbon to form a conductive layer.
- the coating amount of the conductive layer was 5% by mass of the total mass of the crushed particles.
- a sieve was used to obtain second particles having a conductive layer and having an average particle size of 5 ⁇ m.
- a positive electrode was prepared and an electrolytic solution was prepared in the same manner as in Example 1.
- a lead tab was attached to each electrode.
- the positive electrode and the negative electrode were spirally wound via a separator so that the lead was located at the outermost peripheral portion to prepare an electrode group having a substantially elliptical cross section.
- the electrode group was housed in a bottomed square aluminum battery case having an opening.
- a rectangular sealing plate having a negative electrode terminal surrounded by a gasket in the center was placed in the opening of the battery case. After connecting the negative electrode lead to the negative electrode terminal and the positive electrode lead to the lower surface of the sealing plate, the end of the opening and the sealing plate were welded by a laser to seal the opening of the battery case.
- the non-aqueous electrolyte was injected into the battery case through the liquid injection hole of the sealing plate.
- the square non-aqueous electrolyte secondary battery (theoretical capacity 3000 mAh) shown in FIG. 2 was produced.
- the capacity retention rate was measured and a nail piercing test was performed on the produced non-aqueous electrolyte secondary battery in the same manner as in Example 1.
- the nail piercing test instead of deriving the calorific value, the surface temperature of the battery was measured 1 minute after the battery was internally short-circuited.
- a plurality of secondary batteries (batteries A13, A14, C2 to C5) were produced by changing the type of flame retardant, the type of negative electrode active material, and the ratio of the substances in the negative electrode mixture layer.
- the batteries C2 to C5 are comparative examples of batteries.
- the ratio of substances was changed by changing their mixing ratio when preparing the negative electrode slurry. Some of these ratios are shown in Table 2 below. The types of flame retardants will be described later.
- Table 2 shows some of the battery manufacturing conditions and the evaluation results.
- the content of the particles (P) in Table 2 is the content of the particles (P) in the negative electrode active material.
- the content of the flame retardant in Table 2 is the content of the flame retardant in the negative electrode mixture layer.
- the flame retardant R1 represents ethylene-1,2-bispentabromophenyl (SAYTEX®-8010 manufactured by Albemarle Japan Co., Ltd.).
- the flame retardant R2 represents ammonium polyphosphate.
- the battery temperature shown in Table 1 is low. Further, it is preferable that the capacity retention rate is high. As is clear when comparing C2, C3, and C5, when the negative electrode active material contains particles (P), the battery temperature during the nail piercing test is greatly increased. On the other hand, even when the negative electrode active material contains particles (P), the increase in battery temperature during the nail piercing test can be suppressed by adding the flame retardant to the negative electrode mixture layer.
- Example 3 a plurality of secondary batteries were prepared and evaluated by the following procedure.
- the negative electrode active material a mixture of graphite and particles (P) was used.
- a negative electrode active material sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), carbon nanotubes (CNT), and water were mixed at a predetermined mass ratio to prepare a negative electrode slurry.
- the carbon nanotubes used had an average diameter of about 1.5 nm and a length of about 1 ⁇ m to 5 ⁇ m.
- a coating film was formed by applying a negative electrode slurry to the surface of a copper foil (negative electrode current collector). The coating film was dried and then rolled. In this way, the negative electrode active material layer (second layer) was formed on both sides of the copper foil.
- the flame retardant (R), polyvinylidene fluoride (PVdF), and N-methyl-2-pyrrolidone (NMP) were mixed at a predetermined mass ratio to prepare a slurry for the flame retardant layer.
- the obtained slurry was applied to the surface of the negative electrode active material layer and dried to form a flame retardant layer (third layer).
- the flame retardant (R) ethylene-1,2-bispentabromophenyl (SAYTEX®-8010 manufactured by Albemarle Japan Co., Ltd.) was used.
- the basis weight of the flame retardant layer was adjusted to 3 g / m 2 . In this way, a negative electrode having a first layer having a second layer and a third layer formed on the negative electrode current collector was obtained.
- the particles (P) the first particles and / or the second particles produced by the same method as in Example 2 were used.
- a square non-aqueous electrolyte secondary battery (theoretical capacity 3000 mAh) shown in FIG. 2 was produced in the same manner as in Example 2, and secondary batteries A15, A16, C6, and C7 were obtained.
- a negative electrode was prepared, and a secondary battery was obtained.
- the particles (P) a mixture of the first particle and the second particle in a mass ratio of 1: 1 was used.
- a negative electrode was prepared in the same manner as in Example 1 and a secondary battery was obtained. As the particle (P), only the second particle was used.
- a negative electrode was produced in the same manner as in the secondary battery A15 except that the flame retardant layer (third layer) was not formed, and a secondary battery was obtained.
- a negative electrode was produced in the same manner as in the secondary battery A16 except that the flame retardant layer (third layer) was not formed, and a secondary battery was obtained.
- Table 3 shows some of the battery manufacturing conditions and the evaluation results. From Table 1, the higher the content of the particles (P), the easier it is for the temperature to rise after the nail piercing test. However, in the batteries A15 and A16 in which the third layer containing the above-mentioned flame retardant (R) is provided on the surface of the negative electrode active material layer (second layer), a relatively small basis weight of about 3 g / m 2 is sufficient. The effect of suppressing the temperature rise can be obtained.
- Example 4 a plurality of secondary batteries were prepared and evaluated by the following procedure.
- the negative electrode active material a mixture of graphite and particles (P) was used.
- a negative electrode active material sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), carbon nanotubes (CNT), and water were mixed at a predetermined mass ratio to prepare a negative electrode slurry.
- the carbon nanotubes used had an average diameter of about 1.5 nm and a length of about 1 ⁇ m to 5 ⁇ m.
- a coating film was formed by applying a negative electrode slurry to the surface of a copper foil (negative electrode current collector). The coating film was dried and then rolled.
- the negative electrode active material layer (second layer) was formed on both sides of the copper foil.
- the flame retardant (R), polyvinylidene fluoride (PVdF), N-methyl-2-pyrrolidone (NMP), and if necessary, alumina particles ( Al2O3 ) are added in a predetermined mass ratio.
- Mixing was performed to prepare a slurry for the flame retardant layer.
- the obtained slurry was applied to the surface of the negative electrode active material layer and dried to form a flame retardant layer (third layer).
- the second particles produced by the same method as in Example 2 were used.
- a non-aqueous electrolyte secondary battery (theoretical capacity of 100 mAh) was produced in the same manner as in Example 1.
- a plurality of secondary batteries (batteries A17 to A20, C8) were produced by changing the type of the flame retardant contained in the flame retardant layer (third layer) and the ratio of the substances in the flame retardant layer.
- the battery C8 was a comparative example battery and was not provided with a flame retardant layer.
- the proportions of the substances in the flame retardant layer were varied by varying their mixing ratio when preparing the slurry for the flame retardant layer. Some of these ratios are shown in Table 4 below. The types of flame retardants will be described later.
- the battery temperature after the nail piercing test was measured in the same manner as in Example 3.
- Table 4 shows some of the battery manufacturing conditions and the evaluation results.
- the contents of the flame retardant and the binder in Table 4 indicate the contents of the flame retardant and the binder (PVdF) in the slurry for the flame retardant layer, respectively.
- the flame retardant r1 represents ethylene-1,2-bispentabromophenyl (SAYTEX®-8010 manufactured by Albemarle Japan Co., Ltd.).
- the flame retardant r2 represents ethylene bistetraphthalimide.
- the battery A19 corresponds to a battery A17 in which the content of the flame retardant is reduced by replacing a part of the flame retardant contained in the flame retardant layer with alumina particles, and the temperature is sufficient even if the flame retardant content is 60%. The effect of suppressing the rise can be obtained.
- Non-aqueous electrolyte secondary battery 10: Electrode group, 11: Battery case, 12: Seal plate, 13: Negative terminal, 14: Positive lead, 15: Negative lead, 16: Gasket, 17: Seal, 17a: Injection hole, 18: frame, 20: negative electrode current collector, 21: negative electrode active material layer (second layer), 22: flame retardant layer (third layer)
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Abstract
Description
本発明の新規な特徴を添付の請求の範囲に記述するが、本発明は、構成および内容の両方に関し、本発明の他の目的および特徴と併せ、図面を照合した以下の詳細な説明によりさらによく理解されるであろう。
本実施形態に係る二次電池は、正極および負極を含む。負極は、負極活物質を含む第1層を含む。第1層は、通常、負極集電体の表面に配置される。第1層は、負極活物質に加えて、ハロゲン原子を含む難燃剤をさらに含む。第1層は、カーボンナノチューブをさらに含んでもよい。当該難燃剤およびハロゲン原子をそれぞれ、以下では「難燃剤(R)」および「ハロゲン原子(Ha)」と称する場合がある。また、本実施形態に係る二次電池を、以下では「二次電池(S)」と称する場合がある。二次電池(S)は、非水電解質二次電池であってもよい。
負極活物質は、粒子(P)と黒鉛とを含む。粒子(P)は、上述した第1の粒子、第2の粒子、および、第3の粒子からなる群より選択される少なくとも一種の粒子である。
負極活物質は、金属リチウムを含む。
粒子(P)が、第1の粒子、第2の粒子、および、第3の粒子からなる群より選択される複数種の粒子を含む場合、複数種の粒子の少なくとも一つの負極活物質における含有率が1質量%以上であってもよい。
難燃剤(R)は、高温時にハロゲン原子(Ha)を放出することによって難燃効果を発現する。そのため、二次電池(S)によれば、異常時における過剰な発熱を抑制できる。
(1)難燃剤(R)は、ハロゲン原子(Ha)が結合した環状構造を含む。当該環状構造は、芳香環であってもよいし、芳香環でなくてもよい。この場合、すべてのハロゲン原子(Ha)が環状構造に結合していてもよいし、一部のハロゲン原子(Ha)のみが環状構造に結合していてもよい。ハロゲン原子(Ha)が環状構造に結合している構造は、ハロゲン原子の含有率を高めやすい点で好ましい。
(2)難燃剤(R)に占めるハロゲン原子(Ha)の割合は45質量%以上である。この割合は、60質量%以上(例えば70質量%以上)であってもよい。上限に特に限定はないが、95質量%以下(例えば90質量%以上)であってもよい。これらの下限と上限とは任意に組み合わせることができる。
第1の粒子は、SiOX(0.5≦X<1.6)の式で表される酸化ケイ素を含む。第1の粒子は、酸化ケイ素の粒子と、酸化ケイ素の粒子の周囲に配置された炭素層とを含んでもよい。
第2の粒子は、リチウムシリケート相とリチウムシリケート相中に分散したシリコン粒子とを含む。上述したように、リチウムシリケート相は、Li2ZSiO(2+Z)(0<Z<2)の式で表されるリチウムシリケートを含んでもよく、当該リチウムシリケートで構成されてもよい。Zは、0<Z<1の関係を満たすことが好ましい。リチウムシリケート相は、その50質量%以上(例えば60質量%以上)が、0<Z≦0.5を満たすリチウムシリケートで構成されていてもよい。
第3の粒子は、炭素相と当該炭素相中に分散したシリコン粒子とを含む。第3の粒子の炭素相は、無定形炭素(すなわちアモルファス炭素)で構成されてもよい。無定形炭素は、ハードカーボンでもよいし、ソフトカーボンでもよいし、それ以外でもよい。無定形炭素(アモルファス炭素)とは、一般には、X線回折法により測定される(002)面の平均面間隔d002が0.34nmを超える炭素材料を言う。
黒鉛の例には、天然黒鉛、人造黒鉛、黒鉛化メソフェーズカーボン粒子などが含まれる。黒鉛には、負極活物質として用いられている公知の黒鉛を用いてもよい。
第1の粒子は、例えば、以下の方法で製造してもよい。まず、組成がSiO(一酸化ケイ素)の粒子を粉砕・分級して粒度を調整する。次に、得られた粒子の表面を、アルゴン雰囲気下でのCVD法によって、炭素で被覆する。そして、これを解砕・分級することによって、SiOXとして表される第1の粒子を調製する。なお、SiOX粒子を炭素で被覆する方法については、種々の周知の方法を採用することができる。また、SiOX粒子を炭素で被覆する処理については省略してもよい。
次に、第2の粒子の製造方法の一例について詳述する。第2の粒子は、以下で説明する製造方法以外の方法で製造してもよい。第2の粒子は、国際公開第2018/179969号に記載の方法で製造してもよい。
[工程(i)]
式:Li2ZSiO2+Zで表されるリチウムシリケートのZの値は、二酸化ケイ素とリチウム化合物との混合物におけるケイ素のリチウムに対する原子比:Li/Siによって制御すればよい。アルカリ成分の溶出の少ない良質なリチウムシリケートを合成するには、Li/Siを1より小さくすることが好ましい。
次に、リチウムシリケートと原料シリコンとの複合化が行われる。例えば、リチウムシリケートと原料シリコンとの混合物(さらに元素Meを含んでもよい)にせん断力を付与しながら混合物を粉砕すればよい。原料シリコンには、平均粒径が数μm~数十μm程度のシリコンの粗粒子を用いればよい。最終的に得られるシリコン粒子は、XRDパターンのSi(111)面に帰属される回析ピークの半値幅からシェラーの式により算出される結晶子サイズが10nm以上になるように制御することが好ましい。
第3の粒子を製造する方法の例として、第1および第2の方法を以下に説明する。第3の粒子は、以下で説明する製造方法以外の方法で製造してもよい。
負極は、負極活物質を含む第1層を含む。典型的には、負極は、負極集電体と、負極集電体の表面に配置された第1層を含む。第1層は、負極活物質層(負極合剤層)であってもよい。その場合、第1層は、負極活物質および難燃剤(R)を含み、必要に応じて、負極活物質および難燃剤(R)以外の他の成分を含む。他の成分の例には、結着剤、導電剤、増粘剤などが含まれる。それらの他の成分には、公知の二次電池に用いられている成分を用いてもよい。第1層は、カーボンナノチューブを導電材として含んでもよい。
負極活物質としては、電気化学的にリチウムイオンを吸蔵および放出可能な材料が好適に用いられる。このような材料としては、炭素質材料、Si含有材料などが挙げられる。負極活物質は、1種を単独で用いてもよく、2種以上を組み合わせて用いてもよい。
正極は、正極合剤を含む。典型的には、正極は、正極集電体と、正極集電体の表面に形成された正極活物質層(正極合剤層)とを含む。正極合剤層は、正極合剤を分散媒に分散させた正極スラリーを、正極集電体の表面に塗布し、乾燥させることにより形成できる。乾燥後の塗膜を、必要により圧延してもよい。正極合剤は、必須成分として正極活物質を含み、任意成分として、結着剤、導電剤などを含むことができる。
電解質には、溶媒と、溶媒に溶解した溶質とを含む電解液を用いることができる。溶質は、電解液中でイオン解離する電解質塩である。溶質は、例えば、リチウム塩を含み得る。溶媒および溶質以外の電解液の成分は添加剤である。電解液には、様々な添加剤が含まれ得る。
正極と負極との間には、セパレータが配置されてもよい。セパレータには、イオン透過度が高く、適度な機械的強度および絶縁性を備えている部材を適用できる。セパレータとしては、微多孔薄膜、織布、不織布などを用いることができる。セパレータの材質としては、ポリプロピレン、ポリエチレンなどのポリオレフィンが好ましい。
この実施例では、複数の種類の二次電池を以下の手順で作製し、評価した。複数の種類の二次電池は、難燃剤の種類、および/または、負極合剤層中の物質の比率が異なる。
負極活物質には、黒鉛を用いた。まず、負極活物質と、カルボキシメチルセルロースナトリウム(CMC-Na)と、スチレン-ブタジエンゴム(SBR)と、水と、必要に応じて難燃剤とを所定の質量比で混合し、負極スラリーを調製した。次に、銅箔(負極集電体)の表面に負極スラリーを塗布することによって塗膜を形成した。その塗膜を乾燥させた後、圧延した。このようにして、銅箔の両面に負極合剤層を形成した。
正極活物質として、LiNi0.88Co0.09Al0.03O2を用いた。正極活物質、ポリフッ化ビニリデン、N-メチル-2-ピロリドン(NMP)、およびアセチレンブラックを、所定の質量比で混合することによって、正極スラリーを調製した。
エチレンカーボネート(EC)およびエチルメチルカーボネート(EMC)を3:7の体積比で含む混合溶媒に、リチウム塩としてLiPF6を加え、電解液を調製した。非水電解液におけるLiPF6の濃度は1.3mol/リットルとした。
各電極にリードタブをそれぞれ取り付けた。次に、リードが最外周部に位置するように、セパレータを介して正極と負極とを渦巻き状に巻回した。このようにして電極群を作製した。次に、アルミニウム箔をバリア層とするラミネートフィルム製の外装体内に電極群を挿入し、真空乾燥した。次に、外装体内に非水電解液を注入し、外装体の開口部を封止した。このようにして、二次電池を得た。
(1)容量維持率の測定
作製された二次電池の放電容量を以下の方法で測定した。まず、25℃の環境下で、0.5CAの定電流で電池電圧が4.2Vになるまで電池を充電し、その後、電流値が0.02CAになるまで定電圧で充電を継続した。充電後の電池を20分間放置した後、1.0CAの定電流で電池電圧が2.5Vになるまで放電した。その後、20分間放置した。この操作(充放電サイクル)を100回繰り返した。
容量維持率(%)=100×DC1/DC0
作製された二次電池について、下記の手順で釘刺し試験を行った。
(a)25℃の環境下で、0.5CAの定電流で電池電圧が4.2Vになるまで電池を充電し、その後、引き続き、電流値が0.02CAになるまで定電圧で充電を行った。
(b)25℃の環境下で、(a)で充電した電池の中央部に、丸釘(直径2.7mm)の先端を接触させ、1mm/秒の速度で突き刺し、内部短絡による電池電圧降下を検出した直後に、丸釘の突き刺しを停止した。
丸釘によって電池が短絡してから1秒間、短絡電流の電流値Iの測定と電池の電圧Vの測定とを続けた。そして、電流値Iと電圧Vとの積(電力)を時間積算することによって、1秒間の発熱量を求めた。
この実施例では、複数の非水電解質二次電池を作製して評価した。以下の手順で非水電解質二次電池を作製した。
負極活物質には、黒鉛、または、黒鉛と粒子(P)との混合物を用いた。まず、負極活物質と、カルボキシメチルセルロースナトリウム(CMC-Na)と、スチレン-ブタジエンゴム(SBR)と、水と、必要に応じて難燃剤とを所定の質量比で混合し、負極スラリーを調製した。次に、銅箔(負極集電体)の表面に負極スラリーを塗布することによって塗膜を形成した。その塗膜を乾燥させた後、圧延した。このようにして、銅箔の両面に負極合剤層を形成した。
作製した非水電解質二次電池に対して、実施例1と同様にして容量維持率の測定および釘刺し試験を行った。ただし、釘刺し試験では、発熱量の導出に代えて、電池が内部短絡して1分後の電池の表面温度を測定した。
この実施例では、複数の二次電池を以下の手順で作製し、評価した。
負極活物質には、黒鉛と粒子(P)との混合物を用いた。まず、負極活物質と、カルボキシメチルセルロースナトリウム(CMC-Na)と、スチレン-ブタジエンゴム(SBR)と、カーボンナノチューブ(CNT)と、水とを所定の質量比で混合し、負極スラリーを調製した。カーボンナノチューブには、平均径が約1.5nmであり、長さが1μm~5μm程度のものを用いた。次に、銅箔(負極集電体)の表面に負極スラリーを塗布することによって塗膜を形成した。その塗膜を乾燥させた後、圧延した。このようにして、銅箔の両面に負極活物質層(第2層)を形成した。
二次電池C7では、難燃剤層(第3層)を形成しなかったことを除いては、二次電池A16と同様にして負極を作製し、二次電池を得た。
作製された二次電池について、下記の手順で釘刺し試験後の電池温度を測定した。
(a)25℃の環境下で、0.5Cの定電流で電池電圧が4.2Vになるまで電池を充電し、その後、引き続き、電流値が0.02Cになるまで定電圧で充電を行った。
(b)25℃の環境下で、(a)で充電した電池の中央部に、丸釘(直径2.7mm)の先端を接触させ、1mm/秒の速度で突き刺し、内部短絡による電池電圧降下を検出した直後に、丸釘の突き刺しを停止した。そして、電池が短絡して1分後の電池の表面温度を測定した。
この実施例では、複数の二次電池を以下の手順で作製し、評価した。
負極活物質には、黒鉛と粒子(P)との混合物を用いた。まず、負極活物質と、カルボキシメチルセルロースナトリウム(CMC-Na)と、スチレン-ブタジエンゴム(SBR)と、カーボンナノチューブ(CNT)と、水とを所定の質量比で混合し、負極スラリーを調製した。カーボンナノチューブには、平均径が約1.5nmであり、長さが1μm~5μm程度のものを用いた。次に、銅箔(負極集電体)の表面に負極スラリーを塗布することによって塗膜を形成した。その塗膜を乾燥させた後、圧延した。このようにして、銅箔の両面に負極活物質層(第2層)を形成した。負極スラリーに占める各成分の混合比は、黒鉛:粒子(P):CMC-NaとSBRとの合計:CNT=94:5:2.9:0.1の質量比とした。
この実施例では、難燃剤層(第3層)に含まれる難燃剤の種類および難燃剤層中の物質の比率を変化させて複数の二次電池(電池A17~A20、C8)を作製した。なお、電池C8は比較例の電池であり、難燃剤層を設けなかった。難燃剤層中の物質の比率は、難燃剤層用のスラリーを調製する際にそれらの混合比を変化させることによって、変化させた。それらの比率の一部を、後掲の表4に示す。難燃剤の種類については後述する。
本発明を現時点での好ましい実施態様に関して説明したが、そのような開示を限定的に解釈してはならない。種々の変形および改変は、上記開示を読むことによって本発明に属する技術分野における当業者には間違いなく明らかになるであろう。したがって、添付の請求の範囲は、本発明の真の精神および範囲から逸脱することなく、すべての変形および改変を包含する、と解釈されるべきものである。
Claims (18)
- 正極および負極を含み、
前記負極は、負極活物質を含む第1層を含み、
前記第1層は、ハロゲン原子を含む難燃剤をさらに含む、二次電池。 - 前記負極活物質は、
SiOX(0.5≦X<1.6)の式で表される酸化ケイ素を含む第1の粒子、リチウムシリケート相と前記リチウムシリケート相中に分散したシリコン粒子とを含む第2の粒子、および、炭素相と前記炭素相中に分散したシリコン粒子とを含む第3の粒子からなる群より選択される少なくとも一種の粒子と、
黒鉛とを含む、請求項1に記載の二次電池。 - 前記リチウムシリケート相は、Li2ZSiO(2+Z)(0<Z<2)の式で表されるリチウムシリケートを含む、請求項2に記載の二次電池。
- 前記負極活物質における前記少なくとも一種の粒子の含有率が1質量%以上である、請求項2または3に記載の二次電池。
- 前記負極活物質は、前記第1の粒子、前記第2の粒子、および、前記第3の粒子からなる群より選択される複数種の粒子を含む、請求項2~4のいずれか1項に記載の二次電池。
- 前記第1層における前記負極活物質と前記難燃剤との質量比を、前記負極活物質:前記難燃剤=100:aで表したとき、前記aは0より大きく15未満である、請求項1~5のいずれか1項に記載の二次電池。
- 前記aは1以上5未満である、請求項6に記載の二次電池。
- 前記第1層は、前記負極活物質を少なくとも含む第2層と、前記第2層の表面に配置され前記難燃剤を少なくとも含む第3層と、を含む、請求項1~5のいずれか1項に記載の二次電池。
- 前記負極活物質は、金属リチウムを含む、請求項8に記載の二次電池。
- 前記第3層の目付量が0.1g/m2以上10g/m2以下である、請求項8または9に記載の二次電池。
- 前記正極と前記負極との間に介在するセパレータを含み、
前記第3層は、前記第2層と前記セパレータとの間に配置されている、請求項8~10のいずれか1項に記載の二次電池。 - 前記第3層の厚みは、0.1μm以上10μm以下である、請求項8~11のいずれか1項に記載の二次電池。
- 前記第3層における前記難燃剤の含有率は、前記第2層における前記難燃剤の含有率よりも大きい、請求項8~12のいずれか1項に記載の二次電池。
- 前記第3層の全体に占める前記第3層に含まれる前記難燃剤の割合は、質量基準で50%以上である、請求項8~13のいずれか1項に記載の二次電池。
- 前記第1層は、カーボンナノチューブを含む、請求項1~14のいずれか1項に記載の二次電池。
- 前記難燃剤は、前記ハロゲン原子が結合した環状構造を含み、
前記難燃剤に占める前記ハロゲン原子の割合は45質量%以上である、請求項1~15のいずれか1項に記載の二次電池。 - 前記難燃剤は、180℃以上の温度で前記ハロゲン原子を放出する、請求項1~16のいずれか1項に記載の二次電池。
- 前記難燃剤は、エチレン-1,2-ビスペンタブロモフェニル、エチレンビステトラブロモフタルイミド、テトラブロモビスフェノールA、ヘキサブロモシクロドデカン、2,4,6-トリブロモフェノール、1,6,7,8,9,14,15,16,17,17,18,18-ドデカクロロペンタシクロ(12.2.1.16,9.02,13.05,10)オクタデカ-7,15-ジエン、およびトリス(2,2,2-トリフルオロエチル)ホスフェイトからなる群より選択される少なくとも1つである、請求項1~17のいずれか1項に記載の二次電池。
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