JP6317556B2 - Lithium ion secondary battery separator and lithium ion secondary battery using the same - Google Patents
Lithium ion secondary battery separator and lithium ion secondary battery using the same Download PDFInfo
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- 229910001416 lithium ion Inorganic materials 0.000 title claims description 83
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims description 82
- 239000000835 fiber Substances 0.000 claims description 278
- 229920003043 Cellulose fiber Polymers 0.000 claims description 57
- 239000011230 binding agent Substances 0.000 claims description 50
- 229920000728 polyester Polymers 0.000 claims description 49
- 239000002994 raw material Substances 0.000 claims description 6
- 229920002994 synthetic fiber Polymers 0.000 claims description 4
- 239000012209 synthetic fiber Substances 0.000 claims description 4
- 229920000139 polyethylene terephthalate Polymers 0.000 description 55
- 239000005020 polyethylene terephthalate Substances 0.000 description 55
- 230000000052 comparative effect Effects 0.000 description 29
- -1 lithium ion ion Chemical class 0.000 description 15
- 239000011148 porous material Substances 0.000 description 14
- 229920002678 cellulose Polymers 0.000 description 13
- 239000001913 cellulose Substances 0.000 description 13
- 230000007423 decrease Effects 0.000 description 13
- 230000007547 defect Effects 0.000 description 11
- 229910052744 lithium Inorganic materials 0.000 description 11
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 10
- 239000008151 electrolyte solution Substances 0.000 description 9
- 229920005989 resin Polymers 0.000 description 8
- 239000011347 resin Substances 0.000 description 8
- 239000002002 slurry Substances 0.000 description 8
- 238000000034 method Methods 0.000 description 7
- 229910052782 aluminium Inorganic materials 0.000 description 6
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 6
- 230000003247 decreasing effect Effects 0.000 description 6
- 239000003792 electrolyte Substances 0.000 description 5
- 230000014759 maintenance of location Effects 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 229910052751 metal Inorganic materials 0.000 description 5
- 239000002184 metal Substances 0.000 description 5
- 238000004804 winding Methods 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 4
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 4
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
- 229920000297 Rayon Polymers 0.000 description 4
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 4
- 238000003490 calendering Methods 0.000 description 4
- 239000011888 foil Substances 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 3
- 239000002033 PVDF binder Substances 0.000 description 3
- 210000001787 dendrite Anatomy 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 229910003002 lithium salt Inorganic materials 0.000 description 3
- 159000000002 lithium salts Chemical class 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000007773 negative electrode material Substances 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 3
- 239000002964 rayon Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- YEJRWHAVMIAJKC-UHFFFAOYSA-N 4-Butyrolactone Chemical compound O=C1CCCO1 YEJRWHAVMIAJKC-UHFFFAOYSA-N 0.000 description 2
- 229920002749 Bacterial cellulose Polymers 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 229910013870 LiPF 6 Inorganic materials 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 239000006230 acetylene black Substances 0.000 description 2
- 239000005016 bacterial cellulose Substances 0.000 description 2
- 235000009508 confectionery Nutrition 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
- 238000002425 crystallisation Methods 0.000 description 2
- 230000008025 crystallization Effects 0.000 description 2
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000009472 formulation Methods 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 238000009413 insulation Methods 0.000 description 2
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 239000012046 mixed solvent Substances 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 239000007774 positive electrode material Substances 0.000 description 2
- 239000004627 regenerated cellulose Substances 0.000 description 2
- 238000010008 shearing Methods 0.000 description 2
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Chemical compound [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 238000004154 testing of material Methods 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- DEXFNLNNUZKHNO-UHFFFAOYSA-N 6-[3-[4-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]piperidin-1-yl]-3-oxopropyl]-3H-1,3-benzoxazol-2-one Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)C1CCN(CC1)C(CCC1=CC2=C(NC(O2)=O)C=C1)=O DEXFNLNNUZKHNO-UHFFFAOYSA-N 0.000 description 1
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 description 1
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 1
- 229910000733 Li alloy Inorganic materials 0.000 description 1
- 229910011458 Li4/3 Ti5/3O4 Inorganic materials 0.000 description 1
- 229910013063 LiBF 4 Inorganic materials 0.000 description 1
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- 229920002845 Poly(methacrylic acid) Polymers 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- 239000002202 Polyethylene glycol Substances 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 150000001412 amines Chemical class 0.000 description 1
- 239000002518 antifoaming agent Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 206010061592 cardiac fibrillation Diseases 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000011651 chromium Substances 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 239000000571 coke Substances 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- QKSIFUGZHOUETI-UHFFFAOYSA-N copper;azane Chemical compound N.N.N.N.[Cu+2] QKSIFUGZHOUETI-UHFFFAOYSA-N 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
- NKDDWNXOKDWJAK-UHFFFAOYSA-N dimethoxymethane Chemical compound COCOC NKDDWNXOKDWJAK-UHFFFAOYSA-N 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 239000002270 dispersing agent Substances 0.000 description 1
- 229920006240 drawn fiber Polymers 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000002600 fibrillogenic effect Effects 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- 238000001891 gel spinning Methods 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000012210 heat-resistant fiber Substances 0.000 description 1
- 239000011256 inorganic filler Substances 0.000 description 1
- 229910003475 inorganic filler Inorganic materials 0.000 description 1
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 1
- 239000005001 laminate film Substances 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
- 150000002641 lithium Chemical class 0.000 description 1
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 1
- FRMOHNDAXZZWQI-UHFFFAOYSA-N lithium manganese(2+) nickel(2+) oxygen(2-) Chemical compound [O-2].[Mn+2].[Ni+2].[Li+] FRMOHNDAXZZWQI-UHFFFAOYSA-N 0.000 description 1
- 229910001496 lithium tetrafluoroborate Inorganic materials 0.000 description 1
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
- 238000002074 melt spinning Methods 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 125000005487 naphthalate group Chemical group 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 239000010955 niobium Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 239000011255 nonaqueous electrolyte Substances 0.000 description 1
- 239000004745 nonwoven fabric Substances 0.000 description 1
- 239000005486 organic electrolyte Substances 0.000 description 1
- 239000012766 organic filler Substances 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 230000033116 oxidation-reduction process Effects 0.000 description 1
- 229920003207 poly(ethylene-2,6-naphthalate) Polymers 0.000 description 1
- 229920001748 polybutylene Polymers 0.000 description 1
- 229920001707 polybutylene terephthalate Polymers 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- 229920001223 polyethylene glycol Polymers 0.000 description 1
- 239000011112 polyethylene naphthalate Substances 0.000 description 1
- 229920000098 polyolefin Polymers 0.000 description 1
- 229920001296 polysiloxane Polymers 0.000 description 1
- 229920002215 polytrimethylene terephthalate Polymers 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000007784 solid electrolyte Substances 0.000 description 1
- 238000009987 spinning Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000011550 stock solution Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 239000002562 thickening agent Substances 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- 239000011135 tin Substances 0.000 description 1
- QHGNHLZPVBIIPX-UHFFFAOYSA-N tin(II) oxide Inorganic materials [Sn]=O QHGNHLZPVBIIPX-UHFFFAOYSA-N 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- RIUWBIIVUYSTCN-UHFFFAOYSA-N trilithium borate Chemical compound [Li+].[Li+].[Li+].[O-]B([O-])[O-] RIUWBIIVUYSTCN-UHFFFAOYSA-N 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Description
本発明は、リチウムイオン二次電池用セパレータ及びそれを用いてなるリチウムイオン二次電池に関する。 The present invention relates to a separator for a lithium ion secondary battery and a lithium ion secondary battery using the separator.
近年の携帯電子機器の普及及びその高性能化に伴い、高エネルギー密度を有する二次電池が望まれている。この種の電池として、有機電解液（非水電解液）を使用するリチウムイオン二次電池が注目されてきた。このリチウムイオン二次電池の平均電圧は、アルカリ二次電池の約３倍の３．７Ｖであり、高エネルギー密度となるが、アルカリ二次電池のように水系の電解液を用いることができないため、十分な耐酸化還元性を有する非水電解液を用いている。 With the recent spread of portable electronic devices and higher performance, secondary batteries having high energy density are desired. As this type of battery, a lithium ion secondary battery using an organic electrolyte (non-aqueous electrolyte) has attracted attention. The average voltage of the lithium ion secondary battery is 3.7 V, which is about three times that of the alkaline secondary battery, and the energy density is high. However, an aqueous electrolyte solution cannot be used unlike the alkaline secondary battery. A nonaqueous electrolytic solution having sufficient oxidation-reduction resistance is used.
リチウムイオン二次電池用セパレータとしては、ポリオレフィンからなるフィルム状の多孔質フィルムが多く使用されているが（例えば、特許文献１参照）、電解液の保液性が低いため、イオン伝導性が低く、内部抵抗が高くなる問題があった。 As a separator for a lithium ion secondary battery, a film-like porous film made of polyolefin is often used (see, for example, Patent Document 1), but has low ionic conductivity due to low electrolyte retention. There was a problem that the internal resistance increased.
また、リチウムイオン二次電池用セパレータとして、再生セルロース繊維の叩解物を主体とする紙製セパレータ（例えば、特許文献２参照）が提案されている。リチウムイオン二次電池においては、水分がわずかでも混入すると電池特性に悪影響を及ぼすことから、セパレータに含水分率の高い紙製セパレータを用いる場合、リチウムイオン二次電池製造の際に長時間の乾燥処理が必要となる。また、例えば、１０．０ｇ／ｍ２以下の低坪量にした場合、セパレータ強度が極端に弱くなるため、セパレータを低坪量にできない問題があった。 In addition, as a separator for a lithium ion secondary battery, a paper separator (see, for example, Patent Document 2) mainly composed of regenerated cellulose fiber beats has been proposed. Lithium ion secondary batteries have a negative effect on battery characteristics if even a small amount of water is mixed in. Therefore, if a paper separator with a high moisture content is used for the separator, it will dry for a long time when producing lithium ion secondary batteries. Processing is required. In addition, for example, when the basis weight is 10.0 g / m 2 or less, the separator strength is extremely weak.
さらに、リチウムイオン二次電池用セパレータとして、合成繊維からなる不織布セパレータ（例えば、特許文献３〜５参照）についても提案されているが、これらのセパレータは電解液の保液性が低く、内部抵抗が高くなる問題や、セパレータの緻密性が不十分であるため、内部短絡不良率が高くなる、高レート特性や放電特性及びそのバラツキに劣るといった問題があった。 Furthermore, as separators for lithium ion secondary batteries, nonwoven fabric separators made of synthetic fibers (see, for example, Patent Documents 3 to 5) have also been proposed, but these separators have low electrolyte retention and internal resistance. There is a problem that the high short-circuiting rate is high, the internal short-circuit defect rate is high, and the high rate characteristics and discharge characteristics are inferior.
また、リチウムイオン二次電池用セパレータとして、フィブリル化耐熱性繊維、フィブリル化セルロース、非フィブリル化繊維からなるセパレータが提案されているが（例えば、特許文献６参照）、このセパレータでは、低坪量とした場合のセパレータ強度にまだ改善の余地があった。 In addition, as a separator for a lithium ion secondary battery, a separator made of fibrillated heat-resistant fiber, fibrillated cellulose, or non-fibrillated fiber has been proposed (see, for example, Patent Document 6). There was still room for improvement in separator strength.
また、リチウムイオンイオン二次電池用セパレータとして、変法濾水度が０〜２５０ｍｌの溶剤紡糸セルロースと合成繊維を含有する多孔性シートからなるセパレータが提案されている（例えば、特許文献７参照）。しかし、このセパレータでは、低抵抗で高容量化のために、低坪量で、低厚みとした場合、スリット作業や電池製造のハンドリングに必要な引張強度に改善の余地があった。 Further, as a separator for a lithium ion ion secondary battery, a separator made of a porous sheet containing solvent-spun cellulose having a modified freeness of 0 to 250 ml and a synthetic fiber has been proposed (see, for example, Patent Document 7). . However, in this separator, there is room for improvement in the tensile strength necessary for handling of slitting and battery manufacture when the basis weight is low and the thickness is low for low resistance and high capacity.
本発明は、上記実情を鑑みたものであって、低坪量で、機械強度が強く、内部抵抗、内部短絡不良率、サイクル特性に優れたリチウムイオン二次電池用セパレータと、それを用いてなるリチウムイオン二次電池を提供することにある。 The present invention has been made in view of the above circumstances, and has a low basis weight, a high mechanical strength, an internal resistance, an internal short-circuit failure rate, an excellent cycle characteristic, and a separator for a lithium ion secondary battery using the same. It is providing the lithium ion secondary battery which becomes.
上記課題を解決するために鋭意研究した結果、
（１）繊維原料としてフィブリル化した溶剤紡糸セルロース繊維と合成繊維のみを含んでなるシートのみからなるリチウムイオン二次電池用セパレータにおいて、
フィブリル化した溶剤紡糸セルロース繊維を１０〜３０質量％、平均繊維径２．０〜３．５μｍの配向結晶化ポリエステル短繊維を４０〜５０質量％、平均繊維径５．０μｍ以下の未延伸バインダー用ポリエステル短繊維を３０〜４０質量％含有し、
坪量が７．０〜１０．０ｇ／ｍ ２ であり、厚さが１０．０〜１５．０μｍであり、引張強度が４５０〜７００Ｎ／ｍであることを特徴とするリチウムイオン二次電池用セパレータ、
（２）上記（１）に記載のリチウムイオン二次電池用セパレータを用いてなるリチウムイオン二次電池、
を見出した。
As a result of earnest research to solve the above problems,
(1) In a separator for a lithium ion secondary battery consisting only of a sheet comprising only fibrillated solvent-spun cellulose fibers and synthetic fibers as a fiber raw material ,
10-30 mass% of fibrillated solvent-spun cellulose fibers, 40-50 mass% of oriented crystallized polyester short fibers with an average fiber diameter of 2.0-3.5 μm, for unstretched binders with an average fiber diameter of 5.0 μm or less Containing 30-40% by mass of polyester staple fiber ,
Basis weight of 7.0~10.0g / m 2, a thickness of 10.0～15.0Myuemu, lithium ion secondary tensile strength, characterized in 450~700N / m der Rukoto battery Separator,
(2) a lithium ion secondary battery using the lithium ion secondary battery separator according to (1),
I found.
本発明のリチウムイオン二次電池用セパレータは、フィブリル化した溶剤紡糸セルロース繊維を１０〜３０質量％と平均繊維径２．０〜３．５μｍの配向結晶化ポリエステル短繊維を４０〜５０質量％と平均繊維径５．０μｍ以下の未延伸バインダー用ポリエステル短繊維を３０〜４０質量％を含有する。この特定の配合にすることにより、フィブリル化した溶剤紡糸セルロース繊維と細いポリエステル繊維が絡み合い、未延伸バインダー用ポリエステル短繊維で繊維ネットワークの交点を固定化することにより、低坪量でありながら、引張強度、特に突刺強度の機械的強度を高めることができる。その結果、セパレータとしてのハンドリング性や内部短絡不良を飛躍的に向上させることができる。また、リチウムイオン二次電池用セパレータをより緻密で、薄くすることができるため、内部抵抗を低く抑えることができ、放電特性やサイクル特性に優れたものとすることができる。 The separator for a lithium ion secondary battery of the present invention comprises 10-30% by mass of fibrillated solvent-spun cellulose fibers and 40-50% by mass of oriented crystallized polyester short fibers having an average fiber diameter of 2.0-3.5 μm. 30-40 mass% of polyester short fibers for unstretched binders having an average fiber diameter of 5.0 μm or less are contained. With this specific formulation, fibrillated solvent-spun cellulose fibers and fine polyester fibers are intertwined, and by fixing the intersection of the fiber network with polyester short fibers for unstretched binder, the tensile strength is low, while maintaining a low basis weight. Strength, especially mechanical strength of puncture strength can be increased. As a result, handling properties as a separator and internal short circuit defects can be dramatically improved. In addition, since the lithium ion secondary battery separator can be made denser and thinner, the internal resistance can be kept low, and the discharge characteristics and cycle characteristics can be improved.
本発明におけるフィブリル化した溶剤紡糸セルロース繊維とは、従来のビスコースレーヨンや銅アンモニアレーヨンのように、セルロースを一旦セルロース誘導体に化学的に変換させたのち再度セルロースに戻す、いわゆる再生セルロース繊維と異なり、セルロースを化学的に変化させることなく、アミンオキサイドに溶解させた紡糸原液を水中に乾湿式紡糸してセルロースを析出させた繊維を指す。溶剤紡糸セルロース繊維は、天然セルロース繊維やバクテリアセルロース繊維、レーヨン繊維に比べ、繊維長軸方向に分子が高度に配列しているため、湿潤状態で摩擦等の機械的な力が加えられると、微細化しやすく、細くて長い微細繊維が生成する。この微細繊維間に電解液を強固に保持するため、天然セルロース繊維、バクテリアセルロース繊維、レーヨン繊維の微細化物に比べ、フィブリル化した溶剤紡糸セルロース繊維は、電解液の保液性に優れる。フィブリル化とは、フィルム状ではなく、主に繊維軸と平行な方向に非常に細かく分割された部分を有する繊維状で、少なくとも一部が繊維径１μｍ以下になっている繊維を指す。長さと巾のアスペクト比が約２０〜約１０００００の範囲にあることが好ましい。 The fibrillated solvent-spun cellulose fiber in the present invention is different from the so-called regenerated cellulose fiber in which cellulose is once chemically converted into a cellulose derivative and then returned to cellulose like conventional viscose rayon and copper ammonia rayon. This refers to a fiber in which cellulose is precipitated by dry-wet spinning of a spinning stock solution dissolved in amine oxide into water without chemically changing the cellulose. Solvent-spun cellulose fibers have a higher molecular arrangement in the fiber long axis direction than natural cellulose fibers, bacterial cellulose fibers, and rayon fibers, so when mechanical forces such as friction are applied in a wet state, It is easy to form, and fine and long fine fibers are formed. In order to firmly hold the electrolyte solution between the fine fibers, the fibrillated solvent-spun cellulose fiber is superior in liquid retention of the electrolyte solution compared to the refined product of natural cellulose fiber, bacterial cellulose fiber, and rayon fiber. Fibrilization refers to a fiber that is not film-like but has a portion that is divided into a very fine portion mainly in a direction parallel to the fiber axis, and at least a portion of which has a fiber diameter of 1 μm or less. Preferably, the aspect ratio of length to width is in the range of about 20 to about 100,000.
本発明では、変法濾水度８０〜１３０ｍｌのフィブリル化した溶剤紡糸セルロース繊維を用いることが好ましい。フィブリル化した溶剤紡糸セルロース繊維の変法濾水度は、９０〜１２０ｍｌであることがより好ましく、９５〜１１５ｍｌであることがさらに好ましい。変法濾水度が１３０ｍｌより高いと、低坪量とした場合、セパレータの緻密性が不十分になり、内部短絡不良率が高くなる。一方、変法濾水度が８０ｍｌ未満であると、平均繊維長が短くなり、ポリエステル短繊維との絡みが低下するため、セパレータの機械強度が低下するようになる。 In the present invention, it is preferable to use fibrillated solvent-spun cellulose fibers having a modified freeness of 80 to 130 ml. The modified drainage degree of the fibrillated solvent-spun cellulose fiber is more preferably 90 to 120 ml, and further preferably 95 to 115 ml. When the modified freeness is higher than 130 ml, when the basis weight is low, the density of the separator becomes insufficient and the internal short circuit defect rate becomes high. On the other hand, when the modified freeness is less than 80 ml, the average fiber length is shortened and the entanglement with the polyester short fibers is lowered, so that the mechanical strength of the separator is lowered.
本発明における変法濾水度とは、ふるい板として線径０．１４ｍｍ、目開き０．１８ｍｍの８０メッシュ金網を用い、試料濃度０．１％にした以外はＪＩＳ Ｐ８１２１に準拠して測定した値のことである。 The modified freeness in the present invention was measured in accordance with JIS P811, except that an 80 mesh wire net having a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as a sieve plate, and the sample concentration was 0.1%. It is a value.
溶剤紡糸セルロース繊維の場合、微細化が進むに従って、繊維長が短くなっていき、特に試料濃度が薄いと、繊維同士の絡みが少なくなり、繊維ネットワークが形成されにくくなるため、溶剤紡糸セルロース繊維自体がふるい板の穴をすり抜けてしまう。つまり、微細化した溶剤紡糸セルロースの場合は、ＪＩＳ Ｐ８１２１の測定方法では正確な濾水度が計測できないのである。より詳細に説明すると、天然セルロース繊維は、微細化の程度が進むほど、繊維の幹から細かいフィブリルが多数裂けた状態になるため、フィブリルを介して繊維同士が絡みやすく、繊維ネットワークを形成しやすいのに対し、溶剤紡糸セルロース繊維は微細化処理によって繊維の長軸に平行に細かく分割されやすく、分割後の繊維１本１本における繊維径の均一性が高いため、平均繊維長が短くなるほど、繊維同士が絡みにくくなり、繊維ネットワークを形成しにくいと考えられる。そこで、本発明では、溶剤紡糸セルロース繊維の正確な濾水度を測定するために、ふるい板として線径０．１４ｍｍ、目開き０．１８ｍｍの８０メッシュ金網を用い、試料濃度０．１％にした以外はＪＩＳ Ｐ８１２１に準拠して測定する変法濾水度を用いた。 In the case of solvent-spun cellulose fibers, the fiber length becomes shorter as the microfabrication progresses. In particular, when the sample concentration is low, the entanglement between fibers decreases and it becomes difficult to form a fiber network. Will slip through the holes in the sieve plate. That is, in the case of solvent-spun cellulose that has been refined, an accurate freeness cannot be measured by the measuring method of JIS P8121. In more detail, natural cellulose fibers are in a state where many fine fibrils are torn apart from the trunk of the fiber as the degree of refinement progresses. Therefore, the fibers are easily entangled with each other through the fibrils, and a fiber network is easily formed. On the other hand, the solvent-spun cellulose fiber is easily finely divided in parallel to the long axis of the fiber by the refining treatment, and since the uniformity of the fiber diameter in each fiber after division is high, the shorter the average fiber length, It is considered that the fibers do not easily entangle with each other and it is difficult to form a fiber network. Therefore, in the present invention, in order to measure the exact freeness of the solvent-spun cellulose fiber, an 80-mesh wire mesh having a wire diameter of 0.14 mm and an opening of 0.18 mm is used as a sieve plate, and the sample concentration is 0.1%. The modified freeness measured according to JIS P8121 was used.
フィブリル化した溶剤紡糸セルロース繊維を作製する方法としては、リファイナー、ビーター、ミル、摩砕装置、高速の回転刃により剪断力を与える回転刃式ホモジナイザー、高速で回転する円筒形の内刃と固定された外刃との間で剪断力を生じる二重円筒式の高速ホモジナイザー、超音波による衝撃で微細化する超音波破砕器、繊維懸濁液に少なくとも２０ＭＰａの圧力差を与えて小径のオリフィスを通過させて高速度とし、これを衝突させて急減速することにより繊維に剪断力、切断力を加える高圧ホモジナイザー等が挙げられる。この中でも特にリファイナーが好ましい。 A fibrillated solvent-spun cellulose fiber is prepared by a refiner, a beater, a mill, an attritor, a rotary blade homogenizer that applies shear force with a high-speed rotary blade, and a cylindrical inner blade that rotates at high speed. Double-cylindrical high-speed homogenizer that generates shearing force between the outer blades, ultrasonic crusher that is refined by impact by ultrasonic waves, and passes through a small-diameter orifice by applying a pressure difference of at least 20 MPa to the fiber suspension. And a high-pressure homogenizer that applies a shearing force and a cutting force to the fiber by causing a high speed and colliding with this to rapidly decelerate. Of these, refiners are particularly preferred.
フィブリル化した溶剤紡糸セルロース繊維の長さ加重平均繊維長は０．７〜１．２５ｍｍが好ましく、０．８〜１．１ｍｍがより好ましく、０．９０〜１．０５ｍｍがさらに好ましい。繊維長が０．７ｍｍより短いと、セパレータの機械強度が低下する場合があり、１．２５ｍｍより長いと、繊維の緻密性が不十分となり、内部短絡不良率が高くなる場合がある。 The length-weighted average fiber length of the fibrillated solvent-spun cellulose fiber is preferably 0.7 to 1.25 mm, more preferably 0.8 to 1.1 mm, and even more preferably 0.90 to 1.05 mm. When the fiber length is shorter than 0.7 mm, the mechanical strength of the separator may be lowered. When the fiber length is longer than 1.25 mm, the denseness of the fiber may be insufficient and the internal short circuit defect rate may be increased.
本発明のリチウムイオン二次電池用セパレータは、フィブリル化した溶剤紡糸セルロース繊維を１０〜３０質量％含有する。フィブリル化した溶剤紡糸セルロース繊維の含有量は、２０〜３０質量％がより好ましい。フィブリル化した溶剤紡糸セルロース繊維の含有率が１０質量％未満の場合、低坪量とした場合、電解液の保液性が不十分で内部抵抗が高くなる場合や、セパレータの緻密性が不十分で、内部短絡不良率が高くなる。フィブリル化した溶剤紡糸セルロース繊維の含有率が３０質量％を超える場合、ポリエステル短繊維の含有量が減少するため、セパレータの機械強度が低下する。また、熱カレンダーによる厚さ調整において、フィブリル化した溶剤紡糸セルロースが空隙を埋めてしまい、保液性が低下するため、内部抵抗が高くなる。 The separator for lithium ion secondary batteries of this invention contains 10-30 mass% of fibrillated solvent-spun cellulose fibers. The content of the fibrillated solvent-spun cellulose fiber is more preferably 20 to 30% by mass. When the content of fibrillated solvent-spun cellulose fibers is less than 10% by mass, when the basis weight is low, the electrolyte solution has insufficient liquid retention and the internal resistance is high, or the separator is insufficiently dense As a result, the internal short-circuit failure rate increases. When the content of the fibrillated solvent-spun cellulose fiber exceeds 30% by mass, the content of the polyester short fiber is decreased, so that the mechanical strength of the separator is decreased. Further, in the thickness adjustment by the thermal calendar, the fibrillated solvent-spun cellulose fills the gaps and the liquid retaining property is lowered, so that the internal resistance is increased.
本発明のリチウムイオン二次電池セパレータは、平均繊維径２．０〜３．５μｍの配向結晶化ポリエステル短繊維を４０〜５０質量％含有する。配向結晶化ポリエステル短繊維と未延伸バインダー用ポリエステル短繊維との接着性は高いため、例えば、１０ｇ／ｍ２以下の低坪量としても、セパレータの機械強度を高くできる。配向結晶化ポリエステル短繊維の含有量が４０質量％未満の場合、巻回工程に必要なセパレータの機械強度が不十分となる。一方、含有量が５０質量％を越えた場合、未延伸のバインダー用ポリエステル短繊維の含有量が減少するため、巻回工程に必要なセパレータの機械強度が不十分となる。 The lithium ion secondary battery separator of the present invention contains 40 to 50% by mass of oriented crystallized polyester short fibers having an average fiber diameter of 2.0 to 3.5 μm. Since the adhesiveness between the oriented crystallized polyester short fibers and the polyester short fibers for unstretched binder is high, for example, the mechanical strength of the separator can be increased even with a low basis weight of 10 g / m 2 or less. When the content of the oriented crystallized polyester short fiber is less than 40% by mass, the mechanical strength of the separator required for the winding process becomes insufficient. On the other hand, when the content exceeds 50% by mass, the content of unstretched polyester short fibers for binder decreases, so that the mechanical strength of the separator necessary for the winding process becomes insufficient.
配向結晶化ポリエステル短繊維の平均繊維径は２．０〜３．５μｍである。単位面積当たりの繊維本数を増やし、緻密性を向上させるためには、できるだけ細い方が好ましいが、単繊維強度の点から、溶融紡糸し、延伸した繊維を使用することが好ましい。平均繊維径は２．０μｍ未満では溶融紡糸が難しく、繊維の入手が困難である。３．５μｍを越えた場合、緻密性が不十分となり、繊維本数が減るため、セパレータの機械強度が低下する。また、セパレータの厚さを薄くすると、最大細孔径が拡大し、内部短絡不良率が高くなる。 The average fiber diameter of the oriented crystallized polyester short fibers is 2.0 to 3.5 μm. In order to increase the number of fibers per unit area and improve the denseness, the thinner one is preferable, but from the viewpoint of the single fiber strength, it is preferable to use melt-spun and drawn fibers. If the average fiber diameter is less than 2.0 μm, melt spinning is difficult and it is difficult to obtain the fibers. When the thickness exceeds 3.5 μm, the denseness becomes insufficient, and the number of fibers decreases, so that the mechanical strength of the separator decreases. Moreover, when the thickness of the separator is reduced, the maximum pore diameter is enlarged and the internal short circuit defect rate is increased.
本発明のリチウムイオン二次電池セパレータは、平均繊維径５．０μｍ以下の未延伸バインダー用ポリエステル短繊維を３０〜４０質量％含有する。未延伸バインダー用ポリエステル短繊維の含有量が３０質量％未満の場合、フィブリル化した溶剤紡糸セルロース繊維とポリエステル短繊維の接着が甘くなり、セパレータの機械強度が低下する。含有量が４０質量％を越えた場合、未延伸バインダー用ポリエステル短繊維同士が皮膜化し、イオン伝導性が阻害されることで、内部抵抗が高くなり、放電特性が低くなる。 The lithium ion secondary battery separator of this invention contains 30-40 mass% of polyester short fibers for unstretched binders having an average fiber diameter of 5.0 μm or less. When the content of the short polyester fiber for unstretched binder is less than 30% by mass, the adhesion between the fibrillated solvent-spun cellulose fiber and the short polyester fiber becomes sweet, and the mechanical strength of the separator is lowered. When the content exceeds 40% by mass, the polyester short fibers for unstretched binder form a film and the ionic conductivity is inhibited, so that the internal resistance becomes high and the discharge characteristics become low.
未延伸バインダー用ポリエステル短繊維の平均繊維径は５．０μｍ以下である。平均繊維径が５．０μｍを超えた場合、単位面積当たりの繊維本数が少なくなるため、フィブリル化した溶剤紡糸セルロースとポリエステル短繊維との接着が甘くなり、セパレータの強度が低下する。また、セパレータの厚さを薄くすると、最大細孔径が拡大し、内部短絡不良率が高くなる。一方、平均繊維径の下限としては３．０μｍであることが好ましい。平均繊維径が３．０μｍ未満とした場合、延伸倍率が高くなるため、ポリエステル繊維の結晶化が進み、バインダーとしての接着力が低下するため、繊維本数は増やすことができるが、セパレータの機械強度が低下する場合がある。本発明において、平均繊維径は、セパレータの走査型電子顕微鏡写真より、セパレータを形成する繊維の繊維径を計測し、無作為に選んだ１００本の平均値である。 The average fiber diameter of the polyester short fibers for unstretched binder is 5.0 μm or less. When the average fiber diameter exceeds 5.0 μm, the number of fibers per unit area decreases, so that the adhesion between the fibrillated solvent-spun cellulose and the polyester short fibers becomes sweet, and the strength of the separator decreases. Moreover, when the thickness of the separator is reduced, the maximum pore diameter is enlarged and the internal short circuit defect rate is increased. On the other hand, the lower limit of the average fiber diameter is preferably 3.0 μm. When the average fiber diameter is less than 3.0 μm, since the draw ratio becomes high, crystallization of the polyester fiber proceeds and the adhesive strength as a binder decreases, so the number of fibers can be increased, but the mechanical strength of the separator May decrease. In the present invention, the average fiber diameter is an average value of 100 fibers randomly selected by measuring the fiber diameter of the fibers forming the separator from the scanning electron micrograph of the separator.
配向結晶化ポリエステル短繊維と未延伸バインダー用ポリエステル短繊維の繊維長は１〜７ｍｍが好ましく、３〜５ｍｍがより好ましく、２〜３ｍｍがさらに好ましい。繊維長が１ｍｍより短いと、セパレータから脱落することがあり、７ｍｍより長いと、繊維がもつれてダマになることがあり、また、繊維本数が少なくなるため、緻密性が低下する場合がある。 The fiber length of the oriented crystallized polyester short fibers and the polyester short fibers for unstretched binder is preferably 1 to 7 mm, more preferably 3 to 5 mm, and even more preferably 2 to 3 mm. If the fiber length is shorter than 1 mm, the separator may fall off, and if it is longer than 7 mm, the fibers may be entangled and become lumpy, and the number of fibers may be reduced, resulting in a decrease in denseness.
本発明で用いる配向結晶化ポリエステル短繊維と未延伸バインダーポリエステル短繊維の樹脂としては、例えば、ポリエチレンテレフタレート系樹脂、ポリブチレンテレフタレート系樹脂、ポリトリメチレンテレフタレート系樹脂、ポリエチレンナフタレート系樹脂、ポリブチレンナフタレート系樹脂、ポリエチレンイソフタレート系樹脂、これらの誘導体等が挙げられる。これらの中でも、リチウムイオン二次電池用セパレータに使用する場合には、耐熱性と耐電解液性に優れているポリエチレンテレフタレート系樹脂が好ましい。 Examples of the resin of oriented crystallized polyester short fiber and unstretched binder polyester short fiber used in the present invention include, for example, polyethylene terephthalate resin, polybutylene terephthalate resin, polytrimethylene terephthalate resin, polyethylene naphthalate resin, polybutylene. Examples thereof include naphthalate resin, polyethylene isophthalate resin, and derivatives thereof. Among these, when used for a separator for a lithium ion secondary battery, a polyethylene terephthalate resin excellent in heat resistance and electrolyte solution resistance is preferable.
リチウムイオン二次電池用セパレータは、円網、長網、短網、傾斜型短網等の抄紙方式の中から１種の抄紙機方式を有する抄紙機、同種又は異種の２種以上の抄紙方式を組み合わせてなるコンビネーション抄紙機などを用いて抄紙する方法によって製造することができる。原料スラリーには、繊維原料の他に、必要に応じて、分散剤、増粘剤、無機填料、有機填料、消泡剤などを適宜添加することができ、５〜０．００１質量％程度の固形分濃度に原料スラリーを調製する。この原料スラリーをさらに所定濃度に希釈して抄紙し、乾燥する。抄紙して得られたリチウムイオン二次電池用セパレータは、必要に応じて、カレンダー処理、熱カレンダー処理、熱処理などが施される。本発明のリチウムイオン二次電池用セパレータは、平均繊維径が５．０μｍ以下の未延伸バインダー用ポリエステル短繊維を用いることから、熱カレンダー処理が施されることが好ましい。熱カレンダー処理では、金属ロールと金属ロールの間又は金属ロールと弾性ロールの間を通し、未延伸バインダー用ポリエステル短繊維が皮膜化しない温度（未延伸バインダー用ポリエステル短繊維の融点よりも２０℃以上低い温度）で加圧するのが好ましい。未延伸バインダー用ポリエステル短繊維が皮膜化すると、内部抵抗が高くなり、放電特性が低下することに加え、セパレータの機械強度が低下するため好ましくない。 Lithium-ion secondary battery separators are paper machines that have one type of paper machine, such as circular net, long net, short net, and slanted short net, and the same or different two or more types. Can be produced by a method of making paper using a combination paper machine or the like. In addition to the fiber raw material, a dispersant, a thickener, an inorganic filler, an organic filler, an antifoaming agent, and the like can be appropriately added to the raw material slurry, if necessary, and about 5 to 0.001% by mass. Prepare raw slurry to solid content concentration. The raw slurry is further diluted to a predetermined concentration to make a paper, and then dried. The separator for a lithium ion secondary battery obtained by papermaking is subjected to calendering, thermal calendering, heat treatment and the like as necessary. Since the separator for lithium ion secondary batteries of the present invention uses polyester short fibers for an unstretched binder having an average fiber diameter of 5.0 μm or less, it is preferable that a thermal calendar treatment is performed. In the thermal calendering process, the polyester short fiber for unstretched binder is not formed into a film between the metal roll and the metal roll or between the metal roll and the elastic roll (20 ° C. or higher than the melting point of the polyester short fiber for unstretched binder). It is preferable to pressurize at a low temperature. When the polyester short fiber for unstretched binder is formed into a film, it is not preferable because the internal resistance is increased, the discharge characteristics are lowered, and the mechanical strength of the separator is lowered.
リチウムイオン二次電池用セパレータの坪量は、５．０〜２０．０ｇ／ｍ２が好ましく、６．０〜１５．０ｇ／ｍ２がより好ましく、７．０〜１０．０ｇ／ｍ２がさらに好ましい。５．０ｇ／ｍ２未満では、十分な機械強度が得られない場合があり、正極と負極との間の絶縁性が不十分で、内部短絡不良率やサイクル特性が低下する場合がある。２０．０ｇ／ｍ２を超えると、リチウムイオン二次電池の内部抵抗が高くなる場合や、放電特性が低くなる場合がある。本発明のセパレータの坪量は、ＪＩＳ Ｐ８１２４に準拠して測定した値である。 The basis weight of the separator for lithium ion secondary batteries is preferably 5.0~20.0g / m 2, more preferably 6.0~15.0g / m 2, 7.0~10.0g / m 2 is Further preferred. If it is less than 5.0 g / m < 2 >, sufficient mechanical strength may not be obtained, the insulation between a positive electrode and a negative electrode may be inadequate, and an internal short circuit defect rate and cycling characteristics may fall. If it exceeds 20.0 g / m 2 , the internal resistance of the lithium ion secondary battery may increase or the discharge characteristics may decrease. The basis weight of the separator of the present invention is a value measured in accordance with JIS P8124.
リチウムイオン二次電池用セパレータの厚さは、６．０〜３０．０μｍが好ましく、８．０〜２０．０μｍがより好ましく、１０．０〜１５．０μｍがさらに好ましい。６．０μｍ未満では、十分な機械強度が得られなかったり、正極と負極との間の絶縁性が不十分で、内部短絡不良率、サイクル特性が悪くなったりする場合がある。３０．０μｍより厚いと、リチウムイオン二次電池の内部抵抗が高くなり、放電特性が低くなる場合がある。なお、本発明のセパレータの厚さはＪＩＳ Ｂ７５０２に規定された方法により測定した値、つまり、５Ｎ荷重時の外側マイクロメーターにより測定された値を意味する。 The thickness of the lithium ion secondary battery separator is preferably 6.0 to 30.0 μm, more preferably 8.0 to 20.0 μm, and still more preferably 10.0 to 15.0 μm. If the thickness is less than 6.0 μm, sufficient mechanical strength may not be obtained, or insulation between the positive electrode and the negative electrode may be insufficient, resulting in poor internal short circuit failure rate and cycle characteristics. If it is thicker than 30.0 μm, the internal resistance of the lithium ion secondary battery is increased, and the discharge characteristics may be lowered. The thickness of the separator of the present invention means a value measured by a method defined in JIS B7502, that is, a value measured by an outer micrometer at a load of 5N.
リチウムイオン二次電池用セパレータの引張強度は、４５０〜７００Ｎ／ｍであることが好ましく、５００〜６５０Ｎ／ｍであることがさらに好ましい。引張強度が４５０Ｎ／ｍ未満では、捲回作業時において内部短絡不良が発生しやくなる。引張強度が７００Ｎ／ｍを超えた場合、未延伸バインダー用ポリエステル短繊維の皮膜化が生じており、突刺強度が低下しやすく、内部抵抗が高くなることもあり、放電特性が低くなることがある。 The tensile strength of the lithium ion secondary battery separator is preferably 450 to 700 N / m, and more preferably 500 to 650 N / m. If the tensile strength is less than 450 N / m, an internal short circuit failure is likely to occur during the winding operation. When the tensile strength exceeds 700 N / m, the polyester short fiber for unstretched binder is formed into a film, and the puncture strength is likely to be lowered, the internal resistance may be increased, and the discharge characteristics may be lowered. .
リチウムイオン二次電池用セパレータの突刺強度は、０．８Ｎ以上であることが好ましい。フィブリル化した溶剤紡糸セルロース繊維が配向結晶化ポリエステル短繊維と絡み合い、未延伸バインダー用ポリエステル短繊維で接着し、繊維間結合を強めることにより、この突刺強度が達成することができる。突刺強度が０．８Ｎ未満では、捲回作業や捲回物を加熱プレスする際に内部短絡不良が発生しやすくなる。 The puncture strength of the lithium ion secondary battery separator is preferably 0.8 N or more. This puncture strength can be achieved by the fibrillated solvent-spun cellulose fibers entangled with the oriented crystallized polyester short fibers and bonded with the short polyester fibers for unstretched binder to strengthen the bond between the fibers. When the piercing strength is less than 0.8 N, an internal short circuit failure is likely to occur when the winding work or the wound product is heated and pressed.
リチウムイオン二次電池用セパレータの最大ポア径は、８．０μｍ以下であることが好ましい。フィブリル化した溶剤紡糸セルロース繊維を配合したことと、未延伸バインダー用ポリエステル短繊維が溶融することによって、このポア径を達成することができる。最大ポア径が８．０μｍを超えた場合では、リチウムイオン二次電池の内部短絡不良率やサイクル特性が低下する場合がある。 The maximum pore diameter of the lithium ion secondary battery separator is preferably 8.0 μm or less. This pore diameter can be achieved by blending the fibrillated solvent-spun cellulose fibers and melting the polyester short fibers for unstretched binder. When the maximum pore diameter exceeds 8.0 μm, the internal short circuit failure rate and cycle characteristics of the lithium ion secondary battery may be deteriorated.
リチウムイオン二次電池用セパレータのインピーダンスは、電池を組んだ際の内部抵抗と相関があり、０．５Ω以下であることが好ましく、０．４５Ω以下であることがより好ましく、０．４Ω以下であることがさらに好ましい。０．４Ω以下であれば、放電特性やサイクル特性に優れる。０．５Ωを超えた場合、内部抵抗が高くなり、放電特性やサイクル特性が低下する場合がある。 The impedance of the lithium ion secondary battery separator has a correlation with the internal resistance when the battery is assembled, and is preferably 0.5Ω or less, more preferably 0.45Ω or less, and 0.4Ω or less. More preferably it is. If it is 0.4Ω or less, the discharge characteristics and cycle characteristics are excellent. If it exceeds 0.5Ω, the internal resistance increases, and the discharge characteristics and cycle characteristics may deteriorate.
リチウムイオン二次電池の負極活物質としては、黒鉛やコークスなどの炭素材料、金属リチウム、アルミニウム、シリカ、スズ、ニッケル、鉛から選ばれる１種以上の金属とリチウムとの合金、ＳｉＯ、ＳｎＯ、Ｆｅ２Ｏ３、ＷＯ２、Ｎｂ２Ｏ５、Ｌｉ４／３Ｔｉ５／３Ｏ４等の金属酸化物、Ｌｉ０．４ＣｏＮなどの窒化物が用いられる。充放電を繰り返した時に負極表面に金属リチウムが析出する「リチウムデンドライト」という現象が発生し、このリチウムデンドライトは徐々に成長し、セパレータを貫通して正極に達し、内部短絡の原因になることがある。本発明のリチウムイオン二次電池用セパレータは、このリチウムデンドライトが発生し難いチタン酸リチウムを負極活物質として用いたリチウムイオン二次電池に使用されても、内部短絡が発生しにくいという効果が得られる。 Examples of the negative electrode active material of the lithium ion secondary battery include carbon materials such as graphite and coke, metallic lithium, aluminum, silica, tin, nickel, and an alloy of lithium and lithium, SiO, SnO, Metal oxides such as Fe 2 O 3 , WO 2 , Nb 2 O 5 , Li 4/3 Ti 5/3 O 4 , and nitrides such as Li 0.4 CoN are used. A phenomenon called “lithium dendrite” in which metallic lithium is deposited on the negative electrode surface when charging and discharging are repeated, this lithium dendrite gradually grows, penetrates the separator, reaches the positive electrode, and may cause an internal short circuit. is there. The separator for a lithium ion secondary battery of the present invention has an effect that an internal short circuit hardly occurs even when used in a lithium ion secondary battery using lithium titanate as a negative electrode active material in which lithium dendrite is hardly generated. It is done.
正極活物質としては、コバルト酸リチウム、マンガン酸リチウム、ニッケル酸リチウム、チタン酸リチウム、リチウムニッケルマンガン酸化物、リン酸鉄リチウムが用いられる。リン酸鉄リチウムは、さらに、マンガン、クロム、コバルト、銅、ニッケル、バナジウム、モリブデン、チタン、亜鉛、アルミニウム、ガリウム、マグネシウム、ホウ素、ニオブから選ばれる１種以上の金属との複合物でも良い。 As the positive electrode active material, lithium cobaltate, lithium manganate, lithium nickelate, lithium titanate, lithium nickel manganese oxide, or lithium iron phosphate is used. Further, the lithium iron phosphate may be a composite with one or more metals selected from manganese, chromium, cobalt, copper, nickel, vanadium, molybdenum, titanium, zinc, aluminum, gallium, magnesium, boron, and niobium.
リチウムイオン二次電池の電解液には、プロピレンカーボネート、エチレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、ジメトキシエタン、ジメトキシメタン、これらの混合溶媒などの有機溶媒にリチウム塩を溶解させたものが用いられる。リチウム塩としては、六フッ化リン酸リチウム（ＬｉＰＦ６）や四フッ化ホウ酸リチウム（ＬｉＢＦ４）等が挙げられる。固体電解質としては、ポリエチレングリコールやその誘導体、ポリメタクリル酸誘導体、ポリシロキサンやその誘導体、ポリフッ化ビニリデンなどのゲル状ポリマーにリチウム塩を溶解させたものが用いられる。 As an electrolytic solution for a lithium ion secondary battery, a solution obtained by dissolving a lithium salt in an organic solvent such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, dimethoxymethane, or a mixed solvent thereof is used. Examples of the lithium salt include lithium hexafluorophosphate (LiPF 6 ) and lithium tetrafluoroborate (LiBF 4 ). As solid electrolyte, what melt | dissolved lithium salt in gel-like polymers, such as polyethyleneglycol, its derivative (s), polymethacrylic acid derivative, polysiloxane, its derivative (s), polyvinylidene fluoride, is used.
以下、実施例により本発明をさらに詳しく説明するが、本発明は実施例に限定されるものではない。実施例１１〜１５は参考例である。
EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to an Example. Examples 11 to 15 are reference examples.
実施例１
リファイナーを用いて、平均繊維径１０μｍ、繊維長４ｍｍの溶剤紡糸セルロース繊維を処理し、変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を１０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ポリエチレンテレフタレート（ＰＥＴ）短繊維を５０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ポリエチレンテレフタレート（ＰＥＴ）短繊維４０質量％を一緒に混合し、パルパーの水中で離解させ、アジテーターによる撹拌のもと、均一な原料スラリー（０．３％濃度）を調製した。この原料スラリーを、１層目として傾斜型短網抄紙機で、２層目として円網抄紙機を用い、傾斜型短網と円網の坪量比を５０：５０として積層させ、湿潤シートを得て、ヤンキードライヤー温度１３０℃で乾燥した後、表面温度が１９５℃の金属ロールと弾性ルールによる熱カレンダー処理を施して、坪量８．２ｇ／ｍ２、厚さ１４．２μｍのリチウムイオン二次電池用セパレータを得た。
Example 1
Using a refiner, a solvent-spun cellulose fiber having an average fiber diameter of 10 μm and a fiber length of 4 mm was treated, and 10 mass% of a fibrillated solvent-spun cellulose fiber having a modified freeness of 97 ml, an average fiber diameter of 2.4 μm, and a fiber length. 50% by mass of 3 mm oriented crystallized polyethylene terephthalate (PET) short fibers, an average fiber diameter of 4.4 μm, and a fiber length of 3 mm were mixed together with 40% by mass of unstretched polyethylene terephthalate (PET) short fibers for binder. A uniform raw material slurry (0.3% concentration) was prepared by disaggregation in water and stirring with an agitator. This raw material slurry was laminated with an inclined short net paper machine as the first layer and a circular net paper machine as the second layer, and the basis weight ratio between the inclined short net and the circular net was 50:50, and a wet sheet was formed. After drying at a Yankee dryer temperature of 130 ° C., the surface temperature is 195 ° C. and subjected to a heat calender treatment with an elastic rule to obtain a lithium ion 2 having a basis weight of 8.2 g / m 2 and a thickness of 14.2 μm. A separator for a secondary battery was obtained.
実施例２
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を２０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維４０質量％とした以外は、実施例１と同様な方法で、坪量８．３ｇ／ｍ２、厚さ１３．６μｍのリチウムイオン二次電池用セパレータを得た。
Example 2
A modified solvent-spun cellulose fiber having a freeness of 97 ml was 20% by mass, an average fiber diameter of 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm was 40% by mass, an average fiber diameter of 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 8.3 g / m 2 and a thickness of 13.6 μm was obtained in the same manner as in Example 1 except that 40% by mass of PET short fibers for 3 mm of unstretched binder were used. It was.
実施例３
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を３０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維３０質量％とした以外は、実施例１と同様な方法で、坪量８．４ｇ／ｍ２、厚さ１３．７μｍのリチウムイオン二次電池用セパレータを得た。
Example 3
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 30% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 40% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 8.4 g / m 2 and a thickness of 13.7 μm was obtained in the same manner as in Example 1, except that 30% by mass of PET short fibers for 3 mm of unstretched binder was used. It was.
実施例４
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を２０質量％、平均繊維径３．２μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維４０質量％とした以外は、実施例１と同様な方法で、坪量８．３ｇ／ｍ２、厚さ１３．５μｍのリチウムイオン二次電池用セパレータを得た。
Example 4
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 20% by mass, an average fiber diameter is 3.2 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 40% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 8.3 g / m 2 and a thickness of 13.5 μm was obtained in the same manner as in Example 1 except that 40% by mass of PET short fibers for 3 mm of unstretched binder were used. It was.
実施例５
リファイナーを用いて、平均繊維径１０μｍ、繊維長４ｍｍの溶剤紡糸セルロース繊維を処理し、変法濾水度１１３ｍｌのフィブリル化した溶剤紡糸セルロース繊維を２０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維４０質量％とした以外は、実施例１と同様な方法で、坪量８．４ｇ／ｍ２、厚さ１３．４μｍのリチウムイオン二次電池用セパレータを得た。
Example 5
Using a refiner, a solvent-spun cellulose fiber having an average fiber diameter of 10 μm and a fiber length of 4 mm was treated, and 20 mass% of a fibrillated solvent-spun cellulose fiber having a modified freeness of 113 ml, an average fiber diameter of 2.4 μm, and a fiber length. The basis weight was the same as in Example 1 except that 40% by mass of 3 mm oriented crystallized PET short fibers, an average fiber diameter of 4.4 μm, and a fiber length of 3 mm were used. A separator for a lithium ion secondary battery having a thickness of 8.4 g / m 2 and a thickness of 13.4 μm was obtained.
実施例６
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を２０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維４０質量％とした以外は、実施例１と同様な方法で、坪量７．１ｇ／ｍ２、厚さ１１．６μｍのリチウムイオン二次電池用セパレータを得た。
Example 6
A modified solvent-spun cellulose fiber having a freeness of 97 ml was 20% by mass, an average fiber diameter of 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm was 40% by mass, an average fiber diameter of 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 7.1 g / m 2 and a thickness of 11.6 μm was obtained in the same manner as in Example 1 except that 40% by mass of PET short fibers for 3 mm of unstretched binder was used. It was.
実施例７
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を３０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維３０質量％とした以外は、実施例１と同様な方法で、坪量９．９ｇ／ｍ２、厚さ１５．０μｍのリチウムイオン二次電池用セパレータを得た。
Example 7
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 30% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 40% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 9.9 g / m 2 and a thickness of 15.0 μm was obtained in the same manner as in Example 1 except that 3% PET short fiber for unstretched binder of 3 mm was used. It was.
実施例８
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を２０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維４０質量％とした以外は、実施例１と同様な方法で、坪量７．０ｇ／ｍ２、厚さ１０．１μｍのリチウムイオン二次電池用セパレータを得た。
Example 8
A modified solvent-spun cellulose fiber having a freeness of 97 ml was 20% by mass, an average fiber diameter of 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm was 40% by mass, an average fiber diameter of 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 7.0 g / m 2 and a thickness of 10.1 μm was obtained in the same manner as in Example 1 except that 40% by mass of PET short fibers for 3 mm of unstretched binder was used. It was.
実施例９
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を３０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維３０質量％とした以外は、実施例１と同様な方法で、坪量７．５ｇ／ｍ２、厚さ１２．２μｍのリチウムイオン二次電池用セパレータを得た。
Example 9
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 30% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 40% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 7.5 g / m 2 and a thickness of 12.2 μm was obtained in the same manner as in Example 1, except that 30% by mass of 3 mm PET short fibers for unstretched binder was used. It was.
実施例１０
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を１０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を５０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維４０質量％とした以外は、実施例１と同様な方法で、坪量９．０ｇ／ｍ２、厚さ１５．０μｍのリチウムイオン二次電池用セパレータを得た。
Example 10
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 10% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 50% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 9.0 g / m 2 and a thickness of 15.0 μm was obtained in the same manner as in Example 1 except that 40% by mass of PET short fibers for 3 mm of unstretched binder were used. It was.
実施例１１
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を３０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維３０質量％とした以外は、実施例１と同様な方法で、坪量６．５ｇ／ｍ２、厚さ１０．６μｍのリチウムイオン二次電池用セパレータを得た。
Example 11
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 30% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 40% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 6.5 g / m 2 and a thickness of 10.6 μm was obtained in the same manner as in Example 1 except that 3% of PET short fibers for unstretched binder of 3 mm were used. It was.
実施例１２
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を３０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維３０質量％とした以外は、実施例１と同様な方法で、坪量１０．５ｇ／ｍ２、厚さ１５．０μｍのリチウムイオン二次電池用セパレータを得た。
Example 12
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 30% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 40% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 10.5 g / m 2 and a thickness of 15.0 μm was obtained in the same manner as in Example 1, except that 30% by mass of 3 mm PET short fibers for unstretched binder was used. It was.
実施例１３
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を３０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維３０質量％とした以外は、実施例１と同様な方法で、坪量７．２ｇ／ｍ２、厚さ９．８μｍのリチウムイオン二次電池用セパレータを得た。
Example 13
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 30% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 40% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 7.2 g / m 2 and a thickness of 9.8 μm was obtained in the same manner as in Example 1 except that 3% of PET short fibers for unstretched binder of 3 mm were used. It was.
実施例１４
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を３０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維３０質量％とした以外は、実施例１と同様な方法で、坪量８．５ｇ／ｍ２、厚さ１５．５μｍのリチウムイオン二次電池用セパレータを得た。
Example 14
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 30% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 40% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 8.5 g / m 2 and a thickness of 15.5 μm was obtained in the same manner as in Example 1 except that 3% by weight of PET short fibers for unstretched binder of 3 mm was used. It was.
実施例１５
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を１０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を５０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維４０質量％とした以外は、実施例１と同様な方法で、坪量８．８ｇ／ｍ２、厚さ１３．１μｍのリチウムイオン二次電池用セパレータを得た。
Example 15
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 10% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 50% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 8.8 g / m 2 and a thickness of 13.1 μm was obtained in the same manner as in Example 1 except that 40% by mass of PET short fibers for 3 mm of unstretched binder were used. It was.
比較例１
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を３５質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を３５質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維３０質量％とした以外は、実施例１と同様な方法で、坪量８．４ｇ／ｍ２、厚さ１４．２μｍのリチウムイオン二次電池用セパレータを得た。
Comparative Example 1
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 35% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 35% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 8.4 g / m 2 and a thickness of 14.2 μm was obtained in the same manner as in Example 1, except that 30% by mass of 3 mm PET short fiber for unstretched binder was used. It was.
比較例２
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を５質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を５０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維４５質量％とした以外は、実施例１と同様な方法で、坪量８．２ｇ／ｍ２、厚さ１３．５μｍのリチウムイオン二次電池用セパレータを得た。
Comparative Example 2
5 mass% of fibrillated solvent-spun cellulose fibers having a modified freeness of 97 ml, average fiber diameter of 2.4 μm, oriented crystallized PET short fibers of 3 mm in fiber length of 50 mass%, average fiber diameter of 4.4 μm, fiber length A separator for a lithium ion secondary battery having a basis weight of 8.2 g / m 2 and a thickness of 13.5 μm was obtained in the same manner as in Example 1 except that 45% by mass of PET short fibers for 3 mm of unstretched binder was used. It was.
比較例３
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を３０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を３０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維４０質量％とした以外は、実施例１と同様な方法で、坪量８．３ｇ／ｍ２、厚さ１３．５μｍのリチウムイオン二次電池用セパレータを得た。
Comparative Example 3
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 30% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 30% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 8.3 g / m 2 and a thickness of 13.5 μm was obtained in the same manner as in Example 1 except that 40% by mass of PET short fibers for 3 mm of unstretched binder were used. It was.
比較例４
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を１０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を６０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維３０質量％とした以外は、実施例１と同様な方法で、坪量８．２ｇ／ｍ２、厚さ１３．７μｍのリチウムイオン二次電池用セパレータを得た。
Comparative Example 4
10 mass% of fibrillated solvent-spun cellulose fibers with a modified freeness of 97 ml, average fiber diameter of 2.4 μm, oriented crystallized PET short fibers of 3 mm in fiber length of 60 mass%, average fiber diameter of 4.4 μm, fiber length A separator for a lithium ion secondary battery having a basis weight of 8.2 g / m 2 and a thickness of 13.7 μm was obtained in the same manner as in Example 1 except that 3% by weight of PET short fibers for unstretched binder of 3 mm was used. It was.
比較例５
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を１０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維５０質量％とした以外は、実施例１と同様な方法で、坪量８．１ｇ／ｍ２、厚さ１３．５μｍのリチウムイオン二次電池用セパレータを得た。
Comparative Example 5
A modified solvent-spun cellulose fiber having a freeness of 97 ml was 10% by mass, an average fiber diameter of 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm was 40% by mass, an average fiber diameter of 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 8.1 g / m 2 and a thickness of 13.5 μm was obtained in the same manner as in Example 1 except that 50% by mass of PET short fibers for 3 mm of unstretched binder was used. It was.
比較例６
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を３０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を５０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維２０質量％とした以外は、実施例１と同様な方法で、坪量８．２ｇ／ｍ２、厚さ１３．２μｍのリチウムイオン二次電池用セパレータを得た。
Comparative Example 6
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 30% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 50% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 8.2 g / m 2 and a thickness of 13.2 μm was obtained in the same manner as in Example 1, except that 20% by mass of PET short fibers for 3 mm of unstretched binder was used. It was.
比較例７
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を２０質量％、平均繊維径５．３μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維４０質量％とした以外は、実施例１と同様な方法で、坪量８．１ｇ／ｍ２、厚さ１３．５μｍのリチウムイオン二次電池用セパレータを得た。
Comparative Example 7
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 20% by mass, an average fiber diameter is 5.3 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 40% by mass, an average fiber diameter is 4.4 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 8.1 g / m 2 and a thickness of 13.5 μm was obtained in the same manner as in Example 1 except that 40% by mass of PET short fibers for 3 mm of unstretched binder was used. It was.
比較例８
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を２０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径６．５μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維４０質量％とした以外は、実施例１と同様な方法で、坪量８．３ｇ／ｍ２、厚さ１３．６μｍのリチウムイオン二次電池用セパレータを得た。
Comparative Example 8
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 20% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 40% by mass, an average fiber diameter is 6.5 μm, and a fiber length. A separator for a lithium ion secondary battery having a basis weight of 8.3 g / m 2 and a thickness of 13.6 μm was obtained in the same manner as in Example 1 except that 40% by mass of PET short fibers for 3 mm of unstretched binder were used. It was.
比較例９
変法濾水度９７ｍｌのフィブリル化した溶剤紡糸セルロース繊維を７０質量％、平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を１５質量％、平均繊維径３．２μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を１５質量％とし、常温でカレンダー処理した以外は、実施例１と同様な方法で、坪量８．４ｇ／ｍ２、厚さ１３．１μｍのリチウムイオン二次電池用セパレータを得た。
Comparative Example 9
A modified solvent-spun cellulose fiber having a freeness of 97 ml is 70% by mass, an average fiber diameter is 2.4 μm, an oriented crystallized PET short fiber having a fiber length of 3 mm is 15% by mass, an average fiber diameter is 3.2 μm, and a fiber length. Lithium ion secondary having a basis weight of 8.4 g / m 2 and a thickness of 13.1 μm in the same manner as in Example 1 except that 15% by mass of 3 mm oriented crystallized PET short fibers was calendered at room temperature. A battery separator was obtained.
比較例１０
平均繊維径２．４μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を４０質量％、平均繊維径３．２μｍ、繊維長３ｍｍの配向結晶化ＰＥＴ短繊維を２０質量％、平均繊維径４．４μｍ、繊維長３ｍｍの未延伸バインダー用ＰＥＴ短繊維４０質量％とした以外は、実施例１と同様な方法で、坪量８．０ｇ／ｍ２、厚さ１３．０μｍのリチウムイオン二次電池用セパレータを得た。
Comparative Example 10
40% by mass of oriented crystallized PET short fibers having an average fiber diameter of 2.4 μm and a fiber length of 3 mm, 20% by mass of oriented crystallized PET short fibers having an average fiber diameter of 3.2 μm and a fiber length of 3 mm, and an average fiber diameter of 4.4 μm. For a lithium ion secondary battery having a basis weight of 8.0 g / m 2 and a thickness of 13.0 μm, in the same manner as in Example 1 except that the PET length is 40% by mass for unstretched PET fibers with a fiber length of 3 mm. A separator was obtained.
＜リチウムイオン二次電池＞
［負極の作製］
負極活物質として、平均粒子径０．７μｍ、Ｌｉ吸蔵電位が１．５５Ｖであるスピネル構造のＬｉ４Ｔｉ５Ｏ１２で表されるチタン酸リチウムを９５質量％、導電材としてアセチレンブラック２．５質量％と、ポリフッ化ビニリデン２．５質量％を混合し、これをＮ−メチル−２−ピロリドンに分散させたスラリーを調製し、厚さ１５μｍ、平均結晶粒子径３０μｍのアルミニウム箔の両面に塗布して圧延した後、１５０℃で２時間真空乾燥して、厚さ１００μｍのリチウムイオン二次電池用負極を作製し、これを負極とした。
<Lithium ion secondary battery>
[Production of negative electrode]
As a negative electrode active material, 95% by mass of lithium titanate represented by spinel-structured Li 4 Ti 5 O 12 having an average particle diameter of 0.7 μm and a Li occlusion potential of 1.55 V, and acetylene black 2.5 as a conductive material A slurry in which 2% by mass and 2.5% by mass of polyvinylidene fluoride are mixed and dispersed in N-methyl-2-pyrrolidone is prepared and applied to both sides of an aluminum foil having a thickness of 15 μm and an average crystal particle size of 30 μm. Then, after vacuum rolling at 150 ° C. for 2 hours, a negative electrode for a lithium ion secondary battery having a thickness of 100 μm was produced, and this was used as a negative electrode.
［正極の作製］
正極活物質として、リチウムコバルト酸化物（ＬｉＣｏＯ2）粉末を９０質量％、アセチレンブラック３質量％、グラファイト３質量％及びポリフッ化ビニリデン４質量％を混合し、これをＮ−メチル−２−ピロリドンに分散させたスラリーを調製した。このスラリーを厚さ１５μｍ、平均結晶粒子３０μｍのアルミニウム箔からなる集電体の両面に塗布し、圧延した後、１５０℃で２時間真空乾燥して、厚さ１００μｍのリチウムイオン二次電池用正極を作製し、これを正極とした。
[Production of positive electrode]
As a positive electrode active material, 90% by mass of lithium cobalt oxide (LiCoO 2 ) powder, 3% by mass of acetylene black, 3% by mass of graphite and 4% by mass of polyvinylidene fluoride were mixed, and this was mixed with N-methyl-2-pyrrolidone. A dispersed slurry was prepared. The slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm and average crystal particles of 30 μm, rolled, and then vacuum-dried at 150 ° C. for 2 hours to obtain a positive electrode for a lithium ion secondary battery having a thickness of 100 μm. This was used as a positive electrode.
［リチウムイオン二次電池の作製］
正極及び負極の集電体に端子をそれぞれ接続し、正極、セパレータ、負極、セパレータの順番に積層した後、この積層物を正極、負極の端子がセパレータの長手方向に対して直角になるように捲回した。続いて、この捲回物を９０℃で加熱プレスすることにより、７０×１００ｍｍ、厚さ３．０ｍｍの寸法を持つ扁平状電極群を作成した。続いて、両面にポリエチレンフィルムが積層された厚さ４０μｍのアルミニウム箔から構成された厚さ０．１ｍｍのラミネートフィルムからなるパック（袋状外装材）を用意し、この袋状外装内に得られた電極群をその正極、負極の端子が外装材の開口部から外部に延出するように収納し、８０℃で２４時間真空乾燥を施した。次いで、前記の電極群を収納し、袋状外装材内に、電解液として、エチレンカーボネートとγ−ブチロラクトンの混合溶媒（体積比率２５：７５）に電解質として、１．５ｍｏｌ／Ｌの四フッ化ホウ酸リチウムを溶解したものを注入した後、袋状外装材の開口部をヒートシールにより完全密封し、リチウムイオン二次電池を作製した。
[Production of lithium ion secondary battery]
After connecting the terminals to the positive and negative electrode current collectors and laminating the positive electrode, the separator, the negative electrode, and the separator in this order, the laminate is placed so that the positive electrode and negative electrode terminals are perpendicular to the longitudinal direction of the separator. I turned around. Subsequently, the wound product was heated and pressed at 90 ° C. to produce a flat electrode group having dimensions of 70 × 100 mm and a thickness of 3.0 mm. Subsequently, a pack (bag-shaped exterior material) made of a laminate film having a thickness of 0.1 mm made of an aluminum foil having a thickness of 40 μm in which polyethylene films are laminated on both sides is prepared and obtained in the bag-shaped exterior. The electrode group was housed so that the positive and negative terminals extended outside from the opening of the exterior material, and vacuum dried at 80 ° C. for 24 hours. Next, the electrode group is housed, and 1.5 mol / L of tetrafluoride as an electrolyte in a mixed solvent of ethylene carbonate and γ-butyrolactone (volume ratio 25:75) as an electrolytic solution in a bag-shaped exterior material. After injecting a solution in which lithium borate was dissolved, the opening of the bag-shaped exterior material was completely sealed by heat sealing to produce a lithium ion secondary battery.
実施例及び比較例のセパレータ及びリチウムイオン二次電池について、下記評価を行い、結果を表１に示した。 The separators and lithium ion secondary batteries of Examples and Comparative Examples were evaluated as follows, and the results are shown in Table 1.
［坪量］
ＪＩＳ Ｐ８１２４に準拠して坪量を測定した。
[Basis weight]
The basis weight was measured in accordance with JIS P8124.
［厚さ］
ＪＩＳ Ｂ７５０２に規定された方法、つまり、５Ｎ荷重時の外側マイクロメーターにより、厚さを測定した。
[thickness]
The thickness was measured by the method defined in JIS B7502, that is, by an outer micrometer at 5N load.
［引張強度］
作製したセパレータについて、卓上型材料試験機（株式会社オリエンテック製、商品名ＳＴＡ−１１５０）を用いて、ＪＩＳ Ｐ８１１３に準じて縦方向の引張強さを測定した。試験片のサイズは、縦方向２５０ｍｍ、幅５０ｍｍとし、２個のつかみ具の間隔を１００ｍｍ、引張速度を３００ｍｍ／ｍｉｎとした。
[Tensile strength]
About the produced separator, the tensile strength of the vertical direction was measured according to JISP8113 using the desktop type | mold material testing machine (Orientec Co., Ltd. make, brand name STA-1150). The size of the test piece was 250 mm in the vertical direction, 50 mm in width, the interval between the two grippers was 100 mm, and the tensile speed was 300 mm / min.
［突刺強度］
作製したセパレータについて、先端に曲率１．６の丸みをつけた直径１ｍｍの金属針を卓上型材料試験機（株式会社オリエンテック製、商品名ＳＴＡ−１１５０）に装着し、試料面に対して直角に１ｍｍ／ｓの一定速度で貫通するまで降ろした。この時の最大荷重（Ｎ）を計測し、突刺強度を測定した。
[Puncture strength]
About the produced separator, a metal needle having a diameter of 1 mm with a rounded curvature of 1.6 is attached to a desktop material testing machine (product name: STA-1150, manufactured by Orientec Co., Ltd.) and perpendicular to the sample surface. Until it penetrates at a constant speed of 1 mm / s. The maximum load (N) at this time was measured, and the puncture strength was measured.
［最大ポア径］
作製したセパレータについて、ＰＭＩ社製パームポロメーターＣＦＰ−１５００Ａを用いて、ＪＩＳ Ｋ３８３２、ＡＳＴＭ Ｆ３１６−８６、ＡＳＴＭ Ｅ１２９４−８９に準じて測定を行い、最大ポア径を測定した。
[Maximum pore diameter]
About the produced separator, it measured according to JISK3832, ASTM F316-86, and ASTM E1294-89 using the palm porometer CFP-1500A by PMI, and measured the maximum pore diameter.
［インピーダンス］
作製したセパレータについて、電解液（１Ｍ−ＬｉＰＦ６／エチレンカーボネート（ＥＣ）＋ジエチルカーボネート（ＤＥＣ）＋ジメチルカーボネート（ＤＭＣ）（１：１：１、ｖｏｌ比））に浸した後、２つの略円筒形銅電極に挟み、ＬＣＲメーター（Ｉｎｓｔｅｃ社製、装置名：ＬＣＲ−８２１）を使用して、２００ｋＨｚにおける交流インピーダンスの抵抗成分を測定した。
[Impedance]
The produced separator was immersed in an electrolytic solution (1M-LiPF 6 / ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC) (1: 1: 1, vol ratio)), and then two substantially cylinders A resistance component of AC impedance at 200 kHz was measured using an LCR meter (manufactured by Instec, apparatus name: LCR-821) sandwiched between shaped copper electrodes.
［内部短絡不良率］
作製したセパレータをアルミニウム箔からなる電極間に介在して捲回することにより電極群を作製した後、電解液に含浸せずにテスターで電極間の導通を調べることによりショートの有無を確認した。短絡不良率は１００個の電極群を検査して全電極群数に対するショート個数から算出した。
[Internal short-circuit failure rate]
An electrode group was prepared by winding the produced separator between electrodes made of an aluminum foil, and then the presence or absence of a short circuit was confirmed by examining conduction between the electrodes with a tester without impregnating the electrolyte. The short-circuit failure rate was calculated from the number of shorts with respect to the total number of electrode groups by examining 100 electrode groups.
［サイクル特性］
各リチウムイオン二次電池を４５℃環境下において、１Ｃレートで充放電サイクル試験を行い、１０００サイクル目の放電容量を測定し、初期サイクル時のそれに対する放電容量維持率として算出した。
[Cycle characteristics]
Each lithium ion secondary battery was subjected to a charge / discharge cycle test at a 1C rate in a 45 ° C. environment, the discharge capacity at the 1000th cycle was measured, and the discharge capacity maintenance rate relative to that at the initial cycle was calculated.
表１に示した通り、実施例１〜１５のリチウムイオン二次電池用セパレータは、フィブリル化した溶剤紡糸セルロース繊維を１０〜３０質量％、平均繊維径２．０〜３．５μｍの配向結晶化ポリエステル短繊維を４０〜５０質量％、５μｍ以下の未延伸バインダー用ポリエステル短繊維を３０〜４０質量％を含有しているため、低坪量でありながらも、機械強度が強く、内部短絡不良が少ない。また、抵抗成分を表すインピーダンスが低く、サイクル特性に優れている。 As shown in Table 1, the separators for lithium ion secondary batteries of Examples 1 to 15 were 10 to 30% by mass of fibrillated solvent-spun cellulose fibers and oriented crystallization having an average fiber diameter of 2.0 to 3.5 μm. Since the polyester short fiber contains 40 to 50% by mass and the polyester short fiber for unstretched binder of 30 to 40% by mass of 5 μm or less, the mechanical strength is strong and the internal short circuit defect is low although the basis weight is low. Few. In addition, the impedance representing the resistance component is low, and the cycle characteristics are excellent.
実施例１〜５のリチウムイオン二次電池用セパレータは、８ｇ／ｍ２という低坪量である。フィブリル化した溶剤紡糸セルロースを１０〜３０質量％含有しているため、繊維同士が絡みやすく繊維ネットワークが形成されやすくなることから、低坪量であっても、セパレータの引張強度が強かった。特に、セパレータの突刺強度が、比較例１０のポリエステル系繊維のみから構成されたセパレータよりも強くなった。 The separators for lithium ion secondary batteries of Examples 1 to 5 have a low basis weight of 8 g / m 2 . Since 10-30% by mass of the fibrillated solvent-spun cellulose is contained, the fibers are easily entangled with each other and a fiber network is easily formed. Therefore, the tensile strength of the separator was strong even at a low basis weight. In particular, the puncture strength of the separator was stronger than that of the separator composed only of the polyester fiber of Comparative Example 10.
一方、比較例１〜１０のリチウムイオン二次電池用セパレータも、８ｇ／ｍ２という低坪量である。比較例１と比較例２は、フィブリル化した溶剤紡糸セルロース繊維の含有量が１０〜３０質量％を外れた場合である。３０質量％を超えた比較例１では、機械強度の低下が著しく、内部短絡不良が発生した。また、１０質量％未満の比較例２では、最大ポア径が拡大するため、内部短絡不良が発生し、未延伸バインダー用ポリエステル短繊維が増加したため、抵抗成分のインピーダンスが高くなり、サイクル特性が低下した。 On the other hand, the lithium ion secondary battery separators of Comparative Examples 1 to 10 also have a low basis weight of 8 g / m 2 . Comparative Example 1 and Comparative Example 2 are cases where the content of fibrillated solvent-spun cellulose fibers deviated from 10 to 30% by mass. In Comparative Example 1 exceeding 30% by mass, the mechanical strength was remarkably reduced, and an internal short circuit failure occurred. Further, in Comparative Example 2 of less than 10% by mass, the maximum pore diameter is enlarged, so that an internal short circuit failure occurs, and the polyester short fibers for unstretched binders increase, so that the impedance of the resistance component increases and the cycle characteristics deteriorate. did.
比較例３と比較例４は、配向結晶化ポリエステル短繊維の含有量が４０〜５０質量％を外れた場合である。５０質量％を超えた比較例４では、最大ポア径が拡大するため、内部短絡不良が発生した。一方、４０質量未満の比較例３では、機械強度が低下するため、内部短絡不良が発生した。 Comparative Example 3 and Comparative Example 4 are cases where the content of oriented crystallized polyester short fibers deviated from 40 to 50% by mass. In Comparative Example 4 exceeding 50% by mass, the maximum pore diameter was increased, and thus an internal short circuit defect occurred. On the other hand, in Comparative Example 3 having a mass of less than 40 mass, the mechanical strength was reduced, and thus an internal short circuit failure occurred.
比較例５と比較例６は、未延伸バインダー用ポリエステル短繊維の含有量が３０〜４０質量％を外れた場合である。４０質量％を超えた比較例５では、最大ポア径が拡大するため、内部短絡不良が発生した。また、抵抗成分のインピーダンスが高くなり、サイクル特性が低下した。一方、３０質量未満の比較例６では、機械強度が低下するため、内部短絡不良が発生した。 Comparative Example 5 and Comparative Example 6 are cases where the content of polyester short fibers for unstretched binder deviates from 30 to 40% by mass. In Comparative Example 5 exceeding 40% by mass, the maximum pore diameter was increased, and thus an internal short circuit defect occurred. In addition, the impedance of the resistance component increased, and the cycle characteristics deteriorated. On the other hand, in Comparative Example 6 having a mass of less than 30 mass, the mechanical strength was reduced, and therefore an internal short circuit failure occurred.
比較例７は、配向結晶化ポリエステル短繊維の平均繊維径が３．５μｍを超えた場合であるが、機械強度が低下し、最大ポア径が拡大するため、内部短絡不良が発生した。平均繊維径が２．０μｍ未満の配向結晶化ポリエステル短繊維は、上市されていないため、評価はできなかった。 In Comparative Example 7, the average fiber diameter of the oriented crystallized polyester short fibers exceeded 3.5 μm, but the mechanical strength was reduced and the maximum pore diameter was increased, so that an internal short circuit failure occurred. Since oriented crystallized polyester short fibers having an average fiber diameter of less than 2.0 μm have not been put on the market, evaluation cannot be performed.
比較例８は、未延伸バインダー用ポリエステル短繊維の平均繊維径が５．０μｍを超えた場合であるが、未延伸バインダー用ポリエステル短繊維の繊維本数が減少するため、機械強度が低下し、最大ポア径も拡大したため、内部短絡不良が増加した。平均繊維径の太い未延伸バインダー用ポリエステル短繊維は、充放電サイクルの発熱で皮膜化が進むためか、サイクル特性が低下した。 Comparative Example 8 is a case where the average fiber diameter of the polyester short fibers for unstretched binder exceeds 5.0 μm. However, since the number of fibers of the polyester short fibers for unstretched binder decreases, the mechanical strength decreases, and the maximum Since the pore diameter also increased, internal short-circuit defects increased. The short polyester fiber for unstretched binder having a large average fiber diameter has deteriorated cycle characteristics because the film formation proceeds due to heat generation in the charge / discharge cycle.
比較例９は、未延伸バインダー用ポリエステル短繊維を含まない配合であるが、機械強度が極端に低く、内部短絡不良が増加した。 Comparative Example 9 was a composition not containing polyester short fibers for unstretched binder, but the mechanical strength was extremely low and the internal short circuit failure increased.
比較例１０は、フィブリル化した溶剤紡糸セルロース繊維を含まない配合であるが、最大細孔径が大きく、内部短絡不良が発生し、電解液の保持性能が低下するため、サイクル特性が低下した。 Comparative Example 10 was a formulation that did not contain fibrillated solvent-spun cellulose fibers, but the maximum pore size was large, an internal short circuit failure occurred, and the electrolyte retention performance was reduced, resulting in a reduction in cycle characteristics.
実施例１〜３の比較からから、フィブリル化した溶剤紡糸セルロースの配合量が増えるほど、機械強度はやや低下するが、抵抗成分を表すインピーダンスは低下しており、サイクル特性が向上した。実施例４のリチウムイオン二次電池用セパレータは、配向結晶化ポリエステル短繊維を少し太くした場合である。最大ポア径が拡大したが、内部短絡不良は発生せず、サイクル特性も良好であった。実施例５は、溶剤紡糸セルロースのフィブリル化を抑えた場合であるが、変法濾水度が１１３ｍｌであっても、内部短絡不良率やサイクル特性は良好であった。 From the comparison of Examples 1 to 3, the mechanical strength slightly decreased as the blended amount of the fibrillated solvent-spun cellulose increased, but the impedance representing the resistance component decreased and the cycle characteristics improved. The separator for the lithium ion secondary battery of Example 4 is a case where the oriented crystallized polyester short fibers are slightly thickened. Although the maximum pore diameter increased, internal short circuit failure did not occur and cycle characteristics were also good. In Example 5, the fibrillation of the solvent-spun cellulose was suppressed, but the internal short circuit failure rate and cycle characteristics were good even when the modified freeness was 113 ml.
実施例１〜１５を比較すると、坪量が７．０ｇ／ｍ２未満である実施例１１では、実施例１〜１０と比較して、機械強度が低下する傾向が見られ、内部短絡不良が見られた。坪量が１０．０ｇ／ｍ２を超えた実施例１２では、実施例１〜１０と比較して、抵抗成分を表すインピーダンスが上昇し、サイクル特性が低下した。厚さが１０．０μｍ未満の実施例１３では、実施例１〜１０と比較して、抵抗成分を表すインピーダンスが上昇し、サイクル特性が低下した。また、機械強度も低下し、内部短絡不良が発生した。厚さが１５．０μｍを超えた実施例１４では、実施例１〜１０と比較して、未延伸バインダー用ポリエステル短繊維の融着が甘くなったため、機械強度が低下し、内部短絡不良が発生した。引張強度が４５０Ｎ／ｍ未満である実施例１１及び１３では、実施例１〜１０と比較して、内部短絡不良が見られた。引張強度が７００Ｎ／ｍよりも大きくなった実施例１５では、実施例１〜１０と比較して、熱カレンダー処理のカレンダー圧を上げたために、突刺強度が低下し、内部短絡が発生した。また、抵抗成分を表すインピーダンスの上昇が発生し、サイクル特性が低下した。これらの結果から、坪量が７．０〜１０．０ｇ／ｍ２であること、厚さが１０．０〜１５．０μｍであること、引張強度が４５０〜７００Ｎ／ｍであることが好ましいことがわかる。 When Examples 1 to 15 are compared, in Example 11 in which the basis weight is less than 7.0 g / m 2 , the mechanical strength tends to decrease as compared with Examples 1 to 10, and internal short circuit failure is observed. It was seen. In Example 12, in which the basis weight exceeded 10.0 g / m 2 , the impedance representing the resistance component increased and the cycle characteristics decreased as compared with Examples 1-10. In Example 13 having a thickness of less than 10.0 μm, the impedance representing the resistance component increased and the cycle characteristics deteriorated as compared with Examples 1 to 10. In addition, the mechanical strength was reduced and internal short circuit failure occurred. In Example 14 where the thickness exceeded 15.0 μm, compared with Examples 1 to 10, the fusion of polyester short fibers for unstretched binder became sweeter, so the mechanical strength decreased and internal short circuit failure occurred. did. In Examples 11 and 13 having a tensile strength of less than 450 N / m, an internal short circuit failure was observed as compared with Examples 1 to 10. In Example 15 in which the tensile strength was greater than 700 N / m, the puncture strength was reduced and an internal short circuit occurred because the calender pressure of the thermal calendar process was increased as compared with Examples 1 to 10. In addition, an increase in impedance representing a resistance component occurred, and cycle characteristics deteriorated. From these results, it is preferable that the basis weight is 7.0 to 10.0 g / m 2 , the thickness is 10.0 to 15.0 μm, and the tensile strength is 450 to 700 N / m. I understand.
本発明の活用例としては、リチウムイオン二次電池用セパレータ、リチウムイオンポリマー二次電池用セパレータが好適である。 As an application example of the present invention, a lithium ion secondary battery separator and a lithium ion polymer secondary battery separator are suitable.
Claims (2)
フィブリル化した溶剤紡糸セルロース繊維を１０〜３０質量％、平均繊維径２．０〜３．５μｍの配向結晶化ポリエステル短繊維を４０〜５０質量％、平均繊維径５．０μｍ以下の未延伸バインダー用ポリエステル短繊維を３０〜４０質量％含有し、
坪量が７．０〜１０．０ｇ／ｍ ２ であり、厚さが１０．０〜１５．０μｍであり、引張強度が４５０〜７００Ｎ／ｍであることを特徴とするリチウムイオン二次電池用セパレータ。 In a separator for a lithium ion secondary battery consisting only of a sheet comprising only solvent-spun cellulose fibers and synthetic fibers fibrillated as a fiber raw material ,
10-30 mass% of fibrillated solvent-spun cellulose fibers, 40-50 mass% of oriented crystallized polyester short fibers with an average fiber diameter of 2.0-3.5 μm, for unstretched binders with an average fiber diameter of 5.0 μm or less Containing 30-40% by mass of polyester staple fiber ,
Basis weight of 7.0~10.0g / m 2, a thickness of 10.0～15.0Myuemu, lithium ion secondary tensile strength, characterized in 450~700N / m der Rukoto battery Separator.
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