JP4408016B2 - Microporous membrane - Google Patents
Microporous membrane Download PDFInfo
- Publication number
- JP4408016B2 JP4408016B2 JP2002316357A JP2002316357A JP4408016B2 JP 4408016 B2 JP4408016 B2 JP 4408016B2 JP 2002316357 A JP2002316357 A JP 2002316357A JP 2002316357 A JP2002316357 A JP 2002316357A JP 4408016 B2 JP4408016 B2 JP 4408016B2
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- polypropylene
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- Expired - Lifetime
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- 239000012982 microporous membrane Substances 0.000 title claims description 22
- -1 polyethylene Polymers 0.000 claims description 48
- 239000004743 Polypropylene Substances 0.000 claims description 38
- 239000004698 Polyethylene Substances 0.000 claims description 25
- 229920000573 polyethylene Polymers 0.000 claims description 25
- 229920001155 polypropylene Polymers 0.000 claims description 23
- 239000012528 membrane Substances 0.000 claims description 10
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 5
- 229910001416 lithium ion Inorganic materials 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 4
- 239000002356 single layer Substances 0.000 claims description 4
- 239000000470 constituent Substances 0.000 claims description 2
- 239000010408 film Substances 0.000 description 25
- 229920000098 polyolefin Polymers 0.000 description 16
- 238000000034 method Methods 0.000 description 13
- 239000000203 mixture Substances 0.000 description 12
- 230000000704 physical effect Effects 0.000 description 7
- 239000002904 solvent Substances 0.000 description 7
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 description 6
- 238000000862 absorption spectrum Methods 0.000 description 6
- 229920001903 high density polyethylene Polymers 0.000 description 6
- 239000004700 high-density polyethylene Substances 0.000 description 6
- 239000004014 plasticizer Substances 0.000 description 6
- 238000003860 storage Methods 0.000 description 6
- 239000013078 crystal Substances 0.000 description 5
- 238000002844 melting Methods 0.000 description 5
- 230000008018 melting Effects 0.000 description 5
- 229920000642 polymer Polymers 0.000 description 5
- 229920002959 polymer blend Polymers 0.000 description 5
- 239000007772 electrode material Substances 0.000 description 4
- 238000000605 extraction Methods 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 238000002156 mixing Methods 0.000 description 4
- 229940057995 liquid paraffin Drugs 0.000 description 3
- 230000035699 permeability Effects 0.000 description 3
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 description 3
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 description 3
- ZWEHNKRNPOVVGH-UHFFFAOYSA-N 2-Butanone Chemical compound CCC(C)=O ZWEHNKRNPOVVGH-UHFFFAOYSA-N 0.000 description 2
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 2
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 2
- 239000002033 PVDF binder Substances 0.000 description 2
- 239000011149 active material Substances 0.000 description 2
- 150000001298 alcohols Chemical class 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 229920001577 copolymer Polymers 0.000 description 2
- NNBZCPXTIHJBJL-UHFFFAOYSA-N decalin Chemical compound C1CCCC2CCCCC21 NNBZCPXTIHJBJL-UHFFFAOYSA-N 0.000 description 2
- DOIRQSBPFJWKBE-UHFFFAOYSA-N dibutyl phthalate Chemical compound CCCCOC(=O)C1=CC=CC=C1C(=O)OCCCC DOIRQSBPFJWKBE-UHFFFAOYSA-N 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 239000008151 electrolyte solution Substances 0.000 description 2
- 229930195733 hydrocarbon Natural products 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- 238000002188 infrared transmission spectroscopy Methods 0.000 description 2
- 239000010410 layer Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000000691 measurement method Methods 0.000 description 2
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 2
- GLDOVTGHNKAZLK-UHFFFAOYSA-N octadecan-1-ol Chemical compound CCCCCCCCCCCCCCCCCCO GLDOVTGHNKAZLK-UHFFFAOYSA-N 0.000 description 2
- 238000010525 oxidative degradation reaction Methods 0.000 description 2
- 238000006116 polymerization reaction Methods 0.000 description 2
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- ALSTYHKOOCGGFT-KTKRTIGZSA-N (9Z)-octadecen-1-ol Chemical compound CCCCCCCC\C=C/CCCCCCCCO ALSTYHKOOCGGFT-KTKRTIGZSA-N 0.000 description 1
- UOCLXMDMGBRAIB-UHFFFAOYSA-N 1,1,1-trichloroethane Chemical compound CC(Cl)(Cl)Cl UOCLXMDMGBRAIB-UHFFFAOYSA-N 0.000 description 1
- VXNZUUAINFGPBY-UHFFFAOYSA-N 1-Butene Chemical compound CCC=C VXNZUUAINFGPBY-UHFFFAOYSA-N 0.000 description 1
- LIKMAJRDDDTEIG-UHFFFAOYSA-N 1-hexene Chemical compound CCCCC=C LIKMAJRDDDTEIG-UHFFFAOYSA-N 0.000 description 1
- KWKAKUADMBZCLK-UHFFFAOYSA-N 1-octene Chemical compound CCCCCCC=C KWKAKUADMBZCLK-UHFFFAOYSA-N 0.000 description 1
- NLZUEZXRPGMBCV-UHFFFAOYSA-N Butylhydroxytoluene Chemical compound CC1=CC(C(C)(C)C)=C(O)C(C(C)(C)C)=C1 NLZUEZXRPGMBCV-UHFFFAOYSA-N 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- XDTMQSROBMDMFD-UHFFFAOYSA-N Cyclohexane Chemical compound C1CCCCC1 XDTMQSROBMDMFD-UHFFFAOYSA-N 0.000 description 1
- MQIUGAXCHLFZKX-UHFFFAOYSA-N Di-n-octyl phthalate Natural products CCCCCCCCOC(=O)C1=CC=CC=C1C(=O)OCCCCCCCC MQIUGAXCHLFZKX-UHFFFAOYSA-N 0.000 description 1
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 1
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical group C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 1
- 239000005977 Ethylene Substances 0.000 description 1
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 1
- 241000692870 Inachis io Species 0.000 description 1
- 229910013063 LiBF 4 Inorganic materials 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 238000002835 absorbance Methods 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 150000001336 alkenes Chemical class 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 239000003963 antioxidant agent Substances 0.000 description 1
- 230000003078 antioxidant effect Effects 0.000 description 1
- BJQHLKABXJIVAM-UHFFFAOYSA-N bis(2-ethylhexyl) phthalate Chemical compound CCCCC(CC)COC(=O)C1=CC=CC=C1C(=O)OCC(CC)CCCC BJQHLKABXJIVAM-UHFFFAOYSA-N 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- IAQRGUVFOMOMEM-UHFFFAOYSA-N butene Natural products CC=CC IAQRGUVFOMOMEM-UHFFFAOYSA-N 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 239000011889 copper foil Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
- 229920005676 ethylene-propylene block copolymer Polymers 0.000 description 1
- 229920005674 ethylene-propylene random copolymer Polymers 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 150000008282 halocarbons Chemical class 0.000 description 1
- 238000009998 heat setting Methods 0.000 description 1
- 229920001519 homopolymer Polymers 0.000 description 1
- 150000002576 ketones Chemical class 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- 229920005684 linear copolymer Polymers 0.000 description 1
- 229920000092 linear low density polyethylene Polymers 0.000 description 1
- 239000004707 linear low-density polyethylene Substances 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 229920001684 low density polyethylene Polymers 0.000 description 1
- 239000004702 low-density polyethylene Substances 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 229920001179 medium density polyethylene Polymers 0.000 description 1
- 239000004701 medium-density polyethylene Substances 0.000 description 1
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 description 1
- 125000001570 methylene group Chemical group [H]C([H])([*:1])[*:2] 0.000 description 1
- 239000011325 microbead Substances 0.000 description 1
- 239000000178 monomer Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- GOQYKNQRPGWPLP-UHFFFAOYSA-N n-heptadecyl alcohol Natural products CCCCCCCCCCCCCCCCCO GOQYKNQRPGWPLP-UHFFFAOYSA-N 0.000 description 1
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 description 1
- 229940055577 oleyl alcohol Drugs 0.000 description 1
- XMLQWXUVTXCDDL-UHFFFAOYSA-N oleyl alcohol Natural products CCCCCCC=CCCCCCCCCCCO XMLQWXUVTXCDDL-UHFFFAOYSA-N 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 239000012188 paraffin wax Substances 0.000 description 1
- YWAKXRMUMFPDSH-UHFFFAOYSA-N pentene Chemical compound CCCC=C YWAKXRMUMFPDSH-UHFFFAOYSA-N 0.000 description 1
- 238000005191 phase separation Methods 0.000 description 1
- 229920001083 polybutene Polymers 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 229920001384 propylene homopolymer Polymers 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- PXXNTAGJWPJAGM-UHFFFAOYSA-N vertaline Natural products C1C2C=3C=C(OC)C(OC)=CC=3OC(C=C3)=CC=C3CCC(=O)OC1CC1N2CCCC1 PXXNTAGJWPJAGM-UHFFFAOYSA-N 0.000 description 1
- 239000004711 α-olefin Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
- C08J2323/04—Homopolymers or copolymers of ethene
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
- C08J2323/04—Homopolymers or copolymers of ethene
- C08J2323/06—Polyethene
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2423/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2423/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
- C08J2423/10—Homopolymers or copolymers of propene
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2423/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2423/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
- C08J2423/10—Homopolymers or copolymers of propene
- C08J2423/12—Polypropene
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Cell Separators (AREA)
- Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
Description
【0001】
【発明の属する技術分野】
本発明はポリエチレンを50重量%以上含有する微多孔膜、特にリチウムイオン二次電池用セパレータに適した微多孔膜に関する。
【0002】
【従来の技術】
微多孔膜は、電池やコンデンサーのセパレータとして使用されてきているが、中でも小型携帯機器の電源として高い性能を発揮できるリチウムイオン二次電池(LIBと略す)用セパレータの需要が大きく伸びている。近年、小型携帯機器の使用電力が大きくなるに従い、LIBの高容量化が強く求められている。
LIBの高容量化手段には電極活物質の増量および利用率の向上があるが、利用率の向上はほぼ限界まで達しており電極活物質の増量が中心となっている。電池缶の内容積が一定であるため電極活物質の増量のためには活物質以外の部材を減量して活物質の充填可能容積を増加させるとともに充填密度を上げる検討がなされてきている。セパレータには薄膜化が強く要求されている。しかし、電極活物質は電池の充放電とともに体積が膨張収縮するため、高容量LIBでは電極の膨張収縮も容量に比例して大きくなるため正極と負極の間にあり短絡防止が役割であるセパレータには、薄膜化しながら高強度が要求される。また、高容量化した電池はエネルギー密度が大きくなるため、安全性や電池容量の維持に関しても厳しい条件となる。特にセパレータは電池性能に大きな役割を担う部材であり、安全性ではポリエチレンの溶融に基づく孔閉塞現象が不可欠であるとともに電池容量維持に対しても要求がなされてきている。
【0003】
中でも充電電池の高電圧で高温条件下の保存試験では、ガスが発生するとともに放電容量が低下する問題が高容量LIBでは顕在化してきている。このガス発生や放電容量の低下は正極によるポリエチレンの酸化劣化が主原因であると推定されており、ポリプロピレンのようなポリエチレン以外のポリオレフィンでは酸化劣化量がポリエチレンよりも減少しガス発生や容量低下が抑制されることが知られている。これに対して、特許文献1にあるように正極板に対抗する面をポリプロピレン層とする積層の多層膜が提案されている。
【0004】
しかし、多層膜では単層膜に比較して薄膜化が難しいことに加え延伸配向による高強度化が難しいことから、高容量LIBの要求に対応した高強度な薄膜を得ることが困難となる。このため、相分離による開孔と延伸配向によって高強度を発現するポリエチレンが主成分の単層膜からなる微多孔膜を用いた薄膜化セパレータが高容量LIB用セパレータの主流となっている。
正極面でのポリエチレンの酸化量を少なくするためにポリエチレンにポリプロピレン等のポリオレフィンを多量にブレンドして製膜した微多孔膜では、特許文献2にあるように膜強度が大きく低下(突き刺し強度の低下)したり開孔が困難となる(透気度が大きくなる)ことが知られている。このため、ポリエチレンに少量のポリオレフィンをブレンドした組成でガス発生や放電容量の低下が抑制できる微多孔膜が製膜できることが望まれていた。
【0005】
【特許文献1】
特開2001−273880号公報
【特許文献2】
特開平10−298324号公報
【0006】
【発明が解決しようとする課題】
本発明の目的は、高容量LIB用の高性能セパレータとして必要とされる物性を有しつつ高温保存時のガス発生や放電容量の低下を抑制できる微多孔膜を提供しようとするものである。
【0007】
【課題を解決するための手段】
本発明者は前記課題に対して鋭意研究を重ねた結果、ポリエチレンに特定のポリプロピレン等のポリオレフィンを加えてブレンドして製膜すると機構は不明であるがポリオレフィンが表面に偏析して表面近傍のポリエチレンの含有率が減少する場合があり、このような表面の微多孔膜では高温保存時のガス発生や放電容量の低下を抑制できることを見出し、本発明をなすに至った。
【0008】
すなわち本発明は、下記のとおりである。
(1)ポリエチレンを50重量%以上含有する単層の微多孔膜であって、少なくとも片面の膜の表面近傍のポリエチレンの含有率が膜全体の平均値よりも少ないことを特徴とする微多孔膜。
(2)ポリエチレン以外の成分がポリエチレン以外のポリオレフィンであることを特徴とする(1)記載の微多孔膜。
(3)ポリエチレン以外のポリオレフィンが粘度平均分子量が5万以下の低分子量ポリプロピレンを必須成分として含んでいることを特徴とする(2)記載の微多孔膜。
(4)粘度平均分子量が20万以上のポリプロピレンと粘度平均分子量が5万以下の低分子量ポリプロピレンをそれぞれ膜構成材料全体の5〜20重量%含んでいることを特徴とする(3)記載の微多孔膜。
(5)(1)から(4)のいずれかに記載の微多孔膜からなるリチウムイオン二次電池用セパレータ。
【0009】
【発明の実施の形態】
以下、本発明について、特にその好ましい態様を中心に、詳細に説明する。
本発明の微多孔膜は高容量LIB用セパレータとして要求される物性を満たすためにポリエチレンを膜構成材料全体の50重量%以上含有する。ここでいうポリエチレンとは粘度平均分子量が好ましくは10万〜300万、より好ましくは20万〜100万、さらに好ましくは25万〜70万の高密度ポリエチレンである。また、このポリエチレンはエチレン単位に対してプロピレン、ブテン、ペンテン、ヘキセン、オクテン等のα−オレフィンの単位を4モル%以下の割合で含む共重合体(線状共重合ポリエチレン)であってもよい。また、ブレンドや多段重合などの手段によって平均分子量を好ましい範囲に調整したものでもかまわない。さらに、これらに中密度ポリエチレン、線状低密度ポリエチレン、低密度ポリエチレンをブレンドしたものでもかまわない。
【0010】
本発明にいうポリオレフィンとは、ポリエチレン、ポリプロピレンやポリブテンの様なオレフィンモノマーのホモポリマーおよびコポリマーをいい、その低分子量ポリマーであってもかまわない。
本発明で用いるポリプロピレンはプロピレンホモポリマーの他にエチレン−プロピレンランダムコポリマー、エチレン−プロピレンブロックコポリマーであってもよく、それらのブレンドであってもよい。粘度平均分子量は20万〜100万であることが好ましい。低分子量ポリプロピレンは粘度平均分子量が好ましくは5万以下、より好ましくは3千〜3万のポリプロピレンである。低分子量ポリプロピレンの製法は重合法でも高分子量ポリプロピレンを分解する方法でもかまわない。
【0011】
膜の表面近傍とは膜の最表面から1μm程度の深さまでの領域をいい、ATR法と呼ばれる試料表面の全反射光の赤外線吸収スペクトル法で測定される領域に対応している。
膜を構成するポリマーの比率の膜全体と表面近傍の比較は、赤外吸収スペクトルを用いた各種測定法の中で膜全体と表面近傍の測定に適応する測定法を用いて行った。膜全体のポリマー比率は透過IR法(膜を透過する赤外吸収スペクトル)、表面近傍の各ポリマーの比率はATR法を用いて行い、赤外吸収スペクトルの同じ特性吸収ピークの比率を用いた。
【0012】
次に本発明の微多孔膜は、好ましくはポリマーの50重量%以上のポリエチレンとポリエチレン以外のポリオレフィンの混合物に可塑剤を加えて溶融混練後成形し、延伸、抽出等を施すことにより得られる。本発明で使用する可塑剤としては、ポリオレフィンと混合した際にポリオレフィンの融点以上において均一溶液を形成しうる不揮発溶媒であればよい。例えば、流動パラフィンやパラフィンワックス等の炭化水素類、フタル酸ジオクチルやフタル酸ジブチル等のエステル類、オレイルアルコールやステアリルアルコール等の高級アルコールが挙げられる。また本発明における組成物には、酸化防止剤等の添加物を適宜加えても構わない。
【0013】
本発明の微多孔膜を得る好ましい製造法としては、ポリオレフィン混合物と可塑剤からなる組成物を溶融混練し、押し出して冷却固化させゲル状シートを成形する。ポリオレフィンの配合割合は好ましくは20〜70wt%、より好ましくは30〜60wt%である。
続いてこのシートを延伸する工程ではゲル状シートを加熱しテンター法、ロール法、圧延法もしくはこれらの方法を組み合わせて行うが、テンターを用いた同時二軸延伸が好ましい。延伸温度は使用するポリオレフィン混合物の結晶分散温度から結晶融点の間の温度である。好ましくは90〜150℃で、より好ましくは100〜140℃の範囲である。延伸倍率は使用するポリオレフィンによって可能な範囲があるが、延伸時の破膜が生じない範囲でできるだけ高倍率が好ましい。高倍率延伸ほど微多孔膜の強度が大きくなり好ましい。
【0014】
可塑剤を抽出する抽出溶媒は、ポリオレフィンに対して貧溶媒でありかつ可塑剤に対して良溶媒であればよく、沸点が原料ポリオレフィンの融点よりも低いことが望ましい。このような抽出溶媒としては、例えば、n−ヘキサンやシクロヘキサン等の炭化水素類、塩化メチレンや1,1,1-トリクロロエタン等ハロゲン化炭化水素類、エタノールやイソプロパノール等のアルコール類、アセトンや2-ブタノン等のケトン類等が挙げられる。
可塑剤の抽出後さらに少なくとも一軸方向に少なくとも一回延伸操作を行うこともできる。抽出後延伸の延伸倍率は任意の倍率に設定できるが、一軸方向の倍率で5倍以内、二軸方向の面積倍率で20倍以内が好ましい。さらに、結晶分散温度から結晶融点の温度範囲で熱固定を施すこともできる。
【0015】
以下、実施例により本発明を詳細に説明するが、本発明は下記実施例に限定されるものではない。なお、実施例において示される試験方法は次の通りである。
(1)膜厚
ダイヤルゲージ(尾崎製作所製PEACOCK No.25(商標))を用いて測定。
(2)気孔率
20cm角の試料を用意し、その試料体積(cm3 )と質量(g)を測定し得られた結果から次式を用いて気孔率(%)を計算した。
気孔率=(1−質量/(樹脂密度×試料体積))×100
(3)透気度
JIS P−8117に準拠しガーレー式透気度計にて測定。
(4)突刺強度
圧縮試験機(カトーテック製KES−G5(商標))を用いて、先端の曲率半径0.5mmの針を用いて突き刺し速度2mm/sで突き刺し試験を行い最大突き刺し荷重(N)を突刺強度(N)とした。
【0016】
(5)粘度平均分子量
溶剤としてデカリンを用い、測定温度135℃で極限粘度[η]を測定し、ポリエチレンについては次式により粘度平均分子量Mvを求めた。
[η]=6.77×10-4Mv0.67
ポリプロピレンについては、次式によりMvを求めた。
[η]=1.10×10-4Mv0.80
(6)赤外吸収スペクトル測定
測定は日本バイオラッド・ラボラトリーズ社製FTS−60A896(商標)を用いて行った。ATR法はGe結晶板を用いて入射角は60度で測定した。透過IR法はホルダーに膜サンプルを貼り透過光で測定した。
【0017】
(7)膜全体及び表面近傍のPP値
赤外吸収スペクトルのメチル基由来の波数2960cm-1のピーク高さ(吸高度)をメチレン基由来の波数2918cm-1のピーク高さで割った値を100倍した値をPP値として、 膜全体は透過光IR法、表面近傍はATR法の測定チャートから算出。
(8)簡易ボタン電池を用いた高温保存評価
コバルト酸リチウム粉末85重量部とカーボンブラック5重量部とポリフッ化ビニリデン重量部を混合し、N―メチルピロリドンを加えてペースト状に調整した後、これを厚さ20μmのアルミ箔上に塗布乾燥後プレスし正極板を作成した。これを直径15.958mmの円形に打ち抜き正極とした。次にメソフェーズカーボンマイクロビーズ粉末を90重量部とポリフッ化ビニリデン10重量部を混合し、N−メチルピロリドンを加えてペースト状に調整した後、これを厚さ18μmの銅箔上に塗布乾燥後プレスし負極板を作成した。これを直径16.156mmの円形に打ち抜き負極とした。
【0018】
この負極の上に直径18mmの円形に打ち抜いたセパレータを置きさらに正極を重ねて電極層とし、電解液を加えて簡易ボタン電池を作成した。電解液としてはエチレンカーボネートとジエチルカーボネートを重量比で1対1に混合した溶媒にLiBF4を1Mの濃度で溶解した電解液を用いた。
この簡易ボタン電池の0.33C、4.2Vの定電流定電圧充電後の初期放電容量は6.5mAhであった。この電池を90℃の高温槽で3日間放置した後の放電容量を測定し、初期放電容量に対する値を高温保存時の容量維持率(%)として算出した。
【0019】
【実施例1】
粘度平均分子量が28万の高密度ポリエチレン80重量%及び粘度平均分子量が32万のポリプロピレン10重量%及び粘度平均分子量が19000の低分子量ポリプロピレン10重量%からなるポリマー混合物55部、流動パラフィン45部、2,6−ジ−t−ブチル−p−クレゾール0.55部をバッチ式溶融混練機(東洋精機社製:ラボプラストミル)を用いて200℃、50rpmで10分間混練した。得られた混練物を200℃の加熱プレスで成形し2分間そのまま加熱処理をした後25℃の水冷プレスで冷却し、厚さ1000μmの原反とした。これを同時2軸延伸機(東洋精機社製)を用いて120℃で7×7倍に延伸した。この延伸膜を塩化メチレン液に浸漬し流動パラフィンを抽出除去し乾燥した。得られた微多孔膜の物性を表1に示した。全体のPP値に対して表面近傍のPP値は大きな値を示しており、PPが膜内部よりも表面近傍に多いことが判った。
【0020】
【実施例2】
実施例1において、ポリマー混合物の組成を粘度平均分子量が28万の高密度ポリエチレンを80重量%及び粘度平均分子量が32万のポリプロピレンを10重量%及び粘度平均分子量が5700の低分子量プロピレン10重量%とする以外は実施例1と同様の方法で微多孔膜を作成した。得られた微多孔膜の物性を表1に示した。全体のPP値に対して表面近傍のPP値は大きな値を示しており、PPが膜内部よりも表面近傍に多いことが判った。
【0021】
【実施例3】
実施例1において、ポリマー混合物の組成を粘度平均分子量が28万の高密度ポリエチレンを80重量%及び粘度平均分子量が5700の低分子量プロピレン20重量%とする以外は実施例1と同様の方法で微多孔膜を作成した。得られた微多孔膜の物性を表1に示した。全体のPP値に対して表面近傍のPP値は大きな値を示しており、PPが膜内部よりも表面近傍に多いことが判った。
【0022】
【比較例1】
実施例1において、ポリマー混合物の組成を粘度平均分子量が28万の高密度ポリエチレンを80重量%及び粘度平均分子量が32万のポリプロピレンを20重量%とする以外は実施例1と同様の方法で微多孔膜を作成した。得られた微多孔膜の物性を表1に示した。全体のPP値と表面近傍のPP値はほぼ同じ値を示した。
【0023】
【比較例2】
実施例1において、ポリマー混合物の組成を粘度平均分子量が28万の高密度ポリエチレンを60重量%及び粘度平均分子量が32万のポリプロピレンを40重量%とする以外は実施例1と同様の方法で微多孔膜を作成した。得られた微多孔膜の物性を表1に示した。全体のPP値と表面近傍のPP値はほぼ同じ値を示した。
【0024】
【表1】
【0025】
【発明の効果】
本セパレータを用いた高容量リチウムイオン二次電池用の高性能セパレータとして必要とされる物性を有しつつ高温保存時のガス発生や放電容量の低下を抑制できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a microporous membrane containing 50% by weight or more of polyethylene, and particularly to a microporous membrane suitable for a separator for a lithium ion secondary battery.
[0002]
[Prior art]
Microporous membranes have been used as separators for batteries and capacitors. In particular, the demand for separators for lithium ion secondary batteries (abbreviated as LIB) that can exhibit high performance as a power source for small portable devices is greatly increasing. In recent years, as the power consumption of small portable devices increases, there is a strong demand for higher LIB capacity.
The means for increasing the capacity of the LIB includes an increase in the electrode active material and an improvement in the utilization rate. However, the improvement in the utilization rate has almost reached its limit, and the increase in the electrode active material is the center. Since the internal volume of the battery can is constant, in order to increase the electrode active material, studies have been made to increase the packing density while reducing the amount of members other than the active material to increase the active material filling volume. The separator is strongly required to be thin. However, since the volume of the electrode active material expands and contracts as the battery is charged and discharged, the expansion and contraction of the electrode increases in proportion to the capacity in a high capacity LIB. However, high strength is required while thinning. Moreover, since the energy density of a battery with an increased capacity increases, it becomes a severe condition with respect to safety and maintenance of battery capacity. In particular, the separator is a member that plays a major role in battery performance, and in terms of safety, a pore clogging phenomenon based on melting of polyethylene is indispensable, and there is a demand for maintaining battery capacity.
[0003]
In particular, in a storage test under a high voltage and high temperature condition of a rechargeable battery, the problem that gas is generated and the discharge capacity is reduced has become apparent in the high capacity LIB. This decrease in gas generation and discharge capacity is presumed to be mainly caused by oxidative degradation of polyethylene by the positive electrode. Polyolefins other than polyethylene such as polypropylene have a lower amount of oxidative degradation than polyethylene, leading to gas generation and capacity reduction. It is known to be suppressed. On the other hand, as disclosed in Patent Document 1, a multilayer film having a polypropylene layer as a surface facing the positive electrode plate has been proposed.
[0004]
However, since it is difficult to reduce the thickness of a multilayer film as compared with a single-layer film, it is difficult to increase the strength by stretching orientation, so that it is difficult to obtain a high-strength thin film that meets the requirements for a high-capacity LIB. For this reason, a thinned separator using a microporous film composed of a single layer film of polyethylene as a main component, which exhibits high strength by opening by phase separation and stretching orientation, has become the mainstream of high capacity LIB separators.
In the microporous film formed by blending a large amount of polyolefin such as polypropylene with polyethylene in order to reduce the oxidation amount of polyethylene on the positive electrode surface, the film strength is greatly reduced as in Patent Document 2 (the piercing strength is reduced). ) Or opening holes (air permeability increases). For this reason, it has been desired that a microporous membrane capable of suppressing gas generation and reduction in discharge capacity can be formed with a composition in which a small amount of polyolefin is blended with polyethylene.
[0005]
[Patent Document 1]
JP 2001-273880 A [Patent Document 2]
Japanese Patent Laid-Open No. 10-298324
[Problems to be solved by the invention]
An object of the present invention is to provide a microporous membrane that has properties required as a high-performance separator for a high-capacity LIB, and can suppress gas generation and discharge capacity reduction during high-temperature storage.
[0007]
[Means for Solving the Problems]
As a result of intensive research on the above problems, the inventor has added a polyolefin such as specific polypropylene to polyethylene and blended to form a film. It has been found that such a microporous film on the surface can suppress gas generation and discharge capacity reduction during high-temperature storage, and has led to the present invention.
[0008]
That is, the present invention is as follows.
(1) A microporous membrane having a single layer containing 50% by weight or more of polyethylene, wherein the polyethylene content in the vicinity of at least one surface of the membrane is less than the average value of the entire membrane .
(2) The microporous membrane according to (1), wherein the component other than polyethylene is a polyolefin other than polyethylene.
(3) The microporous membrane according to (2), wherein the polyolefin other than polyethylene contains a low molecular weight polypropylene having a viscosity average molecular weight of 50,000 or less as an essential component.
(4) The composition according to (3), wherein 5 to 20% by weight of the total film constituent material is contained in each of polypropylene having a viscosity average molecular weight of 200,000 or more and low molecular weight polypropylene having a viscosity average molecular weight of 50,000 or less. Porous membrane.
(5) A separator for a lithium ion secondary battery comprising the microporous membrane according to any one of (1) to (4).
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with a focus on preferred embodiments.
The microporous membrane of the present invention contains polyethylene in an amount of 50% by weight or more of the entire membrane constituting material in order to satisfy the physical properties required as a high-capacity LIB separator. The polyethylene here is a high-density polyethylene having a viscosity average molecular weight of preferably 100,000 to 3,000,000, more preferably 200,000 to 1,000,000, and still more preferably 250,000 to 700,000. Further, this polyethylene may be a copolymer (linear copolymer polyethylene) containing an α-olefin unit such as propylene, butene, pentene, hexene, octene or the like in an amount of 4 mol% or less with respect to the ethylene unit. . Further, the average molecular weight may be adjusted to a preferred range by means such as blending or multistage polymerization. Further, these may be blended with medium density polyethylene, linear low density polyethylene, or low density polyethylene.
[0010]
The polyolefin referred to in the present invention refers to homopolymers and copolymers of olefin monomers such as polyethylene, polypropylene and polybutene, and may be low molecular weight polymers thereof.
In addition to the propylene homopolymer, the polypropylene used in the present invention may be an ethylene-propylene random copolymer, an ethylene-propylene block copolymer, or a blend thereof. The viscosity average molecular weight is preferably 200,000 to 1,000,000. The low molecular weight polypropylene is a polypropylene having a viscosity average molecular weight of preferably 50,000 or less, more preferably 3,000 to 30,000. The production method of the low molecular weight polypropylene may be a polymerization method or a method of decomposing the high molecular weight polypropylene.
[0011]
The vicinity of the surface of the film means a region from the outermost surface of the film to a depth of about 1 μm, and corresponds to a region measured by the infrared absorption spectrum method of the total reflection light on the sample surface called ATR method.
Comparison of the ratio of the polymer constituting the film between the entire film and the vicinity of the surface was performed using a measurement method adapted to the measurement of the entire film and the vicinity of the surface among various measurement methods using an infrared absorption spectrum. The polymer ratio of the whole film was measured by the transmission IR method (infrared absorption spectrum transmitted through the film), the ratio of each polymer in the vicinity of the surface was determined by the ATR method, and the ratio of the same characteristic absorption peak of the infrared absorption spectrum was used.
[0012]
Next, the microporous membrane of the present invention is preferably obtained by adding a plasticizer to a mixture of polyethylene of 50% by weight or more of polymer and a polyolefin other than polyethylene, melt-kneading, molding, stretching, extraction and the like. The plasticizer used in the present invention may be any non-volatile solvent that can form a uniform solution above the melting point of the polyolefin when mixed with the polyolefin. Examples thereof include hydrocarbons such as liquid paraffin and paraffin wax, esters such as dioctyl phthalate and dibutyl phthalate, and higher alcohols such as oleyl alcohol and stearyl alcohol. Moreover, you may add suitably additives, such as antioxidant, to the composition in this invention.
[0013]
As a preferred production method for obtaining the microporous membrane of the present invention, a composition comprising a polyolefin mixture and a plasticizer is melt-kneaded and extruded to cool and solidify to form a gel sheet. The blending ratio of the polyolefin is preferably 20 to 70 wt%, more preferably 30 to 60 wt%.
Subsequently, in the step of stretching the sheet, the gel-like sheet is heated to perform a tenter method, a roll method, a rolling method, or a combination of these methods. Simultaneous biaxial stretching using a tenter is preferable. The stretching temperature is a temperature between the crystal dispersion temperature and the crystal melting point of the polyolefin mixture used. Preferably it is 90-150 degreeC, More preferably, it is the range of 100-140 degreeC. The draw ratio has a possible range depending on the polyolefin to be used, but is preferably as high as possible within a range where film breakage does not occur during stretching. Higher magnification stretching is preferred because the strength of the microporous membrane increases.
[0014]
The extraction solvent for extracting the plasticizer may be a poor solvent for the polyolefin and a good solvent for the plasticizer, and the boiling point is desirably lower than the melting point of the raw material polyolefin. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane, halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane, alcohols such as ethanol and isopropanol, acetone and 2- Examples include ketones such as butanone.
After the plasticizer is extracted, a stretching operation can be performed at least once in at least a uniaxial direction. The stretching ratio of the stretching after extraction can be set to an arbitrary ratio, but it is preferably within 5 times in the uniaxial direction and within 20 times in the area ratio in the biaxial direction. Furthermore, heat setting can be performed in the temperature range from the crystal dispersion temperature to the crystal melting point.
[0015]
EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to the following Example. In addition, the test method shown in an Example is as follows.
(1) Measured using a film thickness dial gauge (PEACOCK No. 25 (trademark) manufactured by Ozaki Seisakusho).
(2) A sample with a porosity of 20 cm square was prepared, and the porosity (%) was calculated from the results obtained by measuring the sample volume (cm 3 ) and mass (g) using the following equation.
Porosity = (1−mass / (resin density × sample volume)) × 100
(3) Air permeability Measured with a Gurley air permeability meter according to JIS P-8117.
(4) Using a puncture strength compression tester (Katotech KES-G5 (trademark)), a puncture test was conducted at a puncture speed of 2 mm / s using a needle having a radius of curvature of 0.5 mm at the tip, and the maximum puncture load (N ) Was defined as the puncture strength (N).
[0016]
(5) Using decalin as the viscosity average molecular weight solvent, the intrinsic viscosity [η] was measured at a measurement temperature of 135 ° C., and for polyethylene, the viscosity average molecular weight Mv was determined by the following formula.
[Η] = 6.77 × 10 −4 Mv 0.67
For polypropylene, Mv was determined by the following formula.
[Η] = 1.10 × 10 −4 Mv 0.80
(6) The infrared absorption spectrum measurement was performed using FTS-60A896 (trademark) manufactured by Nippon Bio-Rad Laboratories. In the ATR method, a Ge crystal plate was used and the incident angle was measured at 60 degrees. In the transmission IR method, a film sample was attached to a holder and measured with transmitted light.
[0017]
(7) The value obtained by dividing the peak height (absorbance) of the wave number 2960 cm −1 derived from the methyl group of the PP value infrared absorption spectrum of the entire film and the vicinity of the surface by the peak height of the wave number 2918 cm −1 derived from the methylene group. The value multiplied by 100 is taken as the PP value, and the entire film is calculated from the measurement chart of the transmitted light IR method and the vicinity of the surface is calculated from the ATR method.
(8) Evaluation of high-temperature storage using a simple button battery After mixing 85 parts by weight of lithium cobaltate powder, 5 parts by weight of carbon black, and parts by weight of polyvinylidene fluoride, N-methylpyrrolidone was added to prepare a paste. Was coated on an aluminum foil having a thickness of 20 μm, dried and pressed to prepare a positive electrode plate. This was punched into a circular shape with a diameter of 15.958 mm to obtain a positive electrode. Next, 90 parts by weight of mesophase carbon microbead powder and 10 parts by weight of polyvinylidene fluoride were mixed, adjusted to a paste by adding N-methylpyrrolidone, applied onto a 18 μm thick copper foil, dried and pressed. A negative electrode plate was prepared. This was punched into a circle having a diameter of 16.156 mm to obtain a negative electrode.
[0018]
A separator punched into a circle having a diameter of 18 mm was placed on the negative electrode, and the positive electrode was further stacked to form an electrode layer, and an electrolyte was added to prepare a simple button battery. As the electrolytic solution, an electrolytic solution in which LiBF 4 was dissolved at a concentration of 1 M in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a weight ratio of 1: 1 was used.
The initial discharge capacity of this simple button battery after charging with a constant current and a constant voltage of 0.33 C and 4.2 V was 6.5 mAh. The discharge capacity after leaving this battery in a high temperature bath at 90 ° C. for 3 days was measured, and the value for the initial discharge capacity was calculated as the capacity retention rate (%) during high temperature storage.
[0019]
[Example 1]
55 parts of a polymer mixture comprising 80% by weight of high density polyethylene having a viscosity average molecular weight of 280,000, 10% by weight of polypropylene having a viscosity average molecular weight of 320,000 and 10% by weight of low molecular weight polypropylene having a viscosity average molecular weight of 19000, 45 parts of liquid paraffin, 0.55 part of 2,6-di-t-butyl-p-cresol was kneaded at 200 ° C. and 50 rpm for 10 minutes using a batch melt kneader (manufactured by Toyo Seiki Co., Ltd .: Labo Plast Mill). The obtained kneaded material was molded with a 200 ° C. hot press, heat-treated for 2 minutes as it was, then cooled with a 25 ° C. water-cooled press to form a 1000 μm-thick original fabric. This was stretched 7 × 7 times at 120 ° C. using a simultaneous biaxial stretching machine (manufactured by Toyo Seiki Co., Ltd.). This stretched membrane was immersed in a methylene chloride solution, and liquid paraffin was extracted and dried. Table 1 shows the physical properties of the obtained microporous membrane. The PP value in the vicinity of the surface shows a large value with respect to the entire PP value, and it was found that the PP is more in the vicinity of the surface than in the film.
[0020]
[Example 2]
In Example 1, the composition of the polymer mixture was 80% by weight of high density polyethylene having a viscosity average molecular weight of 280,000, 10% by weight of polypropylene having a viscosity average molecular weight of 320,000, and 10% by weight of low molecular weight propylene having a viscosity average molecular weight of 5700. A microporous membrane was prepared in the same manner as in Example 1 except that. Table 1 shows the physical properties of the obtained microporous membrane. The PP value in the vicinity of the surface shows a large value with respect to the entire PP value, and it was found that the PP is more in the vicinity of the surface than in the film.
[0021]
[Example 3]
In Example 1, the composition of the polymer mixture was finely adjusted in the same manner as in Example 1 except that 80% by weight of high density polyethylene having a viscosity average molecular weight of 280,000 and 20% by weight of low molecular weight propylene having a viscosity average molecular weight of 5700 were used. A porous membrane was created. Table 1 shows the physical properties of the obtained microporous membrane. The PP value in the vicinity of the surface shows a large value with respect to the entire PP value, and it was found that the PP is more in the vicinity of the surface than in the film.
[0022]
[Comparative Example 1]
In Example 1, the composition of the polymer mixture was finely determined in the same manner as in Example 1 except that 80% by weight of high density polyethylene having a viscosity average molecular weight of 280,000 and 20% by weight of polypropylene having a viscosity average molecular weight of 320,000. A porous membrane was created. Table 1 shows the physical properties of the obtained microporous membrane. The overall PP value and the PP value near the surface showed almost the same value.
[0023]
[Comparative Example 2]
In Example 1, the composition of the polymer mixture was finely adjusted in the same manner as in Example 1 except that 60% by weight of high-density polyethylene having a viscosity average molecular weight of 280,000 and 40% by weight of polypropylene having a viscosity average molecular weight of 320,000 were used. A porous membrane was created. Table 1 shows the physical properties of the obtained microporous membrane. The overall PP value and the PP value near the surface showed almost the same value.
[0024]
[Table 1]
[0025]
【The invention's effect】
While having the physical properties required as a high-performance separator for a high-capacity lithium ion secondary battery using this separator, it is possible to suppress gas generation and discharge capacity reduction during high-temperature storage.
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WO2013099607A1 (en) | 2011-12-28 | 2013-07-04 | 東レバッテリーセパレータフィルム株式会社 | Polyolefin microporous film and method for producing same |
CN105246692B (en) | 2013-05-31 | 2017-12-08 | 东丽株式会社 | Polyolefin multilayer microporous membrane and its manufacture method |
JP6394596B2 (en) | 2013-05-31 | 2018-09-26 | 東レ株式会社 | Polyolefin multilayer microporous membrane and method for producing the same |
KR102266028B1 (en) | 2013-05-31 | 2021-06-16 | 도레이 카부시키가이샤 | Multilayer, microporous polyolefin membrane, and production method thereof |
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