JP4484191B2 - Battery separator and manufacturing method thereof - Google Patents
Battery separator and manufacturing method thereof Download PDFInfo
- Publication number
- JP4484191B2 JP4484191B2 JP2002222464A JP2002222464A JP4484191B2 JP 4484191 B2 JP4484191 B2 JP 4484191B2 JP 2002222464 A JP2002222464 A JP 2002222464A JP 2002222464 A JP2002222464 A JP 2002222464A JP 4484191 B2 JP4484191 B2 JP 4484191B2
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- Prior art keywords
- methyl
- pentene
- battery separator
- battery
- olefin
- Prior art date
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- Expired - Lifetime
Links
- 238000004519 manufacturing process Methods 0.000 title claims description 11
- WSSSPWUEQFSQQG-UHFFFAOYSA-N 4-methyl-1-pentene Chemical compound CC(C)CC=C WSSSPWUEQFSQQG-UHFFFAOYSA-N 0.000 claims description 42
- 239000004711 α-olefin Substances 0.000 claims description 26
- 239000011148 porous material Substances 0.000 claims description 23
- 239000000835 fiber Substances 0.000 claims description 13
- 238000000034 method Methods 0.000 claims description 13
- 229920000642 polymer Polymers 0.000 claims description 12
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 11
- 229910001416 lithium ion Inorganic materials 0.000 claims description 11
- AFFLGGQVNFXPEV-UHFFFAOYSA-N 1-decene Chemical compound CCCCCCCCC=C AFFLGGQVNFXPEV-UHFFFAOYSA-N 0.000 claims description 8
- CRSBERNSMYQZNG-UHFFFAOYSA-N 1-dodecene Chemical compound CCCCCCCCCCC=C CRSBERNSMYQZNG-UHFFFAOYSA-N 0.000 claims description 8
- GQEZCXVZFLOKMC-UHFFFAOYSA-N 1-hexadecene Chemical compound CCCCCCCCCCCCCCC=C GQEZCXVZFLOKMC-UHFFFAOYSA-N 0.000 claims description 8
- HFDVRLIODXPAHB-UHFFFAOYSA-N 1-tetradecene Chemical compound CCCCCCCCCCCCC=C HFDVRLIODXPAHB-UHFFFAOYSA-N 0.000 claims description 8
- CCCMONHAUSKTEQ-UHFFFAOYSA-N octadec-1-ene Chemical compound CCCCCCCCCCCCCCCCC=C CCCMONHAUSKTEQ-UHFFFAOYSA-N 0.000 claims description 8
- 239000004744 fabric Substances 0.000 claims description 7
- 239000004750 melt-blown nonwoven Substances 0.000 claims description 7
- 229920005604 random copolymer Polymers 0.000 claims description 7
- 125000004432 carbon atom Chemical group C* 0.000 claims description 6
- 238000003825 pressing Methods 0.000 claims description 5
- 229940069096 dodecene Drugs 0.000 claims description 4
- 238000011156 evaluation Methods 0.000 description 24
- 239000004745 nonwoven fabric Substances 0.000 description 17
- -1 nickel metal hydride Chemical class 0.000 description 14
- 238000003490 calendering Methods 0.000 description 13
- 238000002844 melting Methods 0.000 description 13
- 230000008018 melting Effects 0.000 description 13
- 238000009987 spinning Methods 0.000 description 10
- 230000000052 comparative effect Effects 0.000 description 9
- 229920001577 copolymer Polymers 0.000 description 9
- 229920000098 polyolefin Polymers 0.000 description 9
- 239000004698 Polyethylene Substances 0.000 description 8
- 230000007547 defect Effects 0.000 description 7
- 229920000573 polyethylene Polymers 0.000 description 7
- 239000003792 electrolyte Substances 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- VAMFXQBUQXONLZ-UHFFFAOYSA-N n-alpha-eicosene Natural products CCCCCCCCCCCCCCCCCCC=C VAMFXQBUQXONLZ-UHFFFAOYSA-N 0.000 description 6
- 239000004743 Polypropylene Substances 0.000 description 5
- 230000014759 maintenance of location Effects 0.000 description 5
- 238000007600 charging Methods 0.000 description 4
- 239000008151 electrolyte solution Substances 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 239000000155 melt Substances 0.000 description 4
- 229920001155 polypropylene Polymers 0.000 description 4
- 239000002002 slurry Substances 0.000 description 4
- 229910001220 stainless steel Inorganic materials 0.000 description 4
- 239000010935 stainless steel Substances 0.000 description 4
- 229940106006 1-eicosene Drugs 0.000 description 3
- FIKTURVKRGQNQD-UHFFFAOYSA-N 1-eicosene Natural products CCCCCCCCCCCCCCCCCC=CC(O)=O FIKTURVKRGQNQD-UHFFFAOYSA-N 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 3
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 3
- 239000002033 PVDF binder Substances 0.000 description 3
- 229920001519 homopolymer Polymers 0.000 description 3
- 229920000139 polyethylene terephthalate Polymers 0.000 description 3
- 239000005020 polyethylene terephthalate Substances 0.000 description 3
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- LIKMAJRDDDTEIG-UHFFFAOYSA-N 1-hexene Chemical compound CCCCC=C LIKMAJRDDDTEIG-UHFFFAOYSA-N 0.000 description 2
- KWKAKUADMBZCLK-UHFFFAOYSA-N 1-octene Chemical compound CCCCCCC=C KWKAKUADMBZCLK-UHFFFAOYSA-N 0.000 description 2
- YHQXBTXEYZIYOV-UHFFFAOYSA-N 3-methylbut-1-ene Chemical compound CC(C)C=C YHQXBTXEYZIYOV-UHFFFAOYSA-N 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 229910013870 LiPF 6 Inorganic materials 0.000 description 2
- 229920001410 Microfiber Polymers 0.000 description 2
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 2
- 239000004677 Nylon Substances 0.000 description 2
- 239000003125 aqueous solvent Substances 0.000 description 2
- 238000007334 copolymerization reaction Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229920001778 nylon Polymers 0.000 description 2
- 239000007774 positive electrode material Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000011347 resin Substances 0.000 description 2
- 229920005989 resin Polymers 0.000 description 2
- OEPOKWHJYJXUGD-UHFFFAOYSA-N 2-(3-phenylmethoxyphenyl)-1,3-thiazole-4-carbaldehyde Chemical compound O=CC1=CSC(C=2C=C(OCC=3C=CC=CC=3)C=CC=2)=N1 OEPOKWHJYJXUGD-UHFFFAOYSA-N 0.000 description 1
- KLCNJIQZXOQYTE-UHFFFAOYSA-N 4,4-dimethylpent-1-ene Chemical compound CC(C)(C)CC=C KLCNJIQZXOQYTE-UHFFFAOYSA-N 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 1
- 229920005521 TPX™ DX820 Polymers 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000003963 antioxidant agent Substances 0.000 description 1
- 230000003078 antioxidant effect Effects 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- OJIJEKBXJYRIBZ-UHFFFAOYSA-N cadmium nickel Chemical compound [Ni].[Cd] OJIJEKBXJYRIBZ-UHFFFAOYSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 238000000748 compression moulding Methods 0.000 description 1
- 239000006258 conductive agent Substances 0.000 description 1
- 238000010281 constant-current constant-voltage charging Methods 0.000 description 1
- 239000011889 copper foil Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000010292 electrical insulation Methods 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 239000012760 heat stabilizer Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 125000004435 hydrogen atom Chemical group [H]* 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 230000010220 ion permeability Effects 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 239000002931 mesocarbon microbead Substances 0.000 description 1
- 229910052987 metal hydride Inorganic materials 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- TVMXDCGIABBOFY-UHFFFAOYSA-N n-Octanol Natural products CCCCCCCC TVMXDCGIABBOFY-UHFFFAOYSA-N 0.000 description 1
- 239000007773 negative electrode material Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 1
- 239000011255 nonaqueous electrolyte Substances 0.000 description 1
- 239000002667 nucleating agent Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000005191 phase separation Methods 0.000 description 1
- 239000000049 pigment Substances 0.000 description 1
- 229920005594 polymer fiber Polymers 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 230000000707 stereoselective effect Effects 0.000 description 1
- 239000000126 substance 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
Landscapes
- Casting Or Compression Moulding Of Plastics Or The Like (AREA)
- Cell Separators (AREA)
- Secondary Cells (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、分岐α−オレフィンの高融点重合体繊維質多孔シートからなるバッテリーセパレータ及びその製造方法に関する。さらに詳しくは、とくにリチウムイオン電池用として有用な、シャットダウン特性に優れたバッテリーセパレータに関する。
【０００２】
【従来の技術】
従来、充放電可能な二次電池としてニッケル・カドミウム電池が一般的に使用されていたが、携帯電話、ＰＨＳ、モバイルパソコンなどの普及と共に、軽量・コンパクトで、かつ環境にやさしいリチウムイオン電池が広く使われるに至っている。また最近では、二酸化炭素排出量の削減を目指して、自動車の動力としてガソリンとモーターからなるハイブリッド車が商品化され、ニッケル水素電池が使われるようになっているが、低コストの観点からリチウムイオン電池の高性能化が検討されている。
【０００３】
【発明が解決しようとする課題】
このようなリチウムイオン電池のセパレータは、正極材と負極材を隔離し、両極の短絡を防止しつつ電解質もしくはイオンを通過させる役割を果たすものであり、電気的、化学的、機械的な観点から種々の特性が要求されている。例えばバッテリを軽量・コンパクト化するため、薄くても充分な機械的強度を有するものが求められている。
【０００４】
さらには安全性に対する要求はとくに厳しく、外部短絡などで大きな電流が流れたときに電池回路を速やかに遮断することが求められている。現在、リチウムイオン電池のセパレータとして、延伸開孔法又は相分離法により製造されるポリエチレンシートが実用化されているが、これは短絡電流によって発生する熱により比較的低温で溶融して微多孔を塞ぎ、これによって電池回路を遮断することができ、微多孔が閉塞した後の温度上昇を抑えることができるためである。
【０００５】
しかしながらリチウムイオン電池のシャットダウン特性は、このような比較的低温での微多孔閉塞の機能とともに、高温度に上昇した場合の形状保持力も重要であり、形状を保てない場合には電極の直接の接触を引き起こすため危険な状態となる。ポリエチレン製のバッテリーセパレータは、低融点であるが故にこの形状保持力の点において充分な性能を有しているとは言えなかった。このためポリエチレンより高融点のポリプロピレンを積層したセパレータも開発されており、形状保持力の点において改良されているものの、未だ充分なものとは言えなかった。
【０００６】
またさらに高融点のポリオレフィンやポリエチレンテレフタレート（ＰＥＴ）、ナイロンなどの高融点多孔フイルムも検討されている。しかしながらポリオレフィンは高融点ほど成形が困難であり、満足すべき製品を得ることが難しい。例えば、従来、分岐α−オレフィンの重合体において、４−メチル−１−ペンテンや３−メチル−１−ブテンなどの高融点重合体が知られており、高温時における形状保持力に優れたバッテリーセパレータ材料として興味があるが、高融点であるが故に他の要求性能を満たす多孔フイルムの製造が難しく、ポリエチレン製バッテリーセパレータと同様な製造方法では満足すべき製品を得ることができなかった。またＰＥＴやナイロンは、ポリマーの未反応末端水素が電解液（ＬｉＰＦ６＋カーボネート系溶剤）と反応して腐食性物質であるＨＦを発生させるため、実用化は困難であった。
【０００７】
そこで本発明の目的は、満足すべき強度を有する薄肉製品を得ることが容易で、しかも高温下でも形状が安定して絶縁維持することが可能なバッテリーセパレータを提供することにある。
【０００８】
【課題を解決するための手段】
上記目的を達成するために本発明においては、シート厚みが５〜１００μｍ、目付けが５〜５０ｇ／ｍ２、空隙率が１０〜７０％、最大孔径が３０μｍ以下であり、厚み（μｍ）／目付（ｇ／ｍ ２ ）が１．０〜５．０である４−メチル−１−ペンテン重合体繊維質多孔シートからなるバッテリーセパレータが提供される。本発明においてはまた、４−メチル−１−ペンテン重合体の繊維径が１〜５μｍ、目付けが５〜５０ｇ／ｍ２であるメルトブローン不織布を押圧加工することにより、上記バッテリーセパレータ用繊維質多孔シートを製造する方法が提供される。
【０００９】
ここに多孔シートとしては、平均孔径が３〜２０μｍのものが好ましく、また厚み（μｍ）／目付け（ｇ／ｍ２）が１．０〜５．０の範囲にあるものが好ましい。
【００１０】
４−メチル−１−ペンテン重合体においては、４−メチル−１−ペンテン含有量８０〜９９．９重量％及び炭素数２〜２０のα−オレフィン含有量０．１〜２０重量の４−メチル−１−ペンテン・α−オレフィンランダム共重合体であることが好ましく、また該ランダム共重合体のα−オレフィンが、１−デセン、１−ドデセン、１−テトラデセン、１−ヘキサデセン、１−オクタデセン及び１−エイコセンから選ばれる少なくとも１種のα−オレフィンである共重合体が好ましい。
【００１１】
本発明の上記バッテリーセパレータは、好ましくはリチウムイオン電池用として使用される。
【００１２】
さらに上記バッテリーセパレータ用繊維質多孔シートの製造方法において、押圧加工としては、カレンダー加工を採用するのが好ましい。
【００１３】
【発明の実施の形態】
本発明においては、バッテリーセパレータ材料として高融点の分岐α−オレフィン重合体が使用される。分岐α−オレフィン重合体としては、高温での優れた形状保持性を示すために、融点（示差走査熱量計において最大吸熱ピークを示す温度）が２００℃以上であることが好ましく、一方成形性を考慮すると融点が３００℃以下であることが好ましい。とくに好適なものは、融点が２１０〜２８０℃のものである。
【００１４】
より具体的には、４−メチル−１−ペンテン、３−メチル−１−ブテン、４，４−ジメチルー１−ペンテンなどの重合体又はこれら分岐α−オレフィンを主成分とする他のα−オレフィンとの共重合体を挙げることができる。好ましいのは、４−メチル−１−ペンテンの単独重合体及び４−メチル−１−ペンテンと炭素数２〜２０のα−オレフィンとのランダム共重合体から選ばれる４−メチル−１−ペンテン重合体であり、とくに好ましいのは４−メチル−１−ペンテンと炭素数２〜２０のα−オレフィンとのランダム共重合体である。ここに共重合成分となりうる炭素数２〜２０のα−オレフィンとしては、エチレン、プロピレン、１−ブテン、１−ヘキセン、１−オクテン、１−デセン、１−ドデセン、１−テトラデセン、１−ヘキサデセン、１−オクタデセン、１−エイコセンなどを例示することができる。上記共重合体においてこれらα−オレフィンが１種のみならず２種以上共重合されたものであってもよい。
【００１５】
上記４−メチル−１−ペンテンの共重合体においては、耐熱性、機械的特性を考慮すると、４−メチル−１−ペンテンの含有量が８０〜９９．９重量％、好ましくは９０〜９９．９重量％、共重合成分であるα−オレフィンの含有量が０．１〜２０重量％、好ましくは０．１〜１０重量％のものが好ましい。とりわけ好ましい共重合体は、４−メチル−１−ペンテンと炭素数１０〜２０のα−オレフィン、とくに１−デセン、１−ドデセン、１−テトラデセン、１−ヘキサデセン、１−オクタデセン及び１−エイコセンから選ばれる１種又は２種以上のα−オレフィンとのランダム共重合体である。
【００１６】
上記４−メチル−１−ペンテンの単独重合体又は共重合体としてはまた、メルトブローン不織布への加工性や多孔フイルムの機械的強度などを考慮すると、２６０℃、５ｋｇ荷重で測定したメルトフローレートが１００〜１０００ｇ／１０分程度のものを使用するのが好ましい。
【００１７】
このような４−メチル−１−ペンテンの単独重合体又は共重合体は、立体特異性触媒を使用して製造することが可能であり、その製法はすでに広く知られている。
【００１８】
本発明においては、上記分岐α−オレフィン重合体の繊維質多孔シートをバッテリーセパレータとして使用するものである。ここに繊維質多孔シートは、重合体繊維が交絡して有孔シートを形成しているものであって、シート厚みが５〜１００μｍ、好ましくは７〜８０μｍ、目付けが５〜５０ｇ／ｍ２、好ましくは１０〜２０ｇ／ｍ２、空隙率が１０〜７０％、好ましくは４０〜７０％、最大孔径が３０μｍ以下、好ましくは１５μｍ以下のものである。上記繊維質多孔シートとしてはまた、平均孔径が３〜２０μｍ、とくに５〜１０μｍの範囲にあることが好ましく、また厚み（μｍ）／目付け（ｇ／ｍ２）が１．０〜５．０、とくに１．５〜３．０程度の範囲にあることが好ましい。
【００１９】
上記特性を有する繊維質多孔シートをバッテリーセパレータとして使用することにより、膜厚を薄くでき、また電池組立て時や使用時に必要とされる機械的強度を有している。さらに充分な電気絶縁性を有しており、リチウムイオン電池のバッテリーセパレータとして使用したときには、電解液に対して化学的に安定であると共に、電気化学的にも安定である。また電解液を保持した状態で電解質やイオンの透過性がよく、電気抵抗が低い。さらに短絡電流が流れて発生する熱により温度上昇しても、変形に対する抵抗力が強く、形状保持性に優れているので安全性が高い。したがって、リチウムイオン電池のバッテリーセパレータとして好適である。
【００２０】
目付け、空隙率及び最大孔径が、上記範囲を外れるような繊維質多孔シートを使用した場合には、セパレータ特性が悪く満足すべきものとはならない。また平均孔径や厚み／目付けの値が上記範囲にあることにより、コンパクトで電池特性良好なバッテリーセパレータとすることができる。
【００２１】
このような繊維質多孔シートには、バッテリーセパレータの性能を損なわない範囲において、酸化防止剤、耐熱安定剤、核剤、顔料などの各種添加剤や他の重合体を配合することができる。
【００２２】
上記のような特性を有する繊維質多孔シートは、上記α−オレフィン重合体の繊維径が１〜５μｍ、好ましくは１〜４μｍ、一層好ましくは１〜３μｍ、目付けが５〜５０ｇ／ｍ２、好ましくは１０〜２０ｇ／ｍ２のメルトブローン不織布を、その厚みと空隙を減ずるように押圧加工することによって得ることができる。すなわち繊維径があまり大きすぎると、押圧加工後の多孔シートの最大孔径が大きくなりすぎ、セパレータ性能を損なう恐れがあるためである。またメルトブローン不織布の目付けが低すぎると、カレンダー加工後の多孔シートの最大孔径が大きくなり、性能良好なセパレータを得ることが難しく、また目付けが大きすぎると多孔シートの厚みが大きくなり、バッテリーをコンパクトにすることが難しくなる。
【００２３】
上記押圧加工としては、カレンダー加工が工業的に有利である。上記性状の繊維質多孔シートを、分岐α−オレフィン重合体の上記性状のメルトブローン不織布のカレンダー加工によって得るためには、カレンダー加工の際のロール圧及び加工温度を適当な範囲に調節することによって得ることができる。例えばロールの線圧として、４０〜１００ｋｇ／ｃｍ、加工温度として７０〜１００℃の範囲に設定するのがよい。
【００２４】
また上記のような性状のメルトブローン不織布は、従来公知の方法に準じて製造することができる。例えば上記分岐α−オレフィン重合体を溶融押出しし、メルトブロー紡糸口金から紡糸された繊維を、高温、高速の気体によって極細繊維としてブロー紡糸し、捕集装置で極細繊維ウェブとし、必要に応じて熱融着処理することにより製造することができる。
【００２５】
本発明に係る上記繊維質多孔シートをリチウムイオン電池のバッテリーセパレータとして使用する場合、上記多孔シートを単層で使用することができるが、短絡電流による発生熱に対して、より低温で微多孔を閉塞して電池回路を遮断するために、従来使用されているポリエチレン多孔フイルムと積層して用いることもできる。このような積層バッテリーセオパレータは低温及び高温の双方におけるシャットダウン特性に優れており、とくに有用である。
【００２６】
【実施例】
以下、実施例により本発明をさらに詳細に説明する。
【００２７】
［実施例１］
４−メチル−１−ペンテン共重合体（商品名：ＴＰＸ ＤＸ８２０、三井化学（株）製、融点２４０℃、２６０℃、５ｋｇ荷重におけるメルトフローレート１８０ｇ／１０分）をメルトブローン法により、樹脂温度３４０℃、紡糸エア量６０Ｎｍ３／ｋｇ（樹脂１ｋｇを紡糸するのに使用するエア量）で紡糸し、ウェブフォーマーにて捕集して目付け１０ｇ／ｍ２の不織布を得た。これらの不織布の繊維径は２．５μｍであった。この不織布を、加工温度８０℃でカレンダー処理したところ、厚み１５μｍ、最大孔径８．８μｍの多孔シートを得た。その評価結果を表１に示す。
【００２８】
［実施例２］
実施例１において、不織布として繊維径２．５μｍ、目付け２０ｇ／ｍ２のものを製造した後、７０℃でカレンダー加工を行い、厚み６０μｍ、最大孔径２５μｍの多孔シートを得た。その評価結果を表１に示す。
【００２９】
［実施例３］
実施例１において、不織布として繊維径４．０μｍ、目付け４０ｇ／ｍ２のものを製造して同様にカレンダー加工を行い、厚み７０μｍ、最大孔径８．０μｍの多孔シートを得た。その評価結果を表１に示す。
【００３０】
［比較例１］
実施例１において、紡糸エアー量５０Ｎｍ３／ｋｇで紡糸して、繊維径３．１μｍ、目付１５ｇ／ｍ２の不織布を製造した。この不織布を４０℃でカレンダー加工を行い、厚み１００μｍ、最大孔径５０μｍの多孔シートを得た。その評価結果を表１に示す。
【００３１】
［比較例２］
実施例１において、紡糸エアー量４０Ｎｍ３／ｋｇで紡糸して、繊維径４．０μｍ、目付１５ｇ／ｍ２の不織布を製造した。この不織布を４０℃でカレンダー加工を行い、厚み１００μｍ、最大孔径６５μｍの多孔シートを得た。その評価結果を表１に示す。
【００３２】
［比較例３］
実施例１において、紡糸エアー量３０Ｎｍ３／ｋｇで紡糸して、繊維径５．０μｍ、目付１５ｇ／ｍ２の不織布を製造した。この不織布を６０℃でカレンダー加工を行い、厚み７０μｍ、最大孔径７０μｍの多孔シートを得た。その評価結果を表１に示す。
【００３３】
［比較例４］
実施例３において、不織布を２５℃でカレンダー加工して、厚み１２０μｍ、最大孔径８０μｍ以上の多孔シートを得た。その評価結果を表１に示す。
【００３４】
［比較例５］
実施例３において紡糸エアー量２５Ｎｍ３／ｋｇで紡糸し、繊維径６．０μｍ、目付１５ｇ／ｍ２の不織布を得た。この不織布を２５℃でカレンダー加工して、厚み１２０μｍ、最大孔径６０μｍの多孔シートを得た。その評価結果を表１に示す。
【００３５】
［比較例６］
実施例１において得られた不織布を２５℃でカレンダー加工して、厚み１２０μｍ、最大孔径８０μｍ以上の多孔シートを得た。その評価結果を表１に示す。
【００３６】
［比較例７］
厚み２５μｍ、最大孔径０．１μｍの市販のポリエチレン製電池セパレータ用多孔フイルムを用いた。その評価結果を表１に示す。
【００３７】
［比較例８］
メルトフローレート（２３０℃、２１６０ｇ荷重）が４００ｇ／１０分の市販のポリプロピレンから、メルトブローン法により、繊維径３．１μｍ、目付１５ｇ／ｍ２の不織布を製造した。この不織布を５０℃でカレンダー加工を行い、厚み５０μｍ、最大孔径３０μｍの多孔シートを得た。その評価結果を表１に示す。
【００３８】
尚、多孔シートの評価は、次のようにして行った。
（１）最大孔径及び平均孔径
コールター社製ポロメーターIIで測定。
【００３９】
（２）空隙率
次式により求めた。
空隙率(%)＝｛１−目付け(kg/m2)／［厚み(m)×密度(kg/m3)］｝×１００
【００４０】
（３）セパレータの作成
実施例１〜３、比較例１〜８の多孔シートを直径１５ｍｍの円盤状に打ち抜き、セパレータとした。
【００４１】
（４）破膜温度の測定
内径４９ｍｍ、外径１２０ｍｍ、厚み１２ｍｍのドーナツ型ステンレス板２枚を重ね合わせ、その間にセパレータを挟み込み、セパレータが動かないように２枚のドーナツ型ステンレス板を固定した。これを３００℃まで昇温可能な高温槽に入れ、室温から１４０℃まで急速に昇温した後、１４０℃からは２℃／分の速さで昇温しつつ、高温槽についているガラス窓越しに観察して、セパレータの破れる温度を目視で測定した。評価は、破膜温度２３０℃以上を「○」、２３０℃以下を「×」とした。
【００４２】
（５）電解液の作成
エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）とを、ＥＣ：ＤＥＣ＝５８：４２（重量比）の割合で混合して非水溶媒とし、電解質であるＬｉＰＦ６をその非水溶媒に溶解し、電解質濃度が１．０モル／ｌとなるように非水電解液を調製した。
【００４３】
（６）負極の作製
大阪ガス（株）製のメソカーボンマイクロビーズ（商品名：ＭＣＭＢ６−２８、ｄ００２＝０．３３７ｎｍ、密度２．１７ｇ／ｃｍ３）の炭素粉末９０重量部と、結着剤としてのポリフッ化ビニリデン（ＰＶＤＦ）１０重量部とを混合し、溶剤のＮ−メチルピロリドンに分散させ、ペースト状の負極合剤スラリーを調製した。次にこの負極合剤スラリーを厚さ２０μｍの帯状銅箔製の負極集電体に塗布し、乾燥させて帯状の炭素負極を得た。乾燥後の負極合剤の厚さは２５μｍであった。さらにこの帯状電極を、直径１５ｍｍの円盤状に打ち抜いた後、圧縮成形して負極電極とした。
【００４４】
（７）正極の作製
本庄ケミカル（株）製のＬｉＣｏＯ２（商品名：ＨＬＣ−２１、平均粒径８μｍ）微粒子９１重量部と、導電剤としてのグラファイト６重量部と、結着剤としてのポリフッ化ビニリデン（ＰＶＤＦ）３重量部とを混合して正極合剤を調製し、Ｎ−メチルピロリドンに分散させて正極合剤スラリーを得た。このスラリーを厚さ２０μｍの帯状アルミニウム箔製正極集電体に塗布し、乾燥させ、圧縮成形によって帯状正極を得た。乾燥後の正極合剤の厚さは４０μｍであった。この後、この帯状電極を直径１５ｍｍの円盤状に打ち抜くことによって正極電極とした。
【００４５】
（８）電池の作製
このようにして得られたセパレータ、電解液、円盤状負極及び円盤状正極を、ステンレス製の２０３２サイズの電池缶内に負極、セパレータ、正極の順序で各々を積層した後、電解液を入れて、電池缶内にステンレス製の板（厚さ２．４ｍｍ、直径１５．４ｍｍ）を収納し、さらにポリプロピレン製のガスケットを介して、電池缶（蓋）をかしめ、二次電池を作製した。
【００４６】
（９）欠陥数
上記方法により二次電池をそれぞれ２０個作製して、下記に示す放電容量を測定するに当たり、その充電工程において電池内部で激しいショートが起こり、二次電池として使用できなかったものを「欠陥」と判定し、その数を表１に示した。
【００４７】
（１０）微細ショートの判定
それぞれ２０個の二次電池において、下記に示す放電容量を測定するに当たり、２０個中１個以上、充電時に電圧の乱れが生じたものの、二次電池として使用できるものは、「微細ショート有り」、２０個中０個は「微細ショート無し」と判定した。
【００４８】
（１１）欠陥数と微細ショートの評価
欠陥数と微細ショートのいずれも無いものを「○」、欠陥数が５個以下のものを「△」、欠陥数が６個以上のものを「×」とした。
【００４９】
（１２）放電容量の測定
それぞれ２０個の二次電池について、その放電容量を室温にて測定した。尚、本測定では、負極にＬｉ＋がドープされる電流方向を充電、脱ドープされる電流方向を放電とした。充電は、４．２Ｖ、１ｍＡ定電流定電圧充電方法で行い、充電電流が５０μＡ以下になった時点で終了とした。放電は、２．７５Ｖまで１ｍＡに定電流放電を行い終了とし、放電容量を測定した。放電容量は、正極活物質１ｇ当たりの値に換算し、２０個中二次電池として使用できた電池の放電容量の平均値を表１に示した。また放電容量が１２０ｍＡｈ／ｇ以上であれば電池として使用できると判断し、その評価を「○」、それ以外を「×」とした。
【００５０】
（１３）総合評価
破膜温度評価、欠陥数と微細ショート評価及び放電容量評価の３評価において、３評価全てが「○」のものを総合評価「○」、一つでも「△」の項目があれば総合評価「△」、一つでも「×」の項目があれば総合評価「×」とした。
【００５１】
【表１】
【００５２】
【発明の効果】
本発明によれば、リチウムイオン電池用として好適な、薄肉で高温シャットダウン特性に優れたバッテリーセパレータを提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery separator comprising a high melting point polymer fibrous porous sheet of branched α-olefin and a method for producing the same. More specifically, the present invention relates to a battery separator that is particularly useful for lithium ion batteries and has excellent shutdown characteristics.
[0002]
[Prior art]
Conventionally, nickel-cadmium batteries have been commonly used as rechargeable secondary batteries, but with the widespread use of mobile phones, PHS, mobile PCs, etc., lithium-ion batteries that are lightweight, compact, and environmentally friendly are widely used. It has been used. Recently, with the aim of reducing carbon dioxide emissions, hybrid vehicles consisting of gasoline and motors have been commercialized as a power source for vehicles, and nickel metal hydride batteries have been used. High performance batteries are being studied.
[0003]
[Problems to be solved by the invention]
The separator of such a lithium ion battery serves to separate the positive electrode material and the negative electrode material and prevent electrolytes or ions from passing while preventing short-circuit between both electrodes. From the electrical, chemical, and mechanical viewpoints, Various characteristics are required. For example, in order to make a battery lighter and more compact, a thin battery having sufficient mechanical strength is required.
[0004]
Furthermore, safety requirements are particularly severe, and it is required to quickly shut down the battery circuit when a large current flows due to an external short circuit or the like. At present, polyethylene sheets produced by the stretch-opening method or the phase separation method have been put to practical use as separators for lithium ion batteries, but this is melted at a relatively low temperature by the heat generated by the short-circuit current and becomes microporous. This is because the battery circuit can be shut off by this, and the temperature rise after the micropores are blocked can be suppressed.
[0005]
However, the shutdown characteristics of lithium-ion batteries are not only the function of microporous clogging at a relatively low temperature, but also the shape retention force when the temperature rises to a high temperature. It is dangerous because it causes contact. Since the battery separator made of polyethylene has a low melting point, it cannot be said that the battery separator has sufficient performance in terms of the shape retention force. For this reason, a separator in which polypropylene having a melting point higher than that of polyethylene is laminated has been developed, and although it has been improved in terms of shape retention power, it has not yet been sufficient.
[0006]
Further, high melting point porous films such as high melting point polyolefin, polyethylene terephthalate (PET), nylon and the like have been studied. However, polyolefins are more difficult to mold at higher melting points, and it is difficult to obtain satisfactory products. For example, conventionally, high melting point polymers such as 4-methyl-1-pentene and 3-methyl-1-butene are known as branched α-olefin polymers, and batteries having excellent shape retention at high temperatures. Although it is of interest as a separator material, it is difficult to produce a porous film satisfying other required performance due to its high melting point, and a satisfactory product could not be obtained by a production method similar to a polyethylene battery separator. Also, PET and nylon have been difficult to put to practical use because the unreacted terminal hydrogen of the polymer reacts with the electrolyte (LiPF 6 + carbonate solvent) to generate corrosive HF.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to provide a battery separator that is easy to obtain a thin product having satisfactory strength and that can stably maintain insulation even at high temperatures.
[0008]
[Means for Solving the Problems]
In the present invention in order to achieve the above object, a sheet thickness of 5 to 100 [mu] m, a basis weight of 5 to 50 g / m 2, porosity of 10% to 70%, maximum pore diameter Ri der less 30 [mu] m, the thickness ([mu] m) / basis weight (g / m 2) is a battery separator made of 1.0 to 5.0 der Ru 4-methyl-1-pentene polymer fibrous porous sheet is provided. In the present invention, the fibrous porous sheet for a battery separator is obtained by pressing a melt blown nonwoven fabric having a fiber diameter of 1 to 5 μm and a basis weight of 5 to 50 g / m 2 in the 4-methyl-1-pentene polymer. A method of manufacturing is provided.
[0009]
Here, the porous sheet preferably has an average pore diameter of 3 to 20 μm, and preferably has a thickness (μm) / weight per unit area (g / m 2 ) in the range of 1.0 to 5.0.
[0010]
In the 4 -methyl-1-pentene polymer, 4-methyl-1-pentene content of 80 to 99.9% by weight and α-olefin content of 2 to 20 carbon atoms of 0.1 to 20% by weight is 4-methyl. It is preferable that it is a -1-pentene / α-olefin random copolymer, and the α-olefin of the random copolymer is 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and A copolymer that is at least one α-olefin selected from 1-eicosene is preferred.
[0011]
The battery separator of the present invention is preferably used for a lithium ion battery.
[0012]
Furthermore, in the manufacturing method of the said fibrous porous sheet for battery separators, it is preferable to employ | adopt a calendar process as a press process.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a high melting point branched α-olefin polymer is used as a battery separator material. The branched α-olefin polymer preferably has a melting point (temperature at which a maximum endothermic peak is shown in a differential scanning calorimeter) of 200 ° C. or higher in order to exhibit excellent shape retention at high temperatures, In consideration, the melting point is preferably 300 ° C. or lower. Particularly preferred are those having a melting point of 210-280 ° C.
[0014]
More specifically, polymers such as 4-methyl-1-pentene, 3-methyl-1-butene, 4,4-dimethyl-1-pentene, or other α-olefins mainly composed of these branched α-olefins. And a copolymer thereof. Preferred is a 4-methyl-1-pentene polymer selected from a homopolymer of 4-methyl-1-pentene and a random copolymer of 4-methyl-1-pentene and an α-olefin having 2 to 20 carbon atoms. A random copolymer of 4-methyl-1-pentene and an α-olefin having 2 to 20 carbon atoms is particularly preferable. Examples of the α-olefin having 2 to 20 carbon atoms that can be used as a copolymerization component include ethylene, propylene, 1-butene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, and 1-hexadecene. , 1-octadecene, 1-eicosene and the like. In the above copolymer, these α-olefins may be copolymerized not only in one kind but also in two or more kinds.
[0015]
In the copolymer of 4-methyl-1-pentene, considering heat resistance and mechanical properties, the content of 4-methyl-1-pentene is 80 to 99.9% by weight, preferably 90 to 99.99%. The content of 9% by weight and α-olefin as a copolymerization component is 0.1 to 20% by weight, preferably 0.1 to 10% by weight. Particularly preferred copolymers are 4-methyl-1-pentene and α-olefins having 10 to 20 carbon atoms, especially 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosene. It is a random copolymer with one or more selected α-olefins.
[0016]
The 4-methyl-1-pentene homopolymer or copolymer also has a melt flow rate measured at 260 ° C. under a load of 5 kg in consideration of the processability to a melt blown nonwoven fabric and the mechanical strength of the porous film. It is preferable to use a thing of about 100 to 1000 g / 10 minutes.
[0017]
Such a homopolymer or copolymer of 4-methyl-1-pentene can be produced using a stereospecific catalyst, and its production method is already widely known.
[0018]
In the present invention, the fibrous porous sheet of the branched α-olefin polymer is used as a battery separator. Here, the fibrous porous sheet is a sheet in which polymer fibers are entangled to form a porous sheet, and the sheet thickness is 5 to 100 μm, preferably 7 to 80 μm, and the basis weight is 5 to 50 g / m 2 . Preferably, it is 10 to 20 g / m 2 , the porosity is 10 to 70%, preferably 40 to 70%, and the maximum pore diameter is 30 μm or less, preferably 15 μm or less. The fibrous porous sheet also preferably has an average pore diameter of 3 to 20 μm, particularly preferably in the range of 5 to 10 μm, and a thickness (μm) / weight per unit area (g / m 2 ) of 1.0 to 5.0, In particular, it is preferably in the range of about 1.5 to 3.0.
[0019]
By using the fibrous porous sheet having the above characteristics as a battery separator, the film thickness can be reduced, and the mechanical strength required for assembling and using the battery is obtained. Furthermore, it has sufficient electrical insulation, and when used as a battery separator of a lithium ion battery, it is chemically stable to the electrolyte and is also electrochemically stable. In addition, electrolyte and ion permeability are good with the electrolytic solution held, and electric resistance is low. Furthermore, even if the temperature rises due to heat generated by the flow of a short-circuit current, the resistance to deformation is strong and the shape retainability is excellent, so the safety is high. Therefore, it is suitable as a battery separator for lithium ion batteries.
[0020]
When a fibrous porous sheet having a basis weight, a porosity, and a maximum pore diameter that are out of the above ranges is used, the separator characteristics are poor and not satisfactory. In addition, when the average pore diameter and the value of the thickness / weight per unit area are in the above ranges, the battery separator can be compact and have good battery characteristics.
[0021]
Various additives such as an antioxidant, a heat stabilizer, a nucleating agent, and a pigment, and other polymers can be blended with such a fibrous porous sheet as long as the performance of the battery separator is not impaired.
[0022]
The fibrous porous sheet having the above characteristics has a fiber diameter of the α-olefin polymer of 1 to 5 μm, preferably 1 to 4 μm, more preferably 1 to 3 μm, and a basis weight of 5 to 50 g / m 2 , preferably Can be obtained by pressing a melt blown nonwoven fabric of 10 to 20 g / m 2 so as to reduce its thickness and voids. That is, if the fiber diameter is too large, the maximum pore diameter of the porous sheet after pressing becomes too large, which may impair the separator performance. If the basis weight of the melt blown nonwoven fabric is too low, the maximum pore size of the porous sheet after calendering will increase, making it difficult to obtain a separator with good performance.If the basis weight is too large, the thickness of the porous sheet will increase and the battery will be compact. It becomes difficult to make.
[0023]
As the pressing process, a calendar process is industrially advantageous. In order to obtain the fibrous porous sheet having the above properties by calendering of the melt blown nonwoven fabric having the above properties of the branched α-olefin polymer, it is obtained by adjusting the roll pressure and the processing temperature during the calendering to an appropriate range. be able to. For example, the roll linear pressure is preferably set in the range of 40 to 100 kg / cm and the processing temperature in the range of 70 to 100 ° C.
[0024]
Moreover, the melt blown nonwoven fabric of the above characteristics can be manufactured according to a conventionally well-known method. For example, the above-mentioned branched α-olefin polymer is melt-extruded, the fiber spun from the melt blown spinneret is blow-spun as ultra-fine fibers with a high-temperature, high-speed gas, and is made into an ultra-fine fiber web with a collecting device. It can be manufactured by fusing treatment.
[0025]
When the fibrous porous sheet according to the present invention is used as a battery separator for a lithium ion battery, the porous sheet can be used as a single layer, but it is more microporous at a lower temperature against heat generated by a short-circuit current. In order to block the battery circuit by blocking, it can be used by being laminated with a conventionally used polyethylene porous film. Such a laminated battery theoperator is particularly useful since it has excellent shutdown characteristics at both low and high temperatures.
[0026]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[0027]
[Example 1]
4-methyl-1-pentene copolymer (trade name: TPX DX820, manufactured by Mitsui Chemicals Co., Ltd., melting point 240 ° C., 260 ° C., melt flow rate 180 g / 10 min under 5 kg load) is melt-blown, resin temperature 340 Spinning was carried out at a temperature of 60 ° C. and a spinning air amount of 60 Nm 3 / kg (the amount of air used to spin 1 kg of resin) and collected by a web former to obtain a nonwoven fabric having a basis weight of 10 g / m 2 . The fiber diameter of these nonwoven fabrics was 2.5 μm. When this nonwoven fabric was calendered at a processing temperature of 80 ° C., a porous sheet having a thickness of 15 μm and a maximum pore diameter of 8.8 μm was obtained. The evaluation results are shown in Table 1.
[0028]
[Example 2]
In Example 1, a non-woven fabric having a fiber diameter of 2.5 μm and a basis weight of 20 g / m 2 was manufactured, and then calendered at 70 ° C. to obtain a porous sheet having a thickness of 60 μm and a maximum pore diameter of 25 μm. The evaluation results are shown in Table 1.
[0029]
[Example 3]
In Example 1, a nonwoven fabric having a fiber diameter of 4.0 μm and a weight per unit area of 40 g / m 2 was manufactured and calendered in the same manner to obtain a porous sheet having a thickness of 70 μm and a maximum pore diameter of 8.0 μm. The evaluation results are shown in Table 1.
[0030]
[Comparative Example 1]
In Example 1, a nonwoven fabric having a fiber diameter of 3.1 μm and a basis weight of 15 g / m 2 was manufactured by spinning with a spinning air amount of 50 Nm 3 / kg. This nonwoven fabric was calendered at 40 ° C. to obtain a porous sheet having a thickness of 100 μm and a maximum pore diameter of 50 μm. The evaluation results are shown in Table 1.
[0031]
[Comparative Example 2]
In Example 1, a nonwoven fabric having a fiber diameter of 4.0 μm and a basis weight of 15 g / m 2 was produced by spinning with a spinning air amount of 40 Nm 3 / kg. This nonwoven fabric was calendered at 40 ° C. to obtain a porous sheet having a thickness of 100 μm and a maximum pore diameter of 65 μm. The evaluation results are shown in Table 1.
[0032]
[Comparative Example 3]
In Example 1, spinning was performed with a spinning air amount of 30 Nm 3 / kg to produce a nonwoven fabric having a fiber diameter of 5.0 μm and a basis weight of 15 g / m 2 . This nonwoven fabric was calendered at 60 ° C. to obtain a porous sheet having a thickness of 70 μm and a maximum pore diameter of 70 μm. The evaluation results are shown in Table 1.
[0033]
[Comparative Example 4]
In Example 3, the nonwoven fabric was calendered at 25 ° C. to obtain a porous sheet having a thickness of 120 μm and a maximum pore diameter of 80 μm or more. The evaluation results are shown in Table 1.
[0034]
[Comparative Example 5]
In Example 3, spinning was performed with a spinning air amount of 25 Nm 3 / kg to obtain a nonwoven fabric having a fiber diameter of 6.0 μm and a basis weight of 15 g / m 2 . This nonwoven fabric was calendered at 25 ° C. to obtain a porous sheet having a thickness of 120 μm and a maximum pore diameter of 60 μm. The evaluation results are shown in Table 1.
[0035]
[Comparative Example 6]
The nonwoven fabric obtained in Example 1 was calendered at 25 ° C. to obtain a porous sheet having a thickness of 120 μm and a maximum pore diameter of 80 μm or more. The evaluation results are shown in Table 1.
[0036]
[Comparative Example 7]
A commercially available porous film for battery separator made of polyethylene having a thickness of 25 μm and a maximum pore diameter of 0.1 μm was used. The evaluation results are shown in Table 1.
[0037]
[Comparative Example 8]
A non-woven fabric having a fiber diameter of 3.1 μm and a basis weight of 15 g / m 2 was produced from a commercially available polypropylene having a melt flow rate (230 ° C., 2160 g load) of 400 g / 10 minutes by the melt blown method. This nonwoven fabric was calendered at 50 ° C. to obtain a porous sheet having a thickness of 50 μm and a maximum pore diameter of 30 μm. The evaluation results are shown in Table 1.
[0038]
In addition, evaluation of the porous sheet was performed as follows.
(1) Maximum pore size and average pore size Measured with a Porometer II manufactured by Coulter.
[0039]
(2) Porosity It calculated | required by following Formula.
Porosity (%) = {1−weight per unit area (kg / m 2 ) / [thickness (m) × density (kg / m 3 )]} × 100
[0040]
(3) Preparation of separator The porous sheets of Examples 1 to 3 and Comparative Examples 1 to 8 were punched into a disk shape having a diameter of 15 mm to obtain a separator.
[0041]
(4) Measurement of membrane breaking temperature Two donut-shaped stainless steel plates having an inner diameter of 49 mm, an outer diameter of 120 mm, and a thickness of 12 mm were overlapped, and a separator was sandwiched between them, and the two donut-shaped stainless steel plates were fixed so that the separator would not move. . This is put in a high temperature bath that can be heated up to 300 ° C, rapidly heated from room temperature to 140 ° C, and then heated from 140 ° C at a rate of 2 ° C / minute, through the glass window attached to the high temperature bath. The temperature at which the separator breaks was visually measured. In the evaluation, the film breaking temperature of 230 ° C. or higher was set as “◯”, and the temperature of 230 ° C. or lower was set as “X”.
[0042]
(5) Preparation of electrolyte solution Ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a ratio of EC: DEC = 58: 42 (weight ratio) to make a nonaqueous solvent, and LiPF 6 as an electrolyte is mixed with the non-aqueous solvent. A non-aqueous electrolyte was prepared so that it was dissolved in a non-aqueous solvent and the electrolyte concentration was 1.0 mol / l.
[0043]
(6) Production of negative electrode 90 parts by weight of carbon powder of mesocarbon microbeads (trade name: MCMB6-28, d 002 = 0.337 nm, density 2.17 g / cm 3 ) manufactured by Osaka Gas Co., Ltd. 10 parts by weight of polyvinylidene fluoride (PVDF) as an agent was mixed and dispersed in N-methylpyrrolidone as a solvent to prepare a paste-like negative electrode mixture slurry. Next, this negative electrode mixture slurry was applied to a negative electrode current collector made of a strip-shaped copper foil having a thickness of 20 μm and dried to obtain a strip-shaped carbon negative electrode. The thickness of the negative electrode mixture after drying was 25 μm. Further, this strip electrode was punched into a disk shape having a diameter of 15 mm, and then compression molded to obtain a negative electrode.
[0044]
(7) Production of positive electrode LiCoO 2 (trade name: HLC-21, average particle size 8 μm) 91 parts by weight of fine particles manufactured by Honjo Chemical Co., Ltd., 6 parts by weight of graphite as a conductive agent, and polyfluoride as a binder. A positive electrode mixture was prepared by mixing 3 parts by weight of vinylidene chloride (PVDF) and dispersed in N-methylpyrrolidone to obtain a positive electrode mixture slurry. This slurry was applied to a positive electrode current collector made of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and a strip-shaped positive electrode was obtained by compression molding. The thickness of the positive electrode mixture after drying was 40 μm. Thereafter, this strip electrode was punched into a disk shape having a diameter of 15 mm to obtain a positive electrode.
[0045]
(8) Production of Battery After the separator, electrolyte solution, disc-shaped negative electrode, and disc-shaped positive electrode obtained in this manner were laminated in the order of the negative electrode, the separator and the positive electrode in a stainless steel 2032 size battery can. , Put the electrolyte solution, house the stainless steel plate (thickness 2.4mm, diameter 15.4mm) in the battery can, and further crimp the battery can (lid) through the polypropylene gasket, A battery was produced.
[0046]
(9) Number of defects 20 secondary batteries were prepared by the above method, and when measuring the discharge capacity shown below, a severe short circuit occurred inside the battery during the charging process, and the battery could not be used as a secondary battery. Were determined as “defects” and the numbers are shown in Table 1.
[0047]
(10) Determination of micro short circuit In each of 20 secondary batteries, one or more of the 20 batteries can be used as a secondary battery, although voltage disturbance occurred during charging. Was judged as “with fine short”, and 0 out of 20 was judged as “without fine short”.
[0048]
(11) Evaluation of the number of defects and micro shorts “◯” indicates that there are neither defects nor micro shorts, “Δ” indicates that the number of defects is 5 or less, and “×” indicates that the number of defects is 6 or more. It was.
[0049]
(12) Measurement of discharge capacity For each of the 20 secondary batteries, the discharge capacity was measured at room temperature. In this measurement, the current direction in which the negative electrode is doped with Li + is charged, and the current direction in which the dedope is doped is discharge. Charging was performed by a 4.2 V, 1 mA constant current constant voltage charging method, and terminated when the charging current reached 50 μA or less. The discharge was terminated by constant current discharge at 1 mA up to 2.75 V, and the discharge capacity was measured. The discharge capacity was converted to a value per 1 g of the positive electrode active material, and the average value of the discharge capacity of the batteries that could be used as secondary batteries out of 20 was shown in Table 1. Further, if the discharge capacity was 120 mAh / g or more, it was determined that the battery could be used, and the evaluation was “◯”, and the others were “x”.
[0050]
(13) Comprehensive evaluation In 3 evaluations of film breakage temperature evaluation, number of defects and fine short evaluation, and discharge capacity evaluation, all 3 evaluations are “○” and overall evaluation is “○”, and even one item is “△” If there is an item of “総 合” for overall evaluation and “×” for at least one item, the overall evaluation is “×”.
[0051]
[Table 1]
[0052]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the battery separator excellent in the high temperature shutdown characteristic suitable for lithium ion batteries can be provided.
Claims (5)
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| US7183020B2 (en) * | 2004-08-13 | 2007-02-27 | Mitsui Chemicals, Inc. | Separator for battery and lithium ion battery using the same |
| JP4804828B2 (en) * | 2004-08-13 | 2011-11-02 | 三井化学株式会社 | Battery separator and lithium ion battery using the same |
| JP5816178B2 (en) | 2010-08-12 | 2015-11-18 | 東レバッテリーセパレータフィルム株式会社 | Microporous membrane, method for producing such membrane and method for using such membrane |
| FR2977722B1 (en) * | 2011-07-05 | 2014-03-14 | Commissariat Energie Atomique | ELECTRODES SEPARATOR FOR LITHIUM / SULFUR ACCUMULATOR |
| CN114075700B (en) * | 2020-08-19 | 2022-11-29 | 中国科学院宁波材料技术与工程研究所 | Chain type premodulation melt-blowing method, chain type premodulation melt-blowing nozzle and melt-blowing device |
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| JP2002124238A (en) * | 2000-10-18 | 2002-04-26 | Tonen Tapyrus Co Ltd | Heat-resistant separator |
| JP2002246001A (en) * | 2000-12-13 | 2002-08-30 | Michio Shoji | Separator for alkaline storage battery |
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| JP2002124238A (en) * | 2000-10-18 | 2002-04-26 | Tonen Tapyrus Co Ltd | Heat-resistant separator |
| JP2002246001A (en) * | 2000-12-13 | 2002-08-30 | Michio Shoji | Separator for alkaline storage battery |
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