JP4470248B2 - Battery separator - Google Patents
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- JP4470248B2 JP4470248B2 JP31935099A JP31935099A JP4470248B2 JP 4470248 B2 JP4470248 B2 JP 4470248B2 JP 31935099 A JP31935099 A JP 31935099A JP 31935099 A JP31935099 A JP 31935099A JP 4470248 B2 JP4470248 B2 JP 4470248B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Description
【０００１】
【発明の属する技術分野】
本発明は、リチウム電池の構成材料として有用な電池用セパレータに関する。
【０００２】
【従来の技術】
従来、電池用セパレータや電解コンデンサ用隔膜等としてポリオレフィン系多孔質フィルムが使用されている。特に、近年技術の高度化に伴い、リチウム電池等においては高精度、高機能のセパレータが要求されるようになってきた。
【０００３】
電池を例にとってみると、近年高エネルギー密度、高起電力、自己放電の少ないリチウム電池のような非水電解液電池、特にリチウム二次電池が開発、実用化されている。リチウム電池の負極としては例えば金属リチウム、リチウムと他の金属との合金、カーボンやグラファイト等のリチウムイオンを吸着する能力又はインターカレーションにより吸蔵する能力を有する炭素材料、リチウムイオンをドーピングした導電性高分子材料等が知られており、また正極としては例えば（ＣＦx）nで示されるフッ化黒鉛、ＭｎＯ2、Ｖ2Ｏ5、ＣｕＯ、Ａｇ2ＣｒＯ4、ＴｉＯ2、ＬｉＣｏＯ2、ＬｉＭｎ2Ｏ4等の金属酸化物や硫化物、塩化物が知られている。
【０００４】
また、非水電解液として、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネート、γ−ブチロラクトン、アセトニトリル、１，２−ジメトキシエタン、テトラヒドロフラン等の有機溶媒にＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣｌＯ4、ＬｉＣＦ3ＳＯ3、ＬｉＮ（ＳＯ2ＣＦ3）2、ＬｉＮ（ＳＯ2Ｃ2Ｆ5）2等の電解質を溶解したものが使用されている。
【０００５】
このようなリチウム電池の構成材料であるセパレータの役割は、正負両極の短絡を防止するとともに電池反応を阻害しないこと、並びに異常時に熱閉塞して電池の発熱、発火を防ぐことにあり、特に電池の安全性と密接に関係づけられる機械的強度の改良を目的として、以下のような種々の多孔質フィルムが提案されている。
【０００６】
分子量の高い原料樹脂を用いた多孔質フィルム（特開平２−９４３５６号公報、特開平３−１０５８５１号公報等）。
支持体に熱可塑性樹脂や不織布を用いた多孔質フィルム（特開平３−２４５４５７号公報、特開平１−２５８３５８号公報等）。
【０００７】
電池の安全性を反映するセパレータの性状の一つとして、微小突起による表面の傷つき性が挙げられる。リチウム電池の極板表面には、しばしば数μｍ程度の凹凸が存在する。このため、多孔質フィルムを電池用セパレータとしてリチウム電池に組込むと、極板表面の凹凸によってフィルムが損傷されることが懸念されている。セパレータの損傷は電池の短絡を引き起す原因となるため、セパレータそのものの強度はもちろんのこと、微小突起による表面の傷つき性の改良が重要な課題となっている。
【０００８】
一方、強度改良を目的として、ポリオレフィン樹脂からなる多孔質フィルムに無機充填剤を配合する方法或いは無機微粒子を含有した表面保護層を設ける方法等が知られている。無機充填剤を配合する方法（特開昭６２−１６７３３２号公報）では、無機充填剤による強度改良のみならず延伸多孔化の均一性の付与を目的としているために、該無機充填剤の配合量が樹脂量１００重量部に対して５０〜５００重量部と多く、異常時に（樹脂部分が）熱閉塞して電池の発熱、発火を防ぐシャットダウン機能の信頼性が不十分であるために電池用セパレータとしては適さない。また、無機微粒子を含有した表面保護層を設ける方法（特開平１１−８０３９５号公報）では、多孔質フィルムの表面に無機微粒子を含む表面保護層を配する工程が製造工程上煩雑となる上に、表面保護層の塗布によって透気度が増加するために、低い透気度のものが得られず、未だ改良の余地がある。
【０００９】
さらに、無機微粒子等の樹脂改質用添加剤を用いたセパレーター用多孔質膜の改良においては、電池の使用中に電池反応以外の電気化学反応によって添加剤が分解或は変性しないように、先に本願発明者等が出願した特願平１１−６０４５号明細書に記載のように、無機微粒子の酸化電位がリチウムに対して＋４．５Ｖ以上であることが好ましい。
本発明の目的は、リチウム電池用セパレータとして電池使用時の信頼性及び安全性に優れ且つ電池反応を阻害することのない多孔質フィルムすなわち電池用セパレータを提供することにある。
【００１０】
【課題を解決するための手段】
本発明者らは、鋭意研究の結果、特定の金属酸化物を主成分とする無機微粒子を適切に配合することで、信頼性及び安全性に優れ且つ電池反応を阻害することのない多孔質フィルムが得られることを見出した。すなわち本発明は、延伸法により多孔化した単層又は積層多孔質フィルムからなる電池用セパレータであって、該多孔質フィルムが、透気度３０〜８００秒／１００ｃｃを示し、酸化珪素、酸化アルミニウム、酸化マグネシウムの群から選ばれる少なくとも１種の金属酸化物を主成分とする酸化電位がリチウムに対して＋４．５Ｖ以上であって、平均粒径が０．１〜１０μｍの無機微粒子を、１００〜５０００ｐｐｍ含むことを特徴とする電池用セパレータに関する。
【００１１】
【発明の実施の形態】
本発明の電池用セパレータに使用される材料としては、特に制限はなく、ポリプロピレン、ポリエチレン等のポリオレフィン樹脂が利用できる。また、本発明の多孔質フィルムは単層多孔質フィルム及び積層多孔質フィルムのいずれの構成であっても良く、積層多孔質フィルムである場合は、積層した多孔質フィルムの少なくとも１層に無機微粒子を含んでいれば良い。
【００１２】
本発明に使用されるポリプロピレンは、数平均分子量が５万以上、より好ましくは７万以上、数平均分子量と重量平均分子量の比が８以下のものが機械的強度が高く好ましい。また、ポリプロピレンの結晶化温度は１１０℃以上、さらに好ましくは１１２℃以上が好適である。
【００１３】
本発明に使用するポリエチレンとしては、高密度ポリエチレン、中密度ポリエチレン、直鎖低密度ポリエチレン等のいずれであっても良いが、好ましくは高密度ポリエチレンである。ポリエチレンの数平均分子量は１万以上、より好ましくは２万以上のものが機械的強度が高く好ましい。
【００１４】
本発明において、ポリプロピレン及びポリエチレンの数平均分子量は、WATERS社製１５０Ｃ型ゲル浸透クロマトグラフを用いて、標準ポリスチレン換算によって求めた。カラムにはShodex HT-806M２本を使用し、０．３wt／vol％に調製したオルトジクロロベンゼン中、１３５℃で測定を行った。
また、ポリプロピレンの融点は、パーキンエルマー社製ＤＳＣ−７を用いて測定した。試料は熱履歴を取除くために２３０℃で１０分間保持して完全融解した後、１０℃／ｍｉｎで室温まで冷却し、測定は昇温速度１０℃／ｍｉｎにて融解曲線の極大値を融点とした。
【００１５】
本発明の電池用セパレータに含まれる無機微粒子は、酸化珪素、酸化アルミニウム、酸化マグネシウムの群から選ばれる少なくとも１種の金属酸化物を主成分とし、リチウム二次電池の構成材料である非水電解液に膨潤及び溶解しないことが望ましい。無機微粒子が非水電解液に膨潤及び溶解する有機物を含んでいると、電池使用時に電池反応を阻害する可能性があるため適当でない。また、無機微粒子の平均粒径は０．１〜１０μｍ、さらに好ましくは０．５〜３μｍである。無機微粒子の平均粒径がこの範囲より小さい場合、電池用セパレータの傷つき性等の機械的強度改良効果が期待できず、またこの範囲より大きい場合は、無機微粒子の分散不良による電池用セパレータの外観不良が生じるので適当でない。
【００１６】
本発明に使用される無機微粒子の真比重は１．５以上、特に２以上であることが好ましい。無機微粒子の真比重が小さすぎると、電池用セパレータの傷つき性等の機械的強度改良効果が小さいため適当でない。また、無機微粒子の酸化電位は、リチウムに対して＋４．５Ｖ以上、特に＋５Ｖ以上であることが電気化学的に安定で好ましい。
【００１７】
本発明に示す酸化電位の測定は、ジメチルカーボネートにＬｉＰＦ6を溶解して１Ｍ／Ｌに調製した非水電解液を用いて行った。この非水電解液に該無機微粒子を０．０５Ｍ／Ｌになるように懸濁した。参照電極には金属リチウム箔を、作用電極に白金電極を用いて、毎秒１０ｍＶの速度で±０Ｖ〜＋４．５Ｖまで電位を掃引し、０．１ｍＡの電流が検知された電圧を酸化電位とした。
【００１８】
本発明において、無機微粒子をポリプロピレン或いはポリエチレンに配合する方法については特に制限はないが、通常の混練機を用いた混練により配合することができる。例えば、一軸押出機、二軸押出機、ミキシングロール等を用いて溶融混練し、ペレットを得ることできる。また、ヘンシェルミキサー、タンブラー等を用いてドライブレンドによって配合しても良い。電池用セパレータに対する無機微粒子の配合比率は１００〜５０００ｐｐｍ、さらに好ましくは３００〜４０００ｐｐｍである。無機微粒子の配合量がこの範囲より小さい場合、電池用セパレータの傷つき性等の機械的強度改良効果が期待できず、またこの範囲より大きい場合は、延伸法による多孔化が困難となり、透気度の低い電池用セパレータを得ることができないため適当でない。
【００１９】
本発明において、延伸法により多孔化した単層又は積層多孔質フィルムに含まれる無機微粒子の個数は、延伸倍率等によっても異なるが、通常フィルム面積あたり５０〜５０００個／ｍｍ2、特に１００〜３０００個／ｍｍ2に調整するのが好ましい。無機微粒子の分散状態がこの範囲を過度にはずれると、電池用セパレータの傷つき性等の機械的強度改良効果が期待できなくなる。
【００２０】
本発明の電池用セパレータの層構成としては、無機微粒子を含むポリエチレン或いはポリプロピレンの単層多孔質フィルム、無機微粒子を含むポリプロピレンで無機微粒子を含まないポリエチレンを挟み込んだ積層多孔質フィルム、無機微粒子を含まないポリプロピレンで無機微粒子を含むポリエチレンを挟み込んだ積層多孔質フィルム、無機微粒子を含むポリエチレンと無機微粒子を含まないポリエチレンからなる積層多孔質フィルム、無機微粒子を含むポリエチレンと無機微粒子を含むポリプロピレンからなる積層多孔質フィルム等が挙げられ、積層多孔質フィルムの場合、少なくとも１層に無機微粒子が含まれていれば良い。
【００２１】
本発明の電池用セパレータの具体的な製造方法としては、例えば、無機微粒子を含むポリプロピレンで無機微粒子を含まないポリエチレンを挟み込んだ積層多孔質フィルムを製造する場合は、無機微粒子を適宜配合したポリプロピレンとポリエチレンを溶融共押し出しした後延伸多孔化して積層多孔質フィルムを得る方法、無機微粒子を適宜配合したポリプロピレンとポリエチレンフィルムをそれぞれ別々に溶融押し出し積層した後延伸多孔化して積層多孔質フィルムを得る方法等がある。また、延伸多孔化工程において、フィルムの幅方向の長さが大きく減少して透気度、空孔率及び極大孔径等の多孔質フィルムの性能が損われる場合には、先に本発明者等が出願した特開平１１−２９７２９７号公報に記載の方法のように、フィルムの幅方向の両端をチャック、ピンチロール等で固定しつつ延伸する方法、フィルムを縦一軸に延伸した後に一軸延伸時に生じた幅方向のフィルム長さ減少を横延伸によって復元する方法等の手法によって改良することができる。いずれの方法でも本発明の電池用セパレータを製造することができる。
【００２２】
溶融押し出し方法はＴダイによる溶融押し出し成型法、インフレーション法等により行われる。例えばフィルムをＴダイにより溶融成形する場合、一般に樹脂の溶融温度より２０〜６０℃高い温度で、ドラフト比５〜５００、好ましくは５０〜３００のドラフト比で行われ、また引取り速度は特に限定されないが通常１０〜５０ｍ／分で成形される。
溶融押し出しされたフィルムは結晶性及びその配向性を高めるために熱処理される。熱処理温度は、ポリエチレンフィルムについては１００〜１３０℃、好ましくは１１０〜１２５℃、ポリプロピレンフィルムについては１１０〜１６０℃、好ましくは１２０〜１５０℃である。熱処理温度が低いと十分に多孔化されず、また高すぎるとフィルムの溶融が生じるため適当でない。熱処理時間は特に制限はないが、３秒〜１８０秒の範囲で行われる。
【００２３】
熱処理されたポリエチレンフィルムは、その複屈折が２５×１０-3〜４８×１０-3、好ましくは３０×１０-3〜４５×１０-3で、５０％伸長時の弾性回復率が４０〜８０％、好ましくは、５０〜７５％の範囲にあるのが好適である。
また、熱処理されたポリプロピレンフィルムは、その複屈折が１０×１０-3〜２５×１０-3、好ましくは１２×１０-3〜２３×１０-3で、１００％伸長時の弾性回復率が７０〜９４％、好ましくは、７５〜９３％の範囲にあるのが好適である。
複屈折及び弾性回復率がこれらの範囲を外れると、多孔化の程度が十分でなくなり、延伸後の多孔質フィルムの孔径や孔径分布、空孔率、層間剥離強度、機械的強度等に影響し品質にバラツキが生じやすくなるので上記範囲が適当である。
【００２４】
本発明において、複屈折は偏光顕微鏡を使用し、直交ニコル下でベレックコンペンセータを用いて測定された値である。
また、弾性回復率は、次の式（１）及び（２）による。式（１）はポリエチレンフィルムの場合、式（２）はポリプロピレンフィルムの場合である。
尚、ポリエチレンフィルムは、２５℃、６５％相対湿度において試料幅１５ｍｍ、長さ２インチで引張試験機にセットし２インチ／ｍｉｎの速度で５０％まで伸長した後、１分間伸長状態で保持しその後同速度で弛緩させたものを測定し、ポリプロピレンフィルムは、２５℃、６５％相対湿度において試料幅１０ｍｍ、長さ５０ｍｍで引張試験機にセットし５０ｍｍ／ｍｉｎの速度で１００％まで伸長した後、直ちに同速度で弛緩させたものを測定した。
【００２５】
無機微粒子を含むポリプロピレンで無機微粒子を含まないポリエチレンを挟み込んだ三層構成の積層多孔質フィルムを製造する場合は、熱処理されたポリプロピレンフィルム及びポリエチレンフィルムは熱圧着によって積層される。積層は、三枚のフィルムが３組の原反ロールスタンドから巻き出され、加熱されたロール間でニップされ圧着されて積層される。この時、各フィルムの複屈折及び弾性回復率が実質的に低下しないように熱圧着が行われる必要がある。
【００２８】
加熱されたロールの温度、すなわち熱圧着温度は、１１０〜１３０℃、好ましくは１１５〜１２５℃である。温度が低すぎるとフィルム間の接着性が弱くその後の延伸工程で剥がれが生じ、また逆に高すぎるとポリエチレンの溶融によってフィルムの複屈折及び弾性回復率が低下して多孔化が困難となるため上記範囲が適当である。
熱圧着のニップ圧は１〜３ｋｇ／ｃｍ2、巻出し速度は０．５〜８ｍ／ｍｉｎで行われる。また、熱圧着されたフィルム間の剥離強度は、３〜６０ｇ／１５ｍｍの範囲が好適である。
【００２９】
熱処理及び積層されたフィルムは延伸によって多孔化される。延伸は低温延伸、次いで高温延伸の順序で行われ、普通には延伸ロールの周速差で延伸される。
低温延伸の温度は−２０〜５０℃、特に好ましくは２０〜３５℃である。延伸温度が低いと作業中にフィルムの破断が生じやすく、逆に高すぎると多孔化が不十分となるので適当でない。
低温延伸の倍率は５〜２００％、好ましくは１０〜１００％の範囲である。延伸倍率が低すぎると、空孔率が低いものしか得られず、また高すぎると所定の空孔率及び孔径のものが得られなくなるので上記範囲が適当である。
本発明において低温延伸倍率（Ｅ1）は次の式（３）に従う。式（３）のＬ1は低温延伸後のフィルム寸法を意味し、Ｌ0は低温延伸前のフィルム寸法を意味する。
【００３０】
式（３） Ｅ1＝［（Ｌ1−Ｌ0）／Ｌ0］×１００
【００３１】
低温延伸したフィルムは、次いで高温延伸される。高温延伸は加熱空気循環オーブン中で７０〜１３０℃、特に好ましくは１００〜１２５℃の温度範囲で行われる。延伸温度が上記範囲を外れると多孔化が不十分となるので適当でない。また、高温延伸は低温延伸の温度より４０〜１００℃高い温度で行うのが好適である。
高温延伸の倍率は１００〜４００％の範囲である。延伸倍率が低すぎると、多孔化が不十分となり、また高すぎると所定の透気度、空孔率及び孔径のものが得られなくなるので上記範囲が適当である。
本発明において高温延伸倍率（Ｅ2）は次の式（４）に従う。式（４）のＬ2は高温延伸後のフィルム寸法を意味し、Ｌ1は低温延伸後のフィルム寸法を意味する。
【００３２】
式（４） Ｅ2＝［（Ｌ2−Ｌ1）／Ｌ1］×１００
【００３３】
本発明において、低温延伸、高温延伸をした後、多孔質フィルムの熱固定を行う。熱固定は、延伸時に作用した応力残留によるフィルムの延伸方向への収縮を防ぐために予め延伸後のフィルム長さが１０〜５０％減少する程度熱収縮させる方法や、延伸方向の寸法が変化しないように規制して加熱する方法等で行われる。この熱固定によって寸法安定性の良い所期の課題を満たす電池用セパレータにすることができる。
【００３４】
このようにして製造される電池用セパレータは、前記製造条件によっても異なるが、透気度、３０〜８００秒／１００ｃｃ、さらに好ましくは１００〜７００秒／１００ｃｃ、極大孔径０．０２〜３μｍ、空孔率３０〜８５％である。透気度が高すぎるとリチウムイオン伝導性が低下するために電池用セパレータとしての機能が十分でなく、低すぎると機械的強度が低下するので上記範囲が適当である。また、極大孔径及び空孔率がこの範囲にないと、電池の容量特性が低下するために好ましくない。
さらに、電池用セパレータの厚みは機械的強度、性能、小型化等の面から５〜１００μｍ、特に好ましくは２０〜４０μｍに調製される。
【００３５】
本発明では、特定の金属酸化物を主成分とする無機微粒子を適切に配合することで、傷つき性等の機械的強度に優れる電池用セパレータが得られた。ここで、傷つき性とは微小突起の圧入或いは擦過によるセパレータの損傷具合を意味する。
さらに、本発明の電池用セパレータは、多孔質フィルムの絶縁強さと関係づけられる破壊電圧についても、無機粒子の添加によって改良している。
すなわち、本発明では、無機微粒子の配合による傷つけ性及び破壊電圧の改良によって、信頼性及び安全性に優れ且つ電池性能を損なうことのない電池用セパレータを提供することができる。
【００３６】
【実施例】
次に実施例及び比較例を示し、本発明について更に詳細に説明するが、本発明はこれらに限定されるものではない。
【００３７】
実施例１
数平均分子量７００００、結晶化温度１１２℃のポリプロピレンに、酸化珪素を主成分とする真比重２．３６、平均粒径２．１μｍの無機微粒子を、二軸混練機を用いて樹脂に対して２０００ｐｐｍになるように配合した。無機微粒子の酸化電位はリチウムに対して＋４．５Ｖ以上であった。この無機微粒子配合ポリプロピレンは、吐出幅１０００ｍｍ、吐出リップ開度２ｍｍのＴダイを使用してフィルム状に溶融押出しした。
吐出フィルムは、８０℃の冷却ロールに導かれ、２５℃の冷風が吹きつけられて冷却された後、５０ｍ／ｍｉｎで引取られた。
得られたポリプロピレン組成物フィルムの膜厚は１１．４μｍであった。
この未延伸ポリプロピレンフィルムは、引取り方向を固定された状態で、１３５℃に６０秒間熱処理した後、室温まで冷却した。
熱処理された未延伸ポリプロピレンフィルムの複屈折は、２２．６×１０-3、１００％伸長時の弾性回復率は９３％であった
【００３８】
ポリエチレンとして、数平均分子量２００００、密度０．９６４、融点１３４℃の高密度ポリエチレンを、吐出幅１０００ｍｍ、吐出リップ開度２ｍｍのＴダイを使用して溶融押出しした。
吐出フィルムは、１１７℃の冷却ロールに導かれ、２５℃の冷風が吹きつけられて冷却された後、２０ｍ／ｍｉｎで引取られた。
得られたポリエチレンフィルムの膜厚は９．５μｍであった。
この未延伸ポリエチレンフィルムは、引取り方向を固定された状態で、１２０℃に６０秒間熱処理した後、室温まで冷却した。
熱処理された未延伸ポリエチレンフィルムの複屈折は、３５．５×１０-3、５０％伸長時の弾性回復率は５２％であった。
【００３９】
熱処理したポリエチレンフィルム及びポリプロピレンフィルムは、ポリプロピレンを表面層に、ポリエチレンを内層（中間層）に配した三層構成に積層された。積層は、三組のロールスタンドから該ポリプロピレンフィルム及びポリエチレンフィルムをそれぞれ巻出し速度６．５ｍ／ｍｉｎで巻出し、加熱ロールに導き、温度１２０℃、線圧１．８ｋｇ／ｃｍで熱圧着し、その後同速度で５０℃の冷却ロールに導いて巻き取った。巻取り速度は６．５ｍ／ｍｉｎ、巻出し張力は０．９ｋｇであった。
得られた未延伸積層フィルムの膜厚は３１．６μｍであった。
【００４０】
未延伸積層フィルムは、３０℃に保持されたニップロール間で２５％低温延伸された。この時のロール間は３５０ｍｍ、供給側のロール速度は２ｍ／ｍｉｎであった。
低温延伸した積層フィルムは、引続き１２３℃に加熱された熱風循環オーブン中に導かれ、ロール周速差を利用してロール間で総延伸量１８０％になるまで高温延伸された後、１２３℃に加熱されたロールで３０％緩和させて７２秒間熱固定され、連続的に積層多孔質フィルム、すなわち電池用セパレータを得た。
【００４１】
得られた電池用セパレータの膜厚、透気度、極大孔径、空孔率、鉛筆硬度、微小表面硬度、破壊電圧を表１に示す。また、電池用セパレータを、表面粗さ指数（Ｒａ）が０．３μｍになるように研削仕上げを施した金属面を用いて荷重４００ｇｆ／ｃｍ2、移動速度３００ｍｍ／分で擦過させた後の電池用セパレータの顕微鏡写真を図１に示す。図１から明らかなように、セパレータ表面には擦過傷が殆ど見られなかった。上記評価の方法は以下に従って行った。
１）透気度
ＪＩＳ Ｐ８１１７に準じて測定した。測定装置としてＢ型ガーレーデンソメーター（東洋精機社製）を使用した。試料片を直径２８．６ｍｍ、面積６４５ｍｍ2の円孔に締付ける。内筒重量５６７ｇにより、筒内の空気を試験円孔部から筒外へ通過させる。空気１００ｃｃが通過する時間を測定し、透気度（ガーレー値）とした。
２）空孔率、極大孔径
ユアサアイオニクス社製水銀ポロシメータを用いて測定した。試料を０．０３〜０．０７ｇ秤量してガラス製のセル中で真空とした後、水銀を圧入、充填する。充填の際の水銀圧及び圧入水銀量から極大孔径及び空孔率を求めた。
３）鉛筆硬度
東洋精機社製鉛筆引っ掻き試験機を用いて測定した。芯を円柱状に３ｍｍ程度露出させた鉛筆で５０ｇの荷重をかけて電池用セパレータ上を５回引っかき、５回のうち１回傷がつく又は全く傷がつかないで且つその１段階上の硬度の鉛筆で５回のうち２回以上傷がつく硬度記号を鉛筆硬度とした。
４）微小表面硬度
アカシ製微小表面材料特性評価システム（ＭＺＴ−４）を用いて測定を行なった。電池用セパレータを固定し、５００μｍ径の球状圧子にて０．０４ｇｆ／秒の速度で５ｇｆまで荷重を印加し、５秒間保持後に除圧した。圧子の押し込み深さより次式（５）に従って硬さ指数を算出した。
式（５） 押し込み指数＝荷重×２／押し込み深さ／円周率
５）破壊電圧
ＪＩＳ Ｃ２１１０に準じて測定した。５０ｍｍ×５０ｍｍに切り取った電池用セパレータを、２５ｍｍ径の電極間に５００ｇの荷重を付与して挟み、０．２ＫＶ／秒の速度で交流電圧を印加して、絶縁破壊の生じた電圧を破壊電圧とした。
【００４２】
比較例１
ポリプロピレンに無機微粒子を配合しない以外は、実施例１と同様に積層多孔質フィルム、すなわち電池用セパレータを得た。
得られた電池用セパレータの膜厚、透気度、極大孔径、空孔率、鉛筆硬度、微小表面硬度、破壊電圧を表１に示す。また、電池用セパレータを、表面粗さ指数（Ｒａ）が０．３μｍになるように研削仕上げを施した金属面を用いて荷重４００ｇｆ／ｃｍ2、移動速度３００ｍｍ／分で擦過させた後の電池用セパレータの顕微鏡写真を図２に示す。図２から明らかなように、セパレータ表面には無数の擦過傷が見られる。
【００４３】
【表１】
特定の金属酸化物を主成分とする無機微粒子を適切に配合することにより、傷つき性等の機械的強度に優れる電池用セパレータを提供することができる。
【図面の簡単な説明】
【図１】本発明で得られた電池用セパレータにおける擦過テスト後の表面状態を示す写真に代わる図である。
【図２】比較例で得られた電池用セパレータにおける擦過テスト後の表面状態を示す写真に代わる図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery separator useful as a constituent material of a lithium battery.
[0002]
[Prior art]
Conventionally, polyolefin-based porous films have been used as separators for batteries, diaphragms for electrolytic capacitors, and the like. In particular, with the advancement of technology in recent years, high-precision and high-performance separators have been required for lithium batteries and the like.
[0003]
Taking a battery as an example, in recent years, a non-aqueous electrolyte battery such as a lithium battery having a high energy density, a high electromotive force, and a low self-discharge, in particular, a lithium secondary battery has been developed and put into practical use. Examples of negative electrodes of lithium batteries include metallic lithium, alloys of lithium and other metals, carbon materials having the ability to adsorb lithium ions such as carbon and graphite, or the ability to occlude by intercalation, and conductivity doped with lithium ions. Polymer materials and the like are known, and as the positive electrode, for example, fluorinated graphite represented by (CF x ) n , MnO 2 , V 2 O 5 , CuO, Ag 2 CrO 4 , TiO 2 , LiCoO 2 , LiMn 2 Metal oxides such as O 4 , sulfides, and chlorides are known.
[0004]
In addition, as a non-aqueous electrolyte, LiPF 6 , LiBF in an organic solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane, tetrahydrofuran, etc. 4 , LiClO 4 , LiCF 3 SO 3 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2, etc. are used.
[0005]
The role of the separator, which is a constituent material of such a lithium battery, is to prevent the positive and negative electrodes from being short-circuited and to not inhibit the battery reaction, and to prevent heat generation and ignition of the battery by heat clogging in the event of an abnormality. The following various porous films have been proposed for the purpose of improving mechanical strength, which is closely related to safety of the following.
[0006]
A porous film using a raw material resin having a high molecular weight (JP-A-2-94356, JP-A-3-105851, etc.).
A porous film using a thermoplastic resin or a nonwoven fabric as a support (JP-A-3-245457, JP-A-1-258358, etc.).
[0007]
One of the properties of the separator that reflects the safety of the battery is the ability of the surface to be damaged by minute protrusions. On the surface of the electrode plate of a lithium battery, unevenness of about several μm is often present. For this reason, when a porous film is incorporated in a lithium battery as a battery separator, there is a concern that the film may be damaged by irregularities on the surface of the electrode plate. Since the damage of the separator causes a short circuit of the battery, improvement of the surface damage property by the fine protrusions as well as the strength of the separator itself is an important issue.
[0008]
On the other hand, for the purpose of improving the strength, a method of blending an inorganic filler into a porous film made of a polyolefin resin or a method of providing a surface protective layer containing inorganic fine particles is known. In the method of blending the inorganic filler (Japanese Patent Laid-Open No. 62-167332), the purpose is not only to improve the strength by the inorganic filler but also to impart uniformity of the stretched porosity. Battery separator because the amount of resin is 50 to 500 parts by weight with respect to 100 parts by weight of resin and the reliability of the shutdown function to prevent heat generation and ignition of the battery due to thermal clogging (resin part) is abnormal. Not suitable for. Further, in the method of providing a surface protective layer containing inorganic fine particles (Japanese Patent Laid-Open No. 11-80395), the process of arranging the surface protective layer containing inorganic fine particles on the surface of the porous film becomes complicated in the manufacturing process. Since the air permeability is increased by the application of the surface protective layer, a low air permeability cannot be obtained, and there is still room for improvement.
[0009]
Further, in the improvement of the separator porous film using the resin modifying additive such as inorganic fine particles, the additive is not decomposed or modified by an electrochemical reaction other than the battery reaction during the use of the battery. In addition, as described in Japanese Patent Application No. 11-6045 filed by the inventors of the present application, the oxidation potential of the inorganic fine particles is preferably +4.5 V or more with respect to lithium.
An object of the present invention is to provide a porous film that is excellent in reliability and safety when using a battery as a lithium battery separator and does not hinder battery reaction, that is, a battery separator.
[0010]
[Means for Solving the Problems]
As a result of diligent research, the inventors of the present invention have obtained a porous film that is excellent in reliability and safety and does not inhibit the battery reaction by appropriately blending inorganic fine particles mainly composed of a specific metal oxide. It was found that can be obtained. That is, the present invention is a battery separator comprising a single layer or a laminated porous film made porous by a stretching method, wherein the porous film exhibits an air permeability of 30 to 800 seconds / 100 cc, silicon oxide, aluminum oxide Inorganic fine particles having an oxidation potential containing at least one metal oxide selected from the group of magnesium oxide as a main component is +4.5 V or more with respect to lithium and having an average particle size of 0.1 to 10 μm. The present invention relates to a battery separator containing ˜5000 ppm.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
There is no restriction | limiting in particular as a material used for the battery separator of this invention, Polyolefin resin, such as a polypropylene and polyethylene, can be utilized. In addition, the porous film of the present invention may have any structure of a single layer porous film and a laminated porous film, and when it is a laminated porous film, inorganic fine particles are formed in at least one layer of the laminated porous film. Should be included.
[0012]
The polypropylene used in the present invention preferably has a number average molecular weight of 50,000 or more, more preferably 70,000 or more and a ratio of the number average molecular weight to the weight average molecular weight of 8 or less because of high mechanical strength. The crystallization temperature of polypropylene is preferably 110 ° C. or higher, more preferably 112 ° C. or higher.
[0013]
The polyethylene used in the present invention may be any of high-density polyethylene, medium-density polyethylene, linear low-density polyethylene, etc., preferably high-density polyethylene. Polyethylene having a number average molecular weight of 10,000 or more, more preferably 20,000 or more is preferred because of its high mechanical strength.
[0014]
In the present invention, the number average molecular weights of polypropylene and polyethylene were determined by standard polystyrene conversion using a 150C gel permeation chromatograph manufactured by WATERS. Two Shodex HT-806M columns were used for the column, and measurement was performed at 135 ° C. in orthodichlorobenzene prepared to 0.3 wt / vol%.
The melting point of polypropylene was measured using DSC-7 manufactured by PerkinElmer. In order to remove the thermal history, the sample was kept at 230 ° C. for 10 minutes and completely melted, then cooled to room temperature at 10 ° C./min. It was.
[0015]
The inorganic fine particles contained in the battery separator of the present invention contain at least one metal oxide selected from the group of silicon oxide, aluminum oxide, and magnesium oxide as a main component, and are non-aqueous electrolysis that is a constituent material of a lithium secondary battery. It is desirable not to swell or dissolve in the liquid. If the inorganic fine particles contain an organic substance that swells and dissolves in the non-aqueous electrolyte, the battery reaction may be inhibited when the battery is used, which is not appropriate. Moreover, the average particle diameter of inorganic fine particles is 0.1-10 micrometers, More preferably, it is 0.5-3 micrometers. If the average particle size of the inorganic fine particles is smaller than this range, the effect of improving the mechanical strength such as the scratch resistance of the battery separator cannot be expected, and if larger than this range, the appearance of the battery separator due to poor dispersion of the inorganic fine particles can be expected. It is not appropriate because a defect occurs.
[0016]
The true specific gravity of the inorganic fine particles used in the present invention is preferably 1.5 or more, particularly 2 or more. If the true specific gravity of the inorganic fine particles is too small, the effect of improving the mechanical strength such as scratch resistance of the battery separator is small, which is not suitable. Further, the oxidation potential of the inorganic fine particles is preferably +4.5 V or more, particularly +5 V or more with respect to lithium, since it is electrochemically stable.
[0017]
The measurement of the oxidation potential shown in the present invention was performed using a nonaqueous electrolytic solution prepared by dissolving LiPF 6 in dimethyl carbonate to 1 M / L. The inorganic fine particles were suspended in this non-aqueous electrolyte so as to be 0.05 M / L. Using a metal lithium foil as the reference electrode and a platinum electrode as the working electrode, the potential was swept from ± 0 V to +4.5 V at a rate of 10 mV per second, and the voltage at which a current of 0.1 mA was detected was defined as the oxidation potential. .
[0018]
In the present invention, the method of blending the inorganic fine particles with polypropylene or polyethylene is not particularly limited, but can be blended by kneading using an ordinary kneader. For example, a pellet can be obtained by melt-kneading using a single screw extruder, a twin screw extruder, a mixing roll, or the like. Moreover, you may mix | blend by dry blend using a Henschel mixer, a tumbler, etc. The blending ratio of the inorganic fine particles to the battery separator is 100 to 5000 ppm, more preferably 300 to 4000 ppm. If the amount of the inorganic fine particles is smaller than this range, the effect of improving the mechanical strength such as the scratch resistance of the battery separator cannot be expected. This is not suitable because a battery separator having a low value cannot be obtained.
[0019]
In the present invention, the number of inorganic fine particles contained in a single layer or laminated porous film made porous by a stretching method varies depending on the stretching ratio and the like, but is usually 50 to 5000 per mm 2 , particularly 100 to 3000 per film area. It is preferable to adjust to pieces / mm 2 . If the dispersion state of the inorganic fine particles is excessively deviated from this range, the effect of improving the mechanical strength such as the scratch property of the battery separator cannot be expected.
[0020]
The layer structure of the battery separator of the present invention includes a polyethylene or polypropylene single-layer porous film containing inorganic fine particles, a laminated porous film in which polyethylene containing inorganic fine particles and polyethylene not containing inorganic fine particles are sandwiched, and inorganic fine particles included Laminated porous film with polyethylene containing inorganic fine particles sandwiched between polypropylene, laminated porous film made of polyethylene containing inorganic fine particles and polyethylene containing no inorganic fine particles, laminated porous film made of polyethylene containing inorganic fine particles and polypropylene containing inorganic fine particles In the case of a laminated porous film, at least one layer may contain inorganic fine particles.
[0021]
As a specific method for producing the battery separator of the present invention, for example, when producing a laminated porous film in which polyethylene containing inorganic fine particles is sandwiched with polyethylene containing inorganic fine particles, A method for obtaining a laminated porous film by melting and coextrusion of polyethylene to obtain a laminated porous film, a method for obtaining a laminated porous film by subjecting polypropylene and polyethylene film, which are appropriately blended with inorganic fine particles, to melt and extrusion separately, respectively, and then drawing to obtain a laminated porous film, etc. There is. Further, in the stretch porosification step, when the length of the film in the width direction is greatly reduced and the performance of the porous film such as air permeability, porosity, and maximum pore diameter is impaired, the present inventors As in the method described in Japanese Patent Application Laid-Open No. 11-297297 filed by, and a method of stretching while fixing both ends in the width direction of the film with a chuck, a pinch roll, etc. The reduction in the film length in the width direction can be improved by a technique such as a method of restoring by transverse stretching. Either method can produce the battery separator of the present invention.
[0022]
The melt extrusion method is performed by a melt extrusion molding method using a T die, an inflation method, or the like. For example, when a film is melt-molded by a T-die, it is generally performed at a temperature 20 to 60 ° C. higher than the melting temperature of the resin at a draft ratio of 5 to 500, preferably 50 to 300, and the take-off speed is particularly limited. Although it is not, it is usually molded at 10 to 50 m / min.
The melt extruded film is heat treated to enhance crystallinity and its orientation. The heat treatment temperature is 100 to 130 ° C, preferably 110 to 125 ° C for a polyethylene film, and 110 to 160 ° C, preferably 120 to 150 ° C for a polypropylene film. When the heat treatment temperature is low, the film is not sufficiently porous, and when it is too high, the film is melted. The heat treatment time is not particularly limited, but is performed in the range of 3 seconds to 180 seconds.
[0023]
The heat-treated polyethylene film has a birefringence of 25 × 10 −3 to 48 × 10 −3 , preferably 30 × 10 −3 to 45 × 10 −3 , and an elastic recovery rate at 50% elongation of 40 to 80 %, Preferably in the range of 50-75%.
The heat-treated polypropylene film has a birefringence of 10 × 10 −3 to 25 × 10 −3 , preferably 12 × 10 −3 to 23 × 10 −3 , and an elastic recovery rate of 70% when stretched by 100%. It is suitable to be in the range of -94%, preferably 75-93%.
If the birefringence and the elastic recovery rate are outside these ranges, the degree of porosity will be insufficient, affecting the pore size and pore size distribution, porosity, delamination strength, mechanical strength, etc. of the stretched porous film. The above range is appropriate because quality tends to vary.
[0024]
In the present invention, birefringence is a value measured using a Berek compensator under crossed Nicols using a polarizing microscope.
The elastic recovery rate is based on the following formulas (1) and (2). Formula (1) is for a polyethylene film and Formula (2) is for a polypropylene film.
The polyethylene film was set in a tensile tester with a sample width of 15 mm and a length of 2 inches at 25 ° C. and 65% relative humidity, stretched to 50% at a speed of 2 inches / min, and then held in a stretched state for 1 minute. After measuring the relaxed film at the same speed, the polypropylene film was set in a tensile tester with a sample width of 10 mm and a length of 50 mm at 25 ° C. and 65% relative humidity and stretched to 100% at a speed of 50 mm / min. Immediately after relaxing at the same speed, measurements were taken.
[0025]
In the case of producing a laminated porous film having a three-layer structure in which polyethylene containing inorganic fine particles is sandwiched between polypropylene containing inorganic fine particles, the heat-treated polypropylene film and polyethylene film are laminated by thermocompression bonding. In the lamination, three films are unwound from three sets of raw roll stands, nipped and heated between heated rolls, and laminated. At this time, it is necessary to perform thermocompression bonding so that the birefringence and the elastic recovery rate of each film are not substantially lowered.
[0028]
The temperature of the heated roll, that is, the thermocompression bonding temperature is 110 to 130 ° C, preferably 115 to 125 ° C. If the temperature is too low, the adhesiveness between the films will be weak and peeling will occur in the subsequent stretching process. Conversely, if the temperature is too high, the birefringence and elastic recovery of the film will decrease due to the melting of polyethylene, making it difficult to make the film porous. The above range is appropriate.
The nip pressure for thermocompression bonding is 1 to 3 kg / cm 2 and the unwinding speed is 0.5 to 8 m / min. Moreover, the range of 3-60g / 15mm is suitable for the peeling strength between the thermocompression-bonded films.
[0029]
The heat treated and laminated film is made porous by stretching. Stretching is performed in the order of low-temperature stretching and then high-temperature stretching. Usually, stretching is performed with a difference in peripheral speed between stretching rolls.
The temperature of the low temperature stretching is -20 to 50 ° C, particularly preferably 20 to 35 ° C. If the stretching temperature is low, the film is likely to be broken during the operation. On the other hand, if the stretching temperature is too high, the porosity becomes insufficient, which is not suitable.
The low-temperature stretching ratio is 5 to 200%, preferably 10 to 100%. If the draw ratio is too low, only those having a low porosity can be obtained, and if it is too high, a product having a predetermined porosity and pore diameter cannot be obtained.
In the present invention, the low temperature draw ratio (E 1 ) follows the following formula (3). L 1 in the formula (3) means a film size after low-temperature stretching, and L 0 means a film size before low-temperature stretching.
[0030]
Formula (3) E 1 = [(L 1 −L 0 ) / L 0 ] × 100
[0031]
The low temperature stretched film is then hot stretched. The high temperature stretching is performed in a heated air circulating oven at a temperature of 70 to 130 ° C, particularly preferably 100 to 125 ° C. If the stretching temperature is out of the above range, the porosity becomes insufficient, which is not suitable. The high temperature stretching is preferably performed at a temperature 40 to 100 ° C. higher than the temperature of the low temperature stretching.
The hot stretch ratio is in the range of 100 to 400%. If the draw ratio is too low, the porosity becomes insufficient, and if it is too high, a product having a predetermined air permeability, porosity and pore diameter cannot be obtained, so the above range is suitable.
In the present invention, the high temperature draw ratio (E 2 ) follows the following formula (4). L 2 in the formula (4) means a film size after hot stretching, and L 1 means a film size after low temperature stretching.
[0032]
Equation (4) E 2 = [( L 2 -L 1) / L 1] × 100
[0033]
In the present invention, the porous film is heat-set after low-temperature stretching and high-temperature stretching. In the heat setting, in order to prevent shrinkage in the stretching direction of the film due to residual stress acting at the time of stretching, a method of heat shrinking to the extent that the film length after stretching is reduced by 10 to 50% and the dimensions in the stretching direction do not change. It is performed by a method of heating by regulating the temperature. By this heat fixation, it can be set as the battery separator which satisfy | fills the subject with the favorable dimensional stability.
[0034]
The battery separator produced in this manner varies depending on the production conditions, but the air permeability, 30 to 800 seconds / 100 cc, more preferably 100 to 700 seconds / 100 cc, the maximum pore diameter 0.02 to 3 μm, and the empty The porosity is 30 to 85%. If the air permeability is too high, the lithium ion conductivity is lowered, so that the function as a battery separator is not sufficient, and if it is too low, the mechanical strength is lowered, so the above range is appropriate. Further, if the maximum pore diameter and the porosity are not in this range, the capacity characteristics of the battery are deteriorated, which is not preferable.
Furthermore, the thickness of the battery separator is adjusted to 5 to 100 μm, particularly preferably 20 to 40 μm from the viewpoints of mechanical strength, performance, miniaturization, and the like.
[0035]
In the present invention, a battery separator excellent in mechanical strength such as scratch resistance was obtained by appropriately blending inorganic fine particles mainly composed of a specific metal oxide. Here, the scratchability means the degree of damage to the separator due to the press-fitting or rubbing of microprojections.
Furthermore, the battery separator of the present invention improves the breakdown voltage related to the dielectric strength of the porous film by adding inorganic particles.
That is, in the present invention, a battery separator that is excellent in reliability and safety and that does not impair battery performance can be provided by improving scratch resistance and breakdown voltage by blending inorganic fine particles.
[0036]
【Example】
EXAMPLES Next, although an Example and a comparative example are shown and this invention is demonstrated further in detail, this invention is not limited to these.
[0037]
Example 1
To a polypropylene having a number average molecular weight of 70,000 and a crystallization temperature of 112 ° C., inorganic fine particles having a true specific gravity of 2.36 mainly composed of silicon oxide and an average particle diameter of 2.1 μm are 2,000 ppm with respect to the resin using a biaxial kneader. It mix | blended so that it might become. The oxidation potential of the inorganic fine particles was +4.5 V or more with respect to lithium. This inorganic fine particle-blended polypropylene was melt extruded into a film using a T-die having a discharge width of 1000 mm and a discharge lip opening of 2 mm.
The discharged film was guided to an 80 ° C. cooling roll, cooled by blowing 25 ° C. cold air, and then taken up at 50 m / min.
The film thickness of the obtained polypropylene composition film was 11.4 μm.
The unstretched polypropylene film was heat-treated at 135 ° C. for 60 seconds with the take-up direction fixed, and then cooled to room temperature.
The birefringence of the heat-treated unstretched polypropylene film was 22.6 × 10 −3 , and the elastic recovery at 100% elongation was 93%.
As polyethylene, high-density polyethylene having a number average molecular weight of 20000, a density of 0.964, and a melting point of 134 ° C. was melt-extruded using a T-die having a discharge width of 1000 mm and a discharge lip opening of 2 mm.
The discharged film was guided to a 117 ° C. cooling roll, cooled by blowing 25 ° C. cold air, and then taken up at 20 m / min.
The film thickness of the obtained polyethylene film was 9.5 μm.
The unstretched polyethylene film was heat-treated at 120 ° C. for 60 seconds with the take-up direction fixed, and then cooled to room temperature.
The birefringence of the heat-treated unstretched polyethylene film was 35.5 × 10 −3 , and the elastic recovery rate at 50% elongation was 52%.
[0039]
The heat-treated polyethylene film and polypropylene film were laminated in a three-layer structure in which polypropylene was disposed on the surface layer and polyethylene was disposed on the inner layer (intermediate layer). Lamination is performed by unwinding the polypropylene film and the polyethylene film from three sets of roll stands respectively at an unwinding speed of 6.5 m / min, leading to a heating roll, and thermocompression bonding at a temperature of 120 ° C. and a linear pressure of 1.8 kg / cm. Then, it was guided to a 50 ° C. cooling roll at the same speed and wound up. The winding speed was 6.5 m / min, and the unwinding tension was 0.9 kg.
The film thickness of the obtained unstretched laminated film was 31.6 μm.
[0040]
The unstretched laminated film was 25% cold-stretched between nip rolls maintained at 30 ° C. The distance between the rolls at this time was 350 mm, and the roll speed on the supply side was 2 m / min.
The laminated film that has been stretched at a low temperature is continuously introduced into a hot-air circulating oven heated to 123 ° C., and is stretched at a high temperature until the total stretching amount becomes 180% between rolls using a difference in roll peripheral speed. The film was relaxed by 30% with a heated roll and heat-fixed for 72 seconds to continuously obtain a laminated porous film, that is, a battery separator.
[0041]
Table 1 shows the film thickness, air permeability, maximum pore diameter, porosity, pencil hardness, micro surface hardness, and breakdown voltage of the obtained battery separator. The battery separator is rubbed at a load of 400 gf / cm 2 and a moving speed of 300 mm / min using a metal surface that has been ground so that the surface roughness index (Ra) is 0.3 μm. A photomicrograph of the separator for use is shown in FIG. As apparent from FIG. 1, almost no scratches were seen on the separator surface. The evaluation method was performed as follows.
1) Air permeability Measured according to JIS P8117. A B-type Gurley Densometer (manufactured by Toyo Seiki Co., Ltd.) was used as a measuring device. The sample piece is clamped in a circular hole having a diameter of 28.6 mm and an area of 645 mm 2 . With the inner cylinder weight of 567 g, the air in the cylinder is allowed to pass out of the cylinder from the test circular hole. The time required for 100 cc of air to pass through was measured and used as the air permeability (Gurley value).
2) Porosity and maximum pore diameter Measured using a mercury porosimeter manufactured by Yuasa Ionics. 0.03 to 0.07 g of a sample is weighed and evacuated in a glass cell, and then mercury is injected and filled. The maximum pore diameter and porosity were determined from the mercury pressure and the amount of mercury injected during filling.
3) Pencil hardness Measured with a pencil scratch tester manufactured by Toyo Seiki Co., Ltd. A 50mm load is applied with a pencil with the core exposed in a cylindrical shape of about 3mm. The battery separator is scratched 5 times, and the hardness is one step out of the five times or not damaged at all. The hardness symbol that scratches 2 times or more out of 5 times with the pencil was defined as pencil hardness.
4) Micro surface hardness Measurement was performed using a micro surface material property evaluation system (MZT-4) manufactured by Akashi. The battery separator was fixed, and a load was applied to a 5 gf with a spherical indenter having a diameter of 500 μm at a speed of 0.04 gf / sec. The hardness index was calculated from the indentation depth of the indenter according to the following equation (5).
Formula (5) Indentation index = load × 2 / indentation depth / circumference 5) Breakdown voltage Measured according to JIS C2110. A battery separator cut to 50 mm × 50 mm is sandwiched by applying a load of 500 g between 25 mm-diameter electrodes, an AC voltage is applied at a speed of 0.2 KV / sec, and the voltage at which dielectric breakdown occurs is determined as a breakdown voltage. It was.
[0042]
Comparative Example 1
A laminated porous film, that is, a battery separator was obtained in the same manner as in Example 1 except that the inorganic fine particles were not blended with polypropylene.
Table 1 shows the film thickness, air permeability, maximum pore diameter, porosity, pencil hardness, micro surface hardness, and breakdown voltage of the obtained battery separator. The battery separator is rubbed at a load of 400 gf / cm 2 and a moving speed of 300 mm / min using a metal surface that has been ground so that the surface roughness index (Ra) is 0.3 μm. A photomicrograph of the separator for use is shown in FIG. As is clear from FIG. 2, countless scratches are seen on the separator surface.
[0043]
[Table 1]
By appropriately blending inorganic fine particles containing a specific metal oxide as a main component, a battery separator having excellent mechanical strength such as scratch resistance can be provided.
[Brief description of the drawings]
FIG. 1 is a view replacing a photograph showing a surface state after a rubbing test in a battery separator obtained in the present invention.
FIG. 2 is a view replacing a photograph showing a surface state after a rubbing test in a battery separator obtained in a comparative example.
Claims (4)
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP31935099A JP4470248B2 (en) | 1999-11-10 | 1999-11-10 | Battery separator |
| CNB001374796A CN1236508C (en) | 1999-11-10 | 2000-11-10 | Battery spacing membranes and lithium secondary battery |
| US09/709,623 US6627346B1 (en) | 1999-11-10 | 2000-11-10 | Battery separator and lithium secondary battery |
| HK01107893A HK1038100A1 (en) | 1999-11-10 | 2001-11-09 | Battery separator and lithium secondary battery |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP31935099A JP4470248B2 (en) | 1999-11-10 | 1999-11-10 | Battery separator |
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| Publication Number | Publication Date |
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| JP2001135295A JP2001135295A (en) | 2001-05-18 |
| JP4470248B2 true JP4470248B2 (en) | 2010-06-02 |
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|---|---|---|---|
| JP31935099A Expired - Lifetime JP4470248B2 (en) | 1999-11-10 | 1999-11-10 | Battery separator |
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Families Citing this family (30)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6432586B1 (en) * | 2000-04-10 | 2002-08-13 | Celgard Inc. | Separator for a high energy rechargeable lithium battery |
| DE10255122A1 (en) * | 2002-11-26 | 2004-06-03 | Creavis Gesellschaft Für Technologie Und Innovation Mbh | Long-term stable separator for an electrochemical cell |
| US7618743B2 (en) * | 2003-04-04 | 2009-11-17 | Asahi Kasei Chemicals Corporation | Microporous polyolefin film |
| JP5017764B2 (en) * | 2003-08-06 | 2012-09-05 | 三菱化学株式会社 | Nonaqueous electrolyte secondary battery separator and nonaqueous electrolyte secondary battery using the same |
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| JP4586374B2 (en) * | 2004-02-10 | 2010-11-24 | 三菱化学株式会社 | Non-aqueous electrolyte secondary battery |
| KR101094115B1 (en) | 2003-12-15 | 2011-12-15 | 미쓰비시 쥬시 가부시끼가이샤 | Nonaqueous electrolyte secondary battery |
| JP4635432B2 (en) * | 2003-12-15 | 2011-02-23 | 三菱化学株式会社 | Non-aqueous electrolyte secondary battery |
| WO2006062153A1 (en) | 2004-12-08 | 2006-06-15 | Hitachi Maxell, Ltd. | Separator for electrochemical device and electrochemical device |
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| JP4594837B2 (en) * | 2005-09-22 | 2010-12-08 | 三菱樹脂株式会社 | Method for producing porous laminate |
| JP5148360B2 (en) * | 2005-12-08 | 2013-02-20 | 日立マクセル株式会社 | Porous substrate for separator, separator for electrochemical element, electrode and electrochemical element |
| CN102244221A (en) | 2005-12-08 | 2011-11-16 | 日立麦克赛尔株式会社 | Separator for electrochemical device |
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| US7662510B2 (en) * | 2007-09-20 | 2010-02-16 | Celgard Llc | X-ray sensitive battery separator and a method for detecting the position of a separator in a battery |
| EP2261275B1 (en) | 2008-03-31 | 2013-10-02 | Asahi Kasei E-materials Corporation | Microporous film and method for producing the same |
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| JP5039817B2 (en) * | 2010-08-16 | 2012-10-03 | 三菱樹脂株式会社 | Porous laminate |
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| KR102044716B1 (en) * | 2012-04-13 | 2019-11-14 | 도레이 카부시키가이샤 | Multi-layered porous film, electrical cell separator, and electrical cell |
| JP6064926B2 (en) * | 2014-02-07 | 2017-01-25 | ソニー株式会社 | Separator and battery |
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- 1999-11-10 JP JP31935099A patent/JP4470248B2/en not_active Expired - Lifetime
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