JP4812919B2

JP4812919B2 - Non-aqueous electrolyte battery separator

Info

Publication number: JP4812919B2
Application number: JP26967799A
Authority: JP
Inventors: 春二井本; 秀夫遠藤; 英吉佐藤; 泰三松波
Original assignee: Nippon Sheet Glass Co Ltd
Current assignee: Nippon Sheet Glass Co Ltd
Priority date: 1999-09-24
Filing date: 1999-09-24
Publication date: 2011-11-09
Anticipated expiration: 2019-09-24
Also published as: JP2001093498A

Description

【０００１】
【発明の属する技術分野】
本発明は、各種電子機器等の電源として利用されるリチウムイオン二次電池等の非水電解液電池用セパレータに関するものである。
【０００２】
【従来の技術】
従来、小型の二次電池は、ＯＡ、ＦＡ、家電、通信機器等のポータブル電子機器用電源として幅広く使用されており、さらに機器に装備した場合に容積効率がよく、機器の小型化、軽量化につながることからリチウムイオン二次電池を使用したポータブル機器が増加している。一方、大型の二次電池は、ロードレベリング、ＵＰＳ、電気自動車をはじめ、環境問題に関連する多くの分野に置いて研究開発が進められ、大容量、高出力、高電圧、長期保存性に優れている点より非水電解液二次電池の一種であるリチウムイオン二次電池の要求が高まっている。
【０００３】
リチウムイオン二次電池の使用電圧は、通常、４．１から４．２Ｖを上限として設計されている。このような高い電圧では、水溶液は電気分解を起こすので電解液として使うことができない。そのため、高い電圧でも耐えられる電解液として、有機溶媒を使用したいわゆる非水電解液が用いられている。非水電解液用の溶媒は、より多くのリチウムイオンを存在させることができる高誘電率有機溶媒としてポリプロピレンカーボネートやエチレンカーボネート等の有機炭酸エステルが使用されている。また、溶媒中でリチウムイオン源となる支持電解質として、６フッ化リン酸リチウム等の反応性の高い電解質を溶媒中に溶かして使用している。
【０００４】
リチウムイオン二次電池は、構成材料に多くの可燃性物質が使われているので、誤使用されても発火などの事故が起こらないように種々の対策を行っている。特にセパレータは安全性向上で重要な役割を担っており、異常高温時にセパレータが溶融して微孔が閉鎖するいわゆるシャットダウン機能を具備したポリオレフィン系樹脂からなる微多孔質膜がセパレータとして使用されている。しかし、シャットダウン後も何らかの理由で電池温度の上昇が続いてセパレータの耐熱温度を超えると、セパレータが溶融し、極板間の隔離性が著しく低下するため、電池内でショートが発生すると共に電池が発火する問題点がある。この問題を解決するため、ポリオレフィン系樹脂と無機粉体等から構成された耐熱性の優れた無機質含有多孔膜のセパレータが、特開平１０−５０２８７号に開示されている。
【０００５】
【発明が解決しようとする課題】
しかしながら、前記したようにリチウムイオン二次電池は、電解液の中に６フッ化リン酸リチウム等のフッ素等を含んだ反応性の高い電解質を使用しているため、電池内に水分が介在すると、電解質と反応してフッ化水素が発生し、有機電解液や極板を劣化させるため電池容量が低下する問題がある。そこで、電池の製造・組立工程での作業条件、放置・保管において細心の注意を払って水分の管理を行っている。特開平１０−５０２８７号に開示されているポリオレフィン系樹脂と無機粉体とで構成されたセパレータは、付着水分が多かったり、構造中に結合水を含有するために平衡水分が５％以上という水分の多い無機粉体が含まれていたため、乾燥処理で水分を抜くことが難しく、電池使用中に電池容量が低下するという問題があった。
また、特願平１１−１０１８２号に記載されている平衡水分が４％未満の無機粉体でも、湿度の高い雰囲気中に放置された場合、表面に水分が付着してしまう問題があった。
【０００６】
本発明は、セパレータ中の介在水分を少なくし、電池容量の低下が少なく、耐熱性にも優れた非水電解液電池用セパレータを提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明の非水電解液電池用セパレータは、請求項１に記載の通り、ポリオレフィン系樹脂２０〜８０ｗｔ％と無機粉体８０〜２０ｗｔ％とで構成される厚さが１０〜２００μｍの無機質含有多孔膜からなる非水電解液電池用セパレータにおいて、前記ポリオレフィン系樹脂が、重量平均分子量が２００万以上の高密度ポリエチレンを含み、前記無機粉体が、その表面が疎水性であり、平衡水分が０．４％以下であり、前記セパレータを温度２５℃、湿度ＲＨ８０〜９０％に２４時間放置した後、正極材にマンガン酸リチウム、負極材に非晶質炭素材、電解液に有機炭酸エステル、支持電解質に６フッ化リン酸リチウムを使用した電池に組み込み、該電池を、充電電圧４．２Ｖ、充電電流１ＣｍＡ、充電時間３時間にて定電流定電圧充電し、周囲温度２５℃で０．３３ＣｍＡ放電したときの、終止電圧２．７Ｖにおける放電容量が９５％超えで、かつ、前記セパレータを温度２５℃、湿度ＲＨ８０〜９０％に２４時間放置した後、正極材にマンガン酸リチウム、負極材に非晶質炭素材、電解液に有機炭酸エステル、支持電解質に６フッ化リン酸リチウムを使用した電池に組み込み、該電池を、アルゴンで充満させた電気炉内に置き、速度１０℃／分で昇温させたときの、耐熱温度（正負極間の初期の絶縁抵抗値を１００％としたときに１０％以下になった温度）が１８０℃以上であることを特徴とする。
また、請求項２記載の非水電解液電池用セパレータは、請求項１記載の非水電解液電池用セパレータにおいて、前記無機粉体がクロロシランで表面を疎水化した無機粉体であることを特徴とする。
また、請求項３記載の非水電解液電池用セパレータは、請求項１又は２に記載の非水電解液電池用セパレータにおいて、前記無機粉体は、無水ケイ酸、酸化チタン、酸化アルミニウム、チタン酸カリウム、酸化マグネシウム、酸化硼素、雲母から選択される１種又は２種以上を含むことを特徴とする。
また、請求項４記載の非水電解液電池用セパレータは、請求項１乃至３の何れか１項に記載の非水電解液電池用セパレータにおいて、前記ポリオレフィン系樹脂２０〜８０ｗｔ％と前記無機粉体８０〜２０ｗｔ％と適当量の可塑剤を混合し加熱溶融・混練しながら圧延および延伸により所定厚さのシートへの成形を行った後前記可塑剤を抽出除去し乾燥することによって得られるものであることを特徴とする。
【０００８】
【作用】
本発明の非水電解液電池用セパレータによれば、無機質含有多孔膜を構成する無機粉体として、水分の少ない無機粉体を使用しているため、耐熱性に優れ、しかも、電池容量低下の少ない電池を得ることができる。
【０００９】
【発明の実施の形態】
前記のようにセパレータの構成をポリオレフィン系樹脂２０〜８０ｗｔ％と無機粉体８０〜２０ｗｔ％とするのは、ポリオレフィン系樹脂が２０ｗｔ％未満、あるいは、無機粉体が８０ｗｔ％を超える場合は、ポリオレフィン系樹脂がセパレータ全体に均一に分散できず機械的強度が弱くなり好ましくなく、また、ポリオレフィン系樹脂が８０ｗｔ％を超える、あるいは、無機粉体が２０ｗｔ％未満の場合は、実質的な耐熱性向上効果が得られないためである。
【００１０】
前記のように無機質含有多孔膜を構成する無機粉体が特願平１１−１０１８２号に記載されている平衡水分が４％未満の無機粉体でも、湿度の高い雰囲気中に放置された場合、表面に水分が付着してしまい、電池容量が３％以上低下する問題があった。本発明者らがその後に検討を行った結果、表面を疎水化し、平衡水分を０．５％以下とした無機粉体を用いれば電池容量の低下を招かないことが判明した。
【００１１】
表面が疎水性であり、平衡水分が０．５％以下である無機粉体としては、無水ケイ酸、酸化チタン、酸化アルミニウム、チタン酸カリウム、酸化マグネシウム、酸化硼素、雲母等の表面をクロロシランやシラザンなどで疎水化したものが使用できる。その使用方法としては、通常は単独で使用するが、二種以上のものを混合して使用することもできる。また、無機粉体は一次粒子径が０．００１〜１μｍ程度のものの使用が好ましい。
【００１２】
また、前記無機質含有多孔膜を構成するポリオレフィン系樹脂としては、ポリプロピレン、ポリエチレン、ポリブテン及びこれらの共重合物、あるいは、これらの混合物等が使用できる。特に重量平均分子量２００万以上の高密度ポリエチレンを使用すれば、機械的強度の優れた無機質含有多孔膜を得ることができる。また、重量平均分子量の異なる樹脂を混合使用することも可能であり、例えば、重量平均分子量２００万以上の高密度ポリエチレンと重量平均分子量２０万未満の低密度ポリエチレンをブレンドして重量平均分子量７０万以上の高密度ポリエチレンとして使用することができる。
【００１３】
前記セパレータの厚さは１０μｍから２００μｍの範囲にする。これは、厚さが２００μｍを超える場合は、電池におけるセパレータの容積が増えて、その結果、活物質の容積が減少する不都合があり、また、厚さ１０μｍ未満の場合は、セパレータ強度が著しく低下して電池の作成が困難になるからである。
【００１４】
次に、本発明非水電解液電池用セパレータの製造方法について詳述する。
ポリオレフィン系樹脂として、例えば、ポリエチレン樹脂粉体、または、ポリプロピレン樹脂粉体の単独、あるいは、混合物の２０〜８０ｗｔ％と無機粉体８０〜２０ｗｔ％及び可塑剤の適量をレーディゲミキサで混合する。次いで、この混合物を押出機で加熱溶融・混練しながらシート状の成形を行う。シートの厚さはシート成形条件を変更したり、延伸・圧延等の二次加工によって自由に調整できるものである。その後、可塑剤を有機溶媒で抽出除去し、乾燥することで本発明の非水電解液電池用セパレータが得られる。なお、可塑剤としては、パラフィン系、ナフテン系等の工業用潤滑油、あるいは、フタル酸ジオクチル等の樹脂用可塑剤が使用できる。
【００１５】
【実施例】
次に、本発明の実施例を説明する。
（実施例１）
表面をクロロシランで疎水化した平衡水分０．４％の疎水性ケイ酸（１）無機粉体３０ｗｔ％と、重量平均分子量２００万の高密度ポリエチレン樹脂粉体１５ｗｔ％に鉱物オイル５５ｗｔ％を混合し、二軸押出機で加熱溶融・混練しながら０．２ｍｍのシートを得た。その後、１２０℃に加熱した状態で一軸方向に６倍延伸し、鉱物オイルを抽出し、ポリエチレン樹脂５５ｗｔ％と無機粉体４５ｗｔ％とで構成される厚さ４０μｍの多孔質膜セパレータを作成した。
【００１６】
次に、このようにして得られたセパレータを温度２５℃、湿度ＲＨ８０％に２４時間放置した後、正極材にマンガン酸リチウム、負極材に非晶質炭素材、電解液は有機炭酸エステル、支持電解質として６フッ化リン酸リチウムを使用した電池に組み込み、電池の放電容量と耐熱性を測定した。その結果、表１に示すように放電容量、耐熱性とも良好な結果が得られた。
【００１７】
（実施例２）
実施例１と同様にして、疎水性ケイ酸（１）無機粉体２４ｗｔ％、重量平均分子量２００万の高密度ポリエチレン樹脂粉体２０ｗｔ％、鉱物オイル５６ｗｔ％からポリエチレン樹脂５５ｗｔ％と無機粉体４５ｗｔ％とで構成される厚さ４０μｍの多孔質膜セパレータを作成した。得られたセパレータを温度２５℃、湿度ＲＨ８０％に２４時間放置した後、実施例１と同様の試験を行った。その結果、表１に示すように電池の放電容量、耐熱性とも良好な結果が得られた。
【００１８】
（実施例３）
実施例２で得られたセパレータを温度２５℃、湿度ＲＨ９０％に２４時間放置した後、実施例１と同様の試験を行った。その結果、表１に示すように電池の放電容量、耐熱性とも良好な結果が得られた。
【００１９】
（実施例４）
表面をシラザンで疎水化した平衡水分０．４％の疎水性ケイ酸（２）無機粉体２４ｗｔ％と、重量平均分子量２００万の高密度ポリエチレン樹脂粉体２０ｗｔ％に鉱物オイル５６ｗｔ％を混合し、二軸押出機で加熱溶融・混練しながら０．２ｍｍのシートを得た。その後、１２０℃に加熱した状態で一軸方向に６倍延伸し、鉱物オイルを抽出し、ポリエチレン樹脂５５ｗｔ％と無機粉体４５ｗｔ％とで構成される厚さ４０μｍの多孔質膜セパレータを作成した。得られたセパレータを温度２５℃、湿度ＲＨ８０％に２４時間放置した後、実施例１と同様の試験を行った。その結果、表１に示すように電池の放電容量、耐熱性とも良好な結果が得られた。
【００２０】
（実施例５）
実施例４で得られたセパレータを温度２５℃、湿度ＲＨ９０％に２４時間放置した後、実施例１と同様の試験を行った。その結果、表１に示すように電池の放電容量、耐熱性とも良好な結果が得られた。
【００２１】
（比較例１）
平衡水分が２．０％の無水ケイ酸（１）無機粉体２４ｗｔ％と、重量平均分子量２００万の高密度ポリエチレン樹脂粉体２０ｗｔ％に鉱物オイル５６ｗｔ％を混合し、二軸押出機で加熱溶融・混練しながら０．２ｍｍの無機多孔質シートを得た。その後、一軸方向に６倍延伸し、鉱物オイルを抽出し、ポリエチレン樹脂５５ｗｔ％と無機粉体４５ｗｔ％とで構成される厚さ４０μｍの多孔質膜セパレータを作成した。得られたセパレータを温度２５℃、湿度ＲＨ８０％に２４時間放置した後、実施例１と同様の試験を行った。その結果、表１に示すように電池の放電容量が低下することが分かった。尚、耐熱性については良好な結果が得られた。
【００２２】
（比較例２）
比較例１で得られたセパレータを温度２５℃、湿度ＲＨ９０％に２４時間放置した後、実施例１と同様の試験を行った。その結果、表１に示すように電池の放電容量が低下することが分かった。尚、耐熱性については良好な結果が得られた。
【００２３】
（比較例３）
パラフィンで表面処理した平衡水分２．５％の無水ケイ酸（２）無機粉体２４ｗｔ％と、重量平均分子量２００万の高密度ポリエチレン樹脂粉体２０ｗｔ％に鉱物オイル５６ｗｔ％を混合し、二軸押出機で加熱溶融・混練しながら０．２ｍｍの無機多孔質シートを得た。その後、１２０℃に加熱した状態で一軸方向に６倍延伸し、鉱物オイルを抽出し、ポリエチレン樹脂５５ｗｔ％と無機粉体４５ｗｔ％とで構成される厚さ４０μｍの多孔質膜セパレータを作成した。得られたセパレータを温度２５℃、湿度ＲＨ８０％に２４時間放置した後、実施例１と同様の試験を行った。その結果、表１に示すように電池の放電容量が低下することが分かった。尚、耐熱性については良好な結果が得られた。
【００２４】
（比較例４）
ポリエチレン単体の多孔質膜セパレータを温度２５℃、湿度ＲＨ８０％に２４時間放置した後、実施例１と同様の試験を行った。その結果、表１に示すように電池の放電容量は良好であるが、耐熱性は絶縁抵抗値が１５０℃で急激に低下した。
【００２５】
【表１】

【００２６】
上記試験は次のようにして行い、評価した。
１）無機粉体の平衡水分：平衡水分は、まず、温度３７℃、湿度７２％の条件で２日放置した無機粉体の重量を測定し、重量既知の平型秤量ビンに入れ、１０５℃の恒温乾燥器中で２時間乾燥する。その後、デシケータ中に放冷し、重量をはかり、減量を求め、次式によって水分を算出した。
平衡水分（％）＝（減量（ｇ）／試料（ｇ））×１００
２）放電容量（電池特性）：放電容量は、充電電圧４．２Ｖ、充電電流１ＣｍＡ、充電時間３ｈで定電流定電圧充電した電池を周囲温度２５℃で０．３３ＣｍＡ放電し、終止電圧２．７Ｖにおける電池容量をパーセントで表したものであり、比較例４の無機粉体を含有しないセパレータを１００％として示した。
３）耐熱性（電池特性）：アルゴンで充満させた電気炉内に電池を置き、速度１０℃／ｍｉｎで昇温させ、正負極間の初期の絶縁抵抗値を１００％とした時、１０％以下になった温度を耐熱性とした。
評価については、耐熱温度が１８０℃以上で耐熱性有り、放電容量が９５％を超えるものを放電容量に優れるものとして評価し、両者を満たすものを表１中に○で示した。
【００２７】
表１から、本発明の無機質含有多孔膜を構成する無機粉体として、表面が疎水性であり、平衡水分が０．５％以下である無機粉体を使用したセパレータは、湿度の高い雰囲気に放置しても電池の放電容量、耐熱性に優れていることが分かる。
【００２８】
【発明の効果】
本発明の非水電解液電池用セパレータは、無機粉体を含有させることで耐熱性の優れたセパレータに構成され、セパレータを使用した電池は、外部加熱、あるいは、外部ショートによる発熱があっても、セパレータ中の無機粉体による正負極間の絶縁性をより高温まで維持できるため、耐熱性の優れた電池が得られる。また、表面を疎水化した平衡水分が０．５％以下の無機粉体を使用しているため、セパレータが湿度の高い雰囲気で放置されても電池容量が低下しにくく、電解液の中に６フッ化リン酸リチウム等のフッ素等を含んだ反応性の高い電解質を使用していても、有機電解液や極板の劣化がないことから、前記耐熱性に優れるばかりでなく容量低下の少ない電池が得られる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a separator for a non-aqueous electrolyte battery such as a lithium ion secondary battery used as a power source for various electronic devices.
[0002]
[Prior art]
Conventionally, small secondary batteries have been widely used as power sources for portable electronic devices such as OA, FA, home appliances, communication devices, etc., and when equipped with devices, they have good volumetric efficiency, making the devices smaller and lighter. Therefore, portable devices using lithium ion secondary batteries are increasing. On the other hand, large rechargeable batteries are being researched and developed in many fields related to environmental issues, including road leveling, UPS, and electric vehicles, and are excellent in large capacity, high output, high voltage, and long-term storage. Therefore, there is an increasing demand for a lithium ion secondary battery which is a kind of non-aqueous electrolyte secondary battery.
[0003]
The working voltage of a lithium ion secondary battery is usually designed with an upper limit of 4.1 to 4.2V. At such a high voltage, the aqueous solution causes electrolysis and cannot be used as an electrolyte. Therefore, so-called non-aqueous electrolytes using organic solvents are used as electrolytes that can withstand high voltages. As the solvent for the non-aqueous electrolyte, an organic carbonate such as polypropylene carbonate or ethylene carbonate is used as a high dielectric constant organic solvent in which more lithium ions can be present. Further, as a supporting electrolyte that becomes a lithium ion source in a solvent, a highly reactive electrolyte such as lithium hexafluorophosphate is dissolved in the solvent and used.
[0004]
Since many combustible substances are used in the constituent materials of lithium ion secondary batteries, various measures are taken to prevent accidents such as ignition even if misused. In particular, the separator plays an important role in improving safety, and a microporous membrane made of a polyolefin resin having a so-called shutdown function in which the separator melts and closes micropores at an abnormally high temperature is used as the separator. . However, if the battery temperature continues to rise for some reason after shutdown and exceeds the heat resistance temperature of the separator, the separator melts and the separation between the electrodes is significantly reduced. There is a problem of ignition. In order to solve this problem, Japanese Unexamined Patent Publication No. 10-50287 discloses an inorganic-containing porous membrane separator made of polyolefin resin and inorganic powder and having excellent heat resistance.
[0005]
[Problems to be solved by the invention]
However, as described above, the lithium ion secondary battery uses a highly reactive electrolyte containing fluorine or the like such as lithium hexafluorophosphate in the electrolytic solution. However, hydrogen fluoride is generated by reacting with the electrolyte, and the organic electrolyte and the electrode plate are deteriorated. Therefore, moisture is managed with great care in working conditions, neglect and storage in battery manufacturing and assembly processes . Separator made of polyolefin resin and inorganic powder disclosed in Japanese Patent Application Laid-Open No. 10-50287 has a high moisture content of 5% or more due to a large amount of adhering moisture or containing bound water in the structure. Since the inorganic powder is contained in a large amount, it is difficult to remove moisture by a drying process, and there is a problem that the battery capacity is reduced while the battery is used.
Further, even when the inorganic powder having an equilibrium water content of less than 4% described in Japanese Patent Application No. 11-10182 is left in a high humidity atmosphere, there is a problem that the water adheres to the surface.
[0006]
An object of the present invention is to provide a separator for a non-aqueous electrolyte battery in which the interstitial moisture in the separator is reduced, the decrease in battery capacity is small, and the heat resistance is excellent.
[0007]
[Means for Solving the Problems]
The separator for a non-aqueous electrolyte battery according to the present invention, as described in claim 1, is an inorganic-containing porous material having a thickness of 10 to 200 μm composed of 20 to 80 wt% of a polyolefin resin and 80 to 20 wt% of an inorganic powder. in the non-aqueous electrolyte battery separator comprising a film, said polyolefin resin comprises a weight average molecular weight 2,000,000 or more high-density polyethylene, wherein the inorganic powder is a surface hydrophobic its equilibrium moisture There Ri der 0.4% or less, after the separator was left for 24 hours temperature 25 ° C., a humidity RH80～90% lithium manganate cathode material, an amorphous carbon material in the negative electrode material, an organic carbonate in the electrolyte Esters are incorporated into a battery using lithium hexafluorophosphate as a supporting electrolyte, and the battery is charged at a constant current and a constant voltage with a charging voltage of 4.2 V, a charging current of 1 CmA, and a charging time of 3 hours. After discharging 0.33 CmA at a temperature of 25 ° C., the discharge capacity at a final voltage of 2.7 V exceeds 95%, and after leaving the separator at a temperature of 25 ° C. and a humidity of RH 80-90% for 24 hours, The battery was built in a battery using lithium manganate, an amorphous carbon material for the negative electrode material, an organic carbonate ester for the electrolyte, and lithium hexafluorophosphate for the supporting electrolyte, and placed in an electric furnace filled with argon. The heat-resistant temperature (temperature at which the initial insulation resistance value between the positive and negative electrodes becomes 10% or less when the temperature is raised at a rate of 10 ° C / min) is 180 ° C or higher. And
The separator for a non-aqueous electrolyte battery according to claim 2 is the separator for a non-aqueous electrolyte battery according to claim 1, wherein the inorganic powder is an inorganic powder whose surface is hydrophobized with chlorosilane. And
The separator for a non-aqueous electrolyte battery according to claim 3 is the separator for a non-aqueous electrolyte battery according to claim 1 or 2, wherein the inorganic powder is silicic anhydride, titanium oxide, aluminum oxide, titanium. It includes one or more selected from potassium acid, magnesium oxide, boron oxide and mica.
The separator for a non-aqueous electrolyte battery according to claim 4 is the separator for a non-aqueous electrolyte battery according to any one of claims 1 to 3, wherein the polyolefin-based resin is 20 to 80 wt% and the inorganic powder. Obtained by mixing 80 to 20 wt% of a body and an appropriate amount of plasticizer, forming into a sheet of a predetermined thickness by rolling and stretching while heating, melting and kneading, and then extracting and removing the plasticizer It is characterized by being.
[0008]
[Action]
According to the separator for a non-aqueous electrolyte battery of the present invention, since the inorganic powder having a low water content is used as the inorganic powder constituting the inorganic-containing porous film, the heat resistance is excellent and the battery capacity is reduced. Fewer batteries can be obtained.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
As described above, the separator is composed of 20 to 80 wt% polyolefin resin and 80 to 20 wt% inorganic powder because the polyolefin resin is less than 20 wt% or the inorganic powder exceeds 80 wt%. It is not preferable because the resin cannot uniformly disperse throughout the separator and the mechanical strength is weak, and when the polyolefin resin exceeds 80 wt% or the inorganic powder is less than 20 wt%, the substantial improvement in heat resistance is achieved. This is because the effect cannot be obtained.
[0010]
Even when the inorganic powder constituting the inorganic-containing porous film as described above is an inorganic powder having an equilibrium moisture content of less than 4% described in Japanese Patent Application No. 11-10182, when left in a high humidity atmosphere, There was a problem that moisture adhered to the surface and the battery capacity decreased by 3% or more. As a result of subsequent studies by the present inventors, it has been found that the use of inorganic powder with a hydrophobic surface and an equilibrium moisture content of 0.5% or less does not cause a decrease in battery capacity.
[0011]
Examples of inorganic powders having a hydrophobic surface and an equilibrium moisture content of 0.5% or less include silicic acid anhydride, titanium oxide, aluminum oxide, potassium titanate, magnesium oxide, boron oxide, mica and the like surfaces such as chlorosilane and Those hydrophobized with silazane or the like can be used. The method of use is usually used alone, but two or more types can be mixed and used. In addition, it is preferable to use inorganic powder having a primary particle size of about 0.001 to 1 μm.
[0012]
Moreover, as polyolefin resin which comprises the said inorganic containing porous film, a polypropylene, polyethylene, polybutene, these copolymers, these mixtures, etc. can be used. In particular, if high-density polyethylene having a weight average molecular weight of 2 million or more is used, an inorganic-containing porous film having excellent mechanical strength can be obtained. It is also possible to use a mixture of resins having different weight average molecular weights. For example, a high density polyethylene having a weight average molecular weight of 2 million or more and a low density polyethylene having a weight average molecular weight of less than 200,000 are blended to obtain a weight average molecular weight of 700,000. It can be used as the above high density polyethylene.
[0013]
The thickness of the separator is you in the range of 10μm to 200 [mu] m. This is because when the thickness exceeds 200 μm, the volume of the separator in the battery increases, and as a result, the volume of the active material decreases, and when the thickness is less than 10 μm, the separator strength decreases significantly. This is because it becomes difficult to create a battery.
[0014]
Next, the manufacturing method of the separator for nonaqueous electrolyte batteries of the present invention will be described in detail.
As the polyolefin resin, for example, polyethylene resin powder or polypropylene resin powder alone, or 20 to 80 wt% of the mixture, inorganic powder 80 to 20 wt%, and an appropriate amount of plasticizer are mixed by a Ladige mixer. Next, the mixture is heated and melted and kneaded with an extruder to form a sheet. The thickness of the sheet can be freely adjusted by changing the sheet forming conditions or by secondary processing such as stretching and rolling. Thereafter, the plasticizer is extracted and removed with an organic solvent and dried to obtain the separator for a non-aqueous electrolyte battery of the present invention. As the plasticizer, industrial lubricating oils such as paraffinic and naphthenic resins, or plasticizers for resins such as dioctyl phthalate can be used.
[0015]
【Example】
Next, examples of the present invention will be described.
( Example 1)
Hydrophobic silicic acid with an equilibrium water content of 0.4% hydrophobized with chlorosilane (1) 30 wt% inorganic powder and 15 wt% high density polyethylene resin powder with a weight average molecular weight of 2 million were mixed with 55 wt% mineral oil. A 0.2 mm sheet was obtained while being melted and kneaded with a twin screw extruder. Thereafter, the film was stretched 6 times in a uniaxial direction while being heated to 120 ° C., mineral oil was extracted, and a porous membrane separator having a thickness of 40 μm composed of polyethylene resin 55 wt% and inorganic powder 45 wt% was prepared.
[0016]
Next, the separator thus obtained was left at a temperature of 25 ° C. and a humidity of RH 80% for 24 hours, and then the positive electrode material was lithium manganate, the negative electrode material was an amorphous carbon material, and the electrolyte was an organic carbonate. The battery was incorporated in a battery using lithium hexafluorophosphate as an electrolyte, and the discharge capacity and heat resistance of the battery were measured. As a result, as shown in Table 1, good results were obtained in both discharge capacity and heat resistance.
[0017]
( Example 2)
In the same manner as in Example 1, hydrophobic silicic acid (1) inorganic powder 24 wt%, high density polyethylene resin powder 20 wt% with a weight average molecular weight of 2 million, mineral oil 56 wt% to polyethylene resin 55 wt% and inorganic powder 45 wt%. %, A porous membrane separator having a thickness of 40 μm was prepared. The obtained separator was left at a temperature of 25 ° C. and a humidity of RH 80% for 24 hours, and then the same test as in Example 1 was performed. As a result, as shown in Table 1, good results were obtained in both the discharge capacity and heat resistance of the battery.
[0018]
Example 3
The separator obtained in Example 2 was allowed to stand at a temperature of 25 ° C. and a humidity of RH 90% for 24 hours, and then the same test as in Example 1 was performed. As a result, as shown in Table 1, good results were obtained in both the discharge capacity and heat resistance of the battery.
[0019]
( Example 4)
Hydrophobic silicic acid with an equilibrium water content of 0.4% hydrophobized with silazane (2) Inorganic powder 24wt% and high-density polyethylene resin powder 20wt% with a weight average molecular weight of 2 million were mixed with 56wt% mineral oil. A 0.2 mm sheet was obtained while being melted and kneaded with a twin screw extruder. Thereafter, the film was stretched 6 times in a uniaxial direction while being heated to 120 ° C., mineral oil was extracted, and a porous membrane separator having a thickness of 40 μm composed of polyethylene resin 55 wt% and inorganic powder 45 wt% was prepared. The obtained separator was left at a temperature of 25 ° C. and a humidity of RH 80% for 24 hours, and then the same test as in Example 1 was performed. As a result, as shown in Table 1, good results were obtained in both the discharge capacity and heat resistance of the battery.
[0020]
( Example 5)
The separator obtained in Example 4 was left at a temperature of 25 ° C. and a humidity of RH 90% for 24 hours, and then the same test as in Example 1 was performed. As a result, as shown in Table 1, good results were obtained in both the discharge capacity and heat resistance of the battery.
[0021]
(Comparative Example 1)
Silica Anhydride with Equilibrium Moisture 2.0% (1) Inorganic powder 24wt% and high-density polyethylene resin powder 20wt% with a weight average molecular weight of 2 million are mixed with 56wt% mineral oil and heated with a twin screw extruder A 0.2 mm inorganic porous sheet was obtained while melting and kneading. Thereafter, the film was stretched 6 times in the uniaxial direction, mineral oil was extracted, and a porous membrane separator having a thickness of 40 μm composed of 55 wt% polyethylene resin and 45 wt% inorganic powder was prepared. The obtained separator was left at a temperature of 25 ° C. and a humidity of RH 80% for 24 hours, and then the same test as in Example 1 was performed. As a result, it was found that the discharge capacity of the battery decreased as shown in Table 1. In addition, the favorable result was obtained about heat resistance.
[0022]
(Comparative Example 2)
The separator obtained in Comparative Example 1 was allowed to stand at a temperature of 25 ° C. and a humidity of RH 90% for 24 hours, and then the same test as in Example 1 was performed. As a result, it was found that the discharge capacity of the battery decreased as shown in Table 1. In addition, the favorable result was obtained about heat resistance.
[0023]
(Comparative Example 3)
Silica anhydride (2) with an equilibrium water content of 2.5% and surface treated with paraffin (2) Inorganic powder 24 wt% and high density polyethylene resin powder 20 wt% with a weight average molecular weight of 2 million are mixed with 56 wt% mineral oil. A 0.2 mm inorganic porous sheet was obtained while heating and melting and kneading with an extruder. Thereafter, the film was stretched 6 times in a uniaxial direction while being heated to 120 ° C., mineral oil was extracted, and a porous membrane separator having a thickness of 40 μm composed of polyethylene resin 55 wt% and inorganic powder 45 wt% was prepared. The obtained separator was left at a temperature of 25 ° C. and a humidity of RH 80% for 24 hours, and then the same test as in Example 1 was performed. As a result, it was found that the discharge capacity of the battery decreased as shown in Table 1. In addition, the favorable result was obtained about heat resistance.
[0024]
(Comparative Example 4)
A polyethylene membrane porous membrane separator was allowed to stand at a temperature of 25 ° C. and a humidity of RH 80% for 24 hours, and then the same test as in Example 1 was performed. As a result, as shown in Table 1, the discharge capacity of the battery was good, but the heat resistance rapidly decreased when the insulation resistance value was 150 ° C.
[0025]
[Table 1]

[0026]
The above test was conducted and evaluated as follows.
1) Equilibrium moisture of inorganic powder: First, the equilibrium moisture was measured by measuring the weight of the inorganic powder left to stand for 2 days under the conditions of a temperature of 37 ° C. and a humidity of 72%. Dry for 2 hours in a constant temperature dryer. Then, it stood to cool in a desiccator, weighed, calculated | required the weight loss, and calculated | required the water | moisture content by following Formula.
Equilibrium moisture (%) = (weight loss (g) / sample (g)) × 100
2) Discharge capacity (battery characteristics): The discharge capacity was determined by discharging 0.33 CmA at a constant current and constant voltage at a charging voltage of 4.2 V, a charging current of 1 CmA, and a charging time of 3 h at an ambient temperature of 25 ° C. The battery capacity at 7 V was expressed as a percentage, and the separator of Comparative Example 4 containing no inorganic powder was shown as 100%.
3) Heat resistance (battery characteristics): 10% when the battery is placed in an electric furnace filled with argon, heated at a rate of 10 ° C./min, and the initial insulation resistance value between the positive and negative electrodes is 100%. The temperature which became below was made into heat resistance.
Regarding the evaluation, those having a heat resistance of 180 ° C. or higher and having heat resistance and a discharge capacity exceeding 95% were evaluated as being excellent in discharge capacity, and those satisfying both were indicated by ○ in Table 1.
[0027]
From Table 1, as an inorganic powder constituting the inorganic-containing porous membrane of the present invention, a separator using an inorganic powder having a hydrophobic surface and an equilibrium moisture content of 0.5% or less is used in a high humidity atmosphere. It can be seen that the battery has excellent discharge capacity and heat resistance even when left untreated.
[0028]
【The invention's effect】
The separator for a non-aqueous electrolyte battery of the present invention is configured as a separator having excellent heat resistance by containing an inorganic powder, and a battery using the separator may generate heat due to external heating or an external short circuit. Since the insulation between the positive and negative electrodes by the inorganic powder in the separator can be maintained at a higher temperature, a battery having excellent heat resistance can be obtained. In addition, since the inorganic powder whose surface is hydrophobized and having an equilibrium water content of 0.5% or less is used, the battery capacity is hardly reduced even if the separator is left in a high humidity atmosphere. Even when using highly reactive electrolytes containing fluorine such as lithium fluorophosphate, there is no deterioration of the organic electrolyte and electrode plate. Is obtained.

Claims

In the separator for a non-aqueous electrolyte battery comprising an inorganic-containing porous film having a thickness of 10 to 200 μm and comprising a polyolefin resin 20 to 80 wt% and inorganic powder 80 to 20 wt%,
The polyolefin resin comprises a Weight average molecular weight 2,000,000 or more high-density polyethylene, wherein the inorganic powder is a surface hydrophobic their state, and are equilibrium moisture 0.4% or less,
After leaving the separator at a temperature of 25 ° C. and a humidity of RH 80 to 90% for 24 hours, lithium manganate as the positive electrode material, amorphous carbon material as the negative electrode material, organic carbonate ester as the electrolyte, and hexafluorophosphoric acid as the supporting electrolyte Built in a battery using lithium, the battery was charged at a constant voltage and a constant voltage at a charging voltage of 4.2 V, a charging current of 1 CmA and a charging time of 3 hours, and discharged at 0.33 CmA at an ambient temperature of 25 ° C. The discharge capacity at 2.7 V exceeds 95%, and
After leaving the separator at a temperature of 25 ° C. and a humidity of RH 80 to 90% for 24 hours, lithium manganate as the positive electrode material, amorphous carbon material as the negative electrode material, organic carbonate ester as the electrolyte, and hexafluorophosphoric acid as the supporting electrolyte The battery is assembled in a battery using lithium, and the battery is placed in an electric furnace filled with argon and heated at a rate of 10 ° C./min. The heat resistance temperature (the initial insulation resistance value between the positive and negative electrodes is 100 A separator for a non-aqueous electrolyte battery, wherein the temperature is 10% or less when the% is 180% .

The separator for a nonaqueous electrolyte battery according to claim 1, wherein the inorganic powder is an inorganic powder having a surface hydrophobized with chlorosilane.

The inorganic powder contains one or more selected from silicic anhydride, titanium oxide, aluminum oxide, potassium titanate, magnesium oxide, boron oxide, and mica. The separator for nonaqueous electrolyte batteries as described.

20 to 80 wt% of the polyolefin resin, 80 to 20 wt% of the inorganic powder, and an appropriate amount of plasticizer are mixed, heated and melted and kneaded to form a sheet having a predetermined thickness by rolling and stretching. The separator for a nonaqueous electrolyte battery according to any one of claims 1 to 3, wherein the separator is obtained by extracting and removing the agent and drying.