JP3601250B2 - Binder for non-aqueous battery electrode - Google Patents
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- JP3601250B2 JP3601250B2 JP12144497A JP12144497A JP3601250B2 JP 3601250 B2 JP3601250 B2 JP 3601250B2 JP 12144497 A JP12144497 A JP 12144497A JP 12144497 A JP12144497 A JP 12144497A JP 3601250 B2 JP3601250 B2 JP 3601250B2
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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
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Description
【０００１】
【発明の属する技術分野】
本発明は、サイクル特性、保存特性等に優れた非水系電池をもたらすことができる非水系電池電極用バインダーに関する。
【０００２】
【従来の技術】
近年、各種の電子機器について小型軽量化の流れが顕著であり、それに伴ない電源となる電池に対しても小型軽量化が強く望まれている。このような要求を満たすには、従来の一般的な水系電解液を用いた水系電池では不可能なことから、非水系電池が注目されている。
非水系電池としては、リチウム電池に代表される一次電池、さらにはリチウム／二硫化チタン二次電池などが提案されており、その一部についてはすでに実用化されている。
しかしながら、これらの非水系電池は、高エネルギー密度、小型軽量といった性能面では優れているものの、鉛電池に代表される水系電池に比べて、多サイクルの充放電後の容量保持性などの出力特性に難点があり、広く一般に用いられるまでには至っていない。特に出力特性が要求される二次電池の分野では、この欠点が非水系電池の実用化を妨げている一つの要因となっている。
非水系電池が出力特性に劣るのは、水系電解液ではイオン電導度が高く、通常１０−１Ω・ｃｍ−１オーダーであるのに対し、非水系電解液の場合、通常１０−２〜１０−４Ω・ｃｍ−１程度の低いイオン電導度しか有していないことに起因する。このような問題点を解決する一つの方法として、電極面積を大きくすること、すなわち薄膜・大面積電極を用いることが考えられる。
薄膜・大面積電極を製造する手法としては、バインダーと電極活物質を有機溶剤中に分散してスラリー化したのち、このスラリーを集電材に塗工して乾燥することにより、集電材表面に電極活物質を結着させ、電極を成形する方法が知られている。この方法によれば、薄膜・大面積電極が容易に得られる反面、絶縁材料であるバインダーが電極活物質に対して悪影響を与える結果、得られた電極を電池に組み立てた場合、例えば過電圧の著しい上昇がみられ、電池性能を低下させていた。
このような薄膜・大面積電極の製造に使用されるバインダーとしては、水系のバインダーが知られており、例えば、カルボキシルメチルセルロース、ポリビニルアルコール、ポリアクリル酸塩、スターチ等の水溶性ポリマーや、ブタジエン結合含量の高いスチレン−ブタジエン共重合体ラテックス等が知られている（特開平５−７４４６１号公報）。しかし、従来の水系バインダーは、電極活物質の表面に均一に付着されるため電極活物質の導電性を阻害し、さらに電極活物質の集電材への結着性能の面でも十分でなかった。
【０００３】
【発明が解決しようとする課題】
本発明の課題は、電極活物質の良好な導電性を維持し、電極活物質の集電材への結着性および耐電解液性に優れた非水系電池電極を形成でき、特に多サイクルの充放電後および長期保存後の出力特性に優れた二次電池をもたらすことができる非水系電池電極用バインダーを提供することにある。
【０００４】
【課題を解決するための手段】
本発明は、フッ化ビニリデンおよび六フッ化プロピレンを含有する単量体成分（ロ−１）から得られる含フッ素重合体と、（メタ）アクリル酸アルキルエステル類および官能基含有不飽和単量体を含有する単量体成分（ロ−２）から得られる官能基含有重合体との複合化重合体であって、該複合化重合体における官能基含有不飽和単量体の使用量が単量体成分（ロ−１）と単量体成分（ロ−２）との合計に対して０．１〜１０重量％である複合化重合体の水系分散体からなることを特徴とする非水系電池電極用バインダー、を要旨とする。
【０００５】
以下、本発明を詳細に説明する。
本発明における複合化重合体は、フッ化ビニリデン単位および六フッ化プロピレンを含有する単量体成分（ロ−１）から得られる含フッ素重合体と、（メタ）アクリル酸アルキルエステル類および官能基含有不飽和単量体を含有する単量体成分（ロ−２）から得られる官能基含有重合体との複合化重合体であって、該複合化重合体における官能基含有不飽和単量体の使用量が単量体成分（ロ−１）と単量体成分（ロ−２）との合計に対して０．１〜１０重量％である複合化重合体（以下、「官能基含有複合化重合体」という。）からなる。
官能基含有複合化重合体における官能基としては、例えば、カルボキシル基、カルボン酸無水物基、アミド基、アミノ基、シアノ基、エポキシ基、ビニル基等を挙げることができる。
これらの官能基のうち、カルボキシル基、アミド基、エポキシ基が好ましい。
【０００６】
以下、本発明における官能基含有複合化重合体について説明する。
【０００７】
官能基含有複合化重合体に使用される官能基含有不飽和単量体のうち、カルボキシル基含有不飽和単量体としては、例えば、アクリル酸、（メタ）アクリル酸、クロトン酸等の不飽和モノカルボン酸類；マレイン酸、フマル酸、イタコン酸、シトラコン酸、メサコン酸等の不飽和ポリカルボン酸類；前記不飽和ポリカルボン酸の遊離カルボキシル基含有アルキルエステルや遊離カルボキシル基含有アミド類等を挙げることができる。
また、カルボン酸無水物基含有不飽和単量体としては、例えば、前記不飽和ポリカルボン酸の酸無水物類等を挙げることができる。
また、アミド含有不飽和単量体としては、例えば、（メタ）アクリルアミド、α−クロロアクリルアミド、Ｎ，Ｎ’−メチレン（メタ）アクリルアミド、Ｎ，Ｎ’−エチレン（メタ）アクリルアミド、Ｎ−ヒドロキシメチル（メタ）アクリルアミド、Ｎ−２−ヒドロキシエチル（メタ）アクリルアミド、Ｎ−２−ヒドロキシプロピル（メタ）アクリルアミド、Ｎ−３−ヒドロキシプロピル（メタ）アクリルアミド、クトロン酸アミド、マレイン酸ジアミド、フマル酸ジアミド等の不飽和カルボン酸アミド類等を挙げることができる。 また、アミノ基含有不飽和単量体としては、例えば、２−アミノメチル（メタ）アクリレート、２−メチルアミノメチル（メタ）アクリレート、２−ジメチルアミノメチル（メタ）アクリレート、２−アミノエチル（メタ）アクリレート、２−メチルアミノエチル（メタ）アクリレート、２−エチルアミノエチル（メタ）アクリレート、２−ジメチルアミノエチル（メタ）アクリレート、２−ジエチルアミノエチル（メタ）アクリレート、２−ｎ−プロピルアミノエチル（メタ）アクリレート、２−ｎ−ブチルアミノエチル（メタ）アクリレート、２−アミノプロピル（メタ）アクリレート、２−メチルアミノプロピル（メタ）アクリレート、２−ジメチルアミノプロピル（メタ）アクリレート、３−アミノプロピル（メタ）アクリレート、３−メチルアミノプロピル（メタ）アクリレート、３−ジメチルアミノプロピル（メタ）アクリレート等の不飽和カルボン酸のアミノアルキルエステル類；Ｎ−ジメチルアミノメチル（メタ）アクリルアミド、Ｎ−２−アミノエチル（メタ）アクリルアミド、Ｎ−２−メチルアミノエチル（メタ）アクリルアミド、Ｎ−２−エチルアミノエチル（メタ）アクリルアミド、Ｎ−２−ジメチルアミノエチル（メタ）アクリルアミド、Ｎ−２−ジエチルアミノエチル（メタ）アクリルアミド、Ｎ−３−アミノプロピル（メタ）アクリルアミド、Ｎ−３−メチルアミノプロピル（メタ）アクリルアミド、Ｎ−３−ジメチルアミノプロピル（メタ）アクリルアミド等の不飽和カルボン酸アミドのＮ−アミノアルキル誘導体類等を挙げることができる。
また、シアノ基含有不飽和単量体としては、例えば、（メタ）アクリロニトリル、α−クロルアクリロニトリル、シアン化ビニリデン等の不飽和カルボン酸ニトリル類；２−シアノエチル（メタ）アクリレート、２−シアノプロピル（メタ）アクリレート、３−シアノプロピル（メタ）アクリレートの不飽和カルボン酸のシアノアルキルエステル類等を挙げることができる。
また、エポキシ基含有不飽和単量体としては、例えば、グリシジル（メタ）アクリレート、（メタ）アリルグリシジルエーテル等の不飽和基含有グリシジル化合物等を挙げることができる。
これらの官能基含有不飽和単量体は、単独でまたは２種以上を混合して使用することができる。
さらに、官能基含有複合化重合体にビニル基を導入する方法としては、例えば、カルボキシル基含有重合体と前記不飽和基含有グリシジル化合物とのエステル化反応、エポキシ基含有重合体と前記カルボキシル基含有不飽和単量体とのエステル化反応、カルボキシル基含有重合体と前記アミノ基含有不飽和単量体とのアミド化反応、アミノ基含有重合体と前記カルボキシル基含有不飽和単量体とのアミド化反応等を挙げることができる。
【０００９】
単量体成分（ロ−１）は、フッ化ビニリデンおよび六フッ化プロピレン以外の共重合可能な不飽和単量体を含有することができる。
このような不飽和単量体としては、例えば、（メタ）アクリル酸メチル、（メタ）アクリル酸エチル、（メタ）アクリル酸ｎ−プロピル、（メタ）アクリル酸ｉ−プロピル、（メタ）アクリル酸ｎ−ブチル、（メタ）アクリル酸ｉ−ブチル、（メタ）アクリル酸ｎ−アミル、（メタ）アクリル酸ｉ−アミル、（メタ）アクリル酸ｎ−ヘキシル、（メタ）アクリル酸２−エチルヘキシル、（メタ）アクリル酸ｎ−オクチル、（メタ）アクリル酸ｎ−ノニル、（メタ）アクリル酸ｎ−デシル、エチレングリコールジ（メタ）アクリレート、プロピレングリコールジ（メタ）アクリレート、トリメチロールプロパントリ（メタ）アクリレート、ペンタエリスリトールテトラ（メタ）アクリレート、ジペンタエリスリトールヘキサ（メタ）アクリレート等の（メタ）アクリル酸アルキルエステル類；スチレン、α−メチルスチレン、ジビニルベンゼン等の芳香族ビニル化合物；酢酸ビニル、プロピオン酸ビニル等のビニルエステル類；フッ化ビニル、テトラフルオロエチレン、塩化ビニル、塩化ビニリデン等のハロゲン化ビニル系化合物；ブタジエン、イソプレン、クロロプレン等の共役ジエン類、エチレンのほか、前記官能基含有不飽和単量体等を挙げることができる。
これらの不飽和単量体は、単独でまたは２種以上を混合して使用することができる。
単量体成分（ロ−１）中のフッ化ビニリデンの含有率は、好ましくは５０〜８０重量％、さらに好ましくは６０〜８０重量％であり、六フッ化プロピレンの含有率は、好ましくは２０〜５０重量％、さらに好ましくは２０〜４０重量％であり、他の不飽和単量体の含有率は、好ましくは０〜３０重量％、さらに好ましくは０〜２０重量％である。
単量体成分（ロ−２）における（メタ）アクリル酸アルキルエステル類としては、例えば、前記単量体成分（ロ−１）について例示した（メタ）アクリル酸アルキルエステル類を挙げることができる。
これらの（メタ）アクリル酸アルキルエステル類は、単独でまたは２種以上を混合して使用することができる。
また、単量体成分（ロ−２）は、（メタ）アクリル酸アルキルエステル類および官能基含有不飽和単量体以外の共重合可能な不飽和単量体を含有することができる。
このような不飽和単量体としては、例えば、前記単量体成分（ロ−１）について例示した芳香族ビニル化合物、ビニルエステル類、ハロゲン化ビニル系化合物、共役ジエン類、エチレン等を挙げることができる。
これらの不飽和単量体は、単独でまたは２種以上を混合して使用することができる。
本発明における単量体成分（ロ−２）中の各単量体の含有率は、（メタ）アクリル酸アルキルエステルが、好ましくは４０〜６０重量％、さらに好ましくは４０〜５０重量％であり、官能基含有不飽和単量体が、好ましくは０．１〜２０重量％、さらに好ましくは０．５〜１５重量％であり、他の不飽和単量体が、好ましくは０〜４０重量％、さらに好ましくは０〜２０重量％である。
また、官能基含有複合化重合体における官能基含有不飽和単量体の使用量は、単量体成分（ロ−１）と単量体成分（ロ−２）との合計に対して、好ましくは０．１〜１０重量％、さらに好ましくは２〜１０重量％、特に好ましくは３〜１０重量％である。この場合、官能基含有不飽和単量体の使用量が０．１重量％未満では、重合体のバインダー性能、耐薬品性等が低下する傾向があり、一方１０重量％を超えると、重合体の耐水性、水系分散体の貯蔵安定性等が低下する傾向がある。
本発明における官能基含有複合化重合体の好ましい合成法は、具体的には特開平７−２５８４９９号公報に記載されている。
【００１０】
本発明で使用する官能基含有複合化重合体は、トルエン不溶分が、通常、２０〜１００重量％、好ましくは３０〜７４重量％である。この場合、官能基含有複合化重合体のトルエン不溶分が２０重量％未満では、塗工後の乾燥工程でポリマーフローが生じて電極活物質を過度に覆って電極の導電性を阻害する結果、過電圧の原因となるおそれがあり、また電解液への耐久性が低下して電極活物質が集電材から脱離するおそれがある。
また、本発明で使用する官能基含有複合化重合体の融点（Ｔｍ）は、好ましくは１７０℃以下、さらに好ましくは０〜１１０℃、特に好ましくは３０〜６０℃である。この場合、Ｔｍが１７０℃を超えると、重合体が柔軟性や粘着性に乏しくなる結果、電極活物質の集電材への結着性が低下する傾向がある。
本発明における水系分散体は、官能基含有複合化重合体が重合体粒子として水系媒体中に分散しており、該重合体粒子の平均粒子径は、通常、０．０５〜５μｍ、好ましくは０．１〜２μｍであり、電極活物質の平均粒子径の１／３より小さい平均粒子径が望ましい。
【００１１】
本発明の非水系電池電極用バインダーを用いて非水系電池電極を形成する際には、該非水系電池電極用バインダーを構成する水系分散体を電極活物質と配合した電池電極用組成物として使用される。
前記電極活物質としては特に限定されるものではないが、その具体例としては、
ＭｎＯ2 、ＭｏＯ3 、Ｖ2 Ｏ5 、Ｖ6 Ｏ13 、Ｆｅ2 Ｏ3 、Ｆｅ3 Ｏ4 、
Ｌｉ(1-x) Ｃｏ・Ｏ2 、Ｌｉ(1-x) Ｎｉ・Ｏ2 、Ｌｉ(1-x) Ｃｏ(1-x) Ｎｉy ・Ｏ2 、
Ｌｉx Ｃｏy Ｓｎz ・Ｏ2 、ＴｉＳ2 、ＴｉＳ3 、ＭｏＳ3 、ＦｅＳ2 、ＣｕＦ2 、
ＮｉＦ2 等の無機化合物；フッ化カーボン、グラファイト、気相成長炭素繊維および／またはその粉砕物、ポリアクリロニトリル系炭素繊維および／またはその粉砕物、ピッチ系炭素繊維および／またはその粉砕物等の炭素系材料；ポリアセチレン、ポリ−ｐ−フェニレン等の導電性高分子等を挙げることができる。
これらの電極活物質のうち、特に、Ｌｉ(1-x) Ｃｏ・Ｏ2 、Ｌｉ(1-x) Ｎｉ・Ｏ2 、
Ｌｉ(1-x) Ｃｏ(1-x) Ｎｉy ・Ｏ2 、Ｌｉx Ｃｏy Ｓｎz ・Ｏ2 等のリチウムイオン含有複合酸化物が、正極、負極共に放電状態で組み立てることが可能となり好ましい。
非水系電池電極を形成する際に用いられる電極活物質の平均粒子径は、電流効率、スラリーとしての安定性、さらには得られる電極内における粒子間抵抗等の面から、好ましくは０．１〜５０μｍ、さらに好ましくは３〜２５μｍ、特に好ましくは５〜１５μｍの範囲である。
非水系電池電極を形成する際の本発明の非水系電池電極用バインダーの配合量（固形分換算）は、電極活物質１００重量部に対して、好ましくは０．１〜２０重量部、さらに好ましくは０．５〜１０重量部である。この場合、本発明の非水系電池電極用バインダーの配合量が０．１重量部未満では、電極活物質の集電材への結着力が低下する傾向があり、一方２０重量部を超えると、得られる電極の過電圧が上昇して電池性能に悪影響をおよぼすおそれがある。
また、前記電池電極用組成物を調製する際には、必要に応じて、水溶性の増粘剤を添加することができる。
このような増粘剤としては、例えば、カルボキシメチルセルロース、メチルセルロース、ヒドロキシメチルセルロース、エチルセルロース、ポリビニルアルコール、ポリアクリル酸（塩）、酸化澱粉、リン酸化澱粉、カゼイン等を挙げることができる。
これらの増粘剤は、単独でまたは２種以上を混合して使用することができる。 増粘剤の使用量は、本発明の非水系電池電極用バインダー中の官能基含有複合化重合体１００重量部に対して、通常、１〜２００重量部、好ましくは１〜１００重量部である。
さらに、電池電極用組成物には、必要に応じて、ヘキサメタリン酸ソーダ、トリポリリン酸ソーダ、ピロリン酸ソーダ、ポリアクリル酸ソーダ等の分散剤や、ノニオン性界面活性剤、アニオン性界面活性剤等の乳化剤を添加することもできる。
本発明における水系分散体の固形分濃度は、通常、２０〜６５重量％、好ましくは３５〜６０重量％である。
【００１２】
このような電池電極用組成物を、好ましくはスラリー状として集電材に塗工したのち、乾燥することにより、非水系電池電極を形成することができる。
前記集電材としては、例えば、アルミニウム箔、リチウム−アルミニウム合金箔、銅箔等を挙げることができる。
電池電極用組成物を集電材に塗工する際には、例えば、リバースロール法、コンマバー法、グラビヤ法、エアーナイフ法等の任意のコーターヘッドを用いることができる。また、塗工後の電池電極用組成物の乾燥方法としては、例えば、放置乾燥、送風乾燥、温風乾燥、赤外線加熱、遠赤外線加熱等の方法を採用することができるが、通常、１５０℃前後で乾燥される。
このようにして得られた電池電極を用いて非水系電池を組み立てる際に使用される非水系電解液の電解質としては特に限定されないが、アルカリ二次電池の場合について例示すると、ＬｉＣｌＯ４ 、ＬｉＢＦ４ 、ＬｉＡｓＦ６ 、ＣＦ３ ＳＯ３ Ｌｉ、ＬｉＰＦ６ 、ＬｉＩ、ＬｉＡｌＣｌ４ 、ＮａＣｌＯ４ 、ＮａＢＦ４ 、ＮａＩ、（ｎ−Ｂｕ）４ＮＣｌＯ４ 、（ｎ−Ｂｕ）４ＮＢＦ４ 、ＫＰＦ６ 等を挙げることができる。
また、非水系電解液の有機溶媒としては、例えば、エーテル類、ケトン類、ラクトン類、ニトリル類、アミン類、アミド類、硫黄化合物、塩素化炭化水素類、エステル類、カーボネート類、ニトロ化合物、リン酸エステル系化合物、スルホラン系化合物等を用いることができるが、これらのうちエーテル類、ケトン類、ニトリル類、塩素化炭化水素類、カーボネート類、スルホラン系化合物が好ましい。
前記有機溶媒の具体例としては、ジメトキシエタン、テトラヒドロフラン、２−メチルテトラヒドロフラン、１，４−ジオキサン、アニソール、モノグライム、アセトニトリル、プロピオニトリル、４−メチル−２−ペンタノン、ブチロニトリル、バレロニトリル、ベンゾニトリル、ジメチルホルムアミド、ジメチルスルホキシド、ジメチルチオホルムアミド、１，２−ジクロロエタン、γ−ブチロラクトン、メチルフオルメイト、プロピレンカーボネート、エチレンカーボネート、ジエチルカーボネート、リン酸トリメチル、リン酸トリエチル、スルホラン、３−メチルスルホランや、これらの混合溶媒等を挙げることができるが、必ずしもこれらに限定されるものではない。
非水系電池は、電極、集電材のほか、さらに要すればセパレーター、端子、絶縁板等の部品を用いて構成される。また、非水系電池の形態としては、特に限定されるものではないが、正極、負極、セパレーター等を単層または複層としたペーパー型電池や、正極、負極、セパレーター等をロール状に巻いた円筒状電池等を挙げることができる。
本発明の非水系電池電極用バインダーを用いて製造した非水系電池は、例えば、ＯＡ機器、ポータブルタイプのＡＶ機器、携帯電話等に好適に使用することができる。
【００１３】
【発明の実施の形態】
以下、実施例により、本発明の実施の形態をさらに具体的に説明する。但し、本発明は、これらの実施例に何ら制約されるものではない。ここで、「％」および「部」は、特記しない限り重量基準である。
各実施例および比較例における各種測定は、次のようにして行った。
（１）トルエン不溶分（％）の測定
０．５Ｎアンモニア水または０．５Ｎ塩酸でｐＨ８に調整した水系分散体を、適宜の基材に塗布し、１２０℃で１時間乾燥して成膜させたのち、得られた重合体フィルム１重量部をトルエン１００重量部に浸積して、５０℃で３時間振とうさせた。次いで、トルエン相をろ過して不溶分を分離し、溶解分の重量を測定して、トルエン不溶分を次式により求めた。
（１）で得た重合体フィルムを使用し、セイコー電子工業（株）製示差走査熱量計を用いて測定した。
（３）平均粒子径（μｍ）の測定
大塚電子（株）製レーザー粒径解析システムＬＰＡ−３０００ｓ／３１００を用いて測定した。
【００１４】
【実施例】
実施例１
（１） 電磁式撹拌機を備えた内容積約６リットルのオートクレーブの内部を充分に窒素置換したのち、脱酸素した純水２．５リットルおよび乳化剤としてパーフルオロデカン酸アンモニウム２５ｇを仕込み、３５０ｒｐｍで撹拌しながら６０℃まで昇温した。次いで、単量体成分（ロ−１）としてフッ化ビニリデン（ＶＤＦ）４４．２％および六フッ化プロピレン（ＨＦＰ）５５．８％からなる混合ガスを、内圧が２０ｋｇ／ｃｍ2 Ｇに達するまで仕込んだのち、重合開始剤としてジイソプロピルパーオキシジカーボネートを２０％含有するフロン１１３溶液２５ｇを窒素ガスにより圧入して、重合を開始させた。重合中はＶｄＦ６０．２％およびＨＦＰ３９．８％からなる混合ガスを逐次圧入して、圧力を２０ｋｇ／ｃｍ2 Ｇに維持した。また、重合の進行とともに重合速度が低下するため、３時間経過後に、先と同量の重合開始剤を窒素ガスにより圧入して、さらに３時間反応を継続させた。次いで、反応液を冷却し、撹拌を停止したのち、未反応単量体を放出して反応を停止させ、含フッ素重合体のラテックスを得た。
（２） 容量７リットルのセパラブルフラスコの内部を充分に窒素置換したのち、前記（１）で得た含フッ素重合体のラテックス１５０部（固形分換算）および乳化剤として２−（１−アリル）−４−ノニルフェノキシポリエチレングリコールスルフェートアンモニウム３部を仕込み、７５℃に昇温させた。次いで、表１に示す単量体成分（ロ−２）と、場合によりさらに水を加え、７５℃で３０分撹拌した。これに、重合開始剤として過硫酸ナトリウム０．５部を加え、８５〜９５°Ｃで２時間重合したのち、冷却して反応を停止させて、含フッ素重合体と官能基含有重合体との官能基含有複合化重合体の水系分散体を得た。
【００１５】
実施例２〜４
単量体成分（ロ−１）および単量体成分（ロ−２）の組成を表１のとおりとした以外は、実施例１と同様にして含フッ素重合体と官能基含有重合体との官能基含有複合化重合体の水系分散体を得た。
【００１６】
比較例１
単量体成分（ロ−１）および単量体成分（ロ−２）の組成を表１のとおりとした以外は、実施例１と同様にして重合体の水系分散体を得た。
【００１７】
比較例２
撹拌機を備えたオートクレーブに、イオン交換水７０部および重合開始剤として過硫酸カリウム０．３部を仕込み、気相部を１５分間窒素置換したのち、８０℃に昇温した。
また別容器にて、表１に示す単量体成分（ロ−２）および乳化剤としてドデシルベンゼンスルホン酸０．２重量部を混合したのち、この混合物を１５時間かけて、前記オートクレーブに滴下しつつ、８０℃で重合させた。滴下終了後、さらに８５℃で５時間撹拌して、重合を継続させた。次いで、反応液を２５℃に冷却し、水酸化カリウムでｐＨを７に調整したのち、スチームを導入して未反応単量体を除去し、さらに濃縮して、重合体の水系分散体を得た。
【００１８】
【表１】
表１中の各単量体は次のとおりである。
ＶｄＦ ：フッ化ビニリデン
ＨＦＰ ：六フッ化プロピレン
ｎＢＡ ：ｎ−ブチルアクリレート
ＭＭＡ ：メチルメタクリレート
ＳＴ ：スチレン
ＡＡ ：アクリル酸
ＩＡ ：イタコン酸
ＮＭＡＭ：Ｎ−メチロールアクリルアミド
ＧＭＡ ：グリシジルメタクリレート
【００２０】
バインダー性能の評価
ニードルコークス粉砕品（平均粒子径１２μｍ）１００部に、実施例１〜４および比較例１〜２で得た水系分散体１部、増粘剤としてカルボキシメチルセルロース水溶液１部（固形分換算）、並びに０．５Ｎアンモニア水０．５部を配合し、よく混合して、電池電極用組成物を調製した。
得られた各電池電極用組成物を用いて、下記項目について評価を行った。
評価結果を、表２に示す。
（１）銅箔への結着性
各電池電極用組成物を、厚さ５０μｍの銅箔に、ロールコーターを用い、塗布量が２００ｇ／ｍ２ となるように塗工したのち、１５０℃で１０分乾燥して、全厚６０μｍの塗工銅箔試験片を得た。
得られた各試験片に粘着テープを貼り付けて剥がしたとき、塗膜の銅箔からの剥離状態を、粘着テープの粘着面全体の塗膜が銅箔から剥離しない場合を５点、粘着テープの粘着面全体の塗膜が銅箔から剥離した場合を１点として、５段階で評価した。
（２）電気抵抗
各電池電極用組成物を、厚さ１００μｍのポリエチレンテレフタレートフィルムに、ロールコーターを用い、塗布量が２００ｇ／ｍ２ となるように塗工したのち、１５０℃で１０分乾燥して、全厚１２０μｍの試験片を得た。
得られた各試験片について、４端子法により電気抵抗を測定した。
（３）耐電解液性
前記（１）で得た各試験片を、ＬｉＣｌＯ４ ／エチレンカーボネート／ジエチルカーボネート＝８．４％／５２．８％／３８．８％からなる電解液（商品名ＬＩＰＡＳＴＥ−ＥＤＥＣ／１、富士薬品工業（株）製）に、８０℃で７２時間浸積したとき、塗膜の銅箔からの剥離状態を、塗膜が銅箔から全く剥離しない場合を５点、塗膜が銅箔から完全に剥離した場合を１点として、５点法で評価した。
（４）出力特性
平均粒子径２μｍのＬｉ１．０３Ｃｏ０．９５Ｓｎ０．４２・Ｏ２ を１００部、グラファイト粉７．５部およびアセトンブラック２．５部の混合物に、フッ素ゴムのメチルイソブチルケトン溶液（濃度４％）５０部を添加したのち、混合撹拌して、塗工液とした。その後、この塗工液を。厚さ１５μｍのアルミニウム箔に塗布量が２９０ｇ／ｍ２ となるように塗工し、乾燥して、全厚１１０μｍの正極を形成した。
また、前記（１）の塗工銅箔試験片と同様にして得た塗工銅箔を、０．９ｃｍ×５．５ｃｍに切り出して負極とした。
その後、得られた正極と負極を用いて、リチウム二次電池を組み立てた。
得られた各電池を４．２Ｖまで充電したのち１０ｍＡで２．５Ｖまで放電するサイクルを繰り返し、１サイクル後の容量に対する容量保持率を測定した。
また、得られた各電池を４．２Ｖに充電したのち、７０℃で３０日間保存したときの、容量低下率を測定した。
【００２１】
【表２】
その結果、本発明の非水系電池電極用バインダーを用いた電極は、電極活物質の集電材への結着性、導電性および耐電解液性のバランスが優れ、しかも当該電極を用いた二次電池は、多サイクルの充放電後および長期保存後の出力特性に優れている。
これに対して、比較例１は、官能基含有不飽和単量体を用いないバインダーの例であり、電極活物質の集電材への結着性、導電性および耐電解液性に加えて、多サイクルの充放電後および長期保存後の出力特性にも劣っている。
比較例２は、フッ化ビニリデン系重合体を用いないバインダーの例であり、電極活物質の集電材への結着性、導電性および耐電解液性に加えて、多サイクルの充放電後および長期保存後の出力特性にも劣っている。
【００２３】
【発明の効果】
本発明の非水系電池電極用バインダーは、電極活物質の導電性を維持し、かつ電極活物質の集電材への結着性および耐電解液性に優れた非水系電池電極をもたらすことができる。また、当該バインダーは水系媒体を用いるため、電極作製工程も簡便となる。さらに、本発明の非水系電池電極用バインダーを用いた非水系二次電池は、多サイクルの充放電後および長期保存後の出力特性に優れている。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a binder for a non-aqueous battery electrode which can provide a non-aqueous battery having excellent cycle characteristics and storage characteristics.
[0002]
[Prior art]
2. Description of the Related Art In recent years, the trend of reducing the size and weight of various electronic devices has been remarkable, and accordingly, there has been a strong demand for batteries that serve as power sources to be reduced in size and weight. Non-aqueous batteries have attracted attention because satisfying such demands is impossible with conventional aqueous batteries using aqueous electrolytes.
As a non-aqueous battery, a primary battery represented by a lithium battery, a lithium / titanium disulfide secondary battery, and the like have been proposed, and some of them have already been put into practical use.
However, although these non-aqueous batteries are excellent in performance such as high energy density and small size and light weight, they have output characteristics such as capacity retention after multi-cycle charge / discharge compared to aqueous batteries represented by lead batteries. However, it has not been widely used. In particular, in the field of secondary batteries that require output characteristics, this drawback is one factor that hinders the practical use of non-aqueous batteries.
Non-aqueous batteries have inferior output characteristics because of the high ionic conductivity of aqueous electrolytes, usually 10%.-1Ω · cm-1On the other hand, in the case of a non-aqueous electrolyte,-2-10-4Ω · cm-1This is due to having only a low ionic conductivity. As a method for solving such a problem, it is conceivable to increase the electrode area, that is, to use a thin film / large area electrode.
As a method of manufacturing a thin film / large area electrode, a binder and an electrode active material are dispersed in an organic solvent to form a slurry, and then the slurry is applied to a current collector and dried to form an electrode on the current collector surface. A method of binding an active material and forming an electrode is known. According to this method, a thin-film / large-area electrode can be easily obtained, but as a result that the binder, which is an insulating material, has an adverse effect on the electrode active material. An increase was observed, and the battery performance was reduced.
As a binder used in the production of such a thin film / large area electrode, an aqueous binder is known, for example, a water-soluble polymer such as carboxymethylcellulose, polyvinyl alcohol, polyacrylate, starch, or a butadiene bond. A styrene-butadiene copolymer latex having a high content is known (JP-A-5-74461). However, the conventional water-based binder is uniformly adhered to the surface of the electrode active material, hinders the conductivity of the electrode active material, and is not sufficient in binding performance of the electrode active material to the current collector.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to maintain a good conductivity of an electrode active material, form a non-aqueous battery electrode excellent in binding property of the electrode active material to a current collector and resistance to an electrolytic solution, and in particular, in multi-cycle charging. An object of the present invention is to provide a binder for a non-aqueous battery electrode which can provide a secondary battery having excellent output characteristics after discharge and after long-term storage.
[0004]
[Means for Solving the Problems]
The present inventionA fluorinated polymer obtained from a monomer component (b-1) containing vinylidene fluoride and propylene hexafluoride, and a monomer containing an alkyl (meth) acrylate and a functional group-containing unsaturated monomer. Is a composite polymer with a functional group-containing polymer obtained from the monomer component (b-2), and the amount of the functional group-containing unsaturated monomer used in the composite polymer is the monomer component (b) -1) and the monomer component (b-2) is 0.1 to 10% by weight based on the total weight of the composite.A binder for a non-aqueous battery electrode, comprising a water-based dispersion of a polymer.
[0005]
Hereinafter, the present invention will be described in detail.
In the present inventionCompositePolymer is vinylidene fluoride unitAnd a fluoropolymer obtained from a monomer component (b-1) containing propylene hexafluoride, and a monomer component containing an alkyl (meth) acrylate and a functional group-containing unsaturated monomer (B-2) a composite polymer with the functional group-containing polymer obtained from (b-2), wherein the amount of the functional group-containing unsaturated monomer used in the composite polymer is a monomer component (b-1) And 0.1 to 10% by weight based on the total of the monomer component (b-2)Polymer(Hereinafter, referred to as “functional group-containing composite polymer”)Consists of
Functional group containingCompositeExamples of the functional group in the polymer include a carboxyl group, a carboxylic anhydride group, an amide group, an amino group, a cyano group, an epoxy group, and a vinyl group.
Among these functional groups, a carboxyl group, an amide group and an epoxy group are preferred.
[0006]
Less than,In the present inventionFunctional group containingCompositeThe polymer will be described.
[0007]
Complex with functional groupAmong the unsaturated monomers having a functional group used in the polymer, examples of the unsaturated monomer having a carboxyl group include unsaturated monocarboxylic acids such as acrylic acid, (meth) acrylic acid and crotonic acid; Unsaturated polycarboxylic acids such as acid, fumaric acid, itaconic acid, citraconic acid and mesaconic acid; and free carboxyl group-containing alkyl esters and free carboxyl group-containing amides of the unsaturated polycarboxylic acids.
Examples of the carboxylic acid anhydride group-containing unsaturated monomer include acid anhydrides of the above-mentioned unsaturated polycarboxylic acids.
Examples of the amide-containing unsaturated monomer include (meth) acrylamide, α-chloroacrylamide, N, N′-methylene (meth) acrylamide, N, N′-ethylene (meth) acrylamide, and N-hydroxymethyl (Meth) acrylamide, N-2-hydroxyethyl (meth) acrylamide, N-2-hydroxypropyl (meth) acrylamide, N-3-hydroxypropyl (meth) acrylamide, coutronamide, maleic diamide, fumaric diamide, etc. And unsaturated carboxylic acid amides. Examples of the amino group-containing unsaturated monomer include 2-aminomethyl (meth) acrylate, 2-methylaminomethyl (meth) acrylate, 2-dimethylaminomethyl (meth) acrylate, and 2-aminoethyl (meth). ) Acrylate, 2-methylaminoethyl (meth) acrylate, 2-ethylaminoethyl (meth) acrylate, 2-dimethylaminoethyl (meth) acrylate, 2-diethylaminoethyl (meth) acrylate, 2-n-propylaminoethyl ( (Meth) acrylate, 2-n-butylaminoethyl (meth) acrylate, 2-aminopropyl (meth) acrylate, 2-methylaminopropyl (meth) acrylate, 2-dimethylaminopropyl (meth) acrylate, 3-aminopropyl ( Meth) acrylates, Aminoalkyl esters of unsaturated carboxylic acids such as -methylaminopropyl (meth) acrylate and 3-dimethylaminopropyl (meth) acrylate; N-dimethylaminomethyl (meth) acrylamide, N-2-aminoethyl (meth) acrylamide N-2-methylaminoethyl (meth) acrylamide, N-2-ethylaminoethyl (meth) acrylamide, N-2-dimethylaminoethyl (meth) acrylamide, N-2-diethylaminoethyl (meth) acrylamide, N- Examples include N-aminoalkyl derivatives of unsaturated carboxylic acid amides such as 3-aminopropyl (meth) acrylamide, N-3-methylaminopropyl (meth) acrylamide, and N-3-dimethylaminopropyl (meth) acrylamide. Can be.
Examples of the cyano group-containing unsaturated monomer include, for example, unsaturated carboxylic nitriles such as (meth) acrylonitrile, α-chloroacrylonitrile, and vinylidene cyanide; 2-cyanoethyl (meth) acrylate, 2-cyanopropyl ( Examples thereof include cyanoalkyl esters of unsaturated carboxylic acids of (meth) acrylate and 3-cyanopropyl (meth) acrylate.
Examples of the epoxy group-containing unsaturated monomer include, for example, unsaturated group-containing glycidyl compounds such as glycidyl (meth) acrylate and (meth) allyl glycidyl ether.
These unsaturated monomers containing a functional group can be used alone or in combination of two or more.
further,Complex with functional groupExamples of the method for introducing a vinyl group into the polymer include, for example, an esterification reaction between a carboxyl group-containing polymer and the unsaturated group-containing glycidyl compound, a reaction between an epoxy group-containing polymer and the carboxyl group-containing unsaturated monomer. Esterification reaction, amidation reaction between a carboxyl group-containing polymer and the amino group-containing unsaturated monomer, amidation reaction between an amino group-containing polymer and the carboxyl group-containing unsaturated monomer, and the like. it can.
[0009]
The monomer component (b-1) may contain a copolymerizable unsaturated monomer other than vinylidene fluoride and propylene hexafluoride.
Examples of such unsaturated monomers include, for example,Methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, N-Amyl (meth) acrylate, i-amyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, (meth) acrylic acid n-nonyl, n-decyl (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (Meth) acrylateAlkyl (meth) acrylatesStyrene, α-methylstyrene, divinylbenzene, etc.Aromatic vinyl compound; Vinyl acetate, vinyl propionate, etc.Vinyl esters; Vinyl fluoride, tetrafluoroethylene, vinyl chloride, vinylidene chloride, etc.Vinyl halide compounds; Butadiene, isoprene, chloroprene, etc.In addition to conjugated dienes and ethylene, the functional group-containing unsaturated monomers and the like can be mentioned.
These unsaturated monomers can be used alone or in combination of two or more.
The content of vinylidene fluoride in the monomer component (b-1) is preferably 50 to 80% by weight, more preferably 60 to 80% by weight, and the content of propylene hexafluoride is preferably 20 to 80% by weight. -50% by weight, more preferably 20-40% by weight, and the content of other unsaturated monomers is preferably 0-30% by weight, more preferably 0-20% by weight.
Examples of the alkyl (meth) acrylates in the monomer component (b-2) include, for example, the alkyl (meth) acrylates exemplified for the monomer component (b-1).
These alkyl (meth) acrylates can be used alone or in combination of two or more.
Further, the monomer component (b-2) isAlkyl (meth) acrylates andIt may contain a copolymerizable unsaturated monomer other than the functional group-containing unsaturated monomer.
Such unsaturated monomers include, for example, the monomer components (B-1The aromatic vinyl compounds, vinyl esters, vinyl halide compounds, conjugated dienes, ethylene and the like exemplified in the above (2) can be used.
These unsaturated monomers can be used alone or in combination of two or more.
The content of each monomer in the monomer component (b-2) in the present invention is such that the alkyl (meth) acrylate is preferably 40 to 60% by weight, more preferably 40 to 50% by weight. The functional group-containing unsaturated monomer is preferably 0.1 to 20% by weight, more preferably 0.5 to 15% by weight, and the other unsaturated monomer is preferably 0 to 40% by weight. And more preferably 0 to 20% by weight.
Also,Complex with functional groupThe amount of the functional group-containing unsaturated monomer used in the polymer depends on the monomer component (B-1) And monomer components (b-2), Preferably 0.1 to 10% by weight, more preferably 2 to 10% by weight, particularly preferably 3 to 10% by weight. In this case, if the amount of the functional group-containing unsaturated monomer used is less than 0.1% by weight, the binder performance and chemical resistance of the polymer tend to decrease. Of the aqueous dispersion, storage stability of the aqueous dispersion, and the like tend to decrease.
Functional group containing in the present inventionCompositeA preferred method for synthesizing the polymer is specifically described in JP-A-7-258499.
[0010]
Functional group containing used in the present inventionCompositeThe polymer has a toluene insoluble content of usually 20 to 100% by weight, preferably 30 to 74% by weight. In this case, it contains a functional groupCompositeIf the toluene-insoluble content of the polymer is less than 20% by weight, a polymer flow occurs in the drying step after coating, which excessively covers the electrode active material and inhibits the conductivity of the electrode, which may cause an overvoltage. In addition, the durability to the electrolyte may be reduced, and the electrode active material may be detached from the current collector.
In addition, the functional group containing used in the present inventionCompositeThe melting point (Tm) of the polymer is preferably 170 ° C. or lower, more preferably 0 to 110 ° C., and particularly preferably 30 to 60 ° C. In this case, if Tm exceeds 170 ° C., the polymer becomes poor in flexibility and tackiness, and the binding property of the electrode active material to the current collector tends to decrease.
The aqueous dispersion in the present invention contains a functional group.CompositeThe polymer is dispersed in an aqueous medium as polymer particles, and the average particle diameter of the polymer particles is usually 0.05 to 5 μm, preferably 0.1 to 2 μm, and the average particle of the electrode active material is An average particle diameter smaller than 1/3 of the diameter is desirable.
[0011]
When forming a non-aqueous battery electrode using the non-aqueous battery electrode binder of the present invention, it is used as a battery electrode composition obtained by mixing an aqueous dispersion constituting the non-aqueous battery electrode binder with an electrode active material. You.
The electrode active material is not particularly limited, but as a specific example,
MnOTwo, MoOThree, VTwoOFive, V6O13 , FeTwoOThree, FeThreeOFour,
Li(1-x)Co ・ OTwo, Li(1-x)Ni ・ OTwo, Li(1-x)Co(1-x)Niy・ OTwo,
LixCoySnz・ OTwo, TiSTwo, TiSThree, MoSThree, FeSTwo, CuFTwo,
NiFTwoAnd carbonaceous materials such as carbon fluoride, graphite, vapor grown carbon fiber and / or crushed product thereof, polyacrylonitrile-based carbon fiber and / or crushed product thereof, pitch-based carbon fiber and / or crushed product thereof, and the like. A conductive polymer such as polyacetylene and poly-p-phenylene;
Among these electrode active materials, in particular, Li(1-x)Co ・ OTwo, Li(1-x)Ni ・ OTwo,
Li(1-x)Co(1-x)Niy・ OTwo, LixCoySnz・ OTwoAnd the like are preferable because both the positive electrode and the negative electrode can be assembled in a discharged state.
The average particle diameter of the electrode active material used when forming the non-aqueous battery electrode is preferably 0.1 to 0.1 in terms of current efficiency, stability as a slurry, and interparticle resistance in the obtained electrode. The range is 50 μm, more preferably 3 to 25 μm, and particularly preferably 5 to 15 μm.
The amount of the binder for a non-aqueous battery electrode of the present invention (in terms of solid content) when forming the non-aqueous battery electrode is preferably 0.1 to 20 parts by weight, more preferably 0.1 to 20 parts by weight, based on 100 parts by weight of the electrode active material. Is 0.5 to 10 parts by weight. In this case, if the amount of the binder for a non-aqueous battery electrode of the present invention is less than 0.1 part by weight, the binding force of the electrode active material to the current collector tends to decrease. There is a possibility that the overvoltage of the applied electrode may increase and adversely affect battery performance.
When preparing the composition for a battery electrode, a water-soluble thickener can be added as necessary.
Examples of such thickeners include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, casein, and the like.
These thickeners can be used alone or in combination of two or more. The amount of the thickener used depends on the content of the functional group in the binder for a non-aqueous battery electrode of the present invention.CompositeIt is usually 1 to 200 parts by weight, preferably 1 to 100 parts by weight, based on 100 parts by weight of the polymer.
Further, the composition for battery electrodes, if necessary, a dispersant such as sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, sodium polyacrylate, a nonionic surfactant, an anionic surfactant, etc. An emulsifier can also be added.
The solid concentration of the aqueous dispersion in the present invention is usually 20 to 65% by weight, preferably 35 to 60% by weight.
[0012]
A non-aqueous battery electrode can be formed by applying such a battery electrode composition to a current collector, preferably in the form of a slurry, and then drying.
Examples of the current collector include aluminum foil, lithium-aluminum alloy foil, and copper foil.
When the composition for a battery electrode is applied to a current collector, any coater head such as a reverse roll method, a comma bar method, a gravure method, and an air knife method can be used. In addition, as a method for drying the composition for a battery electrode after coating, for example, a method such as standing drying, blast drying, warm air drying, infrared heating, or far infrared heating can be employed. Dry before and after.
The electrolyte of the non-aqueous electrolyte used when assembling the non-aqueous battery using the battery electrode obtained in this manner is not particularly limited. For example, in the case of an alkaline secondary battery, LiClO4, LiBF4, LiAsF6, CF3SO3Li, LiPF6, LiI, LiAlCl4, NaClO4, NaBF4, NaI, (n-Bu)4NCLO4, (N-Bu)4NBF4, KPF6And the like.
Further, as the organic solvent of the non-aqueous electrolyte, for example, ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds, Phosphate ester compounds, sulfolane compounds and the like can be used, and among them, ethers, ketones, nitriles, chlorinated hydrocarbons, carbonates, and sulfolane compounds are preferable.
Specific examples of the organic solvent include dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, acetonitrile, propionitrile, 4-methyl-2-pentanone, butyronitrile, valeronitrile, benzonitrile , Dimethylformamide, dimethylsulfoxide, dimethylthioformamide, 1,2-dichloroethane, γ-butyrolactone, methylformate, propylene carbonate, ethylene carbonate, diethyl carbonate, trimethyl phosphate, triethyl phosphate, sulfolane, 3-methylsulfolane and And a mixed solvent thereof, but are not necessarily limited thereto.
The non-aqueous battery is configured using components such as an electrode, a current collector, and, if necessary, a separator, a terminal, and an insulating plate. Further, the form of the non-aqueous battery is not particularly limited, but a positive electrode, a negative electrode, a paper type battery having a single layer or a multi-layer separator, a positive electrode, a negative electrode, a separator and the like are wound into a roll. Examples include a cylindrical battery.
The non-aqueous battery produced using the non-aqueous battery electrode binder of the present invention can be suitably used for, for example, OA equipment, portable AV equipment, mobile phones, and the like.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these embodiments. Here, “%” and “parts” are based on weight unless otherwise specified.
Various measurements in each example and comparative example were performed as follows.
(1) Measurement of toluene-insoluble matter (%)
An aqueous dispersion adjusted to pH 8 with 0.5N ammonia water or 0.5N hydrochloric acid was applied to an appropriate substrate, dried at 120 ° C. for 1 hour to form a film, and then 1 weight of the obtained polymer film was obtained. Was immersed in 100 parts by weight of toluene and shaken at 50 ° C. for 3 hours. Next, the toluene phase was filtered to separate the insoluble matter, the weight of the dissolved matter was measured, and the toluene insoluble matter was determined by the following formula.
Using the polymer film obtained in (1), the measurement was performed using a differential scanning calorimeter manufactured by Seiko Denshi Kogyo KK.
(3) Measurement of average particle size (μm)
The measurement was performed using a laser particle size analysis system LPA-3000s / 3100 manufactured by Otsuka Electronics Co., Ltd.
[0014]
【Example】
Example 1
(1) After sufficiently replacing the inside of an autoclave having an internal volume of about 6 liters equipped with an electromagnetic stirrer with nitrogen, 2.5 liters of deoxygenated pure water and 25 g of ammonium perfluorodecanoate as an emulsifier were charged, and the mixture was stirred at 350 rpm. The temperature was raised to 60 ° C. while stirring. Next, the monomer component (B-1) As vinylidene fluoride (VDF) A mixed gas consisting of 44.2% and 55.8% of propylene hexafluoride (HFP) was mixed with an internal pressure of 20 kg / cm.TwoAfter charging until the temperature reached G, 25 g of a Freon 113 solution containing 20% of diisopropyl peroxydicarbonate as a polymerization initiator was press-fitted with nitrogen gas to start polymerization. During the polymerization, a mixed gas consisting of 60.2% of VdF and 39.8% of HFP was successively injected to reduce the pressure to 20 kg / cm.TwoG was maintained. Further, since the polymerization rate decreases with the progress of the polymerization, after 3 hours, the same amount of the polymerization initiator as above was injected with nitrogen gas, and the reaction was further continued for 3 hours. Next, the reaction solution was cooled, and after stirring was stopped, unreacted monomers were released to stop the reaction, thereby obtaining a fluoropolymer latex.
(2) After sufficiently replacing the inside of a separable flask having a capacity of 7 liters with nitrogen, 150 parts (in terms of solid content) of the latex of the fluoropolymer obtained in the above (1) and 2- (1-allyl) as an emulsifier were used. 3 parts of 4-nonylphenoxy polyethylene glycol sulfate ammonium were charged, and the temperature was raised to 75 ° C. Next, the monomer component (b-2) shown in Table 1 and optionally water were further added, and the mixture was stirred at 75 ° C for 30 minutes. To this, 0.5 part of sodium persulfate was added as a polymerization initiator, and after polymerization at 85 to 95 ° C for 2 hours, the reaction was stopped by cooling, and the reaction between the fluoropolymer and the functional group-containing polymer was carried out.Functional group containingAn aqueous dispersion of the composite polymer was obtained.
[0015]
Examples 2 to 4
The same procedure as in Example 1 was repeated except that the composition of the monomer component (b-1) and the monomer component (b-2) were as shown in Table 1, and the fluorinated polymer and the functional group-containing polymer were used.Functional group containingAn aqueous dispersion of the composite polymer was obtained.
[0016]
Comparative Example 1
An aqueous dispersion of a polymer was obtained in the same manner as in Example 1, except that the compositions of the monomer component (b-1) and the monomer component (b-2) were as shown in Table 1.
[0017]
Comparative Example 2
In an autoclave equipped with a stirrer, 70 parts of ion-exchanged water and 0.3 part of potassium persulfate as a polymerization initiator were charged, and the gas phase was replaced with nitrogen for 15 minutes, and then heated to 80 ° C.
In a separate container, the monomer component (b-2) shown in Table 1 and 0.2 parts by weight of dodecylbenzenesulfonic acid as an emulsifier were mixed, and the mixture was dropped into the autoclave over 15 hours. At 80 ° C. After the completion of the dropwise addition, the mixture was further stirred at 85 ° C. for 5 hours to continue the polymerization. Next, the reaction solution is cooled to 25 ° C., and after adjusting the pH to 7 with potassium hydroxide, unreacted monomers are removed by introducing steam, and the mixture is further concentrated to obtain an aqueous dispersion of a polymer. Was.
[0018]
[Table 1]
Each monomer in Table 1 is as follows.
VdF: vinylidene fluoride
HFP: Propylene hexafluoride
nBA: n-butyl acrylate
MMA: methyl methacrylate
ST: Styrene
AA: Acrylic acid
IA: Itaconic acid
NMAM: N-methylolacrylamide
GMA: glycidyl methacrylate
[0020]
Evaluation of binder performance
100 parts of the pulverized product of needle coke (average particle diameter: 12 μm), 1 part of the aqueous dispersion obtained in Examples 1 to 4 and Comparative Examples 1 and 2, 1 part of a carboxymethyl cellulose aqueous solution as a thickener (in terms of solid content), and 0.5 part of 0.5N ammonia water was blended and mixed well to prepare a composition for a battery electrode.
Using the obtained compositions for battery electrodes, the following items were evaluated.
Table 2 shows the evaluation results.
(1) Binding to copper foil
Each of the battery electrode compositions was coated on a 50 μm-thick copper foil using a roll coater at an application amount of 200 g / m 2.2And dried at 150 ° C. for 10 minutes to obtain a coated copper foil test piece having a total thickness of 60 μm.
When the adhesive tape was applied to each of the obtained test pieces and peeled off, the peeling state of the coating film from the copper foil was evaluated. The evaluation was given on a scale of 1 to 5, with the case where the coating film of the entire adhesive surface was peeled off from the copper foil taken as one point.
(2) Electric resistance
Each of the battery electrode compositions was applied to a 100 μm-thick polyethylene terephthalate film using a roll coater at an application amount of 200 g / m 2.2And dried at 150 ° C. for 10 minutes to obtain a test piece having a total thickness of 120 μm.
The electrical resistance of each of the obtained test pieces was measured by a four-terminal method.
(3) Electrolyte resistance
Each test piece obtained in the above (1) was subjected to LiClO4/ Ethylene carbonate / diethyl carbonate = 8.4% / 52.8% / 38.8% in an electrolyte (trade name LIPASTE-EDEC / 1, manufactured by Fuji Pharmaceutical Co., Ltd.) at 80 ° C. for 72 hours. When stacked, the state of peeling of the coating film from the copper foil was evaluated by a 5-point method, with 5 points when the coating film did not peel at all from the copper foil and 1 point when the coating film completely peeled from the copper foil. did.
(4) Output characteristics
Li with an average particle size of 2 μm1.03Co0.95Sn0.42・ O2Was added to a mixture of 100 parts, 7.5 parts of graphite powder and 2.5 parts of acetone black, and 50 parts of a solution of fluoro rubber in methyl isobutyl ketone (concentration: 4%) was added, followed by mixing and stirring to obtain a coating liquid. . Then, apply this coating solution. 290g / m coating amount on 15μm thick aluminum foil2And dried to form a positive electrode having a total thickness of 110 μm.
Further, the coated copper foil obtained in the same manner as the coated copper foil test piece of the above (1) was cut into 0.9 cm × 5.5 cm to obtain a negative electrode.
Thereafter, a lithium secondary battery was assembled using the obtained positive electrode and negative electrode.
A cycle in which each of the obtained batteries was charged to 4.2 V and then discharged at 10 mA to 2.5 V was repeated, and the capacity retention with respect to the capacity after one cycle was measured.
Further, after charging each of the obtained batteries to 4.2 V, the capacity reduction rate when stored at 70 ° C. for 30 days was measured.
[0021]
[Table 2]
As a result, the electrode using the binder for a non-aqueous battery electrode of the present invention has an excellent balance between the binding property of the electrode active material to the current collector, the conductivity, and the resistance to the electrolytic solution. The battery has excellent output characteristics after multi-cycle charge / discharge and after long-term storage.
On the other hand, Comparative Example 1 is an example of a binder that does not use a functional group-containing unsaturated monomer, and in addition to the binding property of the electrode active material to the current collector, conductivity, and electrolyte resistance, The output characteristics after multi-cycle charge / discharge and after long-term storage are also inferior.
Comparative Example 2 is an example of a binder that does not use a vinylidene fluoride-based polymer. In addition to the binding property of the electrode active material to the current collector, the conductivity, and the resistance to an electrolytic solution, after a multi-cycle charge and discharge, The output characteristics after long-term storage are also poor.
[0023]
【The invention's effect】
The binder for a non-aqueous battery electrode of the present invention can maintain the conductivity of the electrode active material, and can provide a non-aqueous battery electrode excellent in the binding property of the electrode active material to the current collector and the electrolytic solution resistance. . In addition, since the binder uses an aqueous medium, the electrode manufacturing process is also simplified. Furthermore, the non-aqueous secondary battery using the non-aqueous battery electrode binder of the present invention has excellent output characteristics after multi-cycle charge / discharge and after long-term storage.
Claims (4)
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| JP12144497A JP3601250B2 (en) | 1997-04-25 | 1997-04-25 | Binder for non-aqueous battery electrode |
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| JP12144497A JP3601250B2 (en) | 1997-04-25 | 1997-04-25 | Binder for non-aqueous battery electrode |
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| WO2019065705A1 (en) | 2017-09-29 | 2019-04-04 | 住友精化株式会社 | Binder for nonaqueous electrolyte secondary battery electrode, electrode mixture for nonaqueous electrolyte secondary battery, electrode for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery, and electric apparatus |
| JP6829754B1 (en) | 2019-11-19 | 2021-02-10 | 住友精化株式会社 | Batteries for secondary batteries |
| JPWO2021100520A1 (en) | 2019-11-19 | 2021-05-27 | ||
| JP6888139B1 (en) | 2020-02-26 | 2021-06-16 | 住友精化株式会社 | Batteries for secondary batteries |
| JP6923689B1 (en) | 2020-02-26 | 2021-08-25 | 住友精化株式会社 | Batteries for secondary batteries |
| JP6765022B1 (en) | 2020-02-26 | 2020-10-07 | 住友精化株式会社 | Method for manufacturing polymer compound used for binder for secondary batteries |
-
1997
- 1997-04-25 JP JP12144497A patent/JP3601250B2/en not_active Expired - Lifetime
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8110306B2 (en) | 2005-12-22 | 2012-02-07 | Jsr Corporation | Binder composition for secondary battery electrode, slurry for secondary battery electrode, and secondary battery electrode |
| JP2007231264A (en) * | 2006-02-02 | 2007-09-13 | Jsr Corp | Process of producing composite polymer composition, composite polymer composition, paste for electrode of secondary battery and electrode of secondary battery |
| KR20120027126A (en) | 2009-03-30 | 2012-03-21 | 제이에스알 가부시끼가이샤 | Composition for electrochemical-device electrode binder, electrode slurry for electrochemical device, and electrode for electrochemical device |
| KR101371988B1 (en) | 2012-02-02 | 2014-03-07 | 제이에스알 가부시끼가이샤 | Electrode binder composition, electrode slurry, electrode, and electrical storage device |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH10302799A (en) | 1998-11-13 |
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