JP3642355B2 - Non-aqueous electrolyte secondary battery and manufacturing method thereof - Google Patents
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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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Description
【０００１】
【産業上の利用分野】
本発明は、充放電サイクル特性に優れた非水電解質二次電池に関する。更に詳しくは、炭素材料とバインダー樹脂からなる負極合剤層を備える負極と、正極と、非水電解質とからなる非水電解質二次電池に関し、特にバインダー樹脂に関するものである。
【０００２】
【従来技術】
近年の電子技術のめざましい進歩により、電子機器は小型、軽量化の方向に進み、それに伴って電池も小型、軽量化、更に高エネルギー密度のものが求められている。
従来、一般用途の二次電池としては、鉛電池、ニッケル・カドミウム電池等の水溶液系の電池が主流であった。これらの電池はサイクル特性は優れているが、電池重量やエネルギー密度の点では十分満足できるものではなかった。
【０００３】
近年、鉛電池やニッケル・カドミウム電池に替わる二次電池として、リチウムやリチウム合金を負極に用いた非水電解液二次電池の研究開発が盛んに行われている。この電池は高エネルギー密度を有し、自己放電も少なく、軽量であるという特徴を持っている。しかし、この電池では、充放電サイクルの進行にともない、負極において充電時にリチウムがデンドライト状に結晶成長して、この結晶が正極に到達して内部短絡にいたる可能性が高いという欠点があり、実用化への大きな障害となっていた。
【０００４】
これに対し、負極に負極活物質担持体としての炭素材料を使用した非水電解液二次電池によれば、化学的、物理的方法によって予め負極の炭素材料に担持させたリチウム及び正極活物質の結晶構造中に含有させたリチウム及び電解液中に溶解したリチウムのそれぞれが、充放電時に負極において炭素層間にドープされ且つ炭素層間から脱ドープされる。このため、充放電サイクルが進行しても充電時に負極におけるデンドライト状の結晶の析出はみられずに内部短絡を起こしにくく、良好な充放電サイクル特性を示す。また、エネルギー密度も高く且つ軽量であることから、実用化に向けて開発が進んでいる。
【０００５】
このような非水電解液二次電池の用途としては、ビデオカメラやラップトップパソコン等が挙げられる。このような電子機器は比較的消費電流が大きいため、電池は重負荷に耐えられることが必要である。従って、電池構造として、帯状の正極と帯状の負極とを帯状のセパレータを介してその長さ方向に巻回することによって構成される渦巻状の巻回電極体構造が有効である。この巻回電極体構造の電池によれば、電極面積が大きく取れるために重負荷による使用にも耐えることができる。このような巻回電極体では、電極面積を大きくし且つ活物質または活物質担持体を限られた空間内にできるだけ多く充電するために、電極を薄くすることが望ましい。そのため、帯状の電極の製造方法としては、バインダーと活物質を含むペーストを集電体に塗布、乾燥する方法が望ましい。この方法によれば、帯状の電極における電極合剤層の厚みは数ミクロンから数百ミクロン程度にすることが可能となる。
【０００６】
電極集電体としては従来、網状のエイシパンドメタルや穴が多数形成されているパンチングメタルがよく使用されていたが、これらの電極集電体は重負荷特性を得るために電極を薄くするには不向きである。従って、電極集電体としては金属箔を用いることが好ましく且つこの金属箔はできるだけ薄いほうが好ましい。
【０００７】
【発明が解決しようとする課題】
ところが、このような金属箔は表面が平坦なため、負極合剤ペーストを負極集電体としての金属箔に塗布、乾燥して形成される負極合剤層は、電池の製造中や使用中に剥離したりクラックが生じやすいなどの問題点を有していた。特に、巻回電極体を作成する際に剥離しやすいといった問題があった。また、エネルギー密度を高くし、充放電特性を向上するために電極合剤層中の正極及び負極活物質の充填量を多くすると分散が困難になり、塗膜が剥離するという問題があった。本発明の目的は、正極及び負極活物質の分散性に優れるため、活物質の充填量を多くすることができ、従って、エネルギー密度がたかく、充放電特性の改良された非水電解質二次電池を提供することである。
【０００８】
【課題を解決するための手段】
前記目的を達成するため本発明者等は鋭意研究を重ねた結果、本発明に到達した。即ち、本発明は、負極活物質端持体としての炭素材料とバインダー樹脂とを少なくとも含む負極合剤層を備える負極と、正極活物質とバインダー樹脂を含む正極と、非水電解質とを具備する非水電解質二次電池において、前記バインダー樹脂が還元粘度が０．３ｄｌ／ｇ以上のポリエステル樹脂であり、前記負極合剤における前記バインダー樹脂の含有量が３〜２０重量％であることを特徴とする非水電解質二次電池である。
【０００９】
本発明者等の研究によれば、ポリエステル樹脂は本来、金属箔に対する密着性に優れ、これに更にポリアルキレングリコールを共重合することにより活物質の分散性が向上するため活物質の充填量を多くすることができ、また、可撓性が向上し巻回作業時の塗膜のクラックや剥離が起こりにくくなり、更にガラス転移温度が低下して熱プレス性が向上して活物質の充填密度も向上することを見出した。以下、本発明について述べる。
【００１０】
本発明に使用されるポリエステル樹脂は多価カルボン酸やその低級アルキルエステルと多価アルコールとから溶融重合法等の通常の方法で合成することができる。
本発明のポリエステル樹脂の合成に用いられる芳香族多価カルボン酸としては例えばテレフタル酸、イソフタル酸、オルソフタル酸、２，６ナフタレンジカルボン酸、１，５ナフタレンジカルボン酸、５−ナトリウムスルホイソフタル酸、５−リチウムスルホイソフタル酸、ナトリウムスルホテレフタル酸、４，４’−ジフェニルメタンジカルボン酸、４，４’−ジフェニルエーテルジカルボン酸、４，４’−ビフェニルジカルボン酸、４，４’−スチルベンジカルボン酸等の芳香族ジカルボン酸や、ｐ−オキシ安息香酸、ｐ−（ヒドロキシエトキシ）安息香酸、β−ヒドロキシナフトエ酸などの芳香族オキシカルボン酸が、又、トリメリット酸、トリメシン酸、ピロメリット酸等の３官能以上の芳香族多価カルボン酸が挙げられる。
特にこれらのうち、本発明においてはテレフタル酸とイソフタル酸を用いるのが好ましい。
【００１１】
脂肪族ジカルボン酸としては例えばシュウ酸、マロン酸、コハク酸、グルタル酸、ビメリン酸、スベリン酸、アジピン酸、セバチン酸、アゼライン酸、デカン二酸、ウンデカン二酸、ドデカン二酸、トリデカン二酸などが挙げられ、本発明の目的が達成される範囲で使用できる。
【００１２】
また、脂環族多価カルボン酸としては例えば１，４シクロヘキサンジカルボン酸、１，３シクロヘキサンジカルボン酸、ヘキサヒドロ無水フタル酸、トリシクロデカンジカルボン酸等が挙げられるがこの中では１，４シクロヘキサンジカルボン酸が好ましい。
これらの多価カルボン酸は一種でも二種以上の混合物としても用いることができる。特に、本発明のバインダーには溶剤溶解性と耐電解液性の相矛盾する特性が要求されることから、脂環族ジカルボン酸と芳香族ジカルボン酸の組合せが好ましく、脂環族ジカルボン酸としては１，４シクロヘキサンジカルボン酸が好ましい。
【００１３】
一方、多価アルコールとしては例えばエチレングリコール、１，２プロピレングリコール、１，３プロピレングリコール、１，４ブタンジオール、１，５ペンタンジオール、１，６ヘキサンジオール、１，９ノナンジオール、２，２，４トリメチル−１，３ペンタンジオール、２−ブチル−２−エチル−１，３−プロパンジオール、ジエチレングリコール、トリエチレングリコール、ネオペンチルグリコール、シクロヘキサンジメタノール、トリシクロデカンジメタノール、ビスフェノールＡのエチレンオキシド及び／またはプロピレンオキシド付加物等が挙げられるが、特にこれらの中ではエチレングリコール、１，４ブタンジオール、１，６ヘキサンジオール、ジエチレングリコールを用いるのが好ましい。
【００１４】
また、負極及び正極合剤の分散性を改善し、且つポリエステル樹脂の可撓性を向上させて合剤層のクラックを防ぐためにポリアルキレングリコールを多価アルコールの一部として併用するのが好ましい。ポリアルキレングリコールとしては、例えばポリエチレングリコール、ポリプロピレングリコール、ポリテトラメチレングリコール等が挙げられるが、これらの中ではポリテトラメチレングリコールが好ましく、分子量は２５０〜３０００が好ましい。
【００１５】
本発明で使用するポリエステル樹脂の還元粘度（ｄｌ／ｇ）は０．３以上、好ましくは０．４以上である。還元粘度が０．３未満では可撓性に乏しく巻回時に塗膜が割れたり、クラックが発生する等好ましくない。
【００１６】
本発明のポリエステル樹脂の製造方法としては特に制限はなく、多価カルボン酸と多価アルコールとの直接エステル化法、もしくは多価カルボン酸のアルキルエステルと多価アルコールとのエステル交換法によって多価カルボン酸の多価アルコールエステルを得、しかる後、常圧あるいは減圧下で重合して目的の組成物を得ることができる。このとき必要に応じてエステル化触媒もしくは重縮合触媒を用いることができる。また、本発明のポリエステル樹脂の要求特性を損なわない範囲で各種の添加剤、安定剤を配合しても構わない。
【００１７】
非水電解質二次電池の電極を作る際、正極及び負極の合剤の充填密度を上げるため、熱ロールによるプレス加工を行う。従って、バインダーのガラス転移温度が高すぎると熱プレスの効果が発揮されにくい。本発明のポリエステル樹脂のガラス転移温度は８０℃以下が好ましい。
【００１８】
本発明の正極及び負極合剤層の強靭性、屈曲性、耐非水電解溶液性及び金属箔に対する密着性を更に向上させるために、バインダーの一成分として多官能エポキシ樹脂を配合することができる。多官能エポキシ樹脂は特に制限されず、エチレングリコールジグリシジルエーテル、プロピレングリコールジグリシジルエーテル、グリセリントリグリシジルエーテル、トリメチロールプロパントリグリシジルエーテル、ペンタエリスリトールペンタグリシジルエーテル等の脂肪族多官能エポキシ樹脂、シクロヘキサンジオールジグリシジルエーテル、水添ビスフェノールＡジグリシジルエーテル等の脂環族多官能エポキシ樹脂、ビスフェノールＡジグリシジルエーテル、ビスフェノールＳジグリシジルエーテル、ビスフェノールＦジグリシジルエーテル、フェノールノボラックポリグリシジルエーテル等の芳香族多官能エポキシ樹脂が挙げられる。
【００１９】
本発明のポリエステル樹脂は負極合剤層中のバインダーとして用いられ、このとき負極活物質担持体としての炭素材料とバインダー樹脂との配合比は重量で９７：３〜８０：２０、即ち、負極合剤におけるバインダー樹脂の含有量は３〜２０重量％である。炭素材料が９７重量％を越えると、集電体を巻回するときに負極合剤層にクラックが発生したり、金属箔から剥離しやすくなる。また、炭素材料が８０重量％未満では充放電サイクル特性が低下してしまう。
本発明の負極活物質担持体に用いられる炭素材料としては、ピッチコークス、ニードルコークス等のコークス類、ポリマー類、カーボンファイバー、黒鉛材料などを挙げることができる。
【００２０】
このような炭素材料は、例えば、有機材料を７００〜１５００℃程度で焼成することで炭素化して製造することができる。
炭素材料の原料として、石油ピッチやフラン樹脂などのポリマーが用いられるが、炭素化する際に、リン化合物やホウ素化合物を添加することによって、リチウムに対するドープ量の大きい炭素材料を得ることができて好ましい。
【００２１】
一方、正極における正極活物質としては、二酸化マンガンや五酸化バナジウムのような遷移金属酸化物、硫化鉄や硫化チタンのような遷移金属カルコゲン化物、またはこれらとリチウムとの複合化合物、例えば一般式ＬｉＭＯ2 （但し、ＭはＣｏ，Ｎｉの少なくとも一種をしめす。）で表される複合金属酸化物などを用いることができる。特に、高電圧、高エネルギー密度が得られ、サイクル特性にも優れることから、ＬｉＣｏＯ2 ，ＬｉＣｏ0.8 Ｎｉ0.2 Ｏ2 などのリチウム・コバルト複合酸化物、リチウム・コバルト・ニッケル複合酸化物が好ましい。
【００２２】
また、非水電解質としては、リチウム塩などの電解質を非水有機溶剤に溶解した非水電解液を用いることができる。
ここで有機溶剤としては、特に限定されるものではないが、例えば、エチレンカーボネート、プロピレンカーボネート、１，２−ジメトキシエタン、１，２−エトキシエタン、γ−ブチロラクトン、テトラヒドロフラン、１，３−ジオキソラン、４−メチル−１，３−ジオキソラン、ジエチルエーテル、スルホラン、メチルスルホラン、アセトニトリル、プロピオニトリル等を単独または二種以上を混合して使用できる。
【００２３】
有機溶剤に溶解させる電解質も、ＬｉＣｌＯ4 ，ＬｉＡｓＦ6 ，ＬｉＰＦ6 ，ＬｉＢＦ4 ，ＬｉＢ（Ｃ6 Ｈ5 ）4 ，ＬｉＣｌ，ＬｉＢｒ，ＣＨ3 ＳＯ3 Ｌｉ，ＣＦ3 ＳＯ3 Ｌｉ等の公知のものがいづれも使用できる。
また、前記非水電解質は固体であってもよく、例えば高分子固体電解質などが挙げられる。
【００２４】
【発明の効果】
還元粘度が０．３ｄｌ／ｇ以上で、好ましくはポリアルキレングリコールを共重合したガラス転移温度が８０℃以下のポリエステル樹脂は、正極及び負極活物質の分散性に優れるため正極及び負極合剤のペースト化やこのペーストを金属箔に塗布、乾燥して負極合剤層を形成する際の作業性に優れ、強靭で可撓性、屈曲性に優れた皮膜を形成し、活物質の充填密度が向上し、高エネルギー密度で充放電特性に優れた非水二次電池を提供できる。
【００２５】
【実施例】
以下に、実施例を示し、本発明を更に詳しく説明するが、本発明はこれらの実施例によって制限されるものではない。文中、部とあるのはいずれも重量部を表わす。
尚、各種特性の評価は以下の方法で行った。
１、還元粘度；フェノール／テトラクロロエタン（６／４重量比）の混合溶剤を用い、ポリマー濃度０．１ｇ／２５ｍｌでウベローデ粘度管を使用して３０℃で測定した。
２、ガラス転移温度；示差熱分析器によって測定した。
【００２６】
実験例１；ポリエステル樹脂の合成
テレフタル酸２８部（０．１７モル）、１、４シクロヘキサンジカルボン酸２５．７部（０．１５モル）、１、４ブタンジオール５６．５部（０．６３モル）、およびテトラブチルチタネート０．０４部（０．０００１３モル）を反応容器に投入し、窒素下１５０℃〜２２０℃でエステル化反応を行った後、ポリテトラメチレングリコール（分子量１０００）３９．８部（０．０４モル）および安定剤を０．１部加え、１５分間攪拌した。ついで、２５０℃まで加温しながら徐々に減圧し３０分間で０．１ｍｍＨｇ減圧とし、この条件で１時間縮合を行いポリエステル樹脂Ａを得た。得られたポリエステル樹脂Ａの還元粘度は１．０８ｄｌ／ｇであった。この樹脂を固形分濃度が３０重量％となるようにＮメチル２ピロリドン中に溶解した。
【００２７】
実験例２〜４
実験例１で用いたモノマーの組合せを表１のように変えて、種々のポリエステル樹脂Ｂ、ＣおよびＤを得た。
【００２８】
【表１】
実験例５；炭素材料の調整
石油ピッチに酸素を含む官能基を１０〜２０重量％導入する酸素架橋をした後、この酸素架橋された前駆体を不活性ガスの気流中にて１０００℃で焼成することによって、ガラス状炭素に近い性質を持つ炭素質材料を得た。
【００３０】
実験例６；負極集電体の作成
実験例５で調整した炭素質材料７５〜９８重量部と実験例１で合成したポリエステル樹脂Ａ溶液８８．３〜６．７重量部を混合して、Ｎメチル２ピロリドンで固形分濃度が５０重量部となるように希釈して、ボールミルで分散、混練りしたペーストを１０μの銅箔の両面に乾燥膜厚が８０μとなるように塗布、乾燥した後、１００℃の熱ロールでプレスし、幅４１ｍｍ，長さ２８０ｍｍの帯状体にスリットした。
【００３１】
実験例７；正極の作成
コバルト酸リチウム（ＬｉＣｏＯ2 ）９０重量部とグラファイト５重量部、実験例１で合成したポリエステル樹脂Ａ溶液１６．７重量部、Ｎメチル２ピロリドン８８．３重量部を混合、ボールミルで分散、混練りしたペーストを２０μのアルミニウム箔の両面に乾燥膜厚が８０μとなるように塗布、乾燥した後、２００℃の熱ロールでプレスして幅３９ｍｍ、長さ２３０ｍｍにスリットした。
【００３２】
実験例８；電池の作成
実験例６で作成した負極集電体にニッケル製のリードを取り付けたものと実験例７で作成した正極集電体にアルミニウム製のリードを取り付けたものを厚さ２５μ、幅４４ｍｍの多孔質ポリプロピレンフィルムを介して交互に重ねた４層積層体を作成した。この積層体を長さ方向に、負極集電体を内側にした巻回電極体を作成した。この渦巻状巻回電極体をニッケルめっきした鉄製の電池缶に収容し、電極体の上下に絶縁体を配設し、この電池缶にプロピレンカーボネートと１，２−ジメトキシエタンの等容量混合溶剤にＬｉＰＦ4 を１モル／ｌの濃度に溶解した非水電解液を注入した。
【００３３】
実験例９；充放電サイクルテスト
実験例８で作成した電池について、充電上限電圧を４．１Ｖに設定し、５００ｍＡで２時間の定電流充電をした後、１８Ωの定負荷で終止電圧２．７５Ｖまで放電させる充放電サイクルテストを繰り返した。この充放電サイクルテストの１０サイクル時の容量で、１００サイクル時の放電容量を除した値を、容量維持率とした。
【００３４】
実施例１〜３
実験例６で負極集電体を作成するに際し、炭素質材料とポリエステル樹脂Ａの混合割合を固形分比で９７：３、９０：１０、８０：２０重量比とし、実験例６、７、８に従って非水電解質二次電池を作成した。得られた特性を表２に示す。
【００３５】
実施例４〜６
実験例２〜４で合成したポリエステル樹脂Ｂ〜Ｄをバインダーに用い、実験例６に従って負極集電体を作成するに際し、炭素質材料とバインダーの混合割合を固形分比で９５：５重量比とし、実験例６〜８に従って非水電解質二次電池を作成した。得られた特性を表２に示す。
【００３６】
比較例１
実験例６で負極集電体を作成するに際し、炭素材料とポリエステル樹脂の混合割合を、固形分比で９８：２重量比として負極集電体を作成して、実験例７、８に従って、電極体を作成しようとしたが巻回作業時に負極集電体にクラック及び剥離が発生して使用不可能となった。
【００３７】
比較例２
実験例６で負極集電体を作成するに際し、炭素質材料とポリエステル樹脂の混合割合を固形分比で７５：２５重量比として負極集電体を作成して、実験例７、８に従って、非水電解質二次電池を作成した。得られた特性を表２に示す。
【００３８】
比較例３
ポリエステル樹脂として、東洋紡バイロンＲＶ２２０（テレフタル酸／イソフタル酸／エチレングリコール／ネオペンチルグリコール＝５０／５０／５０／５０モル％；還元粘度が０．１４ｄｌ／ｇ）を用い実施例４と同様な方法で電極体を作成しようとしたが、巻回作業時に負極集電体にクラックが発生して評価ができなかった。
【００３９】
【表２】
[Industrial application fields]
The present invention relates to a non-aqueous electrolyte secondary battery excellent in charge / discharge cycle characteristics. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery including a negative electrode including a negative electrode mixture layer made of a carbon material and a binder resin, a positive electrode, and a non-aqueous electrolyte, and particularly to a binder resin.
[0002]
[Prior art]
Due to remarkable progress in electronic technology in recent years, electronic devices have become smaller and lighter, and accordingly, batteries are also required to be smaller and lighter and have higher energy density.
Conventionally, as secondary batteries for general use, aqueous batteries such as lead batteries and nickel / cadmium batteries have been mainly used. Although these batteries have excellent cycle characteristics, they are not fully satisfactory in terms of battery weight and energy density.
[0003]
In recent years, research and development of non-aqueous electrolyte secondary batteries using lithium or a lithium alloy as a negative electrode have been actively conducted as secondary batteries replacing lead batteries and nickel-cadmium batteries. This battery is characterized by high energy density, low self-discharge and light weight. However, this battery has the disadvantage that as the charge / discharge cycle progresses, lithium grows in a dendritic form during charging in the negative electrode, and this crystal is likely to reach the positive electrode and lead to an internal short circuit. It became a big obstacle to the transformation.
[0004]
On the other hand, according to the non-aqueous electrolyte secondary battery using the carbon material as the negative electrode active material carrier for the negative electrode, the lithium and positive electrode active material previously supported on the carbon material of the negative electrode by chemical and physical methods Each of lithium contained in the crystal structure and lithium dissolved in the electrolyte is doped between the carbon layers and dedoped from the carbon layers in the negative electrode during charge and discharge. For this reason, even if the charge / discharge cycle proceeds, no dendrite-like crystals are deposited on the negative electrode during charging, and an internal short circuit hardly occurs, and good charge / discharge cycle characteristics are exhibited. In addition, since the energy density is high and light, development is progressing toward practical use.
[0005]
Applications of such non-aqueous electrolyte secondary batteries include video cameras and laptop computers. Since such an electronic device has a relatively large current consumption, the battery must be able to withstand a heavy load. Therefore, as the battery structure, a spiral wound electrode body structure constituted by winding a belt-like positive electrode and a belt-like negative electrode in the length direction via a belt-like separator is effective. According to the battery having the wound electrode structure, since the electrode area can be increased, the battery can be used even under heavy loads. In such a wound electrode body, it is desirable to make the electrode thin in order to increase the electrode area and charge the active material or the active material carrier as much as possible in a limited space. Therefore, as a method for manufacturing the strip-shaped electrode, a method in which a paste containing a binder and an active material is applied to a current collector and dried is desirable. According to this method, the thickness of the electrode mixture layer in the belt-like electrode can be set to several microns to several hundred microns.
[0006]
Conventionally, as the electrode current collector, a net-like crushed metal or a punching metal in which many holes are formed are often used. However, these electrode current collectors are used for thinning the electrode in order to obtain heavy load characteristics. Is unsuitable. Therefore, it is preferable to use a metal foil as the electrode current collector, and the metal foil is preferably as thin as possible.
[0007]
[Problems to be solved by the invention]
However, since such a metal foil has a flat surface, the negative electrode mixture layer formed by applying and drying the negative electrode mixture paste on the metal foil as the negative electrode current collector is used during the manufacture and use of the battery. There were problems such as easy peeling and cracking. In particular, there has been a problem that it is easy to peel off when producing a wound electrode body. Further, when the filling amount of the positive electrode and the negative electrode active material in the electrode mixture layer is increased in order to increase the energy density and improve the charge / discharge characteristics, there is a problem that dispersion becomes difficult and the coating film is peeled off. An object of the present invention is to provide a non-aqueous electrolyte secondary battery that is excellent in dispersibility of a positive electrode and a negative electrode active material, and can therefore be filled with a large amount of active material, and therefore has high energy density and improved charge / discharge characteristics. Is to provide.
[0008]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present inventors have intensively studied to arrive at the present invention. That is, the present invention includes a negative electrode including a negative electrode mixture layer including at least a carbon material as a negative electrode active material end-clad body and a binder resin, a positive electrode including a positive electrode active material and a binder resin, and a nonaqueous electrolyte. In the nonaqueous electrolyte secondary battery, the binder resin is a polyester resin having a reduced viscosity of 0.3 dl / g or more, and the content of the binder resin in the negative electrode mixture is 3 to 20% by weight. This is a non-aqueous electrolyte secondary battery.
[0009]
According to the study by the present inventors, the polyester resin is inherently excellent in adhesion to the metal foil, and further, the polyalkylene glycol is further copolymerized therewith to improve the dispersibility of the active material. In addition, the flexibility is improved and the coating film is less likely to crack or peel off during the winding operation, and the glass transition temperature is lowered to improve the heat pressability and the packing density of the active material. Also found to improve. The present invention will be described below.
[0010]
The polyester resin used in the present invention can be synthesized from a polyvalent carboxylic acid or a lower alkyl ester thereof and a polyhydric alcohol by an ordinary method such as a melt polymerization method.
Examples of the aromatic polyvalent carboxylic acid used for the synthesis of the polyester resin of the present invention include terephthalic acid, isophthalic acid, orthophthalic acid, 2,6 naphthalenedicarboxylic acid, 1,5 naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, 5 -Aromatics such as lithium sulfoisophthalic acid, sodium sulfoterephthalic acid, 4,4'-diphenylmethane dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 4,4'-biphenyl dicarboxylic acid, 4,4'-stilbene dicarboxylic acid Dicarboxylic acids, aromatic oxycarboxylic acids such as p-oxybenzoic acid, p- (hydroxyethoxy) benzoic acid, β-hydroxynaphthoic acid, and more than trifunctional such as trimellitic acid, trimesic acid and pyromellitic acid And aromatic polycarboxylic acids.
Of these, terephthalic acid and isophthalic acid are preferably used in the present invention.
[0011]
Examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, vimelic acid, suberic acid, adipic acid, sebacic acid, azelaic acid, decanedioic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, etc. Can be used as long as the object of the present invention is achieved.
[0012]
Examples of the alicyclic polyvalent carboxylic acid include 1,4 cyclohexane dicarboxylic acid, 1,3 cyclohexane dicarboxylic acid, hexahydrophthalic anhydride, and tricyclodecane dicarboxylic acid. Among these, 1,4 cyclohexane dicarboxylic acid Is preferred.
These polyvalent carboxylic acids can be used singly or as a mixture of two or more. In particular, since the binder of the present invention is required to have contradictory properties of solvent solubility and resistance to electrolytic solution, a combination of an alicyclic dicarboxylic acid and an aromatic dicarboxylic acid is preferable. As the alicyclic dicarboxylic acid, 1,4 cyclohexanedicarboxylic acid is preferred.
[0013]
On the other hand, examples of the polyhydric alcohol include ethylene glycol, 1,2 propylene glycol, 1,3 propylene glycol, 1,4 butanediol, 1,5 pentanediol, 1,6 hexanediol, 1,9 nonanediol, 2,2 , 4 trimethyl-1,3-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, diethylene glycol, triethylene glycol, neopentyl glycol, cyclohexanedimethanol, tricyclodecane dimethanol, ethylene oxide of bisphenol A and In particular, ethylene glycol, 1,4 butanediol, 1,6 hexanediol, and diethylene glycol are preferably used.
[0014]
Further, in order to improve the dispersibility of the negative electrode and the positive electrode mixture and to improve the flexibility of the polyester resin and prevent cracks in the mixture layer, it is preferable to use polyalkylene glycol as a part of the polyhydric alcohol. Examples of the polyalkylene glycol include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Among these, polytetramethylene glycol is preferable, and the molecular weight is preferably 250 to 3000.
[0015]
The reduced viscosity (dl / g) of the polyester resin used in the present invention is 0.3 or more, preferably 0.4 or more. If the reduced viscosity is less than 0.3, the flexibility is poor, and the coating film is broken during winding or cracks are not preferable.
[0016]
The production method of the polyester resin of the present invention is not particularly limited, and the polyvalent carboxylic acid can be produced by a direct esterification method of a polyvalent carboxylic acid and a polyhydric alcohol, or a transesterification method of an alkyl ester of a polyvalent carboxylic acid and a polyhydric alcohol. A polyhydric alcohol ester of carboxylic acid is obtained, and then the desired composition can be obtained by polymerization under normal pressure or reduced pressure. At this time, if necessary, an esterification catalyst or a polycondensation catalyst can be used. Moreover, you may mix | blend various additives and stabilizers in the range which does not impair the required characteristic of the polyester resin of this invention.
[0017]
When making the electrode of the nonaqueous electrolyte secondary battery, press working with a hot roll is performed in order to increase the packing density of the mixture of the positive electrode and the negative electrode. Therefore, if the glass transition temperature of the binder is too high, the effect of hot pressing is hardly exhibited. The glass transition temperature of the polyester resin of the present invention is preferably 80 ° C. or lower.
[0018]
In order to further improve the toughness, flexibility, non-aqueous electrolyte solution resistance and adhesion to the metal foil of the positive electrode and negative electrode mixture layers of the present invention, a polyfunctional epoxy resin can be blended as one component of the binder. . The polyfunctional epoxy resin is not particularly limited, and aliphatic polyfunctional epoxy resins such as ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol pentaglycidyl ether, and cyclohexanediol Arocyclic polyfunctional epoxy resins such as diglycidyl ether and hydrogenated bisphenol A diglycidyl ether, aromatic polyfunctional epoxy resins such as bisphenol A diglycidyl ether, bisphenol S diglycidyl ether, bisphenol F diglycidyl ether, and phenol novolac polyglycidyl ether An epoxy resin is mentioned.
[0019]
The polyester resin of the present invention is used as a binder in the negative electrode mixture layer. At this time, the compounding ratio of the carbon material as the negative electrode active material carrier and the binder resin is 97: 3 to 80:20 by weight, that is, the negative electrode mixture. The content of the binder resin in the agent is 3 to 20% by weight. When the carbon material exceeds 97% by weight, a crack is generated in the negative electrode mixture layer when the current collector is wound, or the carbon material is easily peeled off from the metal foil. In addition, if the carbon material is less than 80% by weight, the charge / discharge cycle characteristics deteriorate.
Examples of the carbon material used for the negative electrode active material carrier of the present invention include cokes such as pitch coke and needle coke, polymers, carbon fibers, and graphite materials.
[0020]
Such a carbon material can be produced by, for example, carbonizing the organic material by firing at about 700 to 1500 ° C.
Polymers such as petroleum pitch and furan resin are used as raw materials for carbon materials, but when carbonized, by adding a phosphorus compound or boron compound, a carbon material with a large amount of doping with respect to lithium can be obtained. preferable.
[0021]
On the other hand, as the positive electrode active material in the positive electrode, transition metal oxides such as manganese dioxide and vanadium pentoxide, transition metal chalcogenides such as iron sulfide and titanium sulfide, or composite compounds of these with lithium, for example, a general formula LiMO 2 (wherein M represents at least one of Co and Ni) and the like can be used. In particular, lithium-cobalt composite oxides such as LiCoO 2 and LiCo 0.8 Ni 0.2 O 2 and lithium-cobalt-nickel composite oxides are preferable because high voltage and high energy density are obtained and cycle characteristics are excellent.
[0022]
As the non-aqueous electrolyte, a non-aqueous electrolyte solution in which an electrolyte such as a lithium salt is dissolved in a non-aqueous organic solvent can be used.
Here, the organic solvent is not particularly limited. For example, ethylene carbonate, propylene carbonate, 1,2-dimethoxyethane, 1,2-ethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-Methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile and the like can be used alone or in admixture of two or more.
[0023]
The electrolyte dissolved in the organic solvent may be a known one such as LiClO 4 , LiAsF 6 , LiPF 6 , LiBF 4 , LiB (C 6 H 5 ) 4 , LiCl, LiBr, CH 3 SO 3 Li, CF 3 SO 3 Li, etc. Either can be used.
The nonaqueous electrolyte may be a solid, and examples thereof include a polymer solid electrolyte.
[0024]
【The invention's effect】
A polyester resin having a reduced viscosity of 0.3 dl / g or more, and preferably having a glass transition temperature of 80 ° C. or less copolymerized with polyalkylene glycol is excellent in the dispersibility of the positive electrode and the negative electrode active material. , And this paste is applied to a metal foil and dried to form a negative electrode mixture layer, resulting in an excellent workability, a tough, flexible and flexible film, and an improved active material packing density In addition, a non-aqueous secondary battery having high energy density and excellent charge / discharge characteristics can be provided.
[0025]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the text, “part” means part by weight.
Various characteristics were evaluated by the following methods.
1. Reduced viscosity: Measured using a mixed solvent of phenol / tetrachloroethane (6/4 weight ratio) at a polymer concentration of 0.1 g / 25 ml at 30 ° C. using an Ubbelohde viscosity tube.
2. Glass transition temperature; measured by a differential thermal analyzer.
[0026]
Experimental Example 1: Synthesis of polyester resin 28 parts (0.17 mol) of terephthalic acid, 25.7 parts (0.15 mol) of 1,4 cyclohexanedicarboxylic acid, 56.5 parts of 1,4 butanediol (0.63 mol) ) And 0.04 part (0.00013 mol) of tetrabutyl titanate are charged into a reaction vessel and subjected to an esterification reaction at 150 ° C. to 220 ° C. under nitrogen, and then polytetramethylene glycol (molecular weight 1000) 39.8. Part (0.04 mol) and 0.1 part stabilizer were added and stirred for 15 minutes. Subsequently, the pressure was gradually reduced while heating to 250 ° C., and the pressure was reduced to 0.1 mmHg for 30 minutes. Condensation was performed for 1 hour under these conditions to obtain a polyester resin A. The reduced viscosity of the obtained polyester resin A was 1.08 dl / g. This resin was dissolved in N-methyl-2-pyrrolidone so that the solid content concentration was 30% by weight.
[0027]
Experimental Examples 2-4
Various polyester resins B, C and D were obtained by changing the combinations of monomers used in Experimental Example 1 as shown in Table 1.
[0028]
[Table 1]
Experimental Example 5: Preparation of carbon material After oxygen crosslinking in which 10 to 20% by weight of a functional group containing oxygen was introduced into petroleum pitch, the oxygen-crosslinked precursor was calcined at 1000 ° C. in an inert gas stream. As a result, a carbonaceous material having properties similar to glassy carbon was obtained.
[0030]
Experimental Example 6 Preparation of Negative Electrode Current Collector 75 to 98 parts by weight of the carbonaceous material prepared in Experimental Example 5 and 88.3 to 6.7 parts by weight of the polyester resin A solution synthesized in Experimental Example 1 were mixed. After coating and drying a paste that was diluted with methyl 2 pyrrolidone to a solid content concentration of 50 parts by weight, dispersed and kneaded with a ball mill so that the dry film thickness was 80 μ on both sides of a 10 μ copper foil, It was pressed with a hot roll at 100 ° C. and slit into a strip having a width of 41 mm and a length of 280 mm.
[0031]
Experimental Example 7 Preparation of Positive Electrode 90 parts by weight of lithium cobaltate (LiCoO 2 ), 5 parts by weight of graphite, 16.7 parts by weight of the polyester resin A solution synthesized in Experimental Example 1, and 88.3 parts by weight of N methyl 2-pyrrolidone were mixed. The paste dispersed and kneaded with a ball mill was applied to both sides of a 20 μm aluminum foil so that the dry film thickness was 80 μm, dried, then pressed with a 200 ° C. hot roll and slit to a width of 39 mm and a length of 230 mm. .
[0032]
Experimental Example 8: Production of Battery A negative electrode current collector prepared in Experimental Example 6 with a nickel lead attached and a positive electrode current collector prepared in Experimental Example 7 with an aluminum lead attached to a thickness of 25 μm Then, a four-layer laminate was produced in which the layers were alternately stacked via a porous polypropylene film having a width of 44 mm. A wound electrode body was produced with the laminate in the length direction and the negative electrode current collector inside. This spirally wound electrode body is housed in a nickel-plated iron battery can, and insulators are disposed above and below the electrode body. The battery can is mixed with a mixed solvent of equal volume of propylene carbonate and 1,2-dimethoxyethane. A nonaqueous electrolytic solution in which LiPF 4 was dissolved at a concentration of 1 mol / l was injected.
[0033]
Experimental Example 9: For the battery prepared in Charge / Discharge Cycle Test Experimental Example 8, after setting the charging upper limit voltage to 4.1 V, charging at a constant current of 500 mA for 2 hours, and then terminating voltage 2.75 V at a constant load of 18Ω. The charge / discharge cycle test was repeated until the battery was discharged. The capacity retention rate was a value obtained by dividing the discharge capacity at 100 cycles by the capacity at 10 cycles in this charge / discharge cycle test.
[0034]
Examples 1-3
In preparing the negative electrode current collector in Experimental Example 6, the mixing ratio of the carbonaceous material and the polyester resin A was 97: 3, 90:10, and 80:20 by weight, and Experimental Examples 6, 7, and 8 were used. A non-aqueous electrolyte secondary battery was prepared according to the above. The obtained characteristics are shown in Table 2.
[0035]
Examples 4-6
When the polyester resins B to D synthesized in Experimental Examples 2 to 4 were used as binders and a negative electrode current collector was prepared according to Experimental Example 6, the mixing ratio of the carbonaceous material and the binder was 95: 5 weight ratio in solid content ratio. In accordance with Experimental Examples 6 to 8, nonaqueous electrolyte secondary batteries were prepared. The obtained characteristics are shown in Table 2.
[0036]
Comparative Example 1
In preparing the negative electrode current collector in Experimental Example 6, the negative electrode current collector was prepared by setting the mixing ratio of the carbon material and the polyester resin to a solid content ratio of 98: 2 weight ratio. An attempt was made to make a body, but the negative electrode current collector was cracked and peeled during the winding operation, making it unusable.
[0037]
Comparative Example 2
When preparing the negative electrode current collector in Experimental Example 6, the negative electrode current collector was prepared by setting the mixing ratio of the carbonaceous material and the polyester resin to a solid content ratio of 75:25 weight ratio. A water electrolyte secondary battery was prepared. The obtained characteristics are shown in Table 2.
[0038]
Comparative Example 3
Toyobo Byron RV220 (terephthalic acid / isophthalic acid / ethylene glycol / neopentyl glycol = 50/50/50/50 mol%; reduced viscosity 0.14 dl / g) was used as the polyester resin in the same manner as in Example 4. An attempt was made to make an electrode body, but the negative electrode current collector was cracked during the winding operation and could not be evaluated.
[0039]
[Table 2]
Claims (2)
前記負極合剤に、分子量２５０〜３０００のポリテトラメチレングリコール成分が含有され、還元粘度が０．３ｄｌ／ｇ以上、且つガラス転移温度が８０℃以下である、結晶性ポリエステルバインダー樹脂が３〜２０重量％含有されていることを特徴とする非水電解質二次電池。In a nonaqueous electrolyte secondary battery comprising a negative electrode comprising a negative electrode mixture layer comprising at least a carbon material as a negative electrode active material carrier and a binder resin, a positive electrode comprising a positive electrode active material and a binder resin, and a nonaqueous electrolyte ,
The negative electrode mixture contains a polytetramethylene glycol component having a molecular weight of 250 to 3000, a reduced viscosity of 0.3 dl / g or more, and a glass transition temperature of 80 ° C. or less, and a crystalline polyester binder resin of 3 to 20 A non-aqueous electrolyte secondary battery characterized by being contained by weight% .
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| KR100582518B1 (en) * | 1997-03-04 | 2006-05-24 | 제온 코포레이션 | Binder composition for cell, slurry for cell electrode, electrode for lithium secondary cell and lithium secondary cell |
| JP2002324549A (en) * | 2001-04-24 | 2002-11-08 | Tdk Corp | Manufacturing method for electrode for non-aqueous electrolyte battery and non-aqueous electrolyte secondary battery |
| JP2003007304A (en) * | 2001-06-25 | 2003-01-10 | Hitachi Maxell Ltd | Nonaqueous electrolyte solution secondary battery |
| KR100965276B1 (en) * | 2005-08-16 | 2010-06-22 | 주식회사 엘지화학 | Negative Electrode Slurry Containing Conductive Agent of Improved Dispensability and Lithium Secondary Battery Prepared Therewith |
| JP5812378B2 (en) * | 2010-02-23 | 2015-11-11 | 東レ株式会社 | Lithium ion secondary battery electrode binder |
| JP5618900B2 (en) * | 2011-05-17 | 2014-11-05 | 株式会社ティ−アンドケイ東華 | Polyester resin composition |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01186557A (en) * | 1988-01-12 | 1989-07-26 | Sanyo Electric Co Ltd | Nonaqueous electrolyte cell |
| JP2898647B2 (en) * | 1989-03-06 | 1999-06-02 | 株式会社リコー | Rechargeable battery |
| JP3400056B2 (en) * | 1992-12-25 | 2003-04-28 | ティーディーケイ株式会社 | Lithium secondary battery |
| JPH06325752A (en) * | 1993-03-16 | 1994-11-25 | Dainippon Printing Co Ltd | Plate for nonaqueous electrolytic secondary battery and its manufacture |
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1995
- 1995-09-04 JP JP22628995A patent/JP3642355B2/en not_active Expired - Fee Related
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| JPH0973904A (en) | 1997-03-18 |
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