JP2004247249A

JP2004247249A - Manufacturing method of electrode for secondary battery

Info

Publication number: JP2004247249A
Application number: JP2003038416A
Authority: JP
Inventors: Tsumoru Ohata; 積大畠
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 2003-02-17
Filing date: 2003-02-17
Publication date: 2004-09-02
Anticipated expiration: 2023-02-17
Also published as: JP4219705B2

Abstract

<P>PROBLEM TO BE SOLVED: To overcome the problem caused by scattering of a dispersion medium; and to efficiently provide an electrode having uniform thickness. <P>SOLUTION: This method is used for manufacturing this electrode comprising an electrode core material 105, and an electrode active material layer 108 supported by the electrode core material. The method comprises: (a) a process for preparing a spherical or nearly spherical particulate electrode mix 102 containing at least an electrode active material and a binder; (b) a process for forming a powder mix layer 104a or a mix sheet 104b having uniform thickness; and (c) a process for providing an electrode plate 106 by integrating the powder mix layer or the mix sheet with the electrode core material. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、電極合剤を含むペーストの塗工を行わずに均一な厚さの二次電池用電極を製造する方法に関する。
【０００２】
【従来の技術】
従来の電池用電極の製造法においては、電極活物質および結着剤からなる電極合剤を分散媒と混合したペーストを、電極芯材に塗工し、その塗膜を乾燥して塗膜中の分散媒を飛散させ、乾燥後の塗膜をプレスすることにより、電極活物質層が形成されている。
【０００３】
しかし、上記のような方法では、塗膜を乾燥して分散媒を飛散させる際に、塗膜が収縮するため、電極活物質層に微細なクラックが生じたり、プレス時に内部応力が発生したりするという問題がある。また、塗膜の収縮が大きいため、電極活物質層の厚さの変動も大きく、均一な厚さの電極を得ることは困難である。さらに、分散媒の飛散を管理する必要があるため、電極の製造コストが高くなるという問題もある。
【０００４】
そこで、溶融状態の結着剤と電極活物質を含むペーストをスプレードライ法により粉体化して、芯材に粉体を直接吹き付ける電極活物質層の製造法が提案されている（特許文献１参照）。しかし、この方法では、電極活物質層に微細なクラックが生じたり、プレス時に内部応力が発生したりするという問題は改善されるものの、均一な厚さの電極活物質層を得ることは困難である。電極活物質層の厚さが不均一になると、電極の部位によって放電深度がばらつくため、電池特性が劣化しやすい。しかも、芯材に粉体を直接吹き付ける際に、ペースト中の分散媒が飛散するため、飛散した分散媒の回収等にコストがかかるという問題を払拭することができない。従来のスプレードライ法には、良好なペーストの噴霧状態を得るためには、溶融状態の結着剤を多量にペーストに含める必要があるという問題もあり、高容量な電極を得ることが困難であり、電池の高率放電も困難である。
【０００５】
【特許文献１】
特開平１１−１４９９１８号公報
【０００６】
【発明が解決しようとする課題】
本発明は、上記を鑑みたものであり、分散媒の飛散による問題等を改善するとともに、均一な厚さの電極を効率良く得ることを目的とする。
【０００７】
【課題を解決するための手段】
すなわち、本発明は、電極芯材および前記電極芯材に担持された電極活物質層からなる二次電池用電極の製造法であって、
（ａ）少なくとも電極活物質および結着剤を含む球状もしくはほぼ球状の粒子状電極合剤を調製する工程、
（ｂ）前記粒子状電極合剤から、厚さの均一な粉体合剤層もしくは合剤シートを形成する工程、ならびに
（ｃ）前記粉体合剤層もしくは合剤シートを電極芯材と一体化して極板を得る工程、を有する二次電池用電極の製造法に関する。
ただし、均一な厚さとは、粉体合剤層もしくは合剤シートの部位によって厚さに大きな差がないことを意味し、多少の厚さのばらつきがある場合にも、一見して均一であればよい。粒子状電極合剤は、ほぼ球状であればよく、例えば鶏卵状でもよい。前記粒子状電極合剤には、さらに潤滑剤を含ませることが好ましい。
【０００８】
前記工程（ａ）には、例えば、少なくとも電極活物質、結着剤および分散媒を含むスラリーを調製する工程、ならびに前記スラリーをスプレードライ法により粉体化することにより、前記球状もしくはほぼ球状の粒子状電極合剤を得る工程を適用することができる。
前記工程（ａ）には、また、少なくとも電極活物質を含む粉体を、乾燥雰囲気中に流動させる工程、ならびに流動している前記粉体に、少なくとも結着剤を含む液を噴霧しながら造粒することにより、前記球状もしくはほぼ球状の粒子状電極合剤を得る工程を適用することができる。
【０００９】
前記工程（ｂ）には、例えば、前記粒子状電極合剤を電極芯材上に均一な厚さに配することにより、前記粉体合剤層を得る工程を適用することができる。この場合、前記粒子状電極合剤を電極芯材上に均一な厚さに配する工程には、前記粒子状電極合剤を前記電極芯材上に載置してから前記電極芯材を振動させる工程を適用することができる。
【００１０】
前記工程（ｂ）には、また、加圧治具を用いて前記粒子状電極合剤をプレスもしくはホットプレスすることにより、前記合剤シートを得る工程を採用することができる。この場合、前記粒子状電極合剤を前記加圧治具に導入した後、前記加圧治具を振動させることが好ましい。
【００１１】
前記工程（ｃ）には、加圧治具を用いて前記粉体合剤層もしくは合剤シートを電極芯材とともにプレスもしくはホットプレスする工程を適用することができる。
前記工程（ｃ）は、前記粉体合剤層もしくは合剤シートと前記電極芯材とを、それぞれ一方の端部から、所定長さ毎に、もしくは、連続的に、加圧治具に導入することにより、連続的に行うことができる。
【００１２】
前記工程（ｃ）においては、電極芯材に電極活物質層の未塗工部を設けて電極芯材の露出部を残すことができる。前記結着剤には、ゴム微粒子からなる結着剤を用いることが好ましい。前記工程（ｃ）の後には、さらに、前記極板を圧延する工程を行うことができる。
【００１３】
【発明の実施の形態】
図１を参照しながら本発明について説明する。
本発明においては、少なくとも電極活物質および結着剤を含む球状もしくはほぼ球状の粒子状電極合剤を調製する。球状もしくはほぼ球状の粒子状電極合剤は、流動性が高いため、加圧治具に導入する際に全体が均一に流動することから、厚さの均一な粉体合剤層が得られる。粒子状電極合剤の平均粒径は１０〜８００μｍであることが好ましい。平均粒径が大きすぎると、均一な厚さの電極活物質層を得ることが困難になり、小さすぎると、粒子状電極合剤の流動性が低くなる。
【００１４】
球状もしくはほぼ球状の粒子状電極合剤の調製法には特に限定はないが、例えば、スプレードライ法により、粒子状電極合剤を調製することができる。ここで、スプレードライ法は、流動性を有する混合物を造粒するとともに、高速で乾燥する工程からなる。スプレードライ法を採用する場合には、少なくとも電極活物質、結着剤および分散媒を含むスラリーを調製する。スラリーを、図１（ａ）に示すように、所定の条件で、噴霧ノズル１０１から高温（例えば１００〜１２０℃）の気体とともに噴霧することにより、所望の粒子状電極合剤１０２を得ることができる。粒子状電極合剤１０２は、一旦、受け皿１０３などの容器に回収する。
【００１５】
上述のスプレードライ法の他に、図２に示すような造粒装置を用いて、少なくとも電極活物質を含む粉体を、乾燥雰囲気中に流動させ、流動している粉体に、少なくとも結着剤を含む液を噴霧し、乾燥させながら造粒することによっても粒子状電極合剤を調製することができる。
【００１６】
図２の装置の容器１は、下部の円筒状容器、上部の径が大きくなるようにテーパーを付された筒部、および上部の円筒状容器が相互に連結されて構成されている。容器１の下部には、ヒータ付きのガス導入管４が設けてあり、ここから容器内を乾燥雰囲気とするために一定温度に制御された窒素ガスが導入される。容器１の下部には、塵埃の進入を阻止する金属フィルタ５が設けてある。金属フィルタ５の上方には、多数の通気孔を有する造粒プレート６、および造粒プレート上に固定された、中央に衝突ターゲット８を有する攪拌羽根７が回転可能に設けてある。これらの上方の容器壁面には、衝突ターゲット８に向けて圧縮ガスを噴射する一対の圧縮ガス噴射ノズル９が設けられている。容器１の中程には、高圧スプレー３が設けてある。高圧スプレー３は、容器２内の溶液ないし分散液を容器内へ噴霧する。容器１の上方には、バグフィルタ１０が設けられている。バグフィルタ１０内にはポンプ１１から供給される圧縮ガスを噴出させるためのパイプ１２が挿入されている。適宜ポンプ１１からパイプ１２を通じてバグフィルタ１０内へ圧縮ガスを噴射することにより、バグフィルタの外面に付着した粉末などを払い落とす。容器の上部にはガス排出管１３を有する。
【００１７】
この装置により粒子状電極合剤を製造するには、まず、容器１内の造粒プレート６上に予め電極活物質を入れ、高圧スプレー３から結着剤を含む液を噴霧する。容器１内の電極活物質は、ガス導入管４から供給される一定温度の窒素ガスにより容器の上方へ吹き上げられる。ガス導入管４から導入された窒素ガスは、ガス流れ方向を示した矢印ａ、ｂにしたがって、金属フィルタ５および造粒プレート６から容器内上方へ吹き上がる。造粒プレート６は、流動風量が外周に向かって大きくなるように開孔した通気スリットを有している。この造粒プレート６を通過したガスによる流動風により、容器１に投入された電極活物質は容器の上方へ流動し、そこで結着剤を含む液が付着され、乾燥される。
【００１８】
結着剤が付着されて造粒プレート６の上部に沈降してきた粒子は、回転する造粒プレート６上で造粒される。攪拌羽根７は、高速で回転して、そこに沈降してくる粒子を粉砕する。また、圧縮ガス噴射ノズル９から衝突ターゲット８に向けて間欠的に噴射されるパルスジェットは、流動状態の粒子をジェット粉砕により低次構造の粒子に粉砕する。系内に導入された窒素ガスは、容器内上方に配置されたバグフィルタ１０によって、粒子をフィルトレーションし、窒素ガスのみを排出管１３より系外に排出する。
【００１９】
粒子状電極合剤は、図１（ｂ）に示すように、厚さの均一な粉体合剤層１０４ａもしくは合剤シート１０４ｂに形成する。例えば、粒子状電極合剤を電極芯材１０５の上に均一な厚さに配することにより、粉体合剤層１０４ａを得ることができる。粒子状電極合剤を電極芯材１０５の上に載置してから電極芯材１０５を振動させる場合には、粉体合剤層の厚さを極めて均一にすることができる。電極芯材に付与する振動の振動数は、粒子状電極合剤の性状に合わせて適宜選択されるが、２〜１０００Ｈｚが好適である。
【００２０】
加圧治具を用いて粒子状電極合剤をプレスもしくはホットプレスすることにより、合剤シート１０４ｂを得ることもできる。加圧治具の温度は６０〜２００℃であることが好ましい。加圧治具の温度が高ければ短時間で丈夫な合剤シート１０４ｂを得ることができるが、結着剤の融点に対してあまりに高温では、電極合剤が劣化する可能性がある。粒子状電極合剤を加圧治具に導入した後、加圧治具を振動させることにより、合剤シートの厚さを極めて均一にすることができる。加圧治具に付与する振動の振動数は、粒子状電極合剤の性状に合わせて適宜選択されるが、２〜１０００Ｈｚが好適である。
【００２１】
上述のように、本発明では、一旦、球状もしくはほぼ球状の粒子状電極合剤を調製した後、別工程において粒子状電極合剤を粉体合剤層もしくは合剤シートに成形する。そのため均一な厚さの粉体合剤層もしくは合剤シートを得ることができ、それらから均一な厚さの電極活物質層を効率良く得ることができる。このような方法は、粒子状電極合剤を電極芯材に直接吹き付ける方法とは異なり、加圧治具内に粉体状電極合剤を均一に充填するための振動工程を含めることができる点でも有利である。
【００２２】
粉体合剤層１０４ａや合剤シート１０４ｂを電極芯材と一体化すれば、均一な厚さの極板１０６を得ることができる。例えば、加圧治具１０７ａ、１０７ｂを用いて粉体合剤層もしくは合剤シートを電極芯材とともにプレスもしくはホットプレスすることにより、これらを一体化することができる。この場合にも、加圧治具１０７ａ、１０７ｂの温度は６０〜２００℃であることが好ましい。また、得られた極板をさらに圧延することにより、厚さがより均一で電極活物質層１０８の密度の高い電極を得ることができる。
【００２３】
合剤シートと電極芯材とを、それぞれ一方の端部から、所定長さ毎に、もしくは、連続的に、加圧治具に導入することにより、連続的に電極を作製することができる。また、電極芯材を、一方の端部から、所定長さ毎に加圧治具に導入し、逐次その上に粉体合剤層を形成して電極芯材と一体化することにより、連続的に電極を作製することができる。
【００２４】
ロール状に巻き取られた幅広の帯状極板を作製してから、その極板を所定形状に切り出して所望の電極を得ることも可能であるが、予め電極の最終形状に芯材を切り出し、その後に電極活物質層を形成することもできる。電極活物質層を担持してから電極芯材を切断する場合には、バリの発生が問題になるが、予め芯材を切断しておく場合、本質的にバリの発生は問題にならない。従って、電池の信頼性は大きく向上する。
【００２５】
結着剤には、ゴム微粒子を用いることが好ましい。ゴム微粒子は、電極活物質や導電剤の表面の多くを覆うことがないため、少量でも結着剤としての効果を発揮できるからである。ゴム微粒子は、従来から結着剤として用いられているポリフッ化ビニリデンのようなフッ素樹脂に比べ、電極活物質層の硬度を低くすることから、電池組立工程における極板の捲回時に、電極の破断・亀裂の発生が起こりにくく、極板の製造も容易となる。ゴム微粒子には、例えば、弾性率の高いコアとその表面の粘着性を有するグラフト樹脂部からなるものを用いることができる。ゴム微粒子の粒径は０．１〜０．５μｍであることが好ましい。
【００２６】
本発明は、電極合剤を含むペーストを電極芯材に塗工する工程を要さないため、ペーストの粘度を調整するために増粘剤を用いる必要がない。従って、増粘効果を有さないゴム微粒子を用いる場合であっても増粘剤と併用する必要はなく、高容量な電極を得ることができる。
【００２７】
粒子状電極合剤の調製に用いるスラリー中には、潤滑効果を有する添加剤を加えることが好ましい。このような添加剤を含む粒子状電極合剤であれば、加圧治具内に極めて効率良く、かつ、極めて均一に充填することができ、厚さと合剤密度の均一な電極を得ることが可能である。
【００２８】
【実施例】
《実施例１》
（イ）正極
１００重量部のＬｉＣｏＯ_２に、導電剤としてアセチレンブラックを３重量部、結着剤としてゴム微粒子のエマルジョン（日本ゼオン（株）製のＡＤ６２４（商品名）の水性エマルジョン）をゴム成分で３重量部、純水を適量添加し、攪拌・混合し、固形分が２５重量％の正極スラリーを得た。次いで、正極スラリーをスプレードライ法で造粒するとともに乾燥して、粒径２０〜３００μｍ（平均粒径は２００μｍ）の球状の粒子状電極合剤を得た。スプレードライ法では、噴霧ノズル（ノズル径５ｍｍφ）から、正極スラリーと１２０℃の熱風とを同時に噴霧し、その際に造粒された粒子状正極合剤を、受け皿で回収した。
【００２９】
こうして得られた球状の粒子状正極合剤を所定形状の凹状金型に充填し、凸状金型でプレスした。両金型の温度は２５℃とし、プレス圧は５ＫＰａとした。その結果、厚さ１５０μｍ、幅５０ｍｍの帯状の正極合剤シートが得られた。次に、正極合剤シートを、厚さ２０μｍ、幅５０ｍｍのアルミニウム箔からなる芯材の両面に配し、プレスして、芯材と一体化した正極活物質層を形成して正極を得た。ここでは、合剤シートと電極芯材とを、それぞれ一方の端部から、所定長さ毎に金型に導入することにより、正極活物質層の形成を連続的に行った。プレスに用いた金型の温度は１００℃とし、プレス圧は５ＫＰａとした。正極には、正極活物質層の未塗工部を設け、芯材の一部を露出させた。この露出部には、アルミニウム製正極リードを溶接した。
【００３０】
（ロ）負極
平均粒径が約２０μｍの鱗片状黒鉛１００重量部に、結着剤としてゴム微粒子のエマルジョン（日本ゼオン（株）製のＢＭ４００Ｂ（商品名））をゴム成分で３重量部、純水を適量添加し、攪拌・混合し、固形分が２５重量％の負極スラリーを得た。次いで、負極スラリーをスプレードライ法で造粒するとともに乾燥して、粒径２０〜３００μｍ（平均粒径は２００μｍ）の球状の粒子状電極合剤を得た。スプレードライ法では、噴霧ノズル（ノズル径５ｍｍφ）から、負極スラリーと１２０℃の熱風とを同時に噴霧し、その際に造粒された粒子状負極合剤を、受け皿で回収した。
【００３１】
こうして得られた粒子状負極合剤を所定形状の凹状金型に充填し、凸状金型でプレスした。両金型の温度は６０℃とし、プレス圧は３ＫＰａとした。その結果、厚さ１５０μｍ、幅５２ｍｍの帯状の負極合剤シートが得られた。次に、負極合剤シートを、厚さ１０μｍ、幅５２ｍｍの銅箔からなる芯材の両面に配し、プレスして、芯材と一体化した負極活物質層を形成して負極を得た。ここでは、合剤シートと電極芯材とを、それぞれ一方の端部から、所定長さ毎に金型に導入することにより、負極活物質層の形成を連続的に行った。プレスに用いた金型の温度は１５０℃とし、プレス圧は３ＫＰａとした。負極には、負極活物質層の未塗工部を設け、芯材の一部を露出させた。この露出部には、ニッケル製負極リードを溶接した。
【００３２】
（ハ）非水電解液
非水溶媒として、２５体積％のエチレンカーボネートと７５体積％のエチルメチルカーボネートとの混合物を用いた。前記非水溶媒に１ｍｏｌ／Ｌの濃度でＬｉＰＦ_６を溶解した。
【００３３】
（二）電池の組み立て
図３に示すような角型リチウムイオン二次電池を組み立てた。
正極と負極とを、厚さ２５μｍの微多孔性ポリエチレン樹脂製セパレータを介して捲回して、電極群７０を構成した。正極と負極には、それぞれアルミニウム製正極リード７１およびニッケル製負極リード７２を溶接した。電極群の上部にポリエチレン樹脂製の絶縁板７３を装着し、電池ケース７４内に収容した。正極リードの他端は、所定の安全弁７７を有する封口板７８の下面にスポット溶接した。負極リードの他端は、封口板の中心部にある端子孔に絶縁材料７６を介して挿入されているニッケル製負極端子７５の下部と電気的に接続した。電池ケースの開口端部と封口板の周縁部とをレーザで溶接してから、封口板に設けてある注入孔から所定量の非水電解液を注液した。最後に注入孔をアルミニウム製の封栓７９で塞ぎ、レーザー溶接で注液孔を密封して、電池を完成させた。
【００３４】
《実施例２》
正極合剤シートおよび負極合剤シートを成形する際に、凹状金型内にそれぞれの粒子状電極合剤を充填した後、５０Ｈｚの振動を凹状金型に加えたこと以外、実施例１と同様にして、正極および負極を作製し、それらを用いて、実施例１と同様の角型リチウムイオン二次電池を組み立てた。
【００３５】
《実施例３》
（イ）正極
実施例１と同様の方法で、球状の粒子状正極合剤を調製した。
所定形状の凹状金型の底面に、厚さ３０μｍ、幅３０ｍｍのアルミニウム箔からなる芯材を配し、その上に、厚さがほぼ均一になるように粒子状正極合剤を敷き詰め、粉体合剤層を形成した。前記粉体合剤層を、凸状金型でプレスし、芯材と一体化した厚さ１５０μｍ、幅３０ｍｍの正極活物質層を形成した。プレスにおける両金型の温度は１００℃とし、プレス圧は５ＫＰａとした。その後、芯材を裏返して同様の操作を行い、両面に正極活物質層を有する正極を得た。ここでは、電極芯材を、一方の端部から、所定長さ毎に金型に導入し、逐次その上に粉体合剤層を形成することにより、正極活物質層の形成を連続的に行った。正極には、実施例１と同様に正極活物質層の未塗工部を設け、芯材の一部を露出させた。この露出部には、アルミニウム製正極リードを溶接した。
【００３６】
（ロ）負極
実施例１と同様の方法で、球状の粒子状負極合剤を調製した。
所定形状の凹状金型の底面に、厚さ２０μｍ、幅３１ｍｍの銅箔からなる芯材を配し、その上に、厚さがほぼ均一になるように粒子状負極合剤を敷き詰め、粉体合剤層を形成した。前記粉体合剤層を、凸状金型でプレスし、芯材と一体化した厚さ１５０μｍ、幅３１ｍｍの負極活物質層を形成した。プレスにおける両金型の温度は２５℃とし、プレス圧は３ＫＰａとした。その後、芯材を裏返して同様の操作を行い、両面に負極活物質層を有する負極を得た。ここでは、電極芯材を、一方の端部から、所定長さ毎に金型に導入し、逐次その上に粉体合剤層を形成することにより、負極活物質層の形成を連続的に行った。負極には、実施例１と同様に負極活物質層の未塗工部を設け、芯材の一部を露出させた。この露出部には、ニッケル製負極リードを溶接した。
上記正極と負極とを用いて、実施例１と同様の角型リチウムイオン二次電池を組み立てた。
【００３７】
《実施例４》
正極活物質層および負極活物質層を形成する際に、凹状金型内にそれぞれの粒子状電極合剤を充填した後、５０Ｈｚの振動を凹状金型に加えたこと以外、実施例３と同様にして、正極および負極を作製し、それらを用いて、実施例１と同様の角型リチウムイオン二次電池を組み立てた。
【００３８】
《実施例５》
正極活物質層および負極活物質層を形成する際に、両金型の温度を１５０℃とし、プレス圧を５ＫＰａとしたこと以外、実施例３と同様にして正極および負極を作製し、それらを用いて、実施例１と同様の角型リチウムイオン二次電池を組み立てた。
【００３９】
《実施例６》
正極スラリーおよび負極スラリーに、潤滑剤としてフッ素変性シリコーンオイル（信越シリコーン（株）製のＦＬ１００（商品名））をＬｉＣｏＯ_２１００重量部あたり１重量部添加したこと以外、実施例１と同様にして正極および負極を作製し、それらを用いて、実施例１と同様の角型リチウムイオン二次電池を組み立てた。
【００４０】
《実施例７》
正極スラリーおよび負極スラリーに、潤滑剤として高密度ポリエチレン粉末（住友精化（株）製のＨＥ−３０４０（商品名）、粒径５〜１００μｍ、平均粒径５０μｍ）をＬｉＣｏＯ_２１００重量部あたり５重量部添加したこと以外、実施例１と同様にして正極および負極を作製し、それらを用いて、実施例１と同様の角型リチウムイオン二次電池を組み立てた。
【００４１】
《実施例８》
得られた正極および負極を、さらに、２００ＫＮ／ｍの線圧力でロールプレスして電極活物質層の密度を高めたこと以外、実施例１と同様の角型リチウムイオン二次電池を組み立てた。
【００４２】
《実施例９》
得られた正極および負極を、さらに、２００ＫＮ／ｍの線圧力でロールプレスして電極活物質層の密度を高めたこと以外、実施例３と同様の角型リチウムイオン二次電池を組み立てた。
【００４３】
《実施例１０》
（イ）正極
１００重量部のＬｉＣｏＯ_２および３重量部のアセチレンブラックを、所定の容器内に導入し、ＬｉＣｏＯ_２とアセチレンブラックの混合物を容器内の１００℃の乾燥雰囲気中で流動させた。容器内には、流速１ｍ^３／分の乾燥Ｎ_２により、上昇気流を形成させ、気流によって粉体混合物を攪拌するとともに、乾燥させた。容器の下部には、造粒プレートとその上に堆積する粉体混合物を攪拌する攪拌羽根を設けた。撹拌羽根の回転速度は３００ｒｐｍとした。そして、流動している粉体混合物に、結着剤としてゴム微粒子のエマルジョン（日本ゼオン（株）製のＢＭ５００Ｂ（商品名））を噴霧し、乾燥させて、ゴム微粒子を付着させた。ゴム微粒子の噴霧量は、１００重量部のＬｉＣｏＯ_２あたり３重量部とした。エマルジョンの噴霧速度は１０ｇ／分とした。その結果、粒径５０〜３００μｍ（平均粒径は２００μｍ）の球状の粒子状正極合剤が得られた。こうして得られた粒子状正極合剤を用いたこと以外、実施例１と同様にして正極を作製した。
【００４４】
（ロ）負極
平均粒径が約２０μｍの鱗片状黒鉛１００重量部を、所定の容器内に導入し、鱗片状黒鉛を容器内の１００℃の乾燥雰囲気中で流動させた。容器内には、流速１ｍ^３／分の乾燥Ｎ_２により、上昇気流を形成させ、気流によって鱗片状黒鉛を攪拌するとともに、乾燥させた。容器の下部には、造粒プレートとその上に堆積する粒子を攪拌する攪拌羽根を設けた。撹拌羽根の回転速度は３００ｒｐｍとした。そして、流動している鱗片状黒鉛に、結着剤としてゴム微粒子のエマルジョン（日本ゼオン（株）製のＢＭ４００Ｂ（商品名））を噴霧し、乾燥させて、ゴム微粒子を付着させた。ゴム微粒子の噴霧量は、１００重量部の鱗片状黒鉛あたり２重量部とした。エマルジョンの噴霧速度は１０ｇ／分とした。その結果、粒径５０〜３００μｍ（平均粒径は２００μｍ）の球状の粒子状負極合剤が得られた。こうして得られた粒子状負極合剤を用いたこと以外、実施例１と同様にして負極を作製した。
こうして得られた正極と負極を用いて、実施例１と同様の角型リチウムイオン二次電池を組み立てた。
【００４５】
《比較例１》
特開平１１−１４９９１８号公報に記載の方法に準じて、電極合剤スラリーのスプレードライを行う際に、電極芯材に直接、電極合剤を吹き付けて粉体合剤層を形成したこと以外、実施例３と同様にして正極と負極を作製した。その際、電極芯材には、所定形状の開口部を有するマスクを配し、できる限り実施例１の電極活物質層に近い形状の電極活物質層を形成した。
こうして得られた正極と負極を用いて、実施例１と同様の角型リチウムイオン二次電池を組み立てた。
【００４６】
（ｖ）評価
［極板外観］
実施例１〜１０および比較例１の極板の外観を目視で観察し、電極活物質層における微細なクラックの有無を調べた。また、極板の中心線表面粗さを、表面粗さ測定装置（東京精密（株）サーフコム１４００型）にて測定した。結果を表１に示す。
【００４７】
［電池のサイクル特性］
実施例１〜１０および比較例１の電池の充放電サイクルを２５℃で繰り返した。充電は、０．７Ｃの電流値で、電池電圧が４．２Ｖになるまで行い、次いで電流値が０．０５Ｃになるまで定電圧で充電を続けた。そして、１Ｃの電流値で、電池電圧が３．０Ｖになるまで放電した。このサイクルを１００回繰り返し、初期容量に対する最後のサイクルで得られた容量の割合（％）を求めた。結果を表１に示す。
【００４８】
【表１】

【００４９】
【発明の効果】
表１から明らかなように、スプレードライを採用する従来の電極製造法に比べ、本発明の製造法によれば、表面粗さが小さく、微細クラックのない優れた電極を得ることができる。また、本発明の製造法で得られた電極は、均一な厚さの電極活物質層を有することから、サイクル特性に優れた二次電池を与えることが可能となる。しかも、本発明によれば、分散媒の飛散による問題等を改善することができる。
【図面の簡単な説明】
【図１】本発明に係る電極の製造法の一例を示す工程図である。
【図２】粒子状電極合剤の調製に用いる造粒装置の一例の断面概念図である。
【図３】本発明の実施例にかかる角型電池の一部を切り欠いた斜視図である。
【符号の説明】
１０１噴霧ノズル
１０２粒子状電極合剤
１０３受け皿
１０４ａ粉体合剤層
１０４ｂ合剤シート
１０５電極芯材
１０６極板
１０７ａ、１０７ｂ加圧治具
１０８電極活物質層
１下部円筒状容器
２溶液または分散液の容器
３高圧スプレー
４ガス導入管
５金属フィルタ
６造粒プレート
７撹拌羽根
８衝突ターゲット
９圧縮ガス噴射ノズル
１０バグフィルタ
１１ポンプ
１２パイプ
１３ガス排出管
７０電極群
７１アルミニウム製正極リード
７２ニッケル製負極リード
７３ポリエチレン樹脂製の絶縁板
７４電池ケース
７５ニッケル製負極端子
７６絶縁材料
７７安全弁
７８封口板
７９アルミニウム製の封栓[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a secondary battery electrode having a uniform thickness without applying a paste containing an electrode mixture.
[0002]
[Prior art]
In a conventional method of manufacturing a battery electrode, a paste obtained by mixing an electrode mixture comprising an electrode active material and a binder with a dispersion medium is applied to an electrode core material, and the coating film is dried to form a coating. Is dispersed, and the dried coating film is pressed to form an electrode active material layer.
[0003]
However, in the method described above, when the coating film is dried and the dispersion medium is scattered, the coating film shrinks, so that fine cracks are generated in the electrode active material layer, or internal stress is generated at the time of pressing. There is a problem of doing. Moreover, since the shrinkage of the coating film is large, the thickness of the electrode active material layer varies greatly, and it is difficult to obtain an electrode having a uniform thickness. Furthermore, since it is necessary to control the scattering of the dispersion medium, there is also a problem that the manufacturing cost of the electrode is increased.
[0004]
Therefore, a method for producing an electrode active material layer in which a paste containing a binder and an electrode active material in a molten state is powderized by a spray drying method and the powder is directly sprayed on a core material has been proposed (see Patent Document 1). ). However, in this method, although the problem that fine cracks are generated in the electrode active material layer or internal stress occurs during pressing is improved, it is difficult to obtain an electrode active material layer having a uniform thickness. is there. If the thickness of the electrode active material layer is not uniform, the depth of discharge varies depending on the location of the electrode, and the battery characteristics are likely to deteriorate. In addition, when the powder is directly sprayed on the core material, the dispersion medium in the paste is scattered, so that it is not possible to eliminate the problem that the cost of collecting the scattered dispersion medium is high. The conventional spray drying method has a problem that a large amount of a binder in a molten state must be included in the paste in order to obtain a good paste spray state, and it is difficult to obtain a high-capacity electrode. Therefore, it is difficult to discharge the battery at a high rate.
[0005]
[Patent Document 1]
JP-A-11-149918
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the above, and an object of the present invention is to improve a problem due to scattering of a dispersion medium and the like and efficiently obtain an electrode having a uniform thickness.
[0007]
[Means for Solving the Problems]
That is, the present invention is a method for producing an electrode for a secondary battery comprising an electrode core material and an electrode active material layer supported on the electrode core material,
(A) preparing a spherical or nearly spherical particulate electrode mixture containing at least an electrode active material and a binder;
(B) forming a powder mixture layer or mixture sheet having a uniform thickness from the particulate electrode mixture; and
(C) a step of obtaining the electrode plate by integrating the powder mixture layer or the mixture sheet with an electrode core, and a method for producing an electrode for a secondary battery.
However, a uniform thickness means that there is no significant difference in thickness between the portions of the powder mixture layer or the mixture sheet, and even if there is some variation in the thickness, it may be uniform at first glance. Just fine. The particulate electrode mixture may be substantially spherical, and may be, for example, a chicken egg. It is preferable that the particulate electrode mixture further contains a lubricant.
[0008]
In the step (a), for example, a step of preparing a slurry containing at least an electrode active material, a binder and a dispersion medium, and powdering the slurry by a spray drying method, thereby forming the spherical or almost spherical A step of obtaining a particulate electrode mixture can be applied.
In the step (a), a step of flowing at least a powder containing an electrode active material in a dry atmosphere is performed, and a step of spraying a liquid containing at least a binder onto the flowing powder is performed. The step of obtaining the spherical or substantially spherical particulate electrode mixture by granulation can be applied.
[0009]
In the step (b), for example, a step of obtaining the powder mixture layer by disposing the particulate electrode mixture in a uniform thickness on an electrode core material can be applied. In this case, in the step of disposing the particulate electrode mixture on the electrode core in a uniform thickness, the particulate electrode mixture is placed on the electrode core, and then the electrode core is vibrated. Can be applied.
[0010]
In the step (b), a step of obtaining the mixture sheet by pressing or hot-pressing the particulate electrode mixture using a pressing jig can be employed. In this case, it is preferable to vibrate the pressing jig after introducing the particulate electrode mixture into the pressing jig.
[0011]
In the step (c), a step of pressing or hot pressing the powder mixture layer or the mixture sheet together with an electrode core using a pressing jig can be applied.
In the step (c), the powder mixture layer or the mixture sheet and the electrode core material are introduced into the pressing jig from one end thereof at predetermined lengths or continuously. By doing so, it can be performed continuously.
[0012]
In the step (c), an uncoated portion of the electrode active material layer may be provided on the electrode core to leave an exposed portion of the electrode core. It is preferable to use a binder made of rubber fine particles as the binder. After the step (c), a step of rolling the electrode plate can be further performed.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described with reference to FIG.
In the present invention, a spherical or nearly spherical particulate electrode mixture containing at least an electrode active material and a binder is prepared. Since the spherical or almost spherical particulate electrode mixture has a high fluidity, it flows uniformly when introduced into the pressing jig, so that a powder mixture layer having a uniform thickness can be obtained. The average particle size of the particulate electrode mixture is preferably from 10 to 800 μm. If the average particle size is too large, it will be difficult to obtain an electrode active material layer having a uniform thickness, and if it is too small, the fluidity of the particulate electrode mixture will be low.
[0014]
The method for preparing the spherical or substantially spherical particulate electrode mixture is not particularly limited. For example, the particulate electrode mixture can be prepared by a spray drying method. Here, the spray drying method comprises a step of granulating a fluid mixture and drying at a high speed. When the spray drying method is adopted, a slurry containing at least an electrode active material, a binder and a dispersion medium is prepared. As shown in FIG. 1A, the desired particulate electrode mixture 102 can be obtained by spraying the slurry together with a high-temperature (for example, 100 to 120 ° C.) gas from a spray nozzle 101 under predetermined conditions. it can. The particulate electrode mixture 102 is once collected in a container such as a tray 103.
[0015]
In addition to the above-described spray-drying method, at least powder containing at least the electrode active material is caused to flow in a dry atmosphere using a granulation apparatus as shown in FIG. The particulate electrode mixture can also be prepared by spraying a liquid containing the agent and granulating while drying.
[0016]
The container 1 of the apparatus shown in FIG. 2 includes a lower cylindrical container, an upper cylindrical portion tapered so as to have a larger diameter, and an upper cylindrical container which are interconnected. A gas introduction pipe 4 with a heater is provided at a lower portion of the container 1, from which a nitrogen gas controlled at a constant temperature is introduced to make the inside of the container a dry atmosphere. A metal filter 5 for preventing dust from entering is provided at a lower portion of the container 1. Above the metal filter 5, a granulating plate 6 having a large number of ventilation holes and a stirring blade 7 fixed on the granulating plate and having a collision target 8 in the center are rotatably provided. A pair of compressed gas injection nozzles 9 for injecting compressed gas toward the collision target 8 are provided on the upper container wall. In the middle of the container 1, a high-pressure spray 3 is provided. The high-pressure spray 3 sprays the solution or dispersion in the container 2 into the container. A bag filter 10 is provided above the container 1. A pipe 12 for ejecting a compressed gas supplied from a pump 11 is inserted into the bag filter 10. By appropriately injecting compressed gas into the bag filter 10 from the pump 11 through the pipe 12, powder or the like attached to the outer surface of the bag filter is wiped off. The upper part of the container has a gas discharge pipe 13.
[0017]
In order to manufacture a particulate electrode mixture by this apparatus, first, an electrode active material is put in advance on a granulation plate 6 in a container 1 and a liquid containing a binder is sprayed from a high-pressure spray 3. The electrode active material in the container 1 is blown up by a nitrogen gas at a constant temperature supplied from a gas introduction pipe 4 to an upper portion of the container. The nitrogen gas introduced from the gas introduction pipe 4 blows upward from the metal filter 5 and the granulation plate 6 into the container in accordance with arrows a and b indicating the gas flow direction. The granulation plate 6 has a ventilation slit that is opened so that the amount of flowing air increases toward the outer periphery. Due to the flowing wind of the gas passing through the granulating plate 6, the electrode active material put into the container 1 flows upward of the container, where the liquid containing the binder is attached and dried.
[0018]
The particles that have settled on the upper part of the granulating plate 6 with the binder attached thereto are granulated on the rotating granulating plate 6. The stirring blade 7 rotates at a high speed to pulverize particles settling there. In addition, the pulse jet intermittently jetted from the compressed gas jet nozzle 9 toward the collision target 8 crushes particles in a flowing state into particles having a low-order structure by jet crushing. Nitrogen gas introduced into the system is filtered by a bag filter 10 disposed in the upper part of the container to filter particles, and only nitrogen gas is discharged from the discharge pipe 13 to the outside of the system.
[0019]
As shown in FIG. 1B, the particulate electrode mixture is formed on a powder mixture layer 104a or a mixture sheet 104b having a uniform thickness. For example, the powder mixture layer 104a can be obtained by disposing the particulate electrode mixture on the electrode core material 105 at a uniform thickness. When the electrode core 105 is vibrated after the particulate electrode mixture is placed on the electrode core 105, the thickness of the powder mixture layer can be made extremely uniform. The frequency of the vibration applied to the electrode core material is appropriately selected according to the properties of the particulate electrode mixture, but is preferably 2 to 1000 Hz.
[0020]
By pressing or hot pressing the particulate electrode mixture using a pressing jig, the mixture sheet 104b can also be obtained. The temperature of the pressing jig is preferably 60 to 200 ° C. If the temperature of the pressing jig is high, a strong mixture sheet 104b can be obtained in a short time, but if the temperature is too high with respect to the melting point of the binder, the electrode mixture may deteriorate. After the particulate electrode mixture is introduced into the pressing jig, the thickness of the mixture sheet can be made extremely uniform by vibrating the pressing jig. The frequency of the vibration applied to the pressing jig is appropriately selected according to the properties of the particulate electrode mixture, but is preferably 2 to 1000 Hz.
[0021]
As described above, in the present invention, once a spherical or substantially spherical particulate electrode mixture is prepared, the particulate electrode mixture is formed into a powder mixture layer or a mixture sheet in another step. Therefore, a powder mixture layer or a mixture sheet having a uniform thickness can be obtained, and an electrode active material layer having a uniform thickness can be efficiently obtained therefrom. Such a method differs from a method in which the particulate electrode mixture is directly sprayed on the electrode core material, and can include a vibration step for uniformly filling the powdered electrode mixture in the pressing jig. But it is advantageous.
[0022]
If the powder mixture layer 104a and the mixture sheet 104b are integrated with the electrode core, the electrode plate 106 having a uniform thickness can be obtained. For example, these can be integrated by pressing or hot pressing the powder mixture layer or the mixture sheet together with the electrode core material using the

pressing jigs

107a and 107b. Also in this case, the temperature of the

pressing jigs

107a and 107b is preferably 60 to 200 ° C. Further, by further rolling the obtained electrode plate, an electrode having a more uniform thickness and a high density of the electrode active material layer 108 can be obtained.
[0023]
The electrodes can be manufactured continuously by introducing the mixture sheet and the electrode core material into the pressing jig at predetermined lengths or continuously from one end thereof, respectively. In addition, the electrode core material is introduced into the pressing jig at a predetermined length from one end, and a powder mixture layer is sequentially formed thereon to integrate the electrode core material with the electrode core material. An electrode can be produced in an appropriate manner.
[0024]
After producing a wide band-shaped electrode plate wound in a roll shape, it is possible to obtain a desired electrode by cutting the electrode plate into a predetermined shape, but it is also possible to cut out a core material in advance to the final shape of the electrode, Thereafter, an electrode active material layer can be formed. When the electrode core material is cut after supporting the electrode active material layer, generation of burrs is a problem. However, when the core material is cut in advance, generation of burrs is essentially not a problem. Therefore, the reliability of the battery is greatly improved.
[0025]
It is preferable to use fine rubber particles as the binder. This is because the rubber fine particles do not cover much of the surface of the electrode active material or the conductive agent, and therefore can exert the effect as a binder even in a small amount. The rubber fine particles reduce the hardness of the electrode active material layer as compared with a fluororesin such as polyvinylidene fluoride which has been conventionally used as a binder. Breakage and cracking hardly occur, and the manufacture of the electrode plate is also facilitated. As the rubber fine particles, for example, a rubber fine particle composed of a core having a high elastic modulus and a graft resin portion having a sticky surface can be used. The particle size of the rubber fine particles is preferably from 0.1 to 0.5 μm.
[0026]
Since the present invention does not require a step of applying a paste containing an electrode mixture to an electrode core material, it is not necessary to use a thickener to adjust the viscosity of the paste. Therefore, even when rubber fine particles having no thickening effect are used, it is not necessary to use the fine particles together with a thickener, and a high-capacity electrode can be obtained.
[0027]
It is preferable to add an additive having a lubricating effect to the slurry used for preparing the particulate electrode mixture. With a particulate electrode mixture containing such an additive, it is possible to very efficiently and extremely uniformly fill the pressure jig, and obtain an electrode having a uniform thickness and a uniform mixture density. It is possible.
[0028]
【Example】
<< Example 1 >>
(A) Positive electrode
100 parts by weight of LiCoO ₂ 3 parts by weight of acetylene black as a conductive agent, 3 parts by weight of a rubber component, an emulsion of fine particles of rubber (AD624 (trade name) manufactured by Zeon Corporation) as a binder, and an appropriate amount of pure water. Then, the mixture was stirred and mixed to obtain a positive electrode slurry having a solid content of 25% by weight. Next, the positive electrode slurry was granulated by a spray dry method and dried to obtain a spherical particulate electrode mixture having a particle diameter of 20 to 300 μm (average particle diameter of 200 μm). In the spray drying method, a positive electrode slurry and hot air at 120 ° C. were simultaneously sprayed from a spray nozzle (nozzle diameter: 5 mmφ), and the particulate positive electrode mixture granulated at that time was collected in a tray.
[0029]
The spherical particulate positive electrode mixture thus obtained was filled in a concave mold having a predetermined shape, and pressed with a convex mold. The temperature of both molds was 25 ° C., and the press pressure was 5 KPa. As a result, a belt-shaped positive electrode mixture sheet having a thickness of 150 μm and a width of 50 mm was obtained. Next, the positive electrode mixture sheet was disposed on both sides of a core material made of aluminum foil having a thickness of 20 μm and a width of 50 mm, and pressed to form a positive electrode active material layer integrated with the core material to obtain a positive electrode. . Here, the positive electrode active material layer was continuously formed by introducing the mixture sheet and the electrode core material into the mold at predetermined lengths from one end thereof. The temperature of the mold used for the pressing was 100 ° C., and the pressing pressure was 5 KPa. An uncoated portion of the positive electrode active material layer was provided on the positive electrode, and a part of the core material was exposed. An aluminum positive electrode lead was welded to the exposed portion.
[0030]
(B) Negative electrode
To 100 parts by weight of flaky graphite having an average particle size of about 20 μm, an emulsion of fine rubber particles (BM400B (trade name) manufactured by Nippon Zeon Co., Ltd.) is added as a binder, 3 parts by weight of a rubber component, and an appropriate amount of pure water. The mixture was stirred and mixed to obtain a negative electrode slurry having a solid content of 25% by weight. Next, the negative electrode slurry was granulated by a spray dry method and dried to obtain a spherical particulate electrode mixture having a particle diameter of 20 to 300 μm (average particle diameter of 200 μm). In the spray drying method, a negative electrode slurry and 120 ° C. hot air were simultaneously sprayed from a spray nozzle (nozzle diameter: 5 mmφ), and the particulate negative electrode mixture granulated at that time was collected in a tray.
[0031]
The particulate negative electrode mixture thus obtained was filled in a concave mold having a predetermined shape, and pressed with a convex mold. The temperature of both dies was 60 ° C., and the pressing pressure was 3 KPa. As a result, a strip-shaped negative electrode mixture sheet having a thickness of 150 μm and a width of 52 mm was obtained. Next, a negative electrode mixture sheet was disposed on both sides of a core material made of copper foil having a thickness of 10 μm and a width of 52 mm, and pressed to form a negative electrode active material layer integrated with the core material, thereby obtaining a negative electrode. . Here, the negative electrode active material layer was continuously formed by introducing the mixture sheet and the electrode core material into the mold at predetermined intervals from one end thereof. The temperature of the mold used for pressing was 150 ° C., and the pressing pressure was 3 KPa. The negative electrode was provided with an uncoated portion of the negative electrode active material layer, exposing a part of the core material. A nickel negative electrode lead was welded to the exposed portion.
[0032]
(C) Non-aqueous electrolyte
As the non-aqueous solvent, a mixture of 25% by volume of ethylene carbonate and 75% by volume of ethyl methyl carbonate was used. LiPF at a concentration of 1 mol / L in the non-aqueous solvent ₆ Was dissolved.
[0033]
(2) Battery assembly
A prismatic lithium ion secondary battery as shown in FIG. 3 was assembled.
The positive electrode and the negative electrode were wound through a 25 μm-thick microporous polyethylene resin separator to form an electrode group 70. An aluminum positive electrode lead 71 and a nickel negative electrode lead 72 were welded to the positive electrode and the negative electrode, respectively. An insulating plate 73 made of polyethylene resin was mounted on the upper part of the electrode group, and housed in a battery case 74. The other end of the positive electrode lead was spot-welded to the lower surface of a sealing plate 78 having a predetermined safety valve 77. The other end of the negative electrode lead was electrically connected to a lower portion of a nickel negative electrode terminal 75 inserted into a terminal hole at the center of the sealing plate via an insulating material 76. After the opening end of the battery case and the peripheral edge of the sealing plate were welded by laser, a predetermined amount of nonaqueous electrolyte was injected from an injection hole provided in the sealing plate. Finally, the injection hole was closed with an aluminum stopper 79, and the injection hole was sealed by laser welding to complete the battery.
[0034]
<< Example 2 >>
When molding the positive electrode mixture sheet and the negative electrode mixture sheet, the same as in Example 1 except that the concave mold was filled with the respective particulate electrode mixture and then a vibration of 50 Hz was applied to the concave mold. Then, a positive electrode and a negative electrode were produced, and a prismatic lithium ion secondary battery similar to that of Example 1 was assembled using them.
[0035]
<< Example 3 >>
(A) Positive electrode
In the same manner as in Example 1, a spherical particulate positive electrode mixture was prepared.
A core material made of aluminum foil having a thickness of 30 μm and a width of 30 mm is arranged on the bottom surface of a concave mold having a predetermined shape, and a particulate positive electrode mixture is spread thereon so as to have a substantially uniform thickness. A mixture layer was formed. The powder mixture layer was pressed with a convex mold to form a positive electrode active material layer having a thickness of 150 μm and a width of 30 mm integrated with the core material. The temperature of both molds in the press was 100 ° C., and the press pressure was 5 KPa. Thereafter, the core material was turned over and the same operation was performed to obtain a positive electrode having a positive electrode active material layer on both surfaces. Here, the electrode core material is introduced into the mold at a predetermined length from one end, and a powder mixture layer is sequentially formed thereon, thereby continuously forming the positive electrode active material layer. went. An uncoated portion of the positive electrode active material layer was provided on the positive electrode in the same manner as in Example 1, and a part of the core material was exposed. An aluminum positive electrode lead was welded to the exposed portion.
[0036]
(B) Negative electrode
In the same manner as in Example 1, a spherical particulate negative electrode mixture was prepared.
A core material made of a copper foil having a thickness of 20 μm and a width of 31 mm is arranged on the bottom surface of a concave mold having a predetermined shape, and a particulate negative electrode mixture is spread over the core material so that the thickness becomes substantially uniform. A mixture layer was formed. The powder mixture layer was pressed with a convex mold to form a negative electrode active material layer having a thickness of 150 μm and a width of 31 mm integrated with the core material. The temperature of both dies in the press was 25 ° C., and the press pressure was 3 KPa. Thereafter, the core material was turned over and the same operation was performed to obtain a negative electrode having negative electrode active material layers on both surfaces. Here, the electrode core material is introduced into the mold at a predetermined length from one end, and a powder mixture layer is sequentially formed thereon, thereby continuously forming the negative electrode active material layer. went. The negative electrode was provided with an uncoated portion of the negative electrode active material layer in the same manner as in Example 1, exposing a part of the core material. A nickel negative electrode lead was welded to the exposed portion.
Using the positive electrode and the negative electrode, a prismatic lithium ion secondary battery similar to that of Example 1 was assembled.
[0037]
<< Example 4 >>
Same as Example 3 except that when forming the positive electrode active material layer and the negative electrode active material layer, each of the particulate electrode mixtures was filled in the concave mold, and then a vibration of 50 Hz was applied to the concave mold. Then, a positive electrode and a negative electrode were produced, and a prismatic lithium ion secondary battery similar to that of Example 1 was assembled using them.
[0038]
<< Example 5 >>
When forming the positive electrode active material layer and the negative electrode active material layer, a positive electrode and a negative electrode were prepared in the same manner as in Example 3, except that the temperature of both molds was set to 150 ° C. and the press pressure was set to 5 KPa. Using this, a prismatic lithium ion secondary battery similar to that of Example 1 was assembled.
[0039]
<< Example 6 >>
Fluorine-modified silicone oil (FL100 (trade name, manufactured by Shin-Etsu Silicone Co., Ltd.)) as a lubricant was added to the positive electrode slurry and the negative electrode slurry as LiCoO. ₂ A positive electrode and a negative electrode were prepared in the same manner as in Example 1 except that 1 part by weight was added per 100 parts by weight, and a prismatic lithium ion secondary battery similar to that in Example 1 was assembled using them.
[0040]
<< Example 7 >>
A high-density polyethylene powder (HE-3040 (trade name, manufactured by Sumitomo Seika Co., Ltd., particle size: 5 to 100 μm, average particle size: 50 μm)) as a lubricant was added to the positive electrode slurry and the negative electrode slurry by LiCoO. ₂ A positive electrode and a negative electrode were prepared in the same manner as in Example 1 except that 5 parts by weight were added per 100 parts by weight, and a prismatic lithium ion secondary battery similar to that in Example 1 was assembled using them.
[0041]
<< Embodiment 8 >>
The obtained positive electrode and negative electrode were further roll-pressed at a linear pressure of 200 KN / m to increase the density of the electrode active material layer, thereby assembling a prismatic lithium ion secondary battery as in Example 1.
[0042]
<< Example 9 >>
The obtained positive electrode and negative electrode were further roll-pressed at a linear pressure of 200 KN / m to increase the density of the electrode active material layer, thereby assembling a prismatic lithium ion secondary battery as in Example 3.
[0043]
<< Example 10 >>
(A) Positive electrode
100 parts by weight of LiCoO ₂ And 3 parts by weight of acetylene black were introduced into a predetermined container, and LiCoO ₂ And acetylene black were flowed in a dry atmosphere at 100 ° C. in a container. In the vessel, the flow rate is 1m ³ / Min dry N ₂ As a result, an ascending airflow was formed, and the powder mixture was stirred and dried by the airflow. At the lower part of the vessel, a stirring plate for stirring the granulation plate and the powder mixture deposited thereon was provided. The rotation speed of the stirring blade was 300 rpm. Then, an emulsion of rubber fine particles (BM500B (trade name) manufactured by Zeon Corporation) was sprayed as a binder on the flowing powder mixture, and dried to adhere the rubber fine particles. The spray amount of the rubber fine particles is 100 parts by weight of LiCoO ₂ Per part by weight. The spray rate of the emulsion was 10 g / min. As a result, a spherical particulate positive electrode mixture having a particle size of 50 to 300 μm (average particle size of 200 μm) was obtained. A positive electrode was produced in the same manner as in Example 1, except that the particulate positive electrode mixture thus obtained was used.
[0044]
(B) Negative electrode
100 parts by weight of flaky graphite having an average particle size of about 20 μm was introduced into a predetermined container, and the flaky graphite was flowed in a dry atmosphere at 100 ° C. in the container. In the vessel, the flow rate is 1m ³ / Min dry N ₂ As a result, a rising airflow was formed, and the flake graphite was stirred by the airflow and dried. At the lower part of the vessel, a granulating plate and stirring blades for stirring particles deposited thereon were provided. The rotation speed of the stirring blade was 300 rpm. Then, an emulsion of fine rubber particles (BM400B (trade name) manufactured by Zeon Corporation) was sprayed as a binder onto the flowing flaky graphite, and the fine particles of rubber were adhered by drying. The spray amount of the rubber fine particles was 2 parts by weight per 100 parts by weight of flake graphite. The spray rate of the emulsion was 10 g / min. As a result, a spherical particulate negative electrode mixture having a particle diameter of 50 to 300 μm (average particle diameter of 200 μm) was obtained. A negative electrode was produced in the same manner as in Example 1, except that the thus obtained particulate negative electrode mixture was used.
Using the positive electrode and the negative electrode thus obtained, a prismatic lithium ion secondary battery similar to that of Example 1 was assembled.
[0045]
<< Comparative Example 1 >>
According to the method described in JP-A-11-149918, when performing spray drying of the electrode mixture slurry, except that the electrode mixture was directly sprayed onto the electrode core material to form a powder mixture layer, A positive electrode and a negative electrode were produced in the same manner as in Example 3. At that time, a mask having an opening having a predetermined shape was arranged on the electrode core material, and an electrode active material layer having a shape as close as possible to the electrode active material layer of Example 1 was formed.
Using the positive electrode and the negative electrode thus obtained, a prismatic lithium ion secondary battery similar to that of Example 1 was assembled.
[0046]
(V) Evaluation
[Plate appearance]
The appearance of the electrode plates of Examples 1 to 10 and Comparative Example 1 was visually observed, and the presence or absence of minute cracks in the electrode active material layer was examined. Further, the center line surface roughness of the electrode plate was measured by a surface roughness measuring device (Surfcom 1400 type, Tokyo Seimitsu Co., Ltd.). Table 1 shows the results.
[0047]
[Battery cycle characteristics]
The charge and discharge cycle of the batteries of Examples 1 to 10 and Comparative Example 1 was repeated at 25 ° C. Charging was performed at a current value of 0.7 C until the battery voltage reached 4.2 V, and then charging was performed at a constant voltage until the current value reached 0.05 C. The battery was discharged at a current value of 1 C until the battery voltage reached 3.0 V. This cycle was repeated 100 times, and the ratio (%) of the capacity obtained in the last cycle to the initial capacity was determined. Table 1 shows the results.
[0048]
[Table 1]

[0049]
【The invention's effect】
As is clear from Table 1, according to the manufacturing method of the present invention, an excellent electrode having a small surface roughness and no fine cracks can be obtained as compared with the conventional electrode manufacturing method employing spray drying. Further, since the electrode obtained by the production method of the present invention has an electrode active material layer having a uniform thickness, a secondary battery having excellent cycle characteristics can be provided. In addition, according to the present invention, it is possible to improve problems caused by scattering of the dispersion medium.
[Brief description of the drawings]
FIG. 1 is a process chart showing an example of a method for manufacturing an electrode according to the present invention.
FIG. 2 is a conceptual sectional view of an example of a granulating apparatus used for preparing a particulate electrode mixture.
FIG. 3 is a partially cutaway perspective view of a prismatic battery according to an example of the present invention.
[Explanation of symbols]
101 spray nozzle
102 Particulate electrode mixture
103 saucer
104a Powder mixture layer
104b mixture sheet
105 electrode core material
106 plates
107a, 107b Pressing jig
108 electrode active material layer
1 lower cylindrical container
2 Solution or dispersion container
3 High pressure spray
4 Gas inlet pipe
5 Metal filter
6 Granulation plate
7 stirring blades
8 Collision target
9 Compressed gas injection nozzle
10 Bag Filter
11 pump
12 pipes
13 Gas exhaust pipe
70 electrode group
71 Aluminum positive lead
72 Nickel negative lead
73 Insulation board made of polyethylene resin
74 Battery case
75 Nickel negative terminal
76 Insulation material
77 Safety valve
78 Sealing plate
79 Aluminum cap

Claims

A method for producing an electrode for a secondary battery comprising an electrode core material and an electrode active material layer supported on the electrode core material,
(A) preparing a spherical or nearly spherical particulate electrode mixture containing at least an electrode active material and a binder;
(B) a step of forming a powder mixture layer or mixture sheet having a uniform thickness from the particulate electrode mixture; and (c) integrating the powder mixture layer or mixture sheet with an electrode core. Producing an electrode for a secondary battery.

The step (a) is a step of preparing a slurry containing at least an electrode active material, a binder and a dispersion medium, and the step of pulverizing the slurry by a spray-drying method to obtain the spherical or substantially spherical particulate electrode. The method for producing an electrode for a secondary battery according to claim 1, comprising a step of obtaining a mixture.

The step (a) is a step of flowing a powder containing at least an electrode active material into a dry atmosphere, and granulating the flowing powder with a liquid containing at least a binder. 2. A method for producing an electrode for a secondary battery according to claim 1, comprising the step of: obtaining the spherical or substantially spherical particulate electrode mixture.

The method for producing an electrode for a secondary battery according to claim 1, wherein the particulate electrode mixture further contains a lubricant.

2. The electrode for a secondary battery according to claim 1, wherein the step (b) comprises a step of obtaining the powder mixture layer by arranging the particulate electrode mixture on the electrode core in a uniform thickness. 3. Manufacturing method.

The step of disposing the particulate electrode mixture to a uniform thickness on the electrode core is a step of vibrating the electrode core after placing the particulate electrode mixture on the electrode core. A method for producing an electrode for a secondary battery according to claim 5.

2. The secondary battery electrode according to claim 1, wherein the step (b) comprises a step of pressing or hot pressing the particulate electrode mixture using a pressing jig to obtain the mixture sheet. 3. Manufacturing method.

The method for manufacturing an electrode for a secondary battery according to claim 7, wherein the pressure jig is vibrated after introducing the particulate electrode mixture into the pressure jig.

The method for manufacturing an electrode for a secondary battery according to claim 1, wherein the step (c) is a step of pressing or hot pressing the powder mixture layer or the mixture sheet together with an electrode core using a pressing jig. .

In the step (c), the powder mixture layer or the mixture sheet and the electrode core material are introduced into the pressing jig from one end thereof at predetermined lengths or continuously. The method for producing an electrode for a secondary battery according to claim 1, wherein the method is performed continuously.

2. The method for producing an electrode for a secondary battery according to claim 1, wherein in the step (c), an uncoated portion of the electrode active material layer is provided on the electrode core to leave an exposed portion of the electrode core.

2. The method for producing an electrode for a secondary battery according to claim 1, wherein the binder comprises rubber fine particles.

The method for manufacturing an electrode for a secondary battery according to claim 1, further comprising a step of rolling the electrode plate after the step (c).